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  PRINCIPLES

  OF

  GEOLOGY.




[Illustration: VIEW OF THE TEMPLE OF SERAPIS AT PUZZUOLI IN 1836.]


  PRINCIPLES

  OF

  GEOLOGY;

  OR,

  THE MODERN CHANGES OF THE EARTH AND ITS
  INHABITANTS

  CONSIDERED AS ILLUSTRATIVE OF GEOLOGY.

  BY

  SIR CHARLES LYELL, M.A. F.R.S.

  VICE-PRESIDENT OF THE GEOLOGICAL SOCIETY OF LONDON; AUTHOR OF
  "A MANUAL OF ELEMENTARY GEOLOGY," "TRAVELS IN NORTH AMERICA,"
  "A SECOND VISIT TO THE UNITED STATES," ETC. ETC.

  NEW AND ENTIRELY REVISED EDITION.

  ILLUSTRATED WITH MAPS, PLATES, AND WOODCUTS.

  NEW YORK:
  D. APPLETON & CO., 346 & 348 BROADWAY.

  M.DCCC.LIV.


"Verè scire est per causas scire."--BACON.


"The stony rocks are not primeval, but the daughters of Time."--LINNÆUS,
_Syst. Nat._ ed. 5, _Stockholm_, 1748, p. 219.


"Amid all the revolutions of the globe, the economy of nature has been
uniform, and her laws are the only things that have resisted the general
movement. The rivers and the rocks, the seas and the continents have
been changed in all their parts; but the laws which direct those
changes, and the rules to which they are subject, have remained
invariably the same."--PLAYFAIR, _Illustrations of the Huttonian
Theory_, § 374.

"The inhabitants of the globe, like all the other parts of it, are
subject to change. It is not only the individual that perishes, but
whole species.

"A change in the animal kingdom seems to be a part of the order of
Nature, and is visible in instances to which human power cannot have
extended."--PLAYFAIR, _Illustrations of the Huttonian Theory_, § 413.




PREFACE TO THE NINTH EDITION.


The Principles of Geology in the first five editions embraced not only a
view of the _modern changes_ of the earth and its inhabitants, as set
forth in the present work, but also some account of those monuments of
analogous changes of _ancient_ date, both in the organic and inorganic
world, which it is the business of the geologist to interpret. The
subject last mentioned, or "geology proper," constituted originally a
fourth book, now omitted, the same having been enlarged into a separate
treatise, first published in 1838, in one volume 12mo., and called "The
Elements of Geology," afterwards recast in two volumes 12mo. in 1842,
and again re-edited under the title of "Manual of Elementary Geology,"
in one volume 8vo. in 1851. The "Principles" and "Manual" thus divided,
occupy, with one exception, to which I shall presently allude, very
different ground. The "Principles" treat of such portions of the economy
of existing nature, animate and inanimate, as are illustrative of
Geology, so as to comprise an investigation of the permanent effects of
causes now in action, which may serve as records to after ages of the
present condition of the globe and its inhabitants. Such effects are the
enduring monuments of the ever-varying state of the physical geography
of the globe, the lasting signs of its destruction and renovation, and
the memorials of the equally fluctuating condition of the organic world.
They may be regarded, in short, as a symbolical language, in which the
earth's autobiography is written.

In the "Manual of Elementary Geology," on the other hand, I have treated
briefly of the component materials of the earth's crust, their
arrangement and relative position, and their organic contents, which,
when deciphered by aid of the key supplied by the study of the modern
changes above alluded to, reveal to us the annals of a grand succession
of past events--a series of revolutions which the solid exterior of the
globe, and its living inhabitants, have experienced in times antecedent
to the creation of man.

In thus separating the two works, however, I have retained in the
"Principles" (book i.) the discussion of some matters which might fairly
be regarded as common to both treatises; as for example, an historical
sketch of the early progress of geology, followed by a series of
preliminary essays to explain the facts and arguments which lead me to
believe that the forces now operating upon and beneath the earth's
surface may be the same, both in kind and degree, as those which at
remote epochs have worked out geological changes. (See Analysis of
Contents of this work, p. ix.)

If I am asked whether the "Principles" or the "Manual" should be studied
first, I feel much the same difficulty in answering the question as if a
student should inquire whether he ought to take up first a treatise on
Chemistry, or one on Natural Philosophy, subjects sufficiently distinct,
yet inseparably connected. On the whole, while I have endeavored to make
each of the two treatises, in their present form, quite independent of
the other, I would recommend the reader to study first the modern
changes of the earth and its inhabitants as they are discussed in the
present volume, proceeding afterwards to the classification and
interpretation of the monuments of more remote ages.


  CHARLES LYELL.

   _11 Harley Street, London_, May 24, 1853.


_Dates of the successive Editions of the "Principles" and "Elements" (or
Manual) of Geology, by the Author._

  Principles, 1st vol. in octvo, published in               Jan. 1830.
  ----------,  2d vol.   do.   do.                          Jan. 1832.
  ----------, 1st vol. 2d edition in octavo                      1832.
  ----------,  2d vol. 2d edition do.                       Jan. 1833.
  ----------,  3d vol. 1st edition do.                      May, 1833.
  ----------, New edition (called the 3d) of the whole work
                in 4 vols. 12mo                             May, 1834.
  ----------, 4th edition, 4 vols. 12mo                    June, 1835.
  ----------, 5th do.  do.  do.                             Mar. 1837.
  Elements, 1st edition in one vol                         July, 1838.
  Principles, 6th do.  3 vols. 12mo                        June, 1840.
  Elements, 2d edition in 2 vols. 12mo                     July, 1841.
  Principles, 7th edition in one vol. 8vo                   Feb. 1847.
  ----------, 8th edition in one vol. 8vo                   May, 1850.
  Manual of Elementary Geology (or "Elements," 3d edition)
            in one vol. 8vo                                 Jan. 1851.
  Manual, 4th edition, one vol. 8vo                         Jan. 1852.
  Principles, 9th edition, now published in one vol. 8vo   June, 1853.




  ANALYSIS OF THE CONTENTS
  OF
  THE PRINCIPLES OF GEOLOGY.


  BOOK I. (CHAPTERS I. TO XIII.)

  HISTORICAL SKETCH OF THE PROGRESS OF GEOLOGY, WITH A SERIES OF
    ESSAYS TO SHOW THAT THE MONUMENTS OF THE ANCIENT STATE OF THE
    EARTH AND ITS INHABITANTS, WHICH THIS SCIENCE INTERPRETS, CAN
    ONLY BE UNDERSTOOD BY A PREVIOUS ACQUAINTANCE WITH TERRESTRIAL
    CHANGES NOW IN PROGRESS, BOTH IN THE ORGANIC AND INORGANIC
    WORLDS.

  CHAPTER I.
  Geology defined--Its relation to other Sciences                  Page 1

  CHAPTER II.
  Oriental and Egyptian Cosmogonies--Doctrines of the Greeks
    and Romans bearing on Geology                                       4

  CHAPTER III.
  Historical progress of Geology--Arabian Writers--Italian,
    French, German, and English geologists before the 19th
    century--Physico-theological school                                17

  CHAPTER IV.
  Werner and Hutton--Modern progress of the science                    46

  CHAPTER V.
  Prepossessions in regard to the duration of past time,
    and other causes which have   retarded the progress
    of Geology                                                         61

  CHAPTER VI.
  Agreement of the ancient and modern course of nature
    considered--Changes of climate                                     73

  CHAPTERS VII. VIII.
  Causes of vicissitudes in climate, and their connection
    with changes in physical geography                            92, 114

  CHAPTER IX.
  Theory of the progressive development of organic life
    at successive periods considered--Modern origin of Man            130

  CHAPTER X.
  Supposed intensity of aqueous forces at remote
    periods--Erratic blocks--Deluges                                  153

  CHAPTER XI.
  Supposed former intensity of the igneous forces--Upheaval
    of land--Volcanic action                                          160

  CHAPTER XII.
  Causes of the difference in texture of older and newer
    rocks--Plutonic and Metamorphic action                            175

  CHAPTER XIII.
  Supposed alternate periods of repose and disorder--Opposite
    doctrine, which refers geological phenomena to an
    uninterrupted series of changes in the organic and inorganic
    world, unattended with general catastrophes,
    or the development of paroxysmal forces                           180


  BOOK II. (CHAPTERS XIV. to XXXII.)

  OBSERVED CHANGES IN THE INORGANIC WORLD NOW IN PROGRESS: FIRST,
    THE EFFECTS OF AQUEOUS CAUSES, SUCH AS RIVERS, SPRINGS,
    GLACIERS, WAVES, TIDES, AND CURRENTS; SECONDLY, OF IGNEOUS
    CAUSES, OR SUBTERRANEAN HEAT, AS EXHIBITED IN THE VOLCANO AND
    THE EARTHQUAKE.

  CHAPTER XIV.
  Aqueous causes--Excavating and transporting power of rivers         198

  CHAPTER XV.
  Carrying power of river-ice--Glaciers and Icebergs                  219

  CHAPTER XVI.
  Phenomena of springs                                                232

  CHAPTER XVII.
  Reproductive effects of rivers--Deltas of lakes and inland
    seas                                                              251

  CHAPTER XVIII.
  Deltas of the Mississippi, Ganges, and other rivers exposed
    to tidal action                                                   263

  CHAPTERS XIX. XX. XXI.
  Denuding, transporting, and depositing agency of the waves,
    tides, and currents--Waste of sea-cliffs on the coast
    of England--Delta of the Rhine--Deposition of sediment
    under the influence of marine currents                  290, 321, 337

  CHAPTER XXII.
  Observed effects of igneous causes--Regions of active
    volcanoes                                                         344

  CHAPTERS XXIII. XXIV.
  History of the volcanic eruptions of the district round
    Naples--Structure of Vesuvius--Herculaneum and Pompeii       360, 375

  CHAPTER XXV.
  Etna--Its eruptions--Structure and antiquity of the cone            396

  CHAPTER XXVI.
  Volcanoes of Iceland, Mexico, the Canaries, and Grecian
    Archipelago--Mud volcanoes                                        424

  CHAPTER XXVII.
  Earthquakes and the permanent changes attending them                451

  CHAPTER XXVIII.
  Earthquake of 1783 in Calabria                                      471

  CHAPTER XXIX.
  Elevation and subsidence of dry land, and of the bed of
    the sea during earthquakes--Evidence of the same afforded
    by the Temple of Serapis near Naples                              493

  CHAPTER XXX.
  Elevation and subsidence of land in regions free from
    volcanoes and earthquakes--Rising of land in Sweden               519

  CHAPTERS XXXI. XXXII.
  Causes of earthquakes and volcanoes--Theory of central
    fluidity of the earth--Chemical theory of volcanoes--Causes
    of permanent upheaval and depression of land                 533, 545


  BOOK III. (CHAPTERS XXXIII to L.)

  OBSERVED CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS; FIRST,
    NATURE AND GEOGRAPHICAL DISTRIBUTION OF SPECIES, AND THEORIES
    RESPECTING THEIR CREATION AND EXTINCTION; SECONDLY, THE
    INFLUENCE OF ORGANIC BEINGS IN MODIFYING PHYSICAL GEOGRAPHY;
    THIRDLY, THE LAWS ACCORDING TO WHICH THEY ARE IMBEDDED IN
    VOLCANIC, FRESHWATER, AND MARINE DEPOSITS.

  CHAPTERS XXXIII. XXXIV. XXXV. XXXVI.
  Whether species have a real existence in nature--Theory
    of transmutation of species--Variability of
    species--Phenomena of hybrids in animals and
    plants                                             566, 578, 591, 600

  CHAPTER XXXVII.
  Laws which regulate the geographical distribution of
    species--Distinct provinces of peculiar species of
    plants--Their mode of diffusion                                   612

  CHAPTER XXXVIII.
  Distinct provinces of peculiar species of
    animals--Distribution and dispersion of
    quadrupeds, birds, and reptiles                                   629

  CHAPTER XXXIX.
  Geographical distribution and migrations
    of fish--Of testacea--Of zoophytes--Of
    insects--Geographical distribution and
    diffusion of the human race                                       646

  CHAPTER XL.
  Theories respecting the original introduction of
    species--Reciprocal influence of species on each other            665

  CHAPTERS XLI. XLII.
  Extinction of species--How every extension of the range
    of a species alters the condition of many others--Effect
    of changes of climate                                        677, 689

  CHAPTER XLIII.
  Creation of species--Whether the loss of certain animals
    and plants is compensated by the introduction of
    new species                                                       701

  CHAPTER XLIV.
  Modifications in physical geography caused by organic beings        708

  CHAPTER XLV.
  Imbedding of organic remains in peat, blown sand,
    and volcanic ejections                                            718

  CHAPTER XLVI.
  Imbedding of the same in alluvial deposits and in caves             730

  CHAPTER XLVII.
  Imbedding of organic remains in aqueous deposits--Terrestrial
    plants--Insects, reptiles, birds, quadrupeds                      742

  CHAPTER XLVIII.
  Imbedding of the remains of man and his works                       753

  CHAPTER XLIX.
  Imbedding of aquatic animals and plants, both freshwater
    and marine, in aqueous deposits                                   765

  CHAPTER L.
  Formation of coral reefs                                            775


  LIST OF PLATES.


  DIRECTIONS TO THE BINDER.


  FRONTISPIECE, View of the Temple of Serapis
    at Puzzuoli in 1836,                            _to face_ title page.

  PLATE 1. Map showing the Area in Europe which
             has been covered by Water since the
             beginning of the Eocene Period              _to face_ p. 121

        2. Boulders drifted by Ice on the Shores
             of the St. Lawrence                                      220

        3. View looking up the Val del Bove, Etna                     403

        4. View of the Val del Bove, Etna, as seen from above         404


PRINCIPLES OF GEOLOGY.


BOOK I.




CHAPTER I.


   Geology defined--Compared to History--Its relation to other
   Physical Sciences--Not to be confounded with Cosmogony.


Geology is the science which investigates the successive changes that
have taken place in the organic and inorganic kingdoms of nature; it
inquires into the causes of these changes, and the influence which they
have exerted in modifying the surface and external structure of our
planet.

By these researches into the state of the earth and its inhabitants at
former periods, we acquire a more perfect knowledge of its present
condition, and more comprehensive views concerning the laws now
governing its animate and inanimate productions. When we study history,
we obtain a more profound insight into human nature, by instituting a
comparison between the present and former states of society. We trace
the long series of events which have gradually led to the actual posture
of affairs; and by connecting effects with their causes, we are enabled
to classify and retain in the memory a multitude of complicated
relations--the various peculiarities of national character--the
different degrees of moral and intellectual refinement, and numerous
other circumstances, which, without historical associations, would be
uninteresting or imperfectly understood. As the present condition of
nations is the result of many antecedent changes, some extremely remote,
and others recent, some gradual, others sudden and violent; so the
state, of the natural world is the result of a long succession of
events; and if we would enlarge our experience of the present economy of
nature, we must investigate the effects of her operations in former
epochs.

We often discover with surprise, on looking back into the chronicles of
nations, how the fortune of some battle has influenced the fate of
millions of our contemporaries, when it has long been forgotten by the
mass of the population. With this remote event we may find inseparably
connected the geographical boundaries of a great state, the language now
spoken by the inhabitants, their peculiar manners, laws, and religious
opinions. But far more astonishing and unexpected are the connections
brought to light, when we carry back our researches into the history of
nature. The form of a coast, the configuration of the interior of a
country, the existence and extent of lakes, valleys, and mountains, can
often be traced to the former prevalence of earthquakes and volcanoes in
regions which have long been undisturbed. To these remote convulsions
the present fertility of some districts, the sterile character of
others, the elevation of land above the sea, the climate, and various
peculiarities, may be distinctly referred. On the other hand, many
distinguishing features of the surface may often be ascribed to the
operation, at a remote era, of slow and tranquil causes--to the gradual
deposition of sediment in a lake or in the ocean, or to the prolific
increase of testacea and corals.

To select another example, we find in certain localities subterranean
deposits of coal, consisting of vegetable matter, formerly drifted into
seas and lakes. These seas and lakes have since been filled up, the
lands whereon the forests grew have disappeared or changed their form,
the rivers and currents which floated the vegetable masses can no longer
be traced, and the plants belonged to species which for ages have passed
away from the surface of our planet. Yet the commercial prosperity, and
numerical strength of a nation, may now be mainly dependent on the local
distribution of fuel determined by that ancient state of things.

Geology is intimately related to almost all the physical sciences, as
history is to the moral. An historian should, if possible, be at once
profoundly acquainted with ethics, politics, jurisprudence, the military
art, theology; in a word, with all branches of knowledge by which any
insight into human affairs, or into the moral and intellectual nature of
man, can be obtained. It would be no less desirable that a geologist
should be well versed in chemistry, natural philosophy, mineralogy,
zoology, comparative anatomy, botany; in short, in every science
relating to organic and inorganic nature. With these accomplishments,
the historian and geologist would rarely fail to draw correct and
philosophical conclusions from the various monuments transmitted to them
of former occurrences. They would know to what combination of causes
analogous effects were referable, and they would often be enabled to
supply, by inference, information concerning many events unrecorded in
the defective archives of former ages. But as such extensive
acquisitions are scarcely within the reach of any individual, it is
necessary that men who have devoted their lives to different departments
should unite their efforts; and as the historian receives assistance
from the antiquary, and from those who have cultivated different
branches of moral and political science, so the geologist should avail
himself of the aid of many naturalists, and particularly of those who
have studied the fossil remains of lost species of animals and plants.

The analogy, however, of the monuments consulted in geology, and those
available in history, extends no farther than to one class of historical
monuments--those which may be said to be _undesignedly_ commemorative of
former events. The canoes, for example, and stone hatchets found in our
peat bogs, afford an insight into the rude arts and manners of the
earliest inhabitants of our island; the buried coin fixes the date of
the reign of some Roman emperor; the ancient encampment indicates the
districts once occupied by invading armies, and the former method of
constructing military defences; the Egyptian mummies throw light on the
art of embalming, the rites of sepulture, or the average stature of the
human race in ancient Egypt. This class of memorials yields to no other
in authenticity, but it constitutes a small part only of the resources
on which the historian relies, whereas in geology it forms the only kind
of evidence which is at our command. For this reason we must not expect
to obtain a full and connected account of any series of events beyond
the reach of history. But the testimony of geological monuments, if
frequently imperfect, possesses at least the advantage of being free
from all intentional misrepresentation. We may be deceived in the
inferences which we draw, in the same manner as we often mistake the
nature and import of phenomena observed in the daily course of nature;
but our liability to err is confined to the interpretation, and, if this
be correct, our information is certain.

It was long before the distinct nature and legitimate objects of geology
were fully recognized, and it was at first confounded with many other
branches of inquiry, just as the limits of history, poetry, and
mythology were ill-defined in the infancy of civilization. Even in
Werner's time, or at the close of the eighteenth century, geology
appears to have been regarded as little other than a subordinate
department of mineralogy; and Desmarest included it under the head of
Physical Geography. But the most common and serious source of confusion
arose from the notion, that it was the business of geology to discover
the mode in which the earth originated, or, as some imagined, to study
the effects of those cosmological causes which were employed by the
Author of Nature to bring this planet out of a nascent and chaotic state
into a more perfect and habitable condition. Hutton was the first who
endeavored to draw a strong line of demarcation between his favorite
science and cosmogony, for he declared that geology was in nowise
concerned "with questions as to the origin of things."

An attempt will be made in the sequel of this work to demonstrate that
geology differs as widely from cosmogony, as speculations concerning the
mode of the first creation of man differ from history. But, before
entering more at large on this controverted question, it will be
desirable to trace the progress of opinion on this topic, from the
earliest ages to the commencement of the present century.




CHAPTER II.

HISTORICAL SKETCH OF THE PROGRESS OF GEOLOGY.


   Oriental Cosmogony--Hymns of the Vedas--Institutes of
     Menù--Doctrine of the successive destruction and renovation of
     the world--Origin of this doctrine--Common to the
     Egyptians--Adopted by the Greeks--System of Pythagoras--Of
     Aristotle--Dogmas concerning the extinction and reproduction
     of genera and species--Strabo's theory of elevation by
     earthquakes--Pliny--Concluding Remarks on the knowledge of the
     Ancients.


_Oriental Cosmogony._--The earliest doctrines of the Indian and Egyptian
schools of philosophy agreed in ascribing the first creation of the
world to an omnipotent and infinite Being. They concurred also in
representing this Being, who had existed from all eternity, as having
repeatedly destroyed and reproduced the world and all its inhabitants.
In the sacred volume of the Hindoos, called the Ordinances of Menù,
comprising the Indian system of duties religious and civil, we find a
preliminary chapter treating of the Creation, in which the cosmogony is
known to have been derived from earlier writings and traditions; and
principally from certain hymns of high antiquity, called the Vedas.
These hymns were first put together, according to Mr. Colebrooke,[1] in
a connected series, about thirteen centuries before the Christian era,
but they appear from internal evidence to have been written at various
antecedent periods. In them, as we learn from the researches of
Professor Wilson, the eminent Sanscrit scholar, two distinct
philosophical systems are discoverable. According to one of them, all
things were originally brought into existence by the sole will of a
single First Cause, which existed from eternity; according to the other,
there have always existed two principles, the one material, but without
form, the other spiritual and capable of compelling "inert matter to
develop its sensible properties." This development of matter into
"individual and visible existences" is called creation, and is assigned
to a subordinate agent, or the creative faculty of the Supreme Being
embodied in the person of Brahma.

In the first chapter of the Ordinances of Menù above alluded to, we meet
with the following passages relating to former destructions and
renovations of the world:--

"The Being, whose powers are incomprehensible, having created me (Menù)
and this universe, again became absorbed in the supreme spirit, changing
the time of energy for the hour of repose.

"When that Power awakes, then has this world its full expansion; but
when he slumbers with a tranquil spirit, then the whole system fades
away..... For while he reposes, as it were, embodied spirits endowed
with principles of action depart from their several acts, and the mind
itself becomes inert."

The absorption of all beings into the Supreme essence is then described,
and the Divine soul itself is said to slumber, and to remain for a time
immersed in "the first idea, or in darkness." After which the text thus
proceeds (verse fifty-seven), "Thus that immutable power by waking and
reposing alternately, revivifies and destroys, in eternal succession,
this whole assemblage of locomotive and immovable creatures."

It is then declared that there has been a long succession of
_manwantaras_, or periods, each of the duration of many thousand ages,
and--

"There are creations also, and destructions of worlds innumerable: the
Being, supremely exalted, performs all this with as much ease as if in
sport, again and again, for the sake of conferring happiness."[2]

No part of the Eastern cosmogony, from which these extracts are made, is
more interesting to the geologist than the doctrine, so frequently
alluded to, of the reiterated submersion of the land beneath the waters
of a universal ocean. In the beginning of things, we are told, the First
Sole Cause "with a thought created the waters," and then moved upon
their surface in the form of Brahma the creator, by whose agency the
emergence of the dry land was effected, and the peopling of the earth
with plants, animals, celestial creatures, and man. Afterwards, as often
as a general conflagration at the close of each manwantara had
annihilated every visible and existing thing, Brahma, on awaking from
his sleep, finds the whole world a shapeless ocean. Accordingly, in the
legendary poems called the Puranas, composed at a later date than the
Vedas, the three first Avatars or descents of the Deity upon earth have
for their object to recover the land from the waters. For this purpose
Vishnu is made successively to assume the form of a fish, a tortoise,
and a boar.

Extravagant as may be some of the conceits and fictions which disfigure
these pretended revelations, we can by no means look upon them as a pure
effort of the unassisted imagination, or believe them to have been
composed without regard to opinions and theories founded on the
observation of Nature. In astronomy, for instance, it is declared that,
at the North Pole, the year was divided into a long day and night, and
that their long day was the northern, and their night the southern
course of the sun; and to the inhabitants of the moon, it is said one
day is equal in length to one month of mortals.[3] If such statements
cannot be resolved into mere conjectures, we have no right to refer to
mere chance the prevailing notion that the earth and its inhabitants had
formerly undergone a succession of revolutions and aqueous catastrophes
interrupted by long intervals of tranquillity.

Now there are two sources in which such a theory may have originated.
The marks of former convulsions on every part of the surface of our
planet are obvious and striking. The remains of marine animals imbedded
in the solid strata are so abundant, that they may be expected to force
themselves on the attention of every people who have made some progress
in refinement; and especially where one class of men are expressly set
apart from the rest, like the ancient priesthoods of India and Egypt,
for study and contemplation. If these appearances are once recognized,
it seems natural that the mind should conclude in favor, not only of
mighty changes in past ages, but of alternate periods of repose and
disorder;--of repose, when the animals now fossil lived, grew, and
multiplied--of disorder, when the strata in which they were buried
became transferred from the sea to the interior of continents, and were
uplifted so as to form part of high mountain-chains. Those modern
writers, who are disposed to disparage the former intellectual
advancement and civilization of Eastern nations, may concede some
foundation of observed facts for the curious theories now under
consideration, without indulging in exaggerated opinions of the progress
of science; especially as universal catastrophes of the world, and
exterminations of organic beings, in the sense in which they were
understood by the Brahmins, are untenable doctrines.

We know that the Egyptian priests were aware, not only that the soil
beneath the plains of the Nile, but that also the hills bounding the
great valley, contained marine shells; and Herodotus inferred from these
facts, that all lower Egypt, and even the high lands above Memphis, had
once been covered by the sea.[4] As similar fossil remains occur in all
parts of Asia hitherto explored, far in the interior of the continent as
well as near the sea, they could hardly have escaped detection by some
Eastern sages not less capable than the Greek historian of reasoning
philosophically on natural phenomena.

We also know that the rulers of Asia were engaged in very remote eras in
executing great national works, such as tanks and canals, requiring
extensive excavations. In the fourteenth century of our era (in the year
1360), the removal of soil necessary for such undertakings brought to
light geological facts, which attracted the attention of a people less
civilized than were many of the older nations of the East. The historian
Ferishta relates that fifty thousand laborers were employed in cutting
through a mound, so as to form a junction between the rivers Selima and
Sutlej; and in this mound were found the bones of elephants and men,
some of them petrified, and some of them resembling bone. The gigantic
dimensions attributed to the human bones show them to have belonged to
some of the larger pachydermata.[5]

But, although the Brahmins, like the priests of Egypt, may have been
acquainted with the existence of fossil remains in the strata, it is
possible that the doctrine of successive destructions and renovations of
the world, merely received corroboration from such proofs; and that it
may have been originally handed down, like the religious traditions of
most nations, from a ruder state of society. The system may have had its
source, in part at least, in exaggerated accounts of those dreadful
catastrophes which are occasioned by particular combinations of natural
causes. Floods and volcanic eruptions, the agency of water and fire, are
the chief instruments of devastation on our globe. We shall point out in
the sequel the extent of many of these calamities, recurring at distant
intervals of time, in the present course of nature; and shall only
observe here, that they are so peculiarly calculated to inspire a
lasting terror, and are so often fatal in their consequences to great
multitudes of people, that it scarcely requires the passion for the
marvellous, so characteristic of rude and half-civilized nations, still
less the exuberant imagination of Eastern writers, to augment them into
general cataclysms and conflagrations.

The great flood of the Chinese, which their traditions carry back to the
period of Yaou, something more than 2000 years before our era, has been
identified by some persons with the universal deluge described in the
Old Testament; but according to Mr. Davis, who accompanied two of our
embassies to China, and who has carefully examined their written
accounts, the Chinese cataclysm is therein described as interrupting the
business of agriculture, rather than as involving a general destruction
of the human race. The great Yu was celebrated for having "opened nine
channels to draw off the waters," which "covered the low hills and
bathed the foot of the highest mountains." Mr. Davis suggests that a
great derangement of waters of the Yellow River, one of the largest in
the world, might even now cause the flood of Yaou to be repeated, and
lay the most fertile and populous plains of China under water. In modern
times the bursting of the banks of an artificial canal, into which a
portion of the Yellow River has been turned, has repeatedly given rise
to the most dreadful accidents, and is a source of perpetual anxiety to
the government. It is easy, therefore, to imagine how much greater may
have been the inundation, if this valley was ever convulsed by a violent
earthquake.[6]

Humboldt relates the interesting fact that, after the annihilation of a
large part of the inhabitants of Cumana, by an earthquake in 1766, a
season of extraordinary fertility ensued, in consequence of the great
rains which accompanied the subterranean convulsions. "The Indians," he
says, "celebrated, after the ideas of an antique superstition, by
festivals and dancing, the destruction of the world and the approaching
epoch of its regeneration."[7]

The existence of such rites among the rude nations of South America is
most important, as showing what effects may be produced by local
catastrophes, recurring at distant intervals of time, on the minds of a
barbarous and uncultivated race. I shall point out in the sequel how the
tradition of a deluge among the Araucanian Indians may be explained, by
reference to great earthquake-waves which have repeatedly rolled over
part of Chili since the first recorded flood of 1590. (See chap. 29,
Book II.) The legend also of the ancient Peruvians of an inundation many
years before the reign of the Incas, in which only six persons were
saved on a float, relates to a region which has more than once been
overwhelmed by inroads of the ocean since the days of Pizarro. (Chap.
29, Book II.) I might refer the reader to my account of the submergence
of a wide area in Cutch so lately as the year 1819, when a single tower
only of the fort of Sindree appeared above the waste of waters (see
Chap. 28, Book II.), if it were necessary, to prove how easily the
catastrophes of modern times might give rise to traditionary narratives,
among a rude people, of floods of boundless extent. Nations without
written records, and who are indebted for all their knowledge of past
events exclusively to oral tradition, are in the habit of confounding in
one legend a series of incidents which have happened at various epochs;
nor must we forget that the superstitions of a savage tribe are
transmitted through all the progressive stages of society, till they
exert a powerful influence on the mind of the philosopher. He may find,
in the monuments of former changes on the earth's surface, an apparent
confirmation of tenets handed down through successive generations, from
the rude hunter, whose terrified imagination drew a false picture of
those awful visitations of floods and earthquakes, whereby the whole
earth as known to him was simultaneously devastated.

_Egyptian Cosmogony._--Respecting the cosmogony of the Egyptian priests,
we gather much information from writers of the Grecian sects, who
borrowed almost all their tenets from Egypt, and amongst others that of
the former successive destruction and renovation of the world.[8] We
learn from Plutarch, that this was the theme of one of the hymns of
Orpheus, so celebrated in the fabulous ages of Greece. It was brought by
him from the banks of the Nile; and we even find in his verses, as in
the Indian systems, a definite period assigned for the duration of each
successive world.[9] The returns of great catastrophes were determined
by the period of the Annus Magnus, or great year,--a cycle composed of
the revolutions of the sun, moon, and planets, and terminating when
these return together to the same sign whence they were supposed at some
remote epoch to have set out. The duration of this great cycle was
variously estimated. According to Orpheus, it was 120,000 years;
according to others, 300,000; and by Cassander it was taken to be
360,000 years.[10]

We learn particularly from the Timæus of Plato, that the Egyptians
believed the world to be subject to occasional conflagrations and
deluges, whereby the gods arrested the career of human wickedness, and
purified the earth from guilt. After each regeneration, mankind were in
a state of virtue and happiness, from which they gradually degenerated
again into vice and immorality. From this Egyptian doctrine, the poets
derived the fable of the decline from the golden to the iron age. The
sect of Stoics adopted most fully the system of catastrophes destined at
certain intervals to destroy the world. Those they taught were of two
kinds;--the Cataclysm, or destruction by water, which sweeps away the
whole human race, and annihilates all the animal and vegetable
productions of nature; and the Ecpyrosis, or destruction by fire, which
dissolves the globe itself. From the Egyptians also they derived the
doctrine of the gradual debasement of man from a state of innocence.
Towards the termination of each era, the gods could no longer bear with
the wickedness of men, and a shock of the elements or a deluge
overwhelmed them; after which calamity, Astrea again descended on the
earth to renew the golden age.[11]

The connection between the doctrine of successive catastrophes and
repeated deteriorations in the moral character of the human race is more
intimate and natural than might at first be imagined. For, in a rude
state of society, all great calamities are regarded by the people as
judgments of God on the wickedness of man. Thus, in our own time, the
priests persuaded a large part of the population of Chili, and perhaps
believed themselves, that the fatal earthquake of 1822 was a sign of the
wrath of Heaven for the great political revolution just then consummated
in South America. In like manner, in the account given to Solon by the
Egyptian priests, of the submersion of the island of Atlantis under the
waters of the ocean, after repeated shocks of an earthquake, we find
that the event happened when Jupiter had seen the moral depravity of the
inhabitants.[12] Now, when the notion had once gained ground, whether
from causes before suggested or not, that the earth had been destroyed
by several general catastrophes, it would next be inferred that the
human race had been as often destroyed and renovated. And since every
extermination was assumed to be penal, it could only be reconciled with
divine justice, by the supposition that man, at each successive
creation, was regenerated in a state of purity and innocence.

A very large portion of Asia, inhabited by the earliest nations, whose
traditions have come down to us, has been always subject to tremendous
earthquakes. Of the geographical boundaries of these, and their effects,
I shall speak in the proper place. Egypt has, for the most part, been
exempt from this scourge, and the Egyptian doctrine of great
catastrophes was probably derived in part, as before hinted, from early
geological observations, and in part from Eastern nations.


_Pythagorean Doctrines._--Pythagoras, who resided for more than twenty
years in Egypt, and, according to Cicero, had visited the East, and
conversed with the Persian philosophers, introduced into his own
country, on his return, the doctrine of the gradual deterioration of the
human race from an original state of virtue and happiness; but if we are
to judge of his theory concerning the destruction and renovation of the
earth from the sketch given by Ovid, we must concede it to have been far
more philosophical than any known version of the cosmogonies of Oriental
or Egyptian sects.

Although Pythagoras is introduced by the poet as delivering his doctrine
in person, some of the illustrations are derived from natural events
which happened after the death of the philosopher. But notwithstanding
these anachronisms, we may regard the account as a true picture of the
tenets of the Pythagorean school in the Augustan age; and although
perhaps partially modified, it must have contained the substance of the
original scheme. Thus considered, it is extremely curious and
instructive; for we here find a comprehensive summary of almost all the
great causes of change now in activity on the globe, and these adduced
in confirmation of a principle of a perpetual and gradual revolution
inherent in the nature of our terrestrial system. These doctrines, it is
true, are not directly applied to the explanation of geological
phenomena; or, in other words, no attempt is made to estimate what may
have been in past ages, or what may hereafter be, the aggregate amount
of change brought about by such never-ending fluctuations. Had this been
the case, we might have been called upon to admire so extraordinary an
anticipation with no less interest than astronomers, when they endeavor
to define by what means the Samian philosopher came to the knowledge of
the Copernican system.

Let us now examine the celebrated passages to which we have been
adverting:[13]

"Nothing perishes in this world; but things merely vary and change their
form. To be born, means simply that a thing begins to be something
different from what it was before; and dying, is ceasing to be the same
thing. Yet, although nothing retains long the same image, the sum of the
whole remains constant." These general propositions are then confirmed
by a series of examples, all derived from natural appearances, except
the first, which refers to the golden age giving place to the age of
iron. The illustrations are thus consecutively adduced.

1. Solid land has been converted into sea.

2. Sea has been changed into land. Marine shells lie far distant from
the deep, and the anchor has been found on the summit of hills.

3. Valleys have been excavated by running water, and floods have washed
down hills into the sea.[14]

4. Marshes have become dry ground.

5. Dry lands have been changed into stagnant pools.

6. During earthquakes some springs have been closed up, and new ones
have broken out. Rivers have deserted their channels, and have been
re-born elsewhere, as the Erasinus in Greece, and Mysus in Asia.

7. The waters of some rivers, formerly sweet, have become bitter; as
those of the Anigris, in Greece, &c.[15]

8. Islands have become connected with the mainland by the growth of
deltas and new deposits; as in the case of Antissa joined to Lesbos,
Pharos to Egypt, &c.

9. Peninsulas have been divided from the main land, and have become
islands, as Leucadia; and according to tradition, Sicily, the sea having
carried away the isthmus.

10. Land has been submerged by earthquakes; the Grecian cities of Helice
and Buris, for example, are to be seen under the sea, with their walls
inclined.

11. Plains have been upheaved into hills by the confined air seeking
vent; as at Troezene in the Peloponnesus.

12. The temperature of some springs varies at different periods. The
waters of others are inflammable.[16]

13. There are streams which have a petrifying power, and convert the
substances which they touch into marble.

14. Extraordinary medicinal and deleterious effects are produced by the
water of different lakes and springs.[17]

15. Some rocks and islands, after floating and having been subject to
violent movements, have at length become stationary and immovable; as
Delos and the Cyanean Isles.[18]

16. Volcanic vents shift their position; there was a time when Etna was
not a burning mountain, and the time will come when it will cease to
burn. Whether it be that some caverns become closed up by the movements
of the earth, and others opened, or whether the fuel is finally
exhausted, &c., &c.

The various causes of change in the inanimate world having been thus
enumerated, the doctrine of equivocal generation is next propounded, as
illustrating a corresponding perpetual flux in the animate creation.[19]

In the Egyptian and Eastern cosmogonies, and in the Greek version of
them, no very definite meaning can, in general, be attached to the term
"destruction of the world;" for sometimes it would seem almost to imply
the annihilation of our planetary system, and at others a mere
revolution of the surface of the earth.

_Opinions of Aristotle._--From the works now extant of Aristotle, and
from the system of Pythagoras, as above exposed, we might certainly
infer that these philosophers considered the agents of change now
operating in nature, as capable of bringing about in the lapse of ages a
complete revolution; and the Stagyrite even considers occasional
catastrophes, happening at distant intervals of time, as part of the
regular and ordinary course of nature. The deluge of Deucalion, he says,
affected Greece only, and principally the part called Hellas, and it
arose from great inundations of rivers, during a rainy winter. But such
extraordinary winters, he says, though after a certain period they
return, do not always revisit the same places.[20]

Censorinus quotes it as Aristotle's opinion that there were general
inundations of the globe, and that they alternated with conflagrations;
and that the flood constituted the winter of the great year, or
astronomical cycle, while the conflagration, or destruction by fire, is
the summer, or period of greatest heat.[21] If this passage, as Lipsius
supposes, be an amplification, by Censorinus, of what is written in "the
Meteorics," it is a gross misrepresentation of the doctrine of the
Stagyrite, for the general bearing of his reasoning in that treatise
tends clearly in an opposite direction. He refers to many examples of
changes now constantly going on, and insists emphatically on the great
results which they must produce in the lapse of ages. He instances
particular cases of lakes that had dried up, and deserts that had at
length become watered by rivers and fertilized. He points to the growth
of the Nilotic Delta since the time of Homer, to the shallowing of the
Palus Mæotis within sixty years from his own time; and although, in the
same chapter he says nothing of earthquakes, yet in others of the same
treatise he shows himself not unacquainted with their effects.[22] He
alludes, for example, to the upheaving of one of the Eolian islands
previous to a volcanic eruption. "The changes of the earth," he says,
"are so slow in comparison to the duration of our lives, that they are
overlooked (λανθανει): and the migrations of people after
great catastrophes, and their removal to other regions, cause the event
to be forgotten."[23]

When we consider the acquaintance displayed by Aristotle, in his
various works, with the destroying and renovating powers of Nature, the
introductory and concluding passages of the twelfth chapter of his
"Meteorics" are certainly very remarkable. In the first sentence he
says, "The distribution of land and sea in particular regions does not
endure throughout all time, but it becomes sea in those parts where it
was land, and again it becomes land where it was sea: and there is
reason for thinking that these changes take place according to a certain
system, and within a certain period." The concluding observation is as
follows:--"As time never fails, and the universe is eternal, neither the
Tànais, nor the Nile, can have flowed forever. The places where they
rise were once dry, and there is a limit to their operations; but there
is none to time. So also of all other rivers; they spring up, and they
perish; and the sea also continually deserts some lands and invades
others. The same tracts, therefore, of the earth are not, some always
sea, and others always continents, but every thing changes in the course
of time."

It seems, then, that the Greeks had not only derived from preceding
nations, but had also, in some slight degree, deduced from their own
observations, the theory of periodical revolutions in the inorganic
world: there is, however, no ground for imagining that they contemplated
former changes in the races of animals and plants. Even the fact that
marine remains were inclosed in solid rocks, although observed by some,
and even made the groundwork of geological speculation, never stimulated
the industry or guided the inquiries of naturalists. It is not
impossible that the theory of equivocal generation might have engendered
some indifference on this subject, and that a belief in the spontaneous
production of living beings from the earth or corrupt matter, might have
caused the organic world to appear so unstable and fluctuating, that
phenomena indicative of former changes would not awaken intense
curiosity. The Egyptians, it is true, had taught, and the Stoics had
repeated, that the earth had once given birth to some monstrous animals,
which existed no longer; but the prevailing opinion seems to have been,
that after each great catastrophe the same species of animals were
created over again. This tenet is implied in a passage of Seneca, where,
speaking of a future deluge, he says, "Every animal shall be generated
anew, and man free from guilt shall be given to the earth."[24]

An old Arabian version of the doctrine of the successive revolutions of
the globe, translated by Abraham Ecchellensis,[25] seems to form a
singular exception to the general rule, for here we find the idea of
different genera and species having been created. The Gerbanites, a sect
of astronomers who flourished some centuries before the Christian era,
taught as follows:--"That after every period of thirty-six thousand four
hundred and twenty-five years, there were produced a pair of _every_
species of animal, both male and female, from whom animals might be
propagated and inhabit this lower world. But when a circulation of the
heavenly orbs was completed, which is finished in that space of years,
_other genera and species_ of animals are propagated, as also of plants
and other things, and the first order is destroyed, and so it goes on
forever and ever."[26]

_Theory of Strabo._--As we learn much of the tenets of the Egyptian and
Oriental schools in the writings of the Greeks, so, many speculations of
the early Greek authors are made known to us in the works of the
Augustan and later ages. Strabo, in particular, enters largely, in the
second book of his Geography, into the opinions of Eratosthenes and
other Greeks on one of the most difficult problems in geology, viz., by
what causes marine shells came to be plentifully buried in the earth at
such great elevations and distances from the sea.

He notices, amongst others, the explanation of Xanthus the Lydian, who
said that the seas had once been more extensive, and that they had
afterwards been partially dried up, as in his own time many lakes,
rivers, and wells in Asia had failed during a season of drought.
Treating this conjecture with merited disregard, Strabo passes on to the
hypothesis of Strato, the natural philosopher, who had observed that the
quantity of mud brought down by rivers into the Euxine was so great,
that its bed must be gradually raised, while the rivers still continue
to pour in an undiminished quantity of water. He, therefore, conceived
that, originally, when the Euxine was an inland sea, its level had by
this means become so much elevated that it burst its barrier near
Byzantium, and formed a communication with the Propontis; and this
partial drainage, he supposed, had already converted the left side into
marshy ground, and thus, at last, the whole would be choked up with
soil. So, it was argued, the Mediterranean had once opened a passage for
itself by the Columns of Hercules into the Atlantic; and perhaps the
abundance of sea-shells in Africa, near the Temple of Jupiter Ammon,
might also be the deposit of some former inland sea, which had at length
forced a passage and escaped.

But Strabo rejects this theory, as insufficient to account for all the
phenomena, and he proposes one of his own, the profoundness of which
modern geologists are only beginning to appreciate. "It is not," he
says, "because the lands covered by seas were originally at different
altitudes, that the waters have risen, or subsided, or receded from some
parts and inundated others. But the reason is, that the same land is
sometimes raised up and sometimes depressed, and the sea also is
simultaneously raised and depressed, so that it either overflows or
returns into its own place again. We must, therefore, ascribe the cause
to the ground, either to that ground which is under the sea, or to that
which becomes flooded by it, but rather to that which lies beneath the
sea, for this is more movable and, on account of its humidity, can be
altered with greater celerity.[27] "_It is proper_," he observes in
continuation, "_to derive our explanations from things which are
obvious, and in some measure of daily occurrence, such as deluges,
earthquakes, and volcanic eruptions,[28] and sudden swellings of the
land beneath the sea_; for the last raise up the sea also; and when the
same lands subside again, they occasion the sea to be let down. And it
is not merely the small, but the large islands also, and not merely the
islands, but the continents which can be lifted up together with the
sea; and both large and small tracts may subside, for habitations and
cities, like Bure, Bizona, and many others, have been engulphed by
earthquakes."

In another place, this learned geographer, in alluding to the tradition
that Sicily had been separated by a convulsion from Italy, remarks, that
at present the land near the sea in those parts was rarely shaken by
earthquakes, since there were now open orifices whereby fire and ignited
matters, and waters escape; but formerly, when the volcanoes of Etna,
the Lipari Islands, Ischia, and others, were closed up, the imprisoned
fire and wind might have produced far more vehement movements.[29] The
doctrine, therefore, that volcanoes are safety-valves, and that the
subterranean convulsions are probably most violent when first the
volcanic energy shifts itself to a new quarter, is not modern.

We learn from a passage in Strabo,[30] that it was a dogma of the
Gaulish Druids that the universe was immortal, but destined to survive
catastrophes both of fire and water. That this doctrine was communicated
to them from the East, with much of their learning, cannot be doubted.
Cæsar, it will be remembered, says that they made use of Greek letters
in arithmetical computations.[31]

_Pliny._--This philosopher had no theoretical opinions of his own
concerning changes of the earth's surface; and in this department, as in
others, he restricted himself to the task of a compiler, without
reasoning on the facts stated by him, or attempting to digest them into
regular order. But his enumeration of the new islands which had been
formed in the Mediterranean, and of other convulsions, shows that the
ancients had not been inattentive observers of the changes which had
taken place within the memory of man.

Such, then, appear to have been the opinions entertained before the
Christian era, concerning the past revolutions of our globe. Although no
particular investigations had been made for the express purpose of
interpreting the monuments of ancient changes, they were too obvious to
be entirely disregarded; and the observation of the present course of
nature presented too many proofs of alterations continually in progress
on the earth to allow philosophers to believe that nature was in a state
of rest, or that the surface had remained, and would continue to remain
unaltered. But they had never compared attentively the results of the
destroying and reproductive operations of modern times with those of
remote eras, nor had they ever entertained so much as a conjecture
concerning the comparative antiquity of the human race, or of living
species of animals and plants, with those belonging to former conditions
of the organic world. They had studied the movements and positions of
the heavenly bodies with laborious industry, and made some progress in
investigating the animal, vegetable, and mineral kingdoms; but the
ancient history of the globe was to them a sealed book, and, although
written in characters of the most striking and imposing kind, they were
unconscious even of its existence.




CHAPTER III.

HISTORY OF THE PROGRESS OF GEOLOGY--_continued_.


  Arabian writers of the tenth century--Avicenna--Omar--Cosmogony
    of the Koran--Kazwini--Early Italian writers--Leonardo da
    Vinci--Fracastoro--Controversy as to the real nature of
    fossils--Attributed to the Mosaic deluge--Palissy--Steno
    --Scilla--Quirini--Boyle--Lister--Leibnitz--Hooke's
    Theory of Elevation by Earthquakes--Of lost species of
    animals--Ray--Physico-theological writers--Woodward's Diluvial
    Theory--Burnet--Whiston--Vallisneri--Lazzaro
    Moro--Generelli--Buffon--His theory condemned by the Sorbonne
    as unorthodox--His declaration--Targioni--Arduino--Michell
    --Catcott--Raspe Fuchsel--Fortis--Testa--Whitehurst--Pallas
    --Saussure.


_Arabian writers._--After the decline of the Roman empire, the
cultivation of physical science was first revived with some success by
the Saracens, about the middle of the eighth century of our era. The
works of the most eminent classic writers were purchased at great
expense from the Christians, and translated into Arabic; and Al Mamûn,
son of the famous Harûn-al-Rashid, the contemporary of Charlemagne,
received with marks of distinction, at his court at Bagdad, astronomers
and men of learning from different countries. This caliph, and some of
his successors, encountered much opposition and jealousy from the
doctors of the Mahometan law, who wished the Moslems to confine their
studies to the Koran, dreading the effects of the diffusion of a taste
for the physical sciences.[32]

_Avicenna._--Almost all the works of the early Arabian writers are lost.
Amongst those of the tenth century, of which fragments are now extant,
is a short treatise, "On the Formation and Classification of Minerals,"
by Avicenna, a physician, in whose arrangement there is considerable
merit. The second chapter, "On the Cause of Mountains," is remarkable;
for mountains, he says, are formed, some by essential, others by
accidental causes. In illustration of the essential, he instances "a
violent earthquake, by which land is elevated, and becomes a mountain;"
of the accidental, the principal, he says, is excavation by water,
whereby cavities are produced, and adjoining lands made to stand out and
form eminences.[33]

_Omar--Cosmogony of the Koran._--In the same century, also, Omar,
surnamed "El Aalem," or "The Learned," wrote a work on "The Retreat of
the Sea." It appears that on comparing the charts of his own time with
those made by the Indian and Persian astronomers two thousand years
before, he had satisfied himself that important changes had taken place
since the times of history in the form of the coasts of Asia, and that
the extension of the sea had been greater at some former periods. He was
confirmed in this opinion by the numerous salt springs and marshes in
the interior of Asia,--a phenomenon from which Pallas, in more recent
times, has drawn the same inference.

Von Hoff has suggested, with great probability, that the changes in the
level of the Caspian (some of which there is reason to believe have
happened within the historical era), and the geological appearances in
that district, indicating the desertion by that sea of its ancient bed,
had probably led Omar to his theory of a general subsidence. But
whatever may have been the proofs relied on, his system was declared
contradictory to certain passages in the Koran, and he was called upon
publicly to recant his errors; to avoid which persecution he went into
voluntary banishment from Samarkand.[34]

The cosmological opinions expressed in the Koran are few, and merely
introduced incidentally: so that it is not easy to understand how they
could have interfered so seriously with free discussion on the former
changes of the globe. The Prophet declares that the earth was created in
two days, and the mountains were then placed on it; and during these,
and two additional days, the inhabitants of the earth were formed; and
in two more the seven heavens.[35] There is no more detail of
circumstances; and the deluge, which is also mentioned, is discussed
with equal brevity. The waters are represented to have poured out of an
oven; a strange fable, said to be borrowed from the Persian Magi, who
represented them as issuing from the oven of an old woman.[36] All men
were drowned, save Noah and his family; and then God said, "O earth,
swallow up thy waters; and thou, O heaven, withhold thy rain;" and
immediately the waters abated.[37]

We may suppose Omar to have represented the desertion of the land by the
sea to have been gradual, and that his hypothesis required a greater
lapse of ages than was consistent with Moslem orthodoxy; for it is to be
inferred from the Koran, that man and this planet were created at the
same time; and although Mahomet did not limit expressly the antiquity of
the human race, yet he gave an implied sanction to the Mosaic
chronology, by the veneration expressed by him for the Hebrew
Patriarchs.[38]

A manuscript work, entitled the "Wonders of Nature," is preserved in
the Royal Library at Paris, by an Arabian writer, Mohammed Kazwini, who
flourished in the seventh century of the Hegira, or at the close of the
thirteenth century of our era.[39] Besides several curious remarks on
aerolites, earthquakes, and the successive changes of position which the
land and sea have undergone, we meet with the following beautiful
passage which is given as the narrative of Kidhz, an allegorical
personage:--"I passed one day by a very ancient and wonderfully populous
city, and asked one of its inhabitants how long it had been founded. 'It
is indeed a mighty city,' replied he; 'we know not how long it has
existed, and our ancestors were on this subject as ignorant as
ourselves.' Five centuries afterwards, as I passed by the same place, I
could not perceive the slightest vestige of the city. I demanded of a
peasant, who was gathering herbs upon its former site, how long it had
been destroyed. 'In sooth a strange question!' replied he. 'The ground
here has never been different from what you now behold it.'--'Was there
not of old,' said I, 'a splendid city here?'--'Never,' answered he, 'so
far as we have seen, and never did our fathers speak to us of any such.'
On my return there 500 years afterwards, _I found the sea in the same
place_, and on its shores were a party of fishermen, of whom I inquired
how long the land had been covered by the waters? 'Is this a question,'
said they, 'for a man like you? this spot has always been what it is
now.' I again returned, 500 years afterwards, and the sea had
disappeared; I inquired of a man who stood alone upon the spot, how long
ago this change had taken place, and he gave me the same answer as I had
received before. Lastly, on coming back again after an equal lapse of
time, I found there a flourishing city, more populous and more rich in
beautiful buildings, than the city I had seen the first time, and when I
would fain have informed myself concerning its origin, the inhabitants
answered me, 'Its rise is lost in remote antiquity: we are ignorant how
long it has existed, and our fathers were on this subject as ignorant as
ourselves.'"

_Early Italian writers._--It was not till the earlier part of the
sixteenth century that geological phenomena began to attract the
attention of the Christian nations. At that period a very animated
controversy sprang up in Italy, concerning the true nature and origin of
marine shells, and other organized fossils, found abundantly in the
strata of the peninsula. The celebrated painter Leonardo da Vinci, who
in his youth had planned and executed some navigable canals in the north
of Italy, was one of the first who applied sound reasoning to these
subjects. The mud of rivers, he said, had covered and penetrated into
the interior of fossil shells at a time when these were still at the
bottom of the sea near the coast. "They tell us that these shells were
formed in the hills by the influence of the stars; but I ask where in
the hills are the stars now forming shells of distinct ages and species?
and how can the stars explain the origin of gravel, occurring at
different heights and composed of pebbles rounded as if by the motion of
running water; or in what manner can such a cause account for the
petrifaction in the same places of various leaves, sea-weeds, and
marine-crabs?"[40]

The excavations made in 1517, for repairing the city of Verona, brought
to light a multitude of curious petrifactions, and furnished matter for
speculation to different authors, and among the rest to Fracastoro,[41]
who declared his opinion, that fossil shells had all belonged to living
animals, which had formerly lived and multiplied where there exuviæ are
now found. He exposed the absurdity of having recourse to a certain
"plastic force," which it was said had power to fashion stones into
organic forms; and with no less cogent arguments, demonstrated the
futility of attributing the situation of the shells in question to the
Mosaic deluge, a theory obstinately defended by some. That inundation,
he observed, was too transient; it consisted principally of fluviatile
waters; and if it had transported shells to great distances, must have
strewed them over the surface, not buried them at vast depths in the
interior of mountains. His clear exposition of the evidence would have
terminated the discussion forever, if the passions of mankind had not
been enlisted in the dispute; and even though doubts should for a time
have remained in some minds, they would speedily have been removed by
the fresh information obtained almost immediately afterwards, respecting
the structure of fossil remains, and of their living analogues.

But the clear and philosophical views of Fracastoro were disregarded,
and the talent and argumentative powers of the learned were doomed for
three centuries to be wasted in the discussion of these two simple and
preliminary questions: first, whether fossil remains had ever belonged
to living creatures; and, secondly, whether, if this be admitted, all
the phenomena could not be explained by the deluge of Noah. It had been
the general belief of the Christian world down to the period now under
consideration, that the origin of this planet was not more remote than a
few thousand years; and that since the creation the deluge was the only
great catastrophe by which considerable change had been wrought on the
earth's surface. On the other hand, the opinion was scarcely less
general, that the final dissolution of our system was an event to be
looked for at no distant period. The era, it is true, of the expected
millennium had passed away; and for five hundred years after the fatal
hour when the annihilation of the planet had been looked for, the monks
remained in undisturbed enjoyment of rich grants of land bequeathed to
them by pious donors, who, in the preamble of deeds beginning
"appropinquante mundi termino"----"appropinquante magno judicii die,"
left lasting monuments of the popular delusion.[42]

But although in the sixteenth century it had become necessary to
interpret certain prophecies respecting the millennium more liberally,
and to assign a more distant date to the future conflagration of the
world, we find, in the speculations of the early geologists, perpetual
allusion to such an approaching catastrophe; while in all that regarded
the antiquity of the earth, no modification whatever of the opinions of
the dark ages had been effected. Considerable alarm was at first excited
when the attempt was made to invalidate, by physical proofs, an article
of faith so generally received; but there was sufficient spirit of
toleration and candor amongst the Italian ecclesiastics, to allow the
subject to be canvassed with much freedom. They even entered warmly into
the controversy themselves, often favoring different sides of the
question; and however much we may deplore the loss of time and labor
devoted to the defence of untenable positions, it must be conceded that
they displayed far less polemic bitterness than certain writers who
followed them "beyond the Alps," two centuries and a half later.


CONTROVERSY AS TO THE REAL NATURE OF FOSSIL ORGANIC REMAINS.

_Mattioli--Falloppio._--The system of scholastic disputations,
encouraged in the universities of the middle ages, had unfortunately
trained men to habits of indefinite argumentation; and they often
preferred absurd and extravagant propositions, because greater skill was
required to maintain them; the end and object of these intellectual
combats being victory, and not truth. No theory could be so far-fetched
or fantastical as not to attract some followers, provided it fell in
with popular notions; and as cosmogonists were not at all restricted, in
building their systems, to the agency of known causes, the opponents of
Fracastoro met his arguments by feigning imaginary causes, which
differed from each other rather in name than in substance. Andrea
Mattioli, for instance, an eminent botanist, the illustrator of
Dioscorides, embraced the notion of Agricola, a skilful German miner,
that a certain "materia pinguis," or "fatty matter," set into
fermentation by heat, gave birth to fossil organic shapes. Yet Mattioli
had come to the conclusion, from his own observations, that porous
bodies, such as bones and shells, might be converted into stone, as
being permeable to what he termed the "lapidifying juice." In like
manner, Falloppio of Padua conceived that petrified shells were
generated by fermentation in the spots where they are found, or that
they had in some cases acquired their form from "the tumultuous
movements of terrestrial exhalations." Although celebrated as a
professor of anatomy, he taught that certain tusks of elephants, dug up
in his time in Apulia, were mere earthy concretions; and, consistently
with these principles, he even went so far as to consider it probable,
that the vases of Monte Testaceo at Rome were natural impressions
stamped in the soil.[43] In the same spirit, Mercati, who published, in
1574, faithful figures of the fossil shells preserved by Pope Sixtus V.
in the Museum of the Vatican, expressed an opinion that they were mere
stones, which had assumed their peculiar configuration from the
influence of the heavenly bodies; and Olivi of Cremona, who described
the fossil remains of a rich museum at Verona, was satisfied with
considering them as mere "sports of nature."

Some of the fanciful notions of those times were deemed less
unreasonable, as being somewhat in harmony with the Aristotelian theory
of spontaneous generation, then taught in all the schools.[44] For men
who had been taught in early youth, that a large proportion of living
animals and plants was formed from the fortuitous concourse of atoms, or
had sprung from the corruption of organic matter, might easily persuade
themselves that organic shapes, often imperfectly preserved in the
interior of solid rocks, owed their existence to causes equally obscure
and mysterious.

_Cardano_, 1552.--But there were not wanting some who, during the
progress of this century, expressed more sound and sober opinions. The
title of a work of Cardano's, published in 1552, "De Subtilitate"
(corresponding to what would now be called Transcendental Philosophy),
would lead us to expect, in the chapter on minerals, many far-fetched
theories characteristic of that age; but when treating of petrified
shells, he decided that they clearly indicated the former sojourn of the
sea upon the mountains.[45]

_Cesalpino--Majoli_, 1597.--Cesalpino, a celebrated botanist, conceived
that fossil shells had been left on the land by the retiring sea, and
had concreted into stone during the consolidation of the soil;[46] and
in the following year (1597), Simeone Majoli[47] went still farther;
and, coinciding for the most part with the views of Cesalpino, suggested
that the shells and submarine matter of the Veronese, and other
districts, might have been cast up upon the land by volcanic explosions,
like those which gave rise, in 1538, to Monte Nuovo, near Puzzuoli. This
hint seems to have been the first imperfect attempt to connect the
position of fossil shells with the agency of volcanoes, a system
afterwards more fully developed by Hooke, Lazzaro Moro, Hutton, and
other writers.

Two years afterwards, Imperati advocated the animal origin of fossilized
shells, yet admitted that stones could vegetate by force of "an internal
principle;" and, as evidence of this, he referred to the teeth of fish
and spines of echini found petrified.[48]

_Palissy_, 1580.--Palissy, a French writer on "The Origin of Springs
from Rain-water," and of other scientific works, undertook, in 1580, to
combat the notions of many of his contemporaries in Italy, that
petrified shells had all been deposited by the universal deluge. "He was
the first," said Fontenelle, when, in the French Academy, he pronounced
his eulogy, nearly a century and a half later, "who dared assert," in
Paris, that fossil remains of testacea and fish had once belonged to
marine animals.

_Fabio Colonna._--To enumerate the multitude of Italian writers, who
advanced various hypotheses, all equally fantastical, in the early part
of the seventeenth century, would be unprofitably tedious; but Fabio
Colonna deserves to be distinguished; for, although he gave way to the
dogma, that all fossil remains were to be referred to the deluge of
Noah, he resisted the absurd theory of Stelluti, who taught that fossil
wood and ammonites were mere clay, altered into such forms by
sulphureous waters and subterranean heat; and he pointed out the
different states of shells buried in the strata, distinguishing between,
first, the mere mould or impression; second, the cast or nucleus; and,
thirdly, the remains of the shell itself. He had also the merit of being
the first to point out that some of the fossils had belonged to marine
and some to terrestrial testacea.[49]

_Steno_, 1669.--But the most remarkable work of that period was
published by Steno, a Dane, once professor of anatomy at Padua, and who
afterwards resided many years at the court of the Grand Duke of Tuscany.
His treatise bears the quaint title of "De Solido intra Solidum
naturaltier contento (1669)," by which the author intended to express,
"On Gems, Crystals, and organic Petrifactions inclosed within solid
Rocks." This work attests the priority of the Italian school in
geological research; exemplifying at the same time the powerful
obstacles opposed, in that age, to the general reception of enlarged
views in the science. It was still a favorite dogma, that the fossil
remains of shells and marine creatures were not of animal origin; an
opinion adhered to by many from their extreme reluctance to believe,
that the earth could have been inhabited by living beings before a great
part of the existing mountains were formed. In reference to this
controversy, Steno had dissected a shark recently taken from the
Mediterranean, and had demonstrated that its teeth and bones were
identical with many fossils found in Tuscany. He had also compared the
shells discovered in the Italian strata with living species, pointed out
their resemblance, and traced the various gradations from shells merely
calcined, or which had only lost their animal gluten, to those
petrifactions in which there was a perfect substitution of stony matter.
In his division of mineral masses, he insisted on the secondary origin
of those deposits in which the spoils of animals or fragments of older
rocks were inclosed. He distinguished between marine formations and
those of a fluviatile character, the last containing reeds, grasses,
or the trunks and branches of trees. He argued in favor of the original
horizontality of sedimentary deposits, attributing their present
inclined and vertical position sometimes to the escape of subterranean
vapors heaving the crust of the earth from below upwards, and sometimes
to the falling in of masses overlying subterranean cavities.

He declared that he had obtained proof that Tuscany must successively
have acquired six distinct configurations, having been twice covered by
water, twice laid dry with a level, and twice with an irregular and
uneven surface.[50] He displayed great anxiety to reconcile his new
views with Scripture, for which purpose he pointed to certain rocks as
having been formed before the existence of animals and plants: selecting
unfortunately as examples certain formations of limestone and sandstone
in his own country, now known to contain, though sparingly, the remains
of animals and plants,--strata which do not even rank as the oldest part
of our secondary series. Steno suggested that Moses, when speaking of
the loftiest mountains as having been covered by the deluge, meant
merely the loftiest of the hills then existing, which may not have been
very high. The diluvian waters, he supposed, may have issued from the
interior of the earth into which they had retired, when in the beginning
the land was separated from the sea. These, and other hypotheses on the
same subject, are not calculated to enhance the value of the treatise,
and could scarcely fail to detract from the authority of those opinions
which were sound and legitimate deductions from fact and observation.
They have served, nevertheless, as the germs of many popular theories of
later times, and in an expanded form have been put forth as original
inventions by some of our contemporaries.

_Scilla_, 1670.--Scilla, a Sicilian painter, published, in 1670, a
treatise, in Latin, on the fossils of Calabria, illustrated by good
engravings. This work proves the continued ascendancy of dogmas often
refuted; for we find the wit and eloquence of the author chiefly
directed against the obstinate incredulity of naturalists as to the
organic nature of fossil shells.[51] Like many eminent naturalists of
his day, Scilla gave way to the popular persuasion, that all fossil
shells were the effects and proofs of the Mosaic deluge. It may be
doubted whether he was perfectly sincere, and some of his contemporaries
who took the same course were certainly not so. But so eager were they
to root out what they justly considered an absurd prejudice respecting
the nature of organized fossils, that they seem to have been ready to
make any concessions, in order to establish this preliminary point. Such
a compromising policy was short-sighted, since it was to little purpose
that the nature of the documents should at length be correctly
understood, if men were to be prevented from deducing fair conclusions
from them.

_Diluvial Theory._--The theologians who now entered the field in Italy,
Germany, France, and England, were innumerable; and henceforward, they
who refused to subscribe to the position, that all marine organic
remains were proofs of the Mosaic deluge, were exposed to the imputation
of disbelieving the whole of the sacred writings. Scarcely any step had
been made in approximating to sound theories since the time of
Fracastoro, more than a hundred years having been lost, in writing down
the dogma that organized fossils were mere sports of nature. An
additional period of a century and a half was now destined to be
consumed in exploding the hypothesis, that organized fossils had all
been buried in the solid strata by Noah's flood. Never did a theoretical
fallacy, in any branch of science, interfere more seriously with
accurate observation and the systematic classification of facts. In
recent times, we may attribute our rapid progress chiefly to the careful
determination of the order of succession in mineral masses, by means of
their different organic contents, and their regular superposition. But
the old diluvialists were induced by their system to confound all the
groups of strata together instead of discriminating,--to refer all
appearances to one cause and to one brief period, not to a variety of
causes acting throughout a long succession of epochs. They saw the
phenomena only as they desired to see them, sometimes misrepresenting
facts, and at other times deducing false conclusions from correct data.
Under the influence of such prejudices, three centuries were of as
little avail as a few years in our own times, when we are no longer
required to propel the vessel against the force of an adverse current.

It may be well, therefore, to forewarn the reader, that in tracing the
history of geology from the close of the seventeenth to the end of the
eighteenth century, he must expect to be occupied with accounts of the
retardation, as well as of the advance, of the science. It will be
necessary to point out the frequent revival of exploded errors, and the
relapse from sound to the most absurd opinions; and to dwell on futile
reasoning and visionary hypothesis, because some of the most extravagant
systems were invented or controverted by men of acknowledged talent. In
short, a sketch of the progress of geology is the history of a constant
and violent struggle of new opinions against doctrines sanctioned by the
implicit faith of many generations, and supposed to rest on scriptural
authority. The inquiry, therefore, although highly interesting to one
who studies the philosophy of the human mind, is too often barren of
instruction to him who searches for truths in physical science.

_Quirini_, 1676.--Quirini, in 1676,[52] contended, in opposition to
Scilla, that the diluvian waters could not have conveyed heavy bodies to
the summit of mountains, since the agitation of the sea never (as Boyle
had demonstrated) extended to great depths;[53] and still less could
the testacea, as some pretended, have lived in these diluvian waters;
for "the duration of the flood was brief, and _the heavy rains must have
destroyed the saltness of the sea!_" He was the first writer who
ventured to maintain that the universality of the Mosaic cataclysm ought
not to be insisted upon. As to the nature of petrified shells, he
conceived that as earthy particles united in the sea to form the shells
of mollusca, the same crystallizing process might be effected on the
land; and that, in the latter case, the germs of the animals might have
been disseminated through the substance of the rocks, and afterwards
developed by virtue of humidity. Visionary as was this doctrine, it
gained many proselytes even amongst the more sober reasoners of Italy
and Germany; for it conceded that the position of fossil bodies could
not be accounted for by the diluvial theory.

_Plot--Lister_, 1678.--In the mean time, the doctrine that fossil shells
had never belonged to real animals maintained its ground in England,
where the agitation of the question began at a much later period. Dr.
Plot, in his "Natural History of Oxfordshire" (1677), attributed to a
"plastic virtue latent in the earth" the origin of fossil shells and
fishes; and Lister, to his accurate account of British shells, in 1678,
added the fossil species, under the appellation of _turbinated and
bivalve stones_. "Either," said he, "these were terriginous, or, if
otherwise, the animals they so exactly represent _have become extinct_."
This writer appears to have been the first who was aware of the
continuity over large districts of the principal groups of strata in the
British series, and who proposed the construction of regular geological
maps.[54]

_Leibnitz_, 1680.--The great mathematician Leibnitz published his
"Protogoea" in 1680. He imagined this planet to have been originally a
burning luminous mass, which ever since its creation has been undergoing
refrigeration. When the outer crust had cooled down sufficiently to
allow the vapors to be condensed, they fell, and formed a universal
ocean, covering the loftiest mountains, and investing the whole globe.
The crust, as it consolidated from a state of fusion, assumed a
vesicular and cavernous structure; and being rent in some places,
allowed the water to rush into the subterranean hollows, whereby the
level of the primeval ocean was lowered. The breaking in of these vast
caverns is supposed to have given rise to the dislocated and deranged
position of the strata "which Steno had described," and the same
disruptions communicated violent movements to the incumbent waters,
whence great inundations ensued. The waters, after they had been thus
agitated, deposited their sedimentary matter during intervals of
quiescence, and hence the various stony and earthy strata. "We may
recognize, therefore," says Leibnitz, "a double origin of primitive
masses, the one by refrigeration from igneous fusion, the other by
concretion from aqueous solution."[55] By the repetition of similar
causes (the disruption of the crust and consequent floods), alternations
of new strata were produced, until at length these causes were reduced
to a condition of quiescent equilibrium, and a more permanent state of
things was established.[56]

_Hooke_, 1688.--The "Posthumous Works of Robert Hooke, M. D.," well
known as a great mathematician and natural philosopher, appeared in
1705, containing "A Discourse of Earthquakes," which, we are informed by
his editor, was written in 1668, but revised at subsequent periods.[57]
Hooke frequently refers to the best Italian and English authors who
wrote before his time on geological subjects; but there are no passages
in his works implying that he participated in the enlarged views of
Steno and Lister, or of his contemporary, Woodward, in regard to the
geographical extent of certain groups of strata. His treatise, however,
is the most philosophical production of that age, in regard to the
causes of former changes in the organic and inorganic kingdoms of
nature.

"However trivial a thing," he says, "a rotten shell may appear to some,
yet these monuments of nature are more certain tokens of antiquity than
coins or medals, since the best of those may be counterfeited or made by
art and design, as may also books, manuscripts, and inscriptions, as all
the learned are now sufficiently satisfied has often been actually
practised," &c.; "and though it must be granted that it is very
difficult to read them (the records of nature) and _to raise a
chronology out of them_, and to state the intervals of the time wherein
such or such catastrophes and mutations have happened, yet it is not
impossible."[58]

Respecting the extinction of species, Hooke was aware that the fossil
ammonites, nautili, and many other shells and fossil skeletons found in
England, were of different species from any then known; but he doubted
whether the species had become extinct, observing that the knowledge of
naturalists of all the marine species, especially those inhabiting the
deep sea, was very deficient. In some parts of his writings, however,
he leans to the opinion that species had been lost; and in speculating
on this subject, he even suggests that there might be some connection
between the disappearance of certain kinds of animals and plants, and
the changes wrought by earthquakes in former ages. Some species, he
observes, with great sagacity, are "_peculiar to certain places_, and
not to be found elsewhere. If, then, such a place had been swallowed up,
it is not improbable but that those animate beings may have been
destroyed with it; and this may be true both of aerial and aquatic
animals; for those animated bodies, whether vegetables or animals, which
were naturally nourished or refreshed by the air, would be destroyed by
the water," &c.[59] Turtles, he adds, and such large ammonites as are
found in Portland, seem to have been the productions of hotter
countries; and it is necessary to suppose that England once lay under
the sea within the torrid zone! To explain this and similar phenomena,
he indulges in a variety of speculations concerning changes in the
position of the axis of the earth's rotation, "a shifting of the earth's
centre of gravity, analogous to the revolutions of the magnetic pole,"
&c. None of these conjectures, however, are proposed dogmatically, but
rather in the hope of promoting fresh inquiries and experiments.

In opposition to the prejudices of his age, we find him arguing against
the idea that nature had formed fossil bodies "for no other end than to
play the mimic in the mineral kingdom;"--maintaining that figured stones
were "really the several bodies they represent, or the mouldings of them
petrified," and not, as some have imagined, 'a lusus naturæ,' sporting
herself in the needless formation of useless beings."[60]

It was objected to Hooke, that his doctrine of the extinction of species
derogated from the wisdom and power of the omnipotent Creator; but he
answered, that, as individuals die, there may be some termination to the
duration of a species; and his opinions, he declared, were not repugnant
to Holy Writ: for the Scriptures taught that our system was
degenerating, and tending to its final dissolution; "and as, when that
shall happen, all the species will be lost, why not some at one time and
some at another?"[61]

But his principal object was to account for the manner in which shells
had been conveyed into the higher parts of "the Alps, Apennines, and
Pyrenean hills, and the interior of continents in general." These and
other appearances, he said, might have been brought about by
earthquakes, "which have turned plains into mountains, and mountains
into plains, seas into land, and land into seas, made rivers where there
were none before, and swallowed up others that formerly were, &c., &c.;
and which, since the creation of the world, have wrought many great
changes on the superficial parts of the earth, and have been the
instruments of placing shells, bones, plants, fishes, and the like, in
those places where, with much astonishment, we find them."[62] This
doctrine, it is true, had been laid down in terms almost equally
explicit by Strabo, to explain the occurrence of fossil shells in the
interior of continents, and to that geographer, and other writers of
antiquity, Hooke frequently refers; but the revival and development of
the system was an important step in the progress of modern science.

Hooke enumerated all the examples known to him of subterranean
disturbance, from "the sad catastrophe of Sodom and Gomorrah," down to
the Chilian earthquake of 1646. The elevating of the bottom of the sea,
the sinking and submersion of the land, and most of the inequalities of
the earth's surface, might, he said, be accounted for by the agency of
these subterranean causes. He mentions that the coast near Naples _was
raised during the eruption of Monte Nuovo_; and that, in 1591, land rose
in the island of St. Michael, during an eruption: and although it would
be more difficult, he says, to prove, he does not doubt but that there
had been as many earthquakes in the parts of the earth under the ocean,
as in the parts of the dry land; in confirmation of which, he mentions
the immeasurable depth of the sea near some volcanoes. To attest the
extent of simultaneous subterranean movements, he refers to an
earthquake in the West Indies, in the year 1690, where the space of
earth raised, or "struck upwards," by the shock, exceeded, he affirms,
the length of the Alps and Pyrenees.

_Hooke's diluvial Theory._--As Hooke declared the favorite hypothesis of
the day, "that marine fossil bodies were to be referred to Noah's
flood," to be wholly untenable, he appears to have felt himself called
upon to substitute a diluvial theory of his own, and thus he became
involved in countless difficulties and contradictions. "During the great
catastrophe," he said, "there might have been a changing of that part
which was before dry land into sea by sinking, and of that which was sea
into dry land by raising, and marine bodies might have been buried in
sediment beneath the ocean, in the interval between the creation and the
deluge."[63] Then follows a disquisition on the separation of the land
from the waters, mentioned in Genesis; during which operation some
places of the shell of the earth were forced outwards, and others
pressed downwards or inwards, &c. His diluvial hypothesis very much
resembled that of Steno, and was entirely opposed to the fundamental
principles professed by him, that he would explain the former changes
of the earth _in a more natural manner_ than others had done. When, in
despite of this declaration, he required a former "crisis of nature,"
and taught that earthquakes had become debilitated, and that the Alps,
Andes, and other chains, had been lifted up in a few months, he was
compelled to assume so rapid a rate of change, that his machinery
appeared scarcely less extravagant than that of his most fanciful
predecessors. For this reason, perhaps, his whole theory of earthquakes
met with undeserved neglect.

_Ray_, 1692.--One of his contemporaries, the celebrated naturalist, Ray,
participated in the same desire to explain geological phenomena by
reference to causes less hypothetical than those usually resorted
to.[64] In his essay on "Chaos and Creation," he proposed a system,
agreeing in its outline, and in many of its details, with that of Hooke;
but his knowledge of natural history enabled him to elucidate the
subject with various original observations. Earthquakes, he suggested,
might have been the second causes employed at the creation, in
separating the land from the waters, and in gathering the waters
together into one place. He mentions, like Hooke, the earthquake of
1646, which had violently shaken the Andes for some hundreds of leagues,
and made many alterations therein. In assigning a cause for the general
deluge, he preferred a change in the earth's centre of gravity to the
introduction of earthquakes. Some unknown cause, he said, might have
forced the subterranean waters outwards, as was, perhaps, indicated by
"the breaking up of the fountains of the great deep."

Ray was one of the first of our writers who enlarged upon the effects of
running water upon the land, and of the encroachment of the sea upon the
shores. So important did he consider the agency of these causes, that he
saw in them an indication of the tendency of our system to its final
dissolution; and he wondered why the earth did not proceed more rapidly
towards a general submersion beneath the sea, when so much matter was
carried down by rivers, or undermined in the sea-cliffs. We perceive
clearly from his writings, that the gradual decline of our system, and
its future consummation by fire, was held to be as necessary an article
of faith by the orthodox, as was the recent origin of our planet. His
discourses, like those of Hooke, are highly interesting, as attesting
the familiar association in the minds of philosophers, in the age of
Newton, of questions in physics and divinity. Ray gave an unequivocal
proof of the sincerity of his mind, by sacrificing his preferment in the
church, rather than take an oath against the Covenanters, which he could
not reconcile with his conscience. His reputation, moreover, in the
scientific world placed him high above the temptation of courting
popularity, by pandering to the physico-theological taste of his age. It
is, therefore, curious to meet with so many citations from the
Christian fathers and prophets in his essays on physical science--to
find him in one page proceeding, by the strict rules of induction, to
explain the former changes of the globe, and in the next gravely
entertaining the question, whether the sun and stars, and the whole
heavens, shall be annihilated, together with the earth, at the era of
the grand conflagration.

_Woodward, 1695._--Among the contemporaries of Hooke and Ray, Woodward,
a professor of medicine, had acquired the most extensive information
respecting the geological structure of the crust of the earth. He had
examined many parts of the British strata with minute attention; and his
systematic collection of specimens, bequeathed to the University of
Cambridge, and still preserved there as arranged by him, shows how far
he had advanced in ascertaining the order of superposition. From the
great number of facts collected by him, we might have expected his
theoretical views to be more sound and enlarged than those of his
contemporaries; but in his anxiety to accommodate all observed phenomena
to the scriptural account of the Creation and Deluge, he arrived at most
erroneous results. He conceived "the whole terrestrial globe to have
been taken to pieces and dissolved at the flood, and the strata to have
settled down from this promiscuous mass as any earthy sediment from a
fluid."[65] In corroboration of these views he insisted upon the fact,
that "marine bodies are lodged in the strata according to the order of
their gravity, the heavier shells in stone, the lighter in chalk, and so
of the rest."[66] Ray immediately exposed the unfounded nature of this
assertion, remarking truly that fossil bodies "are often mingled, heavy
with light, in the same stratum;" and he even went so far as to say,
that Woodward "must have invented the phenomena for the sake of
confirming his bold and strange hypothesis"[67]--a strong expression
from the pen of a contemporary.

_Burnet, 1690._--At the same time Burnet published his "Theory of the
Earth."[68] The title is most characteristic of the age,--"The Sacred
Theory of the Earth; containing an Account of the Original of the Earth,
and of all the general Changes which it hath already undergone, or is to
undergo, till the Consummation of all Things." Even Milton had scarcely
ventured in his poem to indulge his imagination so freely in painting
scenes of the Creation and Deluge, Paradise and Chaos. He explained why
the primeval earth enjoyed a perpetual spring before the flood! showed
how the crust of the globe was fissured by "the sun's rays," so that it
burst, and thus the diluvial waters were let loose from a supposed
central abyss. Not satisfied with these themes, he derived from the
books of the inspired writers, and even from heathen authorities,
prophetic views of the future revolutions of the globe, gave a most
terrific description of the general conflagration, and proved that a new
heaven and a new earth will rise out of a _second chaos_--after which
will follow the blessed millennium.

The reader should be informed, that, according to the opinion of many
respectable writers of that age, there was good scriptural ground for
presuming that the garden bestowed upon our first parents was not on the
earth itself, but above the clouds, in the middle region between our
planet and the moon. Burnet approaches with becoming gravity the
discussion of so important a topic. He was willing to concede that the
geographical position of Paradise was not in Mesopotamia, yet he
maintained that it was upon the earth, and in the southern hemisphere,
near the equinoctial line. Butler selected this conceit as a fair mark
for his satire, when, amongst the numerous accomplishments of Hudibras,
he says,--


  "He knew the seat of Paradise,
   Could tell in what degree it lies;
   And, as he was disposed, could prove it
   Below the moon, or else above it."


Yet the same monarch, who is said never to have slept without Butler's
poem under his pillow, was so great an admirer and patron of Burnet's
book, that he ordered it to be translated from the Latin into English.
The style of the "Sacred Theory" was eloquent, and the book displayed
powers of invention of no ordinary stamp. It was, in fact, a fine
historical romance, as Buffon afterwards declared; but it was treated as
a work of profound science in the time of its author, and was
panegyrized by Addison in a Latin ode, while Steele praised it in the
"Spectator."

_Whiston, 1696._--Another production of the same school, and equally
characteristic of the time, was that of Whiston, entitled, "A New Theory
of the Earth; wherein the Creation of the world in Six Days, the
Universal Deluge, and the General Conflagration, as laid down in the
Holy Scriptures, are shown to be perfectly agreeable to Reason and
Philosophy." He was at first a follower of Burnet; but his faith in the
infallibility of that writer was shaken by the declared opinion of
Newton, that there was every presumption in astronomy against any former
change in the inclination of the earth's axis. This was a leading dogma
in Burnet's system, though not original, for it was borrowed from an
Italian, Alessandro degli Alessandri, who had suggested it in the
beginning of the fifteenth century, to account for the former occupation
of the present continents by the sea. La Place has since strengthened
the arguments of Newton, against the probability of any former
revolution of this kind.

The remarkable comet of 1680 was fresh in the memory of every one when
Whiston first began his cosmological studies; and the principal novelty
of his speculations consisted in attributing the deluge to the near
approach to the earth of one of these erratic bodies. Having ascribed an
increase of the waters to this source, he adopted Woodward's theory,
supposing all stratified deposits to have resulted from the "chaotic
sediment of the flood." Whiston was one of the first who ventured to
propose that the text of Genesis should be interpreted differently from
its ordinary acceptation, so that the doctrine of the earth having
existed long previous to the creation of man might no longer be regarded
as unorthodox. He had the art to throw an air of plausibility over the
most improbable parts of his theory, and seemed to be proceeding in the
most sober manner, and, by the aid of mathematical demonstration, to the
establishment of his various propositions. Locke pronounced a panegyric
on his theory, commending him for having explained so many wonderful and
before inexplicable things. His book, as well as Burnet's, was attacked
and refuted by Keill.[69] Like all who introduced purely hypothetical
causes to account for natural phenomena, Whiston retarded the progress
of truth, diverting men from the investigation of the laws of sublunary
nature, and inducing them to waste time in speculations on the power of
comets to drag the waters of the ocean over the land--on the
condensation of the vapors of their tails into water, and other matters
equally edifying.

_Hutchinson, 1724._--John Hutchinson, who had been employed by Woodward
in making his collection of fossils, published afterwards, in 1724, the
first part of his "Moses's Principia," wherein he ridiculed Woodward's
hypothesis. He and his numerous followers were accustomed to declaim
loudly against human learning; and they maintained that the Hebrew
Scriptures, when rightly translated, comprised a perfect system of
natural philosophy, for which reason they objected to the Newtonian
theory of gravitation.

_Celsius._--Andrea Celsius, the Swedish astronomer, published about this
time his remarks on the gradual diminution and sinking of the waters in
the Baltic, to which I shall have occasion to advert more particularly
in the sequel (ch. 29).

_Scheuchzer, 1708._--In Germany, in the mean time, Scheuchzer published
his "Complaint and Vindication of the Fishes" (1708), "Piscium Querelæ
et Vindiciæ," a work of zoological merit, in which he gave some good
plates and descriptions of fossil fish. Among other conclusions he
labored to prove that the earth had been remodelled at the deluge.
Pluche, also, in 1732, wrote to the same effect; while Holbach, in 1753,
after considering the various attempts to refer all the ancient
formations to the flood of Noah, exposed the inadequacy of this cause.

_Italian Geologists--Vallisneri._--I return with pleasure to the
geologists of Italy, who preceded, as has been already shown, the
naturalists of other countries in their investigations into the ancient
history of the earth, and who still maintained a decided pre-eminence.
They refuted and ridiculed the physico-theological systems of Burnet,
Whiston, and Woodward;[70] while Vallisneri,[71] in his comments on the
Woodwardian theory, remarked how much the interests of religion, as well
as those of sound philosophy, had suffered by perpetually mixing up the
sacred writings with questions in physical science. The works of this
author were rich in original observations. He attempted the first
general sketch of the marine deposits of Italy, their geographical
extent, and most characteristic organic remains. In his treatise "On the
Origin of Springs," he explained their dependence on the order, and
often on the dislocations, of the strata, and reasoned philosophically
against the opinions of those who regarded the disordered state of the
earth's crust as exhibiting signs of the wrath of God for the sins of
man. He found himself under the necessity of contending, in his
preliminary chapter, against St. Jerome, and four other principal
interpreters of Scripture, besides several professors of divinity, "that
springs did not flow by subterranean siphons and cavities from the sea
upwards, losing their saltness in the passage," for this theory had been
made to rest on the infallible testimony of Holy Writ.

Although reluctant to generalize on the rich materials accumulated in
his travels, Vallisneri had been so much struck with the remarkable
continuity of the more recent marine strata, from one end of Italy to
the other, that he came to the conclusion that the ocean formerly
extended over the whole earth, and after abiding there for a long time,
had gradually subsided. This opinion, however untenable, was a great
step beyond Woodward's diluvian hypothesis, against which Vallisneri,
and after him all the Tuscan geologists, uniformly contended, while it
was warmly supported by the members of the Institute of Bologna.[72]

Among others of that day, Spada, a priest of Grezzana, in 1737, wrote to
prove that the petrified marine bodies near Verona were not
diluvian.[73] Mattani drew a similar inference from the shells of
Volterra and other places; while Costantini, on the other hand, whose
observations on the valley of the Brenta and other districts were not
without value, undertook to vindicate the truth of the deluge, as also
to prove that Italy had been peopled by the descendants of Japhet.[74]

_Moro_, 1740.--Lazzaro Moro, in his work (published in 1740) "On the
Marine Bodies which are found in the Mountains,"[75] attempted to apply
the theory of earthquakes, as expounded by Strabo, Pliny, and other
ancient authors, with whom he was familiar, to the geological phenomena
described by Vallisneri.[76] His attention was awakened to the
elevating power of subterranean forces by a remarkable phenomenon which
happened in his own time, and which had also been noticed by Vallisneri
in his letters. A new island rose in 1707 from deep water in the Gulf of
Santorin, in the Mediterranean, during continued shocks of an
earthquake, and, increasing rapidly in size, grew in less than a month
to be half a mile in circumference, and about twenty-five feet above
high-water mark. It was soon afterwards covered by volcanic ejections,
but, when first examined, it was found to be a white rock, bearing on
its surface living oysters and crustacea. In order to ridicule the
various theories then in vogue, Moro ingeniously supposes the arrival on
this new island of a party of naturalists ignorant of its recent origin.
One immediately points to the marine shells, as proofs of the universal
deluge; another argues that they demonstrate the former residence of the
sea upon the mountains; a third dismisses them as mere _sports of
nature_; while a fourth affirms that they were born and nourished within
the rock in ancient caverns, into which salt water had been raised in
the shape of vapor by the action of subterranean heat.

Moro pointed with great judgment to the _faults_ and dislocations of the
strata described by Vallisneri, in the Alps and other chains, in
confirmation of his doctrine, that the continents had been heaved up by
subterranean movements. He objected, on solid grounds, to the hypothesis
of Burnet and of Woodward; yet he ventured so far to disregard the
protest of Vallisneri, as to undertake the adaptation of every part of
his own system to the Mosaic account of the creation. On the third day,
he said, the globe was everywhere covered to the same depth by fresh
water; and when it pleased the Supreme Being that the dry land should
appear, volcanic explosions broke up the smooth and regular surface of
the earth composed of primary rocks. These rose in mountain masses above
the waves, and allowed melted metals and salts to ascend through
fissures. The sea gradually acquired its saltness from volcanic
exhalations, and, while it became more circumscribed in area, increased
in depth. Sand and ashes ejected by volcanoes were regularly disposed
along the bottom of the ocean, and formed the secondary strata, which in
their turn were lifted up by earthquakes. We need not follow this author
in tracing the progress of the creation of vegetables and animals on the
other days of creation; but, upon the whole, it may be remarked, that
few of the old cosmological theories had been conceived with so little
violation of known analogies.

_Generelli's illustrations of Moro_, 1749.--The style of Moro was
extremely prolix, and, like Hutton, who, at a later period, advanced
many of the same views, he stood in need of an illustrator. The Scotch
geologist was hardly more fortunate in the advocacy of Playfair, than
was Moro in numbering amongst his admirers Cirillo Generelli, who, nine
years afterwards, delivered at a sitting of Academicians at Cremona a
spirited exposition of his theory. This learned Carmelitan friar does
not pretend to have been an original observer, but he had studied
sufficiently to enable him to confirm the opinions of Moro by arguments
from other writers; and his selection of the doctrines then best
established is so judicious, that a brief abstract of them cannot fail
to be acceptable, as illustrating the state of geology in Europe, and in
Italy in particular, before the middle of the last century.

The bowels of the earth, says he, have carefully preserved the memorials
of past events, and this truth the marine productions so frequent in the
hills attest. From the reflections of Lazzaro Moro, we may assure
ourselves that these are the effects of earthquakes in past times, which
have changed vast spaces of sea into terra firma, and inhabited lands
into seas. In this, more than in any other department of physics, are
observations and experiments indispensable, and we must diligently
consider facts. The land is known, wherever we make excavations, to be
composed of different strata or soils placed one above the other, some
of sand, some of rock, some of chalk, others of marl, coal, pummice,
gypsum, lime, and the rest. These ingredients are sometimes pure, and
sometimes confusedly intermixed. Within are often imprisoned different
marine fishes, like dried mummies, and more frequently shells,
crustacea, corals, plants, &c., not only in Italy, but in France,
Germany, England, Africa, Asia, and America;--sometimes in the lowest,
sometimes in the loftiest beds of the earth, some upon the mountains,
some in deep mines, others near the sea, and others hundreds of miles
distant from it. Woodward conjectured that these marine bodies might be
found everywhere; but there are rocks in which none of them occur, as is
sufficiently attested by Vallisneri and Marsilli. The remains of fossil
animals consist chiefly of their more solid parts, and the most rocky
strata must have been soft when such exuviæ were inclosed in them.
Vegetable productions are found in different states of maturity,
indicating that they were imbedded in different seasons. Elephants,
elks, and other terrestrial quadrupeds, have been found in England and
elsewhere, in superficial strata, never covered by the sea. Alternations
are rare, yet not without example, of marine strata, with those which
contain marshy and terrestrial productions. Marine animals are arranged
in the subterraneous beds with admirable order, in distinct groups,
oysters here, dentalia or corals there, &c., as now, according to
Marsilli,[77] on the shores of the Adriatic. We must abandon the
doctrine, once so popular, which denies that organized fossils were
derived from living beings, and we cannot account for their present
position by the ancient theory of Strabo, nor by that of Leibnitz, nor
by the universal deluge, as explained by Woodward and others; "nor is it
reasonable to call the Deity capriciously upon the stage, and to make
him work miracles for the sake of confirming our preconceived
hypothesis." --"I hold in utter abomination, most learned Academicians!
those systems which are built with their foundations in the air, and
cannot be propped up without a miracle; and I undertake, with the
assistance of Moro, to explain to you how these marine animals were
transported into the mountains by natural causes."[78]

A brief abstract then follows of Moro's theory, by which, says
Generelli, we may explain all the phenomena, as Vallisneri so ardently
desired, "_without violence, without fictions, without hypothesis,
without miracles_."[79] The Carmelitan then proceeds to struggle against
an obvious objection to Moro's system, considered as a method of
explaining the revolutions of the earth, _naturally_. If earthquakes
have been the agents of such mighty changes, how does it happen that
their effects since the times of history have been so inconsiderable?
This same difficulty had, as we have seen, presented itself to Hooke,
half a century before, and forced him to resort to a former "crisis of
nature:" but Generelli defended his position by showing how numerous
were the accounts of eruptions and earthquakes, of new islands, and of
elevations and subsidences of land, and yet how much greater a number of
like events must have been unattested and unrecorded during the last six
thousand years. He also appealed to Vallisneri as an authority to prove
that the mineral masses containing shells, bore, upon the whole, but a
small proportion to those rocks which were destitute of organic remains;
and the latter, says the learned monk, might have been created as they
now exist, _in the beginning_.

Generelli then describes the continual waste of mountains and
continents, by the action of rivers and torrents, and concludes with
these eloquent and original observations:--"Is it possible that this
waste should have continued for six thousand, and _perhaps_ a greater
number of years, and that the mountains should remain so great, unless
their ruins have been repaired? Is it credible that the Author of Nature
should have founded the world upon such laws, as that the dry land
should forever be growing smaller, and at last become wholly submerged
beneath the waters? Is it credible that, amid so many created things,
the mountains alone should daily diminish in number and bulk, without
there being any repair of their losses? This would be contrary to that
order of Providence which is seen to reign in all other things in the
universe. Wherefore I deem it just to conclude, that the same cause
which, in the beginning of time, raised mountains from the abyss, has
down to the present day continued to produce others, in order to restore
from time to time the losses of all such as sink down in different
places, or are rent asunder, or in other way suffer disintegration. If
this be admitted, we can easily understand why there should now be found
upon many mountains so great a number of crustacea and other marine
animals."

In the above extract, I have not merely enumerated the opinions and
facts which are confirmed by recent observation, suppressing all that
has since proved to be erroneous, but have given a faithful abridgment
of the entire treatise, with the omission only of Moro's hypothesis,
which Generelli adopted, with all its faults and excellences. The reader
will therefore remark, that although this admirable essay embraces so
large a portion of the principal objects of geological research, it
makes no allusion to the extinction of certain classes of animals; and
it is evident that no opinions on this head had, at that time, gained a
firm footing in Italy. That Lister and other English naturalists should
long before have declared in favor of the loss of species, while Scilla
and most of his countrymen hesitated, was perhaps natural, since the
Italian museums were filled with fossil shells belonging to species of
which a great portion did actually exist in the Mediterranean; whereas
the English collectors could obtain no recent species from such of their
own strata as were then explored.

The weakest point in Moro's system consisted in deriving _all_ the
stratified rocks from volcanic ejections; an absurdity which his
opponents took care to expose, especially Vito Amici.[80] Moro seems to
have been misled by his anxious desire to represent the formation of
secondary rocks as having occupied an extremely short period, while at
the same time he wished to employ known agents in nature. To imagine
torrents, rivers, currents, partial floods, and all the operations of
moving water, to have gone on exerting an energy many thousand times
greater than at present, would have appeared preposterous and
incredible, and would have required a hundred violent hypotheses; but we
are so unacquainted with the true sources of subterranean disturbances,
that their former violence may in theory be multiplied indefinitely,
without its being possible to prove the same manifest contradiction or
absurdity in the conjecture. For this reason, perhaps, Moro preferred to
derive the materials of the strata from volcanic ejections, rather than
from transportation by running water.

_Marsilli._--Marsilli, whose work is alluded to by Generelli, had been
prompted to institute inquiries into the bed of the Adriatic, by
discovering, in the territory of Parma (what Spada had observed near
Verona, and Schiavo in Sicily), that fossil shells were not scattered
through the rocks at random, but disposed in regular order, according to
certain genera and species.

_Vitaliano Donati_, 1750.--But with a view of throwing further light
upon these questions, Donati, in 1750, undertook a more extensive
investigation of the Adriatic, and discovered, by numerous soundings,
that deposits of sand, marl, and tufaceous incrustations, most strictly
analogous to those of the Subapennine hills, were in the act of
accumulating there. He ascertained that there were no shells in some of
the submarine tracts, while in other places they lived together in
families, particularly the genera Arca, Pecten, Venus, Murex, and some
others. He also states that in divers localities he found a mass
composed of corals, shells, and crustaceous bodies of different species,
confusedly blended with earth, sand, and gravel. At the depth of a foot
or more, the organic substances were entirely petrified and reduced to
marble; at less than a foot from the surface, they approached nearer to
their natural state; while at the surface they were alive, or, if dead,
in a good state of preservation.

_Baldassari_.--A contemporary naturalist, Baldassari, had shown that the
organic remains in the tertiary marls of the Siennese territory were
grouped in families, in a manner precisely similar to that above alluded
to by Donati.

_Buffon_, 1749.--Buffon first made known his theoretical views
concerning the former changes of the earth, in his Natural History,
published in 1749. He adopted the theory of an original volcanic
nucleus, together with the universal ocean of Leibnitz. By this aqueous
envelope the highest mountains were once covered. Marine currents then
acted violently, and formed horizontal strata, by washing away solid
matter in some parts, and depositing it in others; they also excavated
deep submarine valleys. The level of the ocean was then depressed by the
entrance of a part of its waters into subterranean caverns, and thus
some land was left dry. Buffon seems not to have profited, like Leibnitz
and Moro, by the observations of Steno, or he could not have imagined
that the strata were generally horizontal, and that those which contain
organic remains had never been disturbed since the era of their
formation. He was conscious of the great power annually exerted by
rivers and marine currents in transporting earthy materials to lower
levels, and he even contemplated the period when they would destroy all
the present continents. Although in geology he was not an original
observer, his genius enabled him to render his hypothesis attractive;
and by the eloquence of his style, and the boldness of his speculations,
he awakened curiosity, and provoked a spirit of inquiry amongst his
countrymen.

Soon after the publication of his "Natural History," in which was
included his "Theory of the Earth," he received an official letter
(dated January, 1751) from the Sorbonne, or Faculty of Theology in
Paris, informing him that fourteen propositions in his works "were
reprehensible, and contrary to the creed of the church." The first of
these obnoxious passages, and the only one relating to geology, was as
follows:--"The waters of the sea have produced the mountains and valleys
of the land--the waters of the heavens, reducing all to a level, will at
last deliver the whole land over to the sea, and the sea successively
prevailing over the land, will leave dry new continents like those which
we inhabit." Buffon was invited by the College, in very courteous terms,
to send in an explanation, or rather a recantation of his unorthodox
opinions. To this he submitted; and a general assembly of the Faculty
having approved of his "Declaration," he was required to publish it in
his next work. The document begins with these words:--"I declare that I
had no intention to contradict the text of Scripture; that I believe
most firmly all therein related about the creation, both as to order of
time and matter of fact; and _I abandon every thing in my book
respecting the foundation of the earth_, and, generally, all which may
be contrary to the narration of Moses."[81]

The grand principle which Buffon was called upon to renounce was simply
this,--that the present mountains and valleys of the earth are due to
secondary causes, and that the same causes will in time destroy all the
continents, hills, and valleys, and reproduce others like them. Now,
whatever may be the defects of many of his views, it is no longer
controverted that the present continents are of secondary origin. The
doctrine is as firmly established as the earth's rotation on its axis;
and that the land now elevated above the level of the sea will not
endure forever, is an opinion which gains ground daily, in proportion as
we enlarge our experience of the changes now in progress.

_Targioni_, 1751.--Targioni, in his voluminous "Travels in Tuscany, 1751
and 1754," labored to fill up the sketch of the geology of that region
left by Steno sixty years before. Notwithstanding a want of arrangement
and condensation in his memoirs, they contained a rich store of faithful
observations. He has not indulged in many general views, but in regard
to the origin of valleys, he was opposed to the theory of Buffon, who
attributed them principally to submarine currents. The Tuscan naturalist
labored to show that both the larger and smaller valleys of the
Apennines were excavated by rivers and floods, caused by the bursting of
the barriers of lakes, after the retreat of the ocean. He also
maintained that the elephants and other quadrupeds, so frequent in the
lacustrine and alluvial deposits of Italy, had inhabited that peninsula;
and had not been transported thither, as some had conceived, by Hannibal
or the Romans, nor by what they were pleased to term "a catastrophe of
nature."

_Lehman_, 1756.--In the year 1756 the treatise of Lehman, a German
mineralogist, and director of the Prussian mines, appeared, who also
divided mountains into three classes: the first, those formed with the
world, and prior to the creation of animals, and which contained no
fragments of other rocks; the second class, those which resulted from
the partial destruction of the primary rocks by a general revolution;
and a third class, resulting from local revolutions, and in part from
the deluge of Noah.

A French translation of this work appeared in 1759, in the preface of
which, the translator displays very enlightened views respecting the
operations of earthquakes, as well as of the aqueous causes.[82]

_Gesner_, 1758.--In this year Gesner, the botanist, of Zurich,
published an excellent treatise on petrifactions, and the changes of the
earth which they testify.[83] After a detailed enumeration of the
various classes of fossils of the animal and vegetable kingdoms, and
remarks on the different states in which they are found petrified, he
considers the geological phenomena connected with them; observing, that
some, like those of OEningen, resembled the testacea, fish, and plants
indigenous in the neighboring region;[84] while some, such as ammonites,
gryphites, belemnites, and other shells, are either of unknown species,
or found only in the Indian and other distant seas. In order to
elucidate the structure of the earth, he gives sections, from Verenius,
Buffon, and others, obtained in digging wells; distinguishes between
horizontal and inclined strata; and, in speculating on the causes of
these appearances, mentions Donati's examination of the bed of the
Adriatic; the filling up of lakes and seas by sediment; the imbedding of
shells now in progress; and many known effects of earthquakes, such as
the sinking down of districts, or the heaving up of the bed of the sea,
so as to form new islands, and lay dry strata containing petrifactions.
The ocean, he says, deserts its shores in many countries, as on the
borders of the Baltic; but the rate of recession has been so slow in the
last 2000 years, that to allow the Apennines, whose summits are filled
with marine shells, to emerge to their present height, would have
required about 80,000 years,--a lapse of time ten times greater, or
more, than the age of the universe. We must therefore refer the
phenomenon to the command of the Deity, related by Moses, that "the
waters should be gathered together in one place, and the dry land
appear." Gesner adopted the views of Leibnitz, to account for the
retreat of the primeval ocean: his essay displays much erudition; and
the opinions of preceding writers of Italy, Germany, and England, are
commented upon with fairness and discrimination.

_Arduino_, 1759.--In the year following, Arduino,[85] in his memoirs on
the mountains of Padua, Vicenza, and Verona, deduced, from original
observations, the distinction of rocks into primary, secondary, and
tertiary, and showed that in those districts there had been a succession
of submarine volcanic eruptions.

_Michell_, 1760.--In the following year (1760) the Rev. John Michell,
Woodwardian Professor of Mineralogy at Cambridge, published in the
Philosophical Transactions, an Essay on the Cause and Phenomena of
Earthquakes.[86] His attention had been drawn to this subject by the
great earthquake of Lisbon in 1755. He advanced many original and
philosophical views respecting the propagation of subterranean
movements, and the caverns and fissures wherein steam might be
generated. In order to point out the application of his theory to the
structure of the globe, he was led to describe the arrangement and
disturbance of the strata, their usual horizontality in low countries,
and their contortions and fractured state in the neighborhood of
mountain chains. He also explained, with surprising accuracy, the
relations of the central ridges of older rocks to the "long narrow slips
of similar earth, stones, and minerals," which are parallel to these
ridges. In his generalizations, derived in great part from his own
observations on the geological structure of Yorkshire, he anticipated
many of the views more fully developed by later naturalists.

_Catcott_, 1761.--Michell's papers were entirely free from all
physico-theological disquisitions, but some of his contemporaries were
still earnestly engaged in defending or impugning the Woodwardian
hypothesis. We find many of these writings referred to by Catcott, a
Hutchinsonian, who published a "Treatise on the Deluge" in 1761. He
labored particularly to refute an explanation offered by his
contemporary, Bishop Clayton, of the Mosaic writings. That prelate had
declared that the deluge "could not be literally true, save in respect
to that part where Noah lived before the flood." Catcott insisted on the
universality of the deluge, and referred to traditions of inundations
mentioned by ancient writers, or by travellers, in the East Indies,
China, South America, and other countries. This part of his book is
valuable, although it is not easy to see what bearing the traditions
have, if admitted to be authentic, on the Bishop's argument, since no
evidence is adduced to prove that the catastrophes were contemporaneous
events, while some of them are expressly represented by ancient authors
to have occurred in succession.

_Fortis--Odoardi_, 1761.--The doctrines of Arduino, above adverted to,
were afterwards confirmed by Fortis and Desmarest, in their travels in
the same country; and they, as well as Baldassari, labored to complete
the history of the Subapennine strata. In the work of Odoardi,[87] there
was also a clear argument in favor of the distinct ages of the older
Apennine strata, and the Subapennine formations of more recent origin.
He pointed out that the strata of these two groups were _unconformable_,
and must have been the deposits of different seas at distant periods of
time.

_Raspe_, 1763.--A history of the new islands, by Raspe, a Hanoverian,
appeared in 1763, in Latin.[88] In this work, all the authentic accounts
of earthquakes which had produced permanent changes on the solid parts
of the earth were collected together and examined with judicious
criticism. The best systems which had been proposed concerning the
ancient history of the globe, both by ancient and modern writers, are
reviewed; and the merits and defects of the doctrines of Hooke, Ray,
Moro, Buffon, and others, fairly estimated. Great admiration is
expressed for the hypothesis of Hooke, and his explanation of the origin
of the strata is shown to have been more correct than Moro's, while
their theory of the effects of earthquakes was the same. Raspe had not
seen Michell's memoirs, and his views concerning the geological
structure of the earth were perhaps less enlarged; yet he was able to
add many additional arguments in favor of Hook's theory, and to render
it, as he said, a nearer approach to what Hooke would have written had
he lived in later times. As to the periods wherein all the earthquakes
happened, to which we owe the elevation of various parts of our
continents and islands, Raspe says he pretends not to assign their
duration, still less to defend Hooke's suggestion, that the convulsions
almost all took place during the deluge of Noah. He adverts to the
apparent indications of the former tropical heat of the climate of
Europe, and the changes in the species of animals and plants, as among
the most obscure and difficult problems in geology. In regard to the
islands raised from the sea, within the times of history or tradition,
he declares that some of them were composed of strata containing organic
remains, and that they were not, as Buffon had asserted, made of mere
volcanic matter. His work concludes with an eloquent exhortation to
naturalists to examine the isles which rose, in 1707, in the Grecian
Archipelago, and, in 1720, in the Azores, and not to neglect such
splendid opportunities of studying nature "in the act of parturition."
That Hooke's writings should have been neglected for more than half a
century, was matter of astonishment to Raspe; but it is still more
wonderful that his own luminous exposition of that theory should, for
more than another half century, have excited so little interest.

_Fuchsel_, 1762 and 1773.--Fuchsel, a German physician, published, in
1762, a geological description of the country between the Thuringerwald
and the Hartz, and a memoir on the environs of Rudelstadt;[89] and
afterwards, in 1773, a theoretical work on the ancient history of the
earth and of man.[90] He had evidently advanced considerably beyond his
predecessor Lehman, and was aware of the distinctness, both as to
position and fossil contents, of several groups of strata of different
ages, corresponding to the secondary formations now recognized by
geologists in various parts of Germany. He supposed the European
continents to have remained covered by the sea until the formation of
the marine strata, called in Germany "muschelkalk," at the same time
that the terrestrial plants of many European deposits, attested the
existence of dry land which bordered the ancient sea; land which,
therefore, must have occupied the place of the present ocean. The
pre-existing continent had been _gradually_ swallowed up by the sea,
different parts having subsided in succession into subterranean caverns.
All the sedimentary strata were originally horizontal, and their present
state of derangement must be referred to subsequent oscillations of the
ground.

As there were plants and animals in the ancient periods, so also there
must have been men, but they did not all descend from one pair, but were
created at various points on the earth's surface; and the number of
these distinct birth-places was as great as are the original languages
of nations.

In the writings of Fuchsel we see a strong desire manifested to explain
geological phenomena as far as possible by reference to the agency of
known causes; and although some of his speculations were fanciful, his
views coincide much more nearly with those now generally adopted, than
the theories afterwards promulgated by Werner and his followers.

_Brander_, 1766.--Gustavus Brander published, in 1766, his "Fossilia
Hantoniensia," containing excellent figures of fossil shells from the
more modern (or Eocene) marine strata of Hampshire. "Various opinions,"
he says in the preface, "had been entertained concerning the time when
and how these bodies became deposited. Some there are who conceive that
it might have been effected in a wonderful length of time by a gradual
changing and shifting of the sea," &c. But the most common cause
assigned is that of "the deluge." This conjecture, he says, even if the
universality of the flood be not called in question, is purely
hypothetical. In his opinion, fossil animals and testacea were, for the
most part, of unknown species; and of such as were known, the living
analogues now belonged to southern latitudes.

_Soldani_, 1780.--Soldani applied successfully his knowledge of zoology
to illustrate the history of stratified masses. He explained that
microscopic testacea and zoophytes inhabited the depths of the
Mediterranean; and that the fossil species were, in like manner, found
in those deposits wherein the fineness of their particles, and the
absence of pebbles, implied that they were accumulated in a deep sea, or
far from shore. This author first remarked the alternation of marine and
freshwater strata in the Paris basin.[91]

_Fortis--Testa_, 1793.--A lively controversy arose between Fortis and
another Italian naturalist, Testa, concerning the fish of Monte Bolca,
in 1793. Their letters,[92] written with great spirit and elegance, show
that they were aware that a large proportion of the Subapennine shells
were identical with living species, and some of them with species now
living in the torrid zone. Fortis proposed a somewhat fanciful
conjecture, that when the volcanoes of the Vicentin were burning, the
waters of the Adriatic had a higher temperature; and in this manner, he
said, the shells of warmer regions may once have peopled their own seas.
But Testa was disposed to think that these species of testacea were
still common to their own and to equinoctial seas; for many, he said,
once supposed to be confined to hotter regions, had been afterwards
discovered in the Mediterranean.[93]

_Cortesi--Spallanzani--Wallerius--Whitehurst._--While these Italian
naturalists, together with Cortesi and Spallanzani, were busily engaged
in pointing out the analogy between the deposits of modern and ancient
seas, and the habits and arrangement of their organic inhabitants, and
while some progress was making, in the same country, in investigating
the ancient and modern volcanic rocks, some of the most original
observers among the English and German writers, Whitehurst[94] and
Wallerius, were wasting their strength in contending, according to the
old Woodwardian hypothesis, that all the strata were formed by Noah's
deluge. But Whitehurst's description of the rocks of Derbyshire was most
faithful; and he atoned for false theoretical views, by providing data
for their refutation.

_Pallas--Saussure._--Towards the close of the eighteenth century, the
idea of distinguishing the mineral masses on our globe into separate
groups, and studying their relations, began to be generally diffused.
Pallas and Saussure were among the most celebrated whose labors
contributed to this end. After an attentive examination of the two great
mountain chains of Siberia, Pallas announced the result, that the
granitic rocks were in the middle, the schistose at their sides, and the
limestones again on the outside of these; and this he conceived would
prove a general law in the formation of all chains composed chiefly of
primary rocks.[95]

In his "Travels in Russia," in 1793 and 1794, he made many geological
observations on the recent strata near the Wolga and the Caspian, and
adduced proofs of the greater extent of the latter sea at no distant era
in the earth's history. His memoir on the fossil bones of Siberia
attracted attention to some of the most remarkable phenomena in geology.
He stated that he had found a rhinoceros entire in the frozen soil, with
its skin and flesh: an elephant, found afterwards in a mass of ice on
the shore of the North Sea, removed all doubt as to the accuracy of so
wonderful a discovery.[96]

The subjects relating to natural history which engaged the attention of
Pallas, were too multifarious to admit of his devoting a large share of
his labors exclusively to geology. Saussure, on the other hand, employed
the chief portion of his time in studying the structure of the Alps and
Jura, and he provided valuable data for those who followed him. He did
not pretend to deduce any general system from his numerous and
interesting observations; and the few theoretical opinions which escaped
from him, seem, like those of Pallas, to have been chiefly derived from
the cosmological speculations of preceding writers.




CHAPTER IV.

HISTORY OF THE PROGRESS OF GEOLOGY--_continued_.


   Werner's application of geology to the art of
     mining--Excursive character of his lectures--Enthusiasm of his
     pupils--His authority--His theoretical errors--Desmarest's Map
     and Description of Auvergne--Controversy between the
     Vulcanists and Neptunists--Intemperance of the rival
     sects--Hutton's Theory of the earth--His discovery of granite
     veins--Originality of his views--Why opposed--Playfair's
     illustrations--Influence of Voltaire's writings on
     geology--Imputations cast on the Huttonians by Williams,
     Kirwan, and De Luc--Smith's Map of England--Geological Society
     of London--Progress of the science in France--Growing
     importance of the study of organic remains.


_Werner._--The art of mining has long been taught in France, Germany,
and Hungary, in scientific institutions established for that purpose,
where mineralogy has always been a principal branch of instruction.

Werner was named, in 1775, professor of that science in the "School of
Mines," at Freyberg, in Saxony. He directed his attention not merely to
the composition and external characters of minerals, but also to what he
termed "geognosy," or the natural position of minerals in particular
rocks, together with the grouping of those rocks, their geographical
distribution, and various relations. The phenomena observed in the
structure of the globe had hitherto served for little else than to
furnish interesting topics for philosophical discussion; but when Werner
pointed out their application to the practical purposes of mining, they
were instantly regarded by a large class of men as an essential part of
their professional education, and from that time the science was
cultivated in Europe more ardently and systematically. Werner's mind was
at once imaginative and richly stored with miscellaneous knowledge. He
associated every thing with his favorite science, and in his excursive
lectures, he pointed out all the economical uses of minerals, and their
application to medicine; the influence of the mineral composition of
rocks upon the soil, and of the soil upon the resources, wealth, and
civilization of man. The vast sandy plains of Tartary and Africa, he
would say, retained their inhabitants in the shape of wandering
shepherds; the granitic mountains and the low calcareous and alluvial
plains gave rise to different manners, degrees of wealth, and
intelligence. The history even of languages, and the migration of
tribes, had been determined by the direction of particular strata. The
qualities of certain stones used in building would lead him to descant
on the architecture of different ages and nations; and the physical
geography of a country frequently invited him to treat of military
tactics. The charm of his manners and his eloquence kindled enthusiasm
in the minds of his pupils; and many, who had intended at first only to
acquire a slight knowledge of mineralogy, when they had once heard him,
devoted themselves to it as the business of their lives. In a few years,
a small school of mines, before unheard of in Europe, was raised to the
rank of a great university; and men already distinguished in science
studied the German language, and came from the most distant countries to
hear the great oracle of geology.[97]

Werner had a great antipathy to the mechanical labor of writing, and,
with the exception of a valuable treatise on metalliferous veins, he
could never be persuaded to pen more than a few brief memoirs, and those
containing no development of his general views. Although the natural
modesty of his disposition was excessive, approaching even to timidity,
he indulged in the most bold and sweeping generalizations, and he
inspired all his scholars with a most implicit faith in his doctrines.
Their admiration of his genius, and the feelings of gratitude and
friendship which they all felt for him, were not undeserved; but the
supreme authority usurped by him over the opinions of his
contemporaries, was eventually prejudicial to the progress of the
science; so much so, as greatly to counterbalance the advantages which
it derived from his exertions. If it be true that delivery be the first,
second, and third requisite in a popular orator, it is no less certain,
that to travel is of first, second, and third importance to those who
desire to originate just and comprehensive views concerning the
structure of our globe. Now Werner had not travelled to distant
countries; he had merely explored a small portion of Germany, and
conceived, and persuaded others to believe, that the whole surface of
our planet, and all the mountain chains in the world, were made after
the model of his own province. It became a ruling object of ambition in
the minds of his pupils to confirm the generalizations of their great
master, and to discover in the most distant parts of the globe his
"universal formations," which he supposed had been each in succession
simultaneously precipitated over the whole earth from a common
menstruum, or "chaotic fluid." It now appears that the Saxon professor
had misinterpreted many of the most important appearances even in the
immediate neighborhood of Freyberg. Thus, for example, within a day's
journey of his school, the porphyry, called by him primitive, has been
found not only to send forth veins or dikes through strata of the coal
formation, but to overlie them in mass. The granite of the Hartz
mountains, on the other hand, which he supposed to be the nucleus of the
chain, is now well known to traverse the other beds, as near Goslar; and
still nearer Freyberg, in the Erzgebirge, the mica slate does not mantle
round the granite as was supposed, but abuts abruptly against it.
Fragments, also, of the greywacké slate, containing organic remains,
have recently been found entangled in the granite of the Hartz, by M. de
Seckendorf.[98]

The principal merit of Werner's system of instruction consisted in
steadily directing the attention of his scholars to the constant
relations of superposition of certain mineral groups; but he had been
anticipated, as has been shown in the last chapter, in the discovery of
this general law, by several geologists in Italy and elsewhere; and his
leading divisions of the secondary strata were at the same time, and
independently, made the basis of an arrangement of the British strata by
our countryman, William Smith, to whose work I shall refer in the
sequel.

_Controversy between the Vulcanists and Neptunists._--In regard to
basalt and other igneous rocks, Werner's theory was original, but it was
also extremely erroneous. The basalts of Saxony and Hesse, to which his
observations were chiefly confined, consisted of tabular masses capping
the hills, and not connected with the levels of existing valleys, like
many in Auvergne and the Vivarais. These basalts, and all other rocks of
the same family in other countries, were, according to him, chemical
precipitates from water. He denied that they were the products of
submarine volcanoes; and even taught that, in the primeval ages of the
world, there were no volcanoes. His theory was opposed, in a twofold
sense, to the doctrine of the permanent agency of the same causes in
nature; for not only did he introduce, without scruple, many imaginary
causes supposed to have once effected great revolutions in the earth,
and then to have become extinct, but new ones also were feigned to have
come into play in modern times; and, above all, that most violent
instrument of change, the agency of subterranean heat.

So early as 1768, before Werner had commenced his mineralogical studies,
Raspe had truly characterized the basalts of Hesse as of igneous origin.
Arduino, we have seen, had pointed out numerous varieties of trap-rock
in the Vicentin as analogous to volcanic products, and as distinctly
referable to ancient submarine eruptions. Desmarest, as before stated,
had, in company with Fortis, examined the Vicentin in 1766, and
confirmed Arduino's views. In 1772, Banks, Solander, and Troil compared
the columnar basalt of Hecla with that of the Hebrides. Collini, in
1774, recognized the true nature of the igneous rocks on the Rhine,
between Andernach and Bonn. In 1775, Guettard visited the Vivarais, and
established the relation of basaltic currents to lavas. Lastly, in 1779,
Faujas published his description of the volcanoes of the Vivarais and
Velay, and showed how the streams of basalt had poured out from craters
which still remain in a perfect state.[99]

_Desmarest._--When sound opinions had thus for twenty years prevailed in
Europe concerning the true nature of the ancient trap-rocks, Werner by
his simple dictum caused a retrograde movement, and not only overturned
the true theory, but substituted for it one of the most unphilosophical
that can well be imagined. The continued ascendancy of his dogmas on
this subject was the more astonishing, because a variety of new and
striking facts were daily accumulated in favor of the correct opinions
previously entertained. Desmarest, after a careful examination of
Auvergne, pointed out, first, the most recent volcanoes which had their
craters still entire, and their streams of lava conforming to the level
of the present river-courses. He then showed that there were others of
an intermediate epoch, whose craters were nearly effaced, and whose
lavas were less intimately connected with the present valleys; and,
lastly, that there were volcanic rocks, still more ancient, without any
discernible craters or scoriæ, and bearing the closest analogy to rocks
in other parts of Europe, the igneous origin of which was denied by the
school of Freyberg.[100]

Desmarest's map of Auvergne was a work of uncommon merit. He first made
a trigonometrical survey of the district, and delineated its physical
geography with minute accuracy and admirable graphic power. He
contrived, at the same time, to express without the aid of colors, many
geological details, including the different ages and sometimes even the
structure, of the volcanic rocks, and distinguishing them from the
fresh-water and the granitic. They alone who have carefully studied
Auvergne, and traced the different lava streams from their craters to
their termination,--the various isolated basaltic cappings,--the
relation of some lavas to the present valleys,---the absence of such
relations in others,--can appreciate the extraordinary fidelity of this
elaborate work. No other district of equal dimensions in Europe
exhibits, perhaps, so beautiful and varied a series of phenomena; and,
fortunately, Desmarest possessed at once the mathematical knowledge
required for the construction of a map, skill in mineralogy, and a power
of original generalization.

_Dolomieu--Montlosier._--Dolomieu, another of Werner's contemporaries,
had found prismatic basalt among the ancient lavas of Etna; and, in
1784, had observed the alternations of submarine lavas and calcareous
strata in the Val di Noto, in Sicily.[101] In 1790, also, he described
similar phenomena in the Vicentin and in the Tyrol.[102] Montlosier
published, in 1788, an essay on the theories of volcanoes of Auvergne,
combining accurate local observations with comprehensive views.
Notwithstanding this mass of evidence the scholars of Werner were
prepared to support his opinions to their utmost extent; maintaining, in
the fulness of their faith, that even obsidian was an aqueous
precipitate. As they were blinded by their veneration for the great
teacher, they were impatient of opposition, and soon imbibed the spirit
of a faction; and their opponents, the Vulcanists, were not long in
becoming contaminated with the same intemperate zeal. Ridicule and irony
were weapons more frequently employed than argument by the rival sects,
till at last the controversy was carried on with a degree of bitterness
almost unprecedented in questions of physical science. Desmarest alone,
who had long before provided ample materials for refuting such a theory,
kept aloof from the strife; and whenever a zealous Neptunist wished to
draw the old man into an argument, he was satisfied with replying, "Go
and see."[103]

_Hutton_, 1788.--It would be contrary to all analogy, in matters of
graver import, that a war should rage with such fury on the Continent,
and that the inhabitants of our island should not mingle in the affray.
Although in England the personal influence of Werner was wanting to
stimulate men to the defence of the weaker side of the question, they
contrived to find good reason for espousing the Wernerian errors with
great enthusiasm. In order to explain the peculiar motives which led
many to enter, even with party feeling, into this contest, it will be
necessary to present the reader with a sketch of the views unfolded by
Hutton, a contemporary of the Saxon geologist. The former naturalist had
been educated as a physician, but declining the practice of medicine, he
resolved, when young, to remain content with the small independence
inherited from his father, and thenceforth to give his undivided
attention to scientific pursuits. He resided at Edinburgh, where he
enjoyed the society of many men of high attainments, who loved him for
the simplicity of his manners, and the sincerity of his character. His
application was unwearied; and he made frequent tours through different
parts of England and Scotland, acquiring considerable skill as a
mineralogist, and consequently arriving at grand and comprehensive views
in geology. He communicated the results of his observations
unreservedly, and with the fearless spirit of one who was conscious that
love of truth was the sole stimulus of his exertions. When at length he
had matured his views, he published, in 1788, his "Theory of the
Earth,"[104] and the same, afterwards more fully developed in a separate
work, in 1795. This treatise was the first in which geology was declared
to be in no way concerned about "questions as to the origin of things;"
the first in which an attempt was made to dispense entirely with all
hypothetical causes, and to explain the former changes of the earth's
crust by reference exclusively to natural agents. Hutton labored to
give fixed principles to geology, as Newton had succeeded in doing to
astronomy; but, in the former science, too little progress had been made
towards furnishing the necessary data, to enable any philosopher,
however great his genius, to realize so noble a project.

_Huttonian theory._--"The ruins of an older world," said Hutton, "are
visible in the present structure of our planet; and the strata which now
compose our continents have been once beneath the sea, and were formed
out of the waste of pre-existing continents. The same forces are still
destroying, by chemical decomposition or mechanical violence, even the
hardest rocks, and transporting the materials to the sea, where they are
spread out, and form strata analogous to those of more ancient date.
Although loosely deposited along the bottom of the ocean, they become
afterwards altered and consolidated by volcanic heat, and then heaved
up, fractured, and contorted."

Although Hutton had never explored any region of active volcanoes, he
had convinced himself that basalt and many other trap-rocks were of
igneous origin, and that many of them had been injected in a melted
state through fissures in the older strata. The compactness of these
rocks, and their different aspect from that of ordinary lava, he
attributed to their having cooled down under the pressure of the sea;
and in order to remove the objections started against this theory, his
friend, Sir James Hall, instituted a most curious and instructive series
of chemical experiments, illustrating the crystalline arrangement and
texture assumed by melted matter cooled under high pressure.

The absence of stratification in granite, and its analogy, in mineral
character, to rocks which he deemed of igneous origin, led Hutton to
conclude that granite also must have been formed from matter in fusion;
and this inference he felt could not be fully confirmed, unless he
discovered at the contact of granite and other strata a repetition of
the phenomena exhibited so constantly by the trap-rocks. Resolved to try
his theory by this test, he went to the Grampians, and surveyed the line
of junction of the granite and superincumbent stratified masses, until
he found in Glen Tilt, in 1785, the most clear and unequivocal proofs in
support of his views. Veins of red granite are there seen branching out
from the principal mass, and traversing the black micaceous schist and
primary limestone. The intersected stratified rocks are so distinct in
color and appearance as to render the example in that locality most
striking, and the alteration of the limestone in contact was very
analogous to that produced by trap veins on calcareous strata. This
verification of his system filled him with delight, and called forth
such marks of joy and exultation, that the guides who accompanied him,
says his biographer, were convinced that he must have discovered a vein
of silver or gold.[105] He was aware that the same theory would not
explain the origin of the primary schists, but these he called primary,
rejecting the term primitive, and was disposed to consider them as
sedimentary rocks altered by heat, and that they originated in some
other form from the waste of previously existing rocks.

By this important discovery of granite veins, to which he had been led
by fair induction from an independent class of facts, Hutton prepared
the way for the greatest innovation of the systems of his predecessors.
Vallisneri had pointed out the general fact that there were certain
fundamental rocks which contained no organic remains, and which he
supposed to have been formed before the creation of living beings. Moro,
Generelli, and other Italian writers, embraced the same doctrine; and
Lehman regarded the mountains called by him primitive, as parts of the
original nucleus of the globe. The same tenet was an article of faith in
the school of Freyberg; and if any one ventured to doubt the possibility
of our being enabled to carry back our researches to the creation of the
present order of things, the granitic rocks were triumphantly appealed
to. On them seemed written, in legible characters, the memorable
inscription--

  "Dinanzi a me non fur cose create
  Se non eterne;"[106]

and no small sensation was excited when Hutton seemed, with unhallowed
hand, desirous to erase characters already regarded by many as sacred.
"In the economy of the world," said the Scotch geologist, "I can find no
traces of a beginning, no prospect of an end;" a declaration the more
startling when coupled with the doctrine, that all past ages on the
globe had been brought about by the slow agency of existing causes. The
imagination was first fatigued and overpowered by endeavoring to
conceive the immensity of time required for the annihilation of whole
continents by so insensible a process; and when the thoughts had
wandered through these interminable periods, no resting-place was
assigned in the remotest distance. The oldest rocks were represented to
be of a derivative nature, the last of an antecedent series, and that,
perhaps, one of many pre-existing worlds. Such views of the immensity of
past time, like those unfolded by the Newtonian philosophy in regard to
space, were too vast to awaken ideas of sublimity unmixed with a painful
sense of our incapacity to conceive a plan of such infinite extent.
Worlds are seen beyond worlds immeasurably distant from each other, and,
beyond them all, innumerable other systems are faintly traced on the
confines of the visible universe.

The characteristic feature of the Huttonian theory was, as before
hinted, the exclusion of all causes not supposed to belong to the
present order of nature. But Hutton had made no step beyond Hooke, Moro,
and Raspe, in pointing out in what manner the laws now governing
subterranean movements might bring about geological changes, if
sufficient time be allowed. On the contrary, he seems to have fallen far
short of some of their views, especially when he refused to attribute
any part of the external configuration of the earth's crust to
subsidence. He imagined that the continents were first gradually
destroyed by aqueous degradation; and when their ruins had furnished
materials for new continents, they were upheaved by violent convulsions.
He therefore required alternate periods of general disturbance and
repose; and such he believed had been, and would forever be, the course
of nature.

Generelli, in his exposition of Moro's system, had made a far nearer
approximation towards reconciling geological appearances with the state
of nature as known to us; for while he agreed with Hutton, that the
decay and reproduction of rocks were always in progress, proceeding with
the utmost uniformity, the learned Carmelite represented the repairs of
mountains by elevation from below to be effected by an equally constant
and synchronous operation. Neither of these theories, considered singly,
satisfies all the conditions of the great problem, which a geologist,
who rejects cosmological causes, is called upon to solve; but they
probably contain together the germs of a perfect system. There can be no
doubt, that periods of disturbance and repose have followed each other
in succession in every region of the globe; but it may be equally true,
that the energy of the subterranean movements has been always uniform as
regards the _whole earth_. The force of earthquakes may for a cycle of
years have been invariably confined, as it is now, to large but
determinate spaces, and may then have gradually shifted its position, so
that another region, which had for ages been at rest, became in its turn
the grand theatre of action.

_Playfair's illustrations of Hutton._--The explanation proposed by
Hutton, and by Playfair, the illustrator of his theory, respecting the
origin of valleys and of alluvial accumulations, was also very
imperfect. They ascribed none of the inequalities of the earth's surface
to movements which accompanied the upheaving of the land, imagining that
valleys in general were formed in the course of ages by the rivers now
flowing in them; while they seem not to have reflected on the excavating
and transporting power which the waves of the ocean might exert on land
during its emergence.

Although Hutton's knowledge of mineralogy and chemistry was
considerable, he possessed but little information concerning organic
remains; they merely served him, as they did Werner, to characterize
certain strata, and to prove their marine origin. The theory of former
revolutions in organic life was not yet fully recognized; and without
this class of proofs in support of the antiquity of the globe, the
indefinite periods demanded by the Huttonian hypothesis appeared
visionary to many; and some, who deemed the doctrine inconsistent with
revealed truths, indulged very uncharitable suspicions of the motives of
its author. They accused him of a deliberate design of reviving the
heathen dogma of an "eternal succession," and of denying that this world
ever had a beginning. Playfair, in the biography of his friend, has the
following comment on this part of their theory:--"In the planetary
motions, where geometry has carried the eye so far, both into the future
and the past, we discover no mark either of the commencement or
termination of the present order. It is unreasonable, indeed, to suppose
that such marks should anywhere exist. The Author of Nature has not
given laws to the universe, which, like the institutions of men, carry
in themselves the elements of their own destruction. He has not
permitted in His works any symptom of infancy or of old age, or any sign
by which we may estimate either their future or their past duration. _He
may put an end, as he no doubt gave a beginning_, to the present system,
at some determinate period of time; but we may rest assured that this
great catastrophe will not be brought about by the laws now existing,
and that it is not indicated, by any thing which we perceive."[107]

The party feeling excited against the Huttonian doctrines, and the open
disregard of candor and temper in the controversy, will hardly be
credited by the reader, unless he recalls to his recollection that the
mind of the English public was at that time in a state of feverish
excitement. A class of writers in France had been laboring industriously
for many years, to diminish the influence of the clergy, by sapping the
foundations of the Christian faith; and their success, and the
consequences of the Revolution, had alarmed the most resolute minds,
while the imagination of the more timid was continually haunted by dread
of innovation, as by the phantom of some fearful dream.

_Voltaire._--Voltaire had used the modern discoveries in physics as one
of the numerous weapons of attack and ridicule directed by him against
the Scriptures. He found that the most popular systems of geology were
accommodated to the sacred writings, and that much ingenuity had been
employed to make every fact coincide exactly with the Mosaic account of
the creation and deluge. It was, therefore, with no friendly feelings
that he contemplated the cultivators of geology in general, regarding
the science as one which had been successfully enlisted by theologians
as an ally in their cause.[108] He knew that the majority of those who
were aware of the abundance of fossil shells in the interior of
continents, were still persuaded that they were proofs of the universal
deluge; and as the readiest way of shaking this article of faith, he
endeavored to inculcate skepticism as to the real nature of such shells,
and to recall from contempt the exploded dogma of the sixteenth century,
that they were sports of nature. He also pretended that vegetable
impressions were not those of real plants.[109] Yet he was perfectly
convinced that the shells had really belonged to living testacea, as may
be seen in his essay "On the formation of Mountains."[110] He would
sometimes, in defiance of all consistency, shift his ground when
addressing the vulgar; and, admitting the true nature of the shells
collected in the Alps and other places, pretend that they were Eastern
species, which had fallen from the hats of pilgrims coming from Syria.
The numerous essays written by him on geological subjects were all
calculated to strengthen prejudices, partly because he was ignorant of
the real state of the science, and partly from his bad faith.[111] On
the other hand, they who knew that his attacks were directed by a desire
to invalidate Scripture, and who were unacquainted with the true merits
of the question, might well deem the old diluvian hypothesis
incontrovertible, if Voltaire could adduce no better argument against it
than to deny the true nature of organic remains.

It is only by careful attention to impediments originating in extrinsic
causes, that we can explain the slow and reluctant adoption of the
simplest truths in geology. First, we find many able naturalists
adducing the fossil remains of marine animals as proofs of an event
related in Scripture. The evidence is deemed conclusive by the multitude
for a century or more; for it favors opinions which they entertained
before, and they are gratified by supposing them confirmed by fresh and
unexpected proofs. Many who see through the fallacy have no wish to
undeceive those who are influenced by it, approving the effect of the
delusion, and conniving at it as a pious fraud; until, finally, an
opposite party, who are hostile to the sacred writings, labor to explode
the erroneous opinion, by substituting for it another dogma, which they
know to be equally unsound.

The heretical Vulcanists were soon after openly assailed in England, by
imputations of the most illiberal kind. We cannot estimate the
malevolence of such a persecution, by the pain which similar
insinuations might now inflict; for although charges of infidelity and
atheism must always be odious, they were injurious in the extreme at
that moment of political excitement; and it was better, perhaps, for a
man's good reception in society, that his moral character should have
been traduced, than that he should become a mark for these poisoned
weapons.

I shall pass over the works of numerous divines, who may be excused for
sensitiveness on points which then excited so much uneasiness in the
public mind; and shall say nothing of the amiable poet Cowper,[112] who
could hardly be expected to have inquired into the merit of doctrines
in physics. But in the foremost ranks of the intolerant are found
several laymen who had high claims to scientific reputation. Among these
appears Williams, a mineral surveyor of Edinburgh, who published a
"Natural History of the Mineral Kingdom," in 1789; a work of great
merit, for that day, and of practical utility, as containing the best
account of the coal strata. In his preface he misrepresents Hutton's
theory altogether, and charges him with considering all rocks to be
lavas of different colors and structure; and also with "warping every
thing to support the eternity of the world."[113] He descants on the
pernicious influence of such skeptical notions, as leading to downright
infidelity and atheism, "and as being nothing less than to depose the
Almighty Creator of the universe from his office."[114]

_Kirwan_--_De Luc._--Kirwan, president of the Royal Academy of Dublin, a
chemist and mineralogist of some merit, but who possessed much greater
authority in the scientific world than he was entitled by his talents to
enjoy, said, in the introduction to his "Geological Essays, 1799," "that
_sound_ geology _graduated_ into religion, and was required to dispel
certain systems of atheism or infidelity, of which they had had recent
experience."[115] He was an uncompromising defender of the aqueous
theory of all rocks, and was scarcely surpassed by Burnet and Whiston,
in his desire to adduce the Mosaic writings in confirmation of his
opinions.

De Luc, in the preliminary discourse to his Treatise on Geology,[116]
says, "The weapons have been changed by which revealed religion is
attacked; it is now assailed by geology, and the knowledge of this
science has become essential to theologians." He imputes the failure of
former geological systems to their having been anti-Mosaical, and
directed against a "sublime tradition." These and similar imputations,
reiterated in the works of De Luc, seem to have been taken for granted
by some modern writers: it is therefore necessary to state, in justice
to the numerous geologists of different nations, whose works have been
considered, that none of them were guilty of endeavoring, by arguments
drawn from physics, to invalidate scriptural tenets. On the contrary,
the majority of those who were fortunate enough "to discover the true
causes of things," rarely deserved another part of the poet's panegyric,
"_Atque metus omnes subjecit pedibus_." The caution and even timid
reserve, of many eminent Italian authors of the earlier period is very
apparent; and there can hardly be a doubt, that they subscribed to
certain dogmas, and particularly to the first diluvian theory, out of
deference to popular prejudices, rather than from conviction. If they
were guilty of dissimulation, we may feel regret, but must not blame
their want of moral courage, reserving rather our condemnation for the
intolerance of the times, and that inquisitorial power which forced
Galileo to abjure, and the two Jesuits to disclaim the theory of
Newton.[117]

Hutton answered Kirwan's attacks with great warmth, and with the
indignation justly excited by unmerited reproach. "He had always
displayed," says Playfair, "the utmost disposition to admire the
beneficent design manifested in the structure of the world; and he
contemplated with delight those parts of his theory which made the
greatest additions to our knowledge of final causes." We may say with
equal truth, that in no scientific works in our language can more
eloquent passages be found, concerning the fitness, harmony, and
grandeur of all parts of the creation, than in those of Playfair. They
are evidently the unaffected expressions of a mind, which contemplated
the study of nature, as best calculated to elevate our conceptions of
the attributes of the First Cause. At any other time the force and
elegance of Playfair's style must have insured popularity to the
Huttonian doctrines; but by a singular coincidence, Neptunianism and
orthodoxy were now associated in the same creed; and the tide of
prejudice ran so strong, that the majority were carried far away into
the chaotic fluid, and other cosmological inventions of Werner. These
fictions the Saxon professor had borrowed with little modification, and
without any improvement, from his predecessors. They had not the
smallest foundation either in Scripture or in common sense, and were
probably approved of by many as being so ideal and unsubstantial, that
they could never come into violent collision with any preconceived
opinions.

According to De Luc, the first essential distinction to be made between
the various phenomena exhibited on the surface of the earth was, to
determine which were the results of causes still in action, and which
had been produced by causes that had ceased to act. The form and
composition of the mass of our continents, he said, and their existence
above the level of the sea, must be ascribed to causes no longer in
action. These continents emerged, at no very remote period, on the
sudden retreat of the ocean, the waters of which made their way into
subterranean caverns. The formation of the rocks which enter into the
crust of the earth began with the precipitation of granite from a
primordial liquid, after which other strata containing the remains of
organized bodies were deposited, till at last the present sea remained
as the residuum of the primordial liquid, and no longer continued to
produce mineral strata.[118]

_William Smith_, 1790.--While the tenets of the rival schools of
Freyberg and Edinburgh were warmly espoused by devoted partisans, the
labors of an individual, unassisted by the advantages of wealth or
station in society, were almost unheeded. Mr. William Smith, an English
surveyor, published his "Tabular View of the British Strata" in 1790,
wherein he proposed a classification of the secondary formations in the
West of England. Although he had not communicated with Werner, it
appeared by this work that he had arrived at the same views respecting
the laws of superposition of stratified rocks; that he was aware that
the order of succession of different groups was never inverted; and that
they might be identified at very distant points by their peculiar
organized fossils.

From the time of the appearance of the "Tabular View," the author
labored to construct a geological map of the whole of England; and with
the greatest disinterestedness of mind, communicated the results of his
investigations to all who desired information, giving such publicity to
his original views, as to enable his contemporaries almost to compete
with him in the race. The execution of his map was completed in 1815,
and remains a lasting monument of original talent and extraordinary
perseverance; for he had explored the whole country on foot, without the
guidance of previous observers, or the aid of fellow-laborers, and had
succeeded in throwing into natural divisions the whole complicated
series of British rocks. D'Aubuisson, a distinguished pupil of Werner,
paid a just tribute of praise to this remarkable performance, observing,
that "what many celebrated mineralogists had only accomplished for a
small part of Germany in the course of half a century, had been effected
by a single individual for the whole of England."[119]

Werner invented a new language to express his divisions of rocks, and
some of his technical terms, such as grauwacke, gneiss, and others,
passed current in every country in Europe. Smith adopted for the most
part English provincial terms, often of barbarous sound, such as gault,
cornbrash, clunch clay; and affixed them to subdivisions of the British
series. Many of these still retain their place in our scientific
classifications, and attest his priority of arrangement.


MODERN PROGRESS OF GEOLOGY.

The contention of the rival factions of the Vulcanists and Neptunists
had been carried to such a height, that these names had become terms of
reproach; and the two parties had been less occupied in searching for
truth, than for such arguments as might strengthen their own cause or
serve to annoy their antagonists. A new school at last arose, who
professed the strictest neutrality, and the utmost indifference to the
systems of Werner and Hutton, and who resolved diligently to devote
their labors to observation. The reaction, provoked by the intemperance
of the conflicting parties, now produced a tendency to extreme caution.
Speculative views were discountenanced, and, through fear of exposing
themselves to the suspicion of a bias towards the dogmas of a party,
some geologists became anxious to entertain no opinion whatever on the
causes of phenomena, and were inclined to skepticism even where the
conclusions deducible from observed facts scarcely admitted of
reasonable doubt.

_Geological Society of London._--But although the reluctance to theorize
was carried somewhat to excess, no measure could be more salutary at
such a moment than a suspension of all attempts to form what were termed
"theories of the earth." A great body of new data were required; and the
Geological Society of London, founded in 1807, conduced greatly to the
attainment of this desirable end. To multiply and record observations,
and patiently to await the result at some future period, was the object
proposed by them; and it was their favorite maxim that the time was not
yet come for a general system of geology, but that all must be content
for many years to be exclusively engaged in furnishing materials for
future generalizations. By acting up to these principles with
consistency, they in a few years disarmed all prejudice, and rescued the
science from the imputation of being a dangerous, or at best but a
visionary pursuit.

A distinguished modern writer has with truth remarked, that the
advancement of three of the main divisions of geological inquiry have
during the last half century been promoted successively by three
different nations of Europe,--the Germans, the English, and the
French.[120] We have seen that the systematic study of what may be
called mineralogical geology had its origin and chief point of activity
in Germany, where Werner first described with precision the mineral
characters of rocks. The classification of the secondary formations,
each marked by their peculiar fossils, belongs, in a great measure, to
England, where the labors before alluded to of Smith, and those of the
most active members of the Geological Society of London, were steadily
directed to these objects. The foundation of the third branch, that
relating to the tertiary formations, was laid in France by the splendid
work of Cuvier and Brongniart, published in 1808, "On the Mineral
Geography and Organic Remains of the Neighborhood of Paris."

We may still trace, in the language of the science and our present
methods of arrangement, the various countries where the growth of these
several departments of geology was at different times promoted. Many
names of simple minerals and rocks remain to this day German; while the
European divisions of the secondary strata are in great part English,
and are, indeed, often founded too exclusively on English types. Lastly,
the subdivisions first established of the succession of strata in the
Paris basin have served as normal groups to which other tertiary
deposits throughout Europe have been compared, even in cases where this
standard was wholly inapplicable.

No period could have been more fortunate for the discovery, in the
immediate neighborhood of Paris, of a rich store of well-preserved
fossils, than the commencement of the present century; for at no former
era had Natural history been cultivated with such enthusiasm in the
French metropolis. The labors of Cuvier in comparative osteology, and of
Lamarck in recent and fossil shells, had raised these departments of
study to a rank of which they had never previously been deemed
susceptible. Their investigations had eventually a powerful effect in
dispelling the illusion which had long prevailed concerning the absence
of analogy between the ancient and modern state of our planet. A close
comparison of the recent and fossil species and the inferences drawn in
regard to their habits, accustomed the geologist to contemplate the
earth as having been at successive periods the dwelling-place of animals
and plants of different races, some terrestrial, and others
aquatic--some fitted to live in seas, others in the waters of lakes and
rivers. By the consideration of these topics, the mind was slowly and
insensibly withdrawn from imaginary pictures of catastrophes and chaotic
confusion, such as haunted the imagination of the early cosmogonists.
Numerous proofs were discovered of the tranquil deposition of
sedimentary matter, and the slow development of organic life. If many
writers, and Cuvier himself in the number, still continued to maintain,
that "the thread of induction was broken,"[121] yet, in reasoning by the
strict rules of induction from recent to fossil species, they in a great
measure disclaimed the dogma which in theory they professed. The
adoption of the same generic, and, in some cases, even of the same
specific, names for the exuviæ of fossil animals and their living
analogues, was an important step towards familiarizing the mind with the
idea of the identity and unity of the system in distant eras. It was an
acknowledgment, as it were, that part at least of the ancient memorials
of nature were written in a living language. The growing importance,
then, of the natural history of organic remains may be pointed out as
the characteristic feature of the progress of the science during the
present century. This branch of knowledge has already become an
instrument of great utility in geological classification, and is
continuing daily to unfold new data for grand and enlarged views
respecting the former changes of the earth.

When we compare the result of observations in the last fifty years with
those of the three preceding centuries, we cannot but look forward with
the most sanguine expectations to the degree of excellence to which
geology may be carried, even by the labors of the present generation.
Never, perhaps, did any science, with the exception of astronomy,
unfold, in an equally brief period, so many novel and unexpected truths,
and overturn so many preconceived opinions. The senses had for ages
declared the earth to be at rest, until the astronomer taught that it
was carried through space with inconceivable rapidity. In like manner
was the surface of this planet regarded as having remained unaltered
since its creation, until the geologist proved that it had been the
theatre of reiterated change, and was still the subject of slow but
never-ending fluctuations. The discovery of other systems in the
boundless regions of space was the triumph of astronomy; to trace the
same system through various transformations--to behold it at successive
eras adorned with different hills and valleys, lakes and seas, and
peopled with new inhabitants, was the delightful meed of geological
research. By the geometer were measured the regions of space, and the
relative distances of the heavenly bodies;--by the geologist myriads of
ages were reckoned, not by arithmetical computation, but by a train of
physical events--a succession of phenomena in the animate and inanimate
worlds--signs which convey to our minds more definite ideas than figures
can do of the immensity of time.

Whether our investigation of the earth's history and structure will
eventually be productive of as great practical benefits to mankind as a
knowledge of the distant heavens, must remain for the decision of
posterity. It was not till astronomy had been enriched by the
observations of many centuries, and had made its way against popular
prejudices to the establishment of a sound theory, that its application
to the useful arts was most conspicuous. The cultivation of geology
began at a later period; and in every step which it has hitherto made
towards sound theoretical principles, it had to contend against more
violent prepossessions. The practical advantages already derived from it
have not been inconsiderable; but our generalizations are yet imperfect,
and they who come after us may be expected to reap the most valuable
fruits of our labor. Meanwhile, the charm of first discovery is our own;
and, as we explore this magnificent field of inquiry, the sentiment of a
great historian of our times may continually be present to our minds,
that "he who calls what has vanished back again into being, enjoys a
bliss like that of creating."[122]




CHAPTER V.

PREJUDICES WHICH HAVE RETARDED THE PROGRESS OF GEOLOGY


  Prepossessions in regard to the duration of past time--Prejudices
    arising from our peculiar position as inhabitants of the land--Of
    those occasioned by our not seeing subterranean changes now in
    progress--All these causes combine to make the former course of
    Nature appear different from the present--Objections to the
    doctrine, that causes similar in kind and energy to those now
    acting, have produced the former changes of the earth's surface,
    considered.


If we reflect on the history of the progress of geology, as explained in
the preceding chapters, we perceive that there have been great
fluctuations of opinion respecting the nature of the causes to which
all former changes of the earth's surface are referable. The first
observers conceived the monuments which the geologist endeavors to
decipher to relate to an original state of the earth, or to a period
when there were causes in activity, distinct, in kind and degree, from
those now constituting the economy of nature. These views were gradually
modified, and some of them entirely abandoned, in proportion as
observations were multiplied, and the signs of former mutations more
skilfully interpreted. Many appearances, which had for a long time been
regarded as indicating mysterious and extraordinary agency, were finally
recognized as the necessary result of the laws now governing the
material world; and the discovery of this unlooked-for conformity has at
length induced some philosophers to infer, that, during the ages
contemplated in geology, there has never been any interruption to the
agency of the same uniform laws of change. The same assemblage of
general causes, they conceive, may have been sufficient to produce, by
their various combinations, the endless diversity of effects, of which
the shell of the earth has preserved the memorials; and, consistently
with these principles, the recurrence of analogous changes is expected
by them in time to come.

Whether we coincide or not in this doctrine, we must admit that the
gradual progress of opinion concerning the succession of phenomena in
very remote eras, resembles, in a singular manner, that which has
accompanied the growing intelligence of every people, in regard to the
economy of nature in their own times. In an early state of advancement,
when a great number of natural appearances are unintelligible, an
eclipse, an earthquake, a flood, or the approach of a comet, with many
other occurrences afterwards found to belong to the regular course of
events, are regarded as prodigies. The same delusion prevails as to
moral phenomena, and many of these are ascribed to the intervention of
demons, ghosts, witches, and other immaterial and supernatural agents.
By degrees, many of the enigmas of the moral and physical world are
explained, and, instead of being due to extrinsic and irregular causes,
they are found to depend on fixed and invariable laws. The philosopher
at last becomes convinced of the undeviating uniformity of secondary
causes; and, guided by his faith in this principle, he determines the
probability of accounts transmitted to him of former occurrences, and
often rejects the fabulous tales of former times, on the ground of their
being irreconcilable with the experience of more enlightened ages.

_Prepossessions in regard to the duration of past time._--As a belief in
the want of conformity in the causes by which the earth's crust has been
modified in ancient and modern periods was, for a long time, universally
prevalent, and that, too, amongst men who were convinced that the order
of nature had been uniform for the last several thousand years, every
circumstance which could have influenced their minds and given an undue
bias to their opinions deserves particular attention. Now the reader
may easily satisfy himself, that, however undeviating the course of
nature may have been from the earliest epochs, it was impossible for the
first cultivators of geology to come to such a conclusion, so long as
they were under a delusion as to the age of the world, and the date of
the first creation of animate beings. However fantastical some theories
of the sixteenth century may now appear to us,--however unworthy of men
of great talent and sound judgment,--we may rest assured that, if the
same misconception now prevailed in regard to the memorials of human
transactions, it would give rise to a similar train of absurdities. Let
us imagine, for example, that Champollion, and the French and Tuscan
literati lately engaged in exploring the antiquities of Egypt, had
visited that country with a firm belief that the banks of the Nile were
never peopled by the human race before the beginning of the nineteenth
century, and that their faith in this dogma was as difficult to shake as
the opinion of our ancestors that the earth was never the abode of
living beings until the creation of the present continents, and of the
species now existing,--it is easy to perceive what extravagant systems
they would frame, while under the influence of this delusion, to account
for the monuments discovered in Egypt. The sight of the pyramids,
obelisks, colossal statues, and ruined temples, would fill them with
such astonishment, that for a time they would be as men
spell-bound--wholly incapable of reasoning with sobriety. They might
incline at first to refer the construction of such stupendous works to
some superhuman powers of a primeval world. A system might be invented
resembling that so gravely advanced by Manetho, who relates that a
dynasty of gods originally ruled in Egypt, of whom Vulcan, the first
monarch, reigned nine thousand years; after whom came Hercules and other
demigods, who were at last succeeded by human kings.

When some fanciful speculations of this kind had amused their
imaginations for a time, some vast repository of mummies would be
discovered, and would immediately undeceive those antiquaries who
enjoyed an opportunity of personally examining them; but the prejudices
of others at a distance, who were not eye-witnesses of the whole
phenomena, would not be so easily overcome. The concurrent report of
many travellers would, indeed, render it necessary for them to
accommodate ancient theories to some of the new facts, and much wit and
ingenuity would be required to modify and defend their old positions.
Each new invention would violate a greater number of known analogies;
for if a theory be required to embrace some false principle, it becomes
more visionary in proportion as facts are multiplied, as would be the
case if geometers were now required to form an astronomical system on
the assumption of the immobility of the earth.

Amongst other fanciful conjectures concerning the history of Egypt, we
may suppose some of the following to be started. "As the banks of the
Nile have been so recently colonized for the first time, the curious
substances called mummies could never in reality have belonged to men.
They may have been generated by some _plastic virtue_ residing in the
interior of the earth, or they may be abortions of Nature produced by
her incipient efforts in the work of creation. For if deformed beings
are sometimes born even now, when the scheme of the universe is fully
developed, many more may have been 'sent before their time, scarce half
made up,' when the planet itself was in the embryo state. But if these
notions appear to derogate from the perfection of the Divine attributes,
and if these mummies be in all their parts true representations of the
human form, may we not refer them to the future rather than the
past?--May we not be looking into the womb of Nature, and not her grave?
May not these images be like the shades of the unborn in Virgil's
Elysium--the archetypes of men not yet called into existence?"

These speculations, if advocated by eloquent writers, would not fail to
attract many zealous votaries, for they would relieve men from the
painful necessity of renouncing preconceived opinions. Incredible as
such skepticism may appear, it has been rivalled by many systems of the
sixteenth and seventeenth centuries, and among others by that of the
learned Falloppio, who regarded the tusks of fossil elephants as earthy
concretions, and the pottery or fragments of vases in the Monte
Testaceo, near Rome, as works of nature, and not of art. But when one
generation had passed away, and another, not compromised to the support
of antiquated dogmas, had succeeded, they would review the evidence
afforded by mummies more impartially, and would no longer controvert the
preliminary question, that human beings had lived in Egypt before the
nineteenth century: so that when a hundred years perhaps had been lost,
the industry and talents of the philosopher would be at last directed to
the elucidation of points of real historical importance.

But the above arguments are aimed against one only of many prejudices
with which the earlier geologists had to contend. Even when they
conceded that the earth had been peopled with animate beings at an
earlier period than was at first supposed, they had no conception that
the quantity of time bore so great a proportion to the historical era as
is now generally conceded. How fatal every error as to the quantity of
time must prove to the introduction of rational views concerning the
state of things in former ages, may be conceived by supposing the annals
of the civil and military transactions of a great nation to be perused
under the impression that they occurred in a period of one hundred
instead of two thousand years. Such a portion of history would
immediately assume the air of a romance; the events would seem devoid of
credibility, and inconsistent with the present course of human affairs.
A crowd of incidents would follow each other in thick succession. Armies
and fleets would appear to be assembled only to be destroyed, and cities
built merely to fall in ruins. There would be the most violent
transitions from foreign or intestine war to periods of profound peace,
and the works effected during the years of disorder or tranquillity
would appear alike superhuman in magnitude.

He who should study the monuments of the natural world under the
influence of a similar infatuation, must draw a no less exaggerated
picture of the energy and violence of causes, and must experience the
same insurmountable difficulty in reconciling the former and present
state of nature. If we could behold in one view all the volcanic cones
thrown up in Iceland, Italy, Sicily, and other parts of Europe, during
the last five thousand years, and could see the lavas which have flowed
during the same period; the dislocations, subsidences, and elevations
caused during earthquakes; the lands added to various deltas, or
devoured by the sea, together with the effects of devastation by floods,
and imagine that all these events had happened in one year, we must form
most exalted ideas of the activity of the agents, and the suddenness of
the revolutions. Were an equal amount of change to pass before our eyes
in the next year, could we avoid the conclusion that some great crisis
of nature was at hand? If geologists, therefore, have misinterpreted the
signs of a succession of events, so as to conclude that centuries were
implied where the characters imported thousands of years, and thousands
of years where the language of Nature signified millions, they could
not, if they reasoned logically from such false premises, come to any
other conclusion than that the system of the natural world had undergone
a complete revolution.

We should be warranted in ascribing the erection of the great pyramid to
superhuman power, if we were convinced that it was raised in one day;
and if we imagine, in the same manner, a continent or mountain-chain to
have been elevated during an equally small fraction of the time which
was really occupied in upheaving it, we might then be justified in
inferring, that the subterranean movements were once far more energetic
than in our own times. We know that during one earthquake the coast of
Chili may be raised for a hundred miles to the average height of about
three feet. A repetition of two thousand shocks, of equal violence,
might produce a mountain-chain one hundred miles long, and six thousand
feet high. Now, should one or two only of these convulsions happen in a
century, it would be consistent with the order of events experienced by
the Chilians from the earliest times; but if the whole of them were to
occur in the next hundred years, the entire district must be
depopulated, scarcely any animals or plants could survive, and the
surface would be one confused heap of ruin and desolation.

One consequence of undervaluing greatly the quantity of past time, is
the apparent coincidence which it occasions of events necessarily
disconnected, or which are so unusual, that it would be inconsistent
with all calculation of chances to suppose them to happen at one and the
same time. When the unlooked-for association of such rare phenomena is
witnessed in the present course of nature, it scarcely ever fails to
excite a suspicion of the preternatural in those minds which are not
firmly convinced of the uniform agency of secondary causes;--as if the
death of some individual in whose fate they are interested happens to
be accompanied by the appearance of a luminous meteor, or a comet, or
the shock of an earthquake. It would be only necessary to multiply such
coincidences indefinitely, and the mind of every philosopher would be
disturbed. Now it would be difficult to exaggerate the number of
physical events, many of them most rare and unconnected in their nature,
which were imagined by the Woodwardian hypothesis to have happened in
the course of a few months; and numerous other examples might be found
of popular geological theories, which require us to imagine that a long
succession of events happened in a brief and almost momentary period.

Another liability to error, very nearly allied to the former, arises
from the frequent contact of geological monuments referring to very
distant periods of time. We often behold, at one glance, the effects of
causes which have acted at times incalculably remote, and yet there may
be no striking circumstances to mark the occurrence of a great chasm in
the chronological series of Nature's archives. In the vast interval of
time which may really have elapsed between the results of operations
thus compared, the physical condition of the earth may, by slow and
insensible modifications, have become entirely altered; one or more
races of organic beings may have passed away, and yet have left behind,
in the particular region under contemplation, no trace of their
existence.

To a mind unconscious of these intermediate events, the passage from one
state of things to another must appear so violent, that the idea of
revolutions in the system inevitably suggests itself. The imagination is
as much perplexed by the deception, as it might be if two distant points
in space were suddenly brought into immediate proximity. Let us suppose,
for a moment, that a philosopher should lie down to sleep in some arctic
wilderness, and then be transferred by a power, such as we read of in
tales of enchantment, to a valley in a tropical country, where, on
awaking, he might find himself surrounded by birds of brilliant plumage,
and all the luxuriance of animal and vegetable forms of which Nature is
so prodigal in those regions. The most reasonable supposition, perhaps,
which he could make, if by the necromancer's art he were placed in such
a situation, would be, that he was dreaming; and if a geologist form
theories under a similar delusion, we cannot expect him to preserve more
consistency in his speculations than in the train of ideas in an
ordinary dream.

It may afford, perhaps, a lively illustration of the principle here
insisted upon, if I recall to the reader's recollection the legend of
the Seven Sleepers. The scene of that popular fable was placed in the
two centuries which elapsed between the reign of the emperor Decius and
the death of Theodosius the younger. In that interval of time (between
the years 249 and 450 of our era) the union of the Roman Empire had been
dissolved, and some of its fairest provinces overrun by the barbarians
of the north. The seat of government had passed from Rome to
Constantinople, and the throne from a pagan persecutor to a succession
of Christian and orthodox princes. The genius of the empire had been
humbled in the dust, and the altars of Diana and Hercules were on the
point of being transferred to Catholic saints and martyrs. The legend
relates, "that when Decius was still persecuting the Christians, seven
noble youths of Ephesus concealed themselves in a spacious cavern in the
side of an adjacent mountain, where they were doomed to perish by the
tyrant, who gave orders that the entrance should be firmly secured with
a pile of huge stones. They immediately fell into a deep slumber, which
was miraculously prolonged, without injuring the powers of life, during
a period of 187 years. At the end of that time the slaves of Adolius, to
whom the inheritance of the mountain had descended, removed the stones
to supply materials for some rustic edifice: the light of the sun darted
into the cavern, and the Seven Sleepers were permitted to awake. After a
slumber, as they thought, of a few hours, they were pressed by the calls
of hunger, and resolved that Jamblichus, one of their number, should
secretly return to the city to purchase bread for the use of his
companions. The youth could no longer recognize the once familiar aspect
of his native country, and his surprise was increased by the appearance
of a large cross triumphantly erected over the principal gate of
Ephesus. His singular dress and obsolete language confounded the baker,
to whom he offered an ancient medal of Decius as the current coin of the
empire; and Jamblichus, on the suspicion of a secret treasure, was
dragged before the judge. Their mutual inquiries produced the amazing
discovery, that two centuries were almost elapsed since Jamblichus and
his friends had escaped from the rage of a pagan tyrant."[123]

This legend was received as authentic throughout the Christian world
before the end of the sixth century, and was afterwards introduced by
Mahomet as a divine revelation into the Koran, and from hence was
adopted and adorned by all the nations from Bengal to Africa who
professed the Mahometan faith. Some vestiges even of a similar tradition
have been discovered in Scandinavia. "This easy and universal belief,"
observes the philosophical historian of the Decline and Fall, "so
expressive of the sense of mankind, may be ascribed to the genuine merit
of the fable itself. We imperceptibly advance from youth to age, without
observing the gradual, but incessant, change of human affairs; and even,
in our larger experience of history, the imagination is accustomed, by a
perpetual series of causes and effects, to unite the most distant
revolutions. But if the interval between two memorable eras could be
instantly annihilated; if it were possible, after a momentary slumber of
two hundred years, to display the new world to the eyes of a spectator
who still retained a lively and recent impression of the old, his
surprise and his reflections would furnish the pleasing subject of a
philosophical romance."[124]

_Prejudices arising from our peculiar position as inhabitants of the
land._--The sources of prejudice hitherto considered may be deemed
peculiar for the most part to the infancy of the science, but others
are common to the first cultivators of geology and to ourselves, and are
all singularly calculated to produce the same deception, and to
strengthen our belief that the course of nature in the earlier ages
differed widely from that now established. Although these circumstances
cannot be fully explained without assuming some things as proved, which
it will be the object of another part of this work to demonstrate, it
may be well to allude to them briefly in this place.

The first and greatest difficulty, then, consists in an habitual
unconsciousness that our position as observers is essentially
unfavorable, when we endeavor to estimate the nature and magnitude of
the changes now in progress. In consequence of our inattention to this
subject, we are liable to serious mistakes in contrasting the present
with former states of the globe. As dwellers on the land, we inhabit
about a fourth part of the surface; and that portion is almost
exclusively a theatre of decay, and not of reproduction. We know,
indeed, that new deposits are annually formed in seas and lakes, and
that every year some new igneous rocks are produced in the bowels of the
earth, but we cannot watch the progress of their formation; and as they
are only present to our minds by the aid of reflection, it requires an
effort both of the reason and the imagination to appreciate duly their
importance. It is, therefore, not surprising that we estimate very
imperfectly the result of operations thus invisible to us; and that,
when analogous results of former epochs are presented to our inspection,
we cannot immediately recognize the analogy. He who has observed the
quarrying of stone from a rock, and has seen it shipped for some distant
port, and then endeavors to conceive what kind of edifice will be raised
by the materials, is in the same predicament as a geologist, who, while
he is confined to the land, sees the decomposition of rocks, and the
transportation of matter by rivers to the sea, and then endeavors to
picture to himself the new strata which Nature is building beneath the
waters.

_Prejudices arising from our not seeing subterranean changes._--Nor is
his position less unfavorable when, beholding a volcanic eruption, he
tries to conceive what changes the column of lava has produced, in its
passage upwards, on the intersected strata; or what form the melted
matter may assume at great depths on cooling; or what may be the extent
of the subterranean rivers and reservoirs of liquid matter far beneath
the surface. It should, therefore, be remembered, that the task imposed
on those who study the earth's history requires no ordinary share of
discretion; for we are precluded from collating the corresponding parts
of the system of things as it exists now, and as it existed at former
periods. If we were inhabitants of another element--if the great ocean
were our domain, instead of the narrow limits of the land, our
difficulties would be considerably lessened; while, on the other hand,
there can be little doubt, although the reader may, perhaps, smile at
the bare suggestion of such an idea, that an amphibious being, who
should possess our faculties, would still more easily arrive at sound
theoretical opinions in geology, since he might behold, on the one
hand, the decomposition of rocks in the atmosphere, or the
transportation of matter by running water; and, on the other, examine
the deposition of sediment in the sea, and the imbedding of animal and
vegetable remains in new strata. He might ascertain, by direct
observation, the action of a mountain torrent, as well as of a marine
current; might compare the products of volcanoes poured out upon the
land with those ejected beneath the waters; and might mark, on the one
hand, the growth of the forest, and, on the other, that of the coral
reef. Yet, even with these advantages, he would be liable to fall into
the greatest errors, when endeavoring to reason on rocks of subterranean
origin. He would seek in vain, within the sphere of his observation, for
any direct analogy to the process of their formation, and would
therefore be in danger of attributing them, wherever they are upraised
to view, to some "primeval state of nature."

But if we may be allowed so far to indulge the imagination, as to
suppose a being entirely confined to the nether world--some "dusky
melancholy sprite," like Umbriel, who could "flit on sooty pinions to
the central earth," but who was never permitted to "sully the fair face
of light," and emerge into the regions of water and of air; and if this
being should busy himself in investigating the structure of the globe,
he might frame theories the exact converse of those usually adopted by
human philosophers. He might infer that the stratified rocks, containing
shells and other organic remains, were the oldest of created things,
belonging to some original and nascent state of the planet. "Of these
masses," he might say, "whether they consist of loose incoherent sand,
soft clay, or solid stone, none have been formed in modern times. Every
year some part of them are broken and shattered by earthquakes, or
melted by volcanic fire; and when they cool down slowly from a state of
fusion, they assume a new and more crystalline form, no longer
exhibiting that stratified disposition and those curious impressions and
fantastic markings, by which they were previously characterized. This
process cannot have been carried on for an indefinite time, for in that
case all the stratified rocks would long ere this have been fused and
crystallized. It is therefore probable that the whole planet once
consisted of these mysterious and curiously bedded formations at a time
when the volcanic fire had not yet been brought into activity. Since
that period there seems to have been a gradual development of heat; and
this augmentation we may expect to continue till the whole globe shall
be in a state of fluidity and incandescence."

Such might be the system of the Gnome at the very time that the
followers of Leibnitz, reasoning on what they saw on the outer surface,
might be teaching the opposite doctrine of gradual refrigeration, and
averring that the earth had begun its career as a fiery comet, and might
be destined hereafter to become a frozen mass. The tenets of the schools
of the nether and of the upper world would be directly opposed to each
other, for both would partake of the prejudices inevitably resulting
from the continual contemplation of one class of phenomena to the
exclusion of another. Man observes the annual decomposition of
crystalline and igneous rocks, and may sometimes see their conversion
into stratified deposits; but he cannot witness the reconversion of the
sedimentary into the crystalline by subterranean fire. He is in the
habit of regarding all the sedimentary rocks as more recent than the
unstratified, for the same reason that we may suppose him to fall into
the opposite error if he saw the origin of the igneous class only.

It was not an impossible contingency, that astronomers might have been
placed at some period in a situation much resembling that in which the
geologist seems to stand at present. If the Italians, for example, in
the early part of the twelfth century, had discovered at Amalfi, instead
of the pandects of Justinian, some ancient manuscripts filled with
astronomical observations relating to a period of three thousand years,
and made by some ancient geometers who possessed optical instruments as
perfect as any in modern Europe, they would probably, on consulting
these memorials, have come to a conclusion that there had been a great
revolution in the solar and sidereal systems. "Many primary and
secondary planets," they might say, "are enumerated in these tables,
which exist no longer. Their positions are assigned with such precision
that we may assure ourselves that there is nothing in their place at
present but the blue ether. Where one star is visible to us, these
documents represent several thousands. Some of those which are now
single consisted then of two separate bodies, often distinguished by
different colors, and revolving periodically round a common centre of
gravity. There is nothing analogous to them in the universe at present;
for they were neither fixed stars nor planets, but seem to have stood in
the mutual relation of sun and planet to each other. We must conclude,
therefore, that there has occurred, at no distant period, a tremendous
catastrophe, whereby thousands of worlds have been annihilated at once,
and some heavenly bodies absorbed into the substance of others."

When such doctrines had prevailed for ages, the discovery of some of the
worlds, supposed to have been lost (the satellites of Jupiter, for
example), by aid of the first rude telescope invented after the revival
of science, would not dissipate the delusion, for the whole burden of
proof would now be thrown on those who insisted on the stability of the
system from a remote period, and these philosophers would be required to
demonstrate the existence of _all_ the worlds said to have been
annihilated.

Such popular prejudices would be most unfavorable to the advancement of
astronomy; for, instead of persevering in the attempt to improve their
instruments, and laboriously to make and record observations, the
greater number would despair of verifying the continued existence of the
heavenly bodies not visible to the naked eye. Instead of confessing the
extent of their ignorance, and striving to remove it by bringing to
light new facts, they would indulge in the more easy and indolent
employment of framing imaginary theories concerning catastrophes and
mighty revolutions in the system of the universe.

For more than two centuries the shelly strata of the Subapennine hills
afforded matter of speculation to the early geologists of Italy, and few
of them had any suspicion that similar deposits were then forming in the
neighboring sea. They were as unconscious of the continued action of
causes still producing similar effects, as the astronomers, in the case
above supposed, of the existence of certain heavenly bodies still giving
and reflecting light, and performing their movements as of old. Some
imagined that the strata, so rich in organic remains, instead of being
due to secondary agents, had been so created in the beginning of things
by the fiat of the Almighty. Others, as we have seen, ascribed the
imbedded fossil bodies to some plastic power which resided in the earth
in the early ages of the world. In what manner were these dogmas at
length exploded? The fossil relics were carefully compared with their
living analogues, and all doubts as to their organic origin were
eventually dispelled. So, also, in regard to the nature of the
containing beds of mud, sand, and limestone: those parts of the bottom
of the sea were examined where shells are now becoming annually entombed
in new deposits. Donati explored the bed of the Adriatic, and found the
closest resemblance between the strata there forming, and those which
constituted hills above a thousand feet high in various parts of the
Italian peninsula. He ascertained by dredging that living testacea were
there grouped together in precisely the same manner as were their fossil
analogues in the inland strata; and while some of the recent shells of
the Adriatic were becoming incrusted with calcareous rock, he observed
that others had been newly buried in sand and clay, precisely as fossil
shells occur in the Subapennine hills. This discovery of the identity of
modern and ancient submarine operations was not made without the aid of
artificial instruments, which, like the telescope, brought phenomena
into view not otherwise within the sphere of human observation.

In like manner, the volcanic rocks of the Vicentin had been studied in
the beginning of the last century; but no geologist suspected, before
the time of Arduino, that these were composed of ancient submarine
lavas. During many years of controversy, the popular opinion inclined to
a belief that basalt and rocks of the same class had been precipitated
from a chaotic fluid, or an ocean which rose at successive periods over
the continents, charged with the component elements of the rocks in
question. Few will now dispute that it would have been difficult to
invent a theory more distant from the truth; yet we must cease to wonder
that it gained so many proselytes, when we remember that its claims to
probability arose partly from the very circumstance of its confirming
the assumed want of analogy between geological causes and those now in
action. By what train of investigations were geologists induced at
length to reject these views, and to assent to the igneous origin of the
trappean formations? By an examination of volcanoes now active, and by
comparing their structure and the composition of their lavas with the
ancient trap-rocks.

The establishment, from time to time, of numerous points of
identification, drew at length from geologists a reluctant admission,
that there was more correspondence between the condition of the globe at
remote eras and now, and more uniformity in the laws which have
regulated the changes of its surface, than they at first imagined. If,
in this state of the science, they still despaired of reconciling every
class of geological phenomena to the operations of ordinary causes, even
by straining analogy to the utmost limits of credibility, we might have
expected, at least, that the balance of probability would now have been
presumed to incline towards the close analogy of the ancient and modern
causes. But, after repeated experience of the failure of attempts to
speculate on geological monuments, as belonging to a distinct order of
things, new sects continued to persevere in the principles adopted by
their predecessors. They still began, as each new problem presented
itself, whether relating to the animate or inanimate world, to assume an
original and dissimilar order of nature; and when at length they
approximated, or entirely came round to an opposite opinion, it was
always with the feeling, that they were conceding what they had been
justified _à priori_ in deeming improbable. In a word, the same men who,
as natural philosophers, would have been most incredulous respecting any
extraordinary deviations from the known course of nature, if reported to
have happened _in their own time_, were equally disposed, as geologists,
to expect the proofs of such deviations at every period of the past.

I shall proceed in the following chapters to enumerate some of the
principal difficulties still opposed to the theory of the uniform nature
and energy of the causes which have worked successive changes in the
crust of the earth, and in the condition of its living inhabitants. The
discussion of so important a question on the present occasion may appear
premature, but it is one which naturally arises out of a review of the
former history of the science. It is, of course, impossible to enter
into such speculative topics, without occasionally carrying the novice
beyond his depth, and appealing to facts and conclusions with which he
will be unacquainted, until he has studied some elementary work on
geology, but it may be useful to excite his curiosity, and lead him to
study such works by calling his attention at once to some of the
principal points of controversy.[125]




CHAPTER VI.

DOCTRINE OF THE DISCORDANCE OF THE ANCIENT AND MODERN CAUSES OF CHANGE
CONTROVERTED.


  Climate of the Northern Hemisphere formerly different--Direct proofs
    from the organic remains of the Italian strata--Proofs from analogy
    derived from extinct quadrupeds--Imbedding of animals in
    icebergs--Siberian mammoths--Evidence in regard to temperature, from
    the fossils of tertiary and secondary rocks--From the plants of the
    coal formation--Northern limit of these fossils--Whether such plants
    could endure the long continuance of an arctic night.


_Climate of the Northern hemisphere formerly different._--Proofs of
former revolutions in climate, as deduced from fossil remains, have
afforded one of the most popular objections to the theory which
endeavors to explain all geological changes by reference to those now in
progress on the earth. The probable causes, therefore, of fluctuations
in climate, may first be treated of.

That the climate of the Northern hemisphere has undergone an important
change, and that its mean annual temperature must once have more nearly
resembled that now experienced within the tropics, was the opinion of
some of the first naturalists who investigated the contents of the
ancient strata. Their conjecture became more probable when the shells
and corals of the older tertiary and many secondary rocks were carefully
examined; for the organic remains of these formations were found to be
intimately connected by generic affinity with species now living in
warmer latitudes. At a later period, many reptiles, such as turtles,
tortoises, and large saurian animals, were discovered in European
formations in great abundance; and they supplied new and powerful
arguments, from analogy, in support of the doctrine, that the heat of
the climate had been great when our secondary strata were deposited.
Lastly, when the botanist turned his attention to the specific
determination of fossil plants, the evidence acquired still fuller
confirmation; for the flora of a country is peculiarly influenced by
temperature: and the ancient vegetation of the earth might have been
expected more readily than the forms of animals, to have afforded
conflicting proofs, had the popular theory been without foundation. When
the examination of fossil remains was extended to rocks in the most
northern parts of Europe and North America, and even to the Arctic
regions, indications of the same revolution in climate were discovered.

It cannot be said, that in this, as in many other departments of
geology, we have investigated the phenomena of former eras, and
neglected those of the present state of things. On the contrary, since
the first agitation of this interesting question, the accessions to our
knowledge of living animals and plants have been immense, and have far
surpassed all the data previously obtained for generalizing on the
relation of certain types of organization to particular climates. The
tropical and temperate zones of South America and of Australia have been
explored; and, on close comparison, it has been found that scarcely any
of the species of the animate creation in these extensive continents are
identical with those inhabiting the old world. Yet the zoologist and
botanist, well acquainted with the geographical distribution of organic
beings in other parts of the globe, would have been able, if distinct
groups of species had been presented to them from these regions, to
recognize those which had been collected from latitudes within, and
those which were brought from without the tropics.

Before I attempt to explain the probable causes of great vicissitudes of
temperature on the earth's surface, I shall take a rapid view of some of
the principal data which appear to support the popular opinions now
entertained on the subject. To insist on the soundness of these
inferences, is the more necessary, because some zoologists have
undertaken to vindicate the uniformity of the laws of nature, not by
accounting for former fluctuations in climate, but by denying the value
of the evidence in their favor.[126]

_Proofs from fossil shells in tertiary strata._--In Sicily, Calabria,
and in the neighborhood of Naples, the fossil testacea of the most
modern tertiary formations belong almost entirely to species now
inhabiting the Mediterranean; but as we proceed northwards in the
Italian peninsula we find in the strata called Subapennine an assemblage
of fossil shells departing somewhat more widely from the type of the
neighboring seas. The proportion of species identifiable with those now
living in the Mediterranean is still considerable; but it no longer
predominates, as in the South of Italy and part of Sicily, over the
unknown species. Although occurring in localities which are removed
several degrees farther from the equator (as at Sienna, Parma, Asti,
&c.), the shells yield clear indications of a warmer climate. This
evidence is of great weight, and is not neutralized by any facts of a
conflicting character; such, for instance, as the association, in the
same group, of individuals referable to species now confined to arctic
regions. Whenever any of the fossil shells are identified with living
species foreign to the Mediterranean, it is not in the Northern Ocean,
but nearer the tropics, that they must be sought: on the other hand, the
associated unknown species belong, for the most part, to _genera_ which
are now most largely developed in equinoctial regions, as, for example,
the genera Cancellaria, Cassidaria, Pleurotoma, Conus, and Cypræa.

On comparing the fossils of the tertiary deposits of Paris and London
with those of Bourdeaux, and these again with the more modern strata of
Sicily, we should at first expect that they would each indicate a higher
temperature in proportion as they are situated farther to the south.
But the contrary is true; of the shells belonging to these several
groups, whether freshwater or marine, some are of extinct, others of
living species. Those found in the older, or Eocene, deposits of Paris
and London, although six or seven degrees to the north of the Miocene
strata at Bourdeaux, afford evidence of a warmer climate; while those of
Bourdeaux imply that the sea in which they lived was of a higher
temperature than that of Sicily, where the shelly strata were formed six
or seven degrees nearer to the equator. In these cases the greater
antiquity of the several formations (the Parisian being the oldest and
the Sicilian the newest) has more than counterbalanced the influence
which latitude would otherwise exert, and this phenomenon clearly points
to a gradual and successive refrigeration of climate.

_Siberian Mammoths._--It will naturally be asked, whether some recent
geological discoveries bringing evidence to light of a colder, or as it
has been termed "glacial epoch," towards the close of the tertiary
periods throughout the northern hemisphere, does not conflict with the
theory above alluded to, of a warmer temperature having prevailed in the
eras of the Eocene, Miocene, and Pliocene formations. In answer to this
inquiry, it may certainly be affirmed, that an oscillation of climate
has occurred in times immediately antecedent to the peopling of the
earth by man; but proof of the intercalation of a less genial climate at
an era when nearly all the marine and terrestrial testacea had already
become specifically the same as those now living, by no means rebuts the
conclusion previously drawn, in favor of a warmer condition of the
globe, during the ages which elapsed while the tertiary strata were
deposited. In some of the most superficial patches of sand, gravel, and
loam, scattered very generally over Europe, and containing recent
shells, the remains of extinct species of land quadrupeds have been
found, especially in places where the alluvial matter appears to have
been washed into small lakes, or into depressions in the plains
bordering ancient rivers. Similar deposits have also been lodged in
rents and caverns of rocks, where they may have been swept in by land
floods, or introduced by engulphed rivers during changes in the physical
geography of these countries. The various circumstances under which the
bones of animals have been thus preserved, will be more fully considered
hereafter;[127] I shall only state here, that among the extinct mammalia
thus entombed, we find species of the elephant, rhinoceros,
hippopotamus, bear, hyæna, lion, tiger, monkey (macacus[128]), and many
others; consisting partly of genera now confined to warmer regions.

It is certainly probable that when some of these quadrupeds abounded in
Europe, the climate was milder than that now experienced. The
hippopotamus, for example, is now only met with where the temperature of
the water is warm and nearly uniform throughout the year, and where the
rivers are never frozen over. Yet when the great fossil species
(_Hippopotamus major_, Cuv.) inhabited England, the testacea of our
country were nearly the same as those now existing, and the climate
cannot be supposed to have been very hot. The bones of this animal have
lately been found by Mr. Strickland, together with those of a bear and
other mammalia, at Cropthorn, near Evesham, in Worcestershire, in
alluvial sand, together with twenty-three species of terrestrial and
freshwater shells, all, with two exceptions, of British species. The bed
of sand, containing the shells and bones, reposes on lias, and is
covered with alternating strata of gravel, sand, and loam.[129]

The mammoth also appears to have existed in England when the temperature
of our latitudes could not have been very different from that which now
prevails; for remains of this animal have been found at North Cliff, in
the county of York, in a lacustrine formation, in which all the land and
freshwater shells, thirteen in number, can be identified with species
and varieties now existing in that county. Bones of the bison, also, an
animal now inhabiting a cold or temperate climate, have been found in
the same place. That these quadrupeds, and the indigenous species of
testacea associated with them, were all contemporary inhabitants of
Yorkshire, has been established by unequivocal proof. The Rev. W. V.
Vernon Harcourt caused a pit to be sunk to the depth of twenty-two feet
through undisturbed strata, in which the remains of the mammoth were
found imbedded, together with the shells, in a deposit which had
evidently resulted from tranquil waters.[130]

In the valley of the Thames, as at Ilford and Grays, in Essex, bones of
the elephant and rhinoceros occur in strata abounding in freshwater
shells of the genera Unio, Cyclas, Paludina, Valvata, Ancylus, and
others. These fossil shells belong for the most part to species now
living in the same district, yet some few of them are extinct, as, for
example, a species of Cyrena, a genus no longer inhabiting Europe, and
now entirely restricted to warmer latitudes.

When reasoning on such phenomena, the reader must always bear in mind
that the fossil individuals belonged to _species_ of elephant,
rhinoceros, hippopotamus, bear, tiger, and hyæna, distinct from those
which now dwell within or near the tropics. Dr. Fleming, in a discussion
on this subject, has well remarked that a near resemblance in form and
osteological structure is not always followed, in the existing creation,
by a similarity of geographical distribution; and we must therefore be
on our guard against deciding too confidently, from mere analogy of
anatomical structure, respecting the habits and physiological
peculiarities of _species_ now no more. "The zebra delights to roam over
the tropical plains, while the horse can maintain its existence
throughout an Iceland winter. The buffalo, like the zebra, prefers a
high temperature, and cannot thrive even where the common ox prospers.
The musk-ox, on the other hand, though nearly resembling the buffalo,
prefers the stinted herbage of the arctic regions, and is able, by its
periodical migrations, to outlive a northern winter. The jackal (_Canis
aureus_) inhabits Africa, the warmer parts of Asia, and Greece; while
the isatis (_Canis lagopus_) resides in the arctic regions. The African
hare and the polar hare have their geographical distribution expressed
in their trivial names;"[131] and different species of bears thrive in
tropical, temperate, and arctic latitudes.

Recent investigations have placed beyond all doubt the important fact
that a species of tiger, identical with that of Bengal, is common in the
neighborhood of Lake Aral, near Sussac, in the forty-fifth degree of
north latitude; and from time to time this animal is now seen in
Siberia, in a latitude as far north as the parallel of Berlin and
Hamburgh.[132] Humboldt remarks that the part of Southern Asia now
inhabited by this Indian species of tiger is separated from the Himalaya
by two great chains of mountains, each covered with perpetual snow,--the
chain of Kuenlun, lat. 35° N., and that of Mouztagh, lat. 42°,--so that
it is impossible that these animals should merely have made excursions
from India, so as to have penetrated in summer to the forty-eighth and
fifty-third degrees of north latitude. They must remain all the winter
north of the Mouztagh, or Celestial Mountains. The last tiger killed, in
1828, on the Lena, in lat. 52¼°, was in a climate colder than that of
Petersburg and Stockholm.[133]

We learn from Mr. Hodgson's account of the mammalia of Nepal, that the
tiger is sometimes found at the very edge of perpetual snow in the
Himalaya;[134] and Pennant mentions that it is found among the snows of
Mount Ararat in Armenia. The jaguar, also, has been seen in America,
wandering from Mexico, as far north as Kentucky, lat. 37° N.,[135] and
even as far as 42° S. in South America,--a latitude which corresponds to
that of the Pyrenees in the northern hemisphere.[136] The range of the
puma is still wider, for it roams from the equator to the Straits of
Magellan, being often seen at Port Famine, in lat. 53° 38' S.

A new species of panther (_Felis irbis_), covered with long hair, has
been discovered in Siberia, evidently inhabiting, like the tiger, a
region north of the Celestial Mountains, which are in lat. 42°.[137]

The two-horned African rhinoceros occurs without the tropics at the Cape
of Good Hope, in lat. 34° 29' S., where it is accompanied by the
elephant, hippopotamus, and hyæna. Here the migration of all these
species towards the south is arrested by the ocean; but if the continent
had been prolonged still farther, and the land had been of moderate
elevation, it is very probable that they might have extended their
range to a greater distance from the tropics.

Now, if the Indian tiger can range in our own times to the southern
borders of Siberia, or skirt the snows of the Himalaya, and if the puma
can reach the fifty-third degree of latitude in South America, we may
easily understand how large species of the same _genera_ may once have
inhabited our temperate climates. The mammoth (_E. primigenius_),
already alluded to, as occurring fossil in England, was decidedly
different from the two existing species of elephants, one of which is
limited to Asia, south of the 31° of N. lat., the other to Africa, where
it extends, as before stated, as far south as the Cape of Good Hope. The
bones of the great fossil species are very widely spread over Europe and
North America; but are nowhere in such profusion as in Siberia,
particularly near the shores of the Frozen Ocean. Are we, then, to
conclude that this animal preferred a polar climate? If so, it may well
be asked, by what food was it sustained, and why does it not still
survive near the arctic circle?[138]

Pallas and other writers describe the bones of the mammoth as abounding
throughout all the Lowlands of Siberia, stretching in a direction west
and east, from the borders of Europe to the extreme point nearest
America, and south and north, from the base of the mountains of Central
Asia to the shores of the Arctic Sea. (See map, fig. 1.) Within this
space, scarcely inferior in area to the whole of Europe, fossil ivory
has been collected almost everywhere, on the banks of the Irtish, Obi,
Yenesei, Lena, and other rivers. The elephantine remains do not occur in
the marshes and low plains, but where the banks of the rivers present
lofty precipices of sand and clay, from which circumstance Pallas very
justly inferred that, if sections could be obtained, similar bones might
be found in all the elevated lands intervening between the great rivers.
Strahlenberg, indeed, had stated, before the time of Pallas, that
wherever any of the great rivers overflowed and cut out fresh channels
during floods, more fossil remains of the same kind were invariably
disclosed.

[Illustration: MAP OF SIBERIA.

Fig. 1.

_Map showing the course of the Siberian rivers from south to north, from
temperate to arctic regions, in the country where the fossil bones of
the Mammoth abound._]

As to the position of the bones, Pallas found them in some places
imbedded together with marine remains; in others, simply with fossil
wood, or lignite, such as, he says, might have been derived from
carbonized peat. On the banks of the Yenesei, below the city of
Krasnojarsk, in lat. 56°, he observed grinders, and bones of elephants,
in strata of yellow and red loam, alternating with coarse sand and
gravel, in which was also much petrified wood of the willow and other
trees. Neither here nor in the neighboring country were there any marine
shells, but merely layers of black coal.[139] But grinders of the
mammoth were collected much farther down the same river, near the sea,
in lat. 70°, mixed with _marine_ petrifactions.[140] Many other places
in Siberia are cited by Pallas, where sea shells and fishes' teeth
accompany the bones of the mammoth, rhinoceros, and Siberian buffalo, or
bison (_Bos priscus_). But it is not on the Obi nor the Yenesei, but on
the Lena, farther to the east, where, in the same parallels of latitude,
the cold is far more intense, that fossil remains have been found in the
most wonderful state of preservation. In 1772, Pallas obtained from
Wiljuiskoi, in lat. 64°, from the banks of the Wiljui, a tributary of
the Lena, the carcass of a rhinoceros (_R. tichorhinus_), taken from the
sand in which it must have remained congealed for ages, the soil of that
region being always frozen to within a slight depth of the surface. This
carcass was compared to a natural mummy, and emitted an odor like putrid
flesh, part of the skin being still covered with black and gray hairs.
So great, indeed, was the quantity of hair on the foot and head conveyed
to St. Petersburg, that Pallas asked whether the rhinoceros of the Lena
might not have been an inhabitant of the temperate regions of middle
Asia, its clothing being so much warmer than that of the African
rhinoceros.[141]

Professor Brandt, of St. Petersburg, in a letter to Baron Alex. Von
Humboldt, dated 1846, adds the following particulars respecting this
wonderful fossil relic:--"I have been so fortunate as to extract from
cavities in the molar teeth of the Wiljui rhinoceros a small quantity of
its half-chewed food, among which fragments of pine leaves, one-half of
the seed of a polygonaceous plant, and very minute portions of wood with
porous cells (or small fragments of coniferous wood), were still
recognizable. It was also remarkable, on a close investigation of the
head, that the blood-vessels discovered in the interior of the mass
appeared filled, even to the capillary vessels, with a brown mass
(coagulated blood), which in many places still showed the red color of
blood."[142]

After more than thirty years, the entire carcass of a mammoth (or
extinct species of elephant) was obtained in 1803, by Mr. Adams, much
farther to the north. It fell from a mass of ice, in which it had been
encased, on the banks of the Lena, in lat. 70°; and so perfectly had the
soft parts of the carcass been preserved, that the flesh, as it lay, was
devoured by wolves and bears. This skeleton is still in the museum of
St. Petersburg, the head retaining its integument and many of the
ligaments entire. The skin of the animal was covered, first, with black
bristles, thicker than horse hair, from twelve to sixteen inches in
length; secondly, with hair of a reddish brown color, about four inches
long; and thirdly, with wool of the same color as the hair, about an
inch in length. Of the fur, upwards of thirty pounds' weight were
gathered from the wet sand-bank. The individual was nine feet high and
sixteen feet long, without reckoning the large curved tusks: a size
rarely surpassed by the largest living male elephants.[143]

It is evident, then, that the mammoth, instead of being naked, like the
living Indian and African elephants, was enveloped in a thick shaggy
covering of fur, probably as impenetrable to rain and cold as that of
the musk ox.[144] The species may have been fitted by nature to
withstand the vicissitudes of a northern climate; and it is certain
that, from the moment when the carcasses, both of the rhinoceros and
elephant, above described, were buried in Siberia, in latitudes 64° and
70° N., the soil must have remained frozen, and the atmosphere nearly as
cold as at this day.

The most recent discoveries made in 1843 by Mr. Middendorf, a
distinguished Russian naturalist, and which he communicated to me in
September, 1846, afford more precise information as to the climate of
the Siberian lowlands, at the period when the extinct quadrupeds were
entombed. One elephant was found on the Tas, between the Obi and
Yenesei, near the arctic circle, about lat. 66° 30' N., with some parts
of the flesh in so perfect a state that the bulb of the eye is now
preserved in the museum at Moscow. Another carcass, together with a
young individual of the same species, was met with in the same year,
1843, in lat. 75° 15' N., near the river Taimyr, with the flesh decayed.
It was imbedded in strata of clay and sand, with erratic blocks, at
about 15 feet above the level of the sea. In the same deposit Mr.
Middendorf observed the trunk of a larch tree (_Pinus larix_), the same
wood as that now carried down in abundance by the Taimyr to the Arctic
Sea. There were also associated fossil shells of _living northern_
species, and which are moreover characteristic of the drift or _glacial_
deposits of Europe. Among these _Nucula pygmæa_, _Tellina calcarea_,
_Mya truncata_, and _Saxicava rugosa_ were conspicuous.

So fresh is the ivory throughout northern Russia, that, according to
Tilesius, thousands of fossil tusks have been collected and used in
turning; yet others are still procured and sold in great plenty. He
declares his belief that the bones still left in northern Russia must
greatly exceed in number all the elephants now living on the globe.

We are as yet ignorant of the entire geographical range of the mammoth;
but its remains have been recently collected from the cliffs of frozen
mud and ice on the east side of Behring's Straits, in Eschscholtz's Bay,
in Russian America, lat. 66° N. As the cliffs waste away by the thawing
of the ice, tusks and bones fall out, and a strong odor of animal matter
is exhaled from the mud.[145]

On considering all the facts above enumerated, it seems reasonable to
imagine that a large region in central Asia, including, perhaps, the
southern half of Siberia, enjoyed, at no very remote period in the
earth's history, a temperate climate, sufficiently mild to afford food
for numerous herds of elephants and rhinoceroses, _of species distinct
from those now living_. It has usually been taken for granted that
herbivorous animals of large size require a very luxuriant vegetation
for their support; but this opinion is, according to Mr. Darwin,
completely erroneous:--"It has been derived," he says, "from our
acquaintance with India and the Indian islands, where the mind has been
accustomed to associate troops of elephants with noble forests and
impenetrable jungles. But the southern parts of Africa, from the tropic
of Capricorn to the Cape of Good Hope, although sterile and desert, are
remarkable for the number and great bulk of the indigenous quadrupeds.
We there meet with an elephant, five species of rhinoceros, a
hippopotamus, a giraffe, the bos caffer, the elan, two zebras, the
quagga, two gnus, and several antelopes. Nor must we suppose, that while
the species are numerous, the individuals of each kind are few. Dr.
Andrew Smith saw, in one day's march, in lat. 24° S., without wandering
to any great distance on either side, about 150 rhinoceroses, with
several herds of giraffes, and his party had killed, on the previous
night, eight hippopotamuses. Yet the country which they inhabited was
thinly covered with grass and bushes about four feet high, and still
more thinly with mimosa-trees, so that the wagons of the travellers were
not prevented from proceeding in a nearly direct line."[146]

In order to explain how so many animals can find support in this region,
it is suggested that the underwood, of which their food chiefly
consists, may contain much nutriment in a small bulk, and also that the
vegetation has a rapid growth; for no sooner is a part consumed than its
place, says Dr. Smith, is supplied by a fresh stock. Nevertheless, after
making every allowance for this successive production and consumption,
it is clear, from the facts above cited, that the quantity of food
required by the larger herbivora is much less than we have usually
imagined. Mr. Darwin conceives that the amount of vegetation supported
at any one time by Great Britain may exceed, in a ten-fold ratio, the
quantity existing on an equal area in the interior parts of Southern
Africa.[147] It is remarked, moreover, in illustration of the small
connection discoverable between abundance of food and the magnitude of
indigenous mammalia, that while in the desert part of Southern Africa
there are so many huge animals; in Brazil, where the splendor and
exuberance of the vegetation are unrivalled, there is not a single wild
quadruped of large size.[148]

It would doubtless be impossible for herds of mammoths and rhinoceroses
to subsist, at present, throughout the year, even in the southern part
of Siberia, covered as it is with snow during winter; but there is no
difficulty in supposing a vegetation capable of nourishing these great
quadrupeds to have once flourished between the latitudes 40° and 60° N.

Dr. Fleming has hinted, that "the kind of food which the existing
species of elephant prefers, will not enable us to determine, or even to
offer a probable conjecture, concerning that of the extinct species. No
one acquainted with the gramineous character of the food of our
fallow-deer, stag, or roe, would have assigned a lichen to the
reindeer."

Travellers mention that, even now, when the climate of eastern Asia is
so much colder than the same parallels of latitude farther west, there
are woods not only of fir, but of birch, poplar, and alder, on the banks
of the Lena, as far north as latitude 60°.

It has, moreover, been suggested, that as, in our own times, the
northern animals migrate, so the Siberian elephant and rhinoceros may
have wandered towards the north in summer. The musk oxen annually desert
their winter quarters in the south, and cross the sea upon the ice, to
graze for four months, from May to September, on the rich pasturage of
Melville Island, in lat. 75°. The mammoths, without passing so far
beyond the arctic circle, may nevertheless have made excursions, during
the heat of a brief northern summer, from the central or temperate parts
of Asia to the sixtieth parallel of latitude.

Now, in this case, the preservation of their bones, or even occasionally
of their entire carcasses, in ice or frozen soil, may be accounted for,
without resorting to speculations concerning sudden revolutions in the
former state and climate of the earth's surface. We are entitled to
assume, that, in the time of the extinct elephant and rhinoceros, the
Lowland of Siberia was less extensive towards the north than now; for we
have seen (p. 80) that the strata of this Lowland, in which the fossil
bones lie buried, were originally deposited beneath the sea; and we
know, from the facts brought to light in Wrangle's Voyage, in the years
1821, 1822, and 1823, that a slow upheaval of the land along the borders
of the Icy Sea is now constantly taking place, similar to that
experienced in part of Sweden. In the same manner, then, as the shores
of the Gulf of Bothnia are extended, not only by the influx of sediment
brought down by rivers, but also by the elevation and consequent drying
up of the bed of the sea, so a like combination of causes may, in modern
times, have been extending the low tract of land where marine shells
and fossil bones occur in Siberia.[149] Such a change in the physical
geography of that region, implying a constant augmentation in the
quantity of arctic land, would, according to principles to be explained
in the next chapter, tend to increase the severity of the winters. We
may conclude, therefore, that, before the land reached so far to the
north, the temperature of the Siberian winter and summer was more nearly
equalized; and a greater degree of winter's cold may, even more than a
general diminution of the mean annual temperature, have finally
contributed to the extermination of the mammoth and its contemporaries.

On referring to the map (p. 79), the reader will see how all the great
rivers of Siberia flow at present from south to north, from temperate to
arctic regions, and they are all liable, like the Mackenzie, in North
America, to remarkable floods, in consequence of flowing in this
direction. For they are filled with running water in their upper or
southern course when completely frozen over for several hundred miles
near their mouths, where they remain blocked up by ice for six months in
every year. The descending waters, therefore, finding no open channel,
rush over the ice, often changing their direction, and sweeping along
forests and prodigious quantities of soil and gravel mixed with ice. Now
the rivers of Siberia are among the largest in the world, the Yenesei
having a course of 2500, the Lena of 2000 miles; so that we may easily
conceive that the bodies of animals which fall into their waters may be
transported to vast distances towards the Arctic Sea, and, before
arriving there, may be stranded upon and often frozen into thick ice.
Afterwards, when the ice breaks up, they may be floated still farther
towards the ocean, until at length they become buried in fluviatile and
submarine deposits near the mouths of rivers.

Humboldt remarks that near the mouths of the Lena a considerable
thickness of frozen soil may be found at all seasons at the depth of a
few feet; so that if a carcass be once imbedded in mud and ice in such a
region and in such a climate, its putrefaction may be arrested for
indefinite ages.[150] According to Prof. Von Baer of St. Petersburg, the
ground is now frozen permanently to the depth of 400 feet, at the town
of Yakutzt, on the western bank of the Lena, in lat. 62° N., 600 miles
distant from the polar sea. Mr. Hedenstrom tells us that, throughout a
wide area in Siberia, the boundary cliffs of the lakes and rivers
consist of alternate layers of earthy materials and ice, in horizontal
stratification;[151] and Mr. Middendorf informed us, in 1846, that, in
his tour there three years before, he had bored in Siberia to the depth
of seventy feet, and, after passing through much frozen soil mixed with
ice, had come down upon a solid mass of pure transparent ice, the
thickness of which, after penetrating two or three yards, they did not
ascertain. We may conceive, therefore, that even at the period of the
mammoth, when the Lowland of Siberia was less extensive towards the
north, and consequently the climate more temperate than now, the cold
may still have been sufficiently intense to cause the rivers flowing in
their present direction to sweep down from south to north the bodies of
drowned animals, and there bury them in drift ice and frozen mud.

If it be true that the carcass of the mammoth was imbedded in pure ice,
there are two ways in which it may have been frozen in. We may suppose
the animal to have been overwhelmed by drift snow. I have been informed
by Dr. Richardson, that, in the northern parts of America, comprising
regions now inhabited by many herbivorous quadrupeds, the drift snow is
often converted into permanent glaciers. It is commonly blown over the
edges of steep cliffs, so as to form an inclined talus hundreds of feet
high; and when a thaw commences, torrents rush from the land, and throw
down from the top of the cliff alluvial soil and gravel. This new soil
soon becomes covered with vegetation, and protects the foundation of
snow from the rays of the sun. Water occasionally penetrates into the
crevices and pores of the snow; but, as it soon freezes again, it serves
the more rapidly to consolidate the mass into a compact iceberg. It may
sometimes happen that cattle grazing in a valley at the base of such
cliffs, on the borders of a sea or river, may be overwhelmed, and at
length inclosed in solid ice, and then transported towards the polar
regions. Or a herd of mammoths returning from their summer pastures in
the north, may have been surprised, while crossing a stream, by the
sudden congelation of the waters. The missionary Huc relates, in his
travels in Thibet in 1846, that, after many of his party had been frozen
to death, they pitched their tents on the banks of the Mouroui-Ousson
(which lower down becomes the famous Blue River), and saw from their
encampment "some black shapeless objects ranged in file across the
stream. As they advanced nearer no change either in form or distinctness
was apparent; nor was it till they were quite close, that they
recognized in them a troop of the wild oxen, called Yak by the
Thibetans.[152] There were more than fifty of them incrusted in the ice.
No doubt they had tried to swim across at the moment of congelation, and
had been unable to disengage themselves. Their beautiful heads,
surmounted by huge horns, were still above the surface, but their bodies
were held fast in the ice, which was so transparent that the position of
the imprudent beasts was easily distinguishable; they looked as if still
swimming, but the eagles and ravens had pecked out their eyes."[153]

The foregoing investigations, therefore, lead us to infer that the
mammoth, and some other extinct quadrupeds fitted to live in high
latitudes, were inhabitants of Northern Asia at a time when the
geographical conditions and climate of that continent were different
from the present. But the age of this fauna was comparatively modern in
the earth's history. It appears that when the oldest or eocene tertiary
deposits were formed, a warm temperature pervaded the European seas and
lands. Shells of the genus Nautilus and other forms characteristic of
tropical latitudes; fossil reptiles, such as the crocodile, turtle, and
tortoise; plants, such as palms, some of them allied to the cocoa-nut,
the screw-pine, the custard-apple, and the acacia, all lead to this
conclusion. This flora and fauna were followed by those of the miocene
formation, in which indications of a southern, but less tropical climate
are detected. Finally, the pliocene deposits, which come next in
succession, exhibit in their organic remains a much nearer approach to
the state of things now prevailing in corresponding latitudes. It was
towards the close of this period that the seas of the northern
hemisphere became more and more filled with floating icebergs often
charged with erratic blocks, so that the waters and the atmosphere were
chilled by the melting ice, and an arctic fauna enabled, for a time, to
invade the temperate latitudes both of N. America and Europe. The
extinction of a considerable number of land quadrupeds and aquatic
mollusca was gradually brought about by the increasing severity of the
cold; but many species survived this revolution in climate, either by
their capacity of living under a variety of conditions, or by migrating
for a time to more southern lands and seas. At length, by modifications
in the physical geography of the northern regions, and the cessation of
floating ice on the eastern side of the Atlantic, the cold was
moderated, and a milder climate ensued, such as we now enjoy in
Europe.[154]

_Proofs from fossils in secondary and still older strata._--A great
interval of time appears to have elapsed between the formation of the
secondary strata, which constitute the principal portion of the elevated
land in Europe, and the origin of the eocene deposits. If we examine the
rocks from the chalk to the new red sandstone inclusive, we find many
distinct assemblages of fossils entombed in them, all of unknown
species, and many of them referable to genera and families now most
abundant between the tropics. Among the most remarkable are reptiles of
gigantic size; some of them herbivorous, others carnivorous, and far
exceeding in size any now known even in the torrid zone. The genera are
for the most part extinct, but some of them, as the crocodile and
monitor, have still representatives in the warmer parts of the earth.
Coral reefs also were evidently numerous in the seas of the same
periods, composed of species often belonging to genera now
characteristic of a tropical climate. The number of large chambered
shells also, including the nautilus, leads us to infer an elevated
temperature; and the associated fossil plants, although imperfectly
known, tend to the same conclusion, the Cycadeæ constituting the most
numerous family.

But it is from the more ancient coal-deposits that the most
extraordinary evidence has been supplied in proof of the former
existence of a very different climate--a climate which seems to have
been moist, warm, and extremely uniform, in those very latitudes which
are now the colder, and in regard to temperature, the most variable
regions of the globe. We learn from the researches of Adolphe
Brongniart, Goeppert, and other botanists, that in the flora of the
carboniferous era there was a great predominance of ferns, some of which
were arborescent; as, for example, Caulopteris, Protopteris, and
Psarronius; nor can this be accounted for, as some have supposed, by the
greater power which ferns possess of resisting maceration in water.[155]
This prevalence of ferns indicates a moist, equable, and temperate
climate, and the absence of any severe cold; for such are the conditions
which, at the present day, are found to be most favorable to that tribe
of plants. It is only in the islands of the tropical oceans, and of the
southern temperate zone, such as Norfolk Island, Otaheite, the Sandwich
Islands, Tristan d'Acunha, and New Zealand, that we find any near
approach to that remarkable preponderance of ferns which is
characteristic of the Carboniferous flora. It has been observed that
tree ferns and other forms of vegetation which flourished most
luxuriantly within the tropics, extend to a much greater distance from
the equator in the southern hemisphere than in the northern, being found
even as far as 46° S. latitude in New Zealand. There is little doubt
that this is owing to the more uniform and moist climate occasioned by
the greater proportional area of sea. Next to ferns and pines, the most
abundant vegetable forms in the coal formation are the Calamites,
Lepidodendra, Sigillariæ, and Stigmariæ. These were formerly considered
to be so closely allied to tropical genera, and to be so much greater in
size than the corresponding tribes now inhabiting equatorial latitudes,
that they were thought to imply an extremely hot, as well as humid and
equable climate. But recent discoveries respecting the structure and
relations of these fossil plants, have shown that they deviated so
widely from all existing types in the vegetable world, that we have more
reason to infer from this evidence a widely different climate in the
Carboniferous era, as compared to that now prevailing, than a
temperature extremely elevated.[156] Palms, if not entirely wanting
when the strata of the carboniferous group were deposited, appear to
have been exceedingly rare.[157] The Coniferæ, on the other hand, so
abundantly met with in the coal, resemble Araucariæ in structure, a
family of the fir tribe, characteristic at present of the milder regions
of the southern hemisphere, such as Chili, Brazil, New Holland, and
Norfolk Island.

"In regard to the geographical extent of the ancient vegetation, it was
not confined," says M. Brongniart, "to a small space, as to Europe, for
example; for the same forms are met with again at great distances. Thus,
the coal-plants of North America are, for the most part, identical with
those of Europe, and all belong to the same genera. Some specimens,
also, from Greenland, are referable to ferns, analogous to those of our
European coal-mines."[158] The fossil plants brought from Melville
Island, although in a very imperfect state, have been supposed to
warrant similar conclusions;[159] and assuming that they agree with
those of Baffin's Bay, mentioned by M. Brongniart, how shall we explain
the manner in which such a vegetation lived through an arctic night of
several months' duration?[160]

It may seem premature to discuss this question until the true nature of
the fossil flora of the arctic regions has been more accurately
determined; yet, as the question has attracted some attention, let us
assume for a moment that the coal-plants of Melville Island are strictly
analogous to those of the strata of Northumberland--would such a fact
present an inexplicable enigma to the vegetable physiologist?

Plants, it is affirmed, cannot remain in darkness, even for a week,
without serious injury, unless in a torpid state; and if exposed to heat
and moisture they cannot remain torpid, but will grow, and must
therefore perish. If, then, in the latitude of Melville Island, 75° N.,
a high temperature, and consequent humidity, prevailed at that period
when we know the arctic seas were filled with corals and large
multilocular shells, how could plants of tropical forms have flourished?
Is not the bright light of equatorial regions as indispensable a
condition of their well-being as the sultry heat of the same countries?
and how could they annually endure a night prolonged for three
months?[161]

Now, in reply to this objection, we must bear in mind, in the first
place, that, so far as experiments have been made, there is every reason
to conclude, that the range of intensity of light to which living plants
can accommodate themselves is far wider than that of heat. No palms or
tree ferns can live in our temperate latitudes without protection from
the cold; but when placed in hot-houses they grow luxuriantly, even
under a cloudy sky, and where much light is intercepted by the glass and
frame-work. At St. Petersburg, in lat. 60° N., these plants have been
successfully cultivated in hot-houses, although there they must exchange
the perpetual equinox of their native regions, for days and nights which
are alternately protracted to nineteen hours and shortened to five. How
much farther towards the pole they might continue to live, provided a
due quantity of heat and moisture were supplied, has not yet been
determined; but St. Petersburg is probably not the utmost limit, and we
should expect that in lat. 65° at least, where they would never remain
twenty-four hours without enjoying the sun's light, they might still
exist.

It should also be borne in mind, in regard to tree ferns, that they grow
in the gloomiest and darkest parts of the forests of warm and temperate
regions, even extending to nearly the 46th degree of south latitude in
New Zealand. In equatorial countries, says Humboldt, they abound chiefly
in the temperate, humid, and shady parts of _mountains_. As we know,
therefore, that elevation often compensates for the effect of latitude
in the geographical distribution of plants, we may easily understand
that a class of vegetables, which grows at a certain height in the
torrid zone, would flourish on the plains at greater distances from the
equator, if the temperature, moisture, and other necessary conditions,
were equally uniform throughout the year.

Nor must we forget that in all the examples above alluded to, we have
been speaking of _living_ species; but the coal-plants were of perfectly
distinct species, nay, few of them except the ferns and pines can be
referred to genera or even families of the existing vegetable kingdom.
Having a structure, therefore, and often a form which appears to the
botanist so anomalous, they may also have been endowed with a different
constitution, enabling them to bear a greater variation of circumstances
in regard to light. We find that particular species of plants and tree
ferns require at present different degrees of heat; and that some
species can thrive only in the immediate neighborhood of the equator,
others only a distance from it. In the same manner the _minimum of
light_, sufficient for the now existing species, cannot be taken as the
standard for all analogous tribes that may ever have flourished on the
globe.

But granting that the extreme northern point to which a flora like that
of the Carboniferous era could ever reach, may be somewhere between the
latitudes of 65° and 70°, we should still have to inquire whether the
vegetable remains might not have been drifted from thence, by rivers and
currents, to the parallel of Melville Island, or still farther. In the
northern hemisphere, at present, we see that the materials for future
beds of lignite and coal are becoming amassed in high latitudes, far
from the districts where the forests grew, and on shores where scarcely
a stunted shrub can now exist. The Mackenzie, and other rivers of North
America, carry pines with their roots attached for many hundred miles
towards the north, into the Arctic Sea, where they are imbedded in
deltas, and some of them drifted still farther by currents towards the
pole.

Before we can decide on this question of transportation, we must know
whether the fossil coal-plants occurring in high latitudes bear the
marks of friction and of having decayed previously to fossilization.
Many appearances in our English coal-fields certainly prove that the
plants were not floated from great distances; for the outline of the
stems of succulent species preserve their sharp angles, and others have
their surfaces marked with the most delicate lines and streaks. Long
leaves, also, are attached in many instances to the trunks or
branches;[162] and leaves, we know, in general, are soon destroyed when
steeped in water, although ferns will retain their forms after an
immersion of many months.[163] It seems fair to presume, that most of
the coal-plants grew upon the same land which supplied materials for the
sandstones and conglomerates of the strata in which they are imbedded.
The coarseness of the particles of many of these rocks attests that they
were not borne from very remote localities, and that there was land
therefore in the vicinity wasting away by the action of moving waters.
The progress also of modern discovery has led to the very general
admission of the doctrine that beds of coal have for the most part been
formed of the remains of trees and plants that grew on the spot where
the coal now exists; the land having been successively submerged, so
that a covering of mud and sand was deposited upon accumulations of
vegetable mater. That such has been the origin of some coal-seams is
proved by the upright position of fossil trees, both in Europe and
America, in which the roots terminate downwards in beds of coal.[164]

To return, therefore, from this digression,--the flora of the coal
appears to indicate a uniform and mild temperature in the air, while the
fossils of the contemporaneous mountain-limestone, comprising abundance
of lamelliferous corals, large chambered cephalopods, and crinoidea,
naturally lead us to infer a considerable warmth in the waters of the
northern sea of the Carboniferous period. So also in regard to strata
older than the coal, they contain in high northern latitudes mountain
masses of corals which must have lived and grown on the spot, and large
chambered univalves, such as Orthocerata and Nautilus, all seeming to
indicate, even in regions bordering on the arctic circle, the former
prevalence of a temperature more elevated than that now prevailing.

The warmth and humidity of the air, and the uniformity of climate, both
in the different seasons of the year, and in different latitudes,
appears to have been most remarkable when some of the oldest of the
fossiliferous strata were formed. The approximation to a climate similar
to that now enjoyed in these latitudes does not commence till the era of
the formations termed tertiary; and while the different tertiary rocks
were deposited in succession, from the eocene to the pliocene, the
temperature seems to have been lowered, and to have continued to
diminish even after the appearance upon the earth of a considerable
number of the existing species, the cold reaching its maximum of
intensity in European latitudes during the glacial epoch, or the epoch
immediately antecedent to that in which all the species now contemporary
with man were in being.





CHAPTER VII.

FARTHER EXAMINATION OF THE QUESTION AS TO THE ASSUMED DISCORDANCE OF THE
ANCIENT AND MODERN CAUSES OF CHANGE.


  On the causes of vicissitudes in climate--Remarks on the present
    diffusion of heat over the globe--On the dependence of the mean
    temperature on the relative position of land and sea--Isothermal
    Lines--Currents from equatorial regions--Drifting of
    icebergs--Different temperature of Northern and Southern
    hemispheres--Combination of causes which might produce the extreme
    cold of which the earth's surface is susceptible--Conditions
    necessary for the production of the extreme of heat, and its
    probable effects on organic life.


_Causes of Vicissitudes in Climate._[165]--As the proofs enumerated in
the last chapter indicate that the earth's surface has experienced great
changes of climate since the deposition of the older sedimentary strata,
we have next to inquire how such vicissitudes can be reconciled with the
existing order of nature. The cosmogonist has availed himself of this,
as of every obscure problem in geology, to confirm his views concerning
a period when the planet was in a nascent or half-formed state, or when
the laws of the animate and inanimate world differed essentially from
those now established; and he has in this, as in many other cases,
succeeded so far, as to divert attention from that class of facts which,
if fully understood, might probably lead to an explanation of the
phenomena. At first it was imagined that the earth's axis had been for
ages perpendicular to the plane of the ecliptic, so that there was a
perpetual equinox, and uniformity of seasons throughout the year;--that
the planet enjoyed this "paradisiacal" state until the era of the great
flood; but in that catastrophe, whether by the shock of a comet, or some
other convulsion, it lost its equal poise, and hence the obliquity of
its axis, and with that the varied seasons of the temperate zone, and
the long nights and days of the polar circles.

When the progress of astronomical science had exploded this theory, it
was assumed, that the earth at its creation was in a state of fluidity,
and red-hot, and that ever since that era, it had been cooling down,
contracting its dimensions, and acquiring a solid crust,--an hypothesis
hardly less arbitrary, yet more calculated for lasting popularity;
because, by referring the mind directly to the beginning of things, it
requires no support from observation, nor from any ulterior hypothesis.
But if, instead of forming vague conjectures as to what might have been
the state of the planet at the era of its creation, we fix our thoughts
on the connection at present existing between climate and the
distribution of land and sea; and then consider what influence former
fluctuations in the physical geography of the earth must have had on
superficial temperature, we may perhaps approximate to a true theory. If
doubts and obscurities still remain, they should be ascribed to our
limited acquaintance with the laws of Nature, not to revolutions in her
economy;--they should stimulate us to farther research, not tempt us to
indulge our fancies respecting the imaginary changes of internal
temperature in an embryo world.

_Diffusion of Heat over the Globe._--In considering the laws which
regulate the diffusion of heat over the globe, we must be careful, as
Humboldt well remarks, not to regard the climate of Europe as a type of
the temperature which all countries placed under the same latitude
enjoy. The physical sciences, observes this philosopher, always bear the
impress of the places where they began to be cultivated; and as, in
geology, an attempt was at first made to refer all the volcanic
phenomena to those of the volcanoes in Italy, so in meteorology, a small
part of the old world, the centre of the primitive civilization of
Europe, was for a long time considered a type to which the climate of
all corresponding latitudes might be referred. But this region,
constituting only one-seventh of the whole globe, proved eventually to
be the exception to the general rule. For the same reason, we may warn
the geologist to be on his guard, and not hastily to assume that the
temperature of the earth in the present era is a type of that which most
usually obtains, since he contemplates far mightier alterations in the
position of land and sea, at different epochs, than those which now
cause the climate of Europe to differ from that of other countries in
the same parallels.

It is now well ascertained that zones of equal warmth, both in the
atmosphere and in the waters of the ocean, are neither parallel to the
equator nor to each other.[166] It is also known that the _mean_ annual
temperature may be the same in two places which enjoy very different
climates, for the seasons may be nearly uniform, or violently
contrasted, so that the lines of equal winter temperature do not
coincide with those of equal annual heat or isothermal lines. The
deviations of all these lines from the same parallel of latitude are
determined by a multitude of circumstances, among the principal of which
are the position, direction, and elevation of the continents and
islands, the position and depths of the sea, and the direction of
currents and of winds.

On comparing the two continents of Europe and America, it is found that
places in the same latitudes have sometimes a mean difference of
temperature amounting to 11°, or even in a few cases to 17° Fahr.; and
some places on the two continents, which have the same mean temperature,
differ from 7° to 17° in latitude. Thus, Cumberland House, in North
America, having the same latitude (54° N.) as the city of York in
England, stands on the isothermal line of 32°, which in Europe rises to
the North Cape, in lat. 71°, but its summer heat exceeds that of
Brussels or Paris.[167] The principal cause of greater intensity of cold
in corresponding latitudes of North America, as contrasted with Europe,
is the connection of America with the polar circle, by a large tract of
land, some of which is from three to five thousand feet in height; and,
on the other hand, the separation of Europe from the arctic circle by an
ocean. The ocean has a tendency to preserve everywhere a mean
temperature, which it communicates to the contiguous land, so that it
tempers the climate, moderating alike an excess of heat or cold. The
elevated land, on the other hand, rising to the colder regions of the
atmosphere, becomes a great reservoir of ice and snow, arrests,
condenses, and congeals vapor, and communicates its cold to the
adjoining country. For this reason, Greenland, forming part of a
continent which stretches northward to the 82d degree of latitude,
experiences under the 60th parallel a more rigorous climate than Lapland
under the 72d parallel.

But if land be situated between the 40th parallel and the equator, it
produces, unless it be of extreme height, exactly the opposite effect;
for it then warms the tracts of land or sea that intervene between it
and the polar circle. For the surface being in this case exposed to the
vertical, or nearly vertical rays of the sun, absorbs a large quantity
of heat, which it diffuses by radiation into the atmosphere. For this
reason, the western parts of the old continent derive warmth from
Africa, "which, like an immense furnace, distributes its heat to Arabia,
to Turkey in Asia, and to Europe."[168] On the contrary, the
northeastern extremity of Asia experiences in the same latitude extreme
cold; for it has land on the north between the 60th and 70th parallel,
while to the south it is separated from the equator by the Pacific
Ocean.

In consequence of the more equal temperature of the waters of the ocean,
the climate of islands and of coasts differs essentially from that of
the interior of continents, the more maritime climate being
characterized by mild winters, and more temperate summers; for the
sea-breezes moderate the cold of winter, as well as the heat of summer.
When, therefore, we trace round the globe those belts in which the mean
annual temperature is the same, we often find great differences in
climate; for there are _insular_ climates in which the seasons are
nearly equalized, and _excessive_ climates, as they have been termed,
where the temperature of winter and summer is strongly contrasted. The
whole of Europe, compared with the eastern parts of America and Asia,
has an insular climate. The northern part of China, and the Atlantic
region of the United States, exhibit "excessive climates." We find at
New York, says Humboldt, the summer of Rome and the winter of
Copenhagen; at Quebec, the summer of Paris and the winter of Petersburg.
At Pekin, in China, where the mean temperature of the year is that of
the coasts of Brittany, the scorching heats of summer are greater than
at Cairo, and the winters as rigorous as at Upsala.[169]

If lines be drawn round the globe through all those places which have
the same winter temperature, they are found to deviate from the
terrestrial parallels much farther than the lines of equal mean annual
heat. The lines of equal winter in Europe, for example, are often curved
so as to reach parallels of latitude 9° or 10° distant from each other,
whereas the isothermal lines, or those passing through places having the
same mean annual temperature, differ only from 4° to 5° in Europe.

_Influence of currents and drift ice on temperature._--Among other
influential causes, both of remarkable diversity in the mean annual
heat, and of unequal division of heat in the different seasons, are the
direction of currents and the accumulation and drifting of ice in high
latitudes. The temperature of the Lagullas current is 10° or 12° Fahr.
above that of the sea at the Cape of Good Hope; for it derives the
greater part of its waters from the Mozambique channel, and southeast
coast of Africa, and from regions in the Indian Ocean much nearer the
line, and much hotter than the Cape.[170] An opposite effect is produced
by the "equatorial" current, which crosses the Atlantic from Africa to
Brazil, having a breadth varying from 160 to 450 nautical miles. Its
waters are cooler by 3° or 4° Fahr. than those of the ocean under the
line, so that it moderates the heat of the tropics.[171]

But the effects of the Gulf stream on the climate of the North Atlantic
Ocean are far more remarkable. This most powerful of known currents has
its source in the Gulf or Sea of Mexico, which, like the Mediterranean
and other close seas in temperate or low latitudes, is warmer than the
open ocean in the same parallels. The temperature of the Mexican sea in
summer is, according to Rennell, 86° Fahr., or at least 7° above that of
the Atlantic in the same latitude.[172] From this great reservoir or
caldron of warm water, a constant current pours forth through the
straits of Bahama at the rate of 3 or 4 miles an hour; it crosses the
ocean in a northeasterly direction, skirting the great bank of
Newfoundland, where it still retains a temperature of 8° above that of
the surrounding sea. It reaches the Azores in about 78 days, after
flowing nearly 3000 geographical miles, and from thence it sometimes
extends its course a thousand miles farther, so as to reach the Bay of
Biscay, still retaining an excess of 5° above the mean temperature of
that sea. As it has been known to arrive there in the months of November
and January, it may tend greatly to moderate the cold of winter in
countries on the west of Europe. . There is a large tract in the centre
of the North Atlantic, between the parallels of 33° and 45° N. lat.,
which Rennell calls the "recipient of the gulf water." A great part of
it is covered by the weed called sargasso (_Sargassum bacciferum_),
which the current floats in abundance from the Gulf of Mexico. This mass
of water is nearly stagnant, is warmer by 7° or 10° than the waters of
the Atlantic, and may be compared to the fresh water of a river
overflowing the heavier salt water of the sea. Rennell estimates the
area of the "recipient," together with that covered by the main current,
as being 2000 miles in length from E. to W., and 350 in breadth from N.
to S., which, he remarks, is a larger area than that of the
Mediterranean. The heat of this great body of water is kept up by the
incessant and quick arrivals of fresh supplies of warm water from the
south; and there can be no doubt that the general climate of parts of
Europe and America is materially affected by this cause.

It is considered probable by Scoresby that the influence of the Gulf
stream extends even to the sea near Spitzbergen, where its waters may
pass under those of melted ice; for it has been found that in the
neighborhood of Spitzbergen, the water is warmer by 6° or 7° at the
depth of one hundred and two hundred fathoms than at the surface. This
might arise from the known law that fresh water passes the point of
greatest density when cooled down below 40°, and between that and the
freezing point expands again. The water of melted ice might be lighter,
both as being fresh (having lost its salt in the decomposing process of
freezing), and because its temperature is nearer the freezing point than
the inferior water of the Gulf stream.

The great glaciers generated in the valleys of Spitzbergen, in the 79°
of north latitude, are almost all cut off at the beach, being melted by
the feeble remnant of heat still retained by the Gulf stream. In
Baffin's Bay, on the contrary, on the west coast of Old Greenland, where
the temperature of the sea is not mitigated by the same cause, and where
there is no warmer under-current, the glaciers stretch out from the
shore, and furnish repeated crops of mountainous masses of ice which
float off into the ocean.[173] The number and dimensions of these bergs
is prodigious. Captain Sir John Ross saw several of them together in
Baffin's Bay aground in water fifteen hundred feet deep! Many of them
are driven down into Hudson's Bay, and accumulating there, diffuse
excessive cold over the neighboring continent; so that Captain Franklin
reports, that at the mouth of Hayes' River, which lies in the same
latitude as the north of Prussia or the south of Scotland, ice is found
everywhere in digging wells, in summer, at the depth of four feet! Other
bergs have been occasionally met with, at midsummer, in a state of
rapid thaw, as far south as lat. 40° and longitude about 60° west, where
they cool the water sensibly to the distance of forty or fifty miles
around, the thermometer sinking sometimes 17°, or even 18°, Fahrenheit,
in their neighborhood.[174] It is a well-known fact that every four or
five years a large number of icebergs, floating from Greenland, double
Cape Langaness, and are stranded on the west coast of Iceland. The
inhabitants are then aware that their crops of hay will fail, in
consequence of fogs which are generated almost incessantly; and the
dearth of food is not confined to the land, for the temperature of the
water is so changed that the fish entirely desert the coast.

_Difference of climate of the Northern and Southern hemispheres._--When
we compare the climate of the northern and southern hemispheres, we
obtain still more instruction in regard to the influence of the
distribution of land and sea on climate. The dry land in the southern
hemisphere is to that of the northern in the ratio only of one to three,
excluding from our consideration that part which lies between the pole
and the 78° of south latitude, which has hitherto proved inaccessible.
And whereas in the northern hemisphere, between the pole and the
thirtieth parallel of north latitude, the land and sea occupy nearly
equal areas, the ocean in the southern hemisphere covers no less than
fifteen parts in sixteen of the entire space included between the
antarctic circle and the thirtieth parallel of south latitude.

This great extent of sea gives a particular character to climates south
of the equator, the winters being mild and the summers cool. Thus, in
Van Dieman's Land, corresponding nearly in latitude to Rome, the winters
are more mild than at Naples, and the summers not warmer than those at
Paris, which is 7° farther from the equator.[175] The effects on animal
and vegetable life are remarkable. Capt. King observed large shrubs of
Fuchsia and Veronica, which in England are treated as tender plants,
thriving and in full flower in Tierra del Fuego with the temperature at
36°. He states also that humming birds were seen sipping the sweets of
the flowers "after two or three days of constant rain, snow, and sleet,
during which time the thermometer had been at the freezing point." Mr.
Darwin also saw parrots feeding on the seeds of a tree called the
winter's bark, south of lat. 55°, near Cape Horn.[176]

So the orchideous plants which are parasitical on trees, and are
generally characteristic of the tropics, advance to the 38th and 42d
degree of S. lat., and even beyond the 45th degree in New Zealand, where
they were found by Forster. In South America also arborescent grasses
abound in the dense forests of Chiloe, in lat. 42° S., where "they
entwine the trees into one entangled mass to the height of thirty or
forty feet above the ground. Palm-trees in the same quarter of the
globe grow in lat. 37°, an arborescent grass very like a bamboo in 40°,
and another closely allied kind, of great length, but not erect, even as
far south as 45°."[177]

It has long been supposed that the general temperature of the southern
hemisphere was considerably lower than that of the northern, and that
the difference amounted to at least 10° Fahrenheit. Baron Humboldt,
after collecting and comparing a great number of observations, came to
the conclusion that even a much larger difference existed, but that none
was to be observed within the tropics, and only a small difference as
far as the thirty-fifth and fortieth parallel. Captain Cook was of
opinion that the ice of the antarctic predominated greatly over that of
the arctic region, that encircling the southern pole coming nearer to
the equator by 10° than the ice around the north pole. All the recent
voyages of discovery have tended to confirm this opinion, although Capt.
Weddel penetrated, in 1823, three degrees farther south than Capt. Cook,
reaching lat. 74° 15' South, long. 34° 17' West, and Sir James Ross, in
1842, arrived at lat. 78° 10' S., as high a latitude, within three
degrees, as the farthest point attained by Captain Parry in the arctic
circle, or lat. 81° 12' North.

The description given by ancient as well as modern navigators of the sea
and land in high southern latitudes, clearly attests the greater
severity of the climate as compared to arctic regions. In Sandwich Land,
in lat. 59° S., or in nearly the same parallel as the north of Scotland,
Capt. Cook found the whole country, from the summits of the mountains
down to the very brink of the sea-cliffs, "covered many fathoms thick
with everlasting snow," and this on the 1st of February, the hottest
time of the year; and what is still more astonishing, in the island of
S. Georgia, which is in the 54° south latitude, or the same parallel as
Yorkshire, the line of perpetual snow descends to the level of the
ocean.[178] When we consider this fact, and then recollect that the
highest mountains in Scotland, which ascend to an elevation of nearly
5000 feet, and are four degrees farther to the north, do not attain the
limit of perpetual snow on our side of the equator, we learn that
latitude is one only of many powerful causes, which determine the
climate of particular regions of the globe. Capt. Sir James Ross, in his
exploring expedition in 1841-3, found that the temperature south of the
60th degree of latitude seldom rose above 32° Fahr. During the two
summer months of the year 1841 (January and February) the range of the
thermometer was between 11° and 32° Fahr.; and scarcely once rose above
the freezing point. The permanence of snow in the southern hemisphere,
is in this instance partly due to the floating ice, which chills the
atmosphere and condenses the vapor, so that in summer the sun cannot
pierce through the foggy air. But besides the abundance of ice which
covers the sea to the south of Georgia and Sandwich Land, we may also,
as Humboldt suggests, ascribe the cold of those countries in part to the
absence of land between them and the tropics.

If Africa and New Holland extended farther to the south, a diminution of
ice would take place in consequence of the radiation of heat from these
continents during summer, which would warm the contiguous sea and rarefy
the air. The heated aerial currents would then ascend and flow more
rapidly towards the south pole, and moderate the winter. In confirmation
of these views, it is stated that the ice, which extends as far as the
68° and 71° of south latitude, advances more towards the equator
whenever it meets an open sea; that is, where the extremities of the
present continents are not opposite to it; and this circumstance seems
explicable only on the principle above alluded to, of the radiation of
heat from the lands so situated.

The cold of the antarctic regions was conjectured by Cook to be due to
the existence of a large tract of land between the seventieth degree of
south latitude and the pole. The justness of these and other
speculations of that great navigator have since been singularly
confirmed by the investigation made by Sir James Ross in 1841. He found
Victoria Land, extending from 71° to 79° S. latitude, skirted by a great
barrier of ice, the height of the land ranging from 4000 to 14,000 feet,
the whole entirely covered with snow, except a narrow ring of black
earth surrounding the huge crater of the active volcano of Mount Erebus,
rising 12,400 feet above the level of the sea. The position of a
mountainous territory of such altitude, so near the pole, and so obvious
a source of intense cold, fully explains why Graham's and Enderby's
Land, discovered by Captain Biscoe in 1831-2 (between lat. 64° and 68°
S.), presented a most wintry aspect, covered even in summer with ice and
snow, and nearly destitute of animal life. In corresponding latitudes of
the northern hemisphere we not only meet with herds of wild herbivorous
animals, but with land which man himself inhabits, and where he has even
built ports and inland villages.[179]

The distance to which icebergs float from the polar regions on the
opposite sides of the line is, as might have been anticipated, very
different. Their extreme limit in the northern hemisphere is lat. 40°,
as before mentioned, and they are occasionally seen in lat. 42° N., near
the termination of the great bank of Newfoundland, and at the Azores,
lat. 42° N., to which they are sometimes drifted from Baffin's Bay. But
in the other hemisphere they have been seen, within the last few years,
at different points off the Cape of Good Hope, between lat. 36° and
39°.[180] One of these (see fig. 2) was two miles in circumference, and
150 feet high, appearing like chalk when the sun was obscured, and
having the lustre of refined sugar when the sun was shining on it.
Others rose from 250 to 300 feet above the level of the sea, and were
therefore of great volume below; since it is ascertained by experiments
on the buoyancy of ice floating in sea-water, that for every cubic foot
seen above, there must at least be eight cubic feet below water.[181] If
ice islands from the north polar regions floated as far, they might
reach Cape St. Vincent, and there, being drawn by the current that
always sets in from the Atlantic through the Straits of Gibraltar, be
drifted into the Mediterranean, so that the serene sky of that
delightful region might soon be deformed by clouds and mists.

[Illustration: Fig. 2.

Iceberg seen off the Cape of Good Hope, April, 1829. Lat. 89° 18' S.
Long. 48° 46' E.]

Before the amount of difference between the temperature of the two
hemispheres was ascertained, it was referred by many astronomers to the
precession of the equinoxes, or the acceleration of the earth's motion
in its perihelium; in consequence of which the spring and summer of the
southern hemisphere are now shorter, by nearly eight days, than those
seasons north of the equator. But Sir J. Herschel reminds us that the
excess of eight days in the duration of the sun's presence in the
northern hemisphere is not productive of an excess of annual light and
heat; since, according to the laws of elliptic motion, it is
demonstrable that whatever be the ellipticity of the earth's orbit, the
two hemispheres must receive _equal absolute quantities_ of light and
heat per annum, the proximity of the sun in perigee exactly compensating
the effect of its swifter motion.[182] Humboldt, however, observes, that
there must be a greater loss of heat by radiation in the southern
hemisphere during a winter longer by eight days than that on the other
side of the equator.[183]

Perhaps no very sensible effect may be produced by this source of
disturbance; yet the geologist should bear in mind that to a certain
extent it operates alternately on each of the two hemispheres for a
period of upwards of 10,000 years, dividing unequally the times during
which the annual supply of solar light and heat is received. This cause
may sometimes tend to counterbalance inequalities of temperature
resulting from other far more influential circumstances; but, on the
other hand, it must sometimes tend to increase the extreme of deviation
arising from particular combinations of causes.

But whatever may be at present the inferiority of heat in the temperate
and frigid zones south of the line, it is quite evident that the cold
would be far more intense if there happened, instead of open sea, to be
tracts of elevated land between the 55th and 70th parallel; and, on the
other hand, the cold would be moderated if there were more land between
the line and the forty-fifth degree of south latitude.

_Changes in the position of land and sea may give rise to vicissitudes
in climate._--Having offered these brief remarks on the diffusion of
heat over the globe in the present state of the surface, I shall now
proceed to speculate on the vicissitudes of climate, which must attend
those endless variations in the geographical features of our planet
which are contemplated in geology. That our speculations may be confined
within the strict limits of analogy, I shall assume, 1st, That the
proportion of dry land to sea continues always the same. 2dly, That the
volume of the land rising above the level of the sea is a constant
quantity; and not only that its mean, but that its extreme height, is
liable only to trifling variations. 3dly, That both the mean and extreme
depth of the sea are invariable; and 4thly, It may be consistent with
due caution to assume that the grouping together of the land in
continents is a necessary part of the economy of nature; for it is
possible that the laws which govern the subterranean forces, and which
act simultaneously along certain lines, cannot but produce, at every
epoch, continuous mountain-chains; so that the subdivision of the whole
land into innumerable islands may be precluded.

If it be objected, that the maximum of elevation of land and depth of
sea are probably not constant, nor the gathering together of all the
land in certain parts, nor even perhaps the relative extent of land and
water, I reply, that the arguments about to be adduced will be
strengthened if, in these peculiarities of the surface, there be
considerable deviations from the present type. If, for example, all
other circumstances being the same, the land is at one time more divided
into islands than at another, a greater uniformity of climate might be
produced, the mean temperature remaining unaltered; or if, at another
era, there were mountains higher than the Himalaya, these, when placed
in high latitudes, would cause a greater excess of cold. Or, if we
suppose that at certain periods no chain of hills in the world rose
beyond the height of 10,000 feet, a greater heat might then have
prevailed than is compatible with the existence of mountains thrice that
elevation.

However constant may be the relative proportion of sea and land, we know
that there is annually some small variation in their respective
geographical positions, and that in every century the land is in some
parts raised, and in others depressed in level, and so likewise is the
bed of the sea. By these and other ceaseless changes, the configuration
of the earth's surface has been remodelled again and again, since it was
the habitation of organic beings, and the bed of the ocean has been
lifted up to the height of some of the loftiest mountains. The
imagination is apt to take alarm when called upon to admit the formation
of such irregularities in the crust of the earth, after it had once
become the habitation of living creatures; but, if time be allowed, the
operation need not subvert the ordinary repose of nature; and the result
is in a general view insignificant, if we consider how slightly the
highest mountain-chains cause our globe to differ from a perfect sphere.
Chimborazo, though it rises to more than 21,000 feet above the sea,
would be represented, on a globe of about six feet in diameter, by a
grain of sand less than one-twentieth of an inch in thickness.

The superficial inequalities of the earth, then, may be deemed minute in
quantity, and their distribution at any particular epoch must be
regarded in geology as temporary peculiarities, like the height and
outline of the cone of Vesuvius in the interval between two eruptions.
But although, in reference to the magnitude of the globe, the unevenness
of the surface is so unimportant, it is on the position and direction of
these small inequalities that the state of the atmosphere, and both the
local and general climate, are mainly dependent.

Before considering the effect which a material change in the
distribution of land and sea must occasion, it may be well to remark,
how greatly organic life may be affected by those minor variations,
which need not in the least degree alter the general temperature. Thus,
for example, if we suppose, by a series of convulsions, a certain part
of Greenland to become sea, and, in compensation, a tract of land to
rise and connect Spitzbergen with Lapland,--an accession not greater in
amount than one which the geologist can prove to have occurred in
certain districts bordering the Mediterranean, within a comparatively
modern period,--this altered form of the land might cause an interchange
between the climate of certain parts of North America and of Europe,
which lie in corresponding latitudes. Many European species of plants
and animals would probably perish in consequence, because the mean
temperature would be greatly lowered; and others would fail in America,
because it would there be raised. On the other hand, in places where the
mean annual heat remained unaltered, some species which flourish in
Europe, where the seasons are more uniform, would be unable to resist
the greater heat of the North American summer, or the intenser cold of
the winter; while others, now fitted by their habits for the great
contrast of the American seasons, would not be fitted for the _insular_
climate of Europe. The vine, for example, according to Humboldt, can be
cultivated with advantage 10° farther north in Europe than in North
America. Many plants endure severe frost, but cannot ripen their seeds
without a certain intensity of summer heat and a certain quantity of
light; others cannot endure a similar intensity either of heat or cold.

It is now established that many of the existing species of animals have
survived great changes in the physical geography of the globe. If such
species be termed modern, in comparison to races which preceded them,
their remains, nevertheless, enter into submarine deposits many hundred
miles in length, and which have since been raised from the deep to no
inconsiderable altitude. When, therefore, it is shown that changes in
the temperature of the atmosphere may be the consequence of such
physical revolutions of the surface, we ought no longer to wonder that
we find the distribution of existing species to be _local_, in regard to
_longitude_ as well as latitude. If all species were now, by an exertion
of creative power, to be diffused uniformly throughout those zones where
there is an equal degree of heat, and in all respects a similarity of
climate, they would begin from this moment to depart more and more from
their original distribution. Aquatic and terrestrial species would be
displaced, as Hooke long ago observed, so often as land and water
exchanged places; and there would also, by the formation of new
mountains and other changes, be transpositions of climate, contributing,
in the manner before alluded to, to the local extermination of
species.[184]

If we now proceed to consider the circumstances required for a _general_
change of temperature, it will appear, from the facts and principles
already laid down, that whenever a greater extent of high land is
collected in the polar regions, the cold will augment; and the same
result will be produced when there is more sea between or near the
tropics; while, on the contrary, so often as the above conditions are
reversed, the heat will be greater. (See figs. 5 and 6, p. 111.) If this
be admitted, it will follow, that unless the superficial inequalities of
the earth be fixed and permanent, there must be never-ending
fluctuations in the mean temperature of every zone; and that the climate
of one era can no more be a type of every other; than is one of our four
seasons of all the rest.

It has been well said, that the earth is covered by an ocean, in the
midst of which are two great islands, and many smaller ones; for the
whole of the continents and islands occupy an area scarcely exceeding
one-fourth of the whole superficies of the spheroid. Now, according to
this analogy, we may fairly speculate on the probability that there
would not be usually, at any given epoch of the past, more than about
one-fourth dry land in a particular region; as, for example, near the
poles, or between them and the 75th parallels of N. and S. latitude.
If, therefore, at present there should happen to be, in both these
quarters of the globe, much _more_ than this average proportion of land,
some of it in the arctic region, being above, five thousand feet in
height, and if in antarctic latitudes a mountainous country has been
found varying from 4000 to 14,000 feet in height, this alone affords
ground for concluding that, in the present state of things, the mean
heat of the climate is below that which the earth's surface, in its more
ordinary state, would enjoy. This presumption is heightened when we
reflect on the results of the recent soundings made by Sir James Ross,
in the Southern Ocean, and continued for four successive years, ending
1844, which seem to prove that the mean depth of the Atlantic and
Pacific is as great as Laplace and other eminent astronomers had
imagined;[185] for then we might look not only for more than two-thirds
sea in the frigid zones, but for water of great depth, which could not
readily be reduced to the freezing point. The same opinion is confirmed,
when we compare the quantity of land lying between the poles and the
30th parallels of north and south latitude, with the quantity placed
between those parallels and the equator; for, it is clear, that we have
at present not only more than the usual degree of cold in the polar
regions, but also less than the average quantity of heat within the
tropics.

_Position of land and sea which might produce the extreme of cold of
which the earth's surface is susceptible._--To simplify our view of the
various changes in climate, which different combinations of geographical
circumstances may produce, we shall first consider the conditions
necessary for bringing about the extreme of cold, or what would have
been termed in the language of the old writers the winter of the "great
year," or geological cycle, and afterwards, the conditions requisite to
produce the maximum of heat, or the summer of the same year.

To begin with the northern hemisphere. Let us suppose those hills of the
Italian peninsula and of Sicily, which are of comparatively modern
origin, and contain many fossil shells identical with living species, to
subside again into the sea, from which they have been raised, and that
an extent of land of equal area and height (varying from one to three
thousand feet) should rise up in the Arctic Ocean between Siberia and
the north pole. In speaking of such changes, I shall not allude to the
manner in which I conceive it possible that they may be brought about,
nor of the time required for their accomplishment--reserving for a
future occasion, not only the proofs that revolutions of equal magnitude
have taken place, but that analogous operations are still in gradual
progress. The alteration now supposed in the physical geography of the
northern regions, would cause additional snow and ice to accumulate
where now there is usually an open sea; and the temperature of the
greater part of Europe would be somewhat lowered, so as to resemble more
nearly that of corresponding latitudes of North America: or, in other
words, it might be necessary to travel about 10° farther south in order
to meet with the same climate which we now enjoy. No compensation would
be derived from the disappearance of land in the Mediterranean
countries; but the contrary, since the mean heat of the soil in those
latitudes probably exceeds that which would belong to the sea, by which
we imagine it to be replaced.

But let the configuration of the surface be still farther varied, and
let some large district within or near the tropics, such as Brazil, with
its plains and hills of moderate height, be converted into sea, while
lands of equal elevation and extent rise up in the arctic circle. From
this change there would, in the first place, result a sensible
diminution of temperature near the tropic, for the Brazilian soil would
no longer be heated by the sun; so that the atmosphere would be less
warm, as also the neighboring Atlantic. On the other hand, the whole of
Europe, Northern Asia, and North America, would be chilled by the
enormous quantity of ice and snow, thus generated on the new arctic
continent. If, as we have already seen, there are now some points in the
southern hemisphere where snow is perpetual down to the level of the
sea, in latitudes as low as central England, such might assuredly be the
case throughout a great part of Europe, under the change of
circumstances above supposed: and if at present the extreme range of
drifted icebergs is the Azores, they might easily reach the equator
after the assumed alteration. But to pursue the subject still farther,
let the Himalaya mountains, with the whole of Hindostan, sink down, and
their place be occupied by the Indian Ocean, while an equal extent of
territory and mountains, of the same vast height, rise up between North
Greenland and the Orkney Islands. It seems difficult to exaggerate the
amount to which the climate of the northern hemisphere would then be
cooled.[186]

But the refrigeration brought about at the same time in the southern
hemisphere, would be nearly equal, and the difference of temperature
between the arctic and equatorial latitudes would not be much greater
than at present; for no important disturbance can occur in the climate
of a particular region without its immediately affecting all other
latitudes, however remote. The heat and cold which surround the globe
are in a state of constant and universal flux and reflux. The heated and
rarefied air is always rising and flowing from the equator towards the
poles in the higher regions of the atmosphere; while in the lower, the
colder air is flowing back to restore the equilibrium. That this
circulation is constantly going on in the aerial currents is not
disputed; it is often proved by the opposite course of the clouds at
different heights, and the fact has been farther illustrated in a
striking manner by two recent events. The trade wind continually blows
with great force from the island of Barbadoes to that of St. Vincent;
notwithstanding which, during the eruption of the volcano in the island
of St. Vincent, in 1812, ashes fell in profusion from a great height in
the atmosphere upon Barbadoes.[187] In like manner, during the great
eruption of Sumbawa, in 1815, ashes were carried to the islands of
Amboyna and Banda, which last is about 800 miles east from the site of
the volcano. Yet the southeast monsoon was then at its height.[188] This
apparent transposition of matter against the wind, confirmed the opinion
of the existence of a counter-current in the higher regions, which had
previously rested on theoretical conclusions only.

That a corresponding interchange takes place in the seas, is
demonstrated, according to Humboldt, by the cold which is found to exist
at great depths within the tropics; and, among other proofs, may be
mentioned the mass of warmer water which the Gulf stream is constantly
bearing northwards, while a cooler current flows _from_ the north along
the coast of Greenland and Labrador, and helps to restore the
equilibrium.[189]

Currents of colder and therefore specifically heavier water pass from
the poles towards the equator, which cool the inferior parts of the
ocean; so that the heat of the torrid zone and the cold of the polar
circle balance each other. The refrigeration, therefore, of the polar
regions, resulting from the supposed alteration in the distribution of
land and sea, would be immediately communicated to the tropics, and from
them its influence would extend to the antarctic circle, where the
atmosphere and the ocean would be cooled, so that ice and snow would
augment. Although the mean temperature of higher latitudes in the
southern hemisphere is, as before stated, for the most part, lower than
that of the same parallels in the northern, yet, for a considerable
space on each side of the line, the mean annual heat of the waters is
found to be the same in corresponding parallels. If, therefore, by the
new position of the land, the formation of icebergs had become of common
occurrence in the northern temperate zone, and if these were frequently
drifted as far as the equator, the same degree of cold which they
generated would immediately be communicated as far as the tropic of
Capricorn, and from thence to the lands or ocean to the south.

The freedom, then, of the circulation of heat and cold from pole to pole
being duly considered, it will be evident that the mean temperature
which may prevail at the same point at two distinct periods, may differ
far more widely than that of any two points in the same parallels of
latitude, at one and the same period. For the range of temperature, or
in other words, the curvature of the isothermal lines in a given zone,
and at a given period, must always be circumscribed within narrow
limits, the climate of each place in that zone being controlled by the
combined influence of the geographical peculiarities of all other parts
of the earth. Whereas, if we compare the state of things at two distinct
and somewhat distant epochs, a particular zone may at one time be under
the influence of one class of disturbing causes, and at another time may
be affected by an opposite combination. The lands, for example, to the
north of Greenland cause the present climate of North America to be
colder than that of Europe in the same latitudes; but the excess of cold
is not so great as it would have been if the western hemisphere had been
entirely isolated, or separated from the eastern like a distinct planet.
For not only does the refrigeration produced by Greenland chill to a
certain extent the atmosphere of northern and western Europe, but the
mild climate of Europe reacts also upon North America, and moderates the
chilling influence of the adjoining polar lands.

To return to the state of the earth after the changes above supposed, we
must not omit to dwell on the important effects to which a wide expanse
of perpetual snow would give rise. It is probable that nearly the whole
sea, from the poles to the parallels of 45°, would be frozen over; for
it is well known that the immediate proximity of land is not essential
to the formation and increase of field ice, provided there be in some
part of the same zone a sufficient quantity of glaciers generated on or
near the land, to cool down the sea. Captain Scoresby, in his account of
the arctic regions, observes, that when the sun's rays "fall upon the
snow-clad surface of the ice or land, they are in a great measure
reflected, without producing any material elevation of temperature; but
when they impinge on the black exterior of a ship, the pitch on one side
occasionally becomes fluid while ice is rapidly generated at the
other."[190]

Now field ice is almost always covered with snow;[191] and thus not only
land as extensive as our existing continents, but immense tracts of sea
in the frigid and temperate zones, might present a solid surface covered
with snow, and reflecting the sun's rays for the greater part of the
year. Within the tropics, moreover, where the ocean now predominates,
the sky would no longer be serene and clear, as in the present era; but
masses of floating ice would cause quick condensations of vapor, so that
fogs and clouds would deprive the vertical rays of the sun of half their
power. The whole planet, therefore, would receive annually a smaller
portion of the solar influence, and the external crust would part, by
radiation, with some of the heat which had been accumulated in it,
during a different state of the surface. This heat would be dissipated
in the spaces surrounding our atmosphere, which, according to the
calculations of M. Fourier, have a temperature much inferior to that of
freezing water.

After the geographical revolution above assumed, the climate of
equinoctial lands might be brought at last to resemble that of the
present temperate zone, or perhaps be far more wintry. They who should
then inhabit such small isles and coral reefs as are now seen in the
Indian Ocean and South Pacific, would wonder that zoophytes of large
dimensions had once been so prolific in their seas; or if, perchance,
they found the wood and fruit of the cocoa-nut tree or the palm
silicified by the waters of some ancient mineral spring, or incrusted
with calcareous matter, they would muse on the revolutions which had
annihilated such genera, and replaced them by the oak, the chestnut, and
the pine. With equal admiration would they compare the skeletons of
their small lizards with the bones of fossil alligators and crocodiles
more than twenty feet in length, which, at a former epoch, had
multiplied between the tropics: and when they saw a pine included in an
iceberg, drifted from latitudes which we now call temperate, they would
be astonished at the proof thus afforded, that forests had once grown
where nothing could be seen in their own times but a wilderness of snow.

If the reader hesitate to suppose so extensive an alteration of
temperature as the probable consequence of geographical changes,
confined to one hemisphere, he should remember how great are the local
anomalies in climate now resulting from the peculiar distribution of
land and sea in certain regions. Thus, in the island of South Georgia,
before mentioned (p. 98), Captain Cook found the everlasting snows
descending to the level of the sea, between lat. 54° and 55° S.; no
trees or shrubs were to be seen, and in summer a few rocks only, after a
partial melting of the ice and snow, were scantily covered with moss and
tufts of grass. If such a climate can now exist at the level of the sea
in a latitude corresponding to that of Yorkshire in spite of all those
equalizing causes before enumerated, by which the mixture of the
temperatures of distant regions is facilitated throughout the globe,
what rigors might we not anticipate in a winter generated by the
transfer of the mountains of India to our arctic circle!

But we have still to contemplate the additional refrigeration which
might be effected by changes in the relative position of land and sea in
the southern hemisphere. If the remaining continents were transferred
from the equatorial and contiguous latitudes to the south polar regions,
the intensity of cold produced might, perhaps, render the globe
uninhabitable. We are too ignorant of the laws governing the direction
of subterranean forces, to determine whether such a crisis be within the
limits of possibility. At the same time, it may be observed, that no
distribution of land can well be imagined more irregular, or, as it
were, capricious, than that which now prevails; for at present, the
globe may be divided into two equal parts, in such a manner, that one
hemisphere shall be almost entirely covered with water, while the other
shall contain less water than land (see figs. 3 and 4);[192] and, what
is still more extraordinary, on comparing the extratropical lands in the
northern and southern hemispheres, the lands in the northern are found
to be to those in the southern in the proportion of thirteen to
one![193] To imagine all the lands, therefore, in high, and all the sea
in low latitudes, as delineated in fig. 6, p. 111, would scarcely be a
more anomalous state of the surface.

[Illustration: Map showing the present unequal Distribution of LAND and
WATER on the Surface of the GLOBE.

Fig. 3. Here London is taken as a centre, and we behold the greatest
quantity of land existing in one hemisphere.

Fig. 4. Here the centre is the antipodal point to London, and we see the
greatest quantity of water existing in one hemisphere.

The black shading expresses land having land opposite or antipodal to
it.]

[Illustration: Maps showing the position of LAND and SEA which might
produce the Extremes of HEAT and COLD in the Climates of the GLOBE.

Fig. 5.

Extreme of Heat.

Fig. 6.

Extreme of Cold.

OBSERVATIONS.--These maps are intended to show that continents and
islands having the same shape and relative dimensions as those now
existing, might be placed so as to occupy either the equatorial or polar
regions.

In fig. 5, scarcely any of the land extends from the equator towards the
poles beyond the 30th parallel of latitude; and fig. 6, a very small
proportion of it extends from the poles towards the Equator beyond the
40th parallel of latitude.

_Position of land and sea which might give rise to the extreme of
heat._--Let us now turn from the contemplation of the winter of the
"great year," and consider the opposite train of circumstances which
would bring on the spring and summer. To imagine all the lands to be
collected together in equatorial latitudes, and a few promontories only
to project beyond the thirtieth parallel, as represented in the annexed
maps (figs. 5 and 6), would be undoubtedly to suppose an extreme result
of geological change. But if we consider a mere approximation to such a
state of things, it would be sufficient to cause a general elevation of
temperature. Nor can it be regarded as a visionary idea, that amidst the
revolutions of the earth's surface, the quantity of land should, at
certain periods, have been simultaneously lessened in the vicinity of
both the poles, and increased within the tropics. We must recollect that
even now it is necessary to ascend to the height of fifteen thousand
feet in the Andes under the line, and in the Himalaya mountains, which
are without the tropic, to seventeen thousand feet, before we reach the
limit of perpetual snow. On the northern slope, indeed, of the Himalaya
range, where the heat radiated from a great continent moderates the
cold, there are meadows and cultivated land at an elevation equal to the
height of Mont Blanc.[194] If then there were no arctic lands to chill
the atmosphere, and freeze the sea, and if the loftiest chains were near
the line, it seems reasonable to imagine that the highest mountains
might be clothed with a rich vegetation to their summits, and that
nearly all signs of frost would disappear from the earth.

When the absorption of the solar rays was in no region impeded, even in
winter, by a coat of snow, the mean heat of the earth's crust would
augment to considerable depths, and springs, which we know to be in
general an index of the mean temperature of the climate, would be warmer
in all latitudes. The waters of lakes, therefore, and rivers, would be
much hotter in winter, and would be never chilled in summer by melted
snow and ice. A remarkable uniformity of climate would prevail amid the
archipelagoes of the temperate and polar oceans, where the tepid waters
of equatorial currents would freely circulate. The general humidity of
the atmosphere would far exceed that of the present period, for
increased heat would promote evaporation in all parts of the globe. The
winds would be first heated in their passage over the tropical plains,
and would then gather moisture from the surface of the deep, till,
charged with vapor, they arrived at extreme northern and southern
regions, and there encountering a cooler atmosphere, discharged their
burden in warm rain. If, during the long night of a polar winter, the
snows should whiten the summits of some arctic islands, they would be
dissolved as rapidly by the returning sun, as are the snows of Etna by
the blasts of the sirocco.

We learn from those who have studied the geographical distribution of
plants, that in very low latitudes, at present, the vegetation of small
islands remote from continents has a peculiar character; the ferns and
allied families, in particular, bearing a great proportion to the total
number of other plants. Other circumstances being the same, the more
remote the isles are from the continents, the greater does this
proportion become. Thus, in the continent of India, and the tropical
parts of New Holland, the proportion of ferns to the phænogamous plants
is only as one to twenty-six; whereas, in the South-Sea Islands, it is
as one to four, or even as one to three.[195]

We might expect, therefore, in the summer of the "great year," or cycle
of climate, that there would be a predominance of tree ferns and plants
allied to genera now called tropical, in the islands of the wide ocean,
while many forms now confined to arctic and temperate regions, or only
found near the equator on the summit of the loftiest mountains, would
almost disappear from the earth. Then might those genera of animals
return, of which the memorials are preserved in the ancient rocks of our
continents. The pterodactyle might flit again through the air, the huge
iguanodon reappear in the woods, and the ichthyosaurs swarm once more in
the sea. Coral reefs might be prolonged again beyond the arctic circle,
where the whale and the narwal now abound; and droves of turtles might
begin again to wander through regions now tenanted by the walrus and the
seal.

But not to indulge too far in these speculations, I may observe, in
conclusion, that however great, during the lapse of ages, may be the
vicissitudes of temperature in every zone, it accords with this theory
that the general climate should not experience any sensible change in
the course of a few thousand years; because that period is insufficient
to affect the leading features of the physical geography of the globe.

Notwithstanding the apparent uncertainty of the seasons, it is found
that the mean temperature of particular localities is very constant,
when observations made for a sufficient series of years are compared.

Yet there must be exceptions to this rule; and even the labors of man
have, by the drainage of lakes and marshes, and the felling of extensive
forests, caused such changes in the atmosphere as greatly to raise our
conception of the more important influence of those forces to which, in
certain latitudes, even the existence of land or water, hill or valley,
lake or sea, must be ascribed. If we possessed accurate information of
the amount of _local_ fluctuation in climate in the course of twenty
centuries, it would often, undoubtedly, be considerable. Certain tracts,
for example, on the coast of Holland and of England consisted of
cultivated land in the time of the Romans, which the sea, by gradual
encroachments, has at length occupied. Here, at least, a slight
alteration has been effected; for neither the distribution of heat in
the different seasons, nor the mean annual temperature of the atmosphere
investing the sea, is precisely the same as that which rests upon the
land.

In those countries, also, where earthquakes and volcanoes are in full
activity, a much shorter period may produce a sensible variation. The
climate of the great table-land of Malpais in Mexico, must differ
materially from that which prevailed before the middle of the last
century; for, since that time, six mountains, the highest of them rising
sixteen hundred feet above the plateau, have been thrown up by volcanic
eruptions. It is by the repetition of an indefinite number of such local
revolutions, and by slow movements extending simultaneously over wider
areas, as will be afterwards shown, that a general change of climate may
finally be brought about.




CHAPTER VIII.

ON FORMER CHANGES IN PHYSICAL GEOGRAPHY AND CLIMATE.


  Geographical features of the northern hemisphere, at the period of
    the oldest fossiliferous strata--State of the surface when the
    mountain limestone and coal were deposited--Changes in physical
    geography, between the carboniferous period and the chalk--Abrupt
    transition from the secondary to the tertiary fossils--Accession of
    land, and elevation of mountain chains, after the consolidation of
    the secondary rocks--Explanation of Map, showing the area covered by
    sea, since the commencement of the tertiary period--Astronomical
    theories of the causes of variations in climate--Theory of the
    diminution of the supposed primitive heat of the globe.


In the sixth chapter, I stated the arguments derived from organic
remains for concluding that in the period when the carboniferous strata
were deposited, the temperature of the ocean and the air was more
uniform in the different seasons of the year, and in different
latitudes, than at present, and that there was a remarkable absence of
cold as well as great moisture in the atmosphere. It was also shown that
the climate had been modified more than once since that epoch, and that
it had been reduced, by successive changes, more and more nearly to that
now prevailing in the same latitudes. Farther, I endeavored, in the last
chapter, to prove that vicissitudes in climate of no less importance may
be expected to recur in future, if it be admitted that causes now active
in nature have power, in the lapse of ages, to produce considerable
variations in the relative position of land and sea. It remains to
inquire whether the alterations, which the geologist can prove to have
_actually taken place_ at former periods, in the geographical features
of the northern hemisphere, coincide in their nature, and in the time of
their occurrence, with such revolutions in climate as might naturally
have resulted, according to the meteorological principles already
explained.

_Period of the primary fossiliferous rocks._--The oldest system of
strata which afford by their organic remains any evidence as to climate,
or the former position of land and sea, are those formerly known as the
_transition rocks_, or what have since been termed Lower Silurian or
"primary fossiliferous" formations. These have been found in England,
France, Germany, Sweden, Russia, and other parts of central and northern
Europe, as also in the great Lake district of Canada and the United
States. The multilocular or chambered univalves, including the Nautilus,
and the corals, obtained from the limestones of these ancient groups,
have been compared to forms now most largely developed in tropical seas.
The corals, however, have been shown by M. Milne Edwards to differ
generally from all living zoophytes; so that conclusions as to a warmer
climate drawn from such remote analogies must be received with caution.
Hitherto, few, if any, contemporaneous vegetable remains have been
noticed; but such as are mentioned agree more nearly with the plants of
the carboniferous era than any other, and would therefore imply a warm
and humid atmosphere entirely free from intense cold throughout the
year.

This absence or great scarcity of plants as well as of freshwater shells
and other indications of neighboring land, coupled with the wide extent
of marine strata of this age in Europe and North America, are facts
which imply such a state of physical geography (so far at least as
regards the northern hemisphere) as would, according to the principles
before explained, give rise to such a moist and equable climate. (See p.
109, and fig. 5, p. 111.)

_Carboniferous group._--This group comes next in the order of
succession; and one of its principal members, the mountain limestone,
was evidently a marine formation, as is shown by the shells and corals
which it contains. That the ocean of that period was of considerable
extent in our latitudes, we may infer from the continuity of these
calcareous strata over large areas in Europe, Canada, and the United
States. The same group has also been traced in North America, towards
the borders of the arctic sea.[196]

There are also several regions in Scotland, and in the central and
northern parts of England, as well as in the United States, where marine
carboniferous limestones alternate with strata containing coal, in such
a manner as to imply the drifting down of plants by rivers into the sea,
and the alternate occupation of the same space by fresh and salt water.

Since the time of the earlier writers, no strata have been more
extensively investigated, both in Europe and North America, than those
of the ancient carboniferous group, and the progress of science has led
to a general belief that a large portion of the purest coal has been
formed, not, as was once imagined, by vegetable matter floated from a
distance, but by plants which grew on the spot, and somewhat in the
manner of peat on the spaces now covered by the beds of coal. The former
existence of land in some of these spaces has been proved, as already
stated, by the occurrence of numerous upright fossil trees, with their
roots terminating downwards in seams of coal; and still more generally
by the roots of trees (stigmariæ) remaining in their natural position in
the clays which underlie almost every layer of coal.

As some nearly continuous beds of such coal have of late years been
traced in North America, over areas 100 or 200 miles and upwards in
diameter, it may be asked whether the large tracts of ancient land
implied by this fact are not inconsistent with the hypothesis of the
general prevalence of islands at the period under consideration? In
reply, I may observe that the coal-fields must originally have been low
alluvial grounds, resembling in situation the cypress-swamps of the
Mississippi, or the sunderbunds of the Ganges, being liable like them to
be inundated at certain periods by a river or by the sea, if the land
should be depressed a few feet. All the phenomena, organic and
inorganic, imply conditions nowhere to be met with except in the deltas
of large rivers. We have to account for an abundant supply of fluviatile
sediment, carried for ages towards one and the same region, and capable
of forming strata of mud and sand thousands of feet, or even fathoms, in
thickness, many of them consisting of laminated shale, inclosing the
leaves of ferns and other terrestrial plants. We have also to explain
the frequent intercalations of root-beds, and the interposition here and
there of brackish and marine deposits, demonstrating the occasional
presence of the neighboring sea. But these forest-covered deltas could
only have been formed at the termination of large hydrographical basins,
each drained by a great river and its tributaries; and the accumulation
of sediment bears testimony to contemporaneous denudation on a large
scale, and, therefore, to a wide area of land, probably containing
within it one or more mountain chains.

In the case of the great Ohio or Appalachian coal-field, the largest in
the world, it seems clear that the uplands drained by one or more great
rivers were chiefly to the eastward, or they occupied a space now filled
by part of the Atlantic Ocean, for the mechanical deposits of mud and
sand increase greatly in thickness and coarseness of material as we
approach the eastern borders of the coal-field, or the southeast flanks
of the Alleghany mountains, near Philadelphia. In that region numerous
beds of pebbles, often of the size of a hen's egg, are seen to alternate
with beds of pure coal.

But the American coal-fields are all comprised within the 30th and 50th
degrees of north latitude; and there is no reason to presume that the
lands at the borders of which they originated ever penetrated so far or
in such masses into the colder and arctic regions, so as to generate a
cold climate. In the southern hemisphere, where the predominance of sea
over land is now the distinguishing geographical feature, we
nevertheless find a large part of the continent of Australia, as well as
New Zealand, placed between the 30th and 50th degrees of S. latitude.
The two islands of New Zealand taken together, are between 800 and 900
miles in length, with a breadth in some parts of ninety miles, and they
stretch as far south as the 46th degree of latitude. They afford,
therefore, a wide area for the growth of a terrestrial vegetation, and
the botany of this region is characterized by abundance of ferns, one
hundred and forty species of which are already known, some of them
attaining the size of trees. In this respect the southern shores of New
Zealand in the 46th degree of latitude almost vie with tropical islands.
Another point of resemblance between the Flora of New Zealand and that
of the ancient carboniferous period is the prevalence of the fir tribe
or of coniferous wood.

An argument of some weight in corroboration of the theory above
explained respecting the geographical condition of the temperate and
arctic latitudes of the northern hemisphere in the carboniferous period
may also be derived from ah examination of those groups of strata which
immediately preceded the coal. The fossils of the Devonian and Silurian
strata in Europe and North America have led to the conclusion, that they
were formed for the most part in deep seas, far from land. In those
older strata land plants are almost as rare as they are abundant or
universal in the coal measures. Those ancient deposits, therefore, may
be supposed to have belonged to an epoch when dry land had only just
begun to be upraised from the deep; a theory which would imply the
existence during the carboniferous epoch of islands, instead of an
extensive continent, in the area where the coal was formed.

Such a state of things prevailing in the north, from the pole to the
30th parallel of latitude, if not neutralized by circumstances of a
contrary tendency in corresponding regions south of the line, would give
rise to a general warmth and uniformity of climate throughout the globe.

_Changes in physical geography between the formation of the
carboniferous strata and the chalk._--We have evidence in England that
the strata of the ancient carboniferous group, already adverted to,
were, in many instances, fractured and contorted, and often thrown into
a vertical position, before the deposition of some even of the oldest
known secondary rocks, such as the new red sandstone.

Fragments of the older formations are sometimes included in the
conglomerates of the more modern; and some of these fragments still
retain their fossil shells and corals, so as to enable us to determine
the parent rocks from whence they were derived. There are other proofs
of the disturbance at successive epochs of different secondary rocks
before the deposition of others; and satisfactory evidence that, during
these reiterated convulsions, the geographical features of the northern
hemisphere were frequently modified, and that from time to time new
lands emerged from the deep. The vegetation, during some parts of the
period in question (from the lias to the chalk inclusive), when genera
allied to Cycas and Zamia were abundant, appears to have approached to
that of the larger islands of the equatorial zone; such, for example, as
we now find in the West Indian archipelago.[197] These islands appear to
have been drained by rivers of considerable size, which were inhabited
by crocodiles and gigantic oviparous reptiles, both herbivorous and
carnivorous, belonging for the most part to extinct genera. Of the
contemporary inhabitants of the land we have as yet acquired but scanty
information, but we know that there were flying reptiles, insects, and
small mammifers, allied to the marsupial tribes.

A freshwater deposit, called the Wealden, occurs in the upper part of
the secondary series of the south of England, which, by its extent and
fossils, attests the existence in that region of a large river draining
a continent or island of considerable dimensions. We know that this land
was clothed with wood, and inhabited by huge terrestrial reptiles and
birds. Its position so far to the north as the counties of Surrey and
Sussex, at a time when the mean temperature of the climate is supposed
to have been much hotter than at present, may at first sight appear
inconsistent with the theory before explained, that the heat was caused
by the gathering together of all the great masses of land in low
latitudes, while the northern regions were almost entirely sea. But it
must not be taken for granted that the geographical conditions already
described (p. 109, and fig. 5, p. 111) as capable of producing the
extreme of heat were ever combined at any geological period of which we
have yet obtained information. It is more probable, from what has been
stated in the preceding chapters, that a slight approximation to such an
extreme state of things would be sufficient; in other words, if most of
the dry land were tropical, and scarcely any of it arctic or antarctic,
a prodigious elevation of temperature must ensue, even though a part of
some continents should penetrate far into the temperate zones.

_Changes during the tertiary periods._--The secondary and tertiary
formations of Europe, when considered separately, may be contrasted as
having very different characters; the secondary appearing to have been
deposited in open seas, the tertiary in regions where dry land, lakes,
bays, and perhaps inland seas, abounded. The secondary series is almost
exclusively marine; the tertiary, even the oldest part, contains
lacustrine strata, and not unfrequently freshwater and marine beds
alternating. In fact there is evidence of important geographical changes
having occurred between the deposition of the cretaceous system, or
uppermost of the secondary series, and that of the oldest tertiary
group, and still more between the era of the latter and that of the
newer tertiary formations. This change in the physical geography of
Europe and North America was accompanied by an alteration no less
remarkable in organic life, scarcely any _species_ being common both to
the secondary and tertiary rocks, and the fossils of the latter
affording evidence of a different climate.

On the other hand, when we compare the tertiary formations of successive
ages, we trace a gradual approximation in the imbedded fossils, from an
assemblage in which extinct species predominate, to one where the
species agree for the most part with those now existing. In other words,
we find a gradual increase of animals and plants fitted for our present
climates, in proportion as the strata which we examine are more modern.
Now, during all these successive tertiary periods, there are signs of a
great increase of land in European and North American latitudes. By
reference to the map (Pl. 1), and its description, p. 121, the reader
will see that about two-thirds of the present European lands have
emerged since the earliest tertiary group originated. Nor is this the
only revolution which the same region has undergone within the period
alluded to, some tracts which were previously land having gained in
altitude, others, on the contrary, having sunk below their former level.

That the existing lands were not all upheaved at once into their present
position is proved by the most striking evidence. Several Italian
geologists, even before the time of Brocchi, had justly inferred that
the Apennines were elevated several thousand feet above the level of the
Mediterranean before the deposition of the modern Subapennine beds which
flank them on either side. What now constitutes the central calcareous
chain of the Apennines must for a long time have been a narrow ridgy
peninsula, branching off, at its northern extremity, from the Alps near
Savona. This peninsula has since been raised from one to two thousand
feet, by which movement the ancient shores, and, for a certain extent,
the bed of the contiguous sea, have been laid dry, both on the side of
the Mediterranean and the Adriatic.

[Illustration: Fig. 7.]

The nature of these vicissitudes will be explained by the accompanying
diagram, which represents a transverse section across the Italian
peninsula. The inclined strata A are the disturbed formations of the
Apennines, into which the ancient igneous rocks a are supposed to have
intruded themselves. At a lower level on each flank of the chain are the
more recent shelly beds _b b_, which often contain rounded pebbles
derived from the waste of contiguous parts of the older Apennine
limestone. These, it will be seen, are horizontal, and lie in what is
termed "unconformable stratification" on the more ancient series. They
now constitute a line of hills of moderate elevation between the sea and
the Apennines, but never penetrate to the higher and more ancient
valleys of that chain.

The same phenomena are exhibited in the Alps on a much grander scale;
those mountains being composed in some even of their higher regions of
the newer secondary and oldest tertiary formations, while they are
encircled by a great zone of more modern tertiary rocks both on their
southern flank towards the plains of the Po, and on the side of
Switzerland and Austria, and at their eastern termination towards Styria
and Hungary.[198] This newer tertiary zone marks the position of former
seas or gulfs, like the Adriatic, wherein masses of strata accumulated,
some single groups of which are not inferior in thickness to the most
voluminous of our secondary formations in England. Some even of these
newer groups have been raised to the height of three or four thousand
feet, and in proportion to their antiquity, they generally rise to
greater heights, the older of them forming interior zones nearest to the
central ridges of the Alps. We have already ascertained that the Alps
gained accessions to their height and width at several successive
periods, and that the last series of improvements occurred when the
seas were inhabited by many existing species of animals.

We may imagine some future series of convulsions once more to heave up
this stupendous chain, together with the adjoining bed of the sea, so
that the mountains of Europe may rival the Andes in elevation; in which
case the deltas of the Po, Adige, and Brenta, now encroaching upon the
Adriatic, might be uplifted so as to form another exterior belt of
considerable height around the southeastern flank of the Alps.

The Pyrenees, also, have acquired their present altitude, which in Mont
Perdu exceeds eleven thousand feet, since the deposition of the
nummulitic or Eocene division of the tertiary series. Some of the
tertiary strata at the base of the chain are raised to the height of
only a few hundred feet above the sea, and retain a horizontal position,
without partaking in general in the disturbance to which the older
series has been subjected; so that the great barrier between France and
Spain was almost entirely upheaved in the interval between the
deposition of certain groups of tertiary strata.

The remarkable break between the most modern of the known secondary
rocks and the oldest tertiary, may be apparent only, and ascribable to
the present deficiency of our information. Already the marles and green
sand of Heers near Tongres, in Belgium, observed by M. Dumont, and the
"pisolitic limestone" of the neighborhood of Paris, both intermediate in
age between the Maestricht chalk and the lower Eocene strata, begin to
afford us signs of a passage from one state of things to another.
Nevertheless, it is far from impossible that the interval between the
chalk and tertiary formations constituted an era in the earth's history,
when the transition from one class of organic beings to another was,
comparatively speaking, rapid. For if the doctrines above explained in
regard to vicissitudes of temperature are sound, it will follow that
changes of equal magnitude in the geographical features of the globe may
at different periods produce very unequal effects on climate; and, so
far as the existence of certain animals and plants depends on climate,
the duration of species would be shortened or protracted, according to
the rate at which the change of temperature proceeded.

For even if we assume that the intensity of the subterranean disturbing
forces is uniform and capable of producing nearly equal amounts of
alteration on the surface of the planet, during equal periods of time,
still the rate of alteration in climate would be by no means uniform.
Let us imagine the quantity of land between the equator and the tropic
in one hemisphere to be to that in the other as thirteen to one, which,
as before stated, represents the unequal proportion of the
extra-tropical lands in the two hemispheres at present. (See figs. 3 and
4, p. 110.) Then let the first geographical change consist in the
shifting of this preponderance of land from one side of the line to the
other; from the southern hemisphere, for example, to the northern. Now
this need not affect the general temperature of the earth. But if, at
another epoch, we suppose a continuance of the same agency to transfer
an equal volume of land from the torrid zone to the temperate and arctic
regions of the northern and southern hemispheres, or into one of them,
there might be so great a refrigeration of the mean temperature _in all
latitudes_, that scarcely any of the pre-existing races of animals would
survive; and, unless it pleased the Author of Nature that the planet
should be uninhabited, new species, and probably of widely different
forms, would then be substituted in the room of the extinct. We ought
not, therefore, to infer that equal periods of time are always attended
by an equal amount of change in organic life, since a great fluctuation
in the mean temperature of the earth, the most influential cause which
can be conceived in exterminating whole races of animals and plants,
must, in different epochs, require unequal portions of time for its
completion.

[PLATE I. _Map showing the extent of surface in Europe which has at one
period or another been covered by the sea since the commencement of the
deposition of the older or Eocene Tertiary strata._]

This map will enable the reader to perceive at a glance the great extent
of change in the physical geography of Europe, which can be proved to
have taken place since some of the older tertiary strata began to be
deposited. The proofs of submergence, during some part or other of this
period, in all the districts distinguished by ruled lines, are of a most
unequivocal character; for the area thus described is now covered by
deposits containing the fossil remains of animals which could only have
lived in salt water. The most ancient part of the period referred to
cannot be deemed very remote, considered geologically; because the
deposits of the Paris and London basins, and many other districts
belonging to the older tertiary epoch, are newer than the greater part
of the sedimentary rocks (those commonly called secondary and primary
fossiliferous or paleozoic) of which the crust of the globe is composed.
The species, moreover, of marine testacea, of which the remains are
found in these older tertiary formations, are not entirely distinct from
such as now live. Yet, notwithstanding the comparatively recent epoch to
which this retrospect is carried, the variations in the distribution of
land and sea depicted on the map form only a part of those which must
have taken place during the period under consideration. Some
approximation has merely been made to an estimate of the amount of _sea
converted into land_ in parts of Europe best known to geologists; but we
cannot determine how much land has become sea during the same period;
and there may have been repeated interchanges of land and water in the
same places, changes of which no account is taken in the map, and
respecting the amount of which little accurate information can ever be
obtained.

I have extended the sea in some instances beyond the limits of the land
now covered by tertiary formations, and marine drift, because other
geological data have been obtained for inferring the submergence of
these tracts after the deposition of the Eocene strata had begun. Thus,
for example, there are good reasons for concluding that part of the
chalk of England (the North and South Downs, for example, together with
the intervening secondary tracts) continued beneath the sea until the
oldest tertiary beds had begun to accumulate.

A strait of the sea separating England and Wales has also been
introduced, on the evidence afforded by shells of existing species found
in a deposit of gravel, sand, loam, and clay, called the northern drift,
by Sir R. Murchison.[199] And Mr. Trimmer has discovered similar recent
marine shells on the northern coast of North Wales, and on Moel Tryfane,
near the Menai Straits, at the height of 1392 feet above the level of
the sea!

Some raised sea-beaches, and drift containing marine shells, which I
examined in 1843, between Limerick and Dublin, and which have been
traced over other parts of Ireland by different geologists, have
required an extension of the dark lines so as to divide that island into
several. In improving this part of my map I have been especially
indebted to the assistance of Mr. Oldham, who in 1843 announced to the
British Association at Cork the fact that at the period when the drift
or glacial beds were deposited, Ireland must have formed an archipelago
such as is here depicted. A considerable part of Scotland might also
have been represented in a similar manner as under water when the drift
originated.

A portion of Brittany is divided into islands, because it is known to be
covered with patches of marine tertiary strata chiefly miocene. When I
examined these in 1830 and 1843, I convinced myself that the sea must
have covered much larger areas than are now occupied by these small and
detached deposits. The former connection of the White Sea and the Gulf
of Finland is proved by the fact that a multitude of huge erratic blocks
extend over the intervening space, and a large portion of Norway,
Sweden, and Denmark, as well as Germany and Russia, are represented as
sea, on the same evidence, strengthened by the actual occurrence of
fossil sea-shells, of recent species, in the drift of various portions
of those countries. The submergence of considerable areas under large
bodies of fresh water, during the tertiary period, of which there are
many striking geological proofs in Auvergne, and elsewhere, has not been
expressed by ruled lines. They bear testimony to the former existence of
neighboring lands, and a certain elevation of the areas where they occur
above the level of the ocean; they are therefore left blank, together
with all the space that cannot be demonstrated to have been part of the
sea at some time or other, since the commencement of the Eocene epoch.

In compiling this map, which has been entirely recast since the first
edition, I have availed myself of the latest geological maps of the
British isles, and north of Europe; also of those published by the
government surveyors of France, MM. de Beaumont and Dufresnoy; the map
of Germany and part of Europe, by Von Dechen, and that of Italy by M.
Tchihatchoff (Berlin, 1842). Lastly, Sir R. Murchison's important map of
Russia, and the adjoining countries, has enabled me to mark out not only
a considerable area, previously little known, in which tertiary
formations occur; but also a still wider expanse, over which the
northern drift, and erratic blocks with occasional marine shells, are
traceable. The southern limits of these glacial deposits in Russia and
Germany indicate the boundary, so far as we can now determine it, of the
northern ocean, at a period immediately antecedent to that of the human
race.

I was anxious, even in the title of this map, to guard the reader
against the supposition that it was intended to represent the state of
the physical geography of part of Europe at any _one point of time_. The
difficulty, or rather the impossibility, of restoring the geography of
the globe as it may have existed at any former period, especially a
remote one, consists in this, that we can only point out where part of
the sea has been turned into land, and are almost always unable to
determine what land may have become sea. All maps, therefore, pretending
to represent the geography of remote geological epochs must be ideal.
The map under consideration is not a restoration of a former state of
things, at any particular moment of time, but a synoptical view of a
certain amount of one kind of change (the conversion of sea into land)
known to have been brought about within a given period.

It may be proper to remark that the vertical movements to which the land
is subject in certain regions, occasion alternately the subsidence and
the uprising of the surface; and that, by such oscillations at
successive periods, a great area may have been entirely covered with
marine deposits, although the whole may never have been beneath the
waters at one time; nay, even though the relative proportion of land and
sea may have continued unaltered throughout the whole period. I believe,
however, that since the commencement of the tertiary period, the dry
land in the northern hemisphere has been continually on the increase,
both because it is now greatly in excess beyond the average proportion
which land generally bears to water on the globe, and because a
comparison of the secondary and tertiary strata affords indications, as
I have already shown, of a passage from the condition of an ocean
interspersed with islands to that of a large continent.

But supposing it were possible to represent all the vicissitudes in the
distribution of land and sea that have occurred during the tertiary
period, and to exhibit not only the actual existence of land where there
was once sea, but also the extent of surface now submerged which may
once have been land, the map would still fail to express all the
important revolutions in physical geography which have taken place
within the epoch under consideration. For the oscillations of level, as
was before stated, have not merely been such as to lift up the land from
below the water, but in some cases to occasion a rise of many thousand
feet above the sea. Thus the Alps have acquired an additional altitude
of 4000, and even in some places 10,000 feet; and the Apennines owe a
considerable part of their present height to subterranean convulsions
which have happened within the tertiary epoch.

On the other hand, some mountain chains may have been lowered during the
same series of ages, in an equal degree, and shoals may have been
converted into deep abysses.[200] Since this map was recast in 1847,
geologists have very generally come to the conclusion that the
nummulitic limestone, together with the overlying fucoidal grit and
shale, called "Flysch," in the Alps, belongs to the older tertiary or
Eocene group. As these nummulitic rocks enter into the structure of some
of the most lofty and disturbed parts of the Alps, Apennines,
Carpathians, Pyrenees, and other mountain chains, and form many of the
elevated lands of Africa and Asia, their position almost implies the
ubiquity of the post-Eocene ocean, not, indeed, by the simultaneous, but
by the successive, occupancy of the whole ground by its waters.[201]

_Concluding remarks on changes in physical geography._--The foregoing
observations, it may be said, are confined chiefly to Europe, and
therefore merely establish the increase of dry land in a space which
constitutes but a small portion of the northern hemisphere; but it was
stated in the preceding chapter, that the great Lowland of Siberia,
lying chiefly between the latitudes 55° and 75° N. (an area nearly equal
to all Europe), is covered for the most part by marine strata, which,
from the account given by Pallas, and more recently by Sir R. Murchison,
belongs to a period when all or nearly all the shells were of a species
still living in the north. The emergence, therefore, of this area from
the deep is, comparatively speaking, a very modern event, and must, as
before remarked, have caused a great increase of cold throughout the
globe.

Upon a review, then, of all the facts above enumerated, respecting the
ancient geography of the globe as attested by geological monuments,
there appear good grounds for inferring that changes of climate
coincided with remarkable revolutions in the former position of sea and
land. A wide expanse of ocean, interspersed with islands, seems to have
pervaded the northern hemisphere at the periods when the Silurian and
carboniferous rocks were formed, and a warm and very uniform temperature
then prevailed. Subsequent modifications in climate accompanied the
deposition of the secondary formations, when repeated changes were
effected in the physical geography of our northern latitudes. Lastly,
the refrigeration became most decided, and the climate most nearly
assimilated to that now enjoyed, when the lands in Europe and northern
Asia had attained their full extension, and the mountain chains their
actual height.

Soon after the first publication of this theory of climate, an objection
was made by an anonymous German critic in 1833 that there are no
geological proofs of the prevalence at any former period of a
temperature _lower_ than that now enjoyed; whereas, if the causes above
assigned were the true ones, it might reasonably have been expected that
fossil remains would sometimes indicate colder as well as hotter
climates than those now established.[202] In answer to this objection, I
may suggest, that our present climates are probably far more distant
from the extreme of possible heat than from its opposite extreme of
cold. A glance at the map (fig. 6, p. 111) will show that all the
existing lands might be placed between the 30th parallels of latitude on
each side of the equator, and that even then they would by no means fill
that space. In no other position would they give rise to so high a
temperature. But the present geographical condition of the earth is so
far removed from such a state of things, that the land lying between the
poles and the parallels of 30, is in great excess; so much so that,
instead of being to the sea in the proportion of 1 to 3, which is as
near as possible the average general ratio throughout the globe, it is 9
to 23.[203] Hence it ought not to surprise us if, in our geological
retrospect, embracing perhaps a small part only of a complete cycle of
change in the terrestrial climates, we should happen to discover
everywhere the signs of a higher temperature. The strata hitherto
examined may have originated when the quantity of equatorial land was
always decreasing and the land in regions nearer the poles augmenting in
height and area, until at length it attained its present excess in high
latitudes. There is nothing improbable in supposing that the
geographical revolutions of which we have hitherto obtained proofs had
this general tendency; and in that case the refrigeration must have been
constant, although, for reasons before explained, the rate of cooling
may not have been uniform.

It may, however, be as well to recall the reader's attention to what was
before said of the indication brought to light of late years, of a
considerable oscillation of temperature, in the period immediately
preceding the human era. We have seen that on examining some of the most
northern deposits, those commonly called the northern drift in Scotland,
Ireland, and Canada, in which nearly all, in some cases, perhaps all,
the fossil shells are of recent species, we discover the signs of a
climate colder than that now prevailing in corresponding latitudes on
both sides the Atlantic. It appears that an arctic fauna specifically
resembling that of the present seas, extended farther to the south than
now. This opinion is derived partly from the known habitations of the
corresponding living species, and partly from the abundance of certain
genera of shells and the absence of others.[204] The date of the
refrigeration thus inferred appears to coincide very nearly with the era
of the dispersion of erratic blocks over Europe and North America, a
phenomenon which will be ascribed in the sequel (ch. 16) to the cold
then prevailing in the northern hemisphere. The force, moreover, of the
German critic's objection has been since in a great measure destroyed,
by the larger and more profound knowledge acquired in the last few years
of the ancient carboniferous flora, which has led the ablest botanists
to adopt the opinion, that the climate of the coal period was remarkable
for its warmth, moisture, equability, and freedom from cold, rather than
the intensity of its _tropical heat_. We are therefore no longer
entitled to assume that there has been a constant and gradual decline in
the absolute amount of heat formerly contained in the atmosphere and
waters of the ocean, such as it was conjectured might have emanated from
the incandescent central nucleus of a new and nearly fluid planet,
before the interior had lost, by radiation into surrounding space, a
great part of its original high temperature.

_Astronomical causes of fluctuations in climate._--Sir John Herschel has
lately inquired, whether there are any astronomical causes which may
offer a possible explanation of the difference between the actual
climate of the earth's surface, and those which formerly appear to have
prevailed. He has entered upon this subject, he says, "impressed with
the magnificence of that view of geological revolutions, which regards
them rather as regular and necessary effects of great and general
causes, than as resulting from a series of convulsions and catastrophes,
regulated by no laws, and reducible to no fixed principles." Geometers,
he adds, have demonstrated the absolute invariability of the mean
distance of the earth from the sun; whence it would at first seem to
follow, that the mean annual supply of light and heat derived from that
luminary would be alike invariable: but a closer consideration of the
subject will show, that this would not be a legitimate conclusion; but
that on the contrary, the _mean_ amount of solar radiation is dependent
on the eccentricity of the earth's orbit, and therefore liable to
variation.[205]

Now the eccentricity of the orbit, he continues, is actually
diminishing, and has been so for ages beyond the records of history. In
consequence, the ellipse is in a state of approach to a circle, and the
annual average of solar heat radiated to the earth is actually on the
_decrease_. So far this is in accordance with geological evidence, which
indicates a general refrigeration of climate; but the question remains,
whether the amount of diminution which the eccentricity may have ever
undergone can be supposed sufficient to account for any sensible
refrigeration. The calculations necessary to determine this point,
though practicable, have never yet been made, and would be extremely
laborious; for they must embrace all the perturbations which the most
influential planets, Venus, Mars, Jupiter, and Saturn, would cause in
the earth's orbit, and in each other's movements round the sun.

The problem is also very complicated, inasmuch as it depends not merely
on the ellipticity of the earth's orbit, but on the assumed temperature
of the celestial spaces beyond the earth's atmosphere; a matter still
open to discussion, and on which M. Fourier and Sir J. Herschel have
arrived at very different opinions. But if, says Herschel, we suppose an
extreme case, as if the earth's orbit should ever become as eccentric as
that of the planet Juno or Pallas, a great change of climate might be
conceived to result, the winter and summer temperatures being sometimes
mitigated, and at others exaggerated, in the same latitudes.

It is much to be desired that the calculations alluded to were executed,
as even if they should demonstrate, as M. Arago thinks highly
probable,[206] that the mean amount of solar radiation can never be
materially affected by irregularities in the earth's motion, it would
still be satisfactory to ascertain the point. Such inquiries, however,
can never supersede the necessity of investigating the consequences of
the varying position of continents, shifted as we know them to have been
during successive epochs, from one part of the globe to the other.

Another astronomical hypothesis respecting the possible cause of secular
variations in climate, has been proposed by a distinguished
mathematician and philosopher, M. Poisson. He begins by assuming, 1st,
that the sun and our planetary system are not stationary, but carried
onward by a common movement through space; 2dly, that every point in
space receives heat as well as light from innumerable stars surrounding
it on all sides, so that if a right line of indefinite length be
produced in any direction from such a point, it must encounter a star
either visible or invisible to us. 3dly, He then goes on to assume, that
the different regions of space, which in the course of millions of years
are traversed by our system, must be of very unequal temperature,
inasmuch as some of them must receive a greater, others a less, quantity
of radiant heat from the great stellary inclosure. If the earth, he
continues, or any other large body, pass from a hotter to a colder
region, it would not readily lose in the second all the heat which it
has imbibed in the first region, but retain a temperature increasing
downwards from the surface, as in the actual condition of our
planet.[207]

Now the opinion originally suggested by Sir W. Herschel, that our sun
and its attendant planets were all moving onward through space, in the
direction of the constellation Hercules, is very generally thought by
eminent astronomers to be confirmed. But even if its reality be no
longer matter of doubt, conjectures as to its amount are still vague and
uncertain; and great, indeed, must be the extent of the movement before
this cause alone can work any material alteration in the terrestrial
climates. Mr. Hopkins, when treating of this theory, remarked, that so
far as we were acquainted with the position of the stars not very remote
from the sun, they seem to be so distant from each other, that there are
no points in space among them, where the intensity of radiating heat
would be comparable to that which the earth derives from the sun, except
at points very near to each star. Thus, in order that the earth should
derive a degree of heat from stellar radiation comparable to that now
derived from the sun, she must be in close proximity to some particular
star, leaving the aggregate effect of radiation from the other stars
nearly the same as at present. This approximation, however, to a single
star could not take place consistently with the preservation of the
motion of the earth about the sun, according to its present laws.

Suppose our sun should approach a star within the present distance of
Neptune. That planet could no longer remain a member of the solar
system, and the motions of the other planets would be disturbed in a
degree which no one has ever contemplated as probable since the
existence of the solar system. But such a star, supposing it to be no
larger than the sun, and to emit the same quantity of heat, would not
send to the earth much more than one-thousandth part of the heat which
she derives from the sun, and would therefore produce only a very small
change in terrestrial temperature.[208]

_Variable splendor of stars._--There is still another astronomical
suggestion respecting the possible causes of secular variations in the
terrestrial climates which deserves notice. It has long been known that
certain stars are liable to great and periodical fluctuations in
splendor, and Sir J. Herschel has lately ascertained (Jan. 1840), that a
large and brilliant star, called _alpha_ Orionis, sustained, in the
course of six weeks, a loss of nearly half its light. "This phenomenon,"
he remarks, "cannot fail to awaken attention, and revive those
speculations which were first put forth by my father Sir W. Herschel,
respecting the possibility of a change in the lustre of _our sun
itself_. If there really be a community of nature between the sun and
fixed stars, every proof that we obtain of the extensive prevalence of
such periodical changes in those remote bodies, adds to the probability
of finding something of the kind nearer home." Referring then to the
possible bearing of such facts on ancient revolutions, in terrestrial
climates, he says, that "it is a matter of observed fact, that many
stars _have_ undergone, in past ages, within the records of astronomical
history, very extensive changes in apparent lustre, without a change of
distance adequate to producing such an effect. If our sun were even
_intrinsically_ much brighter than at present, the mean temperature of
the surface of our globe would, of course, be proportionally greater. I
speak now not of periodical, but of secular changes. But the argument
is complicated with the consideration of the possibly imperfect
transparency of the celestial spaces, and with the cause of that
imperfect transparency, which may be due to material non-luminous
particles diffused irregularly in patches analogous to nebulæ, but of
greater extent--to _cosmical clouds_, in short--of whose existence we
have, I think, some indication in the singular and apparently capricious
phenomena of temporary stars, and perhaps in the recent extraordinary
sudden increase and hardly less sudden diminution of η _Argus_."[209]

More recently (1852) Schwabe has observed that the spots on the sun
alternately increase and decrease in the course of every ten years, and
Captain Sabine has pointed out that this variable obscuration coincides
in time both as to its maximum and minimum with changes in all those
terrestrial magnetic variations which are caused by the sun. Hence he
infers that the period of alteration in the spots is a _solar magnetic
period_. Assuming such to be the case, the variable light of some stars
may indicate a similar phenomenon, or they may be stellar magnetic
periods, differing only in the degree of obscuration and its duration.
And as hitherto we have perceived no fluctuation in the heat received by
the earth from the sun coincident with the _solar magnetic period_, so
the fluctuations in the brilliancy of the stars may not perhaps be
attended with any perceptible alteration in their power of radiating
heat. But before we can speculate with advantage in this new and
interesting field of inquiry, we require more facts and observations.

_Supposed gradual diminution of the earth's primitive heat._--The
gradual diminution of the supposed primitive heat of the globe has been
resorted to by many geologists as the principal cause of alterations of
climate. The matter of our planet is imagined, in accordance with the
conjectures of Leibnitz, to have been originally in an intensely heated
state, and to have been parting ever since with portions of its heat,
and at the same time contracting its dimensions. There are, undoubtedly,
good grounds for inferring from recent observation and experiment, that
the temperature of the earth increases as we descend from the surface to
that slight depth to which man can penetrate: but there are no positive
proofs of a secular decrease of internal heat accompanied by
contraction. On the contrary, La Place has shown, by reference to
astronomical observations made in the time of Hipparchus, that in the
last two thousand years at least there has been no sensible contraction
of the globe by cooling; for had this been the case, even to an
extremely small amount, the day would have been shortened, whereas its
length has certainly not diminished during that period by 1/300th of a
second.

Baron Fourier, after making a curious series of experiments on the
cooling of incandescent bodies, considers it to be proved
mathematically, that the actual distribution of heat in the earth's
envelope is precisely that which would have taken place if the globe
had been formed in a medium of a very high temperature, and had
afterwards been constantly cooled.[210] He contends, that although no
contraction can be demonstrated to have taken place within the
historical period (the operation being slow and the time of observation
limited), yet it is no less certain that heat is annually passing out by
radiation from the interior of the globe into the planetary spaces. He
even undertook to demonstrate that the quantity of heat thus transmitted
into space in the course of every century, through every square metre of
the earth's surface, would suffice to melt a column of ice having a
square metre for its base, and being three metres (or 9 feet 10 inches)
high.

It is at the same time denied, that there is any assignable mode in
which the heat thus lost by radiation can be again restored to the
earth, and consequently the interior of our planet must, from the moment
of its creation, have been subject to refrigeration, and is destined
together with the sun and stars forever to grow colder. But I shall
point out in the sequel (chapter 31) many objections to these views, and
to the theory of the intense heat of the earth's central nucleus, and
shall then inquire how far the observed augmentation of temperature, as
we descend below the surface, may be referable to other causes
unconnected with the supposed pristine fluidity of the entire globe.




CHAPTER IX.

THEORY OF THE PROGRESSIVE DEVELOPMENT OF ORGANIC LIFE AT SUCCESSIVE
GEOLOGICAL PERIODS.


  Theory of the progressive development of organic life--Evidence in
    its support inconclusive--Vertebrated animals, and plants of the
    most perfect organization, in strata of very high
    antiquity--Differences between the organic remains of successive
    formations--Comparative modern origin of the human race--The popular
    doctrine of successive development not established by the admission
    that man is of modern origin--Introduction of man, to what extent a
    change in the system.


_Progressive development of organic life._--In the preceding chapters I
have considered whether revolutions in the general climate of the globe
afford any just ground of opposition to the doctrine that the former
changes of the earth which are treated of in geology belong to one
uninterrupted series of physical events governed by ordinary causes.
Against this doctrine some popular arguments have been derived from the
great vicissitudes of the organic creation in times past; I shall
therefore proceed to the discussion of such objections, which have been
thus formally advanced by the late Sir Humphrey Davy. "It is
impossible," he affirms, "to defend the proposition, that the present
order of things is the ancient and constant order of nature, only
modified by existing laws: in those strata which are deepest, and which
must, consequently, be supposed to be the earliest deposited, forms even
of vegetable life are rare; shells and vegetable remains are found in
the next order; the bones of fishes and oviparous reptiles exist in the
following class; the remains of birds, with those of the same genera
mentioned before, in the next order; those of quadrupeds of extinct
species in a still more recent class; and it is only in the loose and
slightly consolidated strata of gravel and sand, and which are usually
called diluvian formations, that the remains of animals such as now
people the globe are found, with others belonging to extinct species.
But, in none of these formations, whether called secondary, tertiary, or
diluvial, have the remains of man, or any of his works, been discovered;
and whoever dwells upon this subject must be convinced, that the present
order of things, and the comparatively recent existence of man as the
master of the globe, is as certain as the destruction of a former and a
different order, and the extinction of a number of living forms which
have no types in being. In the oldest secondary strata there are no
remains of such animals as now belong to the surface; and in the rocks,
which may be regarded as more recently deposited, these remains occur
but rarely, and with abundance of extinct species;--there seems, as it
were, a gradual approach to the present system of things, and a
succession of destructions and creations preparatory to the existence of
man."[211]

In the above passages, the author deduces two important conclusions from
geological data: first, that in the successive groups of strata, from
the oldest to the most recent, there is a progressive development of
organic life, from the simplest to the most complicated
forms;--secondly, that man is of comparatively recent origin, and these
conclusions he regards as inconsistent with the doctrine, "that the
present order of things is the ancient and constant order of nature only
modified by existing laws."

With respect, then, to the first of these propositions, we may ask
whether the theory of the progressive development of animal and
vegetable life, and their successive advancement from a simple to a more
perfect state, has any secure foundation in fact? No geologists who are
in possession of all the data now established respecting fossil remains,
will for a moment contend for the doctrine in all its detail, as laid
down by the distinguished philosopher to whose opinions we have
referred: but naturalists, who are not unacquainted with recent
discoveries, continue to defend it in a modified form. They say that in
the first period of the world (by which they mean the earliest of which
we have yet brought to light any memorials), the vegetation was
characterized by a predominance of cryptogamic plants, while the animals
which coexisted were almost entirely confined to zoophytes, testacea,
and a few fish. Plants of a less simple structure, coniferæ and cycadeæ,
flourished largely in the next epoch, when oviparous reptiles began also
to abound. Lastly, the terrestrial flora became most diversified and
most perfect when the highest orders of animals, the mammalia and birds,
were called into existence.

Now in the first place, it may be observed, that many naturalists are
guilty of no small inconsistency in endeavoring to connect the phenomena
of the earliest vegetation with a nascent condition of organic life, and
at the same time to deduce from the numerical predominance of certain
forms, the greater heat or uniformity of the ancient climate. The
arguments in favor of the latter conclusion are without any force,
unless we can assume that the rules followed by the Author of Nature in
the creation and distribution of organic beings were the same formerly
as now; and that, as certain families of animals and plants are now most
abundant in, or exclusively confined to regions where there is a certain
temperature, a certain degree of humidity, a certain intensity of light,
and other conditions, so also analogous phenomena were exhibited at
every former era.

If this postulate be denied, and the prevalence of particular families
be declared to depend on a certain order of precedence in the
introduction of different classes into the earth, and if it be
maintained that the standard of organization was raised successively, we
must then ascribe the numerical preponderance, in the earlier ages, of
plants of simpler structure, _not to the heat_, or other climatal
conditions, but to those different laws which regulate organic life in
newly created worlds.

Before we can infer a warm and uniform temperature in high latitudes,
from the presence of 250 species of ferns, some of them arborescent,
accompanied by lycopadiacæ of large size, and araucariæ, we must be
permitted to assume, that at all times, past, present, and future, a
heated and moist atmosphere pervading the northern hemisphere has a
tendency to produce in the vegetation a predominance of analogous forms.

It should moreover be borne in mind, when we are considering the
question of development from a botanical point of view, that naturalists
are by no means agreed as to the existence of an ascending scale of
organization in the vegetable world corresponding to that which is very
generally recognized in animals. "From the sponge to man," in the
language of De Blainville, there may be a progressive chain of being,
although often broken and imperfect; but if we seek to classify plants
according to a linear arrangement, ascending gradually from the lichen
to the lily or the rose, we encounter incomparably greater difficulties.
Yet the doctrine of a more highly developed organization in the plants
created at successive periods presupposes the admission of such a
graduated scale.

We have as yet obtained but scanty information respecting the state of
the terrestrial flora at periods antecedent to the coal. In the
carboniferous epoch, about 500 species of fossil plants are enumerated
by Adolphe Brongniart, which we may safely regard as a mere fragment of
an ancient flora; since, in Europe alone, there are now no less than
11,000 living species. I have already hinted that the plants which
produced coal were not drifted from a distance, but that nearly all of
them grew on the spots where they became fossil. They appear to have
belonged, as before explained (p. 115), to a peculiar class of
_stations_,--to low level and swampy regions, in the deltas of large
rivers, slightly elevated above the level of the sea. From the study,
therefore, of such a vegetation, we can derive but little insight into
the nature of the contemporaneous upland flora, still less of the plants
of the mountainous or Alpine country; and if so, we are enabled to
account for the apparent monotony of the vegetation, although its
uniform character was doubtless in part owing to a greater uniformity of
climate then prevailing throughout the globe. Some of the commonest
trees of this period, such as the sigillariæ, which united the structure
of ferns and of cycadeæ, departed very widely from all known living
types. The coniferæ and ferns, on the contrary, were very closely allied
to living genera. It is remarkable that none of the exogens of Lindley
(dicotyledonous angiosperms of Brongniart), which comprise four-fifths
of the living flora of the globe, and include all the forest trees of
Europe except the fir-tribe, have yet been discovered in the coal
measures, and a very small number--fifteen species only--of
monocotyledons. If several of these last are true plants, an opinion to
which Messrs. Lindley, Unger, Corda, and other botanists of note
incline, the question whether any of the most highly organized plants
are to be met with in ancient strata is at once answered in the
affirmative. But the determination of these palms being doubtful, we
have as yet in the coal no positive proofs either of the existence of
the most perfect, or of the most simple forms of flowering or flowerless
vegetation. We have no fungi, lichens, hepatici or mosses: yet this
latter class may have been as fully represented then as now.

In the flora of the secondary eras, all botanists agree that palms
existed, although in Europe plants of the family of zamia and cycas
together with coniferæ predominated, and must have given a peculiar
aspect to the flora. As only 200 or 300 species of plants are known in
all the rocks ranging from the Trias to the Oolite inclusive, our data
are too scanty as yet to affirm whether the vegetation of this second
epoch was or was not on the whole of a simpler organization than that of
our own times.

In the Lower Cretaceous formation, near Aix-la-Chapelle, the leaves of a
great many dicotyledonous trees have lately been discovered by Dr.
Debey, establishing the important fact of the coexistence of a large
number of angiosperms with cycadeæ, and with that rich reptilian fauna
comprising the ichthyosaur, plesiosaur, and pterodactyl, which some had
supposed to indicate a state of the atmosphere unfavorable to a
dicotyledonous vegetation.

The number of plants hitherto obtained from _tertiary_ strata of
different ages is very limited, but is rapidly increasing. They are
referable to a much greater variety of families and classes than an
equal number of fossil species taken from secondary or primary rocks,
the angiosperms bearing the same proportion to the gymnosperms and
acrogens as in the present flora of the globe. This greater variety may,
doubtless, be partly ascribed to the greater diversity of stations in
which the plants grew, as we have in this case an opportunity, rarely
enjoyed in studying the secondary fossils, of investigating inland or
lacustrine deposits accumulated at different heights above the sea, and
containing the memorials of plants washed down from adjoining mountains.

In regard, then, to the strata from the cretaceous to the uppermost
tertiary inclusive, we may affirm that we find in them all the principal
classes of living plants, and during this vast lapse of time four or
five complete changes in the vegetation occurred, yet no step whatever
was made in advance at any of these periods by the addition of more
highly organized species.

If we next turn to the fossils of the animal kingdom, we may inquire
whether, when they are arranged by the geologists in a chronological
series, they imply that beings of more highly developed structure and
greater intelligence entered upon the earth at successive epochs, those
of the simplest organization being the first created, and those more
highly organized being the last.

Our knowledge of the Silurian fauna is at present derived entirely from
rocks of marine origin, no fresh-water strata of such high antiquity
having yet been met with. The fossils, however, of these ancient rocks
at once reduce the theory of progressive development to within very
narrow limits, for already they comprise a very full representation of
the radiata, mollusca, and articulata proper to the sea. Thus, in the
great division of radiata, we find asteriod and helianthoid zoophytes,
besides crinoid and cystidean echinoderms. In the mollusca, between 200
and 300 species of cephalopoda are enumerated. In the articulata we have
the crustaceans represented by more than 200 species of trilobites,
besides other genera of the same class. The remains of fish are as yet
confined to the upper part of the Silurian series; but some of these
belong to placoid fish, which occupy a high grade in the scale of
organization. Some naturalists have assumed that the earliest fauna was
exclusively marine, because we have not yet found a single Silurian
helix, insect, bird, terrestrial reptile or mammifer; but when we carry
back our investigation to a period so remote from the present, we ought
not to be surprised if the only accessible strata should be limited to
deposits formed far from land, because the ocean probably occupied then,
as now, the greater part of the earth's surface. After so many entire
geographical revolutions, the chances are nearly three to one in favor
of our finding that such small portions of the existing continents and
islands as expose Silurian strata to view, should coincide in position
with the ancient ocean rather than the land. We must not, therefore,
too hastily infer, from the absence of fossil bones of mammalia in the
older rocks, that the highest class of vertebrated animals did not exist
in remoter ages. There are regions at present, in the Indian and Pacific
Oceans, coextensive in area with the continents of Europe and North
America, where we might dredge the bottom and draw up thousands of
shells and corals, without obtaining one bone of a land quadruped.
Suppose our mariners were to report, that, on sounding in the Indian
Ocean near some coral reefs, and at some distance from the land, they
drew up on hooks attached to their line portions of a leopard, elephant,
or tapir, should we not be skeptical as to the accuracy of their
statements? and if we had no doubt of their veracity, might we not
suspect them to be unskilful naturalists? or, if the fact were
unquestioned, should we not be disposed to believe that some vessel had
been wrecked on the spot?

The casualties must always be rare by which land quadrupeds are swept by
rivers far out into the open sea, and still rarer the contingency of
such a floating body not being devoured by sharks or other predaceous
fish, such as were those of which we find the teeth preserved in some of
the carboniferous strata. But if the carcass should escape, and should
happen to sink where sediment was in the act of accumulating, and if the
numerous causes of subsequent disintegration should not efface all
traces of the body, included for countless ages in solid rock, is it not
contrary to all calculation of chances that we should hit upon the exact
spot--that mere point in the bed of an ancient ocean, where the precious
relic was entombed? Can we expect for a moment, when we have only
succeeded, amidst several thousand fragments of corals and shells, in
finding a few bones of _aquatic_ or _amphibious_ animals, that we should
meet with a single skeleton of an inhabitant of the land?

Clarence, in his dream, saw, "in the slimy bottom of the deep,"


    ----a thousand fearful wrecks;
  A thousand men, that fishes gnaw'd upon:
  Wedges of gold, great anchors, heaps of pearl.


Had he also beheld, amid "the dead bones that lay scattered by," the
carcasses of lions, deer, and the other wild tenants of the forest and
the plain, the fiction would have been deemed unworthy of the genius of
Shakspeare. So daring a disregard of probability and violation of
analogy would have been condemned as unpardonable, even where the poet
was painting those incongruous images which present themselves to a
disturbed imagination during the visions of the night.

Until lately it was supposed that the old red sandstone, or Devonian
rocks, contained no vertebrate remains except those of fish, but in 1850
the footprints of a chelonian, and in 1851 the skeleton of a reptile,
allied both to the batrachians and lizards, were found in a sandstone of
that age near Elgin in Scotland.[212] Up to the year 1844 it was laid
down as a received dogma in many works of high authority in geology,
that reptiles were not created until after the close of the
carboniferous epoch. In the course of that year, however, Hermann Von
Meyer announced the discovery, in the coal measures of Rhenish Bavaria,
of a reptile, called by him Apateon, related to the salamanders; and in
1847 three species of another genus, called archegosaurus by Goldfuss,
were obtained from the coal of Saarbrück, between Treves and Strasburg.
The footprints of a large quadruped, probably batrachian, had also been
observed by Dr. King in the carboniferous rocks of Pennsylvania in 1844.
The first example of the _bones_ of a reptile in the Coal of North
America was detected so lately as September, 1852, by Mr. G. W. Dawson
and myself in Nova Scotia. These remains, referred by Messrs. Wyman and
Owen to a perennibranchiate batrachian, were met with in the interior of
an erect fossil tree, apparently a sigillaria. They seem clearly to have
been introduced together with sediment into the tree, during its
submergence and after it had decayed and was standing as a hollow
cylinder of bark, this bark being now converted into coal.

When Agassiz, in his great work on fossil fish, described 152 species of
ichthyolites from the Coal, he found them to consist of 94 placoids,
belonging to the families of shark and ray, and 58 ganoids. One family
of the latter he called "sauroid fish," including the megalicthys and
holoptychius, often of great size, and all predaceous. Although true
fish, and not intermediate between that class and reptiles, they seem to
have been more highly organized than any living fish, reminding us of
the skeletons of saurians by the close suture of their cranial bones,
their large conical teeth, striated longitudinally, and the articulation
of the spinous processes with the vertebræ. Among living species they
are most nearly allied to the lepidosteus, or bony pike of the North
American rivers. Before the recent progress of discovery above alluded
to had shown the fallacy of such ideas, it was imagined by some
geologists that this ichthyic type was the more highly developed,
because it took the lead at the head of nature before the class of
reptiles had been created. The confident assumption indulged in till the
year 1844, that reptiles were first introduced into the earth in the
Permian period, shows the danger of taking for granted that the date of
the creation of any family of animals or plants in past time coincides
with the age of the oldest stratified rock in which the geologist has
detected its remains. Nevertheless, after repeated disappointments, we
find some naturalists as much disposed as ever to rely on such negative
evidence, and to feel now as sure that reptiles were not introduced into
the earth till after the Silurian epoch, as they were in 1844, that they
appeared for the first time at an era subsequent to the carboniferous.

Scanty as is the information hitherto obtained in regard to the
articulata of the coal formation, we have at least ascertained that some
insects winged their way through the ancient forests. In the ironstone
of Coalbrook Dale, two species of coleoptera of the Linnæan genus
curculio have been met with: and a neuropterous insect resembling a
corydalis, together with another of the same order related to the
phasmidæ. As an example of the insectivorous arachnidæ, I may mention
the scorpion of the Bohemian coal, figured by Count Sternberg, in which
even the eyes, skin, and minute hairs were preserved.[213] We need not
despair, therefore, of obtaining eventually fossil representatives of
all the principal orders of hexapods and arachnidæ in carboniferous
strata.

Next in chronological order above the Coal comes the allied Magnesian
Limestone, or Permian group, and the secondary formations from the Trias
to the Chalk inclusive. These rocks comprise the monuments of a long
series of ages in which reptiles of every variety of size, form, and
structure peopled the earth; so that the whole period, and especially
that of the Lias and Oolite, has been sometimes called "the age of
reptiles." As there are now mammalia entirely confined to the land;
others which, like the bat and vampire, fly in the air; others, again,
of amphibious habits, frequenting rivers, like the hippopotamus, otter,
and beaver; others exclusively aquatic and marine, like the seal, whale,
and narwal; so in the early ages under consideration, there were
terrestrial, winged, and aquatic reptiles. There were iguanodons walking
on the land, pterodactyls winging their way through the air, monitors
and crocodiles in the rivers, and ichthyosaurs and plesiosaurs in the
ocean. It appears also that some of these ancient saurians approximated
more nearly in their organization to the type of living mammalia than do
any of the reptiles now existing.[214]

In the vast range of strata above alluded to, comprising the Permian,
the Upper New Red Sandstone and Muschelkalk, the Lias, Oolite, Wealden,
Green-sand, and Chalk, scarcely any well-authenticated instances of the
occurrence of fossil birds in Europe are on record, and only two or
three of fossil mammalia.

In regard to the absence of birds, they are usually wanting, for reasons
afterwards to be explained (see chap. 47), in deposits of all ages, even
in the tertiary periods, where we know that birds as well as land
quadrupeds abounded. Some at least of the fossil remains formerly
referred to this class in the Wealden (a great freshwater deposit below
the chalk), have been recently shown by Mr. Owen to belong to
pterodactyls.[215] But in North America still more ancient indications
of the existence of the feathered tribe have been detected, the fossil
foot-marks of a great variety of species, of various sizes, some larger
than the ostrich, others smaller than the plover, having been observed.
These bipeds have left marks of their footsteps on strata of an age
decidedly intermediate between the Lias and the Coal.[216]

[Illustration: Fig. 8.

_Natural Size_.

Thylacotherium Prevostii (_Valenciennes_). Amphitherium (_Owen_). Lower
jaw, from the slate of Stonesfield, near Oxford.[218]]

[Illustration: Fig. 9.

Myrmecobius fasciatus (_Waterhouse_). Recent from Swan River. Lower jaw
of the natural size.[219]]

The examples of mammalia, above alluded to, are confined to the Trias
and the Oolite. In the former, the evidence is as yet limited to two
small molar teeth, described by Professor Plieninger in 1847, under the
generic name of Microlestes. They were found near Stuttgart, and
possess the double fangs so characteristic of mammalia.[217] The other
fossil remains of the same class were derived from one of the inferior
members of the oolitic series in Oxfordshire, and afford more full and
satisfactory evidence, consisting of the lower jaws of three species of
small quadrupeds about the size of a mole. Cuvier, when he saw one of
them (during a visit to Oxford in 1818), referred it to the marsupial
order, stating, however, that it differed from all known carnivora in
having ten molar teeth in a row. Professor Owen afterwards pointed out
that the jaw belonged to an extinct genus, having considerable affinity
to a newly discovered Australian mammifer, the _Myrmecobius_ of
Waterhouse, which has nine molar teeth in the lower jaw. (Fig. 9.) A
more perfect specimen enabled Mr. Owen in 1846 to prove that the
inflection of the angular process of the lower jaw was not sufficiently
marked to entitle the osteologist to infer that this quadruped was
marsupial, as the process is not bent inwards in a greater degree than
in the mole or hedgehog. Hence the genus amphitherium, of which there
are two species from Stonesfield, must be referred to the ordinary or
placental type of insectivorous mammals, although it approximates in
some points of structure to the myrmecobius and allied marsupials of
Australia. The other contemporary genus, called phascolotherium, agrees
much more nearly in osteological character and precisely in the number
of the teeth with the opossums; and is believed to have been truly
marsupial. (Fig. 10.)

[Illustration: Fig. 10.

_Natural size._

Phascolotherium Bucklandi, _Owen_. (_Syn._ Didelphis Bucklandi, _Brod._)
Lower jaw, from Stonesfield.[220]

1. The jaw magnified twice in length. 2. The second molar tooth
magnified six times.]

The occurrence of these most ancient memorials of the mammiferous type,
in so low a member of the oolitic series, while no other representatives
of the same class (if we except the microlestes) have yet been found in
any other of the inferior or superior secondary strata, is a striking
fact, and should serve as a warning to us against hasty generalizations,
founded solely on negative evidence. So important an exception to a
general rule may be perfectly consistent with the conclusion, that a
small number only of mammalia inhabited European latitudes when our
secondary rocks were formed; but it seems fatal to the theory of
progressive development, or to the notion that the order of precedence
in the creation of animals, considered chronologically, has precisely
coincided with the order in which they would be ranked according to
perfection or complexity of structure.

It was for many years suggested that the marsupial order to which the
fossil animals of Stonesfield were supposed exclusively to belong
constitutes the lowest grade in the class Mammalia, and that this order,
of which the brain is of more simple form, evinces an inferior degree of
intelligence. If, therefore, in the oolitic period the marsupial tribes
were the only warm-blooded quadrupeds which had as yet appeared upon our
planet, the fact, it was said, confirmed the theory which teaches that
the creation of the more simple forms in each division of the animal
kingdom preceded that of the more complex. But on how slender a support,
even if the facts had continued to hold true, did such important
conclusions hang! The Australian continent, so far as it has been
hitherto explored, contains no indigenous quadrupeds save those of the
marsupial order, with the exception of a few small rodents, while some
neighboring islands to the north, and even southern Africa, in the same
latitude as Australia, abound in mammalia of every tribe except the
marsupial. We are entirely unable to explain on what physiological or
other laws this singular diversity in the habitations of living mammalia
depends; but nothing is more clear than that the causes which stamp so
peculiar a character on two different provinces of wide extent are
wholly independent of time, or of the age or maturity of the planet.

The strata of the Wealden, although of a later date than the oolite of
Stonesfield, and although filled with the remains of large reptiles,
both terrestrial and aquatic, have not yielded as yet a single marsupial
bone. Were we to assume on such scanty data that no warm-blooded
quadrupeds were then to be found throughout the northern hemisphere,
there would still remain a curious subject of speculation, whether the
entire suppression of one important class of vertebrata, such as the
mammiferous, and the great development of another, such as the
reptilian, implies a departure from fixed and uniform rules governing
the fluctuations of the animal world; such rules, for example, as appear
from one century to another to determine the growth of certain tribes of
plants and animals in arctic, and of other tribes in tropical regions.

In Australia, New Zealand, and many other parts of the southern
hemisphere, where the indigenous land quadrupeds are comparatively few,
and of small dimensions, the reptiles do not predominate in number or
size. The deposits formed at the mouth of an Australian river, within
the tropics, might contain the bones of only a few small marsupial
animals, which, like those of Stonesfield, might hereafter be discovered
with difficulty by geologists; but there would, at the same time, be no
megalosauri and other fossil remains, showing that large saurians were
plentiful on the land and in the waters at a time when mammalia were
scarce. This example, therefore, would afford a very imperfect parallel
to the state of the animal kingdom, supposed to have prevailed during
the secondary periods, when a high temperature pervaded European
latitudes.

It may nevertheless be advantageous to point to some existing anomalies
in the geographical development of distinct classes of vertebrata which
may be comparable to former conditions of the animal creation brought to
light by geology. Thus in the arctic regions, at present, reptiles are
small, and sometimes wholly wanting, where birds, large land quadrupeds,
and cetacea abound. We meet with bears, wolves, foxes, musk oxen, and
deer, walruses, seals, whales, and narwals, in regions of ice and snow,
where the smallest snakes, efts, and frogs are rarely, if ever, seen.

A still more anomalous state of things presents itself in the southern
hemisphere. Even in the temperate zone, between the latitudes 52° and
56° S., as, for example, in Tierra del Fuego, as well as in the woody
region immediately north of the Straits of Magellan, and in the Falkland
Islands, no reptiles of any kind are met with, not even a snake, lizard,
or frog; but in these same countries we find the guanaco (a kind of
llama), a deer, the puma, a large species of fox, many small rodentia,
besides the seal and otter, together with the porpoise, whale, and other
cetacea.

On what grand laws in the animal physiology these remarkable phenomena
depend, cannot in the present state of science be conjectured; nor could
we predict whether any opposite condition of the atmosphere, in respect
to heat, moisture, and other circumstances, would bring about a state of
animal life which might be called the converse of that above described,
namely, a state in which reptiles of every size and order might abound,
and mammalia disappear.

The nearest approximation to such a fauna is found in the Galapagos
Archipelago. These islands, situated under the equator, and nearly 600
miles west of the coast of Peru, have been called "the land of
reptiles," so great is the number of snakes, large tortoises, and
lizards, which they support. Among the lizards, the first living species
proper to the ocean has been discovered. Yet, although some of these
islands are from 3000 to 4000 feet high, and one of them 75 miles long,
they contain, with the exception of one small mouse, no indigenous
mammifer. Even here, however, it is true that in the neighboring sea
there are seals, and several kinds of cetacea.[221]

It may be unreasonable to look for a nearer analogy between the fauna
now existing in any part of the globe, and that which we can show to
have prevailed when our secondary strata were deposited, because we must
always recollect that a climate like that now experienced at the
equator, coexisting with the unequal days and nights of European
latitudes, was a state of things to which there is now no counterpart on
the globe. Consequently, the type of animal and vegetable existence
required for such a climate might be expected to deviate almost as
widely from that now established, as do the flora and fauna of our
tropical differ from those of our arctic regions.

_In the Tertiary strata._--The tertiary formations were deposited when
the physical geography of the northern hemisphere had been entirely
altered. Large inland lakes had become numerous, as in central France
and other countries. There were gulfs of the sea, into which
considerable rivers emptied themselves, and where strata like those of
the Paris basin were accumulated. There were also formations in
progress, in shallow seas not far from shore, such as are indicated by
portions of the _Faluns_ of the Loire, and the English _Crag_.

The proximity, therefore, of large tracts of dry land to the seas and
lakes then existing, may, in a great measure, explain why the remains of
land animals, so rare in the older strata, are not uncommon in these
more modern deposits. Yet even these have sometimes proved entirely
destitute of mammiferous relics for years after they had become
celebrated for the abundance of their fossil testacea, fish, and
reptiles. Thus the calcaire grossier, a marine limestone of the district
round Paris, had afforded to collectors more than 1100 species of
shells, besides many zoophytes, echinodermata, and the teeth of fish,
before the bones of one or two land quadrupeds were met with in the same
rock. The strata called London and Plastic clay in England have been
studied for more than half a century, and about 400 species of shells,
50 or more of fish, besides several kinds of chelonian and saurian
reptiles, were known before a single mammifer was detected. At length,
in the year 1839, there were found in this formation the remains of a
monkey, an opossum, a bat,[222] and a species of the extinct genus
Hyracotherium, allied to the Peccary or hog tribe.

If we examine the strata above the London clay in England, we first meet
with mammiferous remains in the Isle of Wight, in beds also belonging to
the Eocene epoch, such as the remains of the Palæotherium,
Anoplotherium, and other extinct quadrupeds, agreeing very closely with
those first found by Cuvier, near Paris, in strata of the same age, and
of similar freshwater origin.

In France we meet with another fauna, both conchological and mammalian
in the Miocene "faluns" of the Loire; above which in the ascending
series in Great Britain we arrive at the coralline crag of Suffolk, a
marine formation which has yielded three or four hundred species of
shells, very different from the Eocene testacea, and of which a large
proportion, although a minority of the whole number, are recent, besides
many corals, echini, foraminifera, and fish, but as yet no relic
decidedly mammalian except the ear-bone of a whale.

In the shelly sand, provincially termed "Red Crag," in Suffolk, which
immediately succeeds the coralline, constituting a newer member of the
same tertiary group, about 250 species of shells have been recognized,
of which a still larger proportion are recent. They are associated with
numerous teeth of fish; but no signs of a warm-blooded quadruped had
been detected until 1839, when the teeth of a leopard, a bear, a hog,
and a species of ruminant, were found at Newbourn, in Suffolk, and since
that time, several other genera of mammalia have been met with in the
same formation, or in the Red Crag.[223]

Of a still newer date is the Norwich Crag, a fluvio-marine deposit of
the Pleiocene epoch, containing a mixture of marine, fluviatile, and
land shells, of which 90 per cent. or more are recent. These beds,
since the time of their first investigation, have yielded a supply of
mammalian bones of the genera mastodon, elephant, rhinoceros, pig,
horse, deer, ox, and others, the bodies of which may have been washed
down into the sea by rivers draining land, of which the contiguity is
indicated by the occasional presence of terrestrial and freshwater
shells.

Our acquaintance with the newer Pleiocene mammalia in Europe, South
America, and Australia, is derived chiefly from cavern deposits, a fact
which we ought never to forget if we desire to appreciate the superior
facilities we enjoy for studying the more modern as compared to the more
ancient terrestrial faunas. We know nothing of the fossil bones which
must have been inclosed in the stalagmite of caverns in the older
Pleiocene, or in the Miocene or Eocene epochs, much less can we derive
any information respecting the inhabitants of the land from a similar
source, when we carry back our inquiries to the Wealden or carboniferous
epochs. We are as well assured that land and rivers then existed, as
that they exist now; but it is evident that even a slight geographical
revolution, accompanied by the submergence and denudation of land, would
reduce to an extreme improbability the chance of our hitting on those
minute points of space where caves may once have occurred in limestone
rocks.

_Fossil quadrumana._--Until within a few years (1836, 1837), not a
single bone of any quadrumanous animal, such as the orang, ape, baboon,
and monkey, had been discovered in a fossil state, although so much
progress had been made in bringing to light the extinct mammalia of
successive tertiary eras, both carnivorous and herbivorous. The total
absence of these anthropomorphous tribes among the records of a former
world, had led some to believe that the type of organization most nearly
resembling the human, came so late in the order of creation, as to be
scarcely, if at all, anterior to that of man. That such generalizations
were premature, I endeavored to point out in the first edition of this
work,[224] in which I stated that the bones of quadrupeds hitherto met
with in tertiary deposits were chiefly those which frequent marshes,
rivers, or the borders of lakes, as the elephant, rhinoceros,
hippopotamus, tapir, hog, deer, and ox, while species which live in
trees are extremely rare in a fossil state. I also hinted, that we had
as yet no data for determining how great a number of the one kind we
ought to find, before we have a right to expect a single individual of
the other. Lastly, I observed that the climate of the more modern (or
Post-Eocene) tertiary periods in England was not tropical, and that in
regard to the London clay, of which the crocodiles, turtles, and fossil
fruits implied a climate hot enough for the quadrumana, we had as yet
made too little progress in ascertaining what were the Eocene
pachydermata of England, to entitle us to expect to have discovered any
quadrumana of the same date.

Since those remarks were first written, in 1829, a great number of
extinct species have been added to our collections of tertiary mammalia
from Great Britain and other parts of the world. At length, between the
years 1836 and 1839, a few remains of quadrumana were found in France
and England, India and Brazil. Those of India, belonging to more than
one extinct species of monkey, were first discovered near the Sutlej, in
lat. 30° N., in tertiary strata, of which the age is not yet determined;
the Brazilian fossil, brought from the basin of the Rio das Velhas,
about lat. 18° S., is referable to a form now peculiar in America,
allied to the genus Callithrix, the species being extinct. The skull and
other bones met with in the South of France belong to a gibbon, or one
of the tailless apes, which stand next in the scale of organization to
the orang. It occurred at Sansan, about forty miles west of Toulouse, in
lat. 43° 40' N., in freshwater strata, probably of the Miocene or middle
tertiary period. Lastly, the English quadrumane first met with, occurred
in a more ancient stratum than the rest, and at a point more remote from
the equator. It belongs to the genus Macacus, is an extinct species, and
was found in Suffolk, in lat. 52°,[225] in the London clay, the fossils
of which, such as crocodiles, turtles, shells of the genus Nautilus, and
many curious fruits, had already led geologists to the conclusion that
the climate of that era (the Eocene) was warm and nearly tropical.

Some years later (in 1846) the jaw of another British species of fossil
monkey, Macacus pliocenus, was announced by Mr. Owen as having been met
with in the newer Pleiocene strata, on the banks of the Thames, at
Grays, in Essex, accompanying the remains of hippopotamus, elephant, and
other quadrupeds, and associated with freshwater and land shells, most
of which are now inhabitants of the British Isles.[226]

When we consider the small area of the earth's surface hitherto
explored geologically, and the new discoveries brought to light daily,
even in the environs of great European capitals, we must feel that it
would be rash to assume that the Lower Eocene deposits mark the era of
the first creation of quadrumana. It would, however, be still more
unphilosophical to infer, as some writers have done, from a single
extinct species of this family obtained in a latitude far from the
tropics, that the Eocene quadrumana did not attain as high a grade of
organization as they do in our own times. What would the naturalist know
of the apes and orangs now contemporary with man, if our investigations
were restricted to such northern latitudes as those where alone the
geologist has hitherto found all the fossil quadrumana of Europe?

_Cetacea._--The absence of Cetacea from rocks older than the Eocene has
been frequently adduced as lending countenance to the theory of the very
late appearance of the highest class of Vertebrata on the earth.
Professor Sedgwick possesses in the Cambridge Museum a mass of
anchylosed cervical vertebræ of a whale, which he found in drift clay
near Ely, and which he has no doubt was washed out of the Kimmeridge
clay, an upper member of the Oolite. According to Professor Owen, it
exhibits well-marked specific characters, distinguishing it from all
other known recent or fossil cetacea. Dr. Leidy, of Philadelphia, has
lately described (1851) two species of cetacea of a new genus, which he
has called Priscodelphinus from the green sand of New Jersey, which
corresponds in age with the English Chalk or the cretaceous strata above
the gault. The specimens consist of dorsal and cervical vertebræ.[227]
Even in the Eocene strata of Europe, the discovery of cetaceans has
never kept pace with that of land quadrupeds. The only instance cited in
Great Britain is a species of Monodon, from the London clay, of doubtful
authenticity as to its geological position. On the other hand, the
gigantic Zeuglodon of North America occurs abundantly in the Middle
Eocene strata of Georgia and Alabama, from which as yet no bones of land
quadrupeds have been obtained.

In the present imperfect state then of our information, we can scarcely
say more than that the cetacea seem to have been scarce in the secondary
and primary periods. It is quite conceivable that when aquatic saurians,
some of them carnivorous, like the Ichthyosaurus, were swarming in the
sea, and when there were large herbivorous reptiles, like the Iguanodon,
on the land, the class of reptiles may, to a certain extent, have
superseded the cetacea, and discharged their functions in the animal
economy.

That mammalia had been created long before the epoch of the Kimmeridge
clay, is shown by the Microlestes of the Trias before alluded to, and by
the Stonesfield quadrupeds from the Inferior Oolite. And we are bound to
remember, whenever we infer the poverty of the flora or fauna of any
given period of the past, from the small number of fossils occurring in
ancient rocks, that it has been evidently no part of the plan of Nature
to hand down to us a complete or systematic record of the former history
of the animate world. We may have failed to discover a single shell,
marine or freshwater, or a single coral or bone in certain sandstones,
such as that of the valley of the Connecticut, where the footprints of
bipeds and quadrupeds abound; but such failure may have arisen, not
because the population of the land or sea was scanty at that era, but
because in general the preservation of any relics of the animals or
plants of former times is the exception to a general rule. Time so
enormous as that contemplated by the geologist may multiply exceptional
cases till they seem to constitute the rule, and so impose on the
imagination as to lead us to infer the non-existence of creatures of
which no monuments happen to remain. Professor Forbes has remarked, that
few geologists are aware how large a proportion of all known species of
fossils are founded on single specimens, while a still greater number
are founded on a few individuals discovered in one spot. This holds true
not only in regard to animals and plants inhabiting the land, the lake,
and the river, but even to a surprising number of the marine mollusca,
articulata, and radiata. Our knowledge, therefore, of the living
creation of any given period of the past may be said to depend in a
great degree on what we commonly call chance, and the casual discovery
of some new localities rich in peculiar fossils may modify or entirely
overthrow all our previous generalizations.

Upon the whole then we derive this result from a general review of the
fossils of the successive tertiary strata, namely, that since the Eocene
period, there have been several great changes in the land quadrupeds
inhabiting Europe, probably not less than five complete revolutions,
during which there has been no step whatever made in advance, no
elevation in the scale of being; so that had man been created at the
commencement of the Eocene era, he would not have constituted a greater
innovation on the state of the animal creation previously established
than now, when we believe him to have begun to exist at the close of the
Pleiocene. The views, therefore, which I proposed in the first edition
of this work, January, 1830, in opposition to the theory of progressive
development, do not seem to me to require material modification,
notwithstanding the large additions since made to our knowledge of
fossil remains.

These views may be thus briefly stated. From the earliest period at
which plants and animals can be proved to have existed, there has been a
continual change going on in the position of land and sea, accompanied
by great fluctuations of climate. To these ever-varying geographical and
climatal conditions the state of the animate world has been unceasingly
adapted. No satisfactory proof has yet been discovered of the gradual
passage of the earth from a chaotic to a more habitable state, nor of
any law of progressive development governing the extinction and
renovation of species, and causing the fauna and flora to pass from an
embryonic to a more perfect condition, from a simple to a more complex
organization.

The principle of adaptation to which I have alluded, appears to have
been analogous to that which now peoples the arctic, temperate, and
tropical regions contemporaneously with distinct assemblages of species
and genera, or which, independently of mere temperature, gives rise to a
predominance of the marsupial or didelphous tribe of quadrupeds in
Australia, of the placental or monodelphous tribe in Asia and Europe, or
which causes a profusion of reptiles without mammalia in the Galapagos
Archipelago, and of mammalia without reptiles in Greenland.

_Recent origin of man._--If, then, the popular theory of the successive
development of the animal and vegetable world, from the simplest to the
most perfect forms, rests on a very insecure foundation; it may be
asked, whether the recent origin of man lends any support to the same
doctrine, or how far the influence of man may be considered as such a
deviation from the analogy of the order of things previously
established, as to weaken our confidence in the uniformity of the course
of nature.

Antecedently to investigation, we might reasonably have anticipated that
the vestiges of man would have been traced back at least as far as those
modern strata in which all the testacea and a certain number of the
mammalia are of existing species, for of all the mammalia the human
species is the most cosmopolite, and perhaps more capable than any other
of surviving considerable vicissitudes in climate, and in the physical
geography of the globe.

No inhabitant of the land exposes himself to so many dangers on the
waters as man, whether in a savage or a civilized state;[228] and there
is no animal, therefore, whose skeleton is so liable to become imbedded
in lacustrine or submarine deposits; nor can it be said that his remains
are more perishable than those of other animals; for in ancient fields
of battle, as Cuvier has observed, the bones of men have suffered as
little decomposition as those of horses which were buried in the same
grave.[229] But even if the more solid parts of our species had
disappeared, the impression of their form would have remained engraven
on the rocks, as have the traces of the tenderest leaves of plants, and
the soft integuments of many animals. Works of art, moreover, composed
of the most indestructible materials, would have outlasted almost all
the organic contents of sedimentary rocks. Edifices, and even entire
cities, have, within the times of history, been buried under volcanic
ejections, submerged beneath the sea, or engulfed by earthquakes; and
had these catastrophes been repeated throughout an indefinite lapse of
ages, the high antiquity of man would have been inscribed in far more
legible characters on the framework of the globe than are the forms of
the ancient vegetation which once covered the islands of the northern
ocean, or of those gigantic reptiles which at still later periods
peopled the seas and rivers of the northern hemisphere.[230]

Dr. Prichard has argued that the human race have not always existed on
the surface of the earth, because "the strata of which our continents
are composed were once a part of the ocean's bed"--"mankind had a
beginning, since we can look back to the period when the surface on
which they lived began to exist."[231] This proof, however, is
insufficient, for many thousands of human beings now dwell in various
quarters of the globe where marine species lived within the times of
history, and, on the other hand, the sea now prevails permanently over
large districts once inhabited by thousands of human beings. Nor can
this interchange of sea and land ever cease while the present causes are
in existence. Terrestrial species, therefore, might be older than the
continents which they inhabit, and aquatic species of higher antiquity
than the lakes and seas which they now people.

But so far as our interpretation of physical movements has yet gone, we
have every reason to infer that the human race is extremely modern, even
when compared to the larger number of species now our contemporaries on
the earth, and we may, therefore, ask whether his creation can be
considered as one step in a supposed progressive system, by which the
organic world has advanced slowly from a more simple to a more complex
and perfect state? If we concede, for a moment, the truth of the
proposition, that the sponge, the cephalopod, the fish, the reptile, the
bird, and the mammifer, have followed each other in regular
chronological order, the creation of each class being separated from the
other by vast intervals of time, should we be able to recognize, in
man's entrance upon the earth, the last term of one and the same series
of progressive developments?

In reply to this question it should first be observed, that the
superiority of man depends not on those faculties and attributes which
he shares in common with the inferior animals, but on his reason, by
which he is distinguished from them. When it is said that the human race
is of far higher dignity than were any pre-existing beings on the earth,
it is the intellectual and moral attributes of our race, rather than the
physical, which are considered; and it is by no means clear that the
organization of man is such as would confer a decided pre-eminence upon
him, if, in place of his reasoning powers, he was merely provided with
such instincts as are possessed by the lower animals.

If this be admitted, it would not follow, even if there were sufficient
geological evidence in favor of the theory of progressive development,
that the creation of man was the last link in the same chain. For the
sudden passage from an irrational to a rational animal, is a phenomenon
of a distinct kind from the passage from the more simple to the more
perfect forms of animal organization and instinct. To pretend that such
a step, or rather leap, can be part of a regular series of changes in
the animal world, is to strain analogy beyond all reasonable bounds.

_Introduction of man, to what extent a change in the system._--But
setting aside the question of progressive development, another and a far
more difficult one may arise out of the admission that man is
comparatively of modern origin. Is not the interference of the human
species, it may be asked, such a deviation from the antecedent course of
physical events, that the knowledge of such a fact tends to destroy all
our confidence in the uniformity of the order of nature, both in regard
to time past and future? If such an innovation could take place after
the earth had been exclusively inhabited for thousands of ages by
inferior animals, why should not other changes as extraordinary and
unprecedented happen from time to time? If one new cause was permitted
to supervene, differing in kind and energy from any before in operation,
why may not others have come into action at different epochs? Or what
security have we that they may not arise hereafter? And if such be the
case, how can the experience of one period, even though we are
acquainted with all the possible effects of the then existing causes, be
a standard to which we can refer all natural phenomena of other periods?

Now these objections would be unanswerable, if adduced against one who
was contending for the absolute uniformity throughout all time of the
succession of sublunary events--if, for example, he was disposed to
indulge in the philosophical reveries of some Egyptian and Greek sects,
who represented all the changes both of the moral and material world as
repeated at distant intervals, so as to follow each other in their
former connection of place and time. For they compared the course of
events on our globe to astronomical cycles; and not only did they
consider all sublunary affairs to be under the influence of the
celestial bodies, but they taught that on the earth, as well as in the
heavens, the same identical phenomena recurred again and again in a
perpetual vicissitude. The same individual men were doomed to be
re-born, and to perform the same actions as before; the same arts were
to be invented, and the same cities built and destroyed. The Argonautic
expedition was destined to sail again with the same heroes, and Achilles
with his Myrmidons to renew, the combat before the walls of Troy.


  Alter erit tum Tiphys, et altera quæ vehat Argo
  Dilectos heroas; erunt etiam altera bella,
  Atque iterum ad Trojam magnus mittetur Achilles.[232]


The geologist, however, may condemn these tenets as absurd, without
running into the opposite extreme, and denying that the order of nature
has, from the earliest periods, been uniform in the same sense in which
we believe it to be uniform at present, and expect it to remain so in
future. We have no reason to suppose, that when man first became master
of a small part of the globe, a greater change took place in its
physical condition than is now experienced when districts, never before
inhabited, become successively occupied by new settlers. When a powerful
European colony lands on the shores of Australia, and introduces at once
those arts which it has required many centuries to mature; when it
imports a multitude of plants and large animals from the opposite
extremity of the earth, and begins rapidly to extirpate many of the
indigenous species, a mightier revolution is effected in a brief period
than the first entrance of a savage horde, or their continued occupation
of the country for many centuries, can possibly be imagined to have
produced. If there be no impropriety in assuming that the system is
uniform when disturbances so unprecedented occur in certain localities,
we can with much greater confidence apply the same language to those
primeval ages when the aggregate number and power of the human race, or
the rate of their advancement in civilization, must be supposed to have
been far inferior. In reasoning on the state of the globe immediately
before our species was called into existence, we must be guided by the
same rules of induction as when we speculate on the state of America in
the interval that elapsed between the introduction of man into Asia, the
supposed cradle of our race, and the arrival of the first adventurers on
the shores of the New World. In that interval, we imagine the state of
things to have gone on according to the order now observed in regions
unoccupied by man. Even now, the waters of lakes, seas, and the great
ocean, which teem with life, may be said to have no immediate relation
to the human race--to be portions of the terrestrial system of which man
has never taken, nor ever can take possession; so that the greater part
of the inhabited surface of the planet may still remain as insensible to
our presence as before any isle or continent was appointed to be our
residence.

If the barren soil around Sydney had at once become fertile upon the
landing of our first settlers; if, like the happy isles whereof the
poets have given such glowing descriptions, those sandy tracts had begun
to yield spontaneously an annual supply of grain, we might then, indeed,
have fancied alterations still more remarkable in the economy of nature
to have attended the first coming of our species into the planet. Or if,
when a volcanic island like Ischia was, for the first time, brought
under cultivation by the enterprise and industry of a Greek colony, the
internal fire had become dormant, and the earthquake had remitted its
destructive violence, there would then have been some ground for
speculating on the debilitation of the subterranean forces, when the
earth was first placed under the dominion of man. But after a long
interval of rest, the volcano bursts forth again with renewed energy,
annihilates one half of the inhabitants, and compels the remainder to
emigrate. The course of nature remains evidently unchanged; and, in like
manner, we may suppose the general condition of the globe, immediately
before and after the period when our species first began to exist, to
have been the same, with the exception only of man's presence.

The modifications in the system of which man is the instrument do not,
perhaps, constitute so great a deviation from previous analogy as we
usually imagine; we often, for example, form an exaggerated estimate of
the extent of our power in extirpating some of the inferior animals, and
causing others to multiply; a power which is circumscribed within
certain limits, and which, in all likelihood, is by no means exclusively
exerted by our species.[233] The growth of human population cannot take
place without diminishing the numbers, or causing the entire
destruction, of many animals. The larger beasts of prey, in particular,
give way before us; but other quadrupeds of smaller size, and
innumerable birds, insects, and plants, which are inimical to our
interests, increase in spite of us, some attacking our food, others our
raiment and persons, and others interfering with our agricultural and
horticultural labors. We behold the rich harvest which we have raised by
the sweat of our brow, devoured by myriads of insects, and are often as
incapable of arresting their depredations, as of staying the shock of an
earthquake, or the course of a stream of lava.

A great philosopher has observed, that we can command nature only by
obeying her laws; and this principle is true even in regard to the
astonishing changes which are superinduced in the qualities of certain
animals and plants by domestication and garden culture. I shall point
out in the third book that we can only effect such surprising
alterations by assisting the development of certain instincts, or by
availing ourselves of that mysterious law of their organization, by
which individual peculiarities are transmissible from one generation to
another.[234]

It is probable from these and many other considerations, that as we
enlarge our knowledge of the system, we shall become more and more
convinced, that the alterations caused by the interference of man
deviate far less from the analogy of those effected by other animals
than is usually supposed.[235] We are often misled, when we institute
such comparisons, by our knowledge of the wide distinction between the
instincts of animals and the reasoning power of man; and we are apt
hastily to infer, that the effects of a rational and irrational species,
considered merely as _physical agents_, will differ almost as much as
the faculties by which their actions are directed.

It is not, however, intended that a real departure from the antecedent
course of physical events cannot be traced in the introduction of man.
If that latitude of action which enables the brutes to accommodate
themselves in some measure to accidental circumstances could be imagined
to have been at any former period so great, that the operations of
instinct were as much diversified as are those of human reason, it
might, perhaps, be contended, that the agency of man did not constitute
an anomalous deviation from the previously established order of things.
It might then have been said, that the earth's becoming at a particular
period the residence of human beings, was an era in the moral, not in
the physical world--that our study and contemplation of the earth, and
the laws which govern its animate productions, ought no more to be
considered in the light of a disturbance or deviation from the system,
than the discovery of the satellites of Jupiter should be regarded as a
physical event affecting those heavenly bodies. Their influence in
advancing the progress of science among men, and in aiding navigation
and commerce, was accompanied by no reciprocal action of the human mind
upon the economy of nature in those distant planets; and so the earth
might be conceived to have become, at a certain period, a place of moral
discipline and intellectual improvement to man, without the slightest
derangement of a previously existing order of change in its animate and
inanimate productions.

The distinctness, however, of the human from all other species,
considered merely as an efficient cause in the physical world, is real;
for we stand in a relation to contemporary species of animals and plants
widely different from that which other irrational animals can ever be
supposed to have held to each other. We modify their instincts, relative
numbers, and geographical distribution, in a manner superior in degree,
and in some respects very different in kind from that in which any other
species can affect the rest. Besides, the progressive movement of each
successive generation of men causes the human species to differ more
from itself in power at two distant periods, than any one species of the
higher order of animals differs from another. The establishment,
therefore, by geological evidence, of the first intervention of such a
peculiar and unprecedented agency, long after other parts of the animate
and inanimate world existed, affords ground for concluding that the
experience during thousands of ages of all the events which may happen
on this globe, would not enable a philosopher to speculate with
confidence concerning future contingencies.

If, then, an intelligent being, after observing the order of events for
an indefinite series of ages, had witnessed at last so wonderful an
innovation as this, to what extent would his belief in the regularity of
the system be weakened?--would he cease to assume that there was
permanency in the laws of nature?--would he no longer be guided in his
speculations by the strictest rules of induction? To these questions it
may be answered, that, had he previously presumed to dogmatize
respecting the absolute uniformity of the order of nature, he would
undoubtedly be checked by witnessing this new and unexpected event, and
would form a more just estimate of the limited range of his own
knowledge, and the unbounded extent of the scheme of the universe. But
he would soon perceive that no one of the fixed and constant laws of the
animate or inanimate world was subverted by human agency, and that the
modifications now introduced for the first time were the accompaniments
of new and extraordinary circumstances, and those not of a _physical_
but a _moral_ nature. The deviation permitted would also appear to be as
slight as was consistent with the accomplishment of the new _moral_ ends
proposed, and to be in a great degree temporary in its nature, so that,
whenever the power of the new agent was withheld, even for a brief
period, a relapse would take place to the ancient state of things; the
domesticated animal, for example, recovering in a few generations its
wild instinct, and the garden-flower and fruit-tree reverting to the
likeness of the parent stock.

Now, if it would be reasonable to draw such inferences with respect to
the future, we cannot but apply the same rules of induction to the
past. We have no right to anticipate any modifications in the results of
existing causes in time to come, which are not conformable to analogy,
unless they be produced by the progressive development of human power,
or perhaps by some other new relations which may hereafter spring up
between the moral and material worlds. In the same manner, when we
speculate on the vicissitudes of the animate and inanimate creation in
former ages, we ought not to look for any anomalous results, unless
where man has interfered, or unless clear indications appear of some
other _moral_ source of temporary derangement.




CHAPTER X.

SUPPOSED INTENSITY OF AQUEOUS FORCES AT REMOTE PERIODS.


  Intensity of aqueous causes--Slow accumulation of strata proved by
    fossils--Rate of denudation can only keep pace with
    deposition--Erratics, and effects of ice--Deluges, and the causes to
    which they are referred--Supposed universality of ancient deposits.


_Intensity of aqueous causes._--The great problem considered in the
preceding chapters, namely, whether the former changes of the earth made
known to us by geology, resemble in kind and degree those now in daily
progress, may still be contemplated from several other points of view.
We may inquire, for example, whether there are any grounds for the
belief entertained by many, that the intensity both of aqueous and of
igneous forces, in remote ages, far exceeded that which we witness in
our own times.

First, then, as to aqueous causes: it has been shown, in our history of
the science, that Woodward did not hesitate, in 1695, to teach that the
entire mass of fossiliferous strata contained in the earth's crust had
been deposited in a few months; and, consequently, as their mechanical
and derivative origin was already admitted, the reduction of rocky
masses into mud, sand, and pebbles, the transportation of the same to a
distance, and their accumulation elsewhere in regular strata, were all
assumed to have taken place with a rapidity unparalleled in modern
times. This doctrine was modified by degrees, in proportion as different
classes of organic remains, such as shells, corals, and fossil plants,
had been studied with attention. Analogy led every naturalist to assume,
that each full-grown individual of the animal or vegetable kingdom, had
required a certain number of months or years for the attainment of
maturity, and the perpetuation of its species by generation; and thus
the first approach was made to the conception of a common standard of
time, without which there are no means whatever of measuring the
comparative rate at which any succession of events has taken place at
two distinct periods. This standard consisted of the average duration of
the lives of individuals of the same genera or families in the animal
and vegetable kingdoms; and the multitude of fossils dispersed through
successive strata implied the continuance of the same species for many
generations. At length the idea that species themselves had had a
limited duration, arose out of the observed fact that sets of strata of
different ages contained fossils of distinct species. Finally, the
opinion became general, that in the course of ages, one assemblage of
animals and plants had disappeared after another again and again, and
new tribes had started into life to replace them.

_Denudation._--In addition to the proofs derived from organic remains,
the forms of stratification led also, on a fuller investigation, to the
belief that sedimentary rocks had been slowly deposited; but it was
still supposed that _denudation_, or the power of running water, and the
waves and currents of the ocean, to strip off superior strata, and lay
bare the rocks below, had formerly operated with an energy wholly
unequalled in our times. These opinions were both illogical and
inconsistent, because deposition and denudation are parts of the same
process, and what is true of the one must be true of the other. Their
speed must be always limited by the same causes, and the conveyance of
solid matter to a particular region can only keep pace with its removal
from another, so that the aggregate of sedimentary strata in the earth's
crust can never exceed in volume the amount of solid matter which has
been ground down and washed away by running water. How vast, then, must
be the spaces which this abstraction of matter has left vacant! how far
exceeding in dimensions all the valleys, however numerous, and the
hollows, however vast, which we can prove to have been cleared out by
aqueous erosion! The evidences of the work of denudation are defective,
because it is the nature of every destroying cause to obliterate the
signs of its own agency; but the amount of reproduction in the form of
sedimentary strata must always afford a true measure of the minimum of
denudation which the earth's surface has undergone.

_Erratics._--The next phenomenon to which the advocates of the excessive
power of running water in times past have appealed, is the enormous size
of the blocks called _erratic_, which lie scattered over the northern
parts of Europe and North America. Unquestionably a large proportion of
these blocks have been transported far from their original position, for
between them and the parent rocks we now find, not unfrequently, deep
seas and valleys intervening, or hills more than a thousand feet high.
To explain the present situation of such travelled fragments, a deluge
of mud has been imagined by some to have come from the north, bearing
along with it sand, gravel, and stony fragments, some of them hundreds
of tons in weight. This flood, in its transient passage over the
continents, dispersed the boulders irregularly over hill, valley, and
plain; or forced them along over a surface of hard rock, so as to polish
it and leave it indented with parallel scratches and grooves--such
markings as are still visible in the rocks of Scandinavia, Scotland,
Canada, and many other countries.

There can be no doubt that the myriads of angular and rounded blocks
above alluded to, cannot have been borne along by ordinary rivers or
marine currents, so great is their volume and weight, and so clear are
the signs, in many places, of time having been occupied in their
successive deposition; for they are often distributed at various depths
through heaps of regularly stratified sand and gravel. No waves of the
sea raised by earthquakes, nor the bursting of lakes dammed up for a
time by landslips or by avalanches of snow, can account for the observed
facts; but I shall endeavor to show, in the next book, chap. 15,[236]
that a combination of existing causes may have conveyed erratics into
their present situations.

The causes which will be referred to are, first, the carrying power of
ice, combined with that of running water; and second, the upward
movement of the bed of the sea, converting it gradually into land.
Without entering at present into any details respecting these causes, I
may mention that the transportation of blocks by ice is now
simultaneously in progress in the cold and temperate latitudes, both of
the northern and southern hemisphere, as, for example, on the coasts of
Canada and Gulf of St. Lawrence, and also in Chili, Patagonia, and the
island of South Georgia. In those regions the uneven bed of the ocean is
becoming strewed over with ice-drifted fragments, which have either
stranded on shoals, or been dropped in deep water by melting bergs. The
entanglement of boulders in drift-ice will also be shown to occur
annually in North America, and these stones, when firmly frozen into
ice, wander year after year from Labrador to the St. Lawrence, and reach
points of the western hemisphere farther south than any part of Great
Britain.

The general absence of erratics in the warmer parts of the equatorial
regions of Asia, Africa, and America, confirms the same views. As to the
polishing and grooving of hard rocks, it has lately been ascertained
that glaciers give rise to these effects when pushing forward sand,
pebbles, and rocky fragments, and causing them to grate along the
bottom. Nor can there be any reasonable doubt that icebergs, when they
run aground on the floor of the ocean, must imprint similar marks upon
it.

It is unnecessary, therefore, to refer to deluges, or even to speculate
on the former existence of a climate more severe than that now
prevailing in the western hemisphere, to explain the geographical
distribution of most of the European erratics.

_Deluges._--As deluges have been often alluded to, I shall say something
of the causes which may be supposed to give rise to these grand
movements of water in addition to those already alluded to (p. 9).
Geologists who believe that mountain-chains have been thrown up
suddenly at many successive epochs, imagine that the waters of the
ocean may be raised by these convulsions, and then break in terrific
waves upon the land, sweeping over whole continents, hollowing out
valleys, and transporting sand, gravel, and erratics, to great
distances. The sudden rise of the Alps or Andes, it is said, may have
produced a flood even subsequently to the time when the earth became the
residence of man. But it seems strange that none of the writers who have
indulged their imaginations in conjectures of this kind, should have
ascribed a deluge to the sudden conversion of part of the unfathomable
ocean into a shoal rather than to the rise of mountain-chains. In the
latter case, the mountains themselves could do no more than displace a
certain quantity of atmospheric air, whereas, the instantaneous
formation of the shoal would displace a vast body of water, which being
heaved up to a great height might roll over and permanently submerge a
large portion of a continent.

If we restrict ourselves to combinations of causes at present known, it
would seem that the two principal sources of extraordinary inundations
are, first, the escape of the waters of a large lake raised far above
the sea; and, secondly, the pouring down of a marine current into lands
depressed below the mean level of the ocean.

As an example of the first of these cases, we may take Lake Superior,
which is more than 400 geographical miles in length and about 150 in
breadth, having an average depth of from 500 to 900 feet. The surface of
this vast body of fresh water is no less than 600 feet above the level
of the ocean; the lowest part of the barrier which separates the lake on
its southwest side from those streams which flow into the head waters of
the Mississippi being about 600 feet high. If, therefore, a series of
subsidences should lower any part of this barrier 600 feet, any
subsequent rending or depression, even of a few yards at a time, would
allow the sudden escape of vast floods of water into a hydrographical
basin of enormous extent. If the event happened in the dry season, when
the ordinary channels of the Mississippi and its tributaries are in a
great degree empty, the inundation might not be considerable; but if in
the flood-season, a region capable of supporting a population of many
millions might be suddenly submerged. But even this event would be
insufficient to cause a violent rush of water, and to produce those
effects usually called diluvial; for the difference of level of 600 feet
between Lake Superior and the Gulf of Mexico, when distributed over a
distance of 1800 miles, would give an average fall of only four inches
per mile.

The second case before adverted to is where there are large tracts of
dry land beneath the mean level of the ocean. It seems, after much
controversy, to be at length a settled point, that the Caspian is really
83 feet 6 inches lower than the Black Sea. As the Caspian covers an area
about equal to that of Spain, and as its shores are in general low and
flat, there must be many thousand square miles of country less than 83
feet above the level of that inland sea, and consequently depressed
below the Black Sea and Mediterranean. This area includes the site of
the populous city of Astrakhan and other towns. Into this region the
ocean would pour its waters, if the land now intervening between the Sea
of Azof and the Caspian should subside. Yet even if this event should
occur, it is most probable that the submergence of the whole region
would not be accomplished simultaneously, but by a series of minor
floods, the sinking of the barrier being gradual.[237]

_Supposed universality of ancient deposits._--The next fallacy which has
helped to perpetuate the doctrine that the operations of water were on a
different and grander scale in ancient times, is founded on the
indefinite areas over which homogeneous deposits were supposed to
extend. No modern sedimentary strata, it is said, equally identical in
mineral character and fossil contents, can be traced continuously from
one quarter of the globe to another. But the first propagators of these
opinions were very slightly acquainted with the inconstancy in mineral
composition of the ancient formations, and equally so of the wide spaces
over which the same kind of sediment is now actually distributed by
rivers and currents in the course of centuries. The persistency of
character in the older series was exaggerated, its extreme variability
in the newer was assumed without proof. In the chapter which treats of
river-deltas and the dispersion of sediment by currents, and in the
description of reefs of coral now growing over areas many hundred miles
in length, I shall have opportunities of convincing the reader of the
danger of hasty generalizations on this head.

In regard to the imagined universality of particular rocks of ancient
date, it was almost unavoidable that this notion, when once embraced,
should be perpetuated; for the same kinds of rock have occasionally been
reproduced at successive epochs; and when once the agreement or
disagreement in mineral character alone was relied on as the test of
age, it followed that similar rocks, if found even at the antipodes,
were referred to the same era, until the contrary could be shown.

Now it is usually impossible to combat such an assumption on geological
grounds, so long as we are imperfectly acquainted with the order of
superposition and the organic remains of these same formations. Thus,
for example, a group of red marl and red sandstone, containing salt and
gypsum, being interposed in England between the Lias and the Coal, all
other red marls and sandstones, associated some of them with salt, and
others with gypsum, and occurring not only in different parts of Europe,
but in North America, Peru, India, the salt deserts of Asia, those of
Africa--in a word, in every quarter of the globe, were referred to one
and the same period. The burden of proof was not supposed to rest with
those who insisted on the identity in age of all these groups--their
identity in mineral composition was thought sufficient. It was in vain
to urge as an objection the improbability of the hypothesis which
implies that all the moving waters on the globe were once simultaneously
charged with sediment of a red color.

But the rashness of pretending to identify, in age, all the red
sandstones and marls in question, has at length been sufficiently
exposed, by the discovery that, even in Europe, they belong decidedly to
many different epochs. It is already ascertained, that the red sandstone
and red marl containing the rock-salt of Cardona in Catalonia is newer
than the Oolitic, if not more modern than the Cretaceous period. It is
also known that certain red marls and variegated sandstones in Auvergne
which are undistinguishable in mineral composition from the New Red
Sandstone of English geologists, belong, nevertheless, to the Eocene
period; and, lastly, the gypseous red marl of Aix, in Provence, formerly
supposed to be a marine secondary group, is now acknowledged to be a
tertiary freshwater formation. In Nova Scotia one great deposit of red
marl, sandstone, and gypsum, precisely resembling in mineral character
the "New Red" of England, occurs as a member of the Carboniferous group,
and in the United States near the Falls of Niagara, a similar formation
constitutes a subdivision of the Silurian series.[238]

Nor was the nomenclature commonly adopted in geology without its
influence in perpetuating the erroneous doctrine of universal
formations. Such names, for example, as Chalk, Green Sand, Oolite, Red
Marl, Coal, and others, were given to some of the principal
fossiliferous groups in consequence of mineral peculiarities which
happened to characterize them in the countries where they were first
studied. When geologists had at length shown, by means of fossils and
the order of superposition, that other strata, entirely dissimilar in
color, texture, and composition, were of contemporaneous date, it was
thought convenient still to retain the old names. That these were often
inappropriate was admitted; but the student was taught to understand
them in no other than a chronological sense; so that the Chalk might not
be a white cretaceous rock, but a hard dolomitic limestone, as in the
Alps, or a brown sandstone or green marl, as in New Jersey, U. S. In
like manner, the Green Sand, it was said, might in some places be
represented by red sandstone, red marl, salt, and gypsum, as in the
north of Spain. So the oolitic texture was declared to be rather an
exception than otherwise to the general rule in rocks of the Oolitic
period; and it often became necessary to affirm that no particle of
carbonaceous matter could be detected in districts where the true Coal
series abounded. In spite of every precaution the habitual use of this
language could scarcely fail to instil into the mind of the pupil an
idea that chalk, coal, salt, red marl, or the Oolitic structure were far
more widely characteristic of the rocks of a given age than was really
the case.

There is still another cause of deception, disposing us to ascribe a
more limited range to the newer sedimentary formations as compared to
the older, namely, the very general concealment of the newer strata
beneath the waters of lakes and seas, and the wide exposure above waters
of the more ancient. The Chalk, for example, now seen stretching for
thousands of miles over different parts of Europe, has become visible to
us by the effect, not of one, but of many distinct series of
subterranean movements. Time has been required, and a succession of
geological periods, to raise it above the waves in so many regions; and
if calcareous rocks of the middle and upper tertiary periods have been
formed, as homogeneous in mineral composition throughout equally
extensive regions, it may require convulsions as numerous as all those
which have occurred since the origin of the Chalk to bring them up
within the sphere of human observation. Hence the rocks of more modern
periods may appear partial, as compared to those of remoter eras, not
because of any original inferiority in their extent, but because there
has not been sufficient time since their origin for the development of a
great series of elevatory movements.

In regard, however, to one of the most important characteristics of
sedimentary rocks, their organic remains, many naturalists of high
authority have maintained that the same species of fossils are more
uniformly distributed through formations of high antiquity than in those
of more modern date, and that distinct zoological and botanical
provinces, as they are called, which form so striking a feature in the
living creation, were not established at remote eras. Thus the plants of
the Coal, the shells, the trilobites of the Silurian rocks, and the
ammonites of the Oolite, have been supposed to have a wider geographical
range than any living species of plants, crustaceans, or mollusks. This
opinion seems in certain cases to be well founded, especially in
relation to the plants of the Carboniferous epoch, owing probably to the
more uniform temperature of the globe, at a time when the position of
sea and land was less favorable to variations in climate, according to
principles already explained in the seventh and eighth chapters. But a
recent comparison of the fossils of North American rocks with those of
corresponding ages in the European series, has proved that the
terrestrial vegetation of the Carboniferous epoch is an exception to the
general rule, and that the fauna and flora of the earth at successive
periods, from the oldest Silurian to the newest Tertiary was as
diversified as now. The shells, corals, and other classes of organic
remains demonstrate the fact that the earth might then have been divided
into separate zoological provinces, in a manner analogous to that
observed in the geographical distribution of species now living.




CHAPTER XI.

ON THE SUPPOSED FORMER INTENSITY OF THE IGNEOUS FORCES.


  Volcanic action at successive geological periods--Plutonic rocks of
    different ages--Gradual development of subterranean
    movements--Faults--Doctrine of the sudden upheaval of parallel
    mountain-chains--Objections to the proof of the suddenness of the
    upheaval, and the contemporaneousness of parallel chains--Trains of
    active volcanoes not parallel--As large tracts of land are rising or
    sinking slowly, so narrow zones of land may be pushed up gradually
    to great heights--Bending of strata by lateral pressure--Adequacy of
    the volcanic power to effect this without paroxysmal convulsions.


When reasoning on the intensity of volcanic action at former periods, as
well as on the power of moving water, already treated of, geologists
have been ever prone to represent Nature as having been prodigal of
violence and parsimonious of time. Now, although it is less easy to
determine the relative ages of the volcanic than of the fossiliferous
formations, it is undeniable that igneous rocks have been produced at
all geological periods, or as often as we find distinct deposits marked
by peculiar animal and vegetable remains. It can be shown that rocks
commonly called trappean have been injected into fissures, and ejected
at the surface, both before and during the deposition of the
Carboniferous series, and at the time when the Magnesian Limestone, and
when the Upper New Red Sandstone were formed, or when the Lias, Oolite,
Green Sand, Chalk, and the several tertiary groups newer than the chalk,
originated in succession. Nor is this all: distinct volcanic products
may be referred to the subordinate divisions of each period, such as the
Carboniferous, as in the county of Fife, in Scotland, where certain
masses of contemporaneous trap are associated with the Lower, others
with the Upper Coal measures. And if one of these masses is more
minutely examined, we find it to consist of the products of a great many
successive outbursts, by which scoriæ and lava were again and again
emitted, and afterwards consolidated, then fissured, and finally
traversed by melted matter, constituting what are called dikes.[239] As
we enlarge, therefore, our knowledge of the ancient rocks formed by
subterranean heat, we find ourselves compelled to regard them as the
aggregate effects of innumerable eruptions, each of which may have been
comparable in violence to those now experienced in volcanic regions.

It may indeed be said that we have as yet no data for estimating the
relative volume of matter simultaneously in a state of fusion at two
given periods, as if we were to compare the columnar basalt of Staffa
and its environs with the lava poured out in Iceland in 1783; but for
this very reason it would be rash and unphilosophical to assume an
excess of ancient as contrasted with modern outpourings of melted matter
at particular periods of time.[240] It would be still more presumptuous
to take for granted that the more deep-seated effects of subterranean
heat surpassed at remote eras the corresponding effects of internal heat
in our own times. Certain porphyries and granites, and all the rocks
commonly called plutonic, are now generally supposed to have resulted
from the slow cooling of materials fused and solidified under great
pressure; and we cannot doubt that beneath existing volcanoes there are
large spaces filled with melted stone, which must for centuries remain
in an incandescent state, and then cool and become hard and crystalline
when the subterranean heat shall be exhausted. That lakes of lava are
continuous for hundreds of miles beneath the Chilian Andes, seems
established by observations made in the year 1835.[241]

Now, wherever the fluid contents of such reservoirs are poured out
successively from craters in the open air, or at the bottom of the sea,
the matter so ejected may afford evidence by its arrangement of having
originated at different periods; but if the subterranean residue after
the withdrawal of the heat be converted into crystalline or plutonic
rock, the entire mass may seem to have been formed at once, however
countless the ages required for its fusion and subsequent refrigeration.
As the idea that all the granite in the earth's crust was produced
simultaneously, and in a primitive state of the planet, has now been
universally abandoned; so the suggestion above adverted to, may put us
on our guard against too readily adopting another opinion, namely, that
each large mass of granite was generated in a brief period of time.

Modern writers indeed, of authority, seem more and more agreed that in
the case of granitic rocks, the passage from a liquid or pasty to a
solid and crystalline state must have been an extremely gradual process.

The doctrine so much insisted upon formerly, that crystalline rocks,
such as granite, gneiss, mica-schist, quartzite, and others were
produced in the greatest abundance in the earlier ages of the planet,
and that their formation has ceased altogether in our own times, will be
controverted in the next chapter.

_Gradual development of subterranean movements._--The extreme violence
of the subterranean forces in remote ages has been often inferred from
the facts that the older rocks are more fractured and dislocated than
the newer. But what other result could we have anticipated if the
quantity of movement had been always equal in equal periods of time?
Time must, in that case, multiply the derangement of strata in the ratio
of their antiquity. Indeed the numerous exceptions to the above rule
which we find in nature, present at first sight the only objection to
the hypothesis of uniformity. For the more ancient formations remain in
many places horizontal, while in others much newer strata are curved and
vertical. This apparent anomaly, however, will be seen in the next
chapter to depend on the irregular manner in which the volcanic and
subterranean agency affect different parts of the earth in succession,
being often renewed again and again in certain areas, while others
remain during the whole time at rest.

That the more impressive effects of subterranean power, such as the
upheaval of mountain-chains, may have been due to multiplied convulsions
of moderate intensity rather than to a few paroxysmal explosions, will
appear the less improbable when the gradual and intermittent development
of volcanic eruptions in times past is once established. It is now very
generally conceded that these eruptions have their source in the same
causes as those which give rise to the permanent elevation and sinking
of land; the admission, therefore, that one of the two volcanic or
subterranean processes has gone on gradually, draws with it the
conclusion that the effects of the other have been elaborated by
successive and gradual efforts.

_Faults._--The same reasoning is applicable to great _faults_, or those
striking instances of the upthrow or downthrow of large masses of rock,
which have been thought by some to imply tremendous catastrophes wholly
foreign to the ordinary course of nature. Thus we have in England
faults, in which the vertical displacement is between 600 and 3000 feet,
and the horizontal extent thirty miles or more, the width of the
fissures since filled up with rubbish varying from ten to fifty feet.
But when we inquire into the proofs of the mass having risen or fallen
suddenly on the one side of these great rents, several hundreds or
thousands of feet above or below the rock with which it was once
continuous on the other side, we find the evidence defective. There are
grooves, it is said, and scratches on the rubbed and polished walls,
which have often one common direction, favoring the theory that the
movement was accomplished by a single stroke, and not by a series of
interrupted movements. But, in fact, the striæ are not always parallel
in such cases, but often irregular, and sometimes the stones and earth
which are in the middle of the fault, or fissure, have been polished and
striated by friction in different directions, showing that there have
been slidings subsequent to the first introduction of the fragmentary
matter. Nor should we forget that the last movement must always tend to
obliterate the signs of previous trituration, so that neither its
instantaneousness nor the uniformity of its direction can be inferred
from the parallelism of the striæ that have been last produced.

When rocks have been once fractured, and freedom of motion communicated
to detached portions of them, these will naturally continue to yield in
the same direction, if the process of upheaval or of undermining be
repeated again and again. The incumbent mass will always give way along
the lines of least resistance, or where it was formerly rent asunder.
Probably, the effects of reiterated movement, whether upward or
downward, in a fault, may be undistinguishable from those of a single
and instantaneous rise or subsidence; and the same may be said of the
rising or falling of continental masses, such as Sweden or Greenland,
which we know to take place slowly and insensibly.

_Doctrine of the sudden upheaval of parallel mountain-chains._--The
doctrine of the suddenness of many former revolutions in the physical
geography of the globe has been thought by some to derive additional
confirmation from a theory respecting the origin of mountain-chains,
advanced in 1833 by a distinguished geologist, M. Elie de Beaumont. In
several essays on this subject, the last published in 1852, he has
attempted to establish two points; first, that a variety of independent
chains of mountains have been thrown up suddenly at particular periods;
and, secondly, that the contemporaneous chains thus thrown up, preserve
a parallelism the one to the other.

These opinions, and others by which they are accompanied, are so adverse
to the method of interpreting the history of geological changes which I
have recommended in this work, that I am desirous of explaining the
grounds of my dissent, a course which I feel myself the more called upon
to adopt, as the generalizations alluded to are those of a skilful
writer, and an original observer of great talent and experience. I shall
begin, therefore, by giving a brief summary of the principal
propositions laid down in the works above referred to.[242]

1st. M. de Beaumont supposes "that in the history of the earth there
have been long periods of comparative repose, during which the
deposition of sedimentary matter has gone on in regular continuity; and
there have also been short periods of paroxysmal violence, during which
that continuity was broken.

"2dly. At each of these periods of violence or 'revolution,' in the
state of the earth's surface, a great number of mountain-chains have
been formed suddenly.

"3dly. The chains thrown up by a particular revolution have one uniform
direction, being parallel to each other within a few degrees of the
compass, even when situated in remote regions; whilst the chains thrown
up at different periods have, for the most part, different directions.

"4thly. Each 'revolution,' or 'great convulsion,' has fallen in with the
date of another geological phenomenon; namely, 'the passage from one
independent sedimentary formation to another,' characterized by a
considerable difference in 'organic types.'

"5thly. There has been a recurrence of these paroxysmal movements from
the remotest geological periods; and they may still be reproduced, and
the repose in which we live may hereafter be broken by the sudden
upthrow of another system of parallel chains of mountains.

"6thly. The origin of these chains depends not on partial volcanic
action, or a reiteration of ordinary earthquakes, but on the secular
refrigeration of the entire planet. For the whole globe, with the
exception of a thin envelope, much thinner in proportion than the shell
to an egg, is a fused mass, kept fluid by heat, but constantly cooling
and contracting its dimensions. The external crust does not gradually
collapse and accommodate itself century after century to the shrunken
nucleus, subsiding as often as there is a slight failure of support, but
it is sustained throughout whole geological periods, so as to become
partially separated from the nucleus, until at last it gives way
suddenly, cracking and falling in along determinate lines of fracture.
During such a crisis the rocks are subjected to great lateral pressure,
the unyielding ones are crushed, and the pliant strata bent, and are
forced to pack themselves more closely into a smaller space, having no
longer the same room to spread themselves out horizontally. At the same
time, a large portion of the mass is squeezed upwards, because it is in
the upward direction only that the excess in size of the envelope, as
compared to the contracted nucleus, can find relief. This excess
produces one or more of those folds or wrinkles in the earth's crust
which we call mountain-chains.

"Lastly, some chains are comparatively modern; such as the Alps, which
were partly upheaved after the middle tertiary period. The elevation of
the Andes was much more recent, and was accompanied by the simultaneous
outburst for the first time of 270 of the principal volcanoes now
active.[243]

"The agitation of the waters of the ocean caused by this convulsion
probably occasioned that transient and general deluge which is noticed
in the traditions of so many nations."[244]

Several of the topics enumerated in the above summary, such as the cause
of interruptions in the sedimentary series, will be discussed in the
thirteenth chapter, and I shall now confine myself to what I conceive to
be the insufficiency of the proofs adduced in favor of the suddenness of
the upthrow, and the contemporaneousness of the origin of the parallel
chains referred to. At the same time I may remark, that the great body
of facts collected together by M. de Beaumont will always form a most
valuable addition to our knowledge, tending as they do to confirm the
doctrine that different mountain-chains have been formed in succession,
and, as Werner first pointed out, that there are certain determinate
lines of direction or strike in the strata of various countries.

The following may serve as an analysis of the evidence on which the
theory above stated depends. "We observe," says M. de Beaumont, "when we
attentively examine nearly all mountain-chains, that the most recent
rocks extend horizontally up to the foot of such chains, as we should
expect would be the case if they were deposited in seas or lakes, of
which these mountains have partly formed the shores; whilst the other
sedimentary beds, tilted up, and more or less contorted, on the flanks
of the mountains, rise in certain points even to their highest
crests."[245] There are, therefore, in and adjacent to each chain, two
classes of sedimentary rocks, the ancient and inclined beds, and the
newer or horizontal. It is evident that the first appearance of the
chain itself was an event "intermediate between the period when the beds
now upraised were deposited, and the period when the strata were
produced horizontally at its feet."

[Illustration: Fig. 11.]

Thus the chain A assumed its present position after the deposition of
the strata _b_, which have undergone great movements, and before the
deposition of the group _c_, in which the strata have not suffered
derangement.

[Illustration: Fig. 12.]

If we then discover another chain B, in which we find not only the
formation _b_, but the group _c_ also, disturbed and thrown on its
edges, we may infer that the latter chain is of subsequent date to A;
for B must have been elevated _after_ the deposition of _c_, and before
that of the group _d_; whereas A had originated _before_ the strata _c_
were formed.

It is then argued, that in order to ascertain whether other mountain
ranges are of contemporaneous date with A and B, or are referable to
_distinct_ periods, we have only to inquire whether the inclined and
undisturbed sets of strata in each range correspond with or differ from
those in the typical chain A and B.

Now all this reasoning is perfectly correct, so long as the period of
time required for the deposition of the strata _b_ and _c_ is not made
identical in duration with the period of time during which the animals
and plants found fossil in _b_ and _c_ may have flourished; for the
latter, that is to say, the duration of certain groups of species, may
have greatly exceeded, and probably did greatly exceed, the former, or
the time required for the accumulation of certain local deposits, such
as _b_ and _c_ (figs. 11 and 12). In order, moreover, to render the
reasoning correct, due latitude must be given to the term
contemporaneous; for this term must be understood to allude, not to a
moment of time, but to the interval, whether brief or protracted, which
elapsed between two events, namely, between the accumulation of the
inclined and that of the horizontal strata.

But, unfortunately, no attempt has been made in the treatises under
review to avoid this manifest source of confusion, and hence the very
terms of each proposition are equivocal; and the possible length of some
of the intervals is so vast, that to affirm that all the chains raised
in such intervals were _contemporaneous_ is an abuse of language.

In order to illustrate this argument, I shall select the Pyrenees as an
example. Originally M. E. de Beaumont spoke of this range of mountains
as having been uplifted suddenly (_à un seul jet_), but he has since
conceded that in this chain, in spite of the general unity and
simplicity of its structure, six, if not seven, systems of dislocation
of different dates can be recognized.[246] In reference, however, to the
latest, and by far the most important of these convulsions, the chain is
said to have attained its present elevation at a certain epoch in the
earth's history, namely, between the deposition of the chalk, or rocks
of about that age, and that of certain tertiary formations "as old as
the plastic clay;" for the chalk is seen in vertical, curved, and
distorted beds on the flanks of the chain, as the beds _b_, fig. 11,
while the tertiary formations rest upon them in horizontal strata at its
base, as _c_, ibid.

The proof, then, of the extreme suddenness of the convulsion is supposed
to be the shortness of the time which intervened between the formation
of the chalk and the origin of certain tertiary strata.[247] Even if the
interval were deducible within these limits, it might comprise an
indefinite lapse of time. In strictness of reasoning, however, the
author cannot exclude the Cretaceous or Tertiary periods from the
possible duration of the interval during which the elevation may have
taken place. For, in the first place, it cannot be assumed that the
movement of upheaval took place after the close of the Cretaceous
period; we can merely say, that it occurred after the deposition of
certain strata of that period; secondly, although it were true that the
event happened before the formation of all the tertiary strata now at
the base of the Pyrenees, it would by no means follow that it preceded
the whole Tertiary epoch.

The age of the strata, both of the inclined and horizontal series, may
have been accurately determined by M. De Beaumont, and still the
upheaving of the Pyrenees may have been going on before the animals of
the Chalk period, such as are found fossil in England, had ceased to
exist, or when the Maestricht beds were in progress, or during the
indefinite ages which may have elapsed between the extinction of the
Maestricht animals and the introduction of the Eocene tribes, or during
the Eocene epoch, or the rise may have been going on throughout one, or
several, or all of these periods.

It would be a purely gratuitous assumption to say that the inclined
cretaceous strata (_b_, fig. 11) on the flanks of the Pyrenees, were the
very last which were deposited during the Cretaceous period, or that, as
soon as they were upheaved, all or nearly all the species of animals and
plants now found fossil in them were suddenly exterminated; yet, unless
this can be affirmed, we cannot say that the Pyrenees were not upheaved
during the Cretaceous period. Consequently, another range of mountains,
at the base of which cretaceous rocks may lie in horizontal
stratification, may have been elevated, like the chain A, fig. 12,
during some part of the same great period.

There are mountains in Sicily two or three thousand feet high, the tops
of which are composed of limestone, in which a large proportion of the
fossil shells agree specifically with those now inhabiting the
Mediterranean. Here, as in many other countries, the deposits now in
progress in the sea must inclose shells and other fossils specifically
identical with those of the rocks constituting the contiguous land. So
there are islands in the Pacific where a mass of dead coral has emerged
to a considerable altitude, while other portions of the mass remain
beneath the sea, still increasing by the growth of living zoophytes and
shells. The chalk of the Pyrenees, therefore, may at a remote period
have been raised to an elevation of several thousand feet, while the
species found fossil in the same chalk still continued to be represented
in the fauna of the neighboring ocean. In a word, we cannot assume that
the origin of a new range of mountains caused the Cretaceous period to
cease, and served as the prelude to a new order of things in the animate
creation.

To illustrate the grave objections above advanced, against the theory
considered in the present chapter, let us suppose, that in some country
three styles of architecture had prevailed in succession, each for a
period of one thousand years; first the Greek, then the Roman, and then
the Gothic; and that a tremendous earthquake was known to have occurred
in the same district during one of the three periods--a convulsion of
such violence as to have levelled to the ground all the buildings then
standing. If an antiquary, desirous of discovering the date of the
catastrophe, should first arrive at a city where several Greek temples
were lying in ruins and half engulphed in the earth, while many Gothic
edifices were standing uninjured, could he determine on these data the
era of the shock? Could he even exclude any one of the three periods,
and decide that it must have happened during one of the other two?
Certainly not. He could merely affirm that it happened at some period
after the introduction of the Greek style, and before the Gothic had
fallen into disuse. Should he pretend to define the date of the
convulsion with greater precision, and decide that the earthquake must
have occurred after the Greek and before the Gothic period, that is to
say, when the Roman style was in use, the fallacy in his reasoning would
be too palpable to escape detection for a moment.

Yet such is the nature of the erroneous induction which I am now
exposing. For as, in the example above proposed, the erection of a
particular edifice is perfectly distinct from the period of architecture
in which it may have been raised, so is the deposition of chalk, or any
other set of strata, from the geological epochs characterized by certain
fossils to which they may belong.

It is almost superfluous to enter into any farther analysis of the
theory of parallelism, because the whole force of the argument depends
on the accuracy of the data by which the contemporaneous or
non-contemporaneous date of the elevation of two independent chains can
be demonstrated. In every case, this evidence, as stated by M. de
Beaumont, is equivocal, because he has not included in the possible
interval of time between the depositions of the deranged and the
horizontal formations, part of the periods to which each of those
classes of formations are referable. Even if all the geological facts,
therefore, adduced by the author were true and unquestionable, yet the
conclusion that certain chains were or were not simultaneously upraised
is by no means a legitimate consequence.

In the third volume of my first edition of the Principles, which
appeared in April, 1833, I controverted the views of M. de Beaumont,
then just published, in the same terms as I have now restated them. At
that time I took for granted that the chronological date of the newest
rocks entering into the disturbed series of the Pyrenees had been
correctly ascertained. It now appears, however, that some of the most
modern of those disturbed strata belong to the nummulitic formation,
which are regarded by the majority of geologists as Eocene or older
tertiary, an opinion not assented to by M. E. de Beaumont, and which I
cannot discuss here without being led into too long a digression.[248]

Perhaps a more striking illustration of the difficulties we encounter,
when we attempt to apply the theory under consideration even to the best
known European countries, is afforded by what is called "The System of
the Longmynds." This small chain, situated in Shropshire, is the third
of the typical systems to which M. E. de Beaumont compares other
mountain ranges corresponding in _strike_ and structure. The date
assigned to its upheaval is "after the unfossiliferous greywacke, or
Cambrian strata, and before the Silurian." But Sir R. I. Murchison had
shown in 1838, in his "Silurian System," and the British government
surveyors, since that time, in their sections (about 1845), that the
Longmynds and other chains of similar composition in North Wales are
_post-Silurian_. In all of them fossiliferous beds of the lower Silurian
formation, or Llandeilo flags are highly inclined, and often vertical.
In one limited region the Caradoc sandstone, a member of the lower
Silurian, rests unconformably on the denuded edges of the inferior (or
Llandeilo) member of the same group; whilst in some cases both of these
sets of strata are upturned. When, therefore, so grave an error is
detected in regard to the age of a typical chain, we are entitled to
inquire with surprise, by what means nine other _parallel_ chains in
France, Germany, and Sweden, assumed to be "ante-Silurian," have been
made to agree precisely in date with the Longmynds? If they are
correctly represented as having been all deposited before the deposition
of the Silurian strata, they cannot be contemporaneous with the
Longmynds, and they only prove how little reliance can be placed on
parallelism as a test of simultaneousness of upheaval. But in truth it
is impossible, for reasons already given, to demonstrate that each of
those nine chains coincide in date with one another, any more than with
the Longmynds.

The reader will see in the sequel (chap. 31[249]) that Mr. Hopkins has
inferred from astronomical calculations, that the solid crust of the
earth cannot be less than 800 or 1000 miles thick, and may be more. Even
if it be solid to the depth of 100 miles, such a thickness would be
inconsistent with M. E. de Beaumont's hypothesis, which requires a shell
not more than thirty miles thick, or even less. Mr. Hopkins admits that
the exterior of the planet, though solid as a whole, may contain within
it vast lakes or seas of lava. If so, the gradual fusion of rocks, and
the expansive power of heat exerted for ages, as well as the subsequent
contraction of the same during slow refrigeration, may perhaps account
for the origin of mountain-chains, for these, as Dolomieu has remarked,
are "far less important, proportionally speaking, than the inequalities
on the surface of an egg-shell, which to the eye appears smooth." A
"centripetal force" affecting the whole planet as it cools, seems a
mightier cause than is required to produce wrinkles of such
insignificant size.

In pursuing his investigations, M. E. de Beaumont has of late greatly
multiplied the number of successive periods of instantaneous upheaval,
admitting at the same time that occasionally new lines of upthrow have
taken the direction of older ones.[250] These admissions render his
views much more in harmony with the principles advocated in this work,
but they impair the practical utility of parallelism considered as a
chronological test; for no rule is laid down for limiting the interval,
whether in time or space, which may separate two parallel lines of
upheaval of different dates.[251]

Among the various propositions above laid down (p. 164), it will be
seen that the sudden rise of the Andes is spoken of as a modern event,
but Mr. Darwin has brought together ample data in proof of the local
persistency of volcanic action throughout a long succession of
geological periods, beginning with times antecedent to the deposition of
the oolitic and cretaceous formations of Chili, and continuing to the
historical epoch. It appears that some of the parallel ridges which
compose the Cordilleras, instead of being contemporaneous, were
successively and slowly upheaved at widely different epochs. The whole
range, after twice subsiding some thousands of feet, was brought up
again by a slow movement in mass, during the era of the Eocene tertiary
formations, after which the whole sank down once more several hundred
feet, to be again uplifted to its present level by a slow and often
interrupted movement.[252] In a portion of this latter period the
"Pampean mud" was formed, in which the Megatherium mylodon and other
extinct quadrupeds are buried. This mud contains in it recent species of
shells, some of them proper to brackish water, and is believed by Mr.
Darwin to be an estuary or delta deposit. M. A. d'Orbigny, however, has
advanced an hypothesis referred to by M. E. de Beaumont, that the
agitation and displacement of the waters of the ocean, caused by the
elevation of the Andes, gave rise to a deluge, of which this Pampean
mud, which rises sometimes to the height of 12,000 feet, is the result
and monument.[253]

In studying many chains of mountains, we find that the strike or line of
outcrop of continuous sets of strata, and the general direction of the
chain, may be far from rectilinear. Curves forming angles of 20° or 30°
may be found in the same range as in the Alleghanies; just as trains of
active volcanoes and the zones throughout which modern earthquakes occur
are often linear, without running in straight lines. Nor are all of
these, though contemporaneous or belonging to our own epoch, by any
means parallel, but some at right angles, the one to the other.

_Slow upheaval and subsidence._--Recent observations have disclosed to
us the wonderful fact, that not only the west coast of South America,
but also other large areas, some of them several thousand miles in
circumference, such as Scandinavia, and certain archipelagoes in the
Pacific, are slowly and insensibly rising; while other regions, such as
Greenland, and parts of the Pacific and Indian Oceans, in which atolls
or circular coral islands abound, are as gradually sinking. That all the
existing continents and submarine abysses may have originated in
movements of this kind, continued throughout incalculable periods of
time, is undeniable, and the denudation which the dry land appears
everywhere to have suffered, favors the idea that it was raised from the
deep by a succession of upward movements, prolonged throughout
indefinite periods. For the action of waves and currents on land slowly
emerging from the deep, affords the only power by which we can conceive
so many deep valleys and wide spaces to have been denuded as those which
are unquestionably the effects of running water.

But perhaps it may be said that there is no analogy between the slow
upheaval of broad plains or table-lands, and the manner in which we must
presume all mountain-chains, with their inclined strata, to have
originated. It seems, however, that the Andes have been rising century
after century, at the rate of several feet, while the Pampas on the east
have been raised only a few inches in the same time. Crossing from the
Atlantic to the Pacific, in a line passing through Mendoza, Mr. Darwin
traversed a plain 800 miles broad, the eastern part of which has emerged
from beneath the sea at a very modern period. The slope from the
Atlantic is at first very gentle, then greater, until the traveller
finds, on reaching Mendoza, that he has gained, almost insensibly, a
height of 4000 feet. The mountainous district then begins suddenly, and
its breadth from Mendoza to the shores of the Pacific is 120 miles, the
average height of the principal chain being from 15,000 to 16,000 feet,
without including some prominent peaks, which ascend much higher. Now
all we require, to explain the origin of the principal inequalities of
level here described, is to imagine, first, a zone of more violent
movement to the west of Mendoza, and, secondly, to the east of that
place, an upheaving force, which died away gradually as it approached
the Atlantic. In short, we are only called upon to conceive, that the
region of the Andes was pushed up four feet in the same period in which
the Pampas near Mendoza rose one foot, and the plains near the shores of
the Atlantic one inch. In Europe we have learnt that the land at the
North Cape ascends about five feet in a century, while farther to the
south the movements diminish in quantity first to a foot, and then, at
Stockholm, to three inches in a century, while at certain points still
farther south there is no movement.

But in what manner, it is asked, can we account for the great lateral
pressure which has been exerted not only in the Andes, Alps, and other
chains, but also on the strata of many low and nearly level countries?
Do not the folding and fracture of the beds, the anticlinal and
synclinal ridges and troughs, as they are called, and the vertical, and
even sometimes the inverted position of the beds, imply an abruptness
and intensity in the disturbing force wholly different in kind and
energy to that which now rends the rocks during ordinary earthquakes? I
shall treat more fully in the sequel (end of chap. 32) of the probable
subterranean sources, whether of upward or downward movement, and of
great lateral pressure; but it may be well briefly to state in this
place that in our own times, as, for example, in Chili, in 1822, the
volcanic force has overcome the resistance, and permanently uplifted a
country of such vast extent that the weight and volume of the Andes must
be insignificant in comparison, even if we indulge the most moderate
conjectures as to the thickness of the earth's crust above the volcanic
foci.

To assume that any set of strata with which we are acquainted are made
up of such cohesive and unyielding materials, as to be able to resist a
power of such stupendous energy, if its direction, instead of being
vertical, happened to be oblique or horizontal, would be extremely rash.
But if they could yield to a sideway thrust, even in a slight degree,
they would become squeezed and folded to any amount if subjected for a
sufficient number of times to the repeated action of the same force. We
can scarcely doubt that a mass of rock several miles thick was uplifted
in Chili in 1822 and 1835, and that a much greater volume of solid
matter is upheaved wherever the rise of the land is very gradual, as in
Scandinavia, the development of heat being probably, in that region, at
a greater distance from the surface. If continents, rocked, shaken, and
fissured, like the western region of South America, or very gently
elevated, like Norway and Sweden, do not acquire in a few days or hours
an additional height of several thousand feet, this can arise from no
lack of mechanical force in the subterranean moving cause, but simply
because the antagonist power, or the strength, toughness, and density of
the earth's crust is insufficient to resist, so long, as to allow the
volcanic energy an indefinite time to accumulate. Instead of the
explosive charge augmenting in quantity for countless ages, it finds
relief continuously, or by a succession of shocks of moderate violence,
so as never to burst or blow up the covering of incumbent rock in one
grand paroxysmal convulsion. Even in its most energetic efforts it
displays an intermittent and mitigated intensity, being never permitted
to lay a whole continent in ruins. Hence the numerous eruptions of lava
from the same vent, or chain of vents, and the recurrence of similar
earthquakes for thousands of years along certain areas or zones of
country. Hence the numerous monuments of the successive ejection and
injection of melted matter in ancient geological epochs, and the
fissures formed in distinct ages, and often widened and filled at
different eras.

Among the causes of lateral pressure, the expansion by heat of large
masses of solid stone intervening between others which have a different
degree of expansibility, or which happen not to have their temperature
raised at the same time, may play an important part. But as we know that
rocks have so often sunk down thousands of feet below their original
level, we can hardly doubt that much of the bending of pliant strata,
and the packing of the same into smaller spaces, has frequently been
occasioned by subsidence. Whether the failure of support be produced by
the melting of porous rocks, which, when fluid, and subjected to great
pressure, may occupy less room than before, or which, by passing from a
pasty to a crystalline condition, may, as in the case of granite,
according to the experiments of Deville, suffer a contraction of 10 per
cent., or whether the sinking be due to the subtraction of lava driven
elsewhere to some volcanic orifice, and there forced outwards, or
whether it be brought on by the shrinking of solid and stony masses
during refrigeration, or by the condensation of gases, or any other
imaginable cause, we have no reason to incline to the idea that the
consequent geological changes are brought about so suddenly, as that
large parts of continents are swallowed up at once in unfathomable
subterranean abysses. If cavities be formed, they will be enlarged
gradually, and as gradually filled. We read, indeed, accounts of
engulphed cities and areas of limited extent which have sunk down many
yards at once; but we have as yet no authentic records of the sudden
disappearance of mountains, or the submergence or emergence of great
islands. On the other hand, the creeps in coal mines[254] demonstrate
that gravitation begins to act as soon as a moderate quantity of matter
is removed even at a great depth. The roof sinks in, or the floor of the
mine rises, and the bent strata often assume as regularly a curved and
crumpled arrangement as that observed on a grander scale in
mountain-chains. The absence, indeed, of chaotic disorder, and the
regularity of the plications in geological formations of high antiquity,
although not unfrequently adduced to prove the unity and
instantaneousness of the disturbing force, might with far greater
propriety be brought forward as an argument in favor of the successive
application of some irresistible but moderated force, such as that which
can elevate or depress a continent.

In conclusion, I may observe that one of the soundest objections to the
theory of the sudden upthrow or downthrow of mountain-chains is this,
that it provides us with too much force of one kind, namely, that of
subterranean movement, while it deprives us of another kind of
mechanical force, namely, that exerted by the waves and currents of the
ocean, which the geologist requires for the denudation of land during
its slow upheaval or depression. It may be safely affirmed that the
quantity of igneous and aqueous action,--of volcanic eruption and
denudation,--of subterranean movement and sedimentary deposition,--not
only of past ages, but of one geological epoch, or even the fraction of
an epoch, has exceeded immeasurably all the fluctuations of the
inorganic world which have been witnessed by man. But we have still to
inquire whether the time to which each chapter or page or paragraph of
the earth's autobiography relates, was not equally immense when
contrasted with a brief era of 3000 or 5000 years. The real point on
which the whole controversy turns, is the relative amount of work done
by mechanical force in given quantities of time, past and present.
Before we can determine the relative intensity of the force employed, we
must have some fixed standard by which to measure the time expended in
its development at two distinct periods. It is not the magnitude of the
effects, however gigantic their proportions, which can inform us in the
slightest degree whether the operation was sudden or gradual, insensible
or paroxysmal. It must be shown that a slow process could never in any
series of ages give rise to the same results.

The advocate of paroxysmal energy might assume a uniform and fixed rate
of variation in times past and present for the animate world, that is to
say, for the dying-out and coming-in of species, and then endeavor to
prove that the changes of the inanimate world have not gone on in a
corresponding ratio. But the adoption of such a standard of comparison
would lead, I suspect, to a theory by no means favorable to the pristine
intensity of natural causes. That the present state of the organic world
is not stationary, can be fairly inferred from the fact, that some
species are known to have become extinct in the course even of the last
three centuries, and that the exterminating causes always in activity,
both on the land and in the waters, are very numerous; also, because man
himself is an extremely modern creation; and we may therefore reasonably
suppose that some of the mammalia now contemporary with man, as well as
a variety of species of inferior classes, may have been recently
introduced into the earth, to supply the places of plants and animals
which have from time to time disappeared. But granting that some such
secular variation in the zoological and botanical worlds is going on,
and is by no means wholly inappreciable to the naturalist, still it is
certainly far less manifest than the revolution always in progress in
the inorganic world. Every year some volcanic eruptions take place, and
a rude estimate might be made of the number of cubic feet of lava and
scoriæ poured or cast out of various craters. The amount of mud and sand
deposited in deltas, and the advance of new land upon the sea, or the
annual retreat of wasting sea-cliffs, are changes the minimum amount of
which might be roughly estimated. The quantity of land raised above or
depressed below the level of the sea might also be computed, and the
change arising from such movements in a century might be conjectured.
Suppose the average rise of the land in some parts of Scandinavia to be
as much as five feet in a hundred years, the present sea-coast might be
uplifted 700 feet in fourteen thousand years; but we should have no
reason to anticipate, from any zoological data hitherto acquired, that
the molluscous fauna of the northern seas would in that lapse of years
undergo any sensible amount of variation. We discover sea-beaches in
Norway 700 feet high, in which the shells are identical with those now
inhabiting the German Ocean; for the rise of land in Scandinavia,
however insensible to the inhabitants, has evidently been rapid when
compared to the rate of contemporaneous change in the testaceous fauna
of the German Ocean. Were we to wait therefore until the mollusca shall
have undergone as much fluctuation as they underwent between the period
of the Lias and the Upper Oolite formations; or between the Oolite and
Chalk, nay, even between any two of eight subdivisions of the Eocene
series, what stupendous revolutions in physical geography ought we not
to expect, and how many mountain-chains might not be produced by the
repetition of shocks of moderate violence, or by movements not even
perceptible by man!

Or, if we turn from the mollusca to the vegetable kingdom, and ask the
botanist how many earthquakes and volcanic eruptions might be expected,
and how much the relative level of land and sea might be altered, or how
far the principal deltas will encroach upon the ocean, or the sea-cliffs
recede from the present shores, before the species of European
forest-trees will die out, he would reply that such alterations in the
inanimate world might be multiplied indefinitely before he should have
reason to anticipate, by reference to any known data, that the existing
species of trees in our forests would disappear and give place to
others. In a word, the movement of the inorganic world is obvious and
palpable, and might be likened to the minute-hand of a clock, the
progress of which can be seen and heard, whereas the fluctuations of the
living creation are nearly invisible, and resemble the motion of the
hour-hand of a timepiece. It is only by watching it attentively for some
time, and comparing its relative position after an interval, that we can
prove the reality of its motion.[255]




CHAPTER XII.

DIFFERENCE IN TEXTURE OF THE OLDER AND NEWER ROCKS.


  Consolidation of fossiliferous strata--Some deposits originally
    solid--Transition and slaty texture--Crystalline character of
    Plutonic and Metamorphic rocks--Theory of their origin--Essentially
    subterranean--No proofs that they were produced more abundantly at
    remote periods.


Another argument in favor of the dissimilarity of the causes operating
at remote and recent eras has been derived by many geologists from the
more compact, stony, and crystalline texture of the older as compared
with the newer rocks.

_Consolidation of strata._--This subject may be considered, first in
reference to the fossiliferous strata; and, secondly, in reference to
those crystalline and stratified rocks which contain no organic remains,
such as gneiss and mica-schist. There can be no doubt that the former of
these classes, or the fossiliferous, are generally more compact and
stony in proportion as they are more ancient. It is also certain that a
great part of them were originally in a soft and incoherent state, and
that they have been since consolidated. Thus we find occasionally that
shingle and sand have been agglutinated firmly together by a ferruginous
or siliceous cement, or that lime in solution has been introduced, so as
to bind together materials previously incoherent. Organic remains have
sometimes suffered a singular transformation, as for example,] where
shells, corals, and wood are silicified, their calcareous or ligneous
matter having been replaced by nearly pure silica. The constituents of
some beds have probably set and become hard for the first time when they
emerged from beneath the water.

But, on the other hand, we observe in certain formations now in
progress, particularly in coral reefs, and in deposits from the waters
of mineral springs, both calcareous and siliceous, that the texture of
rocks may sometimes be stony from the first. This circumstance may
account for exceptions to the general rule, not unfrequently met with,
where solid strata are superimposed on others of a plastic and
incoherent nature, as in the neighborhood of Paris, where the tertiary
formations, consisting often of compact limestone and siliceous grit,
are more stony than the subjacent chalk.

It will readily be understood, that the various solidifying causes,
including those above enumerated, together with the pressure of
incumbent rocks and the influence of subterranean heat, must all of them
require time in order to exert their full power. If in the course of
ages they modify the aspect and internal structure of stratified
deposits, they will give rise to a general distinctness of character in
the older as contrasted with the newer formations. But this distinctness
will not be the consequence of any original diversity; they will be
unlike, just as the wood in the older trees of a forest usually differs
in texture and hardness from that of younger individuals of the same
species.

_Transition texture_.--In the original classification, of Werner, the
highly crystalline rocks, such as granite and gneiss, which contain no
organic remains, were called primary, and the fossiliferous strata
secondary, while to another class of an age intermediate between the
primary and secondary he gave the name of transition. They were termed
transition because they partook in some degree in their mineral
composition of the nature of the most crystalline rocks, such as gneiss
and mica-schist, while they resembled the fossiliferous series in
containing occasionally organic remains, and exhibiting evident signs of
a mechanical origin. It was at first imagined, that the rocks having
this intermediate texture had been all deposited subsequently to the
series called primary, and before all the more earthy and fossiliferous
formations. But when the relative position and organic remains of these
transition rocks were better understood, it was perceived that they did
not all belong to one period. On the contrary, the same mineral
characters were found in strata of very different ages, and some
formations occurring in the Alps, which several of the ablest scholars
of Werner had determined to be transition, were ultimately ascertained,
by means of their fossil contents and position, to be members of the
Cretaceous, and even of the nummulitic or Eocene period. These strata
had, in fact, acquired the _transition_ texture from the influence of
causes which, since their deposition had modified their internal
arrangement.

_Texture and origin of Plutonic and metamorphic rocks_.--Among the most
singular of the changes superinduced on rocks, we have occasionally to
include the slaty texture, the divisional planes of which sometimes
intersect the true planes of stratification, and even pass directly
through imbedded fossils. If, then, the crystalline, the slaty, and
other modes of arrangement, once deemed characteristic of certain
periods in the history of the earth, have in reality been assumed by
fossiliferous rocks of different ages and at different times, we are
prepared to inquire whether the same may not be true of the most highly
crystalline state, such as that of gneiss, mica-schist, and statuary
marble. That the peculiar characteristics of such rocks are really due
to a variety of modifying causes has long been suspected by many
geologists, and the doctrine has gained ground of late, although a
considerable difference of opinion still prevails. According to the
original Neptunian theory, all the crystalline formations were
precipitated from a universal menstruum or chaotic fluid antecedently to
the creation of animals and plants, the unstratified granite having been
first thrown down so as to serve as a floor or foundation on which
gneiss and other stratified rocks might repose. Afterwards, when the
igneous origin of granite was no longer disputed, many conceived that a
thermal ocean enveloped the globe, at a time when the first-formed crust
of granite was cooling, but when it still retained much of its heat. The
hot waters of this ocean held in solution the ingredients of gneiss,
mica-schist, hornblende-schist, clay-slate, and marble, rocks which were
precipitated, one after the other, in a crystalline form. No fossils
could be inclosed in them, the high temperature of the fluid and the
quantity of mineral matter which it held in solution, rendering it unfit
for the support of organic beings.

It would be inconsistent with the plan of this work to enter here into a
detailed account of what I have elsewhere termed the _metamorphic
theory_;[256] but I may state that it is now demonstrable in some
countries that fossiliferous formations, some of them of the age of the
Silurian strata, as near Christiana in Norway, others belonging to the
Oolitic period, as around Carrara in Italy, have been converted
partially into gneiss, mica-schist, and statuary marble. The
transmutation has been effected apparently by the influence of
subterranean heat, acting under great pressure, or by chemical and
electrical causes operating in a manner not yet understood, and which
have been termed _Plutonic_ action, as expressing, in one word, all the
modifying causes which may be brought into play at great depths, and
under conditions never exemplified at the surface. To this Plutonic
action the fusion of granite itself in the bowels of the earth, as well
as the superinducement of the metamorphic texture into sedimentary
strata, must be attributed; and in accordance with these views the age
of each metamorphic formation may be said to be twofold, for we have
first to consider the period when it originated, as an aqueous deposit,
in the form of mud, sand, marl, or limestone; secondly, the date at
which it acquired a crystalline texture. The same strata, therefore,
may, according to this view, be very ancient in reference to the time of
their deposition, and very modern in regard to the period of their
assuming the metamorphic character.

_No proofs that these crystalline rocks were produced more abundantly at
remote periods_.--Several modern writers, without denying the truth of
the Plutonic or metamorphic theory, still contend that the crystalline
and non-fossiliferous formations, whether stratified or unstratified,
such as gneiss and granite, are essentially ancient as a class of rocks.
They were generated, say they, most abundantly in the primeval state of
the globe, since which time the quantity produced has been always on the
decrease, until it became very inconsiderable in the Oolitic and
Cretaceous periods, and quite evanescent before the commencement of the
tertiary epoch.

Now the justness of these views depends almost entirely on the question
whether granite, gneiss, and other rocks of the same order ever
originated at the surface, or whether, according to the opinions above
adopted, they are essentially subterranean in their origin, and
therefore entitled to the appellation of _hypogene_. If they were formed
superficially in their present state, and as copiously in the modern as
in the more ancient periods, we ought to see a greater abundance of
tertiary and secondary than of primary granite and gneiss; but if we
adopt the hypogene theory before explained, their rapid diminution in
volume among the visible rocks in the earth's crust in proportion as we
investigate the formations of newer date, is quite intelligible. If a
melted mass of matter be now cooling very slowly at the depth of several
miles beneath the crater of an active volcano, it must remain invisible
until great revolutions in the earth's crust have been brought about. So
also if stratified rocks have been subjected to Plutonic action, and
after having been baked or reduced to semi-fusion, are now cooling and
crystallizing far under ground, it will probably require the lapse of
many periods before they will be forced up to the surface and exposed to
view, even at a single point. To effect this purpose there may be need
of as great a development of subterranean movement as that which in the
Alps, Andes, and Himalaya has raised marine strata containing ammonites
to the height of 8000, 14,000, and 16,000 feet. By parity of reasoning
we can hardly expect that any hypogene rocks of the tertiary periods
will have been brought within the reach of human observation, seeing
that the emergence of such rocks must always be so long posterior to the
date of their origin, and still less can formations of this class become
generally visible until so much time has elapsed as to confer on them a
high relative antiquity. Extensive denudation must also combine with
upheaval before they can be displayed at the surface throughout wide
areas.

All geologists who reflect on subterranean movements now going on, and
the eruptions of active volcanoes, are convinced that great changes are
now continually in progress in the interior of the earth's crust far
out of sight. They must be conscious, therefore, that the
inaccessibility of the regions in which these alterations are taking
place, compels them to remain in ignorance of a great part of the
working of existing causes, so that they can only form vague conjectures
in regard to the nature of the products which volcanic heat may
elaborate under great pressure.

But when they find in mountain-chains of high antiquity, that what was
once the interior of the earth's crust has since been forced outwards
and exposed to view, they will naturally expect in the examination of
those mountainous regions, to have an opportunity of gratifying their
curiosity by obtaining a sight not only of the superficial strata of
remote eras, but also of the contemporaneous nether-formed rocks. Having
recognized, therefore, in such mountain-chains some ancient rocks of
aqueous and volcanic origin, corresponding in character to superficial
formations of modern date, they will regard any other class of ancient
rocks, such as granite and gneiss, as the _residual phenomena_ of which
they are in search. These latter rocks will not answer the expectations
previously formed of their probable nature and texture, unless they wear
a foreign and mysterious aspect, and have in some places been fused or
altered by subterranean heat; in a word, unless they differ wholly from
the fossiliferous strata deposited at the surface, or from the lava and
scoriæ thrown out by volcanoes in the open air. It is the total
distinctness, therefore, of crystalline formations, such as granite,
hornblende-schist, and the rest, from every substance of which the
origin is familiar to us, that constitutes their claim to be regarded as
the effects of causes now in action in the subterranean regions. They
belong not to an order of things which has passed away; they are not the
monuments of a primeval period, bearing inscribed upon them in obsolete
characters the words and phrases of a dead language; but they teach us
that part of the living language of nature, which we cannot learn by our
daily intercourse with what passes on the habitable surface.




CHAPTER XIII.

UNIFORMITY IN THE SERIES OF PAST CHANGES IN THE ANIMATE AND INANIMATE
WORLD.


  Supposed alternate periods of repose and disorder--Observed facts in
    which this doctrine has originated--These may be explained by
    supposing a uniform and uninterrupted series of changes--Threefold
    consideration of this subject; first, in reference to the living
    creation, extinction of species, and origin of new animals and
    plants; secondly, in reference to the changes produced in the
    earth's crust by the continuance of subterranean movements in
    certain areas, and their transference after long periods to new
    areas; thirdly, in reference to the laws which govern the formation
    of fossiliferous strata, and the shifting of the areas of
    sedimentary deposition--On the combined influence of all these modes
    and causes of change in producing breaks and chasms in the chain of
    records--Concluding remarks on the identity of the ancient and
    present system of terrestrial changes.


_Origin of the doctrine of alternate periods of repose and
disorder._--It has been truly observed, that when we arrange the
fossiliferous formations in chronological order, they constitute a
broken and defective series of monuments: we pass without any
intermediate gradations, from systems of strata which are horizontal to
other systems which are highly inclined, from rocks of peculiar mineral
composition to others which have a character wholly distinct,--from one
assemblage of organic remains to another, in which frequently all the
species, and most of the genera, are different. These violations of
continuity are so common, as to constitute the rule rather than the
exception, and they have been considered by many geologists as
conclusive in favor of sudden revolutions in the inanimate and animate
world. According to the speculations of some writers, there have been in
the past history of the planet alternate periods of tranquillity and
convulsion, the former enduring for ages, and resembling that state of
things now experienced by man: the other brief, transient, and
paroxysmal, giving rise to new mountains, seas, and valleys,
annihilating one set of organic beings, and ushering in the creation of
another.

It will be the object of the present chapter to demonstrate, that these
theoretical views are not borne out by a fair interpretation of
geological monuments. It is true that in the solid framework of the
globe, we have a chronological chain of natural records, and that many
links in this chain are wanting; but a careful consideration of all the
phenomena will lead to the opinion that the series was originally
defective,--that it has been rendered still more so by time--that a
great part of what remains is inaccessible to man, and even of that
fraction which is accessible, nine-tenths are to this day unexplored.

_How the facts may be explained by assuming a uniform series of
changes._--The readiest way, perhaps, of persuading the reader that we
may dispense with great and sudden revolutions in the geological order
of events, is by showing him how a regular and uninterrupted series of
changes in the animate and inanimate world may give rise to such breaks
in the sequence, and such unconformability of stratified rocks, as are
usually thought to imply convulsions and catastrophes. It is scarcely
necessary to state, that the order of events thus assumed to occur, for
the sake of illustration, must be in harmony with all the conclusions
legitimately drawn by geologists from the structure of the earth, and
must be equally in accordance with the changes observed by man to be now
going on in the living as well as in the inorganic creation. It may be
necessary in the present state of science to supply some part of the
assumed course of nature hypothetically; but if so, this must be done
without any violation of probability, and always consistently with the
analogy of what is known both of the past and present economy of our
system. Although the discussion of so comprehensive a subject must carry
the beginner far beyond his depth, it will also, it is hoped, stimulate
his curiosity, and prepare him to read some elementary treatises on
geology with advantage, and teach him the bearing on that science of the
changes now in progress on the earth. At the same time it may enable him
the better to understand the intimate connection between the second and
third books of this work, the former of which is occupied with the
changes in the inorganic, the latter with those of the organic creation.

In pursuance, then, of the plan above proposed, I shall consider in this
chapter, first, what may be the course of fluctuation in the animate
world; secondly, the mode in which contemporaneous subterranean
movements affect the earth's crust; and, thirdly, the laws which
regulate the deposition of sediment.


UNIFORMITY OF CHANGE CONSIDERED FIRST IN REFERENCE TO THE LIVING
CREATION.

First, in regard to the vicissitudes of the living creation, all are
agreed that the sedimentary strata found in the earth's crust are
divisible into a variety of groups, more or less dissimilar in their
organic remains and mineral composition. The conclusion universally
drawn from the study and comparison of these fossiliferous groups is
this, that at successive periods distinct tribes of animals and plants
have inhabited the land and waters, and that the organic types of the
newer formations are more analogous to species now existing, than those
of more ancient rocks. If we then turn to the present state of the
animate creation, and inquire whether it has now become fixed and
stationary, we discover that, on the contrary, it is in a state of
continual flux--that there are many causes in action which tend to the
extinction of species, and which are conclusive against the doctrine of
their unlimited durability. But natural history has been successfully
cultivated for so short a period, that a few examples only of local, and
perhaps but one or two of absolute, extirpation can as yet be proved,
and these only where the interference of man has been conspicuous. It
will nevertheless appear evident, from the facts and arguments detailed
in the third book (from the thirty-seventh to the forty-second chapters,
inclusive) that man is not the only exterminating agent; and that,
independently of his intervention, the annihilation of species is
promoted by the multiplication and gradual diffusion of every animal or
plant. It will also appear, that every alteration in the physical
geography and climate of the globe cannot fail to have the same
tendency. If we proceed still farther, and inquire whether new species
are substituted from time to time for those which die out, and whether
there are certain laws appointed by the Author of Nature to regulate
such new creations, we find that the period of human observation is as
yet too short to afford data for determining so weighty a question. All
that can be done is to show that the successive introduction of new
species may be a constant part of the economy of the terrestrial system,
without our having any right to expect that we should be in possession
of direct proof of the fact. The appearance again and again of new
species may easily have escaped detection, since the numbers of known
animals and plants have augmented so rapidly within the memory of
persons now living, as to have doubled in some classes, and quadrupled
in others. It will also be remarked in the sequel (book iii. chap. 43),
that it must always be more easy if species proceeded originally from
single stocks, to prove that one which formerly abounded in a given
district has ceased to be, than that another has been called into being
for the first time. If, therefore, there be as yet only one or two
unequivocal instances of extinction, namely, those of the dodo and
solitaire (see ch. 41), it is scarcely reasonable as yet to hope that we
should be cognizant of a single instance of the first appearance of a
new species.

_Recent origin of man, and gradual approach in the tertiary fossils of
successive periods from an extinct to the recent fauna._--The geologist,
however, if required to advance some fact which may lend countenance to
the opinion that in the most modern times, that is to say, after the
greater part of the existing fauna and flora were established on the
earth, there has still been a new species superadded, may point to man
himself as furnishing the required illustration--for man must be
regarded by the geologist as a creature of yesterday, not merely in
reference to the past history of the organic world, but also in relation
to that particular state of the animate creation of which he forms a
part. The comparatively modern introduction of the human race is proved
by the absence of the remains of man and his works, not only from all
strata containing a certain proportion of fossil shells of extinct
species, but even from a large part of the newest strata, in which all
the fossil individuals are referable to species still living.

To enable the reader to appreciate the full force of this evidence, I
shall give a slight sketch of the information obtained from the newer
strata, respecting fluctuations in the animate world, in times
immediately antecedent to the appearance of man.

In tracing the series of fossiliferous formations from the more ancient
to the more modern, the first deposits in which we meet with assemblages
of organic remains, having a near analogy to the fauna of certain parts
of the globe in our own time, are those commonly called tertiary. Even
in the Eocene, or oldest subdivision of these tertiary formations, some
few of the testacea belong to existing species, although almost all of
them, and apparently all the associated vertebrata, are now extinct.
These Eocene strata are succeeded by a great number of more modern
deposits, which depart gradually in the character of their fossils from
the Eocene type, and approach more and more to that of the living
creation. In the present state of science, it is chiefly by the aid of
shells that we are enabled to arrive at these results, for of all
classes the testacea are the most generally diffused in a fossil state,
and may be called the medals principally employed by nature, in
recording the chronology of past events. In the Miocene deposits, which
are next in succession to the Eocene, we begin to find a considerable
number, although still a minority, of recent species, intermixed with
some fossils common to the preceding epoch. We then arrive at the
Pliocene strata, in which species now contemporary with man begin to
preponderate, and in the newest of which nine-tenths of the fossils
agree with species still inhabiting the neighboring sea.

In this passing from the older to the newer members of the tertiary
system we meet with many chasms, but none which separate entirely, by a
broad line of demarcation, one state of the organic world from another.
There are no signs of an abrupt termination of one fauna and flora, and
the starting into life of new and wholly distinct forms. Although we are
far from being able to demonstrate geologically an insensible transition
from the Eocene to the Miocene, or even from the latter to the recent
fauna, yet the more we enlarge and perfect our general survey, the more
nearly do we approximate to such a continuous series, and the more
gradually are we conducted from times when many of the genera and nearly
all the species were extinct, to those in which scarcely a single
species flourished which we do not know to exist at present. Dr. A.
Philippi, indeed, after an elaborate comparison of the fossil tertiary
shells of Sicily with those now living in the Mediterranean, announces
as the result of his examination that there are strata in that island,
which attest a very gradual passage from a period, when only thirteen in
a hundred of the shells were like the species now living in the sea, to
an era when the recent species had attained a proportion of ninety-five
in a hundred. There is therefore evidence, he says, in Sicily of this
revolution in the animate world having been effected "without the
intervention of any convulsion or abrupt changes, certain species having
from time to time died out, and others having been introduced, until at
length the existing fauna was elaborated."

It had often been objected that the evidence of fossil species occurring
in two consecutive formations, was confined to the testacea or
zoophytes, the characters of which are less marked and decisive than
those afforded by the vertebrate animals. But Mr. Owen has lately
insisted on the important fact, that not a few of the quadrupeds which
now inhabit our island, and among others the horse, the ass, the hog,
the smaller wild ox, the goat, the red deer, the roe, the beaver, and
many of the diminutive rodents, are the same as those which once
coexisted with the mammoth, the great northern hippopotamus, two kinds
of rhinoceros, and other mammalia long since extinct. "A part," he
observes, "and not the whole of the modern tertiary fauna has perished,
and hence we may conclude that the cause of their destruction has not
been a violent and universal catastrophe from which none could
escape."[257]

Had we discovered evidence that man had come into the earth at a period
as early as that when a large number of the fossil quadrupeds now
living, and almost all the recent species of land, freshwater, and
marine shells were in existence, we should have been compelled to
ascribe a much higher antiquity to our species, than even the boldest
speculations of the ethnologist require, for no small part of the great
physical revolution depicted on the map of Europe (Pl. 3), before
described, took place very gradually after the recent testacea abounded
almost to the exclusion of the extinct. Thus, for example, in the
deposits called the "northern drift," or the glacial formation of Europe
and North America, the fossil marine shells can easily be identified
with species either now inhabiting the neighboring sea, or living in the
seas of higher latitudes. Yet they exhibit no memorials of the human
race, or of articles fabricated by the hand of man. Some of the newest
of these strata passing by the name of "raised beaches," occur at
moderate elevations on the coast of England, Scotland, and Ireland.
Other examples are met with on a more extended scale in Scandinavia, as
at the height of 200 feet at Uddevalla in Sweden, and at twice that
elevation, near Christiana, in Norway, also at an altitude of 600 or 700
feet in places farther north. They consist of beds of sand and clay,
filling hollows in a district of granite and gneiss, and they must
closely resemble the accumulations of shelly matter now in progress at
the bottom of the Norwegian fiords. The rate at which the land is now
rising in Scandinavia, is far too irregular in different places to
afford a safe standard for estimating the minimum of time required for
the upheaval of the fundamental granite, and its marine shelly
covering, to the height of so many hundred feet; but according to the
greatest average, of five or six feet in a century, the period required
would be very considerable, and nearly the whole of it, as well as the
antecedent epoch of submergence, seems to have preceded the introduction
of man into these parts of the earth.

There are other post-tertiary formations of fluviatile origin, in the
centre of Europe, in which the absence of human remains is perhaps still
more striking, because, when formed, they must have been surrounded by
dry land. I allude to the silt or _loess_ of the basin of the Rhine,
which must have gradually filled up the great valley of that river since
the time when its waters, and the contiguous lands, were inhabited by
the existing species of freshwater and terrestrial mollusks. Showers of
ashes, thrown out by some of the last eruptions of the Eifel volcanoes,
fell during the deposition of this fluviatile silt, and were
interstratified with it. But these volcanoes became exhausted, the
valley was re-excavated through the silt, and again reduced to its
present form before the period of human history. The study, therefore,
of this shelly silt reveals to us the history of a long series of
events, which occurred after the testacea now living inhabited the land
and rivers of Europe, and the whole terminated without any signs of the
coming of man into that part of the globe.

To cite a still more remarkable example, we observe in Sicily a lofty
table-land and hills, sometimes rising to the height of 3000 feet,
capped with a limestone, in which from 70 to 85 per cent. of the fossil
testacea are specifically identical with those now inhabiting the
Mediterranean. These calcareous and other argillaceous strata of the
same age are intersected by deep valleys which have been gradually
formed by denudation, but have not varied materially in width or depth
since Sicily was first colonized by the Greeks. The limestone, moreover,
which is of so late a date in geological chronology, was quarried for
building those ancient temples of Girgenti and Syracuse, of which the
ruins carry us back to a remote era in human history. If we are lost in
conjectures when speculating on the ages required to lift up these
formations to the height of several thousand feet above the sea, how
much more remote must be the era when the same rocks were gradually
formed beneath the waters!

To conclude, it appears that, in going back from the recent to the
Eocene period, we are carried by many successive steps from the fauna
now contemporary with man to an assemblage of fossil species wholly
different from those now living. In this retrospect we have not yet
succeeded in tracing back a perfect transition from the recent to an
extinct fauna; but there are usually so many species in common to the
groups which stand next in succession as to show that there is no great
chasm, no signs of a crisis when one class of organic beings was
annihilated to give place suddenly to another. This analogy, therefore,
derived from a period of the earth's history which can best be compared
with the present state of things, and more thoroughly investigated than
any other, leads to the conclusion that the extinction and creation of
species, has been and is the result of a slow and gradual change in the
organic world.


UNIFORMITY OF CHANGE CONSIDERED, SECONDLY, IN REFERENCE TO SUBTERRANEAN
MOVEMENTS.

To pass on to another of the three topics before proposed for
discussion, the reader will find, in the account given in the second
book of the earthquakes recorded in history, that certain countries
have, from time immemorial, been rudely shaken again and again, while
others, comprising by far the largest part of the globe, have remained
to all appearance motionless. In the regions of convulsion rocks have
been rent asunder, the surface has been forced up into ridges, chasms
have opened, or the ground throughout large spaces has been permanently
lifted up above or let down below its former level. In the regions of
tranquillity some areas have remained at rest, but others have been
ascertained by a comparison of measurements, made at different periods,
to have risen by an insensible motion, as in Sweden, or to have subsided
very slowly, as in Greenland. That these same movements, whether
ascending or descending, have continued for ages in the same direction
has been established by geological evidence. Thus, we find both on the
east and west coast of Sweden, that ground which formerly constituted
the bottom of the Baltic and of the ocean has been lifted up to an
elevation of several hundred feet above high-water mark. The rise within
the historical period has not amounted to many yards, but the greater
extent of antecedent upheaval is proved by the occurrence in inland
spots, several hundred feet high, of deposits filled with fossil shells
of species now living either in the ocean or the Baltic.

To detect proofs of slow and gradual subsidence must in general be more
difficult; but the theory which accounts for the form of circular coral
reefs and lagoon islands, and which will be explained in the last
chapter of the third book, will satisfy the reader that there are spaces
on the globe, several thousand miles in circumference, throughout which
the downward movement has predominated for ages, and yet the land has
never, in a single instance, gone down suddenly for several hundred feet
at once. Yet geology demonstrates that the persistency of subterranean
movements in one direction has not been perpetual throughout all past
time. There have been great oscillations of level by which a surface of
dry land has been submerged to a depth of several thousand feet, and
then at a period long subsequent raised again and made to emerge. Nor
have the regions now motionless been always at rest; and some of those
which are at present the theatres of reiterated earthquakes have
formerly enjoyed a long continuance of tranquillity. But although
disturbances have ceased after having long prevailed, or have
recommenced after a suspension for ages, there has been no universal
disruption of the earth's crust or desolation of the surface since
times the most remote. The non-occurrence of such a general convulsion
is proved by the perfect horizontally now retained by some of the most
ancient fossiliferous strata throughout wide areas.

_Inferences derived from unconformable strata._--That the subterranean
forces have visited different parts of the globe at successive periods,
is inferred chiefly from the unconformability of strata belonging to
groups of different ages. Thus, for example, on the borders of Wales and
Shropshire we find the slaty beds of the ancient Silurian system curved
and vertical, while the beds of the overlying carboniferous shale and
sandstone are horizontal. All are agreed, that in such a case the older
set of strata had suffered great dislocation before the deposition of
the newer or carboniferous beds, and that these last have never since
been convulsed by any movements of excessive violence. But the strata of
the inferior group suffered only a local derangement, and rocks of the
same age are by no means found everywhere in a curved or vertical
position. In various parts of Europe, and particularly near Lake Wener
in the south of Sweden, and in many parts of Russia, beds of the same
Silurian system maintain the most perfect horizontality; and a similar
observation may be made respecting limestones and shales of the like
antiquity in the great lake district of Canada and the United States.
They are still as flat and horizontal as when first formed; yet since
their origin not only have most of the actual mountain-chains been
uplifted, but the very rocks of which those mountains are composed
have been formed.

It would be easy to multiply instances of similar unconformability in
formations of other ages; but a few more will suffice. The coal measures
before alluded to as horizontal on the borders of Wales are vertical in
the Mendip Hills in Somersetshire, where the overlying beds of the New
Red Sandstone are horizontal. Again, in the Wolds of Yorkshire the last
mentioned sandstone supports on its curved and inclined beds the
horizontal Chalk. The Chalk again is vertical on the flanks of the
Pyrenees, and the tertiary strata repose unconformably upon it.

_Consistency of local disturbances with general uniformity._--As almost
every country supplies illustrations of the same phenomena, they who
advocate the doctrine of alternate periods of disorder and repose may
appeal to the facts above described, as proving that every district has
been by turns convulsed by earthquakes and then respited for ages from
convulsions. But so it might with equal truth be affirmed that every
part of Europe has been visited alternately by winter and summer,
although it has always been winter and always summer in some part of the
planet, and neither of these seasons has ever reigned simultaneously
over the entire globe. They have been always shifting about from place
to place; but the vicissitudes which recur thus annually in a single
spot are never allowed to interfere with the invariable uniformity of
seasons throughout the whole planet.

So, in regard to subterranean movements, the theory of the perpetual
uniformity of the force which they exert on the earth's crust is quite
consistent with the admission of their alternate development and
suspension for indefinite periods within limited geographical areas.


UNIFORMITY OF CHANGE CONSIDERED, THIRDLY, IN REFERENCE TO SEDIMENTARY
DEPOSITION.

It now remains to speak of the laws governing the deposition of new
strata. If we survey the surface of the globe we immediately perceive
that it is divisible into areas of deposition and non-deposition, or, in
other words, at any given time there are spaces which are the
recipients, others which are not the recipients of sedimentary matter.
No new strata, for example, are thrown down on dry land, which remains
the same from year to year; whereas, in many parts of the bottom of seas
and lakes, mud, sand, and pebbles are annually spread out by rivers and
currents. There are also great masses of limestone growing in some seas,
or in mid-ocean, chiefly composed of corals and shells.

_No sediment deposited on dry land._--As to the dry land, so far from
being the receptacle of fresh accessions of matter, it is exposed almost
everywhere to waste away. Forests may be as dense and lofty as those of
Brazil, and may swarm with quadrupeds, birds, and insects, yet at the
end of ten thousand years one layer of black mould, a few inches thick,
may be the sole representative of those myriads of trees, leaves,
flowers, and fruits, those innumerable bones and skeletons of birds,
quadrupeds, and reptiles, which tenanted the fertile region. Should this
land be at length submerged, the waves of the sea may wash away in a few
hours the scanty covering of mould, and it may merely impart a darker
shade of color to the next stratum of marl, sand, or other matter newly
thrown down. So also at the bottom of the ocean where no sediment is
accumulating, sea-weed, zoophytes, fish, and even shells, may multiply
for ages and decompose, leaving no vestige of their form or substance
behind. Their decay, in water, although more slow, is as certain and
eventually as complete as in the open air. Nor can they be perpetuated
for indefinite periods in a fossil state, unless imbedded in some matrix
which is impervious to water, or which at least does not allow a free
percolation of that fluid, impregnated as it usually is, with a slight
quantity of carbonic or other acid. Such a free percolation may be
prevented either by the mineral nature of the matrix itself, or by the
superposition of an impermeable stratum: but if unimpeded, the fossil
shell or bone will be dissolved and removed, particle after particle,
and thus entirely effaced, unless petrifaction or the substitution of
mineral for organic matter happen to take place.

That there has been land as well as sea at all former geological
periods, we know from the fact, that fossil trees and terrestrial plants
are imbedded in rocks of every age. Occasionally lacustrine and
fluviatile shells, insects, or the bones of amphibious or land reptiles,
point to the same conclusion. The existence of dry land at all periods
of the past implies, as before mentioned, the partial deposition of
sediment, or its limitation to certain areas; and the next point to
which I shall call the reader's attention, is the shifting of these
areas from one region to another.

First, then, variations in the site of sedimentary deposition are
brought about independently of subterranean movements. There is always a
slight change from year to year, or from century to century. The
sediment of the Rhone, for example, thrown into the Lake of Geneva, is
now conveyed to a spot a mile and a half distant from that where it
accumulated in the tenth century, and six miles from the point where the
delta began originally to form. We may look forward to the period when
this lake will be filled up, and then the distribution of the
transported matter will be suddenly altered, for the mud and sand
brought down from the Alps will thenceforth, instead of being deposited
near Geneva, be carried nearly 200 miles southwards, where the Rhone
enters the Mediterranean.

In the deltas of large rivers, such as those of the Ganges and Indus,
the mud is first carried down for many centuries through one arm, and on
this being stopped up it is discharged by another, and may then enter
the sea at a point 50 or 100 miles distant from its first receptacle.
The direction of marine currents is also liable to be changed by various
accidents, as by the heaping up of new sand-banks, or the wearing away
of cliffs and promontories.

But, secondly, all these causes of fluctuation in the sedimentary areas
are entirely subordinate to those great upward or downward movements of
land which have been already described as prevailing over large tracts
of the globe. By such elevation or subsidence certain spaces are
gradually submerged, or made gradually to emerge:--in the one case
sedimentary deposition may be suddenly renewed after having been
suspended for ages, in the other as suddenly made to cease after having
continued for an indefinite period.

_Causes of variation in mineral character of successive sedimentary
groups._--If deposition be renewed after a long interval, the new strata
will usually differ greatly from the sedimentary rocks previously formed
in the same place, and especially if the older rocks have suffered
derangement, which implies a change in the physical geography of the
district since the previous conveyance of sediment to the same spot. It
may happen, however, that, even when the inferior group is horizontal
and conformable to the upper strata, these last may still differ
entirely in mineral character, because since the origin of the older
formation the geography of some distant country has been altered. In
that country rocks before concealed may have become exposed by
denudation; volcanoes may have burst out and covered the surface with
scoriæ and lava, or new lakes may have been formed by subsidence; and
other fluctuations may have occurred, by which the materials brought
down from thence by rivers to the sea have acquired a distinct mineral
character.

It is well known that the stream of the Mississippi is charged with
sediment of a different color from that of the Arkansas and Red Rivers,
which are tinged with red mud, derived from rocks of porphyry in "the
far west." The waters of the Uruguay, says Darwin, draining a granitic
country, are clear and black, those of the Parana, red.[258] The mud
with which the Indus is loaded, says Burnes, is of a clayey hue, that of
the Chenab, on the other hand, is reddish, that of the Sutlej is more
pale.[259] The same causes which make these several rivers, sometimes
situated at no great distance the one from the other, to differ greatly
in the character of their sediment, will make the waters draining the
same country at different epochs, especially before and after great
revolutions in physical geography, to be entirely dissimilar. It is
scarcely necessary to add, that marine currents will be affected in an
analogous manner in consequence of the formation of new shoals, the
emergence of new islands, the subsidence of others, the gradual waste of
neighboring coasts, the growth of new deltas, the increase of coral
reefs, and other changes.

_Why successive sedimentary groups contain distinct fossils._--If, in
the next place, we assume, for reasons before stated, a continual
extinction of species and introduction of others into the globe, it will
then follow that the fossils of strata formed at two distant periods on
the same spot, will differ even more certainly than the mineral
composition of the same. For rocks of the same kind have sometimes been
reproduced in the same district after a long interval of time, whereas
there are no facts leading to the opinion that species which have once
died out have ever been reproduced. The submergence then of land must be
often attended by the commencement of a new class of sedimentary
deposits, characterized by a new set of fossil animals and plants, while
the reconversion of the bed of the sea into land may arrest at once and
for an indefinite time the formation of geological monuments. Should the
land again sink, strata will again be formed; but one or many entire
revolutions in animal or vegetable life may have been completed in the
interval.

_Conditions requisite for the original completeness of a fossiliferous
series._--If we infer, for reasons before explained, that fluctuations
in the animate world are brought about by the slow and successive
removal and creation of species, we shall be convinced that a rare
combination of circumstances alone can give rise to such a series of
strata as will bear testimony to a gradual passage from one state of
organic life to another. To produce such strata nothing less will be
requisite than the fortunate coincidence of the following conditions:
first, a never-failing supply of sediment in the same region throughout
a period of vast duration; secondly, the fitness of the deposit in every
part for the permanent preservation of imbedded fossils; and, thirdly, a
gradual subsidence to prevent the sea or lake from being filled up and
converted into land.

It will appear in the chapter on coral reefs,[260] that, in certain
parts of the Pacific and Indian Oceans, most of these conditions, if not
all, are complied with, and the constant growth of coral, keeping pace
with the sinking of the bottom of the sea, seems to have gone on so
slowly, for such indefinite periods, that the signs of a gradual change
in organic life might probably be detected in that quarter of the globe,
if we could explore its submarine geology. Instead of the growth of
coralline limestone, let us suppose, in some other place, the continuous
deposition of fluviatile mud and sand, such as the Ganges and
Brahmapootra have poured for thousands of years into the Bay of Bengal.
Part of this bay, although of considerable depth, might at length be
filled up before an appreciable amount of change was effected in the
fish, mollusca, and other inhabitants of the sea and neighboring land.
But, if the bottom be lowered by sinking at the same rate that it is
raised by fluviatile mud, the bay can never be turned into dry land. In
that case one new layer of matter may be superimposed upon another for a
thickness of many thousand feet, and the fossils of the inferior beds
may differ greatly from those entombed in the uppermost, yet every
intermediate gradation may be indicated in the passage from an older to
a newer assemblage of species. Granting, however, that such an unbroken
sequence of monuments may thus be elaborated in certain parts of the
sea, and that the strata happen to be all of them well adapted to
preserve the included fossils from decomposition, how many accidents
must still concur before these submarine formations will be laid open to
our investigation! The whole deposit must first be raised several
thousand feet, in order to bring into view the very foundation; and
during the process of exposure the superior beds must not be entirely
swept away by denudation.

In the first place, the chances are as three to one against the mere
emergence of the mass above the waters, because three-fourths of the
globe are covered by the ocean. But if it be upheaved and made to
constitute part of the dry land, it must also, before it can be
available for our instruction, become part of that area already surveyed
by geologists; and this area comprehends perhaps less than a tenth of
the whole earth. In this small fraction of land already explored, and
still very imperfectly known, we are required to find a set of strata,
originally of limited extent, and probably much lessened by subsequent
denudation.

Yet it is precisely because we do not encounter at every step the
evidence of such gradations from one state of the organic world to
another, that so many geologists embrace the doctrine of great and
sudden revolutions in the history of the animate world. Not content with
simply availing themselves, for the convenience of classification, of
those gaps and chasms which here and there interrupt the continuity of
the chronological series, as at present known, they deduce, from the
frequency of these breaks in the chain of records, an irregular mode of
succession in the events themselves both in the organic and inorganic
world. But, besides that some links of the chain which once existed are
now clearly lost and others concealed from view, we have good reason to
suspect that it was never complete originally. It may undoubtedly be
said, that strata have been always forming somewhere, and therefore at
every moment of past time nature has added a page to her archives; but,
in reference to this subject, it should be remembered that we can never
hope to compile a consecutive history by gathering together monuments
which were originally detached and scattered over the globe. For as the
species of organic beings contemporaneously inhabiting remote regions
are distinct, the fossils of the first of several periods which may be
preserved in any one country, as in America, for example, will have no
connection with those of a second period found in India, and will
therefore no more enable us to trace the signs of a gradual change in
the living creation, than a fragment of Chinese history will fill up a
blank in the political annals of Europe.

The absence of any deposits of importance containing recent shells in
Chili, or anywhere on the western coast of South America, naturally led
Mr. Darwin to the conclusion that "where the bed of the sea is either
stationary or rising, circumstances are far less favorable than where
the level is sinking to the accumulation of conchiferous strata of
sufficient thickness and extension to resist the average vast amount of
denudation."[261] An examination of the superficial clay, sand, and
gravel of the most modern date in Norway and Sweden, where the land is
also rising, would incline us to admit a similar proposition. Yet in
these cases there has been a supply of sediment from the waste of the
coast and the interior, especially in Patagonia and Chili. Nevertheless
wherever the bottom of the sea has been continually elevated, the total
thickness of sedimentary matter accumulating at depths suited to the
habitation of most of the species of shells can never be great, nor can
the deposits be thickly covered by superincumbent matter, so as to be
consolidated by pressure. When they are upheaved, therefore, the waves
on the beach will bear down and disperse the loose materials; whereas if
the bed of the sea subsides slowly, a mass of strata containing
abundance of such species as live at moderate depths may increase in
thickness to any amount, and may extend over a broad area, as the water
gradually encroaches on the land. If, then, at particular periods, as in
the Miocene epoch, for example, both in Europe and North America,
contemporaneous shelly deposits have originated, and have been preserved
at very distant points, it may arise from the prevalence at that period
of simultaneous subsidence throughout very wide areas. The absence in
the same quarters of the globe of strata marking the ages which
immediately succeeded, may be accounted for by supposing that the level
of the bed of the sea and the adjoining land was stationary or was
undergoing slow upheaval.

How far some of the great violations of continuity which now exist in
the chronological table of fossiliferous rocks, will hereafter be
removed or lessened, must at present be mere matter of conjecture. The
hiatus which exists in Great Britain between the fossils of the Lias and
those of the Magnesian Limestone, is supplied in Germany by the rich
fauna and flora of the Muschelkalk, Keuper, and Bunter Sandstein, which
we know to be of a date precisely intermediate; those three formations
being interposed in Germany between others which agree perfectly in
their organic remains with our Lias and Magnesian Limestone. Until
lately the fossils of the Coal-measures were separated from those of the
antecedent Silurian group by a very abrupt and decided line of
demarcation; but recent discoveries have brought to light in Devonshire,
Belgium, the Eifel, and Westphalia, the remains of a fauna of an
intervening period. This connecting link is furnished by the fossil
shells, fish, and corals of the Devonian or Old Red Sandstone group, and
some species of this newly intercalated fauna are found to be common to
it and the subjacent Silurian rocks, while other species belong to it in
common with the Coal-measures. We have also in like manner had some
success of late years in diminishing the hiatus which still separates
the Cretaceous and Eocene periods in Europe. Still we must expect, for
reasons before stated, that some such chasms will forever continue to
occur in some parts of our sedimentary series.

_Consistency of the theory of gradual change with the existence of great
breaks in the series._--To return to the general argument pursued in
this chapter, it is assumed, for reasons above explained, that a slow
change of species is in simultaneous operation everywhere throughout the
habitable surface of sea and land; whereas the fossilization of plants
and animals is confined to those areas where new strata are produced.
These areas, as we have seen, are always shifting their position; so
that the fossilizing process, by means of which the commemoration of the
particular state of the organic world, at any given time, is affected,
may be said to move about, visiting and revisiting different tracts in
succession.

To make still more clear the supposed working of this machinery, I shall
compare it to a somewhat analogous case that might be imagined to occur
in the history of human affairs. Let the mortality of the population of
a large country represent the successive extinction of species, and the
births of new individuals the introduction of new species. While these
fluctuations are gradually taking place everywhere, suppose
commissioners to be appointed to visit each province of the country in
succession, taking an exact account of the number, names, and individual
peculiarities of all the inhabitants, and leaving in each district a
register containing a record of this information. If, after the
completion of one census, another is immediately made on the same plan,
and then another, there will, at last, be a series of statistical
documents in each province. When those belonging to any one province
are arranged in chronological order, the contents of such as stand next
to each other will differ according to the length of the intervals of
time between the taking of each census. If, for example, there are sixty
provinces, and all the registers are made in a single year, and renewed
annually, the number of births and deaths will be so small, in
proportion to the whole of the inhabitants, during the interval between
the compiling of the two consecutive documents, that the individuals
described in such documents will be nearly identical; whereas, if the
survey of each of the sixty provinces occupies all the commissioners for
a whole year, so that they are unable to revisit the same place until
the expiration of sixty years, there will then be an almost entire
discordance between the persons enumerated in two consecutive registers
in the same province. There are, undoubtedly, other causes besides the
mere quantity of time, which may augment or diminish the amount of
discrepancy. Thus, at some periods a pestilential disease may have
lessened the average duration of human life, or a variety of
circumstances may have caused the births to be unusually numerous, and
the population to multiply; or, a province may be suddenly colonized by
persons migrating from surrounding districts.

These exceptions may be compared to the accelerated rate of fluctuation
in the fauna and flora of a particular region, in which the climate and
physical geography may be undergoing an extraordinary degree of
alteration.

But I must remind the reader, that the case above proposed has no
pretensions to be regarded as an exact parallel to the geological
phenomena which I desire to illustrate; for the commissioners are
supposed to visit the different provinces in rotation; whereas the
commemorating processes by which organic remains become fossilized,
although they are always shifting from one area to the other, are yet
very irregular in their movements. They may abandon and revisit many
spaces again and again before they once approach another district; and,
besides this source of irregularity, it may often happen that, while the
depositing process is suspended, denudation may take place, which may be
compared to the occasional destruction by fire or other causes of some
of the statistical documents before mentioned. It is evident that, where
such accidents occur, the want of continuity in the series may become
indefinitely great, and that the monuments which follow next in
succession will by no means be equidistant from each other in point of
time.

If this train of reasoning be admitted, the occasional distinctness of
the fossil remains, in formations immediately in contact, would be a
necessary consequence of the existing laws of sedimentary deposition and
subterranean movement, accompanied by a constant mortality and
renovation of species.

As all the conclusions above insisted on are directly opposed to
opinions still popular, I shall add another comparison, in the hope of
preventing any possible misapprehension of the argument. Suppose we had
discovered two buried cities at the foot of Vesuvius, immediately
superimposed upon each other, with a great mass of tuff and lava
intervening, just as Portici and Resina, if now covered with ashes,
would overlie Herculaneum. An antiquary might possibly be entitled to
infer, from the inscriptions on public edifices, that the inhabitants of
the inferior and older city were Greeks, and those of the modern towns
Italians. But he would reason very hastily if he also concluded from
these data that there had been a sudden change from the Greek to the
Italian language in Campania. But if he afterwards found _three_ buried
cities, one above the other, the intermediate one being Roman, while, as
in the former example, the lowest was Greek and the uppermost Italian,
he would then perceive the fallacy of his former opinion, and would
begin to suspect that the catastrophes by which the cities were inhumed
might have no relation whatever to the fluctuations in the language of
the inhabitants; and that, as the Roman tongue had evidently intervened
between the Greek and Italian, so many other dialects may have been
spoken in succession, and the passage from the Greek to the Italian may
have been very gradual; some terms growing obsolete, while others were
introduced from time to time.

If this antiquary could have shown that the volcanic paroxysms of
Vesuvius were so governed as that cities should be buried one above the
other, just as often as any variation occurred in the language of the
inhabitants, then, indeed, the abrupt passage from a Greek to a Roman,
and from a Roman to an Italian city, would afford proof of fluctuations
no less sudden in the language of the people.

So, in Geology, if we could assume that it is part of the plan of Nature
to preserve, in every region of the globe, an unbroken series of
monuments to commemorate the vicissitudes of the organic creation, we
might infer the sudden extirpation of species, and the simultaneous
introduction of others, as often as two formations in contact are found
to include dissimilar organic fossils. But we must shut our eyes to the
whole economy of the existing causes, aqueous, igneous, and organic, if
we fail to perceive _that such in not the plan of Nature_.

_Concluding remarks on the identity of the ancient and present system of
terrestrial changes._--I shall now conclude the discussion of a question
with which we have been occupied since the beginning of the fifth
chapter; namely, whether there has been any interruption, from the
remotest periods, of one uniform system of change in the animate and
inanimate world. We were induced to enter into that inquiry by
reflecting how much the progress of opinion in Geology had been
influenced by the assumption that the analogy was slight in kind, and
still more slight in degree, between the causes which produced the
former revolutions of the globe, and those now in every-day operation.
It appeared clear that the earlier geologists had not only a scanty
acquaintance with existing changes, but were singularly unconscious of
the amount of their ignorance. With the presumption naturally inspired
by this unconsciousness, they had no hesitation in deciding at once that
time could never enable the existing powers of nature to work out
changes of great magnitude, still less such important revolutions as
those which are brought to light by Geology. They, therefore, felt
themselves at liberty to indulge their imaginations in guessing at what
_might be_, rather than inquiring _what is_; in other words, they
employed themselves in conjecturing what might have been the course of
nature at a remote period, rather than in the investigation of what was
the course of nature in their own times.

It appeared to them more philosophical to speculate on the possibilities
of the past, than patiently to explore the realities of the present; and
having invented theories under the influence of such maxims, they were
consistently unwilling to test their validity by the criterion of their
accordance with the ordinary operations of nature. On the contrary, the
claims of each new hypothesis to credibility appeared enhanced by the
great contrast, in kind or intensity, of the causes referred to, and
those now in operation.

Never was there a dogma more calculated to foster indolence, and to
blunt the keen edge of curiosity, than this assumption of the
discordance between the ancient and existing causes of change. It
produced a state of mind unfavorable in the highest degree to the candid
reception of the evidence of those minute but incessant alterations
which every part of the earth's surface is undergoing, and by which the
condition of its living inhabitants is continually made to vary. The
student, instead of being encouraged with the hope of interpreting the
enigmas presented to him in the earth's structure,--instead of being
prompted to undertake laborious inquiries into the natural history of
the organic world, and the complicated effects of the igneous and
aqueous causes now in operation, was taught to despond from the first.
Geology, it was affirmed, could never rise to the rank of an exact
science,--the greater number of phenomena must forever remain
inexplicable, or only be partially elucidated by ingenious conjectures.
Even the mystery which invested the subject was said to constitute one
of its principal charms, affording, as it did, full scope to the fancy
to indulge in a boundless field of speculation.

The course directly opposed to this method of philosophizing consists in
an earnest and patient inquiry, how far geological appearances are
reconcilable with the effect of changes now in progress, or which may be
in progress in regions inaccessible to us, and of which the reality is
attested by volcanoes and subterranean movements. It also endeavors to
estimate the aggregate result of ordinary operations multiplied by time,
and cherishes a sanguine hope that the resources to be derived from
observation and experiment, or from the study of nature such as she now
is, are very far from-being exhausted. For this reason all theories are
rejected which involve the assumption of sudden and violent catastrophes
and revolutions of the whole earth, and its inhabitants,--theories which
are restrained by no reference to existing analogies, and in which a
desire is manifested to cut, rather than patiently to untie, the Gordian
knot.

We have now, at least, the advantage of knowing, from experience, that
an opposite method has always put geologists on the road that leads to
truth,--suggesting views which, although imperfect at first, have been
found capable of improvement, until at last adopted by universal
consent; while the method of speculating on a former distinct state of
things and causes, has led invariably to a multitude of contradictory
systems, which have been overthrown one after the other,--have been
found incapable of modification,--and which have often required to be
precisely reversed.

The remainder of this work will be devoted to an investigation of the
changes now going on in the crust of the earth and its inhabitants. The
importance which the student will attach to such researches will mainly
depend in the degree of confidence which he feels in the principles
above expounded. If he firmly believes in the resemblance or identity of
the ancient and present system of terrestrial changes, he will regard
every fact collected respecting the causes in diurnal action as
affording him a key to the interpretation of some mystery in the past.
Events which have occurred at the most distant periods in the animate
and inanimate world, will be acknowledged to throw light on each other,
and the deficiency of our information respecting some of the most
obscure parts of the present creation will be removed. For as, by
studying the external configuration of the existing land and its
inhabitants, we may restore in imagination the appearance of the ancient
continents which have passed away, so may we obtain from the deposits of
ancient seas and lakes an insight into the nature of the subaqueous
processes now in operation, and of many forms of organic life, which,
though now existing, are veiled from sight. Rocks, also, produced by
subterranean fire in former ages, at great depths in the bowels of the
earth, present us, when upraised by gradual movements, and exposed to
the light of heaven, with an image of those changes which the
deep-seated volcano may now occasion in the nether regions. Thus,
although we are mere sojourners on the surface of the planet, chained to
a mere point in space, enduring but for a moment of time, the human mind
is not only enabled to number worlds beyond the unassisted ken of mortal
eye, but to trace the events of indefinite ages before the creation of
our race, and is not even withheld from penetrating into the dark
secrets of the ocean, or the interior of the solid globe; free, like the
spirit which the poet described as animating the universe,


                  ----ire per omnes
  Terrasque, tractusque maris, coelumque profundum.





BOOK II.

CHANGES IN THE INORGANIC WORLD.

AQUEOUS CAUSES.




CHAPTER XIV.


  Division of the subject into changes of the organic and inorganic
    world--Inorganic causes of change divided into aqueous and
    igneous--Aqueous causes first considered--Fall of rain--Recent
    rain-prints in mud--Destroying and transporting power of running
    water--Newly formed valleys in Georgia--Sinuosities of rivers--Two
    streams when united do not occupy a bed of double
    surface--Inundations in Scotland--Floods caused by landslips in the
    White Mountains--Bursting of a lake in Switzerland--Devastations
    caused by the Anio at Tivoli--Excavations in the lavas of Etna by
    Sicilian rivers--Gorge of the Simeto--Gradual recession of the
    cataract of Niagara.


_Division of the subject._--Geology was defined to be the science which
investigates the former changes that have taken place in the organic as
well as in the inorganic kingdoms of nature. As vicissitudes in the
inorganic world are most apparent, and as on them all fluctuations in
the animate creation must in a great measure depend, they may claim our
first consideration. The great agents of change in the inorganic world
may be divided into two principal classes, the aqueous and the igneous.
To the aqueous belong Rain, Rivers, Torrents, Springs, Currents, and
Tides; to the igneous, Volcanoes, and Earthquakes. Both these classes
are instruments of decay as well as of reproduction; but they may also
be regarded as antagonist forces. For the aqueous agents are incessantly
laboring to reduce the inequalities of the earth's surface to a level;
while the igneous are equally active in restoring the unevenness of the
external crust, partly by heaping up new matter in certain localities,
and partly by depressing one portion, and forcing out another, of the
earth's envelope.

It is difficult, in a scientific arrangement, to give an accurate view
of the combined effects of so many forces in simultaneous operation;
because, when we consider them separately, we cannot easily estimate
either the extent of their efficacy, or the kind of results which they
produce. We are in danger, therefore, when we attempt to examine the
influence exerted singly by each, of overlooking the modifications which
they produce on one another; and these are so complicated, that
sometimes the igneous and aqueous forces co-operate to produce a joint
effect, to which neither of them unaided by the other could give
rise,--as when repeated earthquakes unite with running water to widen a
valley; or when a thermal spring rises up from a great depth, and
conveys the mineral ingredients with which it is impregnated from the
interior of the earth to the surface. Sometimes the organic combine with
the inorganic causes; as when a reef, composed of shells and corals,
protects one line of coast from the destroying power of tides or
currents, and turns them against some other point; or when drift timber,
floated into a lake, fills a hollow to which the stream would not have
had sufficient velocity to convey earthy sediment.

It is necessary, however, to divide our observations on these various
causes, and to classify them systematically, endeavoring as much as
possible to keep in view that the effects in nature are mixed and not
simple, as they may appear in an artificial arrangement.

In treating, in the first place, of the aqueous causes, we may consider
them under two divisions; first, those which are connected with the
circulation of water from the land to the sea, under which are included
all the phenomena of rain, rivers, glaciers, and springs; secondly,
those which arise from the movements of water in lakes, seas, and the
ocean, wherein are comprised the phenomena of waves, tides, and
currents. In turning our attention to the former division, we find that
the effects of rivers may be subdivided into, first, those of a
destroying and transporting, and, secondly, those of a renovating
nature; in the former are included the erosion of rocks and the
transportation of matter to lower levels; in the renovating class, the
formation of deltas by the influx of sediment, and the shallowing of
seas; but these processes are so intimately related to each other, that
it will not always be possible to consider them under their separate
heads.

_Fall of Rain._--It is well known that the capacity of the atmosphere to
absorb aqueous vapor, and hold it in suspension, increases with every
increment of temperature. This capacity is also found to augment in a
higher ratio than the augmentation of the heat. Hence, as was first
suggested by the geologist, Dr. Hutton, when two volumes of air, of
different temperatures, both saturated with moisture, mingle together,
clouds and rain are produced, for a mean degree of heat having resulted
from the union of the two moist airs, the excess of vapor previously
held in suspension by the warmer of the two is given out, and if it be
in sufficient abundance is precipitated in the form of rain.

As the temperature of the atmosphere diminishes gradually from the
equator towards the pole, the evaporation of water and the quantity of
rain diminish also. According to Humboldt's computation, the average
annual depth of rain at the equator is 96 inches, while in lat. 45° it
is only 29 inches, and in lat. 60° not more than 17 inches. But there
are so many disturbing causes, that the actual discharge, in any given
locality, may deviate very widely from this rule. In England, for
example, where the average fall at London is 24½ inches, as
ascertained at the Greenwich Observatory, there is such irregularity in
some districts, that while at Whitehaven, in Cumberland, there fell in
1849, 32 inches, the quantity of rain in Borrowdale, near Keswick (only
15 miles to the westward), was no less than 142 inches![262] In like
manner, in India, Colonel Sykes found by observations made in 1847 and
1848, that at places situated between 17° and 18° north lat., on a line
drawn across the Western Ghauts in the Deccan, the fall of rain varied
from 21 to 219 inches.[263] The annual average in Bengal is probably
below 80 inches, yet Dr. G. Hooker witnessed at Churrapoonjee, in the
year 1850, a fall of 30 inches in 24 hours, and in the same place during
a residence of six months (from June to November) 530 inches! This
occurred on the south face of the Khasia (or Garrow) mountains in
Eastern Bengal (see map, Chap. XVIII.), where the depth during the whole
of the same year probably exceeded 600 inches. So extraordinary a
discharge of water, which, as we shall presently see, is very local, may
be thus accounted for. Warm, southerly winds, blowing over the Bay of
Bengal, and becoming laden with vapor during their passage, reach the
low level delta of the Ganges and Brahmapootra, where the ordinary heat
exceeds that of the sea, and where evaporation is constantly going on
from countless marshes and the arms of the great rivers. A mingling of
two masses of damp air of different temperatures probably causes the
fall of 70 or 80 inches of rain, which takes place on the plains. The
monsoon having crossed the delta, impinges on the Khasia mountains,
which rise abruptly from the plain to a mean elevation of between 4000
and 5000 feet. Here the wind not only encounters the cold air of the
mountains, but, what is far more effective as a refrigerating cause, the
aerial current is made to flow upwards, and to ascend to a height of
several thousand feet above the sea. Both the air and the vapor
contained in it, being thus relieved of much atmospheric pressure,
expand suddenly, and are cooled by rarefaction. The vapor is condensed,
and about 500 inches of rain are thrown down annually, nearly twenty
times as much as falls in Great Britain in a year, and almost all of it
poured down in six months. The channel of every torrent and river is
swollen at this season, and much sandstone horizontally stratified, and
other rocks are reduced to sand and gravel by the flooded streams. So
great is the superficial waste (or _denudation_), that what would
otherwise be a rich and luxuriantly wooded region, is converted into a
wild and barren moorland.

After the current of warm air has been thus drained of a large portion
of its moisture, it still continues its northerly course to the opposite
flank of the Khasia range, only 20 miles farther north, and here the
fall of rain is reduced to 70 inches in the year. The same wind then
blows northwards across the valley of the Brahmapootra, and at length
arrives so dry and exhausted at the Bhootan Himalaya (lat. 28° N.), that
those mountains, up to the height of 5000 feet, are naked and sterile,
and all their outer valleys arid and dusty. The aerial current still
continuing its northerly course and ascending to a higher region,
becomes further cooled, condensation again ensues, and Bhootan, above
5000 feet, is densely clothed with vegetation.[264]

In another part of India, immediately to the westward, similar phenomena
are repeated. The same warm and humid winds, copiously charged with
aqueous vapor from the Bay of Bengal, hold their course due north for
300 miles across the flat and hot plains of the Ganges, till they
encounter the lofty Sikkim mountains. (See map, Chap. XVIII.) On the
southern flank of these they discharge such a deluge of rain that the
rivers in the rainy season rise twelve feet in as many hours. Numerous
landslips, some of them extending three or four thousand feet along the
face of the mountains, composed of granite, gneiss, and slate, descend
into the beds of streams, and dam them up for a time, causing temporary
lakes, which soon burst their barriers. "Day and night," says Dr.
Hooker, "we heard the crashing of falling trees, and the sound of
boulders thrown violently against each other in the beds of torrents. By
such wear and tear rocky fragments swept down from the hills are in part
converted into sand and fine mud; and the turbid Ganges, during its
annual inundation, derives more of its sediment from this source than
from the waste of the fine clay of the alluvial plains below.[265]

On the verge of the tropics a greater quantity of rain falls annually
than at the equator. Yet parts even of the tropical latitudes are
entirely destitute of rain: Peru, for example, which owes its vegetation
solely to rivers and nightly dews. In that country easterly winds
prevail, blowing from the Pacific, and these being intercepted by the
Andes, and cooled as they rise, are made to part with all their moisture
before reaching the low region to the leeward. The desert zone of North
Africa, between lat. 15° and 30° N., is another instance of a rainless
region. Five or six consecutive years may pass in Upper Egypt, Nubia,
and Dongola, or in the Desert of Sahara, without rain.

From the facts above mentioned, the reader will infer that in the course
of successive geological periods there will be great variations in the
quantity of rain falling in one and the same region. At one time there
may be none whatever during the whole year; at another a fall of 100 or
500 inches; and these two last averages may occur on the two opposite
flanks of a mountain-chain, not more than 20 miles wide. While,
therefore, the valleys in one district are widened and deepened
annually, they may remain stationary in another, the superficial soil
being protected from waste by a dense covering of vegetation. This
diversity depends on many geographical circumstances, but principally on
the height of the land above the sea, the direction of the prevailing
winds, and the relative position, at the time being, of the plains,
hills, and the ocean, conditions all of which are liable in the course
of ages to undergo a complete revolution.

_Recent rain-prints._--When examining, in 1842, the extensive mud-flats
of Nova Scotia, which are exposed at low tide on the borders of the Bay
of Fundy, I observed not only the foot-prints of birds which had
recently passed over the mud, but also very distinct impressions of
rain-drops. A peculiar combination of circumstances renders these
mud-flats admirably fitted to receive and retain any markings which may
happen to be made on their surface. The sediment with which the waters
are charged is extremely fine, being derived from the destruction of
cliffs of red sandstone and shale, and as the tides rise fifty feet and
upwards, large areas are laid dry for nearly a fortnight between the
spring and neap tides. In this interval the mud is baked in summer by a
hot sun, so that it solidifies and becomes traversed by cracks, caused
by shrinkage. Portions of the hardened mud between these cracks may then
be taken up and removed without injury. On examining the edges of each
slab, we observe numerous layers, formed by successive tides, each layer
being usually very thin, sometimes only one-tenth of an inch thick. When
a shower of rain falls, the highest portion of the mud-covered flat is
usually too hard to receive any impressions; while that recently
uncovered by the tide near the water's edge is too soft. Between these
areas a zone occurs, almost as smooth and even as a looking-glass, on
which every drop forms a cavity of circular or oval form, and, if the
shower be transient, these pits retain their shape permanently, being
dried by the sun, and being then too firm to be effaced by the action of
the succeeding tide, which deposits upon them a new layer of mud. Hence
we often find, in splitting open a slab an inch or more thick, on the
upper surface of which the marks of recent rain occur, that an inferior
layer, deposited during some previous rise of the tide, exhibits on its
under side perfect casts of rain-prints, which stand out in relief, the
moulds of the same being seen on the layer below. But in some cases,
especially in the more sandy layers, the markings have been somewhat
blunted by the tide, and by several rain-prints having been joined into
one by a repetition of drops falling on the same spot; in which case the
casts present a very irregular and blistered appearance.

The finest examples which I have seen of these rain-prints were sent to
me by Dr. Webster, from Kentville, on the borders of the Bay of Mines,
in Nova Scotia. They were made by a heavy shower which fell on the 21st
of July, 1849, when the rise and fall of the tides were at their
maximum. The impressions (see fig. 13) consist of cup-shaped or
hemispherical cavities, the average size of which is from one-eighth to
one-tenth of an inch across, but the largest are fully half an inch in
diameter, and one-tenth of an inch deep. The depth is chiefly below the
general surface or plane of stratification, but the walls of the cavity
consist partly of a prominent rim of sandy mud, formed of the matter
which has been forcibly expelled from the pit. All the cavities having
an oval form are deeper at one end, where they have also a higher rim,
and all the deep ends have the same direction, showing towards which
quarter the wind was blowing. Two or more drops are sometimes seen to
have interfered with each other; in which case it is usually possible to
determine which drop fell last, its rim being unbroken.

[Illustration: Fig. 13.

Recent rain-prints, formed July 21, 1849, at Kentville, Bay of Fundy,
Nova Scotia. The arrow represents the direction of the shower.]

On some of the specimens the winding tubular tracks of worms are seen,
which have been bored just beneath the surface (see fig. 13, _left
side_). They occasionally pass under the middle of a rain-mark, having
been formed subsequently. Sometimes the worms have dived beneath the
surface, and then reappeared. All these appearances, both of rain-prints
and worm-tracks, are of great geological interest, as their exact
counterparts are seen in rocks of various ages, even in formations of
very high antiquity.[266] Small cavities, often corresponding in size to
those produced by rain, are also caused by air-bubbles rising up through
sand or mud; but these differ in character from rain-prints, being
usually deeper than they are wide, and having their sides steeper.
These, indeed, are occasionally vertical, or overarching, the opening at
the top being narrower than the pit below. In their mode, also, of
mutual interference they are unlike rain-prints.[267]

In consequence of the effects of mountains in cooling currents of moist
air, and causing the condensation of aqueous vapor in the manner above
described, it follows that in every country, as a general rule, the more
elevated regions become perpetual reservoirs of water, which descends
and irrigates the lower valleys and plains. The largest quantity of
water is first carried to the highest region, and then made to descend
by steep declivities towards the sea; so that it acquires superior
velocity, and removes more soil, than it would do if the rain had been
distributed over the plains and mountains equally in proportion to their
relative areas. The water is also made by these means to pass over the
greatest distances before it can regain the sea.

It has already been observed that in higher latitudes, where the
atmosphere being colder is capable of holding less water in suspension,
a diminished fall of rain takes place. Thus at St. Petersburg, the
amount is only 16 inches, and at Uleaborg in the Gulf of Bothnia (N.
lat. 65°), only 13½ inches, or less than half the average of England,
and even this small quantity descends more slowly in the temperate zone,
and is spread more equally over the year than in tropical climates. But
in reference to geological changes, frost in the colder latitude acts as
a compensating power in the disintegration of rocks, and the
transportation of stones to lower levels.

Water when converted into ice augments in bulk more than one-twentieth
of its volume, and owing to this property it widens the minute crevices
(or _joints_) of rocks into which it penetrates. Ice also in various
ways, as will be shown in the next chapter, gives buoyancy to mud and
sand, even to huge blocks of stone, enabling rivers of moderate size and
velocity to carry them to a great distance.

The mechanical force exerted by running water in undermining cliffs, and
rounding off the angles of hard rock, is mainly due to the intermixture
of foreign ingredients. Sand and pebbles, when hurried along by the
violence of the stream, are thrown against every obstacle lying in their
way, and thus a power of attrition is acquired, capable of wearing
through the hardest siliceous stones, on which water alone could make no
impression.

_Newly formed valleys._--When travelling in Georgia and Alabama, in
1846, I saw in both those States the commencement of hundreds of valleys
in places where the native forest had recently been removed. One of
these newly formed gulleys or ravines is represented in the annexed
woodcut (fig. 14), from a drawing which I made on the spot. It occurs
three miles and a half due west of Milledgeville, the capital of
Georgia, and is situated on the farm of Pomona, on the direct road to
Macon.[268]

Twenty years ago, before the land was cleared, it had no existence; but
when the trees of the forest were cut down, cracks three feet deep were
caused by the sun's heat in the clay; and, during the rains, a sudden
rush of water through the principal crack deepened it at its lower
extremity, from whence the excavating power worked backwards, till, in
the course of twenty years, a chasm, measuring no less than 55 feet in
depth, 300 yards in length, and varying in width from 20 to 180 feet,
was the result. The high road has been several times turned to avoid
this cavity, the enlargement of which is still proceeding, and the old
line of road may be seen to have held its course directly over what is
now the wildest part of the ravine. In the perpendicular walls of this
great chasm appear beds of clay and sand, red, white, yellow, and
green, produced by the decomposition in situ of hornblendic gneiss,
with layers and veins of quartz, which remain entire, to prove that the
whole mass was once solid and crystalline.

[Illustration: Fig. 14.

Ravine on the farm of Pomona, near Milledgeville, Georgia, as it
appeared January, 1846.

Excavated in twenty years, 55 feet deep, and 180 feet broad.]

I infer, from the rapidity of the denudation which only began here after
the removal of the native wood, that this spot, elevated about 600 feet
above the sea, has been always covered with a dense forest, from the
remote time when it first emerged from the sea. The termination of the
cavity on the right hand in the foreground is the head or upper end of
the ravine, and in almost every case, such gulleys are lengthened by the
streams cutting their way backwards. The depth at the upper end is
often, as in this case, considerable, and there is usually at this
point, during floods, a small cascade.

_Sinuosities of rivers._--In proportion as such valleys are widened,
sinuosities are caused by the deflection of the stream first to one
side and then to the other. The unequal hardness of the materials
through which the channel is eroded tends partly to give new directions
to the lateral force of excavation. When by these, or by accidental
shiftings of the alluvial matter in the channel, the current is made to
cross its general line of descent, it eats out a curve in the opposite
bank, or in the side of the hills bounding the valley, from which curve
it is turned back again at an equal angle, so that it recrosses the line
of descent, and gradually hollows out another curve lower down in the
opposite bank, till the whole sides of the valley, or river bed, present
a succession of salient and retiring angles. Among the causes of
deviation from a straight course, by which torrents and rivers tend in
mountainous regions to widen the valleys through which they flow, may be
mentioned the confluence of lateral torrents, swollen irregularly at
different seasons by partial storms, and discharging at different times
unequal quantities of sand, mud, and pebbles, into the main channel.

[Illustration: Fig. 15.]

When the tortuous flexures of a river are extremely great, as often
happens in alluvial plains, the aberration from the direct line of
descent may be restored by the river cutting through the isthmus which
separates two neighboring curves. Thus in the annexed diagram, the
extreme sinuosity of the river has caused it to return for a brief space
in a contrary direction to its main course, so that a peninsula is
formed, and the isthmus (at _a_) is consumed on both sides by currents
flowing in opposite directions. In this case an island is soon
formed,--on either side of which a portion of the stream usually
remains.

_Transporting power of water._--In regard to the transporting power of
water, we may often be surprised at the facility with which streams of a
small size, and descending a slight declivity, bear along coarse sand
and gravel; for we usually estimate the weight of rocks in air, and do
not reflect on their comparative buoyancy when submerged in a denser
fluid. The specific gravity of many rocks is not more than twice that of
water, and very rarely more than thrice, so that almost all the
fragments propelled by a stream have lost a third, and many of them a
half, of what we usually term their weight.

It has been proved by experiment, in contradiction to the theories of
the earlier writers on hydrostatics, to be a universal law, regulating
the motion of running water, that the velocity at the bottom of the
stream is everywhere less than in any part above it, and is greatest at
the surface. Also that the superficial particles in the middle of the
stream move swifter than those at the sides. This retardation of the
lowest and lateral currents is produced by friction; and when the
velocity is sufficiently great, the soil composing the sides and bottom
gives way. A velocity of three inches per second at the bottom is
ascertained to be sufficient to tear up fine clay,--six inches per
second, fine sand,--twelve inches per second, fine gravel,--and three
feet per second, stones of the size of an egg.[269]

When this mechanical power of running water is considered, we are
prepared for the transportation before alluded to of large quantities of
gravel, sand, and mud, by torrents which descend from mountainous
regions. But a question naturally arises, How the more tranquil rivers
of the valleys and plains, flowing on comparatively level ground, can
remove the prodigious burden which is discharged into them by their
numerous tributaries, and by what means they are enabled to convey the
whole mass to the sea? If they had not this removing power, their
channels would be annually choked up, and the valleys of the lower
country, and plains at the base of mountain-chains, would be continually
strewed over with fragments of rock and sterile sand. But this evil is
prevented by a general law regulating the conduct of running
water,--that two equal streams do not, when united, occupy a bed of
double surface. Nay, the width of the principal river, after the
junction of a tributary, sometimes remains the same as before, or is
even lessened. The cause of this apparent paradox was long ago explained
by the Italian writers, who had studied the confluence of the Po and its
feeders in the plains of Lombardy.

The addition of a smaller river augments the velocity of the main
stream, often in the same proportion as it does the quantity of water.
Thus the Venetian branch of the Po swallowed up the Ferranese branch and
that of Panaro without any enlargement of its own dimensions. The cause
of the greater velocity is, first, that after the union of two rivers
the water, in place of the friction of four shores, has only that of two
to surmount; 2dly, because the main body of the stream being farther
distant from the banks, flows on with less interruption; and lastly,
because a greater quantity of water moving more swiftly, digs deeper
into the river's bed. By this beautiful adjustment, the water which
drains the interior country is made continually to occupy less room as
it approaches the sea; and thus the most valuable part of our
continents, the rich deltas and great alluvial plains, are prevented
from being constantly under water.

_River floods in Scotland_, 1829.--Many remarkable illustrations of the
power of running water in moving stones and heavy materials were
afforded by the storm and floods which occurred on the 3d and 4th of
August, 1829, in Aberdeenshire and other counties in Scotland. The
elements during this storm assumed all the characters which mark the
tropical hurricanes; the wind blowing in sudden gusts and whirlwinds,
the lightning and thunder being such as is rarely witnessed in our
climate, and heavy rain falling without intermission. The floods
extended almost simultaneously, and with equal violence over that part
of the northeast of Scotland which would be cut off by two lines drawn
from the head of Lochrannoch, one towards Inverness and the other to
Stonehaven. The united line of the different rivers which were flooded,
could not be less than from five to six hundred miles in length; and the
whole of their courses were marked by the destruction of bridges, roads,
crops, and buildings. Sir T. D. Lauder has recorded the destruction of
thirty-eight bridges, and the entire obliteration of a great number of
farms and hamlets. On the Nairn, a fragment of sandstone, fourteen feet
long by three feet wide and one foot thick, was carried above 200 yards
down the river. Some new ravines were formed on the sides of mountains
where no streams had previously flowed, and ancient river-channels,
which had never been filled from time immemorial, gave passage to a
copious flood.[270]

The bridge over the Dee at Ballater consisted of five arches, having
upon the whole a water-way of 260 feet. The bed of the river, on which
the piers rested, was composed of rolled pieces of granite and gneiss.
The bridge was built of granite, and had stood uninjured for twenty
years; but the different parts were swept away in succession by the
flood, and the whole mass of masonry disappeared in the bed of the
river. "The river Don," observes Mr. Farquharson, in his account of the
inundations, "has upon my own premises forced a mass of four or five
hundred tons of stones, many of them two or three hundred pounds'
weight, up an inclined plane, rising six feet in eight or ten yards, and
left them in a rectangular heap, about three feet deep on a flat
ground:--the heap ends abruptly at its lower extremity."[271]

The power even of a small rivulet, when swollen by rain, in removing
heavy bodies, was exemplified in August, 1827, in the College, a small
stream which flows at a slight declivity from the eastern watershed of
the Cheviot Hills. Several thousand tons' weight of gravel and sand were
transported to the plain of the Till, and a bridge, then in progress of
building, was carried away, some of the arch-stones of which, weighing
from half to three quarters of a ton each, were propelled two miles down
the rivulet. On the same occasion, the current tore away from the
abutment of a mill-dam a large block of greenstone-porphyry, weighing
nearly two tons, and transported it to the distance of a quarter of a
mile. Instances are related as occurring repeatedly, in which from one
to three thousand tons of gravel are, in like manner, removed by this
streamlet to still greater distances in one day.[272]

_Floods caused by landslips_, 1826.--The power which running water may
exert in the lapse of ages, in widening and deepening a valley, does not
so much depend on the volume and velocity of the stream usually flowing
in it, as on the number and magnitude of the obstructions which have, at
different periods, opposed its free passage. If a torrent, however
small, be effectually dammed up, the size of the valley above the
barrier, and its declivity below, and not the dimensions of the torrent,
will determine the violence of the débâcle. The most universal source of
local deluges, are landslips, slides, or avalanches, as they are
sometimes called, when great masses of rock and soil, or sometimes ice
and snow, are precipitated into the bed of a river, the boundary cliffs
of which have been thrown down by the shock of an earthquake, or
undermined by springs or other causes. Volumes might be filled with the
enumeration of instances on record of these terrific catastrophes; I
shall therefore select a few examples of recent occurrence, the facts of
which are well authenticated.

Two dry seasons in the White Mountains, in New Hampshire (United
States), were followed by heavy rains on the 28th August, 1826, when
from the steep and lofty declivities which rise abruptly on both sides
of the river Saco, innumerable rocks and stones, many of sufficient size
to fill a common apartment, were detached, and in their descent swept
down before them, in one promiscuous and frightful ruin, forests,
shrubs, and the earth which sustained them. Although there are numerous
indications on the steep sides of these hills of former slides of the
same kind, yet no tradition had been handed down of any similar
catastrophe within the memory of man, and the growth of the forest on
the very spots now devastated, clearly showed that for a long interval
nothing similar had occurred. One of these moving masses was afterwards
found to have slid three miles, with an average breadth of a quarter of
a mile. The natural excavations commenced generally in a trench a few
yards in depth and a few rods in width, and descended the mountains,
widening and deepening till they became vast chasms. At the base of
these hollow ravines was seen a confused mass of ruins, consisting of
transported earth, gravel, rocks, and trees. Forests of spruce-fir and
hemlock, a kind of fir somewhat resembling our yew in foliage, were
prostrated with as much ease as if they had been fields of grain; for,
where they disputed the ground, the torrent of mud and rock accumulated
behind, till it gathered sufficient force to burst the temporary
barrier.

The valleys of the Amonoosuck and Saco presented, for many miles, an
uninterrupted scene of desolation; all the bridges being carried away,
as well as those over their tributary streams. In some places, the road
was excavated to the depth of from fifteen to twenty feet; in others, it
was covered with earth, rocks, and trees, to as great a height. The
water flowed for many weeks after the flood, as densely charged with
earth as it could be without being changed into mud, and marks were seen
in various localities of its having risen on either side of the valley
to more than twenty-five feet above its ordinary level. Many sheep and
cattle were swept away, and the Willey family, nine in number, who in
alarm had deserted their house, were destroyed on the banks of the Saco;
seven of their mangled bodies were afterwards found near the river,
buried beneath drift-wood and mountain ruins.[273] Eleven years after
the event, the deep channels worn by the avalanches of mud and stone,
and the immense heaps of boulders and blocks of granite in the river
channel, still formed, says Professor Hubbard, a picturesque feature in
the scenery.[274]

When I visited the country in 1845, eight years after Professor Hubbard,
I found the signs of devastation still very striking; I also
particularly remarked that although the surface of the bare granitic
rocks had been smoothed by the passage over them of so much mud and
stone, there were no continuous parallel and rectilinear furrows, nor
any of the fine scratches or striæ which characterize _glacial_ action.
The absence of these is nowhere more clearly exemplified than in the
bare rocks over which passed the great "Willey slide" of 1826.[275]

But the catastrophes in the White Mountains are insignificant, when
compared to those which are occasioned by earthquakes, when the boundary
hills, for miles in length, are thrown down into the hollow of a valley.
I shall have opportunities of alluding to inundations of this kind, when
treating expressly of earthquakes, and shall content myself at present
with selecting an example of a flood due to a different cause.

_Flood in the valley of Bagnes_, 1818.--The valley of Bagnes is one of
the largest of the lateral embranchments of the main valley of the
Rhone, above the Lake of Geneva. Its upper portion was, in 1818,
converted into a lake by the damming up of a narrow pass, by avalanches
of snow and ice, precipitated from an elevated glacier into the bed of
the river Dranse. In the winter season, during continued frost, scarcely
any water flows in the bed of this river to preserve an open channel, so
that the ice barrier remained entire until the melting of the snows in
spring, when a lake was formed above, about half a league in length,
which finally attained in some parts a depth of about two hundred feet,
and a width of about seven hundred feet. To prevent or lessen the
mischief apprehended from the sudden bursting of the barrier, an
artificial gallery, seven hundred feet in length, was cut through the
ice, before the waters had risen to a great height. When at length they
accumulated and flowed through this tunnel, they dissolved the ice, and
thus deepened their channel, until nearly half of the whole contents of
the lake were slowly drained off. But at length, on the approach of the
hot season, the central portion of the remaining mass of ice gave way
with a tremendous crash, and the residue of the lake was emptied in half
an hour. In the course of its descent, the waters encountered several
narrow gorges, and at each of these they rose to a great height, and
then burst with new violence into the next basin, sweeping along rocks,
forests, houses, bridges, and cultivated land. For the greater part of
its course the flood resembled a moving mass of rock and mud, rather
than of water. Some fragments of granitic rocks, of enormous magnitude,
and which from their dimensions, might be compared without exaggeration
to houses, were torn out of a more ancient alluvion, and borne down for
a quarter of a mile. One of the fragments moved was sixty paces in
circumference.[276] The velocity of the water, in the first part of its
course, was thirty-three feet per second, which diminished to six feet
before it reached the Lake of Geneva, where it arrived in six hours and
a half, the distance being forty-five miles.[277]

This flood left behind it, on the plains of Martigny, thousands of trees
torn up by the roots, together with the ruins of buildings. Some of the
houses in that town were filled with mud up to the second story. After
expanding in the plain of Martigny, it entered the Rhone, and did no
farther damage; but some bodies of men, who had been drowned above
Martigny, were afterwards found, at the distance of about thirty miles,
floating on the farther side of the Lake of Geneva, near Vevay.

The waters, on escaping from the temporary lake, intermixed with mud and
rock, swept along, for the first four miles, at the rate of above twenty
miles an hour; and M. Escher, the engineer, calculated that the flood
furnished 300,000 cubic feet of water every second--an efflux which is
five times greater than that of the Rhine below Basle. Now, if part of
the lake had not been gradually drained off, the flood would have been
nearly double, approaching in volume to some of the largest rivers in
Europe. It is evident, therefore, that when we are speculating on the
excavating force which a river may have exerted in any particular
valley, the most important question is, not the volume of the existing
stream, nor the present levels of its channel, nor even the nature of
the rocks, but the probability of a succession of floods at some period
since the time when the valley may have been first elevated above the
sea.

For several months after the débâcle of 1818, the Dranse, having no
settled channel, shifted its position continually from one side to the
other of the valley, carrying away newly-erected bridges, undermining
houses, and continuing to be charged with as large a quantity of earthy
matter as the fluid could hold in suspension. I visited this valley four
months after the flood, and was witness to the sweeping away of a
bridge, and the undermining of part of a house. The greater part of the
ice-barrier was then standing, presenting vertical cliffs 150 feet high,
like ravines in the lava-currents of Etna or Auvergne, where they are
intersected by rivers.

Inundations, precisely similar, are recorded to have occurred at former
periods in this district, and from the same cause. In 1595, for example,
a lake burst, and the waters, descending with irresistible fury,
destroyed the town of Martigny, where from sixty to eighty persons
perished. In a similar flood, fifty years before, 140 persons were
drowned.

_Flood at Tivoli_, 1826.--I shall conclude with one more example derived
from a land of classic recollections, the ancient Tibur, and which,
like all the other inundations above alluded to, occurred within the
present century. The younger Pliny, it will be remembered, describes a
flood on the Anio, which destroyed woods, rocks, and houses, with the
most sumptuous villas and works of arts.[278] For four or five centuries
consecutively, this "headlong stream," as Horace truly called it, has
often remained within its bounds, and then, after so long an interval of
rest, has at different periods inundated its banks again, and widened
its channel. The last of these catastrophes happened 15th Nov. 1826,
after heavy rains, such as produced the floods before alluded to in
Scotland. The waters appear also to have been impeded by an artificial
dike, by which they were separated into two parts, a short distance
above Tivoli. They broke through this dike; and leaving the left trench
dry, precipitated themselves, with their whole weight, on the right
side. Here they undermined, in the course of a few hours, a high cliff,
and widened the river's channel about fifteen paces. On this height
stood the church of St. Lucia, and about thirty-six houses of the town
of Tivoli, which were all carried away, presenting as they sank into the
roaring flood, a terrific scene of destruction to the spectators on the
opposite bank. As the foundations were gradually removed, each building,
some of them edifices of considerable height, was first traversed with
numerous rents, which soon widened into large fissures, until at length
the roofs fell in with a crash, and then the walls sunk into the river,
and were hurled down the cataract below.[279]

The destroying agency of the flood came within two hundred yards of the
precipice on which the beautiful temple of Vesta stands; but fortunately
this precious relic of antiquity was spared, while the wreck of modern
structures was hurled down the abyss. Vesta, it will be remembered, in
the heathen mythology, personified the stability of the earth; and when
the Samian astronomer, Aristarchus, first taught that the earth revolved
on its axis, and round the sun, he was publicly accused of impiety, "for
removing the everlasting Vesta from her place." Playfair observed, that
when Hutton ascribed instability to the earth's surface, and represented
the continents which we inhabit as the theatre of incessant change and
movement, his antagonists, who regarded them as unalterable, assailed
him in a similar manner with accusations founded on religious
prejudices.[280] We might appeal to the excavating power of the Anio as
corroborative of one of the most controverted parts of the Huttonian
theory; and if the days of omens had not gone by, the geologists who now
worship Vesta might regard the late catastrophe as portentous. We may,
at least, recommend the modern votaries of the goddess to lose no time
in making a pilgrimage to her shrine, for the next flood may not respect
the temple.

_Excavation of rocks by running water._--The rapidity with which even
the smallest streams hollow out deep channels in soft and destructible
soils is remarkably exemplified in volcanic countries, where the sand
and half-consolidated tuffs opposed but a slight resistance to the
torrents which descend the mountain-side. After the heavy rains which
followed the eruption of Vesuvius in 1824, the water flowing from the
Atrio del Cavallo cut, in three days, a new chasm through strata of tuff
and ejected volcanic matter, to the depth of twenty-five feet. I found
the old mule-road, in 1828, intersected by this new ravine.

The gradual erosion of deep chasms through some of the hardest rocks, by
the constant passage of running water, charged with foreign matter, is
another phenomenon of which striking examples may be adduced.
Illustrations of this excavating power are presented by many valleys in
central France where the channels of rivers have been barred up by solid
currents of lava, through which the streams have re-excavated a passage,
to the depth of from twenty to seventy feet and upwards, and often of
great width. In these cases there are decisive proofs that neither the
sea, nor any denuding wave or extraordinary body of water, has passed
over the spot since the melted lava was consolidated. Every hypothesis
of the intervention of sudden and violent agency is entirely excluded,
because the cones of _loose_ scoriæ, out of which the lavas flowed, are
oftentimes at no great elevation above the rivers, and have remained
undisturbed during the whole period which has been sufficient for the
hollowing out of such enormous ravines.

_Recent excavation by the Simeto._--But I shall at present confine
myself to examples derived from events which have happened since the
time of history.

[Illustration: Fig. 16.

Recent excavation of lava at the foot of Etna by the river Simeto.]

At the western base of Etna, a current of lava (A A, fig. 16),
descending from near the summit of the great volcano, has flowed to the
distance of five or six miles, and then reached the alluvial plain of
the Simeto, the largest of the Sicilian rivers, which skirts the base of
Etna, and falls into the sea a few miles south of Catania. The lava
entered the river about three miles above the town of Aderno, and not
only occupied its channel for some distance, but, crossing to the
opposite side of the valley, accumulated there in a rocky mass.
Gemmellaro gives the year 1603 as the date of the eruption.[281] The
appearance of the current clearly proves, that it is one of the most
modern of those of Etna; for it has not been covered or crossed by
subsequent streams or ejections, and the olives which had been planted
on its surface were all of small size, when I examined the spot in 1828,
yet they were older than the natural wood on the same lava. In the
course, therefore, of about two centuries, the Simeto has eroded a
passage from fifty to several hundred feet wide, and in some parts from
forty to fifty feet deep.

The portion of lava cut through is in no part porous or scoriaceous, but
consists of a compact homogeneous mass of hard blue rock, somewhat
inferior in weight to ordinary basalt, and containing crystals of
olivine and glassy felspar. The general declivity of this part of the
bed of the Simeto is not considerable; but, in consequence of the
unequal waste of the lava, two water-falls occur at Passo Manzanelli,
each about six feet in height. Here the chasm (B, fig. 16) is about
forty feet deep, and only fifty broad.

The sand and pebbles in the river-bed consist chiefly of a brown
quartzose sandstone, derived from the upper country; but the materials
of the volcanic rock itself must have greatly assisted the attrition.
This river, like the Caltabiano on the eastern side of Etna, has not yet
cut down to the ancient bed of which it was dispossessed, and of which
the probable position is indicated in the annexed diagram (C, fig. 16).

On entering the narrow ravine where the water foams down the two
cataracts, we are entirely shut out from all view of the surrounding
country; and a geologist who is accustomed to associate the
characteristic features of the landscape with the relative age of
certain rocks, can scarcely dissuade himself from the belief that he is
contemplating a scene in some rocky gorge of a primary district. The
external forms of the hard blue lava are as massive as any of the most
ancient trap-rocks of Scotland. The solid surface is in some parts
smoothed and almost polished by attrition, and covered in others with a
white lichen, which imparts to it an air of extreme antiquity, so as
greatly to heighten the delusion. But the moment we reascend the cliff
the spell is broken; for we scarcely recede a few paces, before the
ravine and river disappear, and we stand on the black and rugged surface
of a vast current of lava, which seems unbroken, and which we can trace
up nearly to the distant summit of that majestic cone which Pindar
called "the pillar of heaven," and which still continues to send forth a
fleecy wreath of vapor, reminding us that its fires are not extinct, and
that it may again give out a rocky stream, wherein other scenes like
that now described may present themselves to future observers.

[Illustration: Fig. 17. Lake Erie. The Falls.

Limestone Shale.

Lewiston. Niagara River. Queenstown.]

_Falls of Niagara._--The falls of Niagara afford a magnificent example
of the progressive excavation of a deep valley in solid rock. That river
flows over a flat table-land, in a depression of which Lake Erie is
situated. Where it issues from the lake, it is nearly a mile in width,
and 330 feet above Lake Ontario, which is about 30 miles distant. For
the first fifteen miles below Lake Erie the surrounding country,
comprising Upper Canada on the west, and the state of New York on the
east, is almost on a level with its banks, and nowhere more than thirty
or forty feet above them.[282] (See fig. 17.) The river being
occasionally interspersed with low wooded islands, and having sometimes
a width of three miles, glides along at first with a clear, smooth, and
tranquil current, falling only fifteen feet in as many miles, and in
this part of its course resembling an arm of Lake Erie. But its
character is afterwards entirely changed, on approaching the Rapids,
where it begins to rush and foam over a rocky and uneven limestone
bottom, for the space of nearly a mile, till at length it is thrown down
perpendicularly 165 feet at the Falls. Here the river is divided into
two sheets of water by an island, the largest cataract being more than a
third of a mile broad, the smaller one having a breadth of six hundred
feet. When the water has precipitated itself into an unfathomable pool,
it rushes with great velocity down the sloping bottom of a narrow chasm,
for a distance of seven miles. This ravine varies from 200 to 400 yards
in width from cliff to cliff; contrasting, therefore, strongly in its
breadth with that of the river above. Its depth is from 200 to 300 feet,
and it intersects for about seven miles the table-land before described,
which terminates suddenly at Queenstown in an escarpment or long line of
inland cliff facing northwards, towards Lake Ontario. The Niagara, on
reaching the escarpment and issuing from the gorge, enters the flat
country, which is so nearly on a level with Lake Ontario, that there is
only a fall of about four feet in the seven additional miles which
intervene between Queenstown and the shores of that lake.

It has long been the popular belief that the Niagara once flowed in a
shallow valley across the whole platform, from the present site of the
Falls to the escarpment (called the Queenstown heights), where it is
supposed that the cataract was first situated, and that the river has
been slowly eating its way backwards through the rocks for the distance
of seven miles. This hypothesis naturally suggests itself to every
observer, who sees the narrowness of the gorge at its termination, and
throughout its whole course, as far up as the Falls, above which point
the river expands as before stated. The boundary cliffs of the ravine
are usually perpendicular, and in many places undermined on one side by
the impetuous stream. The uppermost rock of the table-land at the Falls
consists of hard limestone (a member of the Silurian series), about
ninety feet thick, beneath which lie soft shales of equal thickness,
continually undermined by the action of the spray, which rises from the
pool into which so large a body of water is projected, and is driven
violently by gusts of wind against the base of the precipice. In
consequence of this action, and that of frost, the shale disintegrates
and crumbles away, and portions of the incumbent rock overhang 40 feet,
and often when unsupported tumble down, so that the Falls do not remain
absolutely stationary at the same spot, even for half a century.
Accounts have come down to us, from the earliest period of observation,
of the frequent destruction of these rocks, and the sudden descent of
huge fragments in 1818 and 1828, are said to have shaken the adjacent
country like an earthquake. The earliest travellers, Hennepin and Kalm,
who in 1678 and 1751 visited the Falls, and published views of them,
attest the fact, that the rocks have been suffering from dilapidation
for more than a century and a half, and that some slight changes, even
in the scenery of the cataract have been brought about within that time.
The idea, therefore, of perpetual and progressive waste is constantly
present to the mind of every beholder; and as that part of the chasm,
which has been the work of the last hundred and fifty years resembles
precisely, in depth, width, and character, the rest of the gorge which
extends seven miles below, it is most natural to infer, that the entire
ravine has been hollowed out in the same manner, by the recession of the
cataract.

It must at least be conceded, that the river supplies an adequate cause
for executing the whole task thus assigned to it, provided we grant
sufficient time for its completion. As this part of the country was a
wilderness till near the end of the last century, we can obtain no
accurate data for estimating the exact rate at which the cataract has
been receding. Mr. Bakewell, son of the eminent geologist of that name,
who visited the Niagara in 1829, made the first attempt to calculate
from the observations of one who had lived forty years at the Falls, and
who had been the first settler there, that the cataract had during that
period gone back about a yard annually. But after the most careful
inquiries which I was able to make, during my visit to the spot in
1841-2, I came to the conclusion that the average of one foot a year
would be a much more probable conjecture. In that case, it would have
required thirty-five thousand years for the retreat of the Falls, from
the escarpment of Queenstown to their present site. It seems by no means
improbable that such a result would be no exaggeration of the truth,
although we cannot assume that the retrograde movement has been uniform.
An examination of the geological structure of the district, as laid open
in the ravine, shows that at every step in the process of excavation,
the height of the precipice, the hardness of the materials at its base,
and the quantity of fallen matter to be removed, must have varied. At
some points it may have receded much faster than at present, but in
general its progress was probably slower, because the cataract, when it
began to recede, must have had nearly twice its present height.

From observations made by me in 1841, when I had the advantage of being
accompanied by Mr. Hall, state geologist of New York, and in 1842, when
I re-examined the Niagara district, I obtained geological evidence of
the former existence of an old river-bed, which, I have no doubt,
indicates the original channel through which the waters once flowed from
the Falls to Queenstown, at the height of nearly three hundred feet
above the bottom of the present gorge. The geological monuments alluded
to, consist of patches of sand and gravel, forty feet thick, containing
fluviatile shells of the genera Unio, Cyclas, Melania, &c., such as now
inhabit the waters of the Niagara above the Falls. The identity of the
fossil species with the recent is unquestionable, and these freshwater
deposits occur at the edge of the cliffs bounding the ravine, so that
they prove the former extension of an elevated shallow valley, four
miles below the falls, a distinct prolongation of that now occupied by
the Niagara, in the elevated region intervening between Lake Erie and
the Falls. Whatever theory be framed for the hollowing out of the ravine
further down, or for the three miles which intervene between the
whirlpool and Queenstown, it will always be necessary to suppose the
former existence of a barrier of _rock_, not of loose and destructible
materials, such as those composing the drift in this district, somewhere
immediately below the whirlpool. By that barrier the waters were held
back for ages, when the fluviatile deposit, 40 feet in thickness, and
250 feet above the present channel of the river, originated. If we are
led by this evidence to admit that the cataract has cut back its way for
four miles, we can have little hesitation in referring the excavation of
the remaining three miles below to a like agency, the shape of the chasm
being precisely similar.

There have been many speculations respecting the future recession of the
Falls, and the deluge that might be occasioned by the sudden escape of
the waters of Lake Erie, if the ravine should ever be prolonged 16 miles
backwards. But a more accurate knowledge of the geological succession of
the rocks, brought to light by the State Survey, has satisfied every
geologist that the Falls would diminish gradually in height before they
travelled back two miles, and in consequence of a gentle dip of the
strata to the south, the massive limestone now at the top would then be
at their base, and would retard, and perhaps put an effectual stop to,
the excavating process.




CHAPTER XV.

TRANSPORTATION OF SOLID MATTER BY ICE.


  Carrying power of river-ice--Rocks annually conveyed into the St.
    Lawrence by its tributaries--Ground-ice; its origin and transporting
    power--Glaciers--Theory of their downward movement--Smoothed and
    grooved rocks--The moraine unstratified--Icebergs covered with mud
    and stones--Limits of glaciers and icebergs--Their effects on the
    bottom when they run aground--Packing of coast-ice--Boulders drifted
    by ice on coast of Labrador--Blocks moved by ice in the Baltic.


The power of running water to carry sand, gravel, and fragments of rock
to considerable distances is greatly augmented in those regions where,
during some part of the year, the frost is of sufficient intensity to
convert the water, either at the surface or bottom of rivers, into ice.

This subject may be considered under three different heads:--first, the
effect of surface-ice and ground-ice in enabling streams to remove
gravel and stones to a distance; secondly, the action of glaciers in the
transport of boulders, and in the polishing and scratching of rocks;
thirdly, the floating off of glaciers charged with solid matter into the
sea, and the drifting of icebergs and coast-ice.

_River-ice._--Pebbles and small pieces of rock may be seen entangled in
ice, and floating annually down the Tay in Scotland, as far as the mouth
of that river. Similar observations might doubtless be made respecting
almost all the larger rivers of England and Scotland; but there seems
reason to suspect that the principal transfer from place to place of
pebbles and stones adhering to ice goes on unseen by us under water. For
although the specific gravity of the compound mass may cause it to sink,
it may still be very buoyant, and easily borne along by a feeble
current. The ice, moreover, melts very slowly at the bottom of running
streams in winter, as the water there is often nearly at the freezing
point, as will be seen from what will be said in the sequel of
ground-ice.

As we traverse Europe in the latitudes of Great Britain, we find the
winters more severe, and the rivers more regularly frozen over. M.
Lariviere relates that, being at Memel on the Baltic in 1821, when the
ice of the river Niemen broke up, he saw a mass of ice thirty feet long
which had descended the stream, and had been thrown ashore. In the
middle of it was a triangular piece of granite, about a yard in
diameter, resembling in composition the red granite of Finland.[283]

When rivers in the northern hemisphere flow from south to north, the ice
first breaks up in the higher part of their course, and the flooded
waters, bearing along large icy fragments, often arrive at parts of the
stream which are still firmly frozen over. Great inundations are thus
frequently occasioned by the obstructions thrown in the way of the
descending waters, as in the case of the Mackenzie in North America, and
the Irtish, Obi, Yenesei, Lena, and other rivers of Siberia. (See map,
fig. 1, p. 79.) A partial stoppage of this kind lately occurred (Jan.
31, 1840) in the Vistula, about a mile and a half above the city of
Dantzic, where the river, choked up by packed ice, was made to take a
new course over its right bank, so that it hollowed out in a few days a
deep and broad channel, many leagues in length, through a tract of
sand-hills which were from 40 to 60 feet high.

In Canada, where the winter's cold is intense, in a latitude
corresponding to that of central France, several tributaries of the St.
Lawrence begin to thaw in their upper course, while they remain frozen
over lower down, and thus large slabs of ice are set free and thrown
upon the unbroken sheet of ice below. Then begins what is called the
packing of the drifted fragments; that is to say, one slab is made to
slide over another, until a vast pile is built up, and the whole being
frozen together, is urged onwards by the force of the dammed up waters
and drift-ice. Thus propelled, it not only forces along boulders, but
breaks off from cliffs, which border the rivers, huge pieces of
projecting rock. By this means several buttresses of solid masonry,
which, up to the year 1836, supported a wooden bridge on the St.
Maurice, which falls into the St. Lawrence, near the town of Trois
Rivières, lat. 46° 20', were thrown down, and conveyed by the ice into
the main river; and instances have occurred at Montreal of wharfs and
stone-buildings, from 30 to 50 feet square, having been removed in a
similar manner. We learn from Captain Bayfield that anchors laid down
within high-water mark, to secure vessels hauled on shore for the
winter, must be cut out of the ice on the approach of spring, or they
would be carried away. In 1834, the Gulnare's bower-anchor, weighing
half a ton, was transported some yards by the ice, and so firmly was it
fixed, that the force of the moving ice broke a chain-cable suited for a
10-gun brig, and which had rode the Gulnare during the heaviest gales in
the gulf. Had not this anchor been cut out of the ice, it would have
been earned into deep water and lost.[284]

[Illustration: PLATE II.

BOULDERS DRIFTED BY ICE ON SHORES OF THE ST. LAWRENCE

View taken by Lieut. Bowen, from the N. E., in the Spring of 1835, at
Richelieu Rapid, lat. 46° N.]

The scene represented in the annexed plate (pl. 2), from a drawing by
Lieutenant Bowen, R. N., will enable the reader to comprehend the
incessant changes which the transport of boulders produces annually on
the low islands, shores, and bed of the St. Lawrence above Quebec. The
fundamental rocks at Richelieu Rapid, situated in lat. 46° N., are
limestone and slate, which are seen at low-water to be covered with
boulders of granite. These boulders owe their spheroidal form chiefly to
weathering, or action of frost, which causes the surface to exfoliate
in concentric plates, so that all the more prominent angles are removed.
At the point _a_ is a cavity in the mud or sand of the beach, now filled
with water, which was occupied during the preceding winter (1835) by the
huge erratic _b_, a mass of granite, 70 tons' weight, found in the
spring following (1836) at a distance of several feet from its former
position. Many small islands are seen on the river, such as _c d_, which
afford still more striking proofs of the carrying and propelling power
of ice. These islets are never under water, yet every winter ice is
thrown upon them in such abundance, that it _packs_ to the height of 20,
and even 30 feet, bringing with it a continual supply of large stones or
boulders, and carrying away others; the greatest number being deposited,
according to Lieutenant Bowen, on the edge of deep water. On the island
_d_, on the left of the accompanying view, a lighthouse is represented,
consisting of a square wooden building, which having no other foundation
than the boulders, requires to be taken down every winter, and rebuilt
on the reopening of the river.

These effects of frost, which are so striking on the St. Lawrence above
Quebec, are by no means displayed on a smaller scale below that city,
where the gulf rises and falls with the tide. On the contrary; it is in
the estuary, between the latitudes 47° and 49°, that the greatest
quantity of gravel and boulders of large dimensions are carried down
annually towards the sea. Here the frost is so intense, that a dense
sheet of ice is formed at low water, which, on the rise of the tide, is
lifted up, broken, and thrown in heaps on the extensive shoals which
border the estuary. When the tide recedes, this packed ice is exposed to
a temperature sometimes 30° below zero, which freezes together all the
loose pieces of ice, as well as the granitic and other boulders. The
whole of these are often swept away by a high tide, or when the river is
swollen by the melting of the snow in Spring. One huge block of granite,
15 feet long by 10 feet both in width and height, and estimated to
contain 1500 cubic feet, was conveyed in this manner to some distance in
the year 1837, its previous position being well known, as up to that
time it had been used by Captain Bayfield as a mark for the surveying
station.

_Ground-ice._--When a current of cold air passes over the surface of a
lake or stream it abstracts from it a quantity of heat, and the specific
gravity of the water being thereby increased, the cooled portion sinks.
This circulation may continue until the whole body of fluid has been
cooled down to the temperature of 40° F., after which, if the cold
increase, the vertical movement ceases, the water which is uppermost
expands and floats over the heavier fluid below, and when it has
attained a temperature of 32° Fahr. it sets into a sheet of ice. It
should seem therefore impossible, according to this law of congelation,
that ice should ever form at the bottom of a river; and yet such is the
fact, and many speculations have been hazarded to account for so
singular a phenomenon. M. Arago is of opinion that the mechanical action
of a running stream produces a circulation by which the entire body of
water is mixed up together, and cooled alike, and the whole being thus
reduced to the freezing point, ice begins to form at the bottom for two
reasons, first, because there is less motion there, and secondly,
because the water is in contact with solid rock or pebbles which have a
cold surface.[285] Whatever explanation we adopt, there is no doubt of
the fact, that in countries where the intensity and duration of the cold
is great, rivers and torrents acquire an increase of carrying power by
the formation of what is called ground-ice. Even in the Thames we learn
from Dr. Plott that pieces of this kind of ice, having gravel frozen on
to their under side, rise up from the bottom in winter, and float on the
surface. In the Siberian rivers, Weitz describes large stones as having
been brought up from the river's bed in the same manner, and made to
float.[286]

_Glaciers._--In the temperate zone, the snow lies for months in winter
on the summit of every high mountain, while in the arctic regions, a
long summer's day of half a year's duration is insufficient to melt the
snow, even on land just raised above the level of the sea. It is
therefore not surprising, since the atmosphere becomes colder in
proportion as we ascend in it, that there should be heights, even in
tropical countries, where the snow never melts. The lowest limit to
which the perpetual snow extends downwards, from the tops of mountains
at the equator, is an elevation of not less than 16,000 feet above the
sea; while in the Swiss Alps, in lat. 46° N. it reaches as low as 8,500
feet above the same level, the loftier peaks of the Alpine chain being
from 12,000 to 15,000 feet high. The frozen mass augmenting from year to
year would add indefinitely to the altitude of alpine summits, were it
not relieved by its descent through the larger and deeper valleys to
regions far below the general snow-line. To these it slowly finds its
way in the form of rivers of ice, called glaciers, the consolidation of
which is produced by pressure, and by the congelation of water
infiltered into the porous mass, which is always undergoing partial
liquefaction, and receiving in summer occasional showers of rain on its
surface. In a day of hot sunshine, or mild rain, innumerable rills of
pure and sparkling water run in icy channels along the surface of the
glaciers, which in the night shrink, and come to nothing. They are often
precipitated in bold cascades into deep fissures in the ice, and
contribute together with springs to form torrents, which flow in tunnels
at the bottom of the glaciers for many a league, and at length issue at
their extremities, from beneath beautiful caverns or arches. The waters
of these streams are always densely charged with the finest mud,
produced by the grinding of rock and sand under the weight of the moving
mass. (See fig. 18.)

[Illustration: Fig 18.

Glacier with medial and lateral moraines and with terminal cave.]

The length of the Swiss glaciers is sometimes twenty miles, their width
in the middle portion, where they are broadest, occasionally two or
three miles; their depth or thickness sometimes more than 600 feet. When
they descend steep slopes, and precipices, or are forced through narrow
gorges, the ice is broken up, and assumes the most fantastic and
picturesque forms, with lofty peaks and pinnacles, projecting above the
general level. These snow-white masses are often relieved by a dark
background of pines, as in the valley of Chamouni; and are not only
surrounded with abundance of the wild rhododendron in full flower, but
encroach still lower into the region of cultivation, and trespass on
fields where the tobacco-plant is flourishing by the side of the
peasant's hut.

The cause of glacier motion has of late been a subject of careful
investigation and much keen controversy. Although a question of physics,
rather than of geology, it is too interesting to allow me to pass it by
without some brief mention. De Saussure, whose travels in the Alps are
full of original observations, as well as sound and comprehensive
general views, conceived that the weight of the ice might be sufficient
to urge it down the slope of the valley, if the sliding motion were
aided by the water flowing at the bottom. For this "gravitation theory"
Charpentier, followed by Agassiz, substituted the hypothesis of
dilatation. The most solid ice is always permeable to water, and
penetrated by innumerable fissures and capillary tubes, often extremely
minute. These tubes imbibe the aqueous fluid during the day, which
freezes, it is said, in the cold of the night, and expands while in the
act of congelation. The distension of the whole mass exerts an immense
force, tending to propel the glacier in the direction of least
resistance--"in other words, down the valley." This theory was opposed
by Mr. Hopkins on mathematical and mechanical grounds, in several able
papers. Among other objections, he pointed out that the friction of so
enormous a body as a glacier on its bed is so great, that the vertical
direction would always be that of least resistance, and if a
considerable distension of the mass should take place, by the action of
freezing, it would tend to increase its thickness, rather than
accelerate its downward progress. He also contended (and his arguments
were illustrated by many ingenious experiments), that a glacier can move
along an extremely slight slope, solely by the influence of gravitation,
owing to the constant dissolution of ice in contact with the rocky
bottom, and the number of separate fragments into which the glacier is
divided by fissures, so that freedom of motion is imparted to its
several parts somewhat resembling that of an imperfect fluid. To this
view Professor James Forbes objected, that gravitation would not supply
an adequate cause for the sliding of solid ice down slopes having an
inclination of no more than four or five degrees, still less would it
explain how the glacier advances where the channel expands and
contracts. The Mer de Glace in Chamouni, for example, after being 2000
yards wide, passes through a strait only 900 yards in width. Such a
gorge, it is contended, would be choked up by the advance of any solid
mass, even if it be broken up into numerous fragments. The same acute
observer remarked, that water in the fissures and pores of glaciers
cannot, and does not part with its latent heat, so as to freeze every
night to a great depth, or far in the interior of the mass. Had the
dilatation theory been true, the chief motion of the glacier would have
occurred about sunset, when the freezing of the water must be greatest,
and it had, in fact, been at first assumed by those who favored that
hypothesis, that the mass moved faster at the sides, where the melting
of ice was promoted by the sun's heat, reflected from boundary
precipices.

Agassiz appears to have been the first to commence, in 1841, aided by a
skilful engineer, M. Escher de la Linth, a series of exact measurements
to ascertain the laws of glacier motion, and he soon discovered,
contrary to his preconceived notions, that the stream of ice moved more
slowly at the sides than at the centre, and faster in the middle region
of the glacier than at its extremity.[287] Professor James Forbes, who
had joined Mr. Agassiz during his earlier investigations in the Alps,
undertook himself an independent series of experiments, which he
followed up with great perseverance, to determine the laws of glacier
motion. These he found to agree very closely with the laws governing the
course of rivers, their progress being greater in the centre than at the
sides, and more rapid at the surface than at the bottom. This fact was
verified by carefully fixing a great number of marks in the ice,
arranged in a straight line, which gradually assumed a beautiful curve,
the middle part pointing down the glacier, and showing a velocity there,
double or treble that of the lateral parts.[288] He ascertained that the
rate of advance by night was nearly the same as by day, and that even
the hourly march of the icy stream could be detected, although the
progress might not amount to more than six or seven inches in twelve
hours. By the incessant though invisible advance of the marks placed on
the ice, "time," says Mr. Forbes, "was marked out as by a shadow on a
dial, and the unequivocal evidence which I obtained, that even while
walking on a glacier we are, day by day, and hour by hour, imperceptibly
carried on by the resistless flow of the icy stream, filled me with
admiration." (Travels in the Alps, p. 133.) In order to explain this
remarkable regularity of motion, and its obedience to laws so strictly
analogous to those of fluids, the same writer proposed the theory that
the ice, instead of being solid and compact, is a viscous or plastic
body, capable of yielding to great pressure, and the more so in
proportion as its temperature is higher, and as it approaches more
nearly to the melting point. He endeavors to show that this hypothesis
will account for many complicated phenomena, especially for a ribboned
or veined structure which is everywhere observable in the ice, and might
be produced by lines of discontinuity, arising from the different rates
at which the various portions of the semi-rigid glacier advance and pass
each other. Many examples are adduced to prove that a glacier can model
itself to the form of the ground over which it is forced, exactly as
would happen if it possessed a certain ductility, and this power of
yielding under intense pressure, is shown not to be irreconcilable with
the idea of the ice being sufficiently compact to break into fragments,
when the strain upon its parts is excessive; as where the glacier turns
a sharp angle, or descends upon a rapid or convex slope. The increased
velocity in summer is attributed partly to the greater plasticity of the
ice, when not exposed to intense cold, and partly to the hydrostatic
pressure of the water in the capillary tubes, which imbibe more of this
liquid in the hot season.

On the assumption of the ice being a rigid mass, Mr. Hopkins attributed
the more rapid motions in the centre to the unequal rate at which the
broad stripes of ice, intervening between longitudinal fissures,
advance; but besides that there are parts of the glacier where no such
fissures exist, such a mode of progression, says Mr. Forbes, would cause
the borders of large transverse rents or "crevasses," to be jagged like
a saw, instead of being perfectly even and straight-edged.[289] An
experiment recently made by Mr. Christie, secretary to the Royal
Society, appears to demonstrate that ice, under great pressure,
possesses a sufficient degree of moulding and self-adapting power to
allow it to be acted upon, as if it were a pasty substance. A hollow
shell of iron an inch and a half thick, the interior being ten inches in
diameter, was filled with water, in the course of a severe winter, and
exposed to the frost, with the fuze-hole uppermost. A portion of the
water expanded in freezing, so as to protrude a cylinder of ice from the
fuze-hole; and this cylinder continued to grow inch by inch in
proportion as the central nucleus of water froze. As we cannot doubt
that an outer shell of ice is first formed, and then another within, the
continued rise of the column through the fuze-hole must proceed from the
squeezing of successive shells of ice concentrically formed, through the
narrow orifice; and yet the protruded cylinder consisted of entire, and
not fragmentary ice.[290]

The agency of glaciers in producing permanent geological changes
consists partly in their power of transporting gravel, sand, and huge
stones to great distances, and partly in the smoothing, polishing, and
scoring of their rocky channels, and the boundary walls of the valleys
through which they pass. At the foot of every steep cliff or precipice
in high Alpine regions, a talus is seen of rocky fragments detached by
the alternate action of frost and thaw. If these loose masses, instead
of accumulating on a stationary base, happen to fall upon a glacier,
they will move along with it, and, in place of a single heap, they will
form in the course of years a long stream of blocks. If a glacier be 20
miles long, and its annual progression about 500 feet, it will require
about two centuries for a block thus lodged upon its surface to travel
down from the higher to the lower regions, or to the extremity of the
icy mass. This terminal point remains usually unchanged from year to
year, although every part of the ice is in motion, because the
liquefaction by heat is just sufficient to balance the onward movement
of the glacier, which may be compared to an endless file of soldiers,
pouring into a breach, and shot down as fast as they advance.

The stones carried along on the ice are called in Switzerland the
"moraines" of the glacier. There is always one line of blocks on each
side or edge of the icy stream, and often several in the middle, where
they are arranged in long ridges or mounds, often several yards high.
(See fig. 18, p. 223.) The cause of these "medial moraines" was first
explained by Agassiz, who referred them to the confluence of tributary
glaciers.[291] Upon the union of two streams of ice, the right lateral
moraine of one of the streams comes in contact with the left lateral
moraine of the other, and they afterwards move on together, in the
centre, if the confluent glaciers are equal in size, or nearer to one
side if unequal.

All sand and fragments of soft stone which fall through fissures and
reach the bottom of the glaciers, or which are interposed between the
glacier and the steep sides of the valley, are pushed along, and ground
down into mud, while the larger and harder fragments have their angles
worn off. At the same time the fundamental and boundary rocks are
smoothed and polished, and often scored with parallel furrows, or with
lines and scratches produced by hard minerals, such as crystals of
quartz, which act like the diamond upon glass.[292] This effect is
perfectly different from that caused by the action of water, or a muddy
torrent forcing along heavy fragments; for when stones are fixed firmly
in the ice, and pushed along by it under great pressure, in straight
lines, they scoop out long rectilinear furrows or grooves parallel to
each other.[293] The discovery of such markings at various heights far
above the surface of the existing glaciers and for miles beyond their
present terminations, affords geological evidence of the former
extension of the ice beyond its present limits in Switzerland and other
countries.

The moraine of the glacier, observes Charpentier, is entirely devoid of
stratification, for there has been no sorting of the materials, as in
the case of sand, mud, and pebbles, when deposited by running water. The
ice transports indifferently, and to the same spots, the heaviest blocks
and the finest particles, mingling all together, and leaving them in one
confused and promiscuous heap wherever it melts.[294]

_Icebergs._--In countries situated in high northern latitudes, like
Spitzbergen, between 70° and 80° N., glaciers, loaded with mud and rock,
descend to the sea, and there huge fragments of them float off and
become icebergs. Scoresby counted 500 of these bergs drifting along in
latitudes 69° and 70° N., which rose above the surface from the height
of 100 to 200 feet, and measured from a few yards to a mile in
circumference.[295] Many of them were loaded with beds of earth and rock
of such thickness, that the weight was conjectured to be from 50,000 to
100,000 tons. Specimens of the rocks were obtained, and among them were
granite, gneiss, mica-schist, clay-slate, granular felspar, and
greenstone. Such bergs must be of great magnitude; because the mass of
ice below the level of the water is about eight times greater than that
above. Wherever they are dissolved, it is evident that the "moraine"
will fall to the bottom of the sea. In this manner may submarine
valleys, mountains, and platforms become strewed over with gravel, sand,
mud, and scattered blocks of foreign rock, of a nature perfectly
dissimilar from all in the vicinity, and which may have been transported
across unfathomable abysses. If the bergs happen to melt in still water,
so that the earthy and stony materials may fall tranquilly to the
bottom, the deposit will probably be unstratified, like the terminal
moraine of a glacier; but whenever the materials are under the influence
of a current of water as they fall, they will be sorted and arranged
according to their relative weight and size, and therefore more or less
perfectly stratified.

In a former chapter it was stated that some ice islands have been known
to drift from Baffin's Bay to the Azores, and from the South Pole to the
immediate neighborhood of the Cape of Good Hope, so that the area over
which the effects of moving ice may be experienced, comprehends a large
portion of the globe.

We learn from Von Buch that the most southern point on the continent of
Europe at which a glacier comes down to the sea is in Norway, in lat.
67° N.[296] But Mr. Darwin has shown, that they extend to the sea, in
South America, in latitudes more than 20° nearer the equator than in
Europe; as, for example, in Chili, where, in the Gulf of Penas, lat. 46°
40' S., or the latitude of central France; and in Sir George Eyre's
Sound, in the latitude of Paris, they give origin to icebergs, which
were seen in 1834 carrying angular pieces of granite, and stranding them
in fiords, where the shores were composed of clay-slate.[297] A large
proportion, however, of the ice-islands seen floating both in the
northern and southern hemispheres, are probably not generated by
glaciers, but rather by the accumulation of coast ice. When the sea
freezes at the base of a lofty precipice, the sheet of ice is prevented
from adhering to the land by the rise and fall of the tide.
Nevertheless, it often continues on the shore at the foot of the cliff,
and receives accessions of drift snow blown from the land. Under the
weight of this snow the ice sinks slowly if the water be deep, and the
snow is gradually converted into ice by partial liquefaction and
re-congelation. In this manner, islands of ice of great thickness and
many leagues in length, originate, and are eventually blown out to sea
by off-shore winds. In their interior are inclosed many fragments of
stone which had fallen upon them from overhanging cliffs during their
formation. Such floating icebergs are commonly flat-topped, but their
lower portions are liable to melt in latitudes where the ocean at a
moderate depth is usually warmer than the surface water and the air.
Hence their centre of gravity changes continually, and they turn over
and assume very irregular shapes.

In a voyage of discovery made in the antarctic regions in 1839, a
dark-colored angular mass of rock was seen imbedded in an iceberg,
drifting along in mid-ocean in lat. 61° S. That part of the rock which
was visible was about 12 feet in height, and from 5 to 6 in width, but
the dark color of the surrounding ice indicated that much more of the
stone was concealed. A sketch made by Mr. Macnab, when the vessel was
within a quarter of a mile of it, is now published.[298] This iceberg,
one of many observed at sea on the same day, was between 250 and 300
feet high, and was no less than 1400 miles from any certainly known
land. It is exceedingly improbable, says Mr. Darwin, in his notice of
this phenomenon, that any land will hereafter be discovered within 100
miles of the spot, and it must be remembered that the erratic was still
firmly fixed in the ice, and may have sailed for many a league farther
before it dropped to the bottom.[299]

Captain Sir James Ross, in his antarctic voyage in 1841, 42, and 43, saw
multitudes of icebergs transporting stones and rocks of various sizes,
with frozen mud, in high southern latitudes. His companion, Dr. J.
Hooker, informs me that he came to the conclusion that most of the
southern icebergs have stones in them, although they are usually
concealed from view by the quantity of snow which falls upon them.

In the account given by Messrs. Dease and Simpson, of their recent
arctic discoveries, we learn that in lat. 71° N., long. 156° W., they
found "a long low spit, named Point Barrow, composed of gravel and
coarse sand, in some parts more than a quarter of a mile broad, which
the pressure of the ice had forced up into numerous mounds, that, viewed
from a distance, assumed the appearance of huge boulder rocks."[300]

This fact is important, as showing how masses of drift ice, when
stranding on submarine banks, may exert a lateral pressure capable of
bending and dislocating any yielding strata of gravel, sand, or mud. The
banks on which icebergs occasionally run aground between Baffin's Bay
and Newfoundland, are many hundred feet under water, and the force with
which they are struck will depend not so much on the velocity as the
momentum of the floating ice-islands. The same berg is often carried
away by a change of wind, and then driven back again upon the same bank,
or it is made to rise and fall by the waves of the ocean, so that it may
alternately strike the bottom with its whole weight, and then be lifted
up again until it has deranged the superficial beds over a wide area. In
this manner the geologist may account, perhaps, for the circumstance
that in Scandinavia, Scotland, and other countries where erratics are
met with, the beds of sand, loam, and gravel are often vertical, bent,
and contorted into the most complicated folds, while the underlying
strata, although composed of equally pliant materials, are horizontal.
But some of these curvatures of loose strata may also have been due to
repeated alternations of layers of gravel and sand, ice and snow, the
melting of the latter having caused the intercalated beds of
indestructible matter to assume their present anomalous position.

There can be little doubt that icebergs must often break off the peaks
and projecting points of submarine mountains, and must grate upon and
polish their surface, furrowing or scratching them in precisely the same
way as we have seen that glaciers act on the solid rocks over which they
are propelled.[301]

To conclude: it appears that large stones, mud, and gravel are carried
down by the ice of rivers, estuaries, and glaciers, into the sea, where
the tides and currents of the ocean, aided by the wind, cause them to
drift for hundreds of miles from the place of their origin. Although it
will belong more properly to the seventh and eighth chapters to treat of
the transportation of solid matter by the movements of the ocean, I
shall add here what I have farther to say on this subject in connection
with ice.

The saline matter which sea-water holds in solution, prevents its
congelation, except where the most intense cold prevails. But the
drifting of the snow from the land often renders the surface-water
brackish near the coast, so that a sheet of ice is readily formed there,
and by this means a large quantity of gravel is frequently conveyed from
place to place, and heavy boulders also, when the coast-ice is packed
into dense masses. Both the large and small stones thus conveyed usually
travel in one direction like shingle-beaches, and this was observed to
take place on the coast of Labrador and Gulf of St. Lawrence, between
the latitudes 50° and 60° N., by Capt. Bayfield, during his late survey.
The line of coast alluded to is strewed over for a distance of 700 miles
with ice-borne boulders, often 6 feet in diameter, which are for the
most part on their way from north to south, or in the direction of the
prevailing current. Some points on this coast have been observed to be
occasionally deserted, and then again at another season thickly
bestrewed with erratics.

[Illustration: Fig. 19.

Boulders, chiefly of granite, stranded by ice on the coast of Labrador,
between lat. 50° and 60° N. (Lieut. Bowen, R. N.)]

The accompanying drawing (fig. 19), for which I am indebted to Lieut.
Bowen, R. N., represents the ordinary appearance of the Labrador coast,
between the latitudes of 50° and 60° N. Countless blocks, chiefly
granitic, and of various sizes, are seen lying between high and
low-water mark. Capt. Bayfield saw similar masses carried by ice
through the Straits of Belle Isle, between Newfoundland and the American
continent, which he conceives may have travelled in the course of years
from Baffin's Bay, a distance which may be compared in our hemisphere to
the drifting of erratics from Lapland and Iceland as far south as
Germany, France, and England.

It may be asked in what manner have these blocks been originally
detached? We may answer that some have fallen from precipitous cliffs,
others have been lifted up from the bottom of the sea, adhering by their
tops to the ice, while others have been brought down by rivers and
glaciers.

The erratics of North America are sometimes angular, but most of them
have been rounded either by friction or decomposition. The granite of
Canada, as before remarked (p. 221 ), has a tendency to concentric
exfoliation, and scales off in spheroidal coats when exposed to the
spray of the sea during severe frosts. The range of the thermometer in
that country usually exceeds, in the course of the year, 100°, and
sometimes 120° F.; and, to prevent the granite used in the buildings of
Quebec from peeling off in winter, it is necessary to oil and paint the
squared stones.

In parts of the Baltic, such as the Gulf of Bothnia, where the quantity
of salt in the water amounts in general to one fourth only of that in
the ocean, the entire surface freezes over in winter to the depth of 5
or 6 feet. Stones are thus frozen in, and afterwards lifted up about 3
feet perpendicularly on the melting of the snow in summer, and then
carried by floating ice-islands to great distances. Professor Von Baer
states, in a communication on this subject to the Academy of St.
Petersburg, that a block of granite, weighing a million of pounds, was
carried by ice during the winter of 1837-8 from Finland to the island of
Hockland, and two other huge blocks were transported about the years
1806 and 1814 by packed ice on the south coast of Finland, according to
the testimony of the pilots and inhabitants, one block having travelled
about a quarter of a mile, and lying about 18 feet above the level of
the sea.[302]

More recently Dr. Forchhammer has shown that in the Sound, the Great
Belt, and other places near the entrance of the Baltic, ground-ice forms
plentifully at the bottom and then rises to the surface, charged with
sand and gravel, stones and sea-weed. Sheets of ice, also, with included
boulders, are driven up on the coast during storms, and "packed" to a
height of 50 feet. To the motion of such masses, but still more to that
of the ground-ice, the Danish professor attributes the striation of
rocky surfaces, forming the shores and bed of the sea, and he relates a
striking fact to prove that large quantities of rocky fragments are
annually carried by ice out of the Baltic. "In the year 1807," he says,
"at the time of the bombardment of the Danish fleet, an English
sloop-of-war, riding at anchor in the roads at Copenhagen, blew up. In
1844, or thirty-seven years afterwards, one of our divers, known to be
a trustworthy man, went down to save whatever might yet remain in the
shipwrecked vessel. He found the space between decks entire, but covered
with blocks from 6 to 8 cubic feet in size, and some of them heaped one
upon the other. He also affirmed, that all the sunk ships which he had
visited in the Sound, were in like manner strewed over with blocks."

Dr. Forchhammer also informs us, that during an intense frost in
February, 1844, the Sound was suddenly frozen over, and sheets of ice,
driven by a storm, were heaped up at the bottom of the Bay of Täarbeijk,
threatening to destroy a fishing-village on the shore. The whole was
soon frozen together into one mass, and forced up on the beach, forming
a mound more than 16 feet high, which threw down the walls of several
buildings. "When I visited the spot next day, I saw ridges of ice, sand,
and pebbles, not only on the shore, but extending far out into the
bottom of the sea, showing how greatly its bed had been changed, and how
easily, where it is composed of rock, it may be furrowed and streaked by
stones firmly fixed in the moving ice."[303]




CHAPTER XVI.

PHENOMENA OF SPRINGS.


 Origin of Springs--Artesian wells--Borings at Paris--Distinct causes
    by which mineral and thermal waters may be raised to the
    surface--Their connection with volcanic agency--Calcareous
    springs--Travertin of the Elsa--Baths of San Vignone and of San
    Filippo, near Radicofani--Spheroidal structure in travertin--Lake of
    the Solfatara, near Rome--Travertin at Cascade of Tivoli--Gypseous,
    siliceous, and ferruginous springs--Brine springs--Carbonated
    springs--Disintegration of granite in Auvergne--Petroleum
    springs--Pitch lake of Trinidad.


_Origin of springs._--The action of running water on the surface of the
land having been considered, we may next turn our attention to what may
be termed "the subterranean drainage," or the phenomena of springs.
Every one is familiar with the fact, that certain porous soils, such as
loose sand and gravel, absorb water with rapidity, and that the ground
composed of them soon dries up after heavy showers. If a well be sunk in
such soils, we often penetrate to considerable depths before we meet
with water; but this is usually found on our approaching the lower parts
of the formation, where it rests on some impervious bed; for here the
water, unable to make its way downwards in a direct line, accumulates as
in a reservoir, and is ready to ooze out into any opening which may be
made, in the same manner as we see the salt water flow into, and fill,
any hollow which we dig in the sands of the shore at low tide.

The facility with which water can percolate loose and gravelly soils is
clearly illustrated by the effect of the tides in the Thames between
Richmond and London. The river, in this part of its course, flows
through a bed of gravel overlying clay, and the porous superstratum is
alternately saturated by the water of the Thames as the tide rises, and
then drained again to the distance of several hundred feet from the
banks when the tide falls, so that the wells in this tract regularly ebb
and flow.

If the transmission of water through a porous medium be so rapid, we
cannot be surprised that springs should be thrown out on the side of a
hill, where the upper set of strata consist of chalk, sand, or other
permeable substances, while the subjacent are composed of clay or other
retentive soils. The only difficulty, indeed, is to explain why the
water does not ooze out everywhere along the line of junction of the two
formations, so as to form one continuous land-soak, instead of a few
springs only, and these far distant from each other. The principal cause
of this concentration of the waters at a few points is, first, the
frequency of rents and fissures, which act as natural drains; secondly,
the existence of inequalities in the upper surface of the impermeable
stratum, which lead the water, as valleys do on the external surface of
a country, into certain low levels and channels.

That the generality of springs owe their supply to the atmosphere is
evident from this, that they become languid, or entirely cease to flow,
after long droughts, and are again replenished after a continuance of
rain. Many of them are probably indebted for the constancy and
uniformity of their volume to the great extent of the subterranean
reservoirs with which they communicate, and the time required for these
to empty themselves by percolation. Such a gradual and regulated
discharge is exhibited, though in a less perfect degree, in every great
lake which is not sensibly affected in its level by sudden showers, but
only slightly raised; so that its channel of efflux, instead of being
swollen suddenly like the bed of a torrent, is enabled to carry off the
surplus water gradually.

Much light has been thrown, of late years, on the theory of springs, by
the boring of what are called by the French "Artesian wells," because
the method has long been known and practised in Artois; and it is now
demonstrated that there are sheets, and in some places currents of fresh
water, at various depths in the earth. The instrument employed in
excavating these wells is a large augur, and the cavity bored is usually
from three to four inches in diameter. If a hard rock is met with, it is
first triturated by an iron rod, and the materials being thus reduced to
small fragments or powder, are readily extracted. To hinder the sides of
the well from falling in, as also to prevent the spreading of the
ascending water in the surrounding soil, a jointed pipe is introduced,
formed of wood in Artois, but in other countries more commonly of metal.
It frequently happens that, after passing through hundreds of feet of
retentive soils, a water-bearing stratum is at length pierced, when the
fluid immediately ascends to the surface, and flows over. The first rush
of the water up the tube is often violent, so that for a time the water
plays like a fountain, and then, sinking, continues to flow over
tranquilly, or sometimes remains stationary at a certain depth below the
orifice of the well. This spouting of the water in the first instance is
probably owing to the disengagement of air and carbonic acid gas, for
both of these have been seen to bubble up with the water.[304]

At Sheerness, at the mouth of the Thames, a well was bored on a low
tongue of land near the sea, through 300 feet of the blue clay of
London, below which a bed of sand and pebbles was entered, belonging,
doubtless, to the plastic clay formation; when this stratum was pierced,
the water burst up with impetuosity, and filled the well. By another
perforation at the same place, the water was found at the depth of 328
feet below the surface clay; it first rose rapidly to the height of 189
feet, and then, in the course of a few hours, ascended to an elevation
of eight feet above the level of the ground. In 1824 a well was dug at
Fulham, near the Thames, at the Bishop of London's, to the depth of 317
feet, which, after traversing the tertiary strata, was continued through
67 feet of chalk. The water immediately rose to the surface, and the
discharge was about 50 gallons per minute. In the garden of the
Horticultural Society at Chiswick, the borings passed through 19 feet of
gravel, 242½ feet of clay and loam, and 67½ feet of chalk, and the
water then rose to the surface from a depth of 329 feet.[305] At the
Duke of Northumberland's, above Chiswick, the borings were carried to
the extraordinary depth of 620 feet, so as to enter the chalk, when a
considerable volume of water was obtained, which rose four feet above
the surface of the ground. In a well of Mr. Brooks, at Hammersmith, the
rush of water from a depth of 360 feet was so great, as to inundate
several buildings and do considerable damage; and at Tooting, a
sufficient stream was obtained to turn a wheel, and raise the water to
the upper stories of the houses.[306] In 1838, the total supply obtained
from the chalk near London was estimated at six million gallons a day,
and, in 1851, at nearly double that amount, the increase being
accompanied by an average fall of no less than two feet a year in the
level to which the water rose. The water stood commonly, in 1822, at
high-water mark, and had sunk in 1851 to 45, and in some wells to 65
feet below high-water mark.[307] This fact shows the limited capacity of
the subterranean reservoir. In the last of three wells bored through the
chalk at Tours, to the depth of several hundred feet, the water rose 32
feet above the level of the soil, and the discharge amounted to 300
cubic yards of water every twenty-four hours.[308]

By way of experiment, the sinking of a well was commenced at Paris in
1834, which had reached, in November, 1839, a depth of more than 1600
English feet, and yet no water ascended to the surface. The government
were persuaded by M. Arago to persevere, if necessary, to the depth of
more than 2000 feet; but when they had descended above 1800 English feet
below the surface, the water rose through the tube (which was about ten
inches in diameter), so as to discharge half a million of gallons of
limpid water every twenty-four hours. The temperature of the water
increased at the rate of 1·8° F. for every 101 English feet, as they
went down, the result agreeing very closely with the anticipations of
the scientific advisers of this most spirited undertaking.

Mr. Briggs, the British consul in Egypt, obtained water between Cairo
and Suez, in a calcareous sand, at the depth of thirty feet; but it did
not rise in the well.[309] But other borings in the same desert, of
variable depth, between 50 and 300 feet, and which passed through
alternations of sand, clay, and siliceous rock, yielded water at the
surface.[310]

The rise and overflow of the water in Artesian wells is generally
referred, and apparently with reason, to the same principle as the play
of an artificial fountain. Let the porous stratum or set of strata, _a_
_a_, rest on the impermeable rock _d_, and be covered by another mass of
an impermeable nature. The whole mass _a_ _a_ may easily, in such a
position, become saturated with water, which may descend from its higher
and exposed parts--a hilly region to which clouds are attracted, and
where rain falls in abundance. Suppose that at some point, as at _b_, an
opening be made, which gives a free passage upwards to the waters
confined in _a_ _a_, at so low a level that they are subjected to the
pressure of a considerable column of water collected in the more
elevated portion of the same stratum. The water will then rush out, just
as the liquid from a large barrel which is tapped, and it will rise to a
height corresponding to the level of its point of departure, or, rather,
to a height which balances the pressure previously exerted by the
confined waters against the roof and sides of the stratum or reservoir
_a_ _a_. In like manner, if there happen to be a natural fissure _c_, a
spring will be produced at the surface on precisely the same principle.

[Illustration: Fig. 20.]

Among the causes of the failure of Artesian wells, we may mention those
numerous rents and faults which abound in some rocks, and the deep
ravines and valleys by which many countries are traversed; for, when
these natural lines of drainage exist, there remains a small quantity
only of water to escape by artificial issues. We are also liable to be
baffled by the great thickness either of porous or impervious strata, or
by the dip of the beds, which may carry off the waters from the
adjoining high lands to some trough in an opposite direction, as when
the borings are made at the foot of an escarpment where the strata
incline inwards, or in a direction opposite to the face of the cliffs.

The mere distance of hills or mountains need not discourage us from
making trials; for the waters which fall on these higher lands readily
penetrate to great depths through highly inclined or vertical strata, or
through the fissures of shattered rocks, and after flowing for a great
distance, must often reascend and be brought up again by other fissures,
so as to approach the surface in the lower country. Here they may be
concealed beneath the covering of undisturbed horizontal beds, which it
may be necessary to pierce in order to reach them. It should be
remembered, that the course of waters flowing under ground bears but a
remote resemblance to that of rivers on the surface, there being, in the
one case, a constant descent from a higher to a lower level from the
source of the stream to the sea; whereas, in the other, the water may at
one time sink far below the level of the ocean, and afterwards rise
again high above it.

Among other curious facts ascertained by aid of the borer, it is proved
that in strata of different ages and compositions, there are often open
passages by which the subterranean waters circulate. Thus, at St. Ouen,
in France, five distinct sheets of water were intersected in a well, and
from each of these a supply obtained. In the third waterbearing stratum,
at the depth of 150 feet, a cavity was found in which the borer fell
suddenly about a foot, and thence the water ascended in great
volume.[311] The same falling of the instrument, as in a hollow space,
has been remarked in England and other countries. At Tours, in 1830, a
well was perforated quite through the chalk, when the water suddenly
brought up, from a depth of 364 feet, a great quantity of fine sand,
with much vegetable matter and shells. Branches of a thorn several
inches long, much blackened by their stay in the water, were recognized,
as also the stems of marsh plants, and some of their roots, which were
still white, together with the seeds of the same in a state of
preservation, which showed that they had not remained more than three or
four months in the water. Among the seeds were those of the marsh plant
_Galium uliginosum_; and among the shells, a freshwater species
(_Planorbis marginatus_), and some land species, as _Helix rotundata_,
and _H. striata_. M. Dujardin, who, with others, observed this
phenomenon, supposes that the waters had flowed from some valleys of
Auvergne or the Vivarais since the preceding autumn.[312]

An analogous phenomenon is recorded at Reimke, near Bochum in
Westphalia, where the water of an Artesian well brought up, from a
depth of 156 feet, several small fish, three or four inches long, the
nearest streams in the country being at a distance of some leagues.[313]

In both cases it is evident that water had penetrated to great depths,
not simply by filtering through a porous mass, for then it would have
left behind the shells, fish, and fragments of plants, but by flowing
through some open channels in the earth. Such examples may suggest the
idea that the leaky beds of rivers are often the feeders of springs.


MINERAL AND THERMAL SPRINGS.

Almost all springs, even those which we consider the purest, are
impregnated with some foreign ingredients, which, being in a state of
chemical solution, are so intimately blended with the water as not to
affect its clearness, while they render it, in general, more agreeable
to our taste, and more nutritious than simple rain-water. But the
springs called mineral contain an unusual abundance of earthy matter in
solution, and the substances with which they are impregnated correspond
remarkably with those evolved in a gaseous form by volcanoes. Many of
these springs are thermal, _i. e._, their temperature is above the mean
temperature of the place, and they rise up through all kinds of rock;
as, for example, through granite, gneiss, limestone, or lava, but are
most frequent in volcanic regions, or where violent earthquakes have
occurred at eras comparatively modern.

The water given out by hot springs is generally more voluminous and less
variable in quantity at different seasons than that proceeding from any
others. In many volcanic regions, jets of steam, called by the Italians
"stufas," issue from fissures, at a temperature high above the boiling
point, as in the neighborhood of Naples, and in the Lipari Isles, and
are disengaged unceasingly for ages. Now, if such columns of steam,
which are often mixed with other gases, should be condensed before
reaching the surface by coming in contact with strata filled with cold
water, they may give rise to thermal and mineral springs of every degree
of temperature. It is, indeed, by this means only, and not by
hydrostatic pressure, that we can account for the rise of such bodies of
water from great depths; nor can we hesitate to admit the adequacy of
the cause, if we suppose the expansion of the same elastic fluids to be
sufficient to raise columns of lava to the lofty summits of volcanic
mountains. Several gases, the carbonic acid in particular, are
disengaged in a free state from the soil in many districts, especially
in the regions of active or extinct volcanoes; and the same are found
more or less intimately combined with the waters of all mineral springs,
both cold and thermal. Dr. Daubeny and other writers have remarked, not
only that these springs are most abundant in volcanic regions, but that
when remote from them, their site usually coincides with the position of
some great derangement in the strata; a fault, for example, or great
fissure, indicating that a channel of communication has been opened with
the interior of the earth at some former period of local convulsion. It
is also ascertained that at great heights in the Pyrenees and Himalaya
mountains hot springs burst out from granitic rocks, and they are
abundant in the Alps also, these chains having all been disturbed and
dislocated at times comparatively modern, as can be shown by independent
geological evidence.

The small area of volcanic regions may appear, at first view, to present
an objection to these views, but not so when we include earthquakes
among the effects of igneous agency. A large proportion of the land
hitherto explored by geologists can be shown to have been rent or shaken
by subterranean movements since the oldest tertiary strata were formed.
It will also be seen, in the sequel, that new springs have burst out,
and others have had the volume of their waters augmented, and their
temperature suddenly raised after earthquakes, so that the description
of these springs might almost with equal propriety have been given under
the head of "igneous causes," as they are agents of a mixed nature,
being at once igneous and aqueous.

But how, it will be asked, can the regions of volcanic heat send forth
such inexhaustible supplies of water? The difficulty of solving this
problem would, in truth, be insurmountable, if we believed that all the
atmospheric waters found their way into the basin of the ocean; but in
boring near the shore we often meet with streams of fresh water at the
depth of several hundred feet below the sea level; and these probably
descend, in many cases, far beneath the bottom of the sea, when not
artificially intercepted in their course. Yet, how much greater may be
the quantity of salt water which sinks beneath the floor of the ocean,
through the porous strata of which it is often composed, or through
fissures rent in it by earthquakes. After penetrating to a considerable
depth, this water may encounter a heat of sufficient intensity to
convert it into vapor, even under the high pressure to which it would
then be subjected. This heat would probably be nearest the surface in
volcanic countries, and farthest from it in those districts which have
been longest free from eruptions or earthquakes.

It would follow from the views above explained, that there must be a
twofold circulation of terrestrial waters; one caused by solar heat, and
the other by heat generated in the interior of our planet. We know that
the land would be unfit for vegetation, if deprived of the waters raised
into the atmosphere by the sun; but it is also true that mineral springs
are powerful instruments in rendering the surface subservient to the
support of animal and vegetable life. Their heat is said to promote the
development of the aquatic tribes in many parts of the ocean, and the
substances which they carry up from the bowels of the earth to the
habitable surface, are of a nature and in a form which adapts them
peculiarly for the nutrition of animals and plants.

As these springs derive their chief importance to the geologist from
the quantity and quality of the earthy materials which, like volcanoes,
they convey from below upwards, they may properly be considered in
reference to the ingredients which they hold in solution. These consist
of a great variety of substances; but chiefly salts with bases of lime,
magnesia, alumine, and iron, combined with carbonic, sulphuric, and
muriatic acids. Muriate of soda, silica, and free carbonic acid are
frequently present; also springs of petroleum, or liquid bitumen, and of
naphtha.

_Calcareous springs._--Our first attention is naturally directed to
springs which are highly charged with calcareous matter, for these
produce a variety of phenomena of much interest in geology. It is known
that rain-water collecting carbonic acid from the atmosphere has the
property of dissolving the calcareous rocks over which it flows, and
thus, in the smallest ponds and rivulets, matter is often supplied for
the earthy secretions of testacea, and for the growth of certain plants
on which they feed. But many springs hold so much carbonic acid in
solution, that they are enabled to dissolve a much larger quantity of
calcareous matter than rain-water; and when the acid is dissipated in
the atmosphere, the mineral ingredients are thrown down, in the form of
porous tufa or of more compact travertin.[314]

_Auvergne._--Calcareous springs, although most abundant in limestone
districts, are by no means confined to them, but flow out
indiscriminately from all rock formations. In central France, a district
where the primary rocks are unusually destitute of limestone, springs
copiously charged with carbonate of lime rise up through the granite and
gneiss. Some of these are thermal, and probably derive their origin from
the deep source of volcanic heat, once so active in that region. One of
these springs, at the northern base of the hill upon which Claremont is
built, issues from volcanic peperino, which rests on granite. It has
formed, by its incrustations, an elevated mound of travertin, or white
concretionary limestone, 240 feet in length, and, at its termination,
sixteen feet high and twelve wide. Another encrusting spring in the same
department, situated at Chaluzet, near Pont Gibaud, rises in a gneiss
country, at the foot of a regular volcanic cone, at least twenty miles
from any calcareous rock. Some masses of tufaceous deposit, produced by
this spring, have an oolitic texture.

_Valley of the Elsa._--If we pass from the volcanic district of France
to that which skirts the Apennines in the Italian peninsula, we meet
with innumerable springs which have precipitated so much calcareous
matter, that the whole ground in some parts of Tuscany is coated over
with tufa and travertin, and sounds hollow beneath the foot.

In other places in the same country, compact rocks are seen descending
the slanting sides of hills, very much in the manner of lava currents,
except that they are of a white color and terminate abruptly when they
reach the course of a river. These consist of a calcareous precipitate
from springs, some of which are still flowing, while others have
disappeared or changed their position. Such masses are frequent on the
slope of the hills which bound the valley of the Elsa, one of the
tributaries of the Arno, which flows near Colle, through a valley
several hundred feet deep, shaped out of a lacustrine formation,
containing fossil shells of existing species. I observed here that the
travertin was unconformable to the lacustrine beds, its inclination
according with the slope of the sides of the valley. One of the finest
examples which I saw was at the Molino delle Caldane, near Colle. The
Senà, and several other small rivulets which feed the Elsa, have the
property of encrusting wood and herbs with calcareous stone. In the bed
of the Elsa itself, aquatic plants, such as Charæ, which absorb large
quantities of carbonate of lime, are very abundant.

[Illustration: Fig. 21.

Section of travertin, San Vignone.]

_Baths of San Vignone._--Those persons who have merely seen the action
of petrifying waters in England, will not easily form an adequate
conception of the scale on which the same process is exhibited in those
regions which lie nearer to the active centres of volcanic disturbance.
One of the most striking examples of the rapid precipitation of
carbonate of lime from thermal waters, occurs in the hill of San Vignone
in Tuscany, at a short distance from Radicofani, and only a few hundred
yards from the high road between Sienna and Rome. The spring issues from
near the summit of a rocky hill, about 100 feet in height. The top of
the hill stretches in a gently inclined platform to the foot of Mount
Amiata, a lofty eminence, which consists in great part of volcanic
products. The fundamental rock, from which the spring issues, is a black
slate, with serpentine (_b_ _b_, fig. 21), belonging to the older
Apennine formation. The water is hot, has a strong taste, and, when not
in very small quantity, is of a bright green color. So rapid is the
deposition near the source, that in the bottom of a conduit-pipe for
carrying off the water to the baths, and which is inclined at an angle
of 30°, half a foot of solid travertin is formed every year. A more
compact rock is produced where the water flows slowly; and the
precipitation in winter, when there is least evaporation, is said to be
more solid, but less in quantity by one-fourth, than in summer. The rock
is generally white; some parts of it are compact, and ring to the
hammer; others are cellular, and with such cavities as are seen in the
carious part of bone or the siliceous millstone of the Paris basin. A
portion of it also below the village of San Vignone consists of
incrustations of long vegetable tubes, and may be called tufa. Sometimes
the travertin assumes precisely the botryoidal and mammillary forms,
common to similar deposits in Auvergne, of a much older date; and, like
them, it often scales off in thin, slightly undulating layers.

A large mass of travertin (_c_, fig. 21) descends the hill from the
point where the spring issues, and reaches to the distance of about half
a mile east of San Vignone. The beds take the slope of the hill at about
an angle of 6°, and the planes of stratification are perfectly parallel.
One stratum, composed of many layers, is of a compact nature, and
fifteen feet thick; it serves as an excellent building stone, and a mass
of fifteen feet in length was, in 1828, cut out for the new bridge over
the Orcia. Another branch of it (_a_, fig. 21) descends to the west, for
250 feet in length, of varying thickness, but sometimes 200 feet deep;
it is then cut off by the small river Orcia, as some glaciers in
Switzerland descend into a valley till their progress is suddenly
arrested by a transverse stream of water.

The abrupt termination of the mass of rock at the river, where its
thickness is undiminished, clearly shows that it would proceed much
farther if not arrested by the stream, over which it impends slightly.
But it cannot encroach upon the channel of the Orcia, being constantly
undermined, so that its solid fragments are seen strewed amongst the
alluvial gravel. However enormous, therefore, the mass of solid rock may
appear which has been given out by this single spring, we may feel
assured that it is insignificant in volume when compared to that which
has been carried to the sea since the time when it began to flow. What
may have been the length of that period of time we have no data for
conjecturing. In quarrying the travertin, Roman tiles have been
sometimes found at the depth of five or six feet.

_Baths of San Filippo._--On another hill, not many miles from that last
mentioned, and also connected with Mount Amiata, the summit of which is
about three miles distant, are the celebrated baths of San Filippo. The
subjacent rocks consist of alternations of black slate, limestone, and
serpentine. There are three warm springs containing carbonate and
sulphate of lime, and sulphate of magnesia. The water which supplies the
baths falls into a pond, where it has been known to deposit a solid mass
_thirty feet thick_ in about _twenty years_.[315] A manufactory of
medallions in basso-relievo is carried on at these baths. The water is
conducted by canals into several pits, in which it deposits travertin
and crystals of sulphate of lime. After being thus freed from its
grosser parts, it is conveyed by a tube to the summit of a small
chamber, and made to fall through a space of ten or twelve feet. The
current is broken in its descent by numerous crossed sticks, by which
the spray is dispersed around upon certain moulds, which are rubbed
lightly over with a solution of soap, and a deposition of solid matter
like marble is the result, yielding a beautiful cast of the figures
formed in the mould. The geologist may derive from these experiments
considerable light, in regard to the high slope of the strata at which
some semi-crystalline precipitations can be formed; for some of the
moulds are disposed almost perpendicularly, yet the deposition is nearly
equal in all parts.

A hard stratum of stone, about a foot in thickness, is obtained from the
waters of San Filippo in four months; and, as the springs are powerful,
and almost uniform in the quantity given out, we are at no loss to
comprehend the magnitude of the mass which descends the hill, which is a
mile and a quarter in length and the third of a mile in breadth, in some
places attaining a thickness of 250 feet at least. To what length it
might have reached it is impossible to conjecture, as it is cut off,
like the travertin of San Vignone, by a small stream, where it
terminates abruptly. The remainder of the matter held in solution is
carried on probably to the sea.

_Spheroidal structure in travertin._--But what renders this recent
limestone of peculiar interest to the geologist, is the spheroidal form
which it assumes, analogous to that of the cascade of Tivoli, afterwards
to be described. (See fig. 22, p. 244.) The lamination of some of the
concentric masses is so minute that sixty may be counted in the
thickness of an inch, yet, notwithstanding these marks of gradual and
successive deposition, sections are sometimes exhibited of what might
seem to be perfect spheres. This tendency to a mammillary and globular
structure arises from the facility with which the calcareous matter is
precipitated in nearly equal quantities on all sides of any fragment of
shell or wood or any inequality of the surface over which the mineral
water flows, the form of the nucleus being readily transmitted through
any number of successive envelopes. But these masses can never be
perfect spheres, although they often appear such when a transverse
section is made in any line not in the direction of the point of
attachment. There are, indeed, occasionally seen small oolitic and
pisolitic grains, of which the form is globular; for the nucleus, having
been for a time in motion in the water, has received fresh accessions of
matter on all sides.

In the same manner I have seen, on the vertical walls of large
steam-boilers, the heads of nails or rivets covered by a series of
enveloping crusts of calcareous matter, usually sulphate of lime; so
that a concretionary nodule is formed, preserving a nearly globular
shape, when increased to a mass several inches in diameter. In these, as
in many travertins, there is often a combination of the concentric and
radiated structure.

_Campagna di Roma._--The country around Rome, like many parts of the
Tuscan States already referred to, has been at some former period the
site of numerous volcanic eruptions; and the springs are still copiously
impregnated with lime, carbonic acid, and sulphuretted hydrogen. A hot
spring was discovered about 1827, near Civita Vecchia, by Signor
Riccioli, which deposits alternate beds of a yellowish travertin, and a
white granular rock, not distinguishable, in hand specimens, either in
grain, color, or composition, from statuary marble. There is a passage
between this and ordinary travertin. The mass accumulated near the
spring is in some places about six feet thick.

_Lake of the Solfatara._--In the Campagna, between Rome and Tivoli, is
the Lake of the Solfatara, called also Lago di Zolfo (lacus albula),
into which flows continually a stream of tepid water from a smaller
lake, situated a few yards above it. The water is a saturated solution
of carbonic acid gas, which escapes from it in such quantities in some
parts of its surface, that it has the appearance of being actually in
ebullition. "I have found by experiment," says Sir Humphry Davy, "that
the water taken from the most tranquil part of the lake, even after
being agitated and exposed to the air, contained in solution more than
its own volume of carbonic acid gas, with a very small quantity of
sulphuretted hydrogen. Its high temperature, which is pretty constant at
80° of Fahr., and the quantity of carbonic acid that it contains, render
it peculiarly fitted to afford nourishment to vegetable life. The banks
of travertin are everywhere covered with reeds, lichen, confervæ, and
various kinds of aquatic vegetables; and at the same time that the
process of vegetable life is going on, the crystallizations of the
calcareous matter, which is everywhere deposited, in consequence of the
escape of carbonic acid, likewise proceed. There is, I believe, no place
in the world where there is a more striking example of the opposition or
contrast of the laws of animate and inanimate nature, of the forces of
inorganic chemical affinity, and those of the powers of life."[316]

The same observer informs us that he fixed a stick in a mass of
travertin covered by the water in the month of May, and in April
following he had some difficulty in breaking, with a sharp-pointed
hammer, the mass which adhered to the stick, and which was several
inches in thickness. The upper part was a mixture of light tufa and the
leaves of confervæ; below this was a darker and more solid travertin,
containing black and decomposed masses of confervæ; in the inferior part
the travertin was more solid, and of a gray color, but with cavities
probably produced by the decomposition of vegetable matter.[317]

The stream which flows out of this lake fills a canal about nine feet
broad and four deep, and is conspicuous in the landscape by a line of
vapor which rises from it. It deposits calcareous tufa in this channel,
and the Tiber probably receives from it, as well as from numerous other
streams, much carbonate of lime in solution, which may contribute to the
rapid growth of its delta. A large proportion of the most splendid
edifices of ancient and modern Rome are built of travertin, derived from
the quarries of Ponte Lucano, where there has evidently been a lake at a
remote period, on the same plain as that already described.

[Illustration: Fig. 22.

Section of spheroidal concretionary Travertin under the Cascade of
Tivoli.]

_Travertin of Tivoli._--In the same neighborhood the calcareous waters
of the Anio incrust the reeds which grow on its banks, and the foam of
the cataract of Tivoli forms beautiful pendant stalactites. On the sides
of the deep chasm into which the cascade throws itself, there is seen an
extraordinary accumulation of horizontal beds of tufa and travertin,
from four to five hundred feet in thickness. The section immediately
under the temples of Vesta and the Sibyl, displays, in a precipice about
four hundred feet high, some spheroids which are from _six to eight feet
in diameter_, each concentric layer being about the eighth of an inch in
thickness. The preceding diagram exhibits about fourteen feet of this
immense mass, as seen in the path cut out of the rock in descending from
the temple of Vesta to the Grotto di Nettuno. I have not attempted to
express in this drawing the innumerable thin layers of which these
magnificent spheroids are composed, but the lines given mark some of the
natural divisions into which they are separated by minute variations in
the size or color of the laminæ. The undulations also are much smaller
in proportion to the whole circumference than in the drawing. The beds
(_a_ _a_) are of hard travertin and soft tufa; below them is a pisolite
(_b_), the globules being of different sizes: underneath this appears a
mass of concretionary travertin (_c_ _c_), some of the spheroids being
of the above-mentioned extraordinary size. In some places (as at _d_)
there is a mass of amorphous limestone, or tufa, surrounded by
concentric layers. At the bottom is another bed of pisolite (_b_), in
which the small nodules are about the size and shape of beans, and some
of them of filberts, intermixed with some smaller oolitic grains. In the
tufaceous strata, wood is seen converted into a light tufa.

There can be little doubt that the whole of this deposit was formed in
an extensive lake which existed when the external configuration of this
country varied greatly from that now observed. The Anio throws itself
into a ravine excavated in the ancient travertin, and its waters give
rise to masses of calcareous stone, scarcely if at all distinguishable
from the older rock. I was shown, in 1828, in the upper part of the
travertin, the hollow left by a cart-wheel, in which the outer circle
and the spokes had been decomposed, and the spaces which they filled
left void. It seemed to me at the time impossible to explain the
position of this mould without supposing that the wheel was imbedded
before the lake was drained; but Sir R. Murchison suggests that it may
have been washed down by a flood into the gorge in modern times, and
then incrusted with calcareous tufa in the same manner as the wooden
beam of the church of St. Lucia was swept down in 1826, and stuck fast
in the Grotto of the Syren, where it still remains, and will eventually
be quite imbedded in travertin.

I have already endeavored to explain (p. 241), when speaking of the
travertin of San Filippo, how the spheroidal masses represented in
figure 22 may have been formed.

_Sulphureous and gypseus springs._--The quantity of other mineral
ingredients wherewith springs in general are impregnated, is
insignificant in comparison to lime, and this earth is most frequently
combined with carbonic acid. But as sulphuric acid, and sulphuretted
hydrogen are very frequently supplied by springs, gypsum may, perhaps,
be deposited largely in certain seas and lakes. Among other gypseous
precipitates at present known on the land, I may mention those of Baden,
near Vienna, which feed the public bath. Some of these supply singly
from 600 to 1000 cubic feet of water per hour, and deposit a fine
powder, composed of a mixture of sulphate of lime with sulphur and
muriate of lime.[318] The thermal waters of Aix, in Savoy, in passing
through strata of Jurassic limestone, turn them into gypsum or sulphate
of lime. In the Andes, at the Puenta del Inca, Lieutenant Brand found a
thermal spring at the temperature of 91° Fahr., containing a large
proportion of gypsum with carbonate of lime and other ingredients.[319]
Many of the mineral springs of Iceland, says Mr. R. Bunsen, deposit
gypsum.[320] and sulphureous acid gas escapes plentifully from them as
from the volcanoes of the same island. It may, indeed, be laid down as a
general rule, that the mineral substances dissolved in hot springs agree
very closely with those which are disengaged in a gaseous form from the
craters of active volcanoes.

_Siliceous springs.--Azores._--In order that water should hold a very
large quantity of silica in solution, it seems necessary that it should
be raised to a high temperature.[321] The hot springs of the Valle das
Fernas, in the island of St. Michael, rising through volcanic rocks,
precipitate vast quantities of siliceous sinter. Around the circular
basin of the largest spring, which is between twenty and thirty feet in
diameter, alternate layers are seen of a coarser variety of sinter mixed
with clay, including grass, ferns, and reeds, in different states of
petrifaction. In some instances, alumina, which is likewise deposited
from the hot waters, is the mineralizing material. Branches of the same
ferns which now flourish in the island are found completely petrified,
preserving the same appearance as when vegetating, except that they
acquire an ash-gray color. Fragments of wood, and one entire bed from
three to five feet in depth, composed of reeds now common in the island,
have become completely mineralized.

The most abundant variety of siliceous sinter occurs in layers, from a
quarter to half an inch in thickness, accumulated on each other often to
the height of a foot and upwards, and constituting parallel, and for the
most part horizontal, strata many yards in extent. This sinter has often
a beautiful semi-opalescent lustre. A recent breccia is also in the act
of forming, composed of obsidian, pumice, and scoriæ, cemented by
siliceous sinter.[322]

_Geysers of Iceland._--But the hot springs in various parts of Iceland,
particularly the celebrated geysers, afford the most remarkable example
of the deposition of silex.[323] The circular reservoirs into which the
geysers fall, are lined in the interior with a variety of opal, and
round the edges with sinter. The plants incrusted with the latter
substance have much the same appearance as those incrusted with
calcareous tufa in our own country. They consist of various grasses, the
horse-tail (_Equisetum_), and leaves of the birch-tree, which are the
most common of all, though no trees of this species now exist in the
surrounding country. The petrified stems also of the birch occur in a
state much resembling agatized wood.[324]

By analysis of the water, Mr. Faraday has ascertained that the solution
of the silex is promoted by the presence of the alkali, soda. He
suggests that the deposition of silica in an insoluble state takes place
partly because the water when cooled by exposure to the air is unable
to retain as much silica as when it issues from the earth at a
temperature of 180° or 190° Fahr.; and partly because the evaporation of
the water decomposes the compound of silica and soda which previously
existed. This last change is probably hastened by the carbonic acid of
the atmosphere uniting with the soda. The alkali, when disunited from
the silica, would readily be dissolved in and removed by running
water.[325]

Mineral waters, even when charged with a small proportion of silica, as
those of Ischia, may supply certain species of corals, sponges, and
infusoria, with matter for their siliceous secretions; but there is
little doubt that rivers obtain silex in solution from another and far
more general source, namely, the decomposition of felspar. When this
mineral, which is so abundant an ingredient in the hypogene and trappean
rocks, has disintegrated, it is found that the residue, called porcelain
clay, contains a small proportion only of the silica which existed in
the original felspar, the other part having been dissolved and removed
by water.[326]

_Ferruginous springs._--The waters of almost all springs contain some
iron in solution; and it is a fact familiar to all, that many of them
are so copiously impregnated with this metal, as to stain the rocks or
herbage through which they pass, and to bind together sand and gravel
into solid masses. We may naturally, then, conclude that this iron,
which is constantly conveyed from the interior of the earth into lakes
and seas, and which does not escape again from them into the atmosphere
by evaporation, must act as a coloring and cementing principle in the
subaqueous deposits now in progress. Geologists are aware that many
ancient sandstones and conglomerates are bound together or colored by
iron.

_Brine springs._--So great is the quantity of muriate of soda in some
springs, that they yield one-fourth of their weight in salt. They are
rarely, however, so saturated, and generally contain, intermixed with
salt, carbonate and sulphate of lime, magnesia, and other mineral
ingredients. The brine springs of Cheshire are the richest in our
country; those of Northwich being almost saturated. Those of Barton
also, in Lancashire, and Droitwich in Worcestershire, are extremely
rich.[327] They are known to have flowed for more than 1000 years, and
the quantity of salt which they have carried into the Severn and Mersey
must be enormous. These brine springs rise up through strata of
sandstone and red marl, which contain large beds of rock salt. The
origin of the brine, therefore, may be derived in this and many other
instances from beds of fossil salt; but as muriate of soda is one of the
products of volcanic emanations and of springs in volcanic regions, the
original source of salt may be as deep seated as that of lava.

Many springs in Sicily contain muriate of soda, and the "fiume salso,"
in particular, is impregnated with so large a quantity, that cattle
refuse to drink of it. A hot spring, rising through granite, at Saint
Nectaire, in Auvergne, may be mentioned as one of many, containing a
large proportion of muriate of soda, together with magnesia and other
ingredients.[328]

_Carbonated springs.--Auvergne._--Carbonic acid gas is very plentifully
disengaged from springs in almost all countries, but particularly near
active or extinct volcanoes. This elastic fluid has the property of
decomposing many of the hardest rocks with which it comes in contact,
particularly that numerous class in whose composition felspar is an
ingredient. It renders the oxide of iron soluble in water, and
contributes, as was before stated, to the solution of calcareous matter.
In volcanic districts these gaseous emanations are not confined to
springs, but rise up in the state of pure gas from the soil in various
places. The Grotto del Cane, near Naples, affords an example, and
prodigious quantities are now annually disengaged from every part of the
Limagne d'Auvergne, where it appears to have been developed in equal
quantity from time immemorial. As the acid is invisible, it is not
observed, except an excavation be made, wherein it immediately
accumulates, so that it will extinguish a candle. There are some springs
in this district, where the water is seen bubbling and boiling up with
much noise, in consequence of the abundant disengagement of this gas. In
the environs of Pont-Gibaud, not far from Clermont, a rock belonging to
the gneiss formation, in which lead-mines are worked, has been found to
be quite saturated with carbonic acid gas, which is constantly
disengaged. The carbonates of iron, lime, and manganese are so
dissolved, that the rock is rendered soft, and the quartz alone remains
unattacked.[329] Not far off is the small volcanic cone of Chaluzet,
which once broke up through the gneiss, and sent forth a lava stream.

_Supposed atmosphere of carbonic acid._--Prof. Bischoff in his history
of volcanoes,[330] has shown what enormous quantities of carbonic acid
gas are exhaled in the vicinity of the extinct craters of the Rhine (in
the neighborhood of the Laacher-see, for example, and the Eifel), and
also in the mineral springs of Nassau and other countries, where there
are no immediate traces of volcanic action. It would be easy to
calculate in how short a period the solid carbon, thus emitted from the
interior of the earth in an invisible form, would amount to a quantity
as great as could be obtained from the trees of a large forest, and how
many thousand years would be required to supply the materials of a dense
seam of pure coal from the same source. Geologists who favor the
doctrine of the former existence of an atmosphere highly charged with
carbonic acid, at the period of the ancient coal-plants, have not
sufficiently reflected on the continual disengagement of carbon, which
is taking place in a gaseous form from springs, as also in a free state
from the ground and from volcanic craters into the air. We know that
all plants are now engaged in secreting carbon, and many thousands of
large trees are annually floated down by great rivers, and buried in
their alluvial deposits; but before we can assume that the quantity of
carbon which becomes permanently locked up in the earth by such agency
will bring about an essential change in the chemical composition of the
atmosphere, we must be sure that the trees annually buried contain more
carbon than is given out from the interior of the earth in the same
lapse of time. Every large area covered by a dense mass of peat, bears
ample testimony to the fact, that several million tons of carbon have
been taken from the air, by the powers of vegetable life, and stored up
in the earth's crust, a large quantity of oxygen having been at the same
time set free; but we cannot infer from these circumstances, that the
constitution of the atmosphere has been materially deranged, until we
have data for estimating the rate at which dead animal and vegetable
substances are daily putrefying,--organic remains and various calcareous
rocks decomposing, and volcanic regions emitting fresh volumes of
carbonic acid gas. That the ancient carboniferous period was one of vast
duration all geologists are agreed; instead, therefore, of supposing an
excess of carbonic acid in the air at that epoch, for the support of a
peculiar flora, we may imagine Time to have multiplied the quantity of
carbon given out annually by mineral springs, volcanic craters, and
other sources, until the component elements of any given number of
coal-seams had been evolved from below, without any variation taking
place in the constitution of the atmosphere. It has been too common, in
reasoning on this question, to compute the loss of carbon by the volume
of coal stored up in the ancient strata, and to take no account of the
annual gain, by the restoration of carbonic acid to the atmosphere,
through the machinery above alluded to.[331]

_Disintegrating effects of carbonic acid._--The disintegration of
granite is a striking feature of large districts in Auvergne, especially
in the neighborhood of Clermont. This decay was called by Dolomieu, "la
maladie du granite;" and the rock may with propriety be said to have
_the rot_, for it crumbles to pieces in the hand. The phenomenon may,
without doubt, be ascribed to the continual disengagement of carbonic
acid gas from numerous fissures.

In the plains of the Po, between Verona and Parma, especially at Villa
Franca, south of Mantua, I observed great beds of alluvium, consisting
chiefly of primary pebbles, percolated by spring-water, charged with
carbonate of lime and carbonic acid in great abundance. They are for the
most part incrusted with calc-sinter; and the rounded blocks of gneiss,
which have all the outward appearance of solidity, have been so
disintegrated by the carbonic acid as readily to fall to pieces.

The subtraction of many of the elements of rocks by the solvent power of
carbonic acid, ascending both in a gaseous state and mixed with
spring-water in the crevices of rocks, must be one of the most powerful
sources of those internal changes and rearrangements of particles so
often observed in strata of every age. The calcareous matter, for
example, of shells, is often entirely removed and replaced by carbonate
of iron, pyrites, silex, or some other ingredient, such as mineral
waters usually contain in solution. It rarely happens, except in
limestone rocks, that the carbonic acid can dissolve all the constituent
parts of the mass; and for this reason, probably, calcareous rocks are
almost the only ones in which great caverns and long winding passages
are found.

_Petroleum springs._--Springs of which the waters contain a mixture of
petroleum and the various minerals allied to it, as bitumen, naphtha,
asphaltum, and pitch, are very numerous, and are, in many cases,
undoubtedly connected with subterranean fires, which raise or sublime
the more subtle parts of the bituminous matters contained in rocks. Many
springs in the territory of Modena and Parma, in Italy, produce
petroleum in abundance; but the most powerful, perhaps, yet known, are
those on the Irawadi, in the Burman empire. In one locality there are
said to be 520 wells, which yield annually 400,000 hogsheads of
petroleum.[332]

_Pitch lake of Trinidad._--Fluid bitumen is seen to ooze from the bottom
of the sea, on both sides of the island of Trinidad, and to rise up to
the surface of the water. Near Cape La Braye there is a vortex which, in
stormy weather, according to Captain Mallet, gushes out, raising the
water five or six feet, and covers the surface for a considerable space
with petroleum, or tar; and the same author quotes Gumilla, as stating,
in his "Description of the Orinoco," that about seventy years ago, a
spot of land on the western coast of Trinidad, near half-way between the
capital and an Indian village, sank suddenly, and was immediately
replaced by a small lake of pitch, to the great terror of the
inhabitants.[333]

It is probable that the great pitch lake of Trinidad owes its origin to
a similar cause; and Dr. Nugent has justly remarked, that in that
district all the circumstances are now combined from which deposits of
pitch may have originated. The Orinoco has for ages been rolling down
great quantities of woody and vegetable bodies into the surrounding sea,
where, by the influence of currents and eddies, they may be arrested and
accumulated in particular places. The frequent occurrence of earthquakes
and other indications of volcanic action in those parts lend countenance
to the opinion, that these vegetable substances may have undergone, by
the agency of subterranean fire, those transformations and chemical
changes which produce petroleum; and this may, by the same causes, be
forced up to the surface, where, by exposure to the air, it becomes
inspissated, and forms the different varieties of pure and earthy pitch,
or asphaltum, so abundant in the island.[334]

It may be stated generally, that a large portion of the finer particles
and the more crystalline substances, found in sedimentary rocks of
different ages, are composed of the same elements as are now held in
solution by springs, while the coarser materials bear an equally strong
resemblance to the pebbles and sedimentary matter carried down by
torrents and rivers. It should also be remembered, that it is not only
during inundations, when the muddy sediment is apparent, that rivers are
busy in conveying solid matter to the sea, but that even when their
waters are perfectly transparent, they are annually bearing along vast
masses of carbon, lime, and silica to the ocean.




CHAPTER XVII.

REPRODUCTIVE EFFECTS OF RIVERS.


  Lake deltas--Growth of the delta of the Upper Rhine in the Lake of
    Geneva--Computation of the age of deltas--Recent deposits in Lake
    Superior--Deltas of inland seas--Course of the Po--Artificial
    embankments of the Po and Adige--Delta of the Po, and other rivers
    entering the Adriatic--Rapid conversion of that gulf into
    land--Mineral characters of the new deposits--Marine delta of the
    Rhone--Various proofs of its increase--Stony nature of its
    deposits--Coast of Asia Minor--Delta of the Nile.


DELTAS IN LAKES.

I have already spoken in the 14th chapter of the action of running
water, and of the denuding power of rivers, but we can only form a just
conception of the excavating and removing force exerted by such bodies
of water, when we have the advantage of examining the reproductive
effects of the same agents: in other words, of beholding in a palpable
form the aggregate amount of matter, which they have thrown down at
certain points in their alluvial plains, or in the basins of lakes and
seas. Yet it will appear, when we consider the action of currents, that
the growth of deltas affords a very inadequate standard by which to
measure the entire carrying power of running water, since a considerable
portion of fluviatile sediment is swept far out to sea.

Deltas may be divided into, first, those which are formed in lakes;
secondly, those in island seas, where the tides are almost
imperceptible; and, thirdly, those on the borders of the ocean. The most
characteristic distinction between the lacustrine and marine deltas
consists in the nature of the organic remains which become imbedded in
their deposits; for, in the case of a lake, it is obvious that these
must consist exclusively of such genera of animals as inhabit the land
or the waters of a river or a lake; whereas, in the other case, there
will be an admixture, and most frequently a predominance, of animals
which inhabit salt water. In regard, however, to the distribution of
inorganic matter, the deposits of lakes and seas are formed under very
analogous circumstances.

_Lake of Geneva._--Lakes exemplify the first reproductive operations in
which rivers are engaged when they convey the detritus of rocks and the
ingredients of mineral springs from mountainous regions. The accession
of new land at the mouth of the Rhone, at the upper end of the Lake of
Geneva, or the Leman Lake, presents us with an example of a considerable
thickness of strata which have accumulated since the historical era.
This sheet of water is about thirty-seven miles long, and its breadth is
from two to eight miles. The shape of the bottom is very irregular, the
depth having been found by late measurements to vary from 20 to 160
fathoms.[335] The Rhone, where it enters at the upper end, is turbid and
discolored; but its waters, where it issues at the town of Geneva, are
beautifully clear and transparent. An ancient town, called Port Vallais
(Portus Valesiæ of the Romans), once situated at the water's edge, at
the upper end, is now more than a mile and a half inland--this
intervening alluvial tract having been acquired in about eight
centuries. The remainder of the delta consists of a flat alluvial plain,
about five or six miles in length, composed of sand and mud, a little
raised above the level of the river, and full of marshes.

Sir Henry De la Beche found, after numerous soundings in all parts of
the lake, that there was a pretty uniform depth of from 120 to 160
fathoms throughout the central region, and on approaching the delta, the
shallowing of the bottom began to be very sensible at a distance of
about a mile and three quarters from the mouth of the Rhone; for a line
drawn from St. Gingoulph to Vevey gives a mean depth of somewhat less
than 600 feet, and from that part of the Rhone, the fluviatile mud is
always found along the bottom.[336] We may state, therefore, that the
new strata annually produced are thrown down upon a slope about two
miles in length; so that, notwithstanding the great depth of the lake,
the new deposits are inclined at so slight an angle, that the dip of the
beds would be termed, in ordinary geological language, horizontal.

The strata probably consist of alternations of finer and coarser
particles; for, during the hotter months from April to August, when the
snows melt, the volume and velocity of the river are greatest, and large
quantities of sand, mud, vegetable matter, and drift-wood are
introduced; but during the rest of the year, the influx is comparatively
feeble, so much so, that the whole lake, according to Saussure, stands
six feet lower. If, then, we could obtain a section of the accumulation
formed in the last eight centuries, we should see a great series of
strata, probably from 600 to 900 feet thick (the supposed original depth
of the head of the lake), and nearly two miles in length, inclined at a
very slight angle. In the mean time, a great number of smaller deltas
are growing around the borders of the lake, at the mouths of rapid
torrents, which pour in large masses of sand and pebbles. The body of
water in these torrents is too small to enable them to spread out the
transported matter over so extensive an area as the Rhone does. Thus,
for example, there is a depth of eighty fathoms within half a mile of
the shore, immediately opposite the great torrent which enters east of
Ripaille, so that the dip of the strata in that minor delta must be
about four times as great as those deposited by the main river at the
upper extremity of the lake.[337]

_Chronological computations of the age of deltas._--The capacity of this
basin being now ascertained, it would be an interesting subject of
inquiry, to determine in what number of years the Leman Lake will be
converted into dry land. It would not be very difficult to obtain the
elements for such a calculation, so as to approximate at least to the
quantity of time required for the accomplishment of the result. The
number of cubic feet of water annually discharged by the river into the
lake being estimated, experiments might be made in the winter and summer
months, to determine the proportion of matter held in suspension or in
chemical solution by the Rhone. It would be also necessary to allow for
the heavier matter drifted along at the bottom, which might be estimated
on hydrostatical principles, when the average size of the gravel and the
volume and velocity of the stream at different seasons were known.
Supposing all these observations to have been made, it would be more
easy to calculate the future than the former progress of the delta,
because it would be a laborious task to ascertain, with any degree of
precision, the original depth and extent of that part of the lake which
is already filled up. Even if this information were actually obtained by
borings, it would only enable us to approximate within a certain number
of centuries to the time when the Rhone began to form its present delta;
but this would not give us the date of the origin of the Leman Lake in
its present form, because the river may have flowed into it for
thousands of years, without importing any sediment whatever. Such would
have been the case, if the waters had first passed through a chain of
upper lakes; and that this was actually the fact, seems indicated by the
course of the Rhone between Martigny and the Lake of Geneva, and, still
more decidedly, by the channels of many of its principal feeders.

If we ascend, for example, the valley through which the Dranse flows, we
find that it consists of a succession of basins, one above the other, in
each of which there is a wide expanse of flat alluvial lands, separated
from the next basin by a rocky gorge, once perhaps the barrier of a
lake. The river seems to have filled these lakes, one after the other,
and to have partially cut through the barriers, some of which it is
still gradually eroding to a greater depth. Before, therefore, we can
pretend even to hazard a conjecture as to the era at which the principal
delta of Lake Leman or any other delta commenced, we must be thoroughly
acquainted with the geographical features and geological history of the
whole system of higher valleys which communicate with the main stream,
and all the changes which they have undergone since the last series of
convulsions which agitated and altered the face of the country.

_Lake Superior._--Lake Superior is the largest body of freshwater in the
world, being above 1700 geographical miles in circumference when we
follow the sinuosities of its coasts, and its length, on a curved line
drawn through its centre, being more than 400, and its extreme breadth
above 150 geographical miles. Its surface is nearly as large as the
whole of England. Its average depth varies from 80 to 150 fathoms; but,
according to Captain Bayfield, there is reason to think that its
greatest depth would not be overrated at 200 fathoms, so that its bottom
is, in some parts, nearly 600 feet below the level of the Atlantic, its
surface being about as much above it. There are appearances in different
parts of this, as of the other Canadian lakes, leading us to infer that
its waters formerly occupied a higher level than they reach at present;
for at a considerable distance from the present shores, parallel lines
of rolled stones and shells are seen rising one above the other, like
the seats of an amphitheatre. These ancient lines of shingle are exactly
similar to the present beaches in most bays, and they often attain an
elevation of 40 or 50 feet above the present level. As the heaviest
gales of wind do not raise the waters more than three or four feet, the
elevated beaches have by some been referred to the subsidence of the
lake at former periods, in consequence of the wearing down of its
barrier; by others to the upraising of the shores by earthquakes, like
those which have produced similar phenomena on the coast of Chili.

The streams which discharge their waters into Lake Superior are several
hundred in number, without reckoning those of smaller size; and the
quantity of water supplied by them is many times greater than that
discharged at the Falls of St. Mary, the only outlet. The evaporation,
therefore, is very great, and such as might be expected from so vast an
extent of surface. On the northern side, which is encircled by primary
mountains, the rivers sweep in many large boulders with smaller gravel
and sand, chiefly composed of granitic and trap rocks. There are also
currents in the lake in various directions, caused by the continued
prevalence of strong winds, and to their influence we may attribute the
diffusion of finer mud far and wide over great areas; for by numerous
soundings made during Captain Bayfield's survey, it was ascertained that
the bottom consists generally of a very adhesive clay, containing shells
of the species at present existing in the lake. When exposed to the air,
this clay immediately becomes indurated in so great a degree, as to
require a smart blow to break it. It effervesces slightly with diluted
nitric acid, and is of different colors in different parts of the lake;
in one district blue, in another red, and in a third white, hardening
into a substance resembling pipeclay.[338] From these statements, the
geologist will not fail to remark how closely these recent lacustrine
formations in America resemble the tertiary argillaceous and calcareous
marls of lacustrine origin in Central France. In both cases many of the
genera of shells most abundant, as Limnea and Planorbis, are the same;
and in regard to other classes of organic remains there must be the
closest analogy, as I shall endeavor more fully to explain when speaking
of the imbedding of plants and animals in recent deposits.


DELTAS OF INLAND SEAS.

Having thus briefly considered some of the lacustrine deltas now in
progress, we may next turn our attention to those of inland seas.

_Course of the Po._--The Po affords an instructive example of the manner
in which a great river bears down to the sea the matter poured into it
by a multitude of tributaries descending from lofty chains of mountains.
The changes gradually effected in the great plain of Northern Italy,
since the time of the Roman republic, are considerable. Extensive lakes
and marshes have been gradually filled up, as those near Placentia,
Parma, and Cremona, and many have been drained naturally by the
deepening of the beds of rivers. Deserted river-courses are not
unfrequent, as that of the Serio Morto, which formerly fell into the
Adda, in Lombardy. The Po also itself has often deviated from its
course, having after the year 1390 deserted part of the territory of
Cremona, and invaded that of Parma; its old channel being still
recognizable, and bearing the name of Po Morto. There is also an old
channel of the Po in the territory of Parma, called Po Vecchio, which
was abandoned in the twelfth century, when a great number of towns were
destroyed.

_Artificial embankments of Italian rivers._--To check these and similar
aberrations, a general system of embankment has been adopted; and the
Po, Adige, and almost all their tributaries, are now confined between
high artificial banks. The increased velocity acquired by streams thus
closed in, enables them to convey a much larger portion of foreign
matter to the sea; and, consequently, the deltas of the Po and Adige
have gained far more rapidly on the Adriatic since the practice of
embankment became almost universal. But, although more sediment is borne
to the sea, part of the sand and mud, which in the natural state of
things would be spread out by annual inundations over the plain, now
subsides in the bottom of the river-channels; and their capacity being
thereby diminished, it is necessary, in order to prevent inundations in
the following spring, to extract matter from the bed, and to add it to
the banks of the river. Hence it happens that these streams now traverse
the plain on the top of high mounds, like the waters of aqueducts, and
at Ferrara the surface of the Po has become more elevated than the roofs
of the houses.[339] The magnitude of these barriers is a subject of
increasing expense and anxiety, it having been sometimes found necessary
to give an additional height of nearly one foot to the banks of the
Adige and Po in a single season.

The practice of embankment was adopted on some of the Italian rivers as
early as the thirteenth century; and Dante, writing in the beginning of
the fourteenth, describes, in the seventh circle of hell, a rivulet of
tears separated from a burning sandy desert by embankments "like those
which, between Ghent and Bruges, were raised against the ocean, or those
which the Paduans had erected along the Brenta to defend their villas on
the melting of the Alpine snows."


  Quale i Fiamminghi tra Guzzante e Bruggia,
  Temendo il fiotto che in ver lor s'avventa,
  Fanno lo schermo, perchè il mar si fuggia,
  E quale i Padovan lungo la Brenta,
  Per difender lor ville e lor castelli,
  Anzi che Chiarentana il caldo senta.--

  _Inferno_, Canto xv.


In the Adriatic, from the northern part of the Gulf of Trieste, where
the Isonzo enters, down to the south of Ravenna, there is an
uninterrupted series of recent accessions of land, more than 100 miles
in length, which, within the last 2000 years, have increased from _two
to twenty miles in breadth_. A line of sand-bars of great length has
been formed nearly all along the western coast of this gulf, inside of
which are lagunes, such as those of Venice, and the large lagune of
Comacchio, 20 miles in diameter. Newly deposited mud brought down by the
streams is continually lessening the depth of the lagunes, and
converting part of them into meadows.[340] The Isonzo, Tagliamento,
Piave, Brenta, Adige, and Po, besides many other inferior rivers,
contribute to this advance of the coast-line and to the shallowing of
the lagunes and the gulf.

_Delta of the Po._--The Po and the Adige may now be considered as
entering by one common delta, for two branches of the Adige are
connected with arms of the Po, and thus the principal delta has been
pushed out beyond those bars which separate the lagunes from the sea.
The rate of the advance of this new land has been accelerated, as before
stated, since the system of embanking the rivers became general,
especially at that point where the Po and Adige enter. The waters are no
longer permitted to spread themselves far and wide over the plains, and
to leave behind them the larger portion of their sediment. Mountain
torrents also have become more turbid since the clearing away of
forests, which once clothed the southern flanks of the Alps. It is
calculated that the mean rate of advance of the delta of the Po on the
Adriatic between the years 1200 and 1600 was 25 yards or metres a year,
whereas the mean annual gain from 1600 to 1804 was 70 metres.[341]

Adria was a seaport in the time of Augustus, and had, in ancient times,
given its name to the gulf; it is now about twenty Italian miles inland.
Ravenna was also a seaport, and is now about four miles from the main
sea. Yet even before the practice of embankment was introduced, the
alluvium of the Po advanced with rapidity on the Adriatic; for Spina, a
very ancient city, originally built in the district of Ravenna, at the
mouth of a great arm of the Po, was, so early as the commencement of our
era, eleven miles distant from the sea.[342]

But although so many rivers are rapidly converting the Adriatic into
land, it appears, by the observations of M. Morlot, that since the time
of the Romans, there has been a general subsidence of the coast and bed
of this sea in the same region to the amount of five feet, so that the
advance of the new-made land has not been so fast as it would have been
had the level of the coast remained unaltered. The signs of a much
greater depression anterior to the historical period have also been
brought to light by an Artesian well, bored in 1847, to the depth of
more than 400 feet, which still failed to penetrate through the modern
fluviatile deposit. The auger passed chiefly through beds of sand and
clay, but at four several depths, one of them very near the bottom of
the excavation, it pierced beds of turf, or accumulations of vegetable
matter, precisely similar to those now formed superficially on the
extreme borders of the Adriatic. Hence we learn that a considerable area
of what was once land has sunk down 400 feet in the course of ages.[343]

The greatest depth of the Adriatic, between Dalmatia and the mouths of
the Po, is twenty-two fathoms; but a large part of the Gulf of Trieste
and the Adriatic, opposite Venice, is less than twelve fathoms deep.
Farther to the south, where it is less affected by the influx of great
rivers, the gulf deepens considerably. Donati, after dredging the
bottom, discovered the new deposits to consist partly of mud and partly
of rock, the rock being formed of calcareous matter, incrusting shells.
He also ascertained, that particular species of testacea were grouped
together in certain places, and were becoming slowly incorporated with
the mud or calcareous precipitates.[344] Olivi, also, found some
deposits of sand, and others of mud, extending half way across the gulf;
and he states that their distribution along the bottom was evidently
determined by the prevailing current.[345] It is probable, therefore,
that the finer sediment of all the rivers at the head of the Adriatic
may be intermingled by the influence of the current; and all the central
parts of the gulf may be considered as slowly filling up with horizontal
deposits, similar to those of the Subapennine hills, and containing many
of the same species of shells. The Po merely introduces at present fine
sand and mud, for it carries no pebbles farther than the spot where it
joins the Trebia, west of Piacenza. Near the northern borders of the
basin, the Isonzo, Tagliamento, and many other streams, are forming
immense beds of sand and some conglomerate; for here some high mountains
of Alpine limestone approach within a few miles of the sea.

In the time of the Romans, the hot-baths of Monfalcone were on one of
several islands of Alpine limestone, between which and the mainland, on
the north, was a channel of the sea, about a mile broad. This channel is
now converted into a grassy plain, which surrounds the islands on all
sides. Among the numerous changes on this coast, we find that the
present channel of the Isonzo is several miles to the west of its
ancient bed, in part of which, at Ronchi, the old Roman bridge which
crossed the Via Appia was lately found buried in fluviatile silt.

_Marine delta of the Rhone._--The lacustrine delta of the Rhone in
Switzerland has already been considered (p. 251), its contemporaneous
marine delta may now be described. Scarcely has the river passed out of
the Lake of Geneva before its pure waters are again filled with sand and
sediment by the impetuous Arve, descending from the highest Alps, and
bearing along in its current the granitic detritus annually brought down
by the glaciers of Mont Blanc. The Rhone afterwards receives vast
contributions of transported matter from the Alps of Dauphiny, and the
primary and volcanic mountains of Central France; and when at length it
enters the Mediterranean, it discolors the blue waters of that sea with
a whitish sediment, for the distance of between six and seven miles,
throughout which space the current of fresh water is perceptible.

Strabo's description of the delta is so inapplicable to its present
configuration, as to attest a complete alteration in the physical
features of the country since the Augustan age. It appears, however,
that the head of the delta, or the point at which it begins to ramify,
has remained unaltered since the time of Pliny, for he states that the
Rhone divided itself at Arles into two arms. This is the case at
present; one of the branches, the western, being now called Le Petit
Rhône, which is again subdivided before entering the Mediterranean. The
advance of the base of the delta, in the last eighteen centuries, is
demonstrated by many curious antiquarian monuments. The most striking of
these is the great and unnatural détour of the old Roman road from
Ugernum to Beziers (_Boeterræ_) which went round by Nismes
(_Nemausus_). It is clear that, when this was first constructed, it was
impossible to pass in a direct line, as now, across the delta, and that
either the sea or marshes intervened in a tract now consisting of terra
firma.[346] Astruc also remarks, that all the places on low lands, lying
to the north of the old Roman road between Nismes and Beziers, have
names of Celtic origin, evidently given to them by the first inhabitants
of the country; whereas, the places lying south of that road, towards
the sea, have names of Latin derivation, and were clearly founded after
the Roman language had been introduced.

Another proof, also, of the great extent of land which has come into
existence since the Romans conquered and colonized Gaul, is derived from
the fact, that the Roman writers never mention the thermal waters of
Balaruc in the delta, although they were well acquainted with those of
Aix, and others still more distant, and attached great importance to
them, as they invariably did to all hot springs. The waters of Balaruc,
therefore, must have formerly issued under the sea--a common phenomenon
on the borders of the Mediterranean; and on the advance of the delta
they continued to flow out through the new deposits.

Among the more direct proofs of the increase of land, we find that Mese,
described under the appellation of Mesua Collis by Pomponius Mela,[347]
and stated by him to be nearly an island, is now far inland. Notre Dame
des Ports, also, was a harbor in 898, but is now a league from the
shore. Psalmodi was an island in 815, and is now two leagues from the
sea. Several old lines of towers and sea-marks occur at different
distances from the present coast, all indicating the successive retreat
of the sea, for each line has in its turn become useless to mariners;
which may well be conceived, when we state that the Tower of Tignaux,
erected on the shore so late as the year 1737, is already a mile remote
from it.[348]

By the confluence of the Rhone and the currents of the Mediterranean,
driven by winds from the south, sand-bars are often formed across the
mouths of the river; by these means considerable spaces become divided
off from the sea, and subsequently from the river also, when it shifts
its channels of efflux. As some of these lagoons are subject to the
occasional ingress of the river when flooded, and of the sea during
storms, they are alternately salt and fresh. Others, after being filled
with salt water, are often lowered by evaporation till they become more
salt than the sea; and it has happened, occasionally, that a
considerable precipitate of muriate of soda has taken place in these
natural salterns. During the latter part of Napoleon's career, when the
excise laws were enforced with extreme rigor, the police was employed to
prevent such salt from being used. The fluviatile and marine shells
inclosed in these small lakes often live together in brackish water; but
the uncongenial nature of the fluid usually produces a dwarfish size,
and sometimes gives rise to strange varieties in form and color.

Captain Smyth in his survey of the coast of the Mediterranean, found the
sea opposite the mouth of the Rhone, to deepen gradually from four to
forty fathoms, within a distance of six or seven miles, over which the
discolored fresh water extends; so that the inclination of the new
deposits must be too slight to be appreciable in such an extent of
section as a geologist usually obtains in examining ancient formations.
When the wind blew from the southwest, the ships employed in the survey
were obliged to quit their moorings; and when they returned, the new
sand-banks in the delta were found covered over with a great abundance
of marine shells. By this means, we learn how occasional beds of drifted
marine shells may become interstratified with freshwater strata at a
river's mouth.

_Stony nature of its deposits._--That a great proportion, at least, of
the new deposit in the delta of the Rhone consists of _rock_, and not of
loose incoherent matter, is perfectly ascertained. In the Museum at
Montpelier is a cannon taken up from the sea near the mouth of the
river, imbedded in a crystalline calcareous rock. Large masses, also,
are continually taken up of an arenaceous rock, cemented by calcareous
matter, including multitudes of broken shells of recent species. The
observations lately made on this subject corroborate the former
statement of Marsilli, that the earthy deposits of the coast of
Languedoc form a stony substance, for which reason he ascribes a certain
bituminous, saline, and glutinous nature to the substances brought down
with sand by the Rhone.[349] If the number of mineral springs charged
with carbonate of lime which fall into the Rhone and its feeders in
different parts of France be considered, we shall feel no surprise at
the lapidification of the newly deposited sediment in this delta. It
should be remembered, that the fresh water introduced by rivers being
lighter than the water of the sea, floats over the latter, and remains
upon the surface for a considerable distance. Consequently it is exposed
to as much evaporation as the waters of a lake; and the area over which
the river-water is spread, at the junction of great rivers and the sea,
may well be compared, in point of extent, to that of considerable lakes.

Now, it is well known, that so great is the quantity of water carried
off by evaporation in some lakes, that it is nearly equal to the water
flowing in; and in some inland seas, as the Caspian, it is quite equal.
We may, therefore, well suppose that, in cases where a strong current
does not interfere, the greater portion not only of the matter held
mechanically in suspension, but of that also which is in chemical
solution, may be precipitated at no great distance from the shore. When
these finer ingredients are extremely small in quantity, they may only
suffice to supply crustaceous animals, corals, and marine plants, with
the earthy particles necessary for their secretions; but whenever it is
in excess (as generally happens if the basin of a river lie partly in a
district of active or extinct volcanoes), then will solid deposits be
formed, and the shells will at once be included in a rocky mass.

_Coast of Asia Minor._--Examples of the advance of the land upon the sea
are afforded by the southern coast of Asia Minor. Admiral Sir F.
Beaufort has pointed out in his survey the great alterations effected
since the time of Strabo, where havens are filled up, islands joined to
the mainland, and where the whole continent has increased many miles in
extent. Strabo himself, on comparing the outline of the coast in his
time with its ancient state, was convinced, like our countryman, that
it had gained very considerably upon the sea. The new-formed strata of
Asia Minor consist _of stone_, not of loose incoherent materials. Almost
all the streamlets and rivers, like many of those in Tuscany and the
south of Italy, hold abundance of carbonate of lime in solution, and
precipitate travertin, or sometimes bind together the sand and gravel
into solid sandstones and conglomerates; every delta and sand-bar thus
acquires solidity, which often prevents streams from forcing their way
through them, so that their mouths are constantly changing their
position.[350]

_Delta of the Nile._--That Egypt was "the gift of the Nile," was the
opinion of her priests before the time of Herodotus; and Rennell
observes, that the "configuration and composition of the low lands leave
no room for doubt that the sea once washed the base of the rocks on
which the pyramids of Memphis stand, the _present_ base of which is
washed by the inundation of the Nile, at an elevation of 70 or 80 feet
above the Mediterranean. But when we attempt to carry back our ideas to
the remote period when the foundation of the delta was first laid, we
are lost in the contemplation of so vast an interval of time."[351]
Herodotus observes, "that the country round Memphis seemed formerly to
have been an arm of the sea gradually filled by the Nile, in the same
manner as the Meander, Achelous, and other streams, had formed deltas.
Egypt, therefore, he says, like the Red Sea, was once a long narrow bay,
and both gulfs were separated by a small neck of land. If the Nile, he
adds, should by any means have an issue into the Arabian Gulf, it might
choke it up with earth in 20,000 or even, perhaps, in 10,000 years; and
why may not the Nile have filled a still greater gulf with mud in the
space of time which has passed before our age?"[352]

The distance between Memphis and the most prominent part of the delta in
a straight line north and south, is about 100 geographical miles; the
length of the base of the delta is more than 200 miles if we follow the
coast between the ancient extreme eastern and western arms; but as these
are now blocked up, that part only of Lower Egypt which intervenes
between the Rosetta and Damietta branches, is usually called the delta,
the coast line of which is about 90 miles in length. The bed of the
river itself, says Sir J. G. Wilkinson, undergoes a gradual increase of
elevation varying in different places, and always lessening in
proportion as the river approaches the sea. "This increase of elevation
in perpendicular height is much smaller in Lower than in Upper Egypt,
and in the delta it diminishes still more; so that, according to an
approximate calculation, the land about Elephantine, or the first
cataract, lat. 24° 5', has been raised nine feet in 1700 years; at
Thebes, lat. 25° 43', about seven feet; and at Heliopolis and Cairo,
lat. 30°, about five feet ten inches. At Rosetta and the mouths of the
Nile, lat. 31° 30', the diminution in the perpendicular thickness of the
deposit is lessened in a much greater decreasing ratio than in the
straitened valley of Central and Upper Egypt, owing to the great extent,
east and west, over which the inundation spreads."[353]

For this reason the alluvial deposit does not cause the delta to
protrude rapidly into the sea, although some ancient cities are now a
mile or more inland, and the mouths of the Nile, mentioned by the
earlier geographers, have been many of them silted up, and the outline
of the coast entirely changed.

The bed of the Nile always keeps pace with the general elevation of the
soil, and the banks of this river, like those of the Mississippi and its
tributaries (see p. 265), are much higher than the flat land at a
distance, so that they are seldom covered during the highest
inundations. In consequence of the gradual rise of the river's bed, the
annual flood is constantly spreading over a wider area, and the alluvial
soil encroaches on the desert, covering, to the depth of six or seven
feet, the base of statues and temples which the waters never reached
3000 years ago. Although the sands of the Libyan deserts have in some
places been drifted into the valley of the Nile, yet these aggressions,
says Wilkinson, are far more than counterbalanced by the fertilizing
effect of the water which now reaches farther inland towards the desert,
so that the number of square miles of arable soil is greater at present
than at any previous period.

_Mud of the Nile._--On comparing the different analyses which have been
published of this mud, it will be found that it contains a large
quantity of argillaceous matter, with much peroxide of iron, some
carbonate of lime, and a small proportion of carbonate of magnesia. The
latest and most careful analysis by M. Lassaigne shows a singularly
close resemblance in the proportions of the ingredients of silica,
alumina, iron, carbon, lime, and magnesia, and those observed in
ordinary mica;[354] but a much larger quantity of calcareous matter is
sometimes present.

In many places, as at Cairo, where artificial excavations have been
made, or where the river has undermined its banks, the mud is seen to be
thinly stratified, the upper part of each annual layer consisting of
earth of a lighter color than the lower, and the whole separating easily
from the deposit of the succeeding year. These annual layers are
variable in thickness; but, according to the calculations of Girard and
Wilkinson, the mean annual thickness of a layer at Cairo cannot exceed
that of a sheet of thin pasteboard, and a stratum of two or three feet
must represent the accumulation of a thousand years.

The depth of the Mediterranean is about twelve fathoms at a small
distance from the shore of the delta; it afterwards increases gradually
to 50, and then suddenly descends to 380 fathoms, which is, perhaps, the
original depth of the sea where it has not been rendered shallower by
fluviatile matter. We learn from Lieut. Newbold that nothing but the
finest and lightest ingredients reach the Mediterranean, where he has
observed the sea discolored by them to the distance of 40 miles from the
shore.[355] The small progress of the delta in the last 2000 years
affords, perhaps, no measure for estimating its rate of growth when it
was an inland bay, and had not yet protruded itself beyond the
coast-line of the Mediterranean. A powerful current now sweeps along the
shores of Africa, from the Straits of Gibraltar to the prominent
convexity of Egypt, the western side of which is continually the prey of
the waves; so that not only are fresh accessions of land checked, but
ancient parts of the delta are carried away. By this cause, Canopus and
some other towns have been overwhelmed; but to this subject I shall
again refer when speaking of tides and currents.




CHAPTER XVIII.

REPRODUCTIVE EFFECTS OF RIVERS--_continued_.


  Deltas formed under the influence of tides--Basin and delta of the
    Mississippi--Alluvial plain--River-banks and bluffs--Curves of the
    river--Natural rafts and snags--New lakes, and effects of
    earthquakes--Antiquity of the delta--Delta of the Ganges and
    Brahmapootra--Head of the delta and Sunderbunds--Islands formed and
    destroyed--Crocodiles--Amount of fluviatile sediment in the
    water--Artesian boring at Calcutta--Proofs of subsidence--Age of the
    delta--Convergence of deltas--Origin of existing deltas not
    contemporaneous--Grouping of strata and stratification in
    deltas--Conglomerates--Constant interchange of land and sea.


In the last chapter several examples were given of the deltas of inland
seas, where the influence of the tides is almost imperceptible. We may
next consider those marine or oceanic deltas, where the tides play an
important part in the dispersion of fluviatile sediment, as in the Gulf
of Mexico, where they exert a moderate degree of force, and then in the
Bay of Bengal, where they are extremely powerful. In regard to
estuaries, which Rennel termed "negative deltas," they will be treated
of more properly when our attention is specially turned to the
operations of tides and currents (chapters 20, 21, and 22). In this
case, instead of the land gaining on the sea at the river's mouth, the
tides penetrate far inland beyond the general coast-line.


BASIN AND DELTA OF THE MISSISSIPPI.

_Alluvial plain._--The hydrographical basin of the Mississippi displays,
on the grandest scale, the action of running water on the surface of a
vast continent. This magnificent river rises nearly in the forty-ninth
parallel of north latitude, and flows to the Gulf of Mexico in the
twenty-ninth--a course, including its meanders, of more than three
thousand miles. It passes from a cold climate, where the hunter obtains
his furs and peltries, traverses the temperate latitudes, and discharges
its waters into the sea in the region of rice, the cotton plant, and the
sugar-cane. From near its mouth at the Balize a steamboat may ascend for
2000 miles with scarcely any perceptible difference in the width of the
river. Several of its tributaries, the Red River, the Arkansas, the
Missouri, the Ohio, and others, would be regarded elsewhere as of the
first importance, and, taken together, are navigable for a distance many
times exceeding that of the main stream. No river affords a more
striking illustration of the law before mentioned, that an augmentation
of volume does not occasion a proportional increase of surface, nay, is
even sometimes attended with a narrowing of the channel. The Mississippi
is half a mile wide at its junction with the Missouri, the latter being
also of equal width; yet the united waters have only, from their
confluence to the mouth of the Ohio, a medial width of about half a
mile. The junction of the Ohio seems also to produce no increase, but
rather a decrease, of surface.[356] The St. Francis, White, Arkansas,
and Red rivers are also absorbed by the main stream with scarcely any
apparent increase of its width, although here and there it expands to a
breadth of 1½, or even to 2 miles. On arriving at New Orleans, it is
somewhat less than half a mile wide. Its depth there is very variable,
the greatest at high water being 168 feet. The mean rate at which the
whole body of water flows is variously estimated; according to Mr.
Forshey the mean velocity of the current at the surface, somewhat
exceeds 2¼ miles an hour when the water is at a mean height. For 300
miles above New Orleans the distance measured by the winding river is
about twice as great as the distance in a right line. For the first 100
miles from the mouth the rate of fall is 1·80 inch per mile, for the
second hundred 2 inches, for the third 2·30, for the fourth 2·57.

The alluvial plain of the Mississippi begins to be of great width below
Cape Girardeau, 50 miles above the junction of the Ohio. At this
junction it is about 50 miles broad, south of which it contracts to
about 30 miles at Memphis, expands again to 80 miles at the mouth of the
White River, and then, after various contractions and expansions,
protrudes beyond the general coast-line, in a large delta, about 90
miles in width, from N. E. to S. W. Mr. Forshey estimates the area of
the great plain as above defined at 31,200 square miles, with a
circumference of about 3000 miles, exceeding the area of Ireland. If
that part of this plain which lies below, or to the south of the
branching off of the highest arm, called the Atchafalaya, be termed the
delta, it constitutes less than half of the whole, being 14,000 square
British miles in area. The delta may be said to be bounded on the east,
west, and south by the sea; on the north chiefly by the broad
valley-plain which entirely resembles it in character as in origin. The
east and west boundaries of the alluvial region above the head of the
delta consists of cliffs or bluffs, which on the east side of the
Mississippi are very abrupt, and are undermined by the river at many
points. They consist, from Baton Rouge in Louisiana, where they
commence, as far north as the borders of Kentucky, of geological
formations newer than the cretaceous, the lowest being Eocene, and the
uppermost consisting of loam, resembling the loess of the Rhine, and
containing freshwater and land shells almost all of existing species.
(See fig. 23.) These recent shells are associated with the bones of the
mastodon, elephant, tapir, mylodon, horse, ox, and other quadrupeds,
most of them of extinct species.

I have endeavored to show in my Second Visit to the United States, that
this extensive formation of loam is either an ancient alluvial plain or
a delta of the great river, formed originally at a lower level, and
since upheaved, and partially denuded.

[Illustration: Fig. 23.

VALLEY OF THE MISSISSIPPI.]

The Mississippi in that part of its course which is below the mouth of
the Ohio, frequently washes the eastern bluffs, but never once comes in
contact with the western. These are composed of similar formations; but
I learn from Mr. Forshey that they rise up more gently from the alluvial
plain (as at _a_, fig. 23). It is supposed that the waters are thrown to
the eastern side, because all the large tributary rivers entering from
the west have filled that side of the great valley with their deltas, or
with a sloping mass of clay and sand; so that the opposite bluffs are
undermined, and the Mississippi is slowly but incessantly advancing
eastward.[357]

_Curves of the Mississippi._--The river traverses the plain in a
meandering course, describing immense curves. After sweeping round the
half of a circle, it is carried in a rapid current diagonally across the
ordinary direction of its channel, to another curve of similar shape.
Opposite to each of these, there is always a sand-bar, answering, in the
convexity of its form, to the concavity of "the bend," as it is
called.[358] The river, by continually wearing these curves deep,
returns, like many other streams before described, on its own track, so
that a vessel in some places, after sailing for twenty-five or thirty
miles, is brought round again to within a mile of the place whence it
started. When the waters approach so near to each other, it often
happens at high floods that they burst through the small tongue of
land, and insulate a portion, rushing through what is called the
"cut-off," so that vessels may pass from one point to another in half a
mile to a distance which it previously required a voyage of twenty miles
to reach. As soon as the river has excavated the new passage, bars of
sand and mud are formed at the two points of junction with the old bend,
which is soon entirely separated from the main river by a continuous
mud-bank covered with wood. The old bend then becomes a semicircular
lake of clear water, inhabited by large gar-fish, alligators, and wild
fowl, which the steam-boats have nearly driven away from the main
river. A multitude of such crescent-shaped lakes, scattered far and wide
over the alluvial plain, the greater number of them to the west, but
some of them also eastward of the Mississippi, bear testimony of the
extensive wanderings of the great stream in former ages. For the last
two hundred miles above its mouth the course of the river is much less
winding than above, there being only in the whole of that distance one
great curve, that called the "English Turn." This great straightness of
the stream is ascribed by Mr. Forshey to the superior tenacity of the
banks, which are more clayey in this region.

[Illustration: Fig. 24.

Section of channel, bank, levees (_a_ and _b_), and swamps of
Mississippi river.]

The Mississippi has been incorrectly described by some of the earlier
geographers, as a river running along the top of a long hill, or mound
in a plain. In reality it runs in a valley, from 100 to 200 or more feet
in depth, as _a_, _c_, _b_, fig. 24, its banks forming long strips of
land parallel to the course of the main stream, and to the swamps _g_,
_f_, and _d_, _e_, lying on each side. These extensive morasses, which
are commonly well-wooded, though often submerged for months
continuously, are rarely more than fifteen feet below the summit level
of the banks. The banks themselves are occasionally overflowed, but are
usually above water for a breadth of about two miles. They follow all
the curves of the great river, and near New Orleans are raised
artificially by embankments (or levees), _a b_, fig. 24, through which
the river when swollen sometimes cuts a deep channel (or crevasse),
inundating the adjoining low lands and swamps, and not sparing the lower
streets of the great city.

The cause of the uniform upward slope of the river-bank above the
adjoining alluvial plain is this: when the waters charged with sediment
pass over the banks in the flood season, their velocity is checked among
the herbage and reeds, and they throw down at once the coarser and more
sandy matter with which they are charged. But the fine particles of mud
are carried farther on, so that at the distance of about two miles, a
thin film of fine clay only subsides, forming a stiff unctuous black
soil, which gradually envelops the base of trees growing on the borders
of the swamps.

_Waste of the banks._--It has been said of a mountain torrent, that "it
lays down what it will remove, and removes what it has laid down;" and
in like manner the Mississippi, by the continual shifting of its course,
sweeps away, during a great portion of the year, considerable tracts of
alluvium, which were gradually accumulated by the overflow of former
years, and the matter now left during the spring-floods will be at some
future time removed. After the flood season, when the river subsides
within its channel, it acts with destructive force upon the alluvial
banks, softened and diluted by the recent overflow. Several acres at a
time, thickly covered with wood, are precipitated into the stream; and
large portions of the islands are frequently swept away.

"Some years ago," observes Captain Hall, "when the Mississippi was
regularly surveyed, all its islands were numbered, from the confluence
of the Missouri to the sea; but every season makes such revolutions, not
only in the number, but in the magnitude and situation of these islands,
that this enumeration is now almost obsolete. Sometimes large islands
are entirely melted away; at other places they have attached themselves
to the main shore, or, which is the more correct statement, the interval
has been filled up by myriads of logs cemented together by mud and
rubbish."[359]

_Rafts._--One of the most interesting features in the great rivers of
this part of America is the frequent accumulation of what are termed
"rafts," or masses of floating trees, which have been arrested in their
progress by snags, islands, shoals, or other obstructions, and made to
accumulate, so as to form natural bridges, reaching entirely across the
stream. One of the largest of these was called the raft of the
Atchafalaya, an arm of the Mississippi, which was certainly at some
former time the channel of the Red River, when the latter found its way
to the Gulf of Mexico by a separate course. The Atchafalaya being in a
direct line with the general direction of the Mississippi, catches a
large portion of the timber annually brought down from the north; and
the drift-trees collected in about thirty-eight years previous to 1816
formed a continuous raft, no less than ten miles in length, 220 yards
wide, and eight feet deep. The whole rose and fell with the water, yet
was covered with green bushes and trees, and its surface enlivened in
the autumn by a variety of beautiful flowers. It went on increasing till
about 1835, when some of the trees upon it had grown to the height of
about sixty feet. Steps were then taken by the State of Louisiana to
clear away the whole raft, and open the navigation, which was effected,
not without great labor, in the space of four years.

The rafts on Red River are equally remarkable: in some parts of its
course, cedar-trees are heaped up by themselves, and in other places,
pines. On the rise of the waters in summer hundreds of these are seen,
some with their green leaves still upon them, just as they have fallen
from a neighboring bank, others leafless, broken and worn in their
passage from a far distant tributary: wherever they accumulate on the
edge of a sand-bar they arrest the current, and soon become covered with
sediment. On this mud the young willows and the poplars called
cotton-wood spring up, their boughs still farther retarding the stream,
and as the inundation rises, accelerating the deposition of new soil.
The bank continuing to enlarge, the channel at length becomes so narrow
that a single long tree may reach from side to side, and the remaining
space is then soon choked up by a quantity of other timber.

"Unfortunately for the navigation of the Mississippi," observes Captain
Hall, "some of the largest trunks, after being cast down from the
position on which they grew, get their roots entangled with the bottom
of the river, where they remain anchored, as it were, in the mud. The
force of the current naturally gives their tops a tendency downwards,
and, by its flowing past, soon strips them of their leaves and branches.
These fixtures, called snags, or planters, are extremely dangerous to
the steam-vessels proceeding up the stream, in which they lie like a
lance in rest, concealed beneath the water, with their sharp ends
pointed directly against the bows of the vessels coming up. For the most
part these formidable snags remain so still that they can be detected
only by a slight ripple above them, not perceptible to inexperienced
eyes. Sometimes, however, they vibrate up and down, alternately showing
their heads above the surface and bathing them beneath it."[360] So
imminent, until lately, was the danger caused by these obstructions,
that almost all the boats on the Mississippi were constructed on a
particular plan, to guard against fatal accidents; but in the last ten
years, by the aid of the power of steam and the machinery of a
snag-boat, as it is called, the greater number of these trunks of trees
have been drawn out of the mud.[361]

The prodigious quantity of wood annually drifted down by the Mississippi
and its tributaries, is a subject of geological interest, not merely as
illustrating the manner in which abundance of vegetable matter becomes,
in the ordinary course of nature, imbedded in submarine and estuary
deposits, but as attesting the constant destruction of soil and
transportation of matter to lower levels by the tendency of rivers to
shift their courses. Each of these trees must have required many years,
some of them centuries, to attain their full size; the soil, therefore,
whereon they grew, after remaining undisturbed for long periods, is
ultimately torn up and swept away.

It is also found in excavating at New Orleans, even at the depth of
several yards below the level of the sea, that the soil of the delta
contains innumerable trunks of trees, layer above layer, some prostrate,
as if drifted, others broken off near the bottom, but remaining still
erect, and with their roots spreading on all sides, as if in their
natural position. In such situations they appeared to me to indicate a
sinking of the ground, as the trees must formerly have grown in marshes
above the sea-level. In the higher parts of the alluvial plain, for many
hundred miles above the head of the delta, similar stools and roots of
trees are also seen buried in stiff clay at different levels, one above
the other, and exposed to view in the banks at low water. They point
clearly to the successive growth of forests in the extensive swamps of
the plain, where the ground was slowly raised, year after year, by the
mud thrown down during inundations. These roots and stools belong
chiefly to the deciduous cypress (_Taxodium distichum_), and other
swamp-trees, and they bear testimony to the constant shifting of the
course of the great river, which is always excavating land originally
formed at some distance from its banks.

_Formation of lakes in Louisiana._.--Another striking feature in the
basin of the Mississippi, illustrative of the changes now in progress,
is the formation by natural causes of great lakes, and the drainage of
others. These are especially frequent in the basin of the Red River in
Louisiana, where the largest of them, called Bistineau, is more than
_thirty miles_ long, and has a medium depth of from _fifteen_ to
_twenty_ feet. In the deepest parts are seen numerous cypress-trees, of
all sizes, now dead, and most of them with their tops broken by the
wind, yet standing erect under water. This tree resists the action of
air and water longer than any other, and, if not submerged throughout
the whole year, will retain life for an extraordinary period. Lake
Bistineau, as well as Black Lake, Cado Lake, Spanish Lake, Natchitoches
Lake, and many others, have been formed, according to Darby, by the
gradual elevation of the bed of Red River, in which the alluvial
accumulations have been so great as to raise its channel, and cause its
waters, during the flood season, to flow up the mouths of many
tributaries, and to convert parts of their courses into lakes. In the
autumn, when the level of Red River is again depressed, the waters rush
back, and some lakes become grassy meadows, with streams meandering
through them.[362] Thus, there is a periodical flux and reflux between
Red River and some of these basins, which are merely reservoirs,
alternately emptied and filled, like our tide estuaries--with this
difference, that in the one case the land is submerged for several
months continuously, and in the other twice in every twenty-four hours.
It has happened, in several cases, that a raft of timber or a bar has
been thrown by Red River across some of the openings of these channels,
and then the lakes become, like Bistineau, constant repositories of
water. But, even in these cases, their level is liable to annual
elevation and depression, because the flood of the main river, when at
its height, passes over the bar; just as, where sand-hills close the
entrance of an estuary on the Norfolk or Suffolk coast, the sea, during
some high tide or storm, has often breached the barrier and inundated
again the interior.

I am informed by Mr. Featherstonhaugh that the plains of the Red River
and the Arkansas are so low and flat, that whenever the Mississippi
rises thirty feet above its ordinary level, those great tributaries are
made to flow back, and inundate a region of vast extent. Both the
streams alluded to contain red sediment, derived from the decomposition
of red porphyry; and since 1833, when there was a great inundation in
the Arkansas, an immense swamp has been formed near the Mammelle
mountain, comprising 30,000 acres, with here and there large lagoons,
where the old bed of the river was situated; in which innumerable trees,
for the most part dead, are seen standing, of cypress, cotton-wood, or
poplar, the triple-thorned acacia, and others, which are of great size.
Their trunks appear as if painted red for about fifteen feet from the
ground; at which height a perfectly level line extends through the whole
forest, marking the rise of the waters during the last flood.[363]

But most probably the causes above assigned for the recent origin of
these lakes are not the only ones. Subterranean movements have altered,
so lately as the years 1811-12, the relative levels of various parts of
the basin of the Mississippi, situated 300 miles northeast of Lake
Bistineau. In those years the great valley, from the mouth of the Ohio
to that of the St. Francis, including a tract 300 miles in length, and
exceeding in area the whole basin of the Thames, was convulsed to such a
degree, as to create new islands in the river, and lakes in the alluvial
plain. Some of these were on the left or east bank of the Mississippi,
and were twenty miles in extent; as, for example, those named Reelfoot
and Obion in Tennessee, formed in the channels or valleys of small
streams bearing the same names.[364]

But the largest area affected by the great convulsion lies eight or ten
miles to the westward of the Mississippi, and inland from the town of
New Madrid, in Missouri. It is called "the sunk country," and is said
to extend along the course of the White Water and its tributaries, for
a distance of between seventy and eighty miles north and south, and
thirty miles or more east and west. Throughout this area, innumerable
submerged trees, some standing leafless, others prostrate, are seen; and
so great is the extent of lake and marsh, that an active trade in the
skins of muskrats, mink, otters, and other wild animals, is now carried
on there. In March, 1846, I skirted the borders of the "sunk country"
nearest to New Madrid, passing along the Bayou St. John and Little
Prairie, where dead trees of various kinds, some erect in the water,
others fallen, and strewed in dense masses over the bottom, in the
shallows, and near the shore, were conspicuous. I also beheld countless
rents in the adjoining dry alluvial plains, caused by the movements of
the soil in 1811-12, and still open, though the rains, frost, and river
inundations, have greatly diminished their original depth. I observed,
moreover, numerous circular cavities, called "sunk holes," from ten to
thirty yards wide, and twenty feet or more in depth, which interrupt the
general level of the plain. These were formed by the spouting out of
large quantities of sand and mud during the earthquakes.[365]

That the prevailing changes of level in the delta and alluvial plain of
the Mississippi have been caused by the subsidence, rather than the
upheaval of land, appears to me established by the fact, that there are
no protuberances of upraised alluvial soil, projecting above the level
surface of the great plain. It is true that the gradual elevation of
that plain, by new accessions of matter, would tend to efface every
inequality derived from this source, but we might certainly have
expected to find more broken ground between the opposite bluffs, had
local upthrows of alluvial strata been of repeated occurrence.

_Antiquity of the delta._--The vast size of the alluvial plain both
above and below the head of the delta, or the branching off of the
uppermost arm of the Atchafalaya, has been already alluded to. Its
superficial dimensions, according to Mr. Forshey, exceed 30,000 square
miles, nearly half of which belong to the true delta. The deposits
consist partly of sand originally formed upon or near the banks of the
river, and its tributaries, partly of gravel, swept down the main
channel, of which the position has continually shifted, and partly of
fine mud slowly accumulated in the swamps. The farther we descend the
river towards its mouth, the finer becomes the texture of the sediment.
The whole alluvial formation, from the base of the delta upwards, slopes
with a very gentle inclination, rising about three inches in a mile from
the level of the sea at the Balize, to the height of about 200 feet in a
distance of about 800 miles.

That a large portion of this fluviatile deposit, together with the
fluvio-marine strata now in progress near the Balize, consists of mud
and sand with much vegetable matter intermixed, may be inferred from
what has been said of the abundance of drift trees floated down every
summer. These are seen matted together into a net-work around the
extensive mud banks at the extreme mouths of the river. Every one
acquainted with the geography of Louisiana is aware that the most
southern part of the delta forms a long narrow tongue of land protruding
for 50 miles into the Gulf of Mexico, at the end of which are numerous
channels of discharge. This singular promontory consists simply of the
river and its two low, flat banks, covered with reeds, young willows,
and poplars. Its appearance answers precisely to that of the banks far
in the interior, when nothing appears above water during inundations but
the higher part of the sloping glacis or bank. In the one case we have
the swamps or an expanse of freshwater with the tops of trees appearing
above, in the other the bluish green surface of the Gulf of Mexico. An
opinion has very commonly prevailed that this narrow promontory, the
newest product of the river, has gained very rapidly upon the sea, since
the foundation of New Orleans; but after visiting the Balize in 1846, in
company with Dr. Carpenter, and making many inquiries of the pilots, and
comparing the present outline of the coast with the excellent Spanish
chart, published by Charlevoix 120 years before, we came to a different
conclusion. The rate of permanent advance of the new land has been very
slow, not exceeding perhaps one mile in a century. The gain may have
been somewhat more rapid in former years, when the new strip of soil
projected less far into the gulf, since it is now much more exposed to
the action of a strong marine current. The tides also, when the waters
of the river are low, enter into each opening, and scour them out,
destroying the banks of mud and the sand-bars newly formed during the
flood season.

An observation of Darby, in regard to the strata composing part of this
delta, deserves attention. In the steep banks of the Atchafalaya, before
alluded to, the following section, he says, is observable at low
water:--first an upper stratum, consisting invariably of bluish clay,
common to the banks of the Mississippi; below this a stratum of red
ochreous earth, peculiar to Red River, under which the blue clay of the
Mississippi again appears; and this arrangement is constant, proving, as
that geographer remarks, that the waters of the Mississippi and the Red
River occupied alternately, at some former periods, considerable tracts
below their present point of union.[366] Such alternations are probably
common in submarine spaces situated between two converging deltas; for,
before the two rivers unite, there must almost always be a certain
period when an intermediate tract will by turns be occupied and
abandoned by the waters of each stream; since it can rarely happen that
the season of highest flood will precisely correspond in each. In the
case of the Red River and Mississippi, which carry off the waters from
countries placed under widely distant latitudes, an exact coincidence in
the time of greatest inundation is very improbable.

The antiquity of the delta, or length of the period which has been
occupied in the deposition of so vast a mass of alluvial matter, is a
question which may well excite the curiosity of every geologist.
Sufficient data have not yet been obtained to afford a full and
satisfactory answer to the inquiry, but some approximation may already
be made to the minimum of time required.

When I visited New Orleans, in February, 1846, I found that Dr. Riddell
had made numerous experiments to ascertain the proportion of sediment
contained in the waters of the Mississippi; and he concluded that the
mean annual amount of solid matter was to the water as 1/1245 in weight,
or about 1/3000 in volume.[367] From the observations of the same
gentleman, and those of Dr. Carpenter and Mr. Forshey, an eminent
engineer, to whom I have before alluded, the average width, depth, and
velocity of the Mississippi, and thence the mean annual discharge of
water were deduced. I assumed 528 feet, or the tenth of a mile, as the
probable thickness of the deposit of mud and sand in the delta; founding
my conjecture chiefly on the depth of the Gulf of Mexico, between the
southern point of Florida and the Balize, which equals on an average 100
fathoms, and partly on some borings 600 feet deep in the delta, near
Lake Pontchartrain, north of New Orleans, in which the bottom of the
alluvial matter is said not to have been reached. The area of the delta
being about 13,600 square statute miles, and the quantity of solid
matter annually brought down by the river 3,702,758,400 cubic feet, it
must have taken 67,000 years for the formation of the whole; and if the
alluvial matter of the plain above be 264 feet deep, or half that of the
delta,[368] it must have required 33,500 more years for its
accumulation, even if its area be estimated as only equal to that of the
delta, whereas it is in fact larger. If some deduction be made from the
time here stated, in consequence of the effect of the drift-wood, which
must have aided in filling up more rapidly the space above alluded to, a
far more important allowance must be made on the other hand, for the
loss of matter, owing to the finer particles of mud not settling at the
mouths of the river, but being swept out far to sea during the
predominant action of the tides, and the waves in the winter months,
when the current of fresh water is feeble. Yet however vast the time
during which the Mississippi has been transporting its earthy burden to
the ocean, the whole period, though far exceeding, perhaps, 100,000
years, must be insignificant in a geological point of view, since the
bluffs or cliffs, bounding the great valley, and therefore older in
date, and which are from 50 to 250 feet in perpendicular height, consist
in great part of loam containing land, fluviatile, and lacustrine shells
of species still inhabiting the same country. (See fig. 23, p. 265.)

Before we take leave of the great delta, we may derive an instructive
lesson from the reflection that the new deposits already formed, or now
accumulating, whether marine or freshwater, must greatly resemble in
composition, and the general character of their organic remains, many
ancient strata, which enter largely into the earth's structure. Yet
there is no sudden revolution in progress, whether on the land or in the
waters, whether in the animate or the inanimate world. Notwithstanding
the excessive destruction of soil and uprooting of trees, the region
which yields a never-failing supply of drift-wood is densely clothed
with noble forests, and is almost unrivalled in its power of supporting
animal and vegetable life. In spite of the undermining of many a lofty
bluff, and the encroachments of the delta on the sea--in spite of the
earthquake, which rends and fissures the soil, or causes areas more than
sixty miles in length to sink down several yards in a few months, the
general features of the district remain unaltered, or are merely
undergoing a slow and insensible change. Herds of wild deer graze on the
pastures, or browse upon the trees; and if they diminish in number, it
is only where they give way to man and the domestic animals which follow
in his train. The bear, the wolf, the fox, the panther, and the
wild-cat, still maintain themselves in the fastnesses of the forests of
cypress and gum-tree. The racoon and the opossum are everywhere
abundant, while the musk-rat, otter, and mink still frequent the rivers
and lakes, and a few beavers and buffaloes have not yet been driven from
their ancient haunts. The waters teem with alligators, tortoises, and
fish, and their surface is covered with millions of migratory waterfowl,
which perform their annual voyage between the Canadian lakes and the
shores of the Mexican Gulf. The power of man begins to be sensibly felt,
and many parts of the wilderness to be replaced by towns, orchards, and
gardens. The gilded steamboats, like moving palaces, stem the force of
the current, or shoot rapidly down the descending stream, through the
solitudes of the forests and prairies. Already does the flourishing
population of the great valley far exceed that of the thirteen United
States when first they declared their independence. Such is the state of
a continent where trees and stones are hurried annually by a thousand
torrents, from the mountains to the plains, and where sand and finer
matter are swept down by a vast current to the sea, together with the
wreck of countless forests and the bones of animals which perish in the
inundations. When these materials reach the gulf, they do not render the
waters unfit for aquatic animals; but on the contrary, the ocean here
swarms with life, as it generally does where the influx of a great river
furnishes a copious supply of organic and mineral matter. Yet many
geologists, when they behold the spoils of the land heaped in successive
strata, and blended confusedly with the remains of fishes, or
interspersed with broken shells and corals; when they see portions of
erect trunks of trees with their roots still retaining their natural
position, and one tier of these preserved in a fossil state above
another, imagine that they are viewing the signs of a turbulent instead
of a tranquil and settled state of the planet. They read in such
phenomena the proof of chaotic disorder and reiterated catastrophes,
instead of indications of a surface as habitable as the most delicious
and fertile districts now tenanted by man.


DELTA OF THE GANGES AND BRAHMAPOOTRA.

[Illustration: Fig. 25.

MAP OF THE DELTA OF THE GANGES AND BRAHMAPOOTRA.]

As an example of a still larger delta advancing upon the sea in
opposition to more powerful tides, I shall next describe that of the
Ganges and Brahmapootra (or Burrampooter). These, the two principal
rivers of India, descend from the highest mountains in the world, and
partially mingle their waters in the low plains of Hindostan, before
reaching the head of the Bay of Bengal. The Brahmapootra, somewhat the
larger of the two, formerly passed to the east of Dacca, even so lately
as the beginning of the present century, pouring most of its waters into
one of the numerous channels in the delta called "the Megna." By that
name the main stream was always spoken of by Rennell and others in their
memoirs on this region. But the main trunk now unites with an arm of the
Ganges considerably higher up, at a point about 100 miles distant from
the sea; and it is constantly, according to Dr. Hooker, working its way
westward, having formerly, as may be seen by ancient maps, moved
eastward for a long period.

The area of the delta of the combined rivers, for it is impossible now
to distinguish what belongs to each, is considerably more than double
that of the Nile, even if we exclude from the delta a large extent of
low, flat, alluvial plain, doubtless of fluviatile origin, which
stretches more than 100 miles to the hills west of Calcutta (see map,
fig. 25), and much farther in a northerly direction beyond the head of
the great delta. The head of a delta is that point where the first arm
is given off. Above that point a river receives the waters of
tributaries flowing from higher levels; below it, on the contrary, it
gives out portions of its waters to lower levels, through channels which
flow into adjoining swamps, or which run directly to the sea. The
Mississippi, as before described, has a single head, which originated at
an unknown period when the Red River joined it. In the great delta of
Bengal there may be said to be two heads nearly equidistant from the
sea, that of the Ganges (G, map, fig. 25), about 30 miles below
Rajmahal, or 216 statute miles in a direct line from the sea, and that
of the Brahmapootra (B), below Chirapoonjee, where the river issues from
the Khasia mountains, a distance of 224 miles from the Bay of Bengal.

It will appear, by reference to the map, that the great body of fresh
water derived from the two rivers enters the bay on its eastern side;
and that a large part of the delta bordering on the sea is composed of a
labyrinth of rivers and creeks, all filled with salt water, except those
immediately communicating with the Hoogly, or principal arm of the
Ganges. This tract alone, known by the name of the Woods, or Sunderbunds
(more properly Soonderbuns), a wilderness infested by tigers and
crocodiles, is, according to Rennell, equal in extent to the whole
principality of Wales.[369]

On the sea-coast there are eight great openings, each of which has
evidently, at some ancient period, served in its turn as the principal
channel of discharge. Although the flux and reflux of the tide extend
even to the heads of the delta when the rivers are low, yet, when they
are periodically swollen by tropical rains, their volume and velocity
counteract the tidal current, so that, except very near the sea, the ebb
and flow become insensible. During the flood season, therefore, the
Ganges and Brahmapootra almost assume in their delta, the character of
rivers entering an inland sea; the movements of the ocean being then
subordinate to the force of the rivers, and only slightly disturbing
their operations. The great gain of the delta in height and area takes
place during the inundations; and, during other seasons of the year, the
ocean makes reprisals, scouring out the channels, and sometimes
devouring rich alluvial plains.

_Islands formed and destroyed._--Major R. H. Colebrooke, in his account
of the course of the Ganges, relates examples of the rapid filling up of
some of its branches, and the excavation of new channels, where the
number of square miles of soil removed in a short time (the column of
earth being 114 feet high) was truly astonishing. Forty square miles, or
25,600 acres, are mentioned as having been carried away, in one place,
in the course of a few years.[370] The immense transportation of earthy
matter by the Ganges and Brahmapootra is proved by the great magnitude
of the islands formed in their channels during a period far short of
that of a man's life. Some of these, many miles in extent, have
originated in large sand-banks thrown up round the points at the angular
turning of the rivers, and afterwards insulated by breaches of the
streams. Others, formed in the main channel, are caused by some
obstruction at the bottom. A large tree, or a sunken boat, is sometimes
sufficient to check the current, and cause a deposit of sand, which
accumulates till it usurps a considerable portion of the channel. The
river then undermines its banks on each side, to supply the deficiency
in its bed, and the island is afterwards raised by fresh deposits during
every flood. In the great gulf below Luckipour, formed by the united
waters of the Ganges and Megna, some of the islands, says Rennell, rival
in size and fertility the Isle of Wight. While the river is forming new
islands in one part, it is sweeping away old ones in others. Those newly
formed are soon overrun with reeds, long grass, the Tamarix Indica, and
other shrubs, forming impenetrable thickets, where the tiger, the
rhinoceros, the buffalo, deer, and other wild animals, take shelter. It
is easy, therefore, to perceive, that both animal and vegetable remains
may occasionally be precipitated into the flood, and become imbedded in
the sediment which subsides in the delta.

Three or four species of crocodile, of two distinct sub-genera, abound
in the Ganges, and its tributary and contiguous waters; and Mr. H. T.
Colebrooke informed me, that he had seen both forms in places far
inland, many hundred miles from the sea. The Gangetic crocodile, or
Gavial (in correct orthography, Garial), is confined to the fresh water,
living exclusively on fish, but the commoner kinds, called Koomiah and
Muggar, frequent both fresh and salt, being much larger and fiercer in
salt and brackish water.[371] These animals swarm in the brackish water
along the line of sand-banks, where the advance of the delta is most
rapid. Hundreds of them are seen together in the creeks of the delta,
or basking in the sun on the shoals without. They will attack men and
cattle, destroying the natives when bathing, and tame and wild animals
which come to drink. "I have not unfrequently," says Mr. Colebrooke,
"been witness to the horrid spectacle of a floating corpse seized by a
crocodile with such avidity, that he half emerged above the water with
his prey in his mouth." The geologist will not fail to observe how
peculiarly the habits and distribution of these saurians expose them to
become imbedded in the horizontal strata of fine mud, which are annually
deposited over many hundred square miles in the Bay of Bengal. The
inhabitants of the land, which happen to be drowned or thrown into the
water, are usually devoured by these voracious reptiles; but we may
suppose the remains of the saurians themselves to be continually
entombed in the new formations. The number, also, of bodies of the
poorer class of Hindoos thrown annually into the Ganges is so great,
that some of their bones or skeletons can hardly fail to be occasionally
enveloped in fluviatile mud.

It sometimes happens, at the season when the periodical flood is at its
height, that a strong gale of wind, conspiring with a high spring-tide,
checks the descending current of the river, and gives rise to most
destructive inundations. From this cause, in 1763, the waters at
Luckipour rose six feet above their ordinary level, and the inhabitants
of a considerable district, with their houses and cattle, were totally
swept away.

The population of all oceanic deltas are particularly exposed to suffer
by such catastrophes, recurring at considerable intervals of time; and
we may safely assume that such tragical events have happened again and
again since the Gangetic delta was inhabited by man. If human experience
and forethought cannot always guard against these calamities, still less
can the inferior animals avoid them; and the monuments of such
disastrous inundations must be looked for in great abundance in strata
of all ages, if the surface of our planet has always been governed by
the same laws. When we reflect on the general order and tranquillity
that reigns in the rich and populous delta of Bengal, notwithstanding
the havoc occasionally committed by the depredations of the ocean, we
perceive how unnecessary it is to attribute the imbedding of successive
races of animals in older strata to extraordinary energy in the causes
of decay and reproduction in the infancy of our planet, or to those
general catastrophes and sudden revolutions so often resorted to.

_Deposits in the delta._--The quantity of mud held in suspension by the
waters of the Ganges and Brahmapootra is found, as might be expected, to
exceed that of any of the rivers alluded to in this or the preceding
chapters; for, in the first place, their feeders flow from mountains of
unrivalled altitude, and do not clear themselves in any lakes, as does
the Rhine in the Lake of Constance, or the Rhone in that of Geneva. And,
secondly, their whole course is nearer the equator than that of the
Mississippi, or any great river, respecting which careful experiments
have been made, to determine the quantity of its water and earthy
contents. The fall of rain, moreover, as we have before seen, is
excessive on the southern flanks of the first range of mountains which
rise from the plains of Hindostan, and still more remarkable is the
quantity sometimes poured down in one day. (See above, p. 200.) The sea,
where the Ganges and Brahmapootra discharge their main stream at the
flood season, only recovers its transparency at the distance of from 60
to 100 miles from the delta; and we may take for granted that the
current continues to transport the finer particles much farther south
than where the surface water first becomes clear. The general slope,
therefore, of the new strata must be extremely gentle. According to the
best charts, there is a gradual deepening from four to about sixty
fathoms, as we proceed from the base of the delta to the distance of
about one hundred miles into the Bay of Bengal. At some few points
seventy, or even one hundred, fathoms are obtained at that distance.

One remarkable exception, however, occurs to the regularity of the shape
of the bottom. Opposite the middle of the delta, at the distance of
thirty or forty miles from the coast, a deep submarine valley occurs,
called the "swatch of no ground," about fifteen miles in diameter, where
soundings of 180, and even 300, fathoms fail to reach the bottom. (See
map, p. 275.) This phenomenon is the more extraordinary, since the
depression runs north to within five miles of the line of shoals; and
not only do the waters charged with sediment pass over it continually,
but, during the monsoons, the sea, loaded with mud and sand, is beaten
back in that direction towards the delta. As the mud is known to extend
for eighty miles farther into the gulf, an enormous thickness of matter
must have been deposited in "the swatch." We may conclude, therefore,
either that the original depth of this part of the Bay of Bengal was
excessive, or that subsidences have occurred in modern times. The latter
conjecture is the less improbable, as the whole area of the delta has
been convulsed in the historical era by earthquakes, and actual
subsidences have taken place in the neighboring coast of Chittagong,
while "the swatch" lies not far from the volcanic band which connects
Sumatra, Barren Island, and Ramree.[372]

Opposite the mouth of the Hoogly river, and immediately south of Saugor
Island, four miles from the nearest land of the delta, a new islet was
formed about twenty years ago, called Edmonstone Island, on the centre
of which a beacon was erected as a landmark in 1817. In 1818 the island
had become two miles long and half a mile broad, and was covered with
vegetation and shrubs. Some houses were then built upon it, and in 1820
it was used as a pilot station. The severe gale of 1823 divided it into
two parts, and so reduced its size as to leave the beacon standing out
in the sea, where, after remaining seven years, it was washed away. The
islet in 1836 had been converted by successive storms into a sand-bank,
half a mile long, on which a sea-mark was placed.

Although there is evidence of gain at some points, the general progress
of the coast is very slow; for the tides, when the river water is low,
are actively employed in removing alluvial matter. In the Sunderbunds
the usual rise and fall of the tides is no more than eight feet, but, on
the east side of the delta, Dr. Hooker observed, in the winter of 1851,
a rise of from sixty to eighty feet, producing among the islands at the
mouths of the Megna and Fenny rivers, a lofty wave or "bore" as they
ascend, and causing the river water to be ponded back, and then to sweep
down with great violence when the tide ebbs. The bay for forty miles
south of Chittagong is so fresh that neither algæ nor mangroves will
grow in it. We may, therefore, conceive how effective may be the current
formed by so great a volume of water in dispersing fine mud over a wide
area. Its power is sometimes augmented by the agitation of the bay
during hurricanes in the month of May. The new superficial strata
consists entirely of fine sand and mud; such, at least, are the only
materials which are exposed to view in regular beds on the banks of the
numerous creeks. Neither here or higher up the Ganges, could Dr. Hooker
discover any land or freshwater shells in sections of the banks, which
in the plains higher up sometimes form cliffs eighty feet in height at
low water. In like manner I have stated[373] that I was unable to find
any buried shells in the delta or modern river cliffs of the
Mississippi.

No substance so coarse as gravel occurs in any part of the delta of the
Ganges and Brahmapootra, nor nearer the sea than 400 miles. Yet it is
remarkable that the boring of an Artesian well at Fort William, near
Calcutta, in the years 1835-1840, displayed, at the depth of 120 feet,
clay and sand with pebbles. This boring was carried to a depth of 481
feet below the level of Calcutta, and the geological section obtained in
the operation has been recorded with great care. Under the surface soil,
at a depth of about ten feet, they came to a stiff blue clay about forty
feet in thickness; below which was sandy clay, containing in its lower
portion abundance of decayed vegetable matter, which at the bottom
assumed the character of a stratum of black peat two feet thick. This
peaty mass was considered as a clear indication (like the "dirt-bed" of
Portland) of an ancient terrestrial surface, with a forest or Sunderbund
vegetation. Logs and branches of a red-colored wood occur both above and
immediately below the peat, so little altered that Dr. Wallich was able
to identify them with the Soondri tree, _Heritiera littoralis_, one of
the most prevalent forms, at the base of the delta. Dr. Falconer tells
me that similar peat has been met with at other points round Calcutta at
the depth of nine feet and twenty-five feet. It appears, therefore, that
there has been a sinking down of what was originally land in this
region, to the amount of seventy feet or more perpendicular; for
Calcutta is only a few feet above the level of the sea, and the
successive peat-beds seem to imply that the subsidence of the ground was
gradual or interrupted by several pauses. Below the vegetable mass they
entered upon a stratum of yellowish clay about ten feet thick,
containing horizontal layers of kunkar (or kankar), a nodular,
concretionary, argillaceous limestone, met with abundantly at greater or
less depths in all parts of the valley of the Ganges, over many
thousand square miles, and always presenting the same characters, even
at a distance of one thousand miles north of Calcutta. Some of this
kunkar is said to be of very recent origin in deposits formed by river
inundations near Saharanpoor. After penetrating 120 feet, they found
loam containing water-worn fragments of mica-slate and other kinds of
rock, which the current of the Ganges can no longer transport to this
region. In the various beds pierced through below, consisting of clay,
marl, and friable sandstone, with kunkar here and there intermixed, no
organic remains of decidedly marine origin were met with. Too positive a
conclusion ought not, it is true, to be drawn from such a fact, when we
consider the narrow bore of the auger and its effect in crushing shells
and bones. Nevertheless, it is worthy of remark, that the only fossils
obtained in a recognizable state were of a fluviatile or terrestrial
character. Thus, at the depth of 350 feet, the bony shell of a tortoise,
or trionyx, a freshwater genus, was found in sand, resembling the living
species of Bengal. From the same stratum, also, they drew up the lower
half of the humerus of a ruminant, at first referred to a hyæna. It was
the size and shape, says Dr. Falconer, of the shoulder-bone of the
_Cervus porcinus_, or common hog-deer, of India. At the depth of 380
feet, clay with fragments of lacustrine shells was incumbent on what
appears clearly to have been another "dirt-bed," or stratum of decayed
wood, implying a period of repose of some duration, and a forest-covered
land, which must have subsided 300 feet, to admit of the subsequent
superposition of the overlying deposits. It has been conjectured that,
at the time when this area supported trees, the land extended much
farther out into the Bay of Bengal than now, and that in later times the
Ganges, while enlarging its delta, has been only recovering lost ground
from the sea.

At the depth of about 400 feet below the surface, an abrupt change was
observed in the character of the strata, which were composed in great
part of sand, shingle, and boulders, the only fossils observed being the
vertebræ of a crocodile, shell of a trionyx, and fragments of wood very
little altered, and similar to that buried in beds far above. These
gravelly beds constituted the bottom of the section at the depth of 481
feet, when the operations were discontinued, in consequence of an
accident which happened to the auger.

The occurrence of pebbles at the depths of 120 and 400 feet implies an
important change in the geographical condition of the region around or
near Calcutta. The fall of the river, or the general slope of the
alluvial plain may have been formerly greater; or, before a general and
perhaps unequal subsidence, hills once nearer the present base of the
delta may have risen several hundred feet, forming islands in the bay,
which may have sunk gradually, and become buried under fluviatile
sediment.

_Antiquity of the delta._--It would be a matter of no small scientific
interest, if experiments were made to enable us to determine, with some
degree of accuracy, the mean quantity of earthy matter discharged
annually into the sea by the united waters of the Ganges and
Brahmapootra. The Rev. Mr. Everest instituted, in 1831-2, a series of
observations on the earthy matter brought down by the Ganges, at
Ghazepoor, 500 miles from the sea. He found that, in 1831, the number of
cubic feet of water discharged by the river per second at that place
was, during the


  Rains (4 months)        494,208
  Winter (5 months)        71,200
  Hot weather (3 months)   36,330


so that we may state in round numbers that 500,000 cubic feet per second
flow down during the four months of the flood season, from June to
September, and less than 60,000 per second during the remaining eight
months.

The average quantity of solid matter suspended in the water during the
rains was, by weight, 1/428th part; but as the water is about one-half
the specific gravity of the dried mud, the solid matter discharged is
1/856th part in bulk, or 577 cubic feet per second. This gives a total
of 6,082,041,600 cubic feet for the discharge in the 122 days of the
rain. The proportion of sediment in the waters at other seasons was
comparatively insignificant, the total amount during the five winter
months being only 247,881,600 cubic feet, and during the three months of
hot weather 38,154,240 cubic feet. The total annual discharge, then,
would be 6,368,077,440 cubic feet.

This quantity of mud would in one year raise a surface of 228½ square
miles, or a square space, each side of which should measure 15 miles, a
height of one foot. To give some idea of the magnitude of this result,
we will assume that the specific gravity of the dried mud is only
one-half that of granite (it would, however, be more); in that case, the
earthy matter discharged in a year would equal 3,184,038,720 cubic feet
of granite. Now about 12½ cubic feet of granite weigh one ton; and it
is computed that the great Pyramid of Egypt, if it were a solid mass of
granite, would weigh about 600,000,000 tons. The mass of matter,
therefore, carried down annually would, according to this estimate, more
than equal in weight and bulk forty-two of the great pyramids of Egypt,
and that borne down in the four months of the rains would equal forty
pyramids. But if, without any conjecture as to what may have been the
specific gravity of the mud, we attend merely to the weight of solid
matter actually proved by Mr. Everest to have been contained in the
water, we find that the number of tons weight which passed down in the
122 days of the rainy season was 339,413,760, which would give the
weight of fifty-six pyramids and a half; and in the whole year
355,361,464 tons, or nearly the weight of sixty pyramids.

The base of the great Pyramid of Egypt covers eleven acres, and its
perpendicular height is about five hundred feet. It is scarcely possible
to present any picture to the mind which will convey an adequate
conception of the mighty scale of this operation, so tranquilly and
almost insensibly carried on by the Ganges, as it glides through its
alluvial plain, even at a distance of 500 miles from the sea. It may,
however, be stated, that if a fleet of more than eighty Indiamen, each
freighted with about 1400 tons' weight of mud, were to sail down the
river every hour of every day and night for four months continuously,
they would only transport from the higher country to the sea a mass of
solid matter equal to that borne down by the Ganges, even in this part
of its course, in the four months of the flood season. Or the exertions
of a fleet of about 2000 such ships going down daily with the same
burden, and discharging it into the gulf, would be no more than
equivalent to the operations of the great river.

The most voluminous current of lava which has flowed from Etna within
historical times was that of 1669. Ferrara, after correcting Borelli's
estimate, calculated the quantity of cubic yards of lava in this current
at 140,000,000. Now, this would not equal in bulk one-fifth of the
sedimentary matter which is carried down in a single year by the Ganges,
past Ghazepoor, according to the estimate above explained; so that it
would require five grand eruptions of Etna to transfer a mass of lava
from the subterranean regions to the surface, equal in volume to the mud
carried down in one year to that place.

Captain R. Strachey, of the Bengal Engineers, has remarked to me, not
only that Ghazepoor, where Mr. Everest's observations were made, is 500
miles from the sea, but that the Ganges has not been joined there by its
most important feeders. These drain upon the whole 750 miles of the
Himalaya, and no more than 150 miles of that mountain-chain have sent
their contributions to the main trunk at Ghazepoor. Below that place,
the Ganges is joined by the Gogra, Gunduk, Khosee, and Teesta from the
north, to say nothing of the Sone flowing from the south, one of the
largest of the rivers which rise in the table-land of central India.
(See map, fig. 25, p. 275.) Moreover the remaining 600 miles of the
Himalaya comprise that eastern portion of the basin where the rains are
heaviest. (See above, p. 200.) The quantity of water therefore carried
down to the sea may probably be four or five times as much as that which
passes Ghazepoor.

The Brahmapootra, according to Major Wilcox,[374] in the month of
January, when it is near its minimum, discharges 150,000 cubic feet of
water per second at Gwalpara, not many miles above the head of its
delta. Taking the proportions observed at Ghazepoor at the different
seasons as a guide, the probable average discharge of the Brahmapootra
for the whole year may be estimated at about the same as that of the
Ganges. Assuming this; and secondly, in order to avoid the risk of
exaggeration, that the proportion of sediment in their waters is about a
third less than Mr. Everest's estimate, the mud borne down to the Bay of
Bengal in one year would equal 40,000 millions of cubic feet, or between
six and seven times as much as that brought down to Ghazepoor, according
to Mr. Everest's calculations in 1831, and ten times as much as that
conveyed annually by the Mississippi to the Gulf of Mexico.

Captain Strachey estimates the annually inundated portion of the delta
at 250 miles in length by 80 in breadth, making an area of 20,000 square
miles. The space south of this in the bay, where sediment is thrown
down, may be 300 miles from E. to W. by 150 N. and S., or 45,000 square
miles, which, added to the former, gives a surface of 65,000 square
miles, over which the sediment is spread out by the two rivers. Suppose
then the solid matter to amount to 40,000 millions of cubic feet per
annum, the deposit, he observes, must be continued for forty-five years
and three-tenths to raise the whole area a height of one foot, or 13,600
years to raise it 300 feet; and this, as we have seen, is much less than
the thickness of the fluviatile strata actually penetrated, (and the
bottom not reached) by the auger at Calcutta.

Nevertheless we can by no means deduce from these data alone, what will
be the future rate of advance of the delta, nor even predict whether the
land will gain on the sea, or remain stationary. At the end of 13,000
years the bay may be less shallow than now, provided a moderate
depression, corresponding to that experienced in part of Greenland for
many centuries shall take place (see chap. 30). A subsidence quite
insensible to the inhabitants of Bengal, not exceeding two feet three
inches in a century, would be more than sufficient to counterbalance all
the efforts of the two mighty rivers to extend the limits of their
delta. We have seen that the Artesian borings at Calcutta attest, what
the vast depth of the "swatch" may also in all likelihood indicate, that
the antagonist force of subsidence has predominated for ages over the
influx of fluviatile mud, preventing it from raising the plains of
Bengal, or from filling up a larger portion of the bay.


CONCLUDING REMARKS ON DELTAS.

_Convergence of deltas._--If we possessed an accurate series of maps of
the Adriatic for many thousand years, our retrospect would, without
doubt, carry us gradually back to the time when the number of rivers
descending from the mountains into that gulf by independent deltas was
far greater in number. The deltas of the Po and the Adige, for instance,
would separate themselves within the _recent_ era, as, in all
probability, would those of the Isonzo and the Torre. If, on the other
hand, we speculate on future changes, we may anticipate the period when
the number of deltas will greatly diminish; for the Po cannot continue
to encroach at the rate of a mile in a hundred years, and other rivers
to gain as much in six or seven centuries upon the shallow gulf, without
new junctions occurring from time to time; so that Eridanus, "the king
of rivers," will continually boast a greater number of tributaries. The
Ganges and the Brahmapootra have perhaps become partially confluent in
the same delta within the historical, or at least within the human era;
and the date of the junction of the Red River and the Mississippi would,
in all likelihood, have been known, if America had not been so recently
discovered. The union of the Tigris and the Euphrates must undoubtedly
have been one of the modern geographical changes of our Earth, for Col.
Rawlinson informs me that the delta of those rivers has advanced two
miles in the last sixty years, and is supposed to have encroached about
forty miles upon the Gulf of Persia in the course of the last
twenty-five centuries.

When the deltas of rivers, having many mouths, converge, a partial union
at first takes place by the confluence of some one or more of their
arms; but it is not until the main trunks are connected above the head
of the common delta, that a complete intermixture of their joint waters
and sediment takes place. The union, therefore, of the Po and Adige, and
of the Ganges and Brahmapootra, is still incomplete. If we reflect on
the geographical extent of surface drained by rivers such as now enter
the Bay of Bengal, and then consider how complete the blending together
of the greater part of their transported matter has already become, and
throughout how vast a delta it is spread by numerous arms, we no longer
feel so much surprise at the area occupied by some ancient formations of
homogeneous mineral composition. But our surprise will be still farther
lessened, when we afterwards inquire (ch. 21) into the action of tides
and currents in disseminating sediment.

_Age of existing deltas._--If we could take for granted, that the
relative level of land and sea had remained stationary ever since all
the existing deltas began to be formed--could we assume that their
growth commenced at one and the same instant when the present continents
acquired their actual shape--we might understand the language of
geologists who speak of "the epoch of existing continents." They
endeavor to calculate the age of deltas from this imaginary fixed
period; and they calculate the gain of new land upon the sea, at the
mouths of rivers, as having begun everywhere simultaneously. But the
more we study the history of deltas, the more we become convinced that
upward and downward movements of the land and contiguous bed of the sea
have exerted, and continue to exert, an influence on the physical
geography of many hydrographical basins, on a scale comparable in
magnitude or importance to the amount of fluviatile deposition effected
in an equal lapse of time. In the basin of the Mississippi, for example,
proofs both of descending and ascending movements to a vertical amount
of several hundred feet can be shown to have taken place since the
existing species of land and freshwater shells lived in that
region.[375]

The deltas also of the Po and Ganges have each, as we have seen (p.
257), when probed by the Artesian auger, borne testimony to a gradual
subsidence of land to the extent of several hundred feet--old
terrestrial surfaces, turf, peat, forest-land, and "dirt-beds," having
been pierced at various depths. The changes of level at the mouth of the
Indus in Cutch (see below, chap. 27), and those of New Madrid in the
valley of the Mississippi (see p. 270, and chap. 27), are equally
instructive, as demonstrating unceasing fluctuations in the levels of
those areas into which running water is transporting sediment. If,
therefore, the exact age of all modern deltas could be known, it is
scarcely probable that we should find any two of them in the world to
have coincided in date, or in the time when their earliest deposits
originated.

_Grouping of strata in deltas._--The changes which have taken place in
deltas, even within the times of history, may suggest many important
considerations in regard to the manner in which subaqueous sediment is
distributed. With the exception of some cases hereafter to be noticed,
there are some general laws of arrangement which must evidently hold
good in almost all the lakes and seas now filling up. If a lake, for
example, be encircled on two sides by lofty mountains, receiving from
them many rivers and torrents of different sizes, and if it be bounded
on the other sides, where the surplus waters issue, by a comparatively
low country, it is not difficult to define some of the leading
geological features which must characterize the lacustrine formation,
when this basin shall have been gradually converted into dry land by the
influx of sediment. The strata would be divisible into two principal
groups: the _older_ comprising those deposits which originated on the
side adjoining the mountains, where numerous deltas first began to form;
and the _newer_ group consisting of beds deposited in the more central
parts of the basin, and towards the side farthest from the mountains.
The following characters would form the principal marks of distinction
between the strata in each series:--The more ancient system would be
composed, for the most part, of coarser materials, containing many beds
of pebbles and sand, often of great thickness, and sometimes dipping at
a considerable angle. These, with associated beds of finer ingredients,
would, if traced round the borders of the basin, be seen to vary greatly
in color and mineral composition, and would also be very irregular in
thickness. The beds, on the contrary, in the newer group, would consist
of finer particles, and would be horizontal, or very slightly inclined.
Their color and mineral composition would be very homogeneous throughout
large areas, and would differ from almost all the separate beds in the
older series.

The following causes would produce the diversity here alluded to between
the two great members of such lacustrine formations:--When the rivers
and torrents first reach the edge of the lake, the detritus washed down
by them from the adjoining heights sinks at once into deep water, all
the heavier pebbles and sand subsiding near the shore. The finer mud is
carried somewhat farther out, but not to the distance of many miles, for
the greater part may be seen, as, for example, where the Rhone enters
the Lake of Geneva, to fall down in clouds to the bottom, not far from
the river's mouth. Thus alluvial tracts are soon formed at the mouths of
every torrent and river, and many of these in the course of ages become
of considerable extent. Pebbles and sand are then transported farther
from the mountains; but in their passage they decrease in size by
attrition, and are in part converted into mud and sand. At length some
of the numerous deltas, which are all directed towards a common centre,
approach near to each other; those of adjoining torrents become united,
and each is merged, in its turn, in the delta of the largest river,
which advances most rapidly into the lake, and renders all the minor
streams, one after the other, its tributaries. The various mineral
ingredients of all are thus blended together into one homogeneous
mixture, and the sediment is poured out from a common channel into the
lake.

As the average size of the transported particles decreases, while the
force and volume of the main river augments, the newer deposits are
diffused continually over a wider area, and are consequently more
horizontal than the older. When at first there were many independent
deltas near the borders of the basin, their separate deposits differed
entirely from each other; one may have been charged, like the Arve where
it joins the Rhone, with white sand and sediment derived from
granite--another may have been black, like many streams in the Tyrol,
flowing from the waste of decomposing rocks of dark slate--a third may
have been colored by ochreous sediment, like the Red River in
Louisiana--a fourth, like the Elsa in Tuscany, may have held much
carbonate of lime in solution. At first they would each form distinct
deposits of sand, gravel, limestone, marl, or other materials; but,
after their junction, new chemical combinations and a distinct color
would be the result, and the particles, having been conveyed ten,
twenty, or a greater number of miles over alluvial plains, would become
finer.

In those deltas where the tides and strong marine currents interfere,
the above description would only be applicable, with certain
modifications. If a series of earthquakes accompany the growth of a
delta, and change the levels of the land from time to time, as in the
region where the Indus now enters the sea, the phenomena will depart
still more widely from the ordinary type. If, after a protracted period
of rest, a delta sinks down, pebbles may be borne along in shallow water
near the foot of the boundary hills, so as to form conglomerates
overlying the fine mud previously thrown into deeper water in the same
area.

_Causes of stratification in deltas._--The stratified arrangement, which
is observed to prevail so generally in aqueous deposits, is most
frequently due to variations in the velocity of running water, which
cannot sweep along particles of more than a certain size and weight when
moving at a given rate. Hence, as the force of the stream augments or
decreases, the materials thrown down in successive layers at particular
places are rudely sorted, according to their dimensions, form, and
specific gravity. Where this cause has not operated, as where sand, mud,
and fragments of rock are conveyed by a glacier, a confused heap of
rubbish devoid of all stratification is produced.

Natural divisions are also occasioned in deltas, by the interval of time
which separates annually the deposition of matter during the periodical
rains, or melting of snow upon the mountains. The deposit of each year
may acquire some degree of consistency before that of the succeeding
year is superimposed. A variety of circumstances also give rise
annually, or sometimes from day to day, to slight variations in color,
fineness of the particles, and other characters, by which alternations
of strata distinct in texture and mineral ingredients must be produced.
Thus, for example, at one period of the year, drift-wood may be carried
down, and, at another, mud, as was before stated to be the case in the
delta of the Mississippi; or at one time, when the volume and velocity
of the stream are greatest, pebbles and sand may be spread over a
certain area, over which, when the waters are low, fine matter or
chemical precipitates are formed. During inundations, the turbid current
of fresh water often repels the sea for many miles; but when the river
is low, salt water again occupies the same space. When two deltas are
converging, the intermediate space is often, for reasons before
explained, alternately the receptacle of different sediments derived
from the converging streams (see p. 272). The one is, perhaps, charged
with calcareous, the other with argillaceous matter; or one sweeps down
sand and pebbles, the other impalpable mud. These differences may be
repeated with considerable regularity, until a thickness of hundreds of
feet of alternating beds is accumulated. The multiplication, also, of
shells and corals in particular spots, and for limited periods, gives
rise occasionally to lines of separation, and divides a mass which might
otherwise be homogeneous into distinct strata.

An examination of the shell marl now forming in the Scotch lakes, or the
sediment termed "warp," which subsides from the muddy water of the
Humber and other rivers, shows that recent deposits are often composed
of a great number of extremely thin layers, either even or slightly
undulating, and preserving a general parallelism to the planes of
stratification. Sometimes, however, the laminæ in modern strata are
disposed diagonally at a considerable angle, which appears to take place
where there are conflicting movements in the waters. In January, 1829, I
visited, in company with Professor L. A. Necker, of Geneva, the
confluence of the Rhone and Arve, when those rivers were very low, and
were cutting channels through the vast heaps of débris thrown down from
the waters of the Arve in the preceding spring. One of the sandbanks
which had formed, in the spring of 1828, where the opposing currents of
the two rivers neutralized each other, and caused a retardation in the
motion, had been undermined; and the following is an exact
representation of the arrangement of laminæ exposed in a vertical
section. The length of the portion here seen is about twelve feet, and
the height five. The strata A A consist of irregular alternations of
pebbles and sand in undulating beds: below these are seams of very fine
sand B B, some as thin as paper, others about a quarter of an inch
thick. The strata C C are composed of layers of fine greenish-gray sand
as thin as paper. Some of the inclined beds will be seen to be thicker
at their upper, others at their lower extremity, the inclination of some
being very considerable. These layers must have accumulated one on the
other by lateral apposition, probably when one of the rivers was very
gradually increasing or diminishing in velocity, so that the point of
greatest retardation caused by their conflicting currents shifted
slowly, allowing the sediment to be thrown down in successive layers on
a sloping bank. The same phenomenon is exhibited in older strata of all
ages.[376]

[Illustration: Fig. 26.

Section of a sand-bank in the bed of the Arve at its confluence with the
Rhone, showing the stratification of deposits where currents meet.]

If the bed of a lake or of the sea be sinking, whether at a uniform or
an unequal rate, or oscillating in level during the deposition of
sediment, these movements will give rise to a different class of
phenomena, as, for example, to repeated alternations of shallow-water
and deep-water deposits, each with peculiar organic remains, or to
frequent repetitions of similar beds, formed at a uniform depth, and
inclosing the same organic remains, and to other results too complicated
and varied to admit of enumeration here.

_Formation of conglomerates._--Along the base of the Maritime Alps,
between Toulon and Genoa, the rivers, with few exceptions, are now
forming strata of conglomerate and sand. Their channels are often
several miles in breadth, some of them being dry, and the rest easily
forded for nearly eight months in the year, whereas during the melting
of the snow they are swollen, and a great transportation of mud and
pebbles takes place. In order to keep open the main road from France to
Italy, now carried along the sea-coast, it is necessary to remove
annually great masses of shingle brought down during the flood season. A
portion of the pebbles are seen in some localities, as near Nice, to
form beds of shingle along the shore, but the greater part are swept
into a deep sea. The small progress made by the deltas of minor rivers
on this coast need not surprise us, when we recollect that there is
sometimes a depth of two thousand feet at a few hundred yards from the
beach, as near Nice. Similar observations might be made respecting a
large proportion of the rivers in Sicily, and among others, respecting
that which, immediately north of the port of Messina, hurries annually
vast masses of granitic pebbles into the sea.

_Constant interchange of land and sea._--I may here conclude my remarks
on deltas, observing that, imperfect as is our information of the
changes which they have undergone within the last three thousand years,
they are sufficient to show how constant an interchange of sea and land
is taking place on the face of our globe. In the Mediterranean alone,
many flourishing inland towns, and a still greater number of ports, now
stand where the sea rolled its waves since the era of the early
civilization of Europe. If we could compare with equal accuracy the
ancient and actual state of all the islands and continents, we should
probably discover that millions of our race are now supported by lands
situated where deep seas prevailed in earlier ages. In many districts
not yet occupied by man, land animals and forests now abound where ships
once sailed; and, on the other hand, we shall find, on inquiry, that
inroads of the ocean have been no less considerable. When to these
revolutions, produced by aqueous causes, we add analogous changes
wrought by igneous agency, we shall, perhaps, acknowledge the justice of
the conclusion of Aristotle, who declared that the whole land and sea on
our globe periodically changed places.[377]




CHAPTER XIX.

DESTROYING AND TRANSPORTING EFFECTS OF TIDES AND CURRENTS.


  Difference in the rise of tides--Lagullas and Gulf
    currents--Velocity of currents--Causes of currents--Action of the
    sea on the British coast--Shetland Islands--Large blocks
    removed--Isles reduced to clusters of rocks--Orkney isles--Waste of
    East coast of Scotland--and East coast of England--Waste of the
    cliffs of Holderness, Norfolk, and Suffolk--Sand-dunes, how far
    chronometers--Silting up of estuaries--Yarmouth estuary--Suffolk
    coast--Dunwich--Essex coast--Estuary of the Thames--Goodwin
    Sands--Coast of Kent--Formation of the Straits of Dover--South coast
    of England--Sussex--Hants--Dorset--Portland--Origin of the Chesil
    Bank--Cornwall--Coast of Brittany.


Although the movements of great bodies of water, termed tides and
currents, are in general due to very distinct causes, their effects
cannot be studied separately; for they produce, by their joint action,
aided by that of the waves, those changes which are objects of
geological interest. These forces may be viewed in the same manner as we
before considered rivers, first, as employed in destroying portions of
the solid crust of the earth and removing them to other places;
secondly, as reproductive of new strata.

_Tides._--It would be superfluous at the present day to offer any
remarks on the cause of the tides. They are not perceptible in lakes or
in most inland seas; in the Mediterranean even, deep and extensive as is
that sea, they are scarcely sensible to ordinary observation, their
effects being quite subordinate to those of the winds and currents. In
some places, however, as in the Straits of Messina, there is an ebb and
flow to the amount of two feet and upwards; at Naples and at the
Euripus, of twelve or thirteen inches; and at Venice, according to
Rennell, of five feet.[378] In the Syrtes, also, of the ancients, two
wide shallow gulfs, which penetrate very far within the northern coast
of Africa, between Carthage and Cyrene, the rise is said to exceed five
feet.[379]

In islands remote from any continent, the ebb and flow of the ocean is
very slight, as at St. Helena, for example, where it is rarely above
three feet.[380] In any given line of coast, the tides are greatest in
narrow channels, bays, and estuaries, and least in the intervening
tracts where the land is prominent. Thus, at the entrance of the estuary
of the Thames and Medway, the rise of the spring tides is eighteen feet;
but when we follow our eastern coast from thence northward, towards
Lowestoff and Yarmouth, we find a gradual diminution, until at the
places last mentioned, the highest rise is only seven or eight feet.
From this point there begins again to be an increase, so that at Comer,
where the coast again retires towards the west, the rise is sixteen
feet; and towards the extremity of the gulf called "the Wash," as at
Lynn and in Boston Deeps, it is from twenty-two to twenty-four feet, and
in some extraordinary cases twenty-six feet. From thence again there is
a decrease towards, the north, the elevation at the Spurn Point being
from nineteen to twenty feet, and at Flamborough Head and the Yorkshire
coast from fourteen to sixteen feet.[381]

At Milford Haven in Pembrokeshire, at the mouth of the Bristol Channel,
the tides rise thirty-six feet; and at King-Road near Bristol, forty-two
feet. At Chepstow on the Wye, a small river which opens into the estuary
of the Severn, they reach fifty feet, and sometimes sixty-nine, and even
seventy-two feet. A current which sets in on the French coast, to the
west of Cape La Hague, becomes pent up by Guernsey, Jersey, and other
islands, till the rise of the tide is from twenty to forty-five feet,
which last height it attains at Jersey, and at St. Malo, a seaport of
Brittany. The tides in the Basin of Mines, at the head of the Bay of
Fundy in Nova Scotia, rise to the height of seventy feet.

There are, however, some coasts where the tides seem to offer an
exception to the rule above mentioned; for while there is scarcely any
rise in the estuary of the Plata in S. America, there is an extremely
high tide on the open coast of Patagonia, farther to the south. Yet even
in this region the tides reach their greatest elevation (about fifty
feet) in the Straits of Magellan, and so far at least they conform to
the general rule.[382]

_Currents._--The most extensive and best determined system of currents,
is that which has its source in the Indian Ocean under the influence of
the trade winds; and which, after doubling the Cape of Good Hope,
inclines to the northward, along the western coast of Africa, then
across the Atlantic, near the equator, where it is called the equatorial
current, and is lost in the Caribbean Sea, yet seems to be again revived
in the current which issues from the Gulf of Mexico. From thence it
flows rapidly through the Straits of Bahama, taking the name of the Gulf
Stream, and passing in a northeasterly direction, by the Banks of
Newfoundland, towards the Azores.

We learn from the posthumous work of Rennell on this subject, that the
Lagullas current, so called from the cape and bank of that name, is
formed by the junction of two streams, flowing from the Indian Ocean;
the one from the channel of Mozambique, down the southeast coast of
Africa; the other from the ocean at large. The collective stream is from
ninety to one hundred miles in breadth, and runs at the rate of from two
and a half to more than four miles per hour. It is at length turned
westward by the Lagullas bank, which rises from a sea of great depth to
within one hundred fathoms of the surface. It must therefore be
inferred, says Rennell, that the current here is more than one hundred
fathoms deep, otherwise the main body of it would pass across the bank,
instead of being deflected westward, so as to flow round the Cape of
Good Hope. From this cape it flows northward, as before stated, along
the western coast of Africa, taking the name of the South Atlantic
current. It then enters the Bight, or Bay of Benin, and is turned
westward, partly by the form of the coast there, and partly, perhaps, by
the Guinea current, which runs from the north into the same great bay.
From the centre of this bay proceeds the equatorial current already
mentioned, holding a westerly direction across the Atlantic, which it
traverses, from the coast of Guinea to that of Brazil, flowing
afterwards by the shores of Guiana to the West Indies. The breadth of
this current varies from 160 to 450 geographical miles, and its velocity
is from twenty-five to seventy-nine miles per day, the mean rate being
about thirty miles. The length of its whole course is about 4000 miles.
As it skirts the coast of Guiana, it is increased by the influx of the
waters of the Amazon and Orinoco, and by their junction acquires
accelerated velocity. After passing the island of Trinidad it expands,
and is almost lost in the Caribbean Sea; but there appears to be a
general movement of that sea towards the Mexican Gulf, which discharges
the most powerful of all currents through the Straits of Florida, where
the waters run in the northern part with a velocity of four or five
miles an hour, having a breadth of from thirty-five to fifty miles.[383]

The temperature of the Gulf of Mexico is 86° F. in summer, or 6° higher
than that of the ocean, in the same parallel (25° N. lat.), and a large
proportion of this warmth is retained, even where the stream reaches the
43° N. lat. After issuing from the Straits of Florida, the current runs
in a northerly direction to Cape Hatteras, in North Carolina, about 35°
N. lat., where it is more than seventy miles broad, and still moves at
the rate of seventy-five miles per day. In about the 40° N. lat., it is
turned more towards the Atlantic by the extensive banks of Nantucket and
St. George, which are from 200 to 300 feet beneath the surface of the
sea; a clear proof that the current exceeds that depth. On arriving near
the Azores, the stream widens, and overflows, as it were, forming a
large expanse of warm water in the centre of the North Atlantic, over a
space of 200 or 300 miles from north to south, and having a temperature
of from 8° to 10° Fahr. above the surrounding ocean. The whole area,
covered by the Gulf water, is estimated by Rennell at 2000 miles in
length, and, at a mean, 350 miles in breadth; an area more extensive
than that of the Mediterranean. The warm water has been sometimes known
to reach the Bay of Biscay, still retaining five degrees of temperature
above that of the adjoining ocean; and a branch of the Gulf current
occasionally drifts fruits, plants, and wood, the produce of America and
the West Indies, to the shores of Ireland and the Hebrides.

From the above statements we may understand why Rennell has
characterized some of the principal currents as oceanic rivers, which he
describes as being from 50 to 250 miles in breadth, and having a
rapidity exceeding that of the largest navigable rivers of the
continents, and so deep as to be sometimes obstructed, and occasionally
turned aside, by banks, the tops of which do not rise within forty,
fifty, or even one hundred fathoms of the surface of the sea.[384]

_Greatest velocity of currents._--The ordinary velocity of the principal
currents of the ocean is from one to three miles per hour; but when the
boundary lands converge, large bodies of water are driven gradually into
a narrow space, and then wanting lateral room, are compelled to raise
their level. Whenever this occurs their velocity is much increased. The
current which runs through the Race of Alderney, between the island of
that name and the main land, has a velocity of about eight English miles
an hour. Captain Hewett found that in the Pentland Firth, the stream, in
ordinary spring tides, runs ten miles and a half an hour, and about
thirteen miles during violent storms. The greatest velocity of the tidal
current through the "Shoots" or New Passage, in the Bristol Channel, is
fourteen English miles an hour; and Captain King observed, in his survey
of the Straits of Magellan, that the tide ran at the same rate through
the "First Narrows," and about eight geographical miles an hour, in
other parts of those straits.

_Causes of currents._--That movements of no inconsiderable magnitude
should be impressed on an expansive ocean, by winds blowing for many
months in one direction, may easily be conceived, when we observe the
effects produced in our own seas by the temporary action of the same
cause. It is well known that a strong southwest or northwest wind
invariably raises the tides to an unusual height along the west coast of
England and in the Channel; and that a northwest wind of any
continuance causes the Baltic to rise two feet and upwards above its
ordinary level. Smeaton ascertained by experiment, that in a canal four
miles in length, the water was kept up four inches higher at one end
than at the other, merely by the action of the wind along the canal; and
Rennell informs us that a large piece of water, ten miles broad, and
generally only three feet deep, has, by a strong wind, had its waters
driven to one side, and sustained so as to become six feet deep, while
the windward side was laid dry.[385]

As water, therefore, he observes, when pent up so that it cannot escape,
acquires a higher level, so, in a place _where it can escape_, the same
operation produces a current; and this current will extend to a greater
or less distance, according to the force by which it is produced. By the
side of the principal oceanic currents, such as the Lagullas and the
Gulf Stream, are parallel "counter-currents" running steadily in an
opposite direction.

Currents flowing alternately in opposite directions are occasioned by
the rise and fall of the tides. The effect of this cause is, as before
observed, most striking in estuaries and channels between islands.

A third cause of oceanic currents is evaporation by solar heat, of which
the great current setting through the Straits of Gibraltar into the
Mediterranean is a remarkable example, and will be fully considered in
the next chapter. A stream of colder water also flows from the Black Sea
into the Mediterranean. It must happen in many other parts of the world
that large quantities of water raised from one tract of the ocean by
solar heat, are carried to some other where the vapor is condensed and
falls in the shape of rain, and this, in flowing back again to restore
equilibrium, will cause sensible currents.

These considerations naturally lead to the inquiry whether the level of
those seas out of which currents flow, is higher than that of seas into
which they flow. If not, the effect must be immediately equalized by
under-currents or counter-currents. Arago is of opinion that, so far as
observations have gone, there are no exact proofs of any such difference
of level. It was inferred from the measurements of M. Lepére, that the
level of the Mediterranean, near Alexandria, was lower by 26 feet 6
inches, than the Red Sea near Suez at low water, and about 30 feet lower
than the Red Sea at the same place at high water,[386] but Mr. Robert
Stevenson affirms, as the result of a more recent survey, that there is
no difference of level between the two seas.[387]

It was formerly imagined that there was an equal, if not greater,
diversity in the relative levels of the Atlantic and Pacific, on the
opposite sides of the Isthmus of Panama. But the levellings carried
across that isthmus by Capt. Lloyd, in 1828, to ascertain the relative
height of the Pacific Ocean at Panama, and of the Atlantic at the mouth
of the river Chagres, have shown, that the difference of mean level
between those oceans is not considerable, and, contrary to expectation,
the difference which does exist is in favor of the greater height of the
Pacific. According to this survey, the mean height of the Pacific is
three feet and a half, or 3·52 above the Atlantic, if we assume the mean
level of a sea to coincide with the mean between the extremes of the
elevation and depression of the tides; for between the extreme levels of
the greatest tides in the Pacific, at Panama, there is a difference of
27·44 feet; and at the usual spring tides 21·22 feet; whereas at Chagres
this difference is only 1·16 feet, and is the same at all seasons of the
year.

The tides, in short, in the Caribbean Sea are scarcely perceptible, not
equalling those in some parts of the Mediterranean, whereas the rise is
very high in the Bay of Panama; so that the Pacific is at high tide
lifted up several feet above the surface of the Gulf of Mexico, and then
at low water let down as far below it.[388] But astronomers are agreed
that, on mathematical principles, the rise of the tidal wave above the
mean level of a particular sea must be greater than the fall below it;
and although the difference has been hitherto supposed insufficient to
cause an appreciable error, it is, nevertheless, worthy of observation,
that the error, such as it may be, would tend to reduce the small
difference, now inferred, from the observations of Mr. Lloyd, to exist
between the levels of the two oceans.

There is still another way in which heat and cold must occasion great
movements in the ocean, a cause to which, perhaps, currents are
principally due. Whenever the temperature of the surface of the sea is
lowered, condensation takes place, and the superficial water, having its
specific gravity increased, falls to the bottom, upon which lighter
water rises immediately and occupies its place. When this circulation of
ascending and descending currents has gone on for a certain time in high
latitudes, the inferior parts of the sea are made to consist of colder
or heavier fluid than the corresponding depths of the ocean between the
tropics. If there be a free communication, if no chain of submarine
mountains divide the polar from the equatorial basins, a horizontal
movement will arise by the flowing of colder water from the poles to the
equator, and there will then be a reflux of warmer superficial water
from the equator to the poles. A well-known experiment has been adduced
to elucidate this mode of action in explanation of the "trade
winds."[389] If a long trough, divided in the middle by a sluice or
partition, have one end filled with water and the other with
quicksilver, both fluids will remain quiet so long as they are divided;
but when the sluice is drawn up, the heavier fluid will rush along the
bottom of the trough, while the lighter, being displaced, will rise,
and, flowing in an opposite direction, spread itself at the top. In like
manner the expansion and contraction of sea-water by heat and cold, have
a tendency to set under-currents in motion from the poles to the
equator, and to cause counter-currents at the surface, which are
impelled in a direction contrary to that of the prevailing trade winds.
The geographical and other circumstances being very complicated, we
cannot expect to trace separately the movements due to each cause, but
must be prepared for many anomalies, especially as the configuration of
the bed of the ocean must often modify and interfere with the course of
the inferior currents, as much as the position and form of continents
and islands alter the direction of those on the surface. Thus on
sounding at great depths in the Mediterranean, Captains Berard and
D'Urville have found that the cold does not increase in a high ratio as
in the tropical regions of the ocean, the thermometer remaining fixed at
about 55° F. between the depths of 1000 and 6000 feet. This might have
been anticipated, as Captain Smyth in his survey had shown that the
deepest part of the Straits of Gibraltar is only 1320 feet, so that a
submarine barrier exists there which must prevent the influx of any
under-current of the ocean cooled by polar ice.

Each of the four causes above mentioned, the wind, the tides,
evaporation, and the expansion and contraction of water by heat and
cold, may be conceived to operate independently of the others, and
although the influence of all the rest were annihilated. But there is
another cause, the rotation of the earth on its axis, which can only
come into play when the waters have already been set in motion by some
one or all of the forces above described, and when the direction of the
current so raised happens to be from south to north, or from north to
south.

The principle on which this cause operates is probably familiar to the
reader, as it has long been recognized in the case of the trade winds.
Without enlarging, therefore, on the theory, it will be sufficient to
offer an example of the mode of action alluded to. When a current flows
from the Cape of Good Hope towards the Gulf of Guinea, it consists of a
mass of water, which, on doubling the Cape, in lat. 35°, has a rotatory
velocity of about 800 miles an hour; but when it reaches the line, where
it turns westward, it has arrived at a parallel where the surface of the
earth is whirled round at the rate of 1000 miles an hour, or about 200
miles faster. If this great mass of water was transferred suddenly from
the higher to the lower latitude, the deficiency of its rotatory motion,
relatively to the land and water with which it would come into
juxtaposition, would be such as to cause an apparent motion of the most
rapid kind (of no less than 200 miles an hour) from east to west.

In the case of such a sudden transfer, the eastern coast of America,
being carried round in an opposite direction, might strike against a
large body of water with tremendous violence, and a considerable part of
the continent might be submerged. This disturbance does not occur,
because the water of the stream, as it advances gradually into new zones
of the sea which are moving more rapidly, acquires by friction an
accelerated velocity. Yet as this motion is not imparted
instantaneously, the fluid is unable to keep up with the full speed of
the new surface over which it is successively brought. Hence, to borrow
the language of Herschel, when he speaks of the trade winds, "it lags or
hangs back, in a direction opposite to the earth's rotation, that is,
from east to west,"[390] and thus a current, which would have run simply
towards the north but for the rotation, may acquire a relative direction
towards the west.

We may next consider a case where the circumstances are the converse of
the above. The Gulf Stream flowing from about lat. 20° is at first
impressed with a velocity of rotation of about 940 miles an hour, and
runs to the lat. 40°, where the earth revolves only at the rate of 766
miles, or 174 miles slower. In this case a relative motion of an
opposite kind may result; and the current may retain an excess of
rotatory velocity, tending continually to deflect it eastward. Polar
currents, therefore, or those flowing from high to low latitudes, are
driven towards the eastern shores of continents, while tropical currents
flowing towards the poles are directed against their western shores.

Thus it will be seen that currents depend, like the tides, on no
temporary or accidental circumstances, but on the laws which preside
over the motions of the heavenly bodies. But although the sum of their
influence in altering the surface of the earth may be very constant
throughout successive epochs, yet the points where these operations are
displayed in fullest energy shift perpetually. The height to which the
tides rise, and the violence and velocity of currents, depend in a great
measure on the actual configuration of the land, the contour of a long
line of continental or insular coast, the depth and breadth of channels,
the peculiar form of the bottom of seas--in a word, on a combination of
circumstances which are made to vary continually by many igneous and
aqueous causes, and, amongst the rest, by the tides and currents
themselves. Although these agents, therefore, of decay and reproduction
are local in reference to periods of short duration, such as those which
history embraces, they are nevertheless universal, if we extend our
views to a sufficient lapse of ages.

_Destroying and transporting power of currents._--After these
preliminary remarks on the nature and causes of currents, their velocity
and direction, we may next consider their action on the solid materials
of the earth. We shall find that their efforts are, in many respects,
strictly analogous to those of rivers. I have already treated in the
third chapter, of the manner in which currents sometimes combine with
ice, in carrying mud, pebbles, and large fragments of rock to great
distances. Their operations are more concealed from our view than those
of rivers, but extend over wider areas, and are therefore of more
geological importance.

_Waste of the British coasts._--_Shetland Islands_.--If we follow the
eastern and southern shores of the British islands, from our Ultima
Thule in Shetland to the Land's End in Cornwall, we shall find evidence
of a series of changes since the historical era, very illustrative of
the kind and degree of force exerted by tides and currents co-operating
with the waves of the sea. In this survey we shall have an opportunity
of tracing their joint power on islands, promontories, bays, and
estuaries; on bold, lofty cliffs, as well as on low shores; and on every
description of rock and soil, from granite to blown sand.

The northernmost group of the British islands, the Shetland, are
composed of a great variety of rocks, including granite, gneiss,
mica-slate, serpentine, greenstone, and many others, with some secondary
rocks, chiefly sandstone and conglomerate. These islands are exposed
continually to the uncontrolled violence of the Atlantic, for no land
intervenes between their western shores and America. The prevalence,
therefore, of strong westerly gales, causes the waves to be sometimes
driven with irresistible force upon the coast, while there is also a
current setting from the north. The spray of the sea aids the
decomposition of the rocks, and prepares them to be breached by the
mechanical force of the waves. Steep cliffs are hollowed out into deep
caves and lofty arches; and almost every promontory ends in a cluster of
rocks, imitating the forms of columns, pinnacles, and obelisks.

_Drifting of large masses of rock._--Modern observations show that the
reduction of continuous tracts to such insular masses is a process in
which nature is still actively engaged. "The isle of Stenness," says Dr.
Hibbert, "presents a scene of unequalled desolation. In stormy winters,
huge blocks of stones are overturned, or are removed from their native
beds, and hurried up a slight acclivity to a distance almost incredible.
In the winter of 1802, a tabular-shaped mass, eight feet two inches by
seven feet, and five feet one inch thick, was dislodged from its bed,
and removed to a distance of from eighty to ninety feet. I measured the
recent bed from which a block had been carried away the preceding winter
(A. D. 1818), and found it to be seventeen feet and a half by seven
feet, and the depth two feet eight inches. The removed mass had been
borne to a distance of thirty feet, when it was shivered into thirteen
or more lesser fragments, some of which, were carried still farther,
from 30 to 120 feet. A block, nine feet two inches by six feet and a
half, and four feet thick, was hurried up the acclivity to a distance of
150 feet."[391]

At Northmavine, also, angular blocks of stone have been removed in a
similar manner to considerable distances by the waves of the sea, some
of which are represented in the annexed figure.

_Effects of lightning._--In addition to numerous examples of masses
detached and driven by the waves, tides, and currents from their place,
some remarkable effects of lightning are recorded in these isles. At
Funzie, in Fetlar, about the middle of the last century, a rock of
mica-schist, 105 feet long, ten feet broad, and in some places four feet
thick, was in an instant torn by a flash of lightning from its bed, and
broken into three large and several smaller fragments. One of these,
twenty-six feet long, ten feet broad, and four feet thick, was simply
turned over. The second, which was twenty-eight feet long, seventeen
broad, and five feet in thickness, was hurled across a high point to the
distance of fifty yards. Another broken mass, about forty feet long, was
thrown still farther, but in the same direction, quite into the sea.
There were also many smaller fragments scattered up and down.[392]

[Illustration: Fig. 27.

Stony fragments drifted by the sea. Northmavine, Shetland.]

When we thus see electricity co-operating with the violent movements of
the ocean in heaping up piles of shattered rocks on dry land and beneath
the waters, we cannot but admit that a region which shall be the
theatre, for myriads of ages, of the action of such disturbing causes,
might present, at some future period, if upraised far above the bosom of
the deep, a scene of havoc and ruin that may compare with any now found
by the geologist on the surface of our continents.

In some of the Shetland Isles, as on the west of Meikle Roe, dikes, or
veins of soft granite, have mouldered away; while the matrix in which
they were inclosed, being of the same substance, but of a firmer
texture, has remained unaltered. Thus, long narrow ravines, sometimes
twenty feet wide, are laid open, and often give access to the waves.
After describing some huge cavernous apertures into which the sea flows
for 250 feet in Roeness, Dr. Hibbert, writing in 1822, enumerates other
ravages of the ocean. "A mass of rock, the average dimensions of which
may perhaps be rated at twelve or thirteen feet square, and four and a
half or five in thickness, was first moved from its bed, about fifty
years ago, to a distance of thirty feet, and has since been twice turned
over."

_Passage forced by the sea through porphyritic rocks._--"But the most
sublime scene is where a mural pile of porphyry, escaping the process
of disintegration that is devastating the coast, appears to have been
left as a sort of rampart against the inroads of the ocean;--the
Atlantic, when provoked by wintry gales, batters against it with all the
force of real artillery--the waves having, in their repeated assaults,
forced themselves an entrance. This breach, named the Grind of the Navir
(fig. 28), is widened every winter by the overwhelming surge that,
finding a passage through it, separates large stones from its sides, and
forces them to a distance of no less than 180 feet. In two or three
spots, the fragments which have been detached are brought together in
immense heaps, that appear as an accumulation of cubical masses, the
product of some quarry."[393]

[Illustration: Fig. 28.

Grind of the Navir--passage forced by the sea through rocks of hard
porphyry.]

It is evident from this example, that although the greater
indestructibility of some rocks may enable them to withstand, for a
longer time, the action of the elements, yet they cannot permanently
resist. There are localities in Shetland, in which rocks of almost every
variety of mineral composition are suffering disintegration; thus the
sea makes great inroads on the clay slate of Fitfel Head, on the
serpentine of the Vord Hill in Fetlar, and on the mica-schist of the Bay
of Triesta, on the east coast of the same island, which decomposes into
angular blocks. The quartz rock on the east of Walls, and the gneiss and
mica-schist of Garthness, suffer the same fate.

_Destruction of islands._--Such devastation cannot be incessantly
committed for thousands of years without dividing islands, until they
become at last mere clusters of rocks, the last shreds of masses once
continuous. To this state many appear to have been reduced, and
innumerable fantastic forms are assumed by rocks adjoining these islands
to which the name of Drongs is applied, as it is to those of similar
shape in Feroe.

[Illustration: Fig. 29.

Granitic rocks named the Drongs, between Papa Stour and Hillswick Ness.]

[Illustration: Fig. 30.

Granitic rocks to the south of Hillswick Ness, Shetland.]

The granite rocks (fig. 29), between Papa Stour and Hillswick Ness
afford an example. A still more singular cluster of rocks is seen to the
south of Hillswick Ness (fig. 30), which presents a variety of forms as
viewed from different points, and has often been likened to a small
fleet of vessels with spread sails.[394] We may imagine that in the
course of time Hillswick Ness itself may present a similar wreck, from
the unequal decomposition of the rocks whereof it is composed,
consisting of gneiss and mica-schist traversed in all directions by
veins of felspar-porphyry.

Midway between the groups of Shetland and Orkney is Fair Island, said to
be composed of sandstone with high perpendicular cliffs. The current
runs with such velocity, that during a calm, and when there is no swell,
the rocks on its shores are white with the foam of the sea driven
against them. The Orkneys, if carefully examined, would probably
illustrate our present topic as much as the Shetland group. The
northeast promontory of Sanda, one of these islands, has been cut off in
modern times by the sea, so that it became what is now called Start
Island, where a lighthouse was erected in 1807, since which time the new
strait has grown broader.

_East coast of Scotland._--To pass over to the main land of Scotland, we
find that in Inverness-shire there have been inroads of the sea at Fort
George, and others in Morayshire, which have swept away the old town of
Findhorn. On the coast of Kincardineshire, an illustration was afforded
at the close of the last century, of the effect of promontories in
protecting a line of low shore. The village of Mathers, two miles south
of Johnshaven, was built on an ancient shingle beach, protected by a
projecting ledge of limestone rock. This was quarried for lime to such
an extent that the sea broke through, and in 1795 carried away the whole
village in one night, and penetrated 150 yards inland, where it has
maintained its ground ever since, the new village having been built
farther inland on the new shore. In the bay of Montrose, we find the
North Esk and the South Esk rivers pouring annually into the sea large
quantities of sand and pebbles; yet they have formed no deltas, for the
waves, aided by the current, setting across their mouths, sweep away all
the materials. Considerable beds of shingle, brought down by the North
Esk, are seen along the beach.

Proceeding southwards, we learn that at Arbroath, in Forfarshire, which
stands on a rock of red sandstone, gardens and houses have been carried
away since the commencement of the present century by encroachments of
the sea. It had become necessary before 1828, to remove the lighthouses
at the mouth of the estuary of the Tay, in the same county, at Button
Ness, which were built on a tract of blown sand, the sea having
encroached for three-quarters of a mile.

_Force of waves and currents in estuaries._--The combined power which
waves and currents can exert in _estuaries_ (a term which I confine to
bays entered both by rivers and the tides of the sea), was remarkably
exhibited during the building of the Bell Rock Lighthouse, off the mouth
of the Tay. The Bell Rock is a sunken reef, consisting of red sandstone,
being from twelve to sixteen feet under the surface at high water, and
about twelve miles from the mainland. At the distance of 100 yards,
there is a depth, in all directions of two or three fathoms at low
water. In 1807, during the erection of the lighthouse, six large blocks
of granite, which had been landed on the reef, were removed by the force
of the sea, and thrown over a rising ledge to the distance of twelve or
fifteen paces; and an anchor, weighing about 22 cwt., was thrown up upon
the rock.[395] Mr. Stevenson informs us moreover, that drift stones,
measuring upwards of thirty cubic feet, or more than two tons' weight,
have, during storms, been often thrown upon the rock from the deep
water.[396]

_Submarine forests._--Among the proofs that the sea has encroached on
the land bordering the estuary of the Tay, Dr. Fleming has mentioned a
submarine forest which has been traced for several miles along the
northern shore of the county of Fife.[397] But subsequent surveys seem
to have shown that the bed of peat containing tree-roots, leaves, and
branches, now occurring at a lower level than the Tay, must have come
into its present position by a general sinking of the ground on which
the forest grew. The peat-bed alluded to is not confined, says Mr.
Buist, to the present channel of the Tay, but extends far beyond it, and
is covered by stratified clay from fifteen to twenty-five feet in
thickness, in the midst of which, in some places, is a bed full of
sea-shells.[398] Recent discoveries having established the fact that
upward and downward movements have affected our island since the general
coast-line had nearly acquired its present shape, we must hesitate
before we attribute any given change to a single cause, such as the
local encroachment of the sea upon low land.

On the coast of Fife, at St. Andrew's, a tract of land, said to have
intervened between the castle of Cardinal Beaton and the sea, has been
entirely swept away, as were the last remains of the Priory of Crail, in
the same county, in 1803. On both sides of the Frith of Forth, land has
been consumed; at North Berwick in particular, and at Newhaven, where an
arsenal and dock, built in the reign of James IV., in the fifteenth
century, has been overflowed.

_East coast of England._--If we now proceed to the English coast, we
find records of numerous lands having been destroyed in Northumberland,
as those near Bamborough and Holy Island, and at Tynemouth Castle, which
now overhangs the sea, although formerly separated from it by a strip of
land. At Hartlepool, and several other parts of the coast of Durham
composed of magnesian limestone, the sea has made considerable inroads.

_Coast of Yorkshire._--Almost the whole coast of Yorkshire, from the
mouth of the Tees to that of the Humber, is in a state of gradual
dilapidation. That part of the cliffs which consist of lias, the oolite
series, and chalk, decays slowly. They present abrupt and naked
precipices, often 300 feet in height; and it is only at a few points
that the grassy covering of the sloping talus marks a temporary
relaxation of the erosive action of the sea. The chalk cliffs are worn
into caves and needles in the projecting headland of Flamborough, where
they are decomposed by the salt spray, and slowly crumble away. But the
waste is most rapid between that promontory and Spurn Point, or the
coast of Holderness, as it is called, a tract consisting of beds of
clay, gravel, sand, and chalk rubble. The irregular intermixture of the
argillaceous beds causes many springs to be thrown out, and this
facilitates the undermining process, the waves beating against them, and
a strong current setting chiefly from the north. The wasteful action is
very conspicuous at Dimlington Height, the loftiest point in Holderness,
where the beacon stands on a cliff 146 feet above high water, the whole
being composed of clay, with pebbles scattered through it.[399] "For
many years," says Professor Phillips, "the rate at which the cliffs
recede from Bridlington to Spurn, a distance of thirty-six miles, has
been found by measurement to equal on an average two and a quarter yards
annually, which, upon thirty-six miles of coast, would amount to about
thirty acres a year. At this rate, the coast, the mean height of which
above the sea is about forty feet, has lost one mile in breadth since
the Norman Conquest, and more than two miles since the occupation of
York (Eboracum) by the Romans."[400] The extent of this denudation, as
estimated by the number of cubic feet of matter removed annually, will
be again spoken of in chapter 22.

In the old maps of Yorkshire, we find spots, now sand-banks in the sea,
marked as the ancient sites of the towns and villages of Auburn,
Hartburn, and Hyde. "Of Hyde," says Pennant, "only the tradition is
left; and near the village of Hornsea, a street called Hornsea Beck has
long since been swallowed."[401] Owthorne and its church have also been
in great part destroyed, and the village of Kilnsea; but these places
are now removed farther inland. The annual rate of encroachment at
Owthorne for several years preceding 1830, is stated to have averaged
about four yards. Not unreasonable fears are entertained that at some
future time the Spurn Point will become an island, and that the ocean,
entering into the estuary of the Humber, will cause great
devastation.[402] Pennant, after speaking of the silting up of some
ancient ports in that estuary, observes, "But, in return, the sea has
made most ample reprisals; the site, and even the very names of several
places, once towns of note upon the Humber, are now only recorded in
history; and Ravensper was at one time a rival to Hull (Madox, Ant.
Exch. i. 422), and a port so very considerable in 1332, that Edward
Baliol and the confederated English barons sailed from hence to invade
Scotland; and Henry IV., in 1399, made choice of this port to land at,
to effect the deposal of Richard II.; yet the whole of this has long
since been devoured by the merciless ocean; extensive sands, dry at low
water, are to be seen in their stead."[403]

Pennant describes Spurn Head as a promontory in the form of a sickle,
and says the land, for some miles to the north, was "perpetually preyed
on by the fury of the German Sea, which devours whole acres at a time,
and exposes on the shores considerable quantities of beautiful amber."

_Lincolnshire._--The maritime district of Lincolnshire consists chiefly
of lands that lie below the level of the sea, being protected by
embankments. Some of the fens were embanked and drained by the Romans;
but after their departure the sea returned, and large tracts were
covered with beds of silt, containing marine shells, now again converted
into productive lands. Many dreadful catastrophes are recorded by
incursions of the sea, whereby several parishes have been at different
times overwhelmed.

_Norfolk._--The decay of the cliffs of Norfolk and Suffolk is incessant.
At Hunstanton, on the north, the undermining of the lower arenaceous
beds at the foot of the cliff, causes masses of red and white chalk to
be precipitated from above. Between Hunstanton and Weybourne, low hills,
or dunes, of blown sand, are formed along the shore, from fifty to sixty
feet high. They are composed of dry sand, bound in a compact mass by the
long creeping roots of the plant called Marram (_Arundo arenaria_). Such
is the present set of the tides, that the harbors of Clay, Wells, and
other places are securely defended by these barriers; affording a clear
proof that it is not the strength of the material at particular points
that determines whether the sea shall be progressive or stationary, but
the general contour of the coast.

The waves constantly undermine the low chalk cliffs, covered with sand
and clay, between Weybourne and Sherringham, a certain portion of them
being annually removed. At the latter town I ascertained, in 1829, some
facts which throw light on the rate at which the sea gains upon the
land. It was computed, when the present inn was built, in 1805, that it
would require seventy years for the sea to reach the spot: the mean loss
of land being calculated, from previous observations, to be somewhat
less than one yard, annually. The distance between the house and the sea
was fifty yards; but no allowance was made for the slope of the ground
being _from_ the sea, in consequence of which the waste was naturally
accelerated every year, as the cliff grew lower, there being at each
succeeding period less matter to remove when portions of equal area fell
down. Between the years 1824 and 1829, no less than seventeen yards were
swept away, and only a small garden was then left between the building
and the sea. There was, in 1829, a depth of twenty feet (sufficient to
float a frigate) at one point in the harbor of that port, where, only
forty-eight years before, there stood a cliff fifty feet high, with
houses upon it! If once in half a century an equal amount of change were
produced suddenly by the momentary shock of an earthquake, history would
be filled with records of such wonderful revolutions of the earth's
surface; but, if the conversion of high land into deep sea be gradual,
it excites only local attention. The flagstaff of the Preventive Service
station, on the south side of this harbor, was thrice removed inland
between the years 1814 and 1829, in consequence of the advance of the
sea.

Farther to the south we find cliffs, composed, like those of Holderness
before mentioned, of alternating strata of blue clay, gravel, loam, and
fine sand. Although they sometimes exceed 300 feet in height, the havoc
made on the coast is most formidable. The whole site of ancient Cromer
now forms part of the German Ocean, the inhabitants having gradually
retreated inland to their present situation, from whence the sea still
threatens to dislodge them. In the winter of 1825, a fallen mass was
precipitated from near the lighthouse, which covered twelve acres,
extending far into the sea, the cliffs being 250 feet in height.[404]
The undermining by springs has sometimes caused large portions of the
upper part of the cliffs, with houses still standing upon them, to give
way, so that it is impossible, by erecting breakwaters at the base of
the cliffs, permanently to ward off the danger.

[Illustration: Fig. 31.

Tower of the buried Church of Eccles, Norfolk, A. D. 1839.

The inland slope of the hills of blown sand is shown in this view, with
the lighthouse of Hasborough in the distance.]

On the same coast, says Mr. R. C. Taylor, the ancient villages of
Shipden, Wimpwell, and Eccles have disappeared; several manors and large
portions of neighboring parishes having, piece after piece, been
swallowed up; nor has there been any intermission, from time immemorial,
in the ravages of the sea along a line of coast twenty miles in length,
in which these places stood.[405] Of Eccles, however, a monument still
remains in the rained tower of the old church, which is half buried in
the dunes of sand within a few paces (60?) of the sea-beach (fig. 31).
So early as 1605 the inhabitants petitioned James I. for a reduction of
taxes, as 300 acres of land, and all their houses, save fourteen, had
then been destroyed by the sea. Not one half that number of acres now
remains in the parish, and hills of blown sand now occupy the site of
the houses which were still extant in 1605. When I visited the spot in
1839, the sea was fast encroaching on the sand-hills, and had laid open
on the beach the foundations of a house fourteen yards square, the upper
part of which had evidently been pulled down before it had been buried
under sand. The body of the church has also been long buried, but the
tower still remains visible.

M. E. de Beaumont has suggested that sand-dunes in Holland and other
countries may serve as natural chronometers, by which the date of the
existing continents may be ascertained. The sands, he says, are
continually blown inland by the force of the winds, and by observing the
rate of their march we may calculate the period when the movement
commenced.[406] But the example just given will satisfy every geologist
that we cannot ascertain the starting-point of dunes, all coasts being
liable to waste, and the shores of the Low Countries in particular,
being not only exposed to inroads of the sea, but, as M. de Beaumont
himself has well shown, having even in historical times undergone a
change of level. The dunes may indeed, in some cases, be made use of as
chronometers, to enable us to assign a minimum of antiquity to existing
coast-lines; but this test must be applied with great caution, so
variable is the rate at which the sands may advance into the interior.

Hills of blown sand, between Eccles and Winterton, have barred up and
excluded the tide for many hundred years from the mouths of several
small estuaries; but there are records of nine breaches, from 20 to 120
yards wide, having been made through these, by which immense damage was
done to the low grounds in the interior. A few miles south of
Happisburgh, also, are hills of blown sand, which extend to Yarmouth.
These _dunes_ afford a temporary protection to the coast, and an inland
cliff, about a mile long, at Winterton, shows clearly that at that point
the sea must have penetrated formerly farther than at present.

_Silting up of estuaries/_--At Yarmouth, the sea has not advanced upon
the sands in the slightest degree since the reign of Elizabeth. In the
time of the Saxons, a great estuary extended as far as Norwich, which
city, is represented; even in the thirteenth and fourteenth centuries,
as "situated on the banks of an arm of the sea." The sands whereon
Yarmouth is built, first became firm and habitable ground about the year
1008, from which time a line of dunes has gradually increased in height
and breadth, stretching across the whole entrance of the ancient
estuary, and obstructing the ingress of the tides so completely, that
they are only admitted by the narrow passage which the river keeps open,
and which has gradually shifted several miles to the south. The ordinary
tides at the river's mouth rise, at present, only to the height, of
three or four feet, the spring tides to about eight or nine.

By the exclusion of the sea, thousands of acres in the interior have
become cultivated lands; and, exclusive of smaller pools, upwards of
sixty freshwater lakes have been formed, varying in depth from fifteen
to thirty feet, and in extent from one acre to twelve hundred.[407] The
Yare, and other rivers, frequently communicate with these sheets of
water; and thus they are liable to be filled up gradually with
lacustrine and fluviatile deposits, and to be converted into land
covered with forests. Yet it must not be imagined, that the acquisition
of new land fit for cultivation in Norfolk and Suffolk indicates any
permanent growth of the eastern limits of our island to compensate its
reiterated losses. No _delta_ can form on such a shore.

Immediately off Yarmouth, and parallel to the shore, is a great range of
sand-banks, the shape of which varies slowly from year to year, and
often suddenly after great storms. Captain Hewitt, R. N., found in these
banks, in 1836, a broad channel sixty-five feet deep, where there was
only a depth of four feet during a prior survey in 1822. The sea had
excavated to the depth of sixty feet in the course of fourteen years, or
perhaps a shorter period. The new channel thus formed serves at present
(1838), for the entrance of ships into Yarmouth Roads; and the magnitude
of this change shows how easily a new set of the waves and currents
might endanger the submergence of the land gained within the ancient
estuary of the Yare.

That great banks should be thrown across the mouths of estuaries on our
eastern coast, where there is not a large body of river-water to
maintain an open channel, is perfectly intelligible, when we bear in
mind that the marine current, sweeping along the coast, is charged with
the materials of wasting cliffs, and ready to form a bar anywhere the
instant its course is interrupted or checked by any opposing stream. The
mouth of the Yare has been, within the last five centuries, diverted
about four miles to the south. In like manner it is evident that, at
some remote period, the river Alde entered the sea at Aldborough, until
its ancient outlet was barred up and at length transferred to a point no
less than ten miles distant to the southwest. In this case, ridges of
sand and shingle, like those of Lowestoff Ness, which will be described
by and by, have been thrown up between the river and the sea; and an
ancient sea-cliff is to be seen now inland.

It may be asked why the rivers on our east coast are always deflected
southwards, although the tidal current flows alternately from the south
and north? The cause is to be found in the superior force of what is
commonly called "the flood tide from the north," a tidal wave derived
from the Atlantic, a small part of which passes eastward up the English
Channel, and through the Straits of Dover and then northwards, while the
principal body of water, moving much more rapidly in a more open sea, on
the western side of Britain, first passes the Orkneys, and then turning,
flows down between Norway and Scotland, and sweeps with great velocity
along our eastern coast. It is well known that the highest tides on this
coast are occasioned by a powerful northwest wind, which raises the
eastern part of the Atlantic, and causes it to pour a greater volume of
water into the German Ocean. This circumstance of a violent _off-shore_
wind being attended with a rise of the waters, instead of a general
retreat of the sea, naturally excites the wonder of the inhabitants of
our coast. In many districts they look with confidence for a rich
harvest of that valuable manure, the sea-weed, when the north-westerly
gales prevail, and are rarely disappointed.

[Illustration: Fig. 32.

Map of Lowestoff Ness, Suffolk.[408]

_a_, _a_. The dotted lines express a series of sand and shingle, forming
the extremity of the triangular space called the Ness.

_b_, _b_, _b_. The dark line represents the inland cliff on which the
town of Lowestoff stands, between which and the sea is the Ness.]

_Coast of Suffolk._--The cliffs of Suffolk, to which we next proceed,
are somewhat less elevated than those of Norfolk, but composed of
similar alternations of clay, sand, and gravel. From Gorleston in
Suffolk, to within a few miles north of Lowestoff, the cliffs are slowly
undermined. Near the last-mentioned town, there is an inland cliff about
sixty feet high, the sloping talus of which is covered with turf and
heath. Between the cliff and the sea is a low flat tract of sand called
the Ness, nearly three miles long, and for the most part out of reach of
the highest tides. The point of the Ness projects from the base of the
original cliff to the distance of 660 yards. This accession of land,
says Mr. Taylor, has been effected at distinct and distant intervals, by
the influence of currents running between the land and a shoal about a
mile off Lowestoff, called the Holm Sand. The lines of growth in the
Ness are indicated by a series of concentric ridges or embankments
inclosing limited areas, and several of these ridges have been formed
within the observation of persons now living. A rampart of heavy
materials is first thrown up to an unusual altitude by some
extraordinary tide, attended with a violent gale. Subsequent tides
extend the base of this high bank of shingle, and the interstices are
then filled with sand blown from the beach. The Arundo and other marine
plants by degrees obtain a footing; and creeping along the ridge, give
solidity to the mass, and form in some cases a matted covering of turf.
Meanwhile another mound is forming externally, which by the like process
rises and gives protection to the first. If the sea forces its way
through one of the external and incomplete mounds, the breach is soon
repaired. After a while the marine plants within the areas inclosed by
these embankments are succeeded by a better species of herbage affording
good pasturage, and the sands become sufficiently firm to support
buildings.

_Destruction of Dunwich by the sea._--Of the gradual destruction of
Dunwich, once the most considerable seaport on this coast, we have many
authentic records. Gardner, in his history of that borough, published
in 1754, shows, by reference to documents, beginning with Doomsday Book,
that the cliffs at Dunwich, Southwold, Eastern, and Pakefield, have been
always subject to wear away. At Dunwich, in particular, two tracts of
land which had been taxed in the eleventh century, in the time of King
Edward the Confessor, are mentioned in the Conqueror's survey, made but
a few years afterwards, as having been devoured by the sea. The losses,
at a subsequent period, of a monastery,--at another of several
churches,--afterwards of the old port,--then of four hundred houses at
once,--of the church of St. Leonard, the high-road, town-hall, jail, and
many other buildings, are mentioned, with the dates when they perished.
It is stated that, in the sixteenth century, not one-quarter of the town
was left standing; yet the inhabitants retreating inland, the name was
preserved, as has been the case with many other ports when their ancient
site has been blotted out. There is, however, a church of considerable
antiquity still standing, the last of twelve mentioned in some records.
In 1740, the laying open of the churchyard of St. Nicholas and St.
Francis, in the sea-cliffs, is well described by Gardner, with the
coffins and skeletons exposed to view--some lying on the beach, and
rocked


  "In cradle of the rude imperious surge."


Of these cemeteries no remains can now be seen. Ray also says, "that
ancient writings make mention of a wood a mile and a half to the east of
Dunwich, the site of which must at present be so far within the
sea."[409] This city, once so flourishing and populous, is now a small
village, with about twenty houses, and one hundred inhabitants.

There is an old tradition, "that the tailors sat in their shops at
Dunwich, and saw the ships in Yarmouth Bay;" but when we consider how
far the coast at Lowestoff Ness projects between these places, we cannot
give credit to the tale, which, nevertheless, proves how much the
inroads of the sea in times of old had prompted men of lively
imagination to indulge their taste for the marvellous.

Gardner's description of the cemeteries laid open by the waves reminds
us of the scene which has been so well depicted by Bewick,[410] and of
which numerous points on the same coast might have suggested the idea.
On the verge of a cliff, which the sea has undermined, are represented
the unshaken tower and western end of an abbey. The eastern aisle is
gone, and the pillars of the cloister are soon to follow. The waves have
almost isolated the promontory, and invaded the cemetery, where they
have made sport with the mortal relics, and thrown up a skull upon the
beach. In the foreground is seen a broken tombstone, erected, as its
legend tells, "to _perpetuate_ the memory"--of one whose name is
obliterated, as is that of the county for which he was "Custos
Rotulorum." A cormorant is perched on the monument, defiling it, as if
to remind some moralizer like Hamlet, of "the base uses" to which things
sacred may be turned. Had this excellent artist desired to satirize
certain popular theories of geology, he might have inscribed the stone
to the memory of some philosopher who taught "the permanency of existing
continents"--"the era of repose"--"the impotence of modern causes."

The incursions of the sea at Aldborough, were formerly very destructive,
and this borough is known to have been once situated a quarter of a mile
east of the present shore. The inhabitants continued to build farther
inland, till they arrived at the extremity of their property, and then
the town decayed greatly; but two sand-banks, thrown up at a short
distance, now afford a temporary safeguard to the coast. Between these
banks and the present shore, where the current now flows, the sea is
twenty-four feet deep on the spot where the town formerly stood.

_Essex._--Harwich is said to have owed its rise to the destruction of
Orwell, a town which stood on the spot now called "the west rocks," and
was overwhelmed by an inroad of the sea since the Conquest.
Apprehensions have been entertained that the isthmus on which Harwich
stands may at no remote period become an island, for the sea may be
expected to make a breach near Lower Dover Court, where Beacon Cliff is
composed of horizontal beds of London clay containing septaria. It had
wasted away considerably between the years 1829 and 1838, at both which
periods I examined this coast. In that short interval several gardens
and many houses had been swept into the sea, and in April, 1838, a whole
street was threatened with destruction. The advance of the sea is much
accelerated by the traffic carried on in septaria, which are shipped off
for cement as fast as they fall down upon the beach. These stones, if
allowed to remain in heaps on the shore, would break the force of the
waves and retard the conversion of the peninsula into an island, an
event which might be followed by the destruction of the town of Harwich.
Captain Washington, R. N., ascertained in 1847, that Beacon Cliff, above
mentioned, which is about fifty feet high, had given way at the rate of
forty feet in forty-seven years, between 1709 and 1756; eighty feet
between 1756 and 1804; and three hundred and fifty feet between the
latter period and 1841; showing a rapidly accelerated rate of
destruction.[411]

Among other losses it is recorded that, since the year 1807, a field
called the Vicar's Field, which belonged to the living of Harwich, has
been overwhelmed;[412] and in the year 1820 there was a considerable
space between the battery at Harwich, built in the beginning of the
present century, and the sea; part of the fortification had been swept
away in 1829, and the rest then overhung the water.

At Walton Naze, in the same county, the cliffs, composed of London clay,
capped by the shelly sands of the crag, reach the height of about 100
feet, and are annually undermined by the waves. The old churchyard of
Walton has been washed away, and the cliffs to the south are constantly
disappearing.

_Kent.--Isle of Sheppey._--On the coast bounding the estuary of the
Thames, there are numerous examples both of the gain and loss of land.
The Isle of Sheppey, which is now about six miles long by four in
breadth, is composed of London clay. The cliffs on the north, which are
from sixty to eighty feet high, decay rapidly, fifty acres having been
lost in twenty years, between 1810 and 1830. The church at Minster, now
near the coast, is said to have been in the middle of the island in
1780; and if the present rate of destruction should continue, we might
calculate the period, and that not a very remote one, when the whole
island will be annihilated. On the coast of the mainland, to the east of
Sheppey, is Herne Bay: a place still retaining the name of a bay,
although it is no longer appropriate, as the waves and currents have
swept away the ancient headlands. There was formerly a small promontory
in the line of the shoals where the present pier is built, by which the
larger bay was divided into two, called the Upper and Lower.[413]

[Illustration: Fig. 33.

View of Reculver Church, taken in the year 1781.

1. Isle of Sheppey. 2. Ancient chapel now destroyed. The cottage between
this chapel and the cliff was demolished by the sea, in 1782.]

Still farther east stands the church of Reculver, upon a cliff composed
of clay and sand, about twenty-five feet high. Reculver (Regulvium) was
an important military station in the time of the Romans, and appears,
from Leland's account, to have been, so late as Henry VIII.'s reign,
nearly one mile distant from the sea. In the "Gentleman's Magazine,"
there is a view of it, taken in 1781, which still represents a
considerable space as intervening between the north wall of the
churchyard and the cliff.[414] Sometime before the year 1780, the waves
had reached the site of the ancient Roman camp or fortification, the
walls of which had continued for several years after they were
undermined to overhang the sea, being firmly cemented into one mass.
They were eighty yards nearer the sea than the church, and they are
spoken of in the "Topographica Britannica," in the year 1780, as having
recently fallen down. In 1804, part of the churchyard with some
adjoining houses was washed away, and the ancient church, with its two
spires, was dismantled and abandoned as a place of worship, but kept in
repair as a landmark well known to mariners. I visited the spot in June,
1851, and saw human bones and part of a wooden coffin projecting from
the cliff, near the top. The whole building would probably have been
swept away long ere this, had not the force of the waves been checked by
an artificial causeway of stones and large wooden piles driven into the
sands on the beach to break the force of the waves.

[Illustration: Fig. 34.

Reculver Church, in 1834.]

_Isle of Thanet._--The isle of Thanet was, in the time of the Romans,
separated from the rest of Kent by a navigable channel, through which
the Roman fleets sailed on their way to and from London. Bede describes
this small estuary as being, in the beginning of the eighth century,
three furlongs in breadth; and it is supposed that it began to grow
shallow about the period of the Norman conquest. It was so far silted up
in the year 1485, that an act was then obtained to build a bridge across
it; and it has since become marsh land with small streams running
through it. On the coast, Bedlam Farm, belonging to the hospital of that
name, lost eight acres in the twenty years preceding 1830, the land
being composed of chalk from forty to fifty feet above the level of the
sea. It has been computed that the average waste of the cliff between
the North Foreland and the Reculvers, a distance of about eleven miles,
is not less than two feet per annum. The chalk cliffs on the south of
Thanet, between Ramsgate and Pegwell Bay, have on an average lost three
feet per annum for the last ten years (preceding 1830).

_Goodwin Sands._--The Goodwin Sands lie opposite this part of the
Kentish coast. They are about ten miles in length, and are in some parts
three, and in others seven, miles distant from the shore; and, for a
certain space, are laid bare at low water. That they are a remnant of
land, and not "a mere accumulation of sea sand," as Rennell
imagined,[415] may be presumed from the fact that, when the erection of
a lighthouse on this shoal was in contemplation by the Trinity Board in
the year 1817, it was found, by borings, that the bank consisted of
fifteen feet of sand, resting on blue clay; and, by subsequent borings,
the subjacent chalk has been reached. An obscure tradition has come down
to us, that the estates of Earl Goodwin, the father of Harold, who died
in the year 1053, were situated here, and some have conjectured that
they were overwhelmed by the flood mentioned in the Saxon chronicle,
_sub anno 1099_. The last remains of an island, consisting, like
Sheppey, of clay, may perhaps have been carried away about that time.

[Illustration: Fig. 35.

Shakspeare's Cliff in 1836, seen from the northeast.]

There are other records of waste in the county of Kent, as at Deal; and
at Dover, where Shakspeare's Cliff, composed entirely of chalk, has
suffered greatly, and continually diminishes in height, the slope of the
hill being towards the land. (See fig. 35.) There was an immense
landslip from this cliff in 1810, by which Dover was shaken as if by an
earthquake, and a still greater one in 1772.[416] We may suppose,
therefore, that the view from the top of the precipice in the year 1600,
when the tragedy of King Lear was written, was more "fearful and dizzy"
than it is now. The best antiquarian authorities are agreed, that Dover
Harbor was formerly an estuary, the sea flowing up a valley between the
chalk hills. The remains found in different excavations confirm the
description of the spot given by Cæsar and Antoninus, and there is clear
historical evidence to prove that at an early period there was no
shingle at all at Dover.[417]

_Straits of Dover._--In proceeding from the northern parts of the German
Ocean towards the Straits of Dover, the water becomes gradually more
shallow, so that, in the distance of about two hundred leagues, we pass
from a depth of 120 to that of 58, 38, 18, and even less than 2 fathoms.
The shallowest part follows a line drawn between Romney Marsh and
Boulogne. From this point the English Channel again deepens
progressively as we proceed westward, so that the Straits of Dover may
be said to part two seas.[418]

Whether England was formerly united with France has often been a
favorite subject of speculation. So early as 1605 our countryman
Verstegan, in his "Antiquities of the English Nation," observed that
many preceding writers had maintained this opinion, but without
supporting it by any weighty reasons. He accordingly endeavors himself
to confirm it by various arguments, the principal of which are, first,
the proximity and identity of the composition of the opposite cliffs and
shores of Albion and Gallia, which, whether flat and sandy, or steep and
chalky, correspond exactly with each other; secondly the occurrence of a
submarine ridge, called "our Lady's Sand," extending from shore to shore
at no great depth, and which, from its composition, appears to be the
original basis of the isthmus; thirdly, the identity of the noxious
animals in France and England, which could neither have swum across, nor
have been introduced by man. Thus no one, he says, would have imported
wolves, therefore "these wicked beasts did of themselves pass over." He
supposes the ancient isthmus to have been about six English miles in
breadth, composed entirely of chalk and flint, and in some places of no
great height above the sea-level. The operation of the waves and tides,
he says, would have been more powerful when the straits were narrower,
and even now they are destroying cliffs composed of similar materials.
He suggests the possible co-operation of earthquakes; and when we
consider how many submarine forests skirt the southern and eastern
shores of England, and that there are raised beaches at many points
above the sea-level, containing fossil shells of recent species, it
seems reasonable to suppose that such upward and downward movements,
taking place perhaps as slowly as those now in progress in Sweden and
Greenland, may have greatly assisted the denuding force of "the ocean
stream," Ποταμοιο μεγα σθενος Ωχεανοτο.

_Folkstone._--At Folkstone, the sea undermines the chalk and subjacent
strata. About the year 1716 there was a remarkable sinking of a tract of
land near the sea, so that houses became visible from certain points at
sea, and from particular spots on the sea cliffs, from whence they could
not be seen previously. In the description of this subsidence in the
Phil. Trans. 1716, it is said, "that the land consisted of a solid stony
mass (chalk), resting on wet clay (gault), so that it slid forwards
towards the sea, just as a ship is launched on tallowed planks." It is
also stated that, within the memory of persons then living, the cliff
there had been washed away to the extent of ten rods.

Encroachments of the sea at Hythe are also on record; but between this
point and Rye there has been a gain of land within the times of history;
the rich level tract called Romney Marsh, or Dungeness, about ten miles
in width and five in breadth, and formed of silt, having received great
accession. It has been necessary, however, to protect it from the sea,
from the earliest periods, by embankments, the towns of Lydd and Romney
being the only parts of the marsh above the level of the highest
tides.[419] Mr. Redman has cited numerous old charts and trustworthy
authorities to prove that the average annual increase of the promontory
of shingle called Dungeness amounted for two centuries, previous to
1844, to nearly six yards. Its progress, however, has fluctuated during
that period; for between 1689 and 1794, a term of 105 years, the rate
was as much as 8¼ yards per annum.[420] It is ascertained that the
shingle is derived from the westward. Whether the pebbles are stopped by
the meeting of the tide from the north flowing through the Straits of
Dover, with that which comes up the Channel from the west, as was
formerly held, or by the check given to the tidal current by the waters
of the Rother, as some maintain, is still a disputed question.

Rye, situated to the south of Romney Marsh, was once destroyed by the
sea, but it is now two miles distant from it. The neighboring town of
Winchelsea was destroyed in the reign of Edward I., the mouth of the
Rother stopped up, and the river diverted into another channel. In its
old bed, an ancient vessel, apparently a Dutch merchantman, was found
about the year 1824. It was built entirely of oak, and much
blackened.[421] Large quantities of hazel-nuts, peat, and wood are found
in digging in Romney Marsh.

_South coast of England._--Westward of Hastings, or of St. Leonard's,
the shore line has been giving way as far as Pevensey Bay, where
formerly there existed a haven now entirely blocked up by shingle. The
degradation has equalled for a series of years seven feet per annum in
some places, and several martello towers had in consequence, before
1851, been removed by the Ordnance.[422] At the promontory of Beachy
Head a mass of chalk, three hundred feet in length, and from seventy to
eighty in breadth, fell in the year 1813 with a tremendous crash; and
similar slips have since been frequent.[423]

About a mile to the west of the town of Newhaven, the remains of an
ancient intrenchment are seen on the brow of Castle Hill. This
earth-work, supposed to be Roman, was evidently once of considerable
extent and of an oval form, but the greater part has been cut away by
the sea. The cliffs, which are undermined here, are high; more than one
hundred feet of chalk being covered by tertiary clay and sand, from
sixty to seventy feet in thickness. In a few centuries the last vestiges
of the plastic clay formation on the southern borders of the chalk of
the South Downs on this coast will probably be annihilated, and future
geologists will learn, from historical documents, the ancient
geographical boundaries of this group of strata in that direction. On
the opposite side of the estuary of the Ouse, on the east of Newhaven
harbor, a bed of shingle, composed of chalk flints derived from the
waste of the adjoining cliffs, had accumulated at Seaford for several
centuries. In the great storm of November, 1824, this bank was entirely
swept away, and the town of Seaford inundated. Another great beach of
shingle is now forming from fresh materials.

The whole coast of Sussex has been incessantly encroached upon by the
sea from time immemorial; and, although sudden inundations only, which
overwhelmed fertile or inhabited tracts, are noticed in history, the
records attest an extraordinary amount of loss. During a period of no
more than eighty years, there are notices of about _twenty_ inroads, in
which tracts of land of from twenty to _four hundred acres_ in extent
were overwhelmed at once, the value of the tithes being mentioned in the
Taxatio Ecclesiastica.[424] In the reign of Elizabeth, the town of
Brighton was situated on that tract where the chain pier now extends
into the sea. In the year 1665, twenty-two tenements had been destroyed
under the cliff. At that period there still remained under the cliff 113
tenements, the whole of which were overwhelmed in 1703 and 1705. No
traces of the ancient town are now perceptible, yet there is evidence
that the sea has merely resumed its ancient position at the base of the
cliffs, the site of the whole town having been merely a beach abandoned
by the ocean for ages.

_Hampshire.--Isle of Wight._--It would be endless to allude to all the
localities on the Sussex and Hampshire coasts where the land has given
way; but I may point out the relation which the geological structure of
the Isle of Wight bears to its present shape, as attesting that the
coast owes its outline to the continued action of the sea. Through the
middle of the island runs a high ridge of chalk strata, in a vertical
position, and in a direction east and west. This chalk forms the
projecting promontory of Culver Cliff on the east, and of the Needles on
the west; while Sandown Bay on the one side, and Compton Bay on the
other, have been hollowed out of the softer sands and argillaceous
strata, which are inferior, in geological position, to the chalk.

The same phenomena are repeated in the Isle of Purbeck, where the line
of vertical chalk forms the projecting promontory of Handfast Point; and
Swanage Bay marks the deep excavation made by the waves in the softer
strata, corresponding to those of Sandown Bay.

_Hurst Castle bank--progressive motion of sea beaches._--Although the
loose pebbles and grains of sand composing any given line of sea-beach
are carried sometimes one way, sometimes another, they have,
nevertheless, an ultimate motion in one particular direction.[425] Their
progress, for example, on the south coast of England, is from west to
east, which is owing partly to the action of the waves driven eastwards
by the prevailing wind, and partly to the current, or the motion of the
general body of water caused by the tides and winds. The force of the
waves gives motion to pebbles which the velocity of the currents alone
would be unable to carry forwards; but as the pebbles are finally
reduced to sand or mud, by continual attrition, they are brought within
the influence of a current; and this cause must determine the course
which the main body of matter derived from wasting cliffs will
eventually take.

It appears, from the observations of Mr. Palmer and others, that if a
pier or groin be erected anywhere on our southern or southeastern coast
to stop the progress of the beach, a heap of shingle soon collects on
the western side of such artificial barriers. The pebbles continue to
accumulate till they rise as high as the pier or groin, after which they
pour over in great numbers during heavy gales.[426]

The western entrance of the Channel, called the Solent, is crossed for
more than two-thirds of its width by the shingle-bank of Hurst Castle,
which is about two miles long, seventy yards broad, and twelve feet
high, presenting an inclined plane to the west. This singular bar
consists of a bed of rounded chalk flints, resting on a submarine
argillaceous base. The flints and a few other pebbles, intermixed, are
derived from the waste of Hordwell, and other cliffs to the westward,
where tertiary strata, capped with a covering of broken chalk flints,
from five to fifty feet thick, are rapidly undermined. In the great
storm of November, 1824, this bank of shingle was moved bodily forwards
for forty yards towards the northeast; and certain piles, which served
to mark the boundaries of two manors, were found after the storm on the
opposite side of the bar. At the same time many acres of pasture land
were covered by shingle, on the farm of Westover, near Lymington. But
the bar was soon restored in its old position by pebbles drifted from
the west; and it appears from ancient maps that it has preserved the
same general outline and position for centuries.[427]

Mr. Austen remarks that, as a general rule, it is only when high tides
concur with a gale of wind, that the sea reaches the base of cliffs so
as to undermine them and throw down earth and stone. But the waves are
perpetually employed in abrading and fashioning the materials already
strewed over the beach. Much of the gravel and shingle is always
travelling up and down, between high-water mark and a slight depth below
the level of the lowest tides, and occasionally the materials are swept
away and carried into deeper water. Owing to these movements every
portion of our southern coast may be seen at one time or other in the
condition of bare rock. Yet other beds of sand and shingle soon collect,
and, although composed of new materials, invariably exhibit on the same
spots precisely similar characters.[428]

The cliffs between Hurst Shingle Bar and Christchurch are undermined
continually, the sea having often encroached for a series of years at
the rate of a yard annually. Within the memory of persons now living, it
has been necessary thrice to remove the coast-road farther inland. The
tradition, therefore, is probably true, that the church of Hordwell was
once in the middle of that parish, although now (1830) very near the
sea. The promontory of Christchurch Head gives way slowly. It is the
only point between Lymington and Poole Harbor, in Dorsetshire, where any
hard stony masses occur in the cliffs. Five layers of large ferruginous
concretions, somewhat like the septaria of the London clay, have
occasioned a resistance at this point, to which we may ascribe this
headland. In the mean time, the waves have cut deeply into the soft
sands and loam of Poole Bay; and, after severe frosts, great landslips
take place, which by degrees become enlarged into narrow ravines, or
chines, as they are called, with vertical sides. One of these chines,
near Boscomb, has been deepened twenty feet within a few years. At the
head of each there is a spring, the waters of which have been chiefly
instrumental in producing these narrow excavations, which are sometimes
from 100 to 150 feet deep.

_Isle of Portland._--The peninsulas of Purbeck and Portland are
continually wasting away. In the latter, the soft argillaceous
substratum (Kimmeridge clay) hastens the dilapidation of the
superincumbent mass of limestone.

In 1655 the cliffs adjoining the principal quarries in Portland gave way
to the extent of one hundred yards, and fell into the sea; and in
December, 1734, a slide to the extent of 150 yards occurred on the east
side of the isle, by which several skeletons buried between slabs of
stone, were discovered. But a much more memorable occurrence of this
nature, in 1792, occasioned probably by the undermining of the cliffs,
is thus described in Hutchin's History of Dorsetshire:--"Early in the
morning the road was observed to crack: this continued increasing, and
before two o'clock the ground had sunk several feet, and was in one
continued motion, but attended with no other noise than what was
occasioned by the separation of the roots and brambles, and now and then
a falling rock. At night it seemed to stop a little, but soon moved
again; and, before morning, the ground from the top of the cliff to the
water-side had sunk in some places fifty feet perpendicular. The extent
of ground that moved was about _a mile and a quarter_ from north to
south, and 600 yards from east to west."

_Formation of the Chesil Bank._--Portland is connected with the mainland
by the Chesil Bank, a ridge of shingle about seventeen miles in length,
and, in most places, nearly a quarter of a mile in breadth. The pebbles
forming this immense barrier are chiefly siliceous, all loosely thrown
together, and rising to the height of from twenty to thirty feet above
the ordinary high-water mark; and at the southeastern end, which is
nearest the Isle of Portland, where the pebbles are largest, forty feet.
The fundamental rocks whereon the shingle rests are found at the depth
of a few yards only below the level of the sea. The formation of that
part of the bar which attaches Portland to the mainland may have been
due to an original shoal or reef, or to the set of the tides in the
narrow channel, by which the course of the pebbles, which are always
coming from the west, has been arrested. It is a singular fact that,
throughout the Chesil Bank, the pebbles increase gradually in size as we
proceed southeastward, or as we go farther from the quarter which
supplied them. Had the case been reversed, we should naturally have
attributed the circumstance to the constant wearing down of the pebbles
by friction, as they are rolled along a beach seventeen miles in length.
But the true explanation of the phenomenon is doubtless this: the tidal
current runs strongest from west to east, and its power is greater in
the more open channel or farther from the land. In other words its force
increases southwards, and as the direction of the bank is from northwest
to southeast, the size of the masses coming from the westward and thrown
ashore must always be largest where the motion of the water is most
violent. Colonel Reid states that all calcareous stones rolled along
from the west are soon ground into sand, and in this form they pass
round Portland Island.[429]

The storm of 1824 burst over the Chesil Bank with great fury, and the
village of Chesilton, built upon its southern extremity, was
overwhelmed, with many of the inhabitants. The same storm carried away
part of the Breakwater at Plymouth, and huge masses of rock, from two to
five tons in weight, were lifted from the bottom of the weather side,
and rolled fairly to the top of the pile. One block of limestone,
weighing seven tons, was washed round the western extremity of the
Breakwater, and carried 150 feet.[430] The propelling power is derived
in these cases from the breaking of the waves, which run fastest in
shallow water, and for a short space far exceed the most rapid currents
in swiftness. It was in the same month, and also during a spring-tide,
that a great flood is mentioned on the coasts of England, in the year
1099. Florence of Worcester says, "On the third day of the nones of Nov.
1099, the sea came out upon the shore and buried towns and men very
many, and oxen and sheep innumerable." We also read in the Saxon
Chronicle, for the year 1099, "This year eke on St. Martin's mass day,
the 11th of Novembre, sprung up so much of the sea flood, and so myckle
harm did, as no man minded that it ever afore did, and there was the ylk
day a new moon."

South of the Bill, or southern point of Portland, is a remarkable shoal
in the channel at the depth of seven fathoms, called "the Shambles,"
consisting entirely of rolled and broken shells of Purpura lapillus,
Mytilus edulis, and other species now living. This mass of light
materials is always in motion, varying in height from day to day, and
yet the shoal remains constant.

_Dorsetshire.--Devonshire._--At Lyme Regis, in Dorsetshire, the "Church
Cliffs," as they are called, consisting of lias about one hundred feet
in height, gradually fell away at the rate of one yard a year, from 1800
to 1829.[431]

[Illustration: Fig. 36.

Landslip, near Axmouth, Dec. 1839. (Rev. W. D. Conybeare.)


  A. Tract of Downs still remaining at their original level.
  B. New ravine.
  C, D. Sunk and fractured strip united to A, before the convulsion.
  D, E. Bendon undercliff as before, but more fissured, and thrust
          forward about fifty feet, towards the sea.
  F. Pyramidal crag, sunk from seventy to twenty feet in height.
  G. New reef upheaved from the sea.


]

An extraordinary landslip occurred on the 24th of December, 1839, on the
coast between Lyme Regis and Axmouth, which has been described by the
Rev. W. D. Conybeare, to whose kindness I am indebted for the
accompanying section, fig. 36. The tract of downs ranging there along
the coast is capped by chalk (_h_), which rests on sandstone,
alternating with chert (_i_), beneath which is more than 100 feet of
loose sand (_k_), with concretions at the bottom, and belonging like _i_
to the green-sand formation; the whole of the above masses, _h_, _i_,
_k_, reposing on retentive beds of clay (_l_), belonging to the lias,
which shelves towards the sea. Numerous springs issuing from the loose
sand (_k_), have gradually removed portions of it, and thus undermined
the superstratum, so as to have caused subsidences at former times, and
to have produced a line of undercliff between D and E. In 1839 an
excessively wet season had saturated all the rocks with moisture, so as
to increase the weight of the incumbent mass, from which the support had
already been withdrawn by the action of springs. Thus the superstrata
were precipitated into hollows prepared for them, and the adjacent
masses of partially undermined rock, to which the movement was
communicated, were made to slide down on a slippery basis of watery sand
towards the sea. These causes gave rise to a convulsion, which began on
the morning of the 24th of December, with a crashing noise; and, on the
evening of the same day, fissures were seen opening in the ground, and
the walls of tenements rending and sinking, until a deep chasm or
ravine, B, was formed, extending nearly three-quarters of a mile in
length, with a depth of from 100 to 150 feet, and a breadth exceeding
240 feet. At the bottom of this deep gulf lie fragments of the original
surface thrown together in the wildest confusion. In consequence of
lateral movements, the tract intervening between the new fissure and the
sea, including the ancient undercliff, was fractured, and the whole line
of sea-cliff carried bodily forwards for many yards. "A remarkable
pyramidal crag, F, off Culverhole Point, which lately formed a
distinguishing landmark, has sunk from a height of about seventy to
twenty feet, and the main cliff, E, before more than fifty feet distant
from this insulated crag, is now brought almost close to it. This motion
of the sea-cliff has produced a farther effect, which may rank among the
most striking phenomena of this catastrophe. The lateral pressure of the
descending rocks has urged the neighboring strata, extending beneath the
shingle of the shore, by their state of unnatural condensation, to burst
upwards in a line parallel to the coast--thus an elevated ridge, G, more
than a mile in length, and rising more than forty feet, covered by a
confused assemblage of broken strata, and immense blocks of rock,
invested with sea-weed and corallines, and scattered over with shells
and star-fish, and other productions of the deep, forms an extended reef
in front of the present range of cliffs."[432]

A full account of this remarkable landslip, with a plan, sections, and
many fine illustrative drawings, was published by Messrs. Conybeare and
Buckland,[433] from one of which the annexed cut has been reduced, fig.
37.

[Illustration: Fig. 37.

View of the Axmouth landslip from Great Bindon, looking westward to the
Sidmouth hills, and estuary of the Exe. From an original drawing by Mrs.
Buckland.]

_Cornwall._--Near Penzance, in Cornwall, there is a projecting tongue of
land, called the "Green," formed of granitic sand, from which more than
thirty acres of pasture land have been gradually swept away, in the
course of the last two or three centuries.[434] It is also said that St.
Michael's Mount, now an insular rock, was formerly situated in a wood,
several miles from the sea; and its old Cornish name (Caraclowse in
Cowse) signifies, according to Carew, the Hoar Rock in the wood.[435]
Between the Mount and Newlyn there is seen under the sand, black
vegetable mould, full of hazel-nuts, and the branches, leaves, roots,
and trunks of forest-trees, all of indigenous species. This stratum has
been traced seaward as far as the ebb permits, and many proofs of a
submerged vegetable accumulation, with stumps of trees in the position
in which they grew, have been traced, says Sir Henry De la Beche, round
the shores of Devon, Cornwall, and Western Somerset. The facts not only
indicate a change in the relative level of the sea and land, since the
species of animals and plants were the same as those now living in this
district; but, what is very remarkable, there seems evidence of the
submergence having been effected, in part at least, since the country
was inhabited by man.[436]

A submarine forest occurring at the mouth of the Parret in
Somersetshire, on the south side of the Bristol Channel, was described
by Mr. L. Horner, in 1815, and its position attributed to subsidence. A
bed of peat is there seen below the level of the sea, and the trunks of
large trees, such as the oak and yew, having their roots still
diverging as they grew, and fixed in blue clay.[437]

_Tradition of loss of land in Cornwall._--The oldest historians mention
a tradition in Cornwall, of the submersion of the Lionnesse, a country
said to have stretched from the Land's End to the Scilly Islands. The
tract, if it existed, must have been thirty miles in length, and perhaps
ten in breadth. The land now remaining on either side is from two
hundred to three hundred feet high; the intervening sea about three
hundred feet deep. Although there is no authentic evidence for this
romantic tale, it probably originated in some former inroads of the
Atlantic, accompanying, perhaps, a subsidence of land on this
coast.[438]

_West coast of England._--Having now brought together an ample body of
proofs of the destructive operations of the waves, tides, and currents,
on our eastern and southern shores, it will be unnecessary to enter into
details of changes on the western coast, for they present merely a
repetition of the same phenomena, and in general on an inferior scale.
On the borders of the estuary of the Severn the flats of Somersetshire
and Gloucestershire have received enormous accessions, while, on the
other hand, the coast of Cheshire, between the rivers Mersey and Dee,
has lost, since the year 1764, many hundred yards, and some affirm more
than half a mile, by the advance of the sea upon the abrupt cliffs of
red clay and marls. Within the period above mentioned several
lighthouses have been successively abandoned.[439] There are traditions
in Pembrokeshire[440] and Cardiganshire[441] of far greater losses of
territory than that which the Lionnesse tale of Cornwall pretends to
commemorate. They are all important, as demonstrating that the earliest
inhabitants were familiar with the phenomenon of incursions of the sea.

_Loss of land on the coast of France._--The French coast, particularly
that part of Brittany, where the tides rise to an extraordinary height,
is the constant prey of the waves. In the ninth century many villages
and woods are reported to have been carried away, the coast undergoing
great change, whereby the hill of St. Michael was detached from the
mainland. The parish of Bourgneuf, and several others in that
neighborhood, were overflowed in the year 1500. In 1735, during a great
storm, the ruins of Palnel were seen uncovered in the sea.[442]




CHAPTER XX.

ACTION OF TIDES AND CURRENTS--_continued_.


  Inroads of the sea at the mouths of the Rhine in Holland--Changes in
    the arms of the Rhine--Proofs of subsidence of land--Estuary of the
    Bies Bosoh, formed in 1421--Zuyder Zee, in the 13th century--Islands
    destroyed--Delta of the Ems converted into a bay--Estuary of the
    Dollart formed--Encroachment of the sea on the coast of Sleswick--On
    shores of North America--Tidal wave, called the Bore--Influence of
    tides and currents on the mean level of seas--Action of currents in
    inland lakes and seas--Baltic--Cimbrian deluge--Straits of
    Gibraltar--No under-current there--Whether salt is precipitated in
    the Mediterranean--Waste of shores of Mediterranean.


_Inroads of the sea at the mouths of the Rhine._--The line of British
coast considered in the preceding chapter offered no example of the
conflict of two great antagonist forces; the influx, on the one hand, of
a river draining a large continent, and, on the other, the action of the
waves, tides, and currents of the ocean. But when we pass over by the
Straits of Dover to the Continent, and proceed northeastwards, we find
an admirable illustration of such a contest, where the ocean and the
Rhine are opposed to each other, each disputing the ground now occupied
by Holland; the one striving to shape out an estuary, the other to form
a delta. There was evidently a period when the river obtained the
ascendancy, when the shape and perhaps the relative level of the coast
and set of the tides were very different; but for the last two thousand
years, during which man has witnessed and actively participated in the
struggle, the result has been in favor of the ocean; the area of the
whole territory having become more and more circumscribed; natural and
artificial barriers having given away, one after another; and many
hundred thousand human beings having perished in the waves.

_Changes in the arms of the Rhine._--The Rhine, after flowing from the
Grison Alps, copiously charged with sediment, first purifies itself in
the Lake of Constance, where a large delta is formed; then swelled by
the Aar and numerous other tributaries, it flows for more than six
hundred miles towards the north; when, entering a low tract, it divides
into two arms, about ten miles northeast of Cleves,--a point which must
therefore be considered the head of its delta. (See[A], map, fig. 8.)
In speaking of the delta, I do not mean to assume that all that part of
Holland which is comprised within the several arms of the Rhine can be
called a delta in the strictest sense of the term; because some portion
of the country thus circumscribed, as, for example, a part of Gelderland
and Utrecht, consists of strata which may have been deposited in the sea
before the Rhine existed. These older tracts may either have been raised
like the Ullah Bund in Cutch, during the period when the sediment of
the Rhine was converting a part of the sea into land, or they may have
constituted islands previously.

[Illustration: Fig. 38.

The dark tint between Antwerp and Nieuport, represents part of the
Netherlands which was land in the time of the Romans, then overflowed by
the sea before and during the 5th century, and afterwards reconverted
into land.]

When the river divides north of Cleves, the left arm takes the name of
the Waal; and the right, retaining that of the Rhine, is connected, a
little farther to the north, by an artificial canal with the river
Yssel. The Rhine then flowing westward divides again southeast of
Utrecht, and from this point it takes the name of the Leck, a name which
was given to distinguish it from the northern arm called the old Rhine,
which was sanded up until the year 1825, when a channel was cut for it,
by which it now enters the sea at Catwyck. It is common, in all great
deltas, that the principal channels of discharge should shift from time
to time, but in Holland so many magnificent canals have been
constructed, and have so diverted, from time to time, the course of the
waters, that the geographical changes in this delta are endless, and
their history, since the Roman era, forms a complicated topic of
antiquarian research. The present head of the delta is about forty
geographical miles from the nearest part of the gulf called the Zuyder
Zee, and more than twice that distance from the general coast-line. The
present head of the delta of the Nile is about 80 or 90 geographical
miles from the sea; that of the Ganges, as before stated, 220; and that
of the Mississippi about 180, reckoning from the point where the
Atchafalaya branches off to the extremity of the new tongue of land in
the Gulf of Mexico. But the comparative distance between the heads of
deltas and the sea affords no positive data for estimating the relative
magnitude of the alluvial tracts formed by their respective rivers, for
the ramifications depend on many varying and temporary circumstances,
and the area over which they extend does not hold any constant
proportion to the volume of water in the river.

The Rhine therefore has at present three mouths. About two-thirds of its
waters flow to the sea by the Waal, and the remainder is carried partly
to the Zuyder Zee by the Yssel, and partly to the ocean by the Leck. As
the whole coast to the south as far as Ostend, and on the north to the
entrance of the Baltic, has, with few exceptions, from time immemorial,
yielded to the force of the waves, it is evident that the common delta
of the Rhine, Meuse, and Scheldt, for these three rivers may all be
considered as discharging their waters into the same part of the sea,
would, if its advance had not been checked, have become extremely
prominent; and even if it had remained stationary, would long ere this
have projected far beyond the rounded outline of the coast, like that
strip of land already described at the mouth of the Mississippi. But we
find, on the contrary, that the islands which skirt the coast have not
only lessened in size, but in number also, while great bays have been
formed in the interior by incursions of the sea.

In order to explain the incessant advance of the ocean on the shores and
inland country of Holland, M. E. de Beaumont has suggested that there
has in all probability been a general depression or sinking of the land
below its former level over a wide area. Such a change of level would
enable the sea to break through the ancient line of sand-banks and
islands which protected the coast,--would lead to the enlargement of
bays, the formation of new estuaries, and ultimately to the entire
submergence of land. These views appear to be supported by the fact that
several peat-mosses of fresh-water origin now occur under the level of
the sea, especially on the site of the Zuyder Zee and Lake Flevo,
presently to be mentioned. Several excavations also made for wells at
Utrecht, Amsterdam, and Rotterdam have proved, that below the level of
the ocean, the soil near the coast consists of alternations of sand with
marine shells, and beds of peat and clay, which have been traced to the
depth of fifty feet and upwards.[443]

I have said that the coast to the south as far as Ostend has given way.
This statement may at first seem opposed to the fact, that the tract
between Antwerp and Nieuport, shaded black in the annexed map (fig. 38),
although now dry land, and supporting a large population, has, within
the historical period, been covered with the sea. This region, however,
consisted, in the time of the Romans, of woods, marshes, and
peat-mosses, protected from the ocean by a chain of sandy dunes, which
were afterwards broken through during storms, especially in the fifth
century. The waters of the sea during these irruptions threw down upon
the barren peat a horizontal bed of fertile clay, which is in some
places three yards thick, full of recent shells and works of art. The
inhabitants, by the aid of embankments and the sand dunes of the coast,
have succeeded, although not without frequent disasters, in defending
the soil thus raised by the marine deposit.[444]

_Inroads of the Sea in Holland._--If we pass to the northward of the
territory just alluded to, and cross the Scheldt, we find that between
the fourteenth and eighteenth centuries parts of the islands Walcheren
and Beveland were swept away, and several populous districts of Kadzand,
losses which far more than counterbalance the gain of land caused by the
sanding up of some pre-existing creeks. In 1658 the Island Orisant was
annihilated. One of the most memorable inroads of the sea occurred in
1421, when the tide, pouring into the mouth of the united Meuse and
Waal, burst through a dam in the district between Dort and
Gertrudenberg, and overflowed seventy-two villages, forming a large
sheet of water called the Bies Bosch. (See map, fig. 38.) Thirty-five of
the villages were irretrievably lost, and no vestige, even of their
ruins, was afterwards seen. The rest were redeemed, and the site of the
others, though still very generally represented on maps as an estuary,
has in fact been gradually filled up by alluvial deposits, and had
become in 1835, as I was informed by Professor Moll, an immense plain,
yielding abundant crops of hay, though still uninhabited. To the north
of the Meuse is a long line of shore covered with sand dunes, where
great encroachments have taken place from time to time, in consequence
chiefly of the prevalence of southeasterly winds, which blow down the
sands towards the sea. The church of Scheveningen, not far from the
Hague, was once in the middle of the village, and now stands on the
shore, half the place having been overwhelmed by the waves in 1570.
Catwyck, once far from the sea, is now upon the shore; two of its
streets having been overflowed, and land torn away to the extent of 200
yards, in 1719. It is only by the aid of embankments that Petten, and
several other places farther north, have been defended against the sea.

_Formation of the Zuyder Zee and Straits of Staveren._--Still more
important are the changes which have taken place on the coast opposite
the right arm of the Rhine, or the Yssel, where the ocean has burst
through a large isthmus, and entered the inland lake Flevo, which, in
ancient times, was, according to Pomponius Mela, formed by the
overflowing of the Rhine over certain lowlands. It appears that, in the
time of Tacitus, there were several lakes on the present site of the
Zuyder Zee, between Friesland and Holland. The successive inroads by
which these and a great part of the adjoining territory, were
transformed into a great gulf, began about the commencement, and were
completed towards the close, of the thirteenth century. Alting gives the
following relation of the occurrence, drawn from manuscript documents of
contemporary inhabitants of the neighboring provinces. In the year
1205, the island now called Wieringen, to the south of the Texel, was
still a part of the mainland, but during several high floods, of which
the dates are given, ending in December, 1251, it was separated from the
continent. By subsequent incursions the sea consumed great parts of the
rich and populous isthmus, a low tract which stretched on the north of
Lake Flevo, between Staveren in Friesland and Medemblick in Holland,
till at length a breach was completed about the year 1282, and
afterwards widened. Great destruction of land took place when the sea
first broke in, and many towns were swept away; but there was afterwards
a reaction to a certain extent, large tracts, at first submerged, having
been gradually redeemed. The new straits south of Staveren are more than
half the width of those of Dover, but are very shallow, the greatest
depth not exceeding two or three fathoms. The new bay is of a somewhat
circular form, and between _thirty_ and _forty_ miles in diameter. How
much of this space may formerly have been occupied by Lake Flevo is
unknown. (See map, fig. 38.)

_Destruction of islands._--A series of islands stretching from the Texel
to the mouths of the Weser and Elbe are probably the last relics of a
tract once continuous. They have greatly diminished in size, and have
lost about a third of their number, since the time of Pliny; for that
naturalist counted twenty-three islands between the Texel and Eider,
whereas there are now only sixteen, including Heligoland and
Neuwerk.[445] The island of Heligoland, at the mouth of the Elbe,
consists of a rock of red marl of the Keuper formation (of the Germans),
and is bounded by perpendicular red cliffs, above 200 feet high.
Although, according to some accounts, it has been greatly reduced in
size since the year 800, M. Wiebel assures us, that the ancient map by
Meyer cannot be depended upon, and that the island, according to the
description still extant by Adam of Bremen, was not much larger than
now, in the time of Charlemagne. On comparing the map made in the year
1793 by the Danish engineer Wessel, the average encroachment of the sea
on the cliffs, between that period and the year 1848 (or about half a
century), did not amount to more than three feet.[446] On the other
hand, some few islands have extended their bounds in one direction, or
become connected with others, by the sanding-up of channels; but even
these, like Juist, have generally given way as much on the north towards
the sea as they have gained on the south, or land side.

_The Dollart formed._--While the delta of the Rhine has suffered so
materially from the movements of the ocean, it can hardly be supposed
that minor rivers on the same coast should have been permitted to extend
their deltas. It appears that in the time of the Romans there was an
alluvial plain of great fertility, where the Ems entered the sea by
three arms. This low country stretched between Groningen and Friesland,
and sent out a peninsula to the northeast towards Emden. A flood in 1277
first destroyed part of the peninsula. Other inundations followed at
different periods throughout the fifteenth century. In 1507, a part only
of Torum, a considerable town, remained standing; and in spite of the
erection of dams, the remainder of that place, together with
market-towns, villages, and monasteries, to the number of fifty, were
finally overwhelmed. The new gulf, which was called the Dollart,
although small in comparison to the Zuyder Zee, occupied no less than
six square miles at first; but part of this space was, in the course of
the two following centuries, again redeemed from the sea. The small bay
of Leybucht, farther north, was formed in a similar manner in the
thirteenth century; and the bay of Harlbucht in the middle of the
sixteenth. Both of these have since been partially reconverted into dry
land. Another new estuary, called the Gulf of Jahde, near the mouth of
the Weser, scarcely inferior in size to the Dollart, has been gradually
hollowed out since the year 1016, between which era and 1651 a space of
about four square miles has been added to the sea. The rivulet which now
enters this inlet is very small; but Arens conjectures that an arm of
the Weser had once an outlet in that direction.

_Coast of Sleswick._--Farther north we find so many records of waste on
the western coast of Sleswick, as to lead us to anticipate that, at no
distant period in the history of the physical geography of Europe,
Jutland may become an island, and the ocean may obtain a more direct
entrance into the Baltic. Indeed, the temporary insulation of the
northern extremity of Jutland has been affected no less than four times
within the records of history, the ocean having as often made a breach
through the bar of sand, which usually excludes it from the Lym Fiord.
This long frith is 120 miles in length including its windings, and
communicates at its eastern end with the Baltic. The last irruption of
salt water happened in 1824, and the fiord was still open in 1837, when
some vessels of thirty tons' burden passed through.

The Marsh islands between the rivers Elbe and Eider are mere banks, like
the lands formed of the "warp" in the Humber, protected by dikes. Some
of them, after having been inhabited with security for more than ten
centuries, have been suddenly overwhelmed. In this manner, in 1216, no
less than ten thousand of the inhabitants of Eiderstede and Ditmarsch
perished; and on the 11th of October, 1634, the islands and the whole
coast, as far as Jutland, suffered by a dreadful deluge.

_Destruction of Northstrand by the sea._--Northstrand, up to the year
1240, was, with the islands Sylt and Föhr, so nearly connected with the
mainland as to appear a peninsula, and was called North Friesland, a
highly cultivated and populous district. It measured from nine to eleven
geographical miles from north to south, and six to eight from east to
west. In the above-mentioned year it was torn asunder from the
continent, and in part overwhelmed. The Isle of Northstrand, thus
formed, was, towards the end of the sixteenth century, only four
geographical miles in circumference, and was still celebrated for its
cultivation and numerous population. After many losses, it still
contained nine thousand inhabitants. At last, in the year 1634, on the
evening of the 11th of October, a flood passed over the whole island,
whereby 1300 houses, with many churches, were lost; fifty thousand head
of cattle perished, and above six thousand men. Three small islets, one
of them still called Northstrand, alone remained, which are now
continually wasting.

The redundancy of river water in the Baltic, especially during the
melting of ice and snow in spring, causes in general an outward current
through the channel called the Cattegat. But after a continuance of
northwesterly gales, especially during the height of the spring-tides,
the Atlantic rises, and pouring a flood of water into the Baltic,
commits dreadful devastations on the isles of the Danish Archipelago.
This current even acts, though with diminished force, as far eastward as
the vicinity of Dantzic.[447] Accounts written during the last ten
centuries attest the wearing down of promontories on the Danish coast,
the deepening of gulfs, the severing of peninsulas from the mainland,
and the waste of islands, while in several cases marsh land, defended
for centuries by dikes, has at last been overflowed, and thousands of
the inhabitants whelmed in the waves. Thus the island Barsoe, on the
coast of Sleswick, has lost, year after year, an acre at a time, and the
island Alsen suffers in like manner.

_Cimbrian deluge._--As we have already seen that during the flood before
mentioned, 6000 men and 50,000 head of cattle perished on Northstrand on
the western coast of Jutland, we are all well prepared to find that this
peninsula, the Cimbrica Chersonesus of the ancients, has from a remote
period been the theatre of like catastrophes. Accordingly, Strabo
records a story, although he treats it as an incredible fiction, that,
during a high tide, the ocean rose upon this coast so rapidly, that men
on horseback were scarcely able to escape.[448] Florus, alluding to the
same tradition, says, "Cimbri, Teutoni, atque Tigurini, ab extremis
Galliæ profugi, cùm terras eorum inundasset Oceanus, novas sedes toto
orbe quærebant."[449] This event, commonly called the "Cimbrian Deluge,"
is supposed to have happened about three centuries before the Christian
era; but it is not improbable that the principal catastrophe was
preceded and followed by many devastations like those experienced in
modern times on the islands and shores of Jutland, and such calamities
may well be conceived to have forced on the migration of some maritime
tribes.

_Inroads of the sea on the eastern shores of North America._--After so
many authentic details respecting the destruction of the coast in parts
of Europe best known, it will be unnecessary to multiply examples of
analogous changes in more distant regions of the world. It must not,
however, be imagined that our own seas form any exception to the general
rule. Thus, for example, if we pass over to the eastern coast of North
America, where the tides rise, in the Bay of Fundy, to a great
elevation, we find many facts attesting the incessant demolition of
land. Cliffs, often several hundred feet high, composed of sandstone,
red marl, and other rocks, which border that bay and its numerous
estuaries, are perpetually undermined. The ruins of these cliffs are
gradually carried, in the form of mud, sand, and large boulders, into
the Atlantic by powerful currents, aided at certain seasons by drift
ice, which forms along the coast, and freezes round large stones.

At Cape May, on the north side of Delaware Bay, in the United States,
the encroachment of the sea was shown by observations made consecutively
for sixteen years, from 1804 to 1820, to average about nine feet a
year;[450] and at Sullivan's Island, which lies on the north side of the
entrance of the harbor of Charleston, in South Carolina, the sea carried
away a quarter of a mile of land in three years, ending in 1786.[451]

_Tidal wave called "the Bore."_--Before concluding my remarks on the
action of the tides, I must not omit to mention the wave called "the
Bore," which is sometimes produced in a river where a large body of
water is made to rise suddenly, in consequence of the contraction of the
channel. This wave terminates abruptly on the inland side; because the
quantity of water contained in it is so great, and its motion so rapid,
that time is not allowed for the surface of the river to be immediately
raised by means of transmitted pressure. A tide wave thus rendered
abrupt has a close analogy, observes Mr. Whewell, to the waves which
curl over and break on a shelving shore.[452]

The Bore which enters the Severn, where the phenomenon is of almost
daily occurrence, is sometimes nine feet high, and at spring-tides
rushes up the estuary with extraordinary rapidity. The finest example
which I have seen of this wave was at Nova Scotia,[453] where the tide
is said to rise in some places seventy feet perpendicular, and to be the
highest in the world. In the large estuary of the Shubenacadie, which
connects with another estuary called the Basin of Mines, itself an
embranchment of the Bay of Fundy, a vast body of water comes rushing up,
with a roaring noise, into a long narrow channel, and while it is
ascending, has all the appearance of pouring down a slope as steep as
that of the celebrated rapids of the St. Lawrence. In picturesque
effect, however, it bears no comparison, for instead of the transparent
green water and snow-white foam of the St. Lawrence, the whole current
of the Shubenacadie is turbid and densely charged with red mud. The same
phenomenon is frequently witnessed in the principal branches of the
Ganges and in the Megna as before mentioned (p. 279). "In the Hoogly,"
says Rennell, "the Bore commences at Hoogly Point, the place where the
river first contracts itself, and is perceptible above Hoogly Town; and
so quick is its motion, that it hardly employs four hours in travelling
from one to the other, though the distance is nearly seventy miles. At
Calcutta it sometimes occasions an instantaneous rise of five feet; and
both here, and in every other part of its track, the boats, on its
approach, immediately quit the shore, and make for safety to the middle
of the river. In the channels, between the islands in the mouth of the
Megna, the height of the Bore is said to exceed twelve feet; and is so
terrific in its appearance, and dangerous in its consequences, that no
boat will venture to pass at spring-tide."[454] These waves may
sometimes cause inundations, undermine cliffs, and still more frequently
sweep away trees and land animals from low shores, so that they may be
carried down, and ultimately imbedded in fluviatile or submarine
deposits.


CURRENTS IN INLAND LAKES AND SEAS.

In such large bodies of water as the North American lakes, the
continuance of a strong wind in one direction often causes the elevation
of the water, and its accumulation on the leeward side; and while the
equilibrium is restoring itself, powerful currents are occasioned. In
October, 1833, a strong current in Lake Erie, caused partly by the set
of the waters towards the outlet of the lake, and partly by the
prevailing wind, burst a passage through the extensive peninsula called
Long Point, and soon excavated a channel more than nine feet deep and
nine hundred feet wide. Its width and depth have since increased, and a
new and costly pier has been erected; for it is hoped that this event
will permanently improve the navigation of Lake Erie for
steamboats.[455] On the opposite, or southern coast of this lake, in
front of the town of Cleveland, the degradation of the cliffs had been
so rapid for several years preceding a survey made in 1837, as to
threaten many towns with demolition.[456] In the Black Sea, also,
although free from tides, we learn from Pallas that there is a
sufficiently strong current to undermine the cliffs in many parts, and
particularly in the Crimea.

_Straits of Gibraltar._--It is well known that a powerful current sets
constantly from the Atlantic into the Mediterranean, and its influence
extends along the whole southern borders of that sea, and even to the
shores of Asia Minor. Captain Smyth found, during his survey, that the
central current ran constantly at the rate of from three to six miles an
hour eastward into the Mediterranean, the body of water being three
miles and a half wide. But there are also two lateral currents--one on
the European, and one on the African side; each of them about two miles
and a half broad, and flowing at about the same rate as the central
stream. These lateral currents ebb and flow with the tide, setting
alternately into the Mediterranean and into the Atlantic. The excess of
water constantly flowing in is very great, and there is only one cause
to which this can be attributed, the loss of water in the Mediterranean
by evaporation. That the level of this sea should be considerably
depressed by this cause is quite conceivable, since we know that the
winds blowing from the shores of Africa are hot and dry; and
hygrometrical experiments recently made in Malta and other places, show
that the mean quantity of moisture in the air investing the
Mediterranean is equal only to one half of that in the atmosphere of
England. The temperature also of the great inland sea is upon an average
higher, by 3½° of Fahrenheit, than the eastern part of the Atlantic
Ocean in the same latitude, which must greatly promote its evaporation.
The Black Sea being situated in a higher latitude, and being the
receptacle of rivers flowing from the north, is much colder, and its
expenditure far less; accordingly it does not draw any supply from the
Mediterranean, but, on the contrary, contributes to it by a current
flowing outwards, for the most part of the year, through the
Dardanelles. The discharge, however, at the Bosphorus is so small, when
compared to the volume of water carried in by rivers, as to imply a
great amount of evaporation in the Black Sea.

_Whether salt be precipitated in the Mediterranean._--It is, however,
objected, that evaporation carries away only fresh water, and that the
current from the Atlantic is continually bringing in salt water: why,
then, do not the component parts of the waters of the Mediterranean
vary? or how can they remain so nearly the same as those of the ocean?
Some have imagined that the excess of salt might be carried away by an
under-current running in a contrary direction to the superior; and this
hypothesis appeared to receive confirmation from a late discovery, that
the water taken up about fifty miles within the Straits, from a depth of
670 fathoms, contained a quantity of salt _four times greater_ than the
water of the surface. Dr. Wollaston,[457] who analyzed this water
obtained by Captain Smyth, truly inferred that an under-current of such
denser water flowing outward, if of equal breadth and depth with the
current near the surface, would carry out as much salt below as is
brought in above, although it moved with less than one-fourth part of
the velocity, and would thus prevent a perpetual increase of saltness in
the Mediterranean beyond that existing in the Atlantic. It was also
remarked by others, that the result would be the same, if the swiftness
being equal, the inferior current had only one-fourth of the volume of
the superior. At the same time there appeared reason to conclude that
this great specific gravity was only acquired by water at immense
depths; for two specimens of the water, taken within the Mediterranean,
at the distance of some hundred miles from the Straits, and at depths of
400 and even 450 fathoms, were found by Dr. Wollaston not to exceed in
density that of many ordinary samples of sea-water. Such being the case,
we can now prove that the vast amount of salt brought into the
Mediterranean _does not_ pass out again by the Straits; for it appears
by Captain Smyth's soundings, which Dr. Wallaston had not seen, that
between the capes of Trafalgar and Spartel, which are twenty-two miles
apart, and where the Straits are shallowest, the deepest part, which is
on the side of Cape Spartel, is only 220 fathoms. It is therefore
evident, that if water sinks in certain parts of the Mediterranean, in
consequence of the increase of its specific gravity, to greater depths
than 220 fathoms, it can never flow out again into the Atlantic, since
it must be stopped by the submarine barrier which crosses the shallowest
part of the Straits of Gibraltar.

The idea of the existence of a counter-current, at a certain depth,
first originated in the following circumstances:--M. De l'Aigle,
commander of a privateer called the Phoenix of Marseilles, gave chase
to a Dutch merchant-ship, near Ceuta Point, and coming up with her in
the middle of the gut, between Tariffa and Tangier, gave her one
broadside, which directly sunk her. A few days after, the sunken ship,
with her cargo of brandy and oil, was cast ashore near Tangier, which is
at least four leagues to the westward of the place where she went down,
and to which she must have floated in a direction contrary to the course
of the _central_ current.[458] This fact, however, affords no evidence
of an under-current, because the ship, when it approached the coast,
would necessarily be within the influence of a lateral current, which
running westward twice every twenty-four hours, might have brought back
the vessel to Tangier.

What, then, becomes of the excess of salt?--for this is an inquiry of
the highest geological interest. The Rhone, the Po, the Nile, and many
hundred minor streams and springs, pour annually into the Mediterranean
large quantities of carbonate of lime, together with iron, magnesia,
silica, alumina, sulphur, and other mineral ingredients in a state of
chemical solution. To explain why the influx of this matter does not
alter the composition of this sea has never been regarded as a
difficulty; for it is known that calcareous rocks are forming in the
delta of the Rhone, in the Adriatic, on the coast of Asia Minor, and in
other localities. Precipitation is acknowledged to be the means whereby
the surplus mineral matter is disposed of, after the consumption of a
certain portion in the secretions of testacea, zoophytes, and other
marine animals. But before muriate of soda can, in like manner, be
precipitated, the whole Mediterranean ought, according to the received
principles of chemistry, to become as much saturated with salt as Lake
Aral, the Dead Sea, or the brine-springs of Cheshire.

It is undoubtedly true, in regard to small bodies of water, that every
particle must be fully saturated with muriate of soda before a single
crystal of salt can be formed; such is probably the case in all natural
salterns: such, for example, as those described by travellers as
occurring on the western borders of the Black Sea, where extensive
marshes are said to be covered by thin films of salt after a rapid
evaporation of sea-water. The salt _étangs_ of the Rhone, where salt has
sometimes been precipitated in considerable abundance, have been already
mentioned. In regard to the depth of the Mediterranean, it appears that
between Gibraltar and Ceuta, Captain Smyth sounded to the enormous depth
of 950 fathoms, and found there a gravelly bottom, with fragments of
broken shells. Saussure sounded to the depth of two thousand feet,
within a few yards of the shore, at Nice; and M. Bérard has lately
fathomed to the depth of more than six thousand feet in several places
without reaching the bottom.[459]

The central abysses, therefore, of this sea are, in all likelihood, at
least as deep as the Alps are high; and, as at the depth of seven
hundred fathoms only, water has been found to contain a proportion of
salt four times greater than at the surface, we may presume that the
excess of salt may be much greater at the depth of two or three miles.
After evaporation, the surface water becomes impregnated with a slight
excess of salt, and its specific gravity being thus increased, it
instantly falls to the bottom, while lighter water rises to the top, or
flows in laterally, being always supplied by rivers and the current from
the Atlantic. The heavier fluid, when it arrives at the bottom, cannot
stop if it can gain access to any lower part of the bed of the sea, not
previously occupied by water of the same density.

How far this accumulation of brine can extend before the inferior strata
of water will part with any of their salt, and what difference in such a
chemical process the immense pressure of the incumbent ocean, or the
escape of heated vapors, thermal springs, or submarine volcanic
eruptions, might occasion, are questions which cannot be answered in the
present state of science.

The Straits of Gibraltar are said to become gradually wider by the
wearing down of the cliffs on each side at many points; and the current
sets along the coast of Africa, so as to cause considerable inroads in
various parts, particularly near Carthage. Near the Canopic mouth of the
Nile, at Aboukir, the coast was greatly devastated in the year 1784,
when a small island was nearly consumed. By a series of similar
operations, the old site of the cities of Nicropolis, Taposiris, Parva
and Canopus, have become a sand-bank.[460]




CHAPTER XXI.

REPRODUCTIVE EFFECTS OF TIDES AND CURRENTS.


  Estuaries, how formed--Silting up of estuaries does not compensate
    the loss of land on the borders of the ocean--Bed of the German
    Ocean--Composition and extent of its sand-banks--Strata deposited by
    currents in the English channel--On the shores of the
    Mediterranean--At the mouths of the Amazon, Orinoco, and
    Mississippi--Wide area over which strata may be formed by this
    cause.


From the facts enumerated in the last chapter, it appears that on the
borders of the ocean, currents and tides co-operating with the waves of
the sea are most powerful instruments in the destruction and
transportation of rocks; and as numerous tributaries discharge their
alluvial burden into the channel of one great river, so we find that
many rivers deliver their earthy contents to one marine current, to be
borne by it to a distance, and deposited in some deep receptacle of the
ocean. The current, besides receiving this tribute of sedimentary matter
from streams draining the land, acts also itself on the coast, as does a
river on the cliffs which bound a valley. Yet the waste of cliffs by
marine currents constitutes on the whole a very insignificant portion of
the denudation annually effected by aqueous causes, as I shall point out
in the sequel of this chapter (p. 339).

In inland seas, where the tides are insensible, or on those parts of the
borders of the ocean where they are feeble, it is scarcely possible to
prevent a harbor at a river's mouth from silting up; for a bar of sand
or mud is formed at points where the velocity of the turbid river is
checked by the sea, or where the river and a marine current neutralize
each other's force. For the current, as we have seen, may, like the
river, hold in suspension a large quantity of sediment, or, co-operating
with the waves, may cause the progressive motion of a shingle beach in
one direction. I have already alluded to the erection of piers and
groins at certain places on our southern coast, to arrest the course of
the shingle and sand (see p. 318). The immediate effect of these
temporary obstacles is to cause a great accumulation of pebbles on one
side of the barrier, after which the beach still moves on round the end
of the pier at a greater distance from the land. This system, however,
is often attended with a serious evil, for during storms the waves throw
suddenly into the harbor the vast heap of pebbles which have collected
for years behind the groin or pier, as happened during a great gale
(Jan. 1839) at Dover.

The formation and keeping open of large estuaries are due to the
_combined influence_ of tidal currents and rivers; for when the tide
rises, a large body of water suddenly enters the mouth of the river,
where, becoming confined within narrower bounds, while its momentum is
not destroyed, it is urged on, and, having to pass through a contracted
channel, rises and runs with increased velocity, just as a stream when
it reaches the arch of a bridge scarcely large enough to give passage to
its waters, rushes with a steep fall through the arch. During the ascent
of the tide, a body of fresh water, flowing down in an opposite
direction from the higher country, is arrested in its course for several
hours; and thus a large lake of fresh and brackish water is accumulated,
which, when the sea ebbs, is let loose, as on the removal of an
artificial sluice or dam. By the force of this retiring water, the
alluvial sediment both of the river and of the sea is swept away, and
transported to such a distance from the mouth of the estuary, that a
small part only can return with the next tide.

It sometimes happens, that during a violent storm a large bar of sand is
suddenly made to shift its position, so as to prevent the free influx of
the tides, or efflux of river water. Thus about the year 1500 the sands
at Bayonne were suddenly thrown across the mouth of the Adour. That
river, flowing back upon itself, soon forced a passage to the northward
along the sandy plain of Capbreton, till at last it reached the sea at
Boucau, at the distance of _seven leagues_ from the point where it had
formerly entered. It was not till the year 1579 that the celebrated
architect Louis de Foix undertook, at the desire of Henry III., to
reopen the ancient channel, which he at last effected with great
difficulty.[461]

In the estuary of the Thames at London, and in the Gironde, the tide
rises only for five hours and ebbs seven, and in all estuaries the water
requires a longer time to run down than up; so that the preponderating
force is always in the direction which tends to keep open a deep and
broad passage. But for reasons already explained, there is naturally a
tendency in all estuaries to silt up partially, since eddies, and
backwaters, and points where opposing streams meet, are very numerous,
and constantly change their position.

Many writers have declared that the gain on our eastern coast, since the
earliest periods of history, has more than counterbalanced the loss; but
they have been at no pains to calculate the amount of loss, and have
often forgotten that, while the new acquisitions are manifest, there are
rarely any natural monuments to attest the former existence of the land
that has been carried away. They have also taken into their account
those tracts artificially recovered, which are often of great
agricultural importance, and may remain secure, perhaps, for thousands
of years, but which are only a few feet above the mean level of the sea,
and are therefore exposed to be overflowed again by a small proportion
of the force required to move cliffs of considerable height on our
shores. If it were true that the area of land annually abandoned by the
sea in estuaries were equal to that invaded by it, there would still be
no compensation _in kind_.

The tidal current which flows out from the northwest, and bears against
the eastern coast of England, transports, as we have seen, materials of
various kinds. Aided by the waves, it undermines and sweeps away the
granite, gneiss, trap-rocks, and sandstone of Shetland, and removes the
gravel and loam of the cliffs of Holderness, Norfolk, and Suffolk, which
are between twenty and three hundred feet in height, and which waste at
various rates of from one foot to six yards annually. It also bears
away, in co-operation with the Thames and the tides, the strata of
London clay on the coast of Essex and Sheppey. The sea at the same time
consumes the chalk with its flints for many miles continuously on the
shores of Kent and Sussex--commits annual ravages on the freshwater
beds, capped by a thick covering of chalk-flint gravel, in Hampshire,
and continually saps the foundations of the Portland limestone. It
receives, besides, during the rainy months, large supplies of pebbles,
sand, and mud, which numerous streams from the Grampians, Cheviots, and
other chains, send down to the sea. To what regions, then, is all this
matter consigned? It is not retained in mechanical suspension by the
waters of the ocean, nor does it mix with them in a state of chemical
solution--it is deposited _somewhere_, yet certainly not in the
immediate neighborhood of our shores; for, in that case, there would
soon be a cessation of the encroachment of the sea, and large tracts of
low land, like Romney Marsh, would almost everywhere encircle our
island.

As there is now a depth of water exceeding thirty feet, in some spots
where towns like Dunwich flourished but a few centuries ago, it is clear
that the current not only carries far away the materials of the wasted
cliffs, but is capable also of excavating the bed of the sea to a
certain moderate depth.

So great is the quantity of matter held in suspension by the tidal
current on our shores, that the waters are in some places artificially
introduced into certain lands below the level of the sea; and by
repeating this operation, which is called "warping," for two or three
years, considerable tracts have been raised, in the estuary of the
Humber, to the height of about six feet. If a current, charged with such
materials, meets with deep depressions in the bed of the ocean, it must
often fill them up; just as a river, when it meets with a lake in its
course, fills it gradually with sediment.

I have said (p. 337) that the action of the waves and currents on
sea-cliffs, or their power to remove matter from above to below the
sea-level, is insignificant in comparison with the power of rivers to
perform the same task. As an illustration we may take the coast of
Holderness described in the last chapter (p. 304). It is composed, as we
have seen, of very destructible materials, is thirty-six miles long, and
its average height may be taken at forty feet. As it has wasted away at
the rate of two and a quarter yards annually, for a long period, it will
be found on calculation that the quantity of matter thrown down into the
sea every year, and removed by the current, amounts to 51,321,600 cubic
feet. It has been shown that the united Ganges and Brahmapootra carry
down to the Bay of Bengal 40,000,000,000 of cubic feet of solid matter
every year, so that their transporting power is no less than 780 times
greater than that of the sea on the coast above-mentioned; and in order
to produce a result equal to that of the two Indian rivers, we must have
a line of wasting coast, like that of Holderness, nearly 28,000 miles in
length, or longer than the entire circumference of the globe by above
3000 miles. The reason of so great a difference in the results may be
understood when we reflect that the operations of the ocean are limited
to a single line of cliff surrounding a large area, whereas great rivers
with their tributaries, and the mountain torrents which flow into them,
act simultaneously on a length of bank almost indefinite.

Nevertheless we are by no means entitled to infer, that the denuding
force of the great ocean is a geological cause of small efficacy, or
inferior to that of rivers. Its chief influence is exerted at moderate
depths below the surface, on all those areas which are slowly rising, or
are attempting, as it were, to rise above the sea. From data hitherto
obtained respecting subterranean movements, we can scarcely speculate on
an average rate of upheaval of more than two or three feet in a century.
An elevation to this amount is taking place in Scandinavia, and probably
in many submarine areas as vast as those which we know to be sinking
from the proofs derived from circular lagoon islands or coral atolls.
(See chap. 50.) Suppose strata as destructible as those of the Wealden,
or the lower and upper cretaceous formation, or the tertiary deposits of
the British Isles to be thus slowly upheaved, how readily might they all
be swept away by waves and currents in an open sea! How entirely might
each stratum disappear as it was brought up successively and exposed to
the breakers! Shoals of wide extent might be produced, but it is
difficult to conceive how any continent could ever be formed under such
circumstances. Were it not indeed for the hardness and toughness of the
crystalline and volcanic rocks, which are often capable of resisting the
action of the waves, few lands might ever emerge from the midst of an
open sea.

_Supposed filling up of the German Ocean._--The German Ocean is deepest
on the Norwegian side, where the soundings give 190 fathoms; but the
mean depth of the whole basin may be stated at no more than thirty-one
fathoms.[462] The bed of this sea is traversed by several enormous
banks, the greatest of which is the Dogger Bank, extending for upwards
of 354 miles from north to south. The whole superficies of these shoals
is equal to about one-third of the whole extent of England and Scotland.
The average height of the banks measures, according to Mr. Stevenson,
about seventy-eight feet; the upper portion of them consisting of fine
and coarse siliceous sand, mixed with comminuted corals and shells.[463]
It had been supposed that these vast submarine hills were made up bodily
of loose materials supplied from the waste of the English, Dutch, and
other coasts; but the survey of the North Sea, conducted by Captain
Hewett, affords ground for suspecting this opinion to be erroneous. If
such immense mounds of sand and mud had been accumulated under the
influence of currents, the same causes ought nearly to have reduced to
one level the entire bottom of the German Ocean; instead of which some
long narrow ravines are found to intersect the banks. One of these
varies from seventeen to forty-four fathoms in depth, and has very
precipitous sides; in one part, called the "Inner Silver Pits," it is
fifty-five fathoms deep. The shallowest parts of the Dogger Bank were
found to be forty-two feet under water, except in one place, where the
wreck of a ship had caused a shoal. Such uniformity in the minimum depth
of water seems to imply that the currents, which vary in their velocity
from a mile to two miles and a half per hour, have power to prevent the
accumulation of drift matter in places of less depth.

_Strata deposited by currents._--It appears extraordinary, that in some
tracts of the sea, adjoining the coast of England, where we know that
currents are not only sweeping along rocky masses, thrown down, from
time to time, from the high cliffs, but also occasionally scooping out
channels in the regular strata, there should exist fragile shells and
tender zoophytes in abundance, which live uninjured by these violent
movements. The ocean, however, is in this respect a counterpart of the
land; and as, on the continents, rivers may undermine their banks,
uproot trees, and roll along sand and gravel, while their waters are
inhabited by testacea and fish, and their alluvial plains are adorned
with rich vegetation and forests, so the sea may be traversed by rapid
currents, and its bed may here and there suffer great local derangement,
without any interruption of the general order and tranquillity. It has
been ascertained by soundings in all parts of the world, that where new
deposits are taking place in the sea, coarse sand and small pebbles
commonly occur near the shore, while farther from land, and in deeper
water, finer sand and broken shells are spread out over the bottom.
Still farther out, the finest mud and ooze are alone met with. Mr.
Austen observes that this rule holds good in every part of the English
Channel examined by him. He also informs us, that where the tidal
current runs rapidly in what are called "races," where surface
undulations are perceived in the calmest weather, over deep banks, the
discoloration of the water does not arise from the power of such a
current to disturb the bottom at a depth of 40 or 80 fathoms, as some
have supposed. In these cases, a column of water sometimes 500 feet in
height, is moving onwards with the tide clear and transparent above,
while the lower portion holds fine sediment in suspension (a fact
ascertained by soundings), when suddenly it impinges upon a bank, and
its height is reduced to 300 feet. It is thus made to boil up and flow
off at the surface, a process which forces up the lower strata of water
charged with fine particles of mud, which in their passage from the
coast had gradually sunk to a depth of 300 feet or more.[464]

One important character in the formations produced by currents is, the
immense extent over which they may be the means of diffusing homogeneous
mixtures, for these are often coextensive with a great line of coast;
and, by comparison with their deposits, the deltas of rivers must shrink
into significance. In the Mediterranean, the same current which is
rapidly destroying many parts of the African coast, between the Straits
of Gibraltar and the Nile, checks also the growth of the delta of the
Nile, and drifts the sediment of that great river to the eastward. To
this source may be attributed the rapid accretions of land on parts of
the Syrian shores where rivers do not enter.

Among the greatest deposits now in progress, and of which the
distribution is chiefly determined by currents, we may class those
between the mouths of the Amazon and the southern coast of North
America. Captain Sabine found that the equatorial current before
mentioned (p. 292) was running with the rapidity of four miles an hour
where it crosses the stream of the Amazon, which river preserves part of
its original impulse, and has its waters not wholly mingled with those
of the ocean at the distance of 300 miles from its mouth.[465] The
sediment of the Amazon is thus constantly carried to the northwest as
far as to the mouths of the Orinoco, and an immense tract of swamp is
formed along the coast of Guiana, with a long range of muddy shoals
bordering the marshes, and becoming converted into land.[466] The
sediment of the Orinoco is partly detained, and settles near its mouth,
causing the shores of Trinidad to extend rapidly, and is partly swept
away into the Carribean Sea by the Guinea current. According to
Humboldt, much sediment is carried again out of the Carribean Sea into
the Gulf of Mexico.

It should not be overlooked that marine currents, even on coasts where
there are no large rivers, may still be the agents of spreading not only
sand and pebbles, but the finest mud, far and wide over the bottom of
the ocean. _For several thousand miles_ along the western coast of South
America, comprising the larger parts of Peru and Chili, there is a
perpetual rolling of shingle along the shore, part of which, as Mr.
Darwin has shown, are incessantly reduced to the finest mud by the
waves, and swept into the depths of the Pacific by the tides and
currents. The same author however has remarked that, notwithstanding the
great force of the waves on that shore, all rocks 60 feet under water
are covered by sea-weed, showing that the bed of the sea is not denuded
at that depth, the effects of the winds being comparatively superficial.

In regard to the distribution of sediment by currents it may be
observed, that the rate of subsidence of the finer mud carried down by
every great river into the ocean, or of that caused by the rolling of
the waves upon a shore, must be extremely slow; for the more minute the
separate particles of mud, the slower will they sink to the bottom, and
the sooner will they acquire what is called their terminal velocity. It
is well known that a solid body, descending through a resisting medium,
falls by the force of gravity, which is constant, but its motion is
resisted by the medium more and more as its velocity increases, until
the resistance becomes sufficient to counteract the farther increase of
velocity. For example, a leaden ball, one inch diameter, falling through
air of density as at the earth's surface, will never acquire greater
velocity than 260 feet per second, and, in water, its greatest velocity
will be 8 feet 6 inches per second. If the diameter of the ball were
1/100 of an inch, the terminal velocities in air would be 26 feet, and
in water ·86 of a foot per second.

Now, every chemist is familiar with the fact, that minute particles
descend with extreme slowness through water, the extent of their surface
being very great in proportion to their weight, and the resistance of
the fluid depending on the amount of surface. A precipitate of sulphate
of baryta, for example, will sometimes require more than five or six
hours to subside one inch;[467] while oxalate and phosphate of lime
require nearly an hour to subside about an inch and a half and two
inches respectively,[468] so exceedingly small are the particles of
which these substances consist.

When we recollect that the depth of the ocean is supposed frequently to
exceed three miles, and that currents run through different parts of
that ocean at the rate of four miles an hour, and when at the same time
we consider that some fine mud carried away from the mouths of rivers
and from sea-beaches, where there is a heavy surf, as well as the
impalpable powder showered down by volcanoes, may subside at the rate of
only an inch per hour, we shall be prepared to find examples of the
transportation of sediment over areas of indefinite extent.

It is not uncommon for the emery powder used in polishing glass to take
more than an hour to sink one foot. Suppose mud composed of coarser
particles to fall at the rate of two feet per hour, and these to be
discharged into that part of the Gulf Stream which preserves a mean
velocity of three miles an hour for a distance of two thousand miles; in
twenty-eight days these particles will be carried 2016 miles, and will
have fallen only to a depth of 224 fathoms.

In this example, however, it is assumed that the current retains its
superficial velocity at the depth of 224 fathoms, for which we have as
yet no data, although we have seen that the motion of a current may
continue at the depth of 100 fathoms. (See above, p. 28.) Experiments
should be made to ascertain the rate of currents at considerable
distances from the surface, and the time taken by the finest sediment to
settle in sea-water of a given depth, and then the geologist may
determine the area over which homogeneous mixtures may be simultaneously
distributed in certain seas.




CHAPTER XXII.

IGNEOUS CAUSES.


  Changes of the inorganic world, _continued_--Igneous
    causes--Division of the subject--Distinct volcanic regions--Region
    of the Andes--System of volcanoes extending from the Aleutian isles
    to the Molucca and Sunda islands--Polynesian archipelago--Volcanic
    region extending from Central Asia to the Azores--Tradition of
    deluges on the shores of the Bosphorus, Hellespont, and Grecian
    isles--Periodical alternation of earthquakes in Syria and Southern
    Italy--Western limits of the European region--Earthquakes rarer and
    more feeble as we recede from the centres of volcanic action.
    Extinct volcanoes not to be included in lines of active vents.


We have hitherto considered the changes wrought, since the times of
history and tradition, by the continued action of aqueous causes on the
earth's surface; and we have next to examine those resulting from
igneous agency. As the rivers and springs on the land, and the tides and
currents in the sea, have, with some slight modifications, been fixed
and constant to certain localities from the earliest periods of which we
have any records, so the volcano and the earthquake have, with few
exceptions, continued, during the same lapse of time, to disturb the
same regions. But as there are signs, on almost every part of our
continent, of great power having been exerted by running water on the
surface of the land, and by waves, tides, and currents on cliffs
bordering the sea, where, in modern times, no rivers have excavated, and
no waves or tidal currents undermined--so we find signs of volcanic
vents and violent subterranean movements in places where the action of
fire or internal heat has long been dormant. We can explain why the
intensity of the force of aqueous causes should be developed in
succession in different districts. Currents, for example, tides, and the
waves of the sea, cannot destroy coasts, shape out or silt up estuaries,
break through isthmuses, and annihilate islands, form shoals in one
place, and remove them from another, without the direction and position
of their destroying and transporting power becoming transferred to new
localities. Neither can the relative levels of the earth's crust, above
and beneath the waters, vary from time to time, as they are admitted to
have varied at former periods, and as it will be demonstrated that they
still do, without the continents being, in the course of ages, modified,
and even entirely altered, in their external configuration. Such events
must clearly be accompanied by a complete change in the volume,
velocity, and direction of the streams and land floods to which certain
regions give passage. That we should find, therefore, cliffs where the
sea once committed ravages, and from which it has now retired--estuaries
where high tides once rose, but which are now dried up--valleys hollowed
out by water, where no streams now flow, is no more than we should
expect; these and similar phenomena are the necessary consequences of
physical causes now in operation; and if there be no instability in the
laws of nature, similar fluctuations must recur again and again in time
to come.

But, however natural it may be that the force of running water in
numerous valleys, and of tides and currents in many tracts of the sea,
should now be _spent_, it is by no means so easy to explain why the
violence of the earthquake and the fire of the volcano should also have
become locally extinct at successive periods. We can look back to the
time when the marine strata, whereon the great mass of Etna rests, had
no existence; and that time is extremely modern in the earth's history.
This alone affords ground for anticipating that the eruptions of Etna
will one day cease.


  Nec quæ sulfureis ardet fornacibus, Ætna
  Ignea semper erit, _neque enim fuit ignea semper_,

  (Ovid, _Metam._ lib. 15-340,)


are the memorable words which are put into the mouth of Pythagoras by
the Roman poet, and they are followed by speculations as to the cause of
volcanic vents shifting their positions. Whatever doubts the philosopher
expresses as to the nature of these causes, it is assumed, as
incontrovertible, that the points of eruption will hereafter vary,
_because they have formerly done so_; a principle of reasoning which, as
I have endeavored to show in former chapters, has been too much set at
naught by some of the earlier schools of geology, which refused to
conclude that great revolutions in the earth's surface are now in
progress, or that they will take place hereafter, _because_ they have
often been repeated in former ages.

_Division of the subject._--Volcanic action may be defined to be "the
influence exerted by the heated interior of the earth on its external
covering." If we adopt this definition, without connecting it, as
Humboldt has done, with the theory of secular refrigeration, or the
cooling down of an original heated and fluid nucleus, we may then class
under a general head all the subterranean phenomena, whether of
volcanoes, or earthquakes, and those insensible movements of the land,
by which, as will afterwards appear, large districts may be depressed or
elevated, without convulsions. According to this view, I shall consider
first, the volcano; secondly, the earthquake; thirdly, the rising or
sinking of land in countries where there are no volcanoes or
earthquakes; fourthly, the probable _causes_ of the changes which result
from subterranean agency.

It is a very general opinion that earthquakes and volcanoes have a
common origin; for both are confined to certain regions, although the
subterranean movements are least violent in the immediate proximity of
volcanic vents, especially where the discharge of aeriform fluids and
melted rock is made constantly from the same crater. But as there are
particular regions, to which both the points of eruption and the
movements of great earthquakes are confined, I shall begin by tracing
out the geographical boundaries of some of these, that the reader may
be aware of the magnificent scale on which the agency of subterranean
fire is now simultaneously developed. Over the whole of the vast tracts
alluded to, active volcanic vents are distributed at intervals, and most
commonly arranged in a linear direction. Throughout the intermediate
spaces there is often abundant evidence that the subterranean fire is at
work continuously, for the ground is convulsed from time to time by
earthquakes; gaseous vapors, especially carbonic acid gas, are
disengaged plentifully from the soil; springs often issue at a very high
temperature, and their waters are usually impregnated with the same
mineral matters as are discharged by volcanoes during eruptions.


VOLCANIC REGIONS.

_Region of the Andes._--Of these great regions, that of the Andes of
South America is one of the best defined, extending from the southward
of Chili to the northward of Quito, from about lat. 43° S. to about 2°
N. of the equator. In this range, however, comprehending forty-five
degrees of latitude, there is an alternation on a grand scale of
districts of active with those of extinct volcanoes, or which, if not
spent, have at least been dormant for the last three centuries. How long
an interval of rest may entitle us to consider a volcano as entirely
extinct is not easily determined; but we know that in Ischia there
intervened between two consecutive eruptions a pause of seventeen
centuries; and the discovery of America is an event of far too recent a
date to allow us even to conjecture whether different portions of the
Andes, nearly the whole of which are subject to earthquakes, may not
experience alternately a cessation and renewal of eruptions.

The first line of active vents which have been seen in eruption in the
Andes extends from lat. 43° 28' S.; or, from Yantales, opposite the isle
of Chiloe, to Coquimbo, in lat. 30° S.; to these thirteen degrees of
latitude succeed more than eight degrees in which no recent volcanic
eruptions have been observed. We then come to the volcanoes of Bolivia
and Peru, reaching six degrees from S. to N., or from lat. 21° S. to
lat. 15° S. Between the Peruvian volcanoes and those of Quito, another
space intervenes of no less than fourteen degrees of latitude, said to
be free from volcanic action so far as yet known. The volcanoes of Quito
then succeed, beginning about 100 geographical miles south of the
equator, and continuing for about 130 miles north of the line, when
there occurs another undisturbed interval of more than six degrees of
latitude, after which we arrive at the volcanoes of Guatemala or Central
America, north of the Isthmus of Panama.[469]

Having thus traced out the line from south to north, I may first state,
in regard to the numerous vents of Chili, that the volcanoes of Yantales
and Osorno were in eruption during the great earthquake of 1835, at the
same moment that the land was shaken in Chiloe, and in some parts of the
Chilian coast permanently upheaved; whilst at Juan Fernandez, at the
distance of no less than 720 geographical miles from Yantales, an
eruption took place beneath the sea. Some of the volcanoes of Chili are
of great height, as that of Antuco, in lat. 37° 40' S., the summit of
which is at least 16,000 feet above the sea. From the flanks of this
volcano, at a great height, immense currents of lava have issued, one of
which flowed in the year 1828. This event is said to be an exception in
the general rule; few volcanoes in the Andes, and none of those in
Quito, having been seen in modern times to pour out lava, but having
merely ejected vapor or scoriæ.

Both the basaltic (or augitic) lavas, and those of the felspathic class,
occur in Chili and other parts of the Andes; but the volcanic rocks of
the felspathic family are said by Von Buch to be generally not trachyte,
but a rock which has been called andesite, or a mixture of augite and
albite. The last-mentioned mineral contains soda instead of the potash
found in common felspar.

The volcano of Rancagua, lat. 34° 15' S., is said to be always throwing
out ashes and vapors like Stromboli, a proof of the permanently heated
state of certain parts of the interior of the earth below. A year rarely
passes in Chili without some slight shocks of earthquakes, and in
certain districts not a month. Those shocks which come from the side of
the ocean are the most violent, and the same is said to be the case in
Peru. The town of Copiapo was laid waste by this terrible scourge in the
years 1773, 1796, and 1819, or in both cases after regular intervals of
twenty-three years. There have, however, been other shocks in that
country in the periods intervening between the dates above mentioned,
although probably all less severe, at least on the exact site of
Copiapo. The evidence against a regular recurrence of volcanic
convulsions at stated periods is so strong as a general fact, that we
must be on our guard against attaching too much importance to a few
striking but probably accidental coincidences. Among these last might be
adduced the case of Lima, violently shaken by an earthquake on the 17th
of June, 1578, and again on the very same day, 1678; or the eruptions of
Coseguina in the year 1709 and 1809, which are the only two recorded of
that volcano previous to that of 1835.[470]

Of the permanent upheaval of land after earthquakes in Chili, I shall
have occasion to speak in the next chapter, when it will also be seen
that great shocks often coincide with eruptions, either submarine or
from the cones of the Andes, showing the identity of the force which
elevates continents with that which causes volcanic outbursts.[471]

The space between Chili and Peru, in which no volcanic action has been
observed, is 160 nautical leagues from south to north. It is, however,
as Von Buch observes, that part of the Andes which is least known,
being thinly peopled, and in some parts entirely desert. The volcanoes
of Peru rise from a lofty platform to vast heights above the level of
the sea, from 17,000 to 20,000 feet. The lava which has issued from
Viejo, lat. 16° 55' S., accompanied by pumice, is composed of a mixture
of crystals of albitic felspar, hornblende, and mica, a rock which has
been considered as one of the varieties of andesite. Some tremendous
earthquakes which have visited Peru in modern times will be mentioned in
a subsequent chapter.

The volcanoes of Quito, occurring between the second degree of south and
the third degree of north latitude, rise to vast elevations above the
sea, many of them being between 14,000 and 18,000 feet high. The Indians
of Lican have a tradition that the mountain called L'Altar, or Capac
Urcu, which means "the chief," was once the highest of those near the
equator, being higher than Chimborazo; but in the reign of Ouainia
Abomatha, before the discovery of America, a prodigious eruption took
place, which lasted eight years, and broke it down. The fragments of
trachyte, says M. Boussingault, which once formed the conical summit of
this celebrated mountain, are at this day spread over the plain.[472]
Cotopaxi is the most lofty of all the South American volcanoes which
have been in a state of activity in modern times, its height being
18,858 feet; and its eruptions have been more frequent and destructive
than those of any other mountain. It is a perfect cone, usually covered
with an enormous bed of snow, which has, however, been sometimes melted
suddenly during an eruption; as in January, 1803, for example, when the
snows were dissolved in one night.

Deluges are often caused in the Andes by the liquefaction of great
masses of snow, and sometimes by the rending open, during earthquakes,
of subterranean cavities filled with water. In these inundations fine
volcanic sand, loose stones, and other materials which the water meets
with in its descent, are swept away, and a vast quantity of mud, called
"moya," is thus formed and carried down into the lower regions. Mud
derived from this source descended, in 1797, from the sides of
Tunguragua in Quito, and filled valleys a thousand feet wide to the
depth of six hundred feet, damming up rivers and causing lakes. In these
currents and lakes of moya, thousands of small fish are sometimes
enveloped, which, according to Humboldt, have lived and multiplied in
subterranean cavities. So great a quantity of these fish were ejected
from the volcano of Imbaburu in 1691, that fevers, which prevailed at
the period, were attributed to the effluvia arising from the putrid
animal matter.

In Quito, many important revolutions in the physical features of the
country are said to have resulted, within the memory of man, from the
earthquakes by which it has been convulsed. M. Boussingault declares his
belief, that if a full register had been kept of all the convulsions
experienced here and in other populous districts of the Andes, it would
be found that the trembling of the earth had been incessant. The
frequency of the movement, he thinks, is not due to volcanic explosions,
but to the continual falling in of masses of rock which have been
fractured and upheaved in a solid form at a comparatively recent epoch;
but a longer series of observations would be requisite to confirm this
opinion. According to the same author, the height of several mountains
of the Andes has diminished in modern times.[473]

The great crest or cordillera of the Andes is depressed at the Isthmus
of Panama to a height of about 1000 feet, and at the lowest point of
separation between the two seas near the Gulf of San Miguel, to 150
feet. What some geographers regard as a continuation of that chain in
Central America lies to the east of a series of volcanoes, many of which
are active in the provinces of Pasto, Popayan, and Guatemala. Coseguina,
on the south side of the Gulf of Fonseca, was in eruption in January,
1835, and some of its ashes fell at Truxillo, on the shores of the Gulf
of Mexico. What is still more remarkable, on the same day, at Kingston,
in Jamaica, the same shower of ashes fell, having been carried by an
upper counter-current against the regular east wind which was then
blowing. Kingston is about 700 miles distant from Coseguina, and these
ashes must have been more than four days in the air, having travelled
170 miles a day. Eight leagues to the southward of the crater, the ashes
covered the ground to the depth of three yards and a half, destroying
the woods and dwellings. Thousands of cattle perished, their bodies
being in many instances one mass of scorched flesh. Deer and other wild
animals sought the towns for protection; many birds and quadrupeds were
found suffocated in the ashes, and the neighboring streams were strewed
with dead fish.[474] Such facts throw light on geological monuments, for
in the ashes thrown out at remote periods from the volcanoes of
Auvergne, now extinct, we find the bones and skeletons of lost species
of quadrupeds.

_Mexico._--The great volcanic chain, after having thus pursued its
course for several thousand miles from south to north, sends off a
branch in a new direction in Mexico, in the parallel of the city of that
name, and is prolonged in a great platform between the eighteenth and
twenty-second degrees of north latitude. Five active volcanoes traverse
Mexico from west to east--Tu[\x]tla, Orizaba, Popocatepetl, Jorullo, and
Colima. Jorullo, which is in the centre of the great platform, is no
less than 120 miles from the nearest ocean--an important circumstance,
as showing that the proximity of the sea is not a necessary condition,
although certainly a very general characteristic of the position of
active volcanoes. The extraordinary eruption of this mountain, in 1759,
will be described in the sequel. If the line which connects these five
vents be prolonged in a westerly direction, it cuts the volcanic group
of islands called the Isles of Revillagigedo.

To the north of Mexico there are said to be three, or according to
some, five volcanoes in the peninsula of California; and a volcano is
reported to have been in eruption in the N. W. coast of America, near
the Colombia river, lat. 45° 37' N.

_West Indies._--To return to the Andes of Quito: Von Buch inclines to
the belief that if we were better acquainted with the region to the east
of the Madalena, and with New Granada and the Caraccas, we might find
the volcanic chain of the Andes to be connected with that of the West
Indian or Carribee Islands. The truth of this conjecture has almost been
set at rest by the eruption, in 1848, of the volcano of Zamba, in New
Grenada, at the mouth of the river Madalena.[475]

Of the West Indian islands there are two parallel series: the one to the
west, which are all volcanic, and which rise to the height of several
thousand feet; the others to the east, for the most part composed of
calcareous rocks, and very low. In the former or volcanic series, are
Granada, St. Vincent, St. Lucia, Martinique, Dominica, Guadaloupe,
Montserrat, Nevis, and St. Eustace. In the calcareous chain are Tobago,
Barbadoes, Mariegallante, Grandeterre, Desirade, Antigua, Barbuda, St.
Bartholomew, and St. Martin. The most considerable eruptions in modern
times have been those of St. Vincent. Great earthquakes have agitated
St. Domingo, as will be seen in the twenty-ninth chapter.

I have before mentioned (p. 270) the violent earthquake which in 1812
convulsed the valley of the Mississippi at New Madrid, for the space of
300 miles in length, of which more will be said in the twenty-seventh
chapter. This happened exactly at the same time as the great earthquake
of Caraccas, so that it is possible that these two points are parts of
one subterranean volcanic region. The island of Jamaica, with a tract of
the contiguous sea, has often experienced tremendous shocks; and these
are frequent along a line extending from Jamaica to St. Domingo and
Porto Rico.

Thus it will be seen that, without taking account of the West Indian and
Mexican branches, a linear train of volcanoes and tracts shaken by
earthquakes may be traced from the island of Chiloe and opposite coast
to Mexico, or even perhaps to the mouth of the Colombia river--a
distance upon the whole as great as from the pole to the equator. In
regard to the western limits of the region, they lie deep beneath the
waves of the Pacific, and must continue unknown to us. On the east they
are not prolonged, except where they include the West Indian Islands, to
a great distance; for there seem to be no indications of volcanic
disturbances in Buenos Ayres, Brazil, and the United States of North
America.

[Illustration: Fig. 89.

MAP OF ACTIVE VOLCANOES AND ATOLLS of THE INDIAN ARCHIPELAGO, and Part
of the adjoining PACIFIC OCEAN.]

_Volcanic region from the Aleutian Isles to the Moluccas and Isles of
Sunda._--On a scale which equals or surpasses that of the Andes, is
another line of volcanic action, which commences, on the north, with the
Aleutian Isles in Russian America, and extends, first in a westerly
direction for nearly 200 geographical miles, and then southwards, with
few interruptions, throughout a space of between sixty and seventy
degrees of latitude to the Moluccas, where it sends off a branch to the
southeast while the principal train continues westerly through Sumbawa
and Java to Sumatra, and then in a northwesterly direction to the Bay of
Bengal.[476] This volcanic line, observes Von Buch, may be said to
follow throughout its course the external border of the continent of
Asia; while the branch which has been alluded to as striking southeast
from the Moluccas, passes from New Guinea to New Zealand, conforming,
though somewhat rudely, to the outline of Australia.[477]

The connection, however, of the New Guinea volcanoes with the line in
Java (as laid down in Von Buch's map) is not clearly made out. By
consulting Darwin's map of coral reefs and active volcanoes,[478] the
reader will see that we might almost with equal propriety include the
Mariana and Bonin volcanoes in a band with New Guinea. Or if we allow so
much latitude in framing zones of volcanic action, we must also suppose
the New Hebrides, Solomon Isles, and New Ireland to constitute one line
(see map, fig. 39, p. 351).

The northern extremity of the volcanic region of Asia, as described by
Von Buch, is on the borders of Cook's Inlet, northeast of the Peninsula
of Alaska, where one volcano, in about the sixtieth degree of latitude,
is said to be 14,000 feet high. In Alaska itself are cones of vast
height, which have been seen in eruption, and which are covered for
two-thirds of their height downwards with perpetual snow. The summit of
the loftiest peak is truncated, and is said to have fallen in during an
eruption in 1786. From Alaska the line is continued through the Aleutian
or Fox Islands to Kamtschatka. In the Aleutian Archipelago eruptions are
frequent, and about thirty miles to the north of Unalaska, near the Isle
of Umnack, a new island was formed in 1796. It was first observed after
a storm, at a point in the sea from which a column of smoke had been
seen to rise. Flames then issued from the new islet which illuminated
the country for ten miles round; a frightful earthquake shook the
new-formed cone, and showers of stones were thrown as far as Umnack. The
eruption continued for several months, and eight years afterwards, in
1804, when it was explored by some hunters, the soil was so hot in some
places that they could not walk on it. According to Langsdorf and
others, this new island, which is now several thousand feet high, and
two or three miles in circumference, has been continually found to have
increased in size when successively visited by different travellers; but
we have no accurate means of determining how much of its growth, if any,
has been due to upheaval, or how far it has been exclusively formed by
the ejection of ashes and streams of lava. It seems, however, to be well
attested that earthquakes of the most terrific description agitate and
alter the bed of the sea and surface of the land throughout this tract.

The line is continued in the southern extremity of the Peninsula of
Kamtschatka, where there are many active volcanoes, which, in some
eruptions, have scattered ashes to immense distances. The largest and
most active of these is Klutschew, lat. 56° 3' N., which rises at once
from the sea to the prodigious height of 15,000 feet. Within 700 feet of
the summit, Erman saw, in 1829, a current of lava, emitting a vivid
light, flow down the northwest side to the foot of the cone. A flow of
lava from the summit of Mont Blanc to its base in the valley of Chamouni
would afford but an inadequate idea of the declivity down which this
current descended. Large quantities of ice and snow opposed for a time a
barrier to the lava, until at length the fiery torrent overcame, by its
heat and pressure, this obstacle, and poured down the mountain side with
a frightful noise, which was heard for a distance of more than fifty
miles.[479]

The Kurile chain of islands constitutes the prolongation of the
Kamtschatka range, where a train of volcanic mountains, nine of which
are known to have been in eruption, trends in a southerly direction. The
line is then continued to the southwest in the great island of Jesso,
and again in Nipon, the principal of the Japanese group. It then extends
by Loo Choo and Formosa to the Philippine Islands, and thence by Sangir
and the northeastern extremity of Celebes to the Moluccas (see map, fig.
39). Afterwards it passes westward through Sumbawa to Java.

There are said to be thirty-eight considerable volcanoes in Java, some
of which are more than 10,000 feet high. They are remarkable for the
quantity of sulphur and sulphureous vapors which they discharge. They
rarely emit lava, but rivers of mud issue from them, like the moya of
the Andes of Quito. The memorable eruption of Galongoon, in 1822, will
be described in the twenty-fifth chapter. The crater of Taschem, at the
eastern extremity of Java, contains a lake strongly impregnated with
sulphuric acid, a quarter of a mile long, from which a river of acid
water issues, which supports no living creature, nor can fish live in
the sea near its confluence. There is an extinct crater near Batur,
called Guevo Upas, or the Valley of Poison, about half a mile in
circumference, which is justly an object of terror to the inhabitants of
the country. Every living being which penetrates into this valley falls
down dead, and the soil is covered with the carcasses of tigers, deer,
birds, and even the bones of men; all killed by the abundant emanations
of carbonic acid gas, by which the bottom of the valley is filled.

In another crater in this land of wonders, near the volcano of Talaga
Bodas, we learn from M. Reinwardt, that the sulphureous exhalations have
killed tigers, birds, and innumerable insects; and the soft parts of
these animals, such as the fibres, muscles, nails, hair, and skin,
are very well preserved, while the bones are corroded, and entirely
destroyed.

We learn from observations made in 1844, by Mr. Jukes, that a recent
tertiary formation composed of limestone and resembling the coral rock
of a fringing reef, clings to the flanks of all the volcanic islands
from the east end of Timor to the west end of Java. These modern
calcareous strata are often white and chalk-like, sometimes 1000 feet
and upwards above the sea, regularly stratified in thick horizontal
beds, and they show that there has been a general elevation of these
islands at a comparatively modern period.[480]

The same linear arrangement which is observed in Java holds good in the
volcanoes of Sumatra, some of which are of great height, as Berapi,
which is more than 12,000 feet above the sea, and is continually
smoking. Hot springs are abundant at its base. The volcanic line then
inclines slightly to the northwest, and points to Barren Island, lat.
12° 15´ N., in the Bay of Bengal. This volcano was in eruption in 1792,
and will be described in the twenty-sixth chapter. The volcanic train
then extends, according to Dr. Macclelland, to the island of Narcondam,
lat. 13° 22´ N., which is a cone seven or eight hundred feet high,
rising from deep water, and said to present signs of lava currents
descending from the crater to the base. Afterwards the train stretches
in the same direction to the volcanic island of Ramree, about lat. 19°
N., and the adjoining island of Cheduba, which is represented in old
charts as a burning mountain. Thus we arrive at the Chittagong coast,
which in 1762 was convulsed by a tremendous earthquake (see chap.
29).[481]

To enumerate all the volcanic regions of the Indian and Pacific oceans
would lead me far beyond the proper limits of this treatise; but it will
appear in the last chapter of this volume, when coral reefs are treated
of, that the islands of the Pacific consist alternately of linear groups
of two classes, the one lofty, and containing active volcanoes, and
marine strata above the sea-level, and which have been undergoing
upheaval in modern times; the other very low, consisting of reefs of
coral, usually with lagoons in their centres, and in which there is
evidence of a gradual subsidence of the ground. The extent and direction
of these parallel volcanic bands have been depicted with great care by
Darwin in his map before cited (p. 351).

The most remarkable theatre of volcanic activity in the Northern
Pacific--or, perhaps, in the whole world--occurs in the Sandwich
Islands, which have been admirably treated of in a recent work by Mr.
Dana.[482]

_Volcanic region from central Asia to the Azores._--Another great region
of subterranean disturbance is that which has been imagined to extend
through a large part of Central Asia to the Azores, that is to say,
from China and Tartary through Lake Aral and the Caspian to the
Caucasus, and the countries bordering the Black Sea, then again through
part of Asia Minor to Syria, and westward to the Grecian Islands,
Greece, Naples, Sicily, the southern part of Spain, Portugal and the
Azores. Respecting the eastern extremity of this line in China, we have
little information, but many violent earthquakes are known to have
occurred there. The volcano said to have been in eruption in the seventh
century in Central Tartary is situated on the northern declivity of the
Celestial Mountains, not far distant from the large lake called
Issikoul; and Humboldt mentions other vents and solfataras in the same
quarter, which are all worthy of notice, as being far more distant from
the ocean (260 geographical miles) than any other known points of
eruption.

We find on the western shores of the Caspian, in the country round Baku,
a tract called the Field of Fire, which continually emits inflammable
gas, while springs of naphtha and petroleum occur in the same vicinity,
as also mud volcanoes. Syria and Palestine abound in volcanic
appearances, and very extensive areas have been shaken, at different
periods, with great destruction of cities and loss of lives. Continual
mention is made in history of the ravages committed by earthquakes in
Sidon, Tyre, Berytus, Laodicea, and Antioch, and in the Island of
Cyprus. The country around the Dead Sea appears evidently, from the
accounts of modern travellers, to be volcanic. A district near Smyrna,
in Asia Minor, was termed by the Greeks Catacecaumene, or "the burnt
up," where there is a large arid territory, without trees, and with a
cindery soil.[483] This country was visited in 1841 by Mr. W. J.
Hamilton, who found in the valley of the Hermus perfect cones of scoriæ,
with lava-streams, like those of Auvergne, conforming to the existing
river-channels, and with their surface undecomposed.[484]

_Grecian Archipelago._--Proceeding westwards, we reach the Grecian
Archipelago, where Santorin, afterwards to be described, is the grand
centre of volcanic action.

It was Von Buch's opinion that the volcanoes of Greece were arranged in
a line running N. N. W. and S. S. E., and that they afforded the only
example in Europe of active volcanoes having a linear direction; but M.
Virlet, on the contrary, announces as the result of his investigations,
made during the French expedition to the Morea in 1829, that there is no
one determinate line of direction for the volcanic phenomena in Greece,
whether we follow the points of eruptions, or the earthquakes, or any
other signs of igneous agency.[485]

Macedonia, Thrace, and Epirus, have always been subject to earthquakes,
and the Ionian Isles are continually convulsed.

Respecting Southern Italy, Sicily, and the Lipari Isles, it is
unnecessary to enlarge here, as I shall have occasion again to allude to
them. I may mention, however, that a band of volcanic action has been
traced by Dr. Daubeny across the Italian Peninsula, from Ischia to Mount
Vultur, in Apulia, the commencement of the line being found in the hot
springs of Ischia, after which it is prolonged through Vesuvius to the
Lago d'Ansanto, where gases similar to those of Vesuvius are evolved.
Its farther extension strikes Mount Vultur, a lofty cone composed of
tuff and lava, from one side of which carbonic acid and sulphuretted
hydrogen are emitted.[486]

_Traditions of deluges._--The traditions which have come down to us from
remote ages of great inundations said to have happened in Greece and on
the confines of the Grecian settlements, had doubtless their origin in a
series of local catastrophes, caused principally by earthquakes. The
frequent migrations of the earlier inhabitants, and the total want of
written annals long after the first settlement of each country, make it
impossible for us at this distance of time to fix either the true
localities or probable dates of these events. The first philosophical
writers of Greece were, therefore, as much at a loss as ourselves to
offer a reasonable conjecture on these points, or to decide how many
catastrophes might sometimes have become confounded in one tale, or how
much this tale may have been amplified, in after times, or obscured by
mythological fiction. The floods of Ogyges and Deucalion are commonly
said to have happened before the Trojan war; that of Ogyges more than
seventeen, and that of Deucalion more than fifteen centuries before our
era. As to the Ogygian flood, it is generally described as having laid
waste Attica, and was referred by some writers to a great overflowing of
rivers, to which cause Aristotle also attributed the deluge of
Deucalion, which, he says, affected Hellas only, or the central part of
Thessaly. Others imagined the same event to have been due to an
earthquake, which drew down masses of rock, and stopped up the course of
the Peneus in the narrow defile between mounts Ossa and Olympus.

As to the deluge of Samothrace, which is generally referred to a
distinct date, it appears that the shores of that small island and the
adjoining mainland of Asia were inundated by the sea. Diodorus Siculus
says that the inhabitants had time to take refuge in the mountains, and
save themselves by flight; he also relates, that long after the event
the fishermen of the island drew up in their nets the capitals of
columns, which were the remains of cities submerged by that terrible
catastrophe.[487] These statements scarcely leave any doubt that there
occurred, at the period alluded to, a subsidence of the coast,
accompanied by earthquakes and inroads of the sea. It is not impossible
that the story of the bursting of the Black Sea through the Thracian
Bosphorus into the Grecian Archipelago, which accompanied, and, as some
say, caused the Samothracian deluge, may have reference to a wave, or
succession of waves, raised in the Euxine by the same convulsion.

We know that subterranean movements and volcanic eruptions are often
attended not only by incursions of the sea, but also by violent rains,
and the complete derangement of the river drainage of the inland
country, and by the damming up of the outlets of lakes by landslips, or
obstructions in the courses of subterranean rivers, such as abound in
Thessaly and the Morea. We need not therefore be surprised at the
variety of causes assigned for the traditional floods of Greece, by
Herodotus, Aristotle, Diodorus, Strabo, and others. As to the area
embraced, had all the Grecian deluges occurred simultaneously, instead
of being spread over many centuries, and had they, instead of being
extremely local, reached at once from the Euxine to the southwestern
limit of the Peloponnese, and from Macedonia to Rhodes, the devastation
would still have been more limited than that which visited Chili in
1835, when a volcanic eruption broke out in the Andes, opposite Chiloe,
and another at Juan Fernandez, distant 720 geographical miles, at the
same time that several lofty cones, in the Cordillera, 400 miles to the
eastward of that island, threw out vapor and ignited matter. Throughout
a great part of the space thus recently shaken in South America, cities
were laid in ruins, or the land was permanently upheaved, or mountainous
waves rolled inland from the Pacific.

_Periodical alternation of Earthquakes in Syria and Southern Italy._--It
has been remarked by Von Hoff, that from the commencement of the
thirteenth to the latter half of the seventeenth century, there was an
almost entire cessation of earthquakes in Syria and Judea; and, during
this interval of quiescence, the Archipelago, together with part of the
adjacent coast of Lesser Asia, as also Southern Italy and Sicily,
suffered greatly from earthquakes; while volcanic eruptions were
unusually frequent in the same regions. A more extended comparison,
also, of the history of the subterranean convulsions of these tracts
seems to confirm the opinion, that a violent crisis of commotion never
visits both at the same time. It is impossible for us to declare, as
yet, whether this phenomenon is constant in this and other regions,
because we can rarely trace back a connected series of events farther
than a few centuries; but it is well known that, where numerous vents
are clustered together within a small area, as in many archipelagoes for
instance, two of them are never in violent eruption at once. If the
action of one becomes very great for a century or more, the others
assume the appearance of spent volcanoes. It is, therefore, not
improbable that separate provinces of the same great range of volcanic
fires may hold a relation to one deep-seated focus, analogous to that
which the apertures of a small group bear to some more superficial rent
or cavity. Thus, for example, we may conjecture that, at a comparatively
small distance from the surface, Ischia and Vesuvius mutually
communicate with certain fissures, and that each affords relief
alternately to elastic fluids and lava there generated. So we may
suppose Southern Italy and Syria to be connected, at a much greater
depth, with a lower part of the very same system of fissures; in which
case any obstruction occurring in one duct may have the effect of
causing almost all the vapor and melted matter to be forced up the
other, and if they cannot get vent, they may be the cause of violent
earthquakes. Some objections advanced against this doctrine that
"volcanoes act as safety-valves," will be considered in the sequel.[488]

The northeastern portion of Africa, including Egypt, which lies six or
seven degrees south of the volcanic line already traced, has been almost
always exempt from earthquakes; but the northwestern portion, especially
Fez and Morocco, which fall within the line, suffer greatly from time to
time. The southern part of Spain also, and Portugal, have generally been
exposed to the same scourge simultaneously with Northern Africa. The
provinces of Malaga, Murcia, and Granada, and in Portugal the country
round Lisbon, are recorded at several periods to have been devastated by
great earthquakes. It will be seen, from Michell's account of the great
Lisbon shock, in 1755, that the first movement proceeded from the bed of
the ocean ten or fifteen leagues from the coast. So late as February 2,
1816, when Lisbon was vehemently shaken, two ships felt a shock in the
ocean west from Lisbon; one of them at the distance of 120, and the
other 262 French leagues from the coast[489]--a fact which is more
interesting, because a line drawn through the Grecian Archipelago, the
volcanic region of Southern Italy, Sicily, Southern Spain, and Portugal,
will, if prolonged westward through the ocean, strike the volcanic group
of the Azores, which may possibly therefore have a submarine connection
with the European line.

In regard to the volcanic system of Southern Europe, it may be observed,
that there is a central tract where the greatest earthquakes prevail, in
which rocks are shattered, mountains rent, the surface elevated or
depressed, and cities laid in ruins. On each side of this line of
greatest commotion there are parallel bands of country where the shocks
are less violent. At a still greater distance (as in Northern Italy, for
example, extending to the foot of the Alps), there are spaces where the
shocks are much rarer and more feeble, yet possibly of sufficient force
to cause, by continued repetition, some appreciable alteration in the
external form of the earth's crust. Beyond these limits, again, all
countries are liable to slight tremors, at distant intervals of time,
when some great crisis of subterranean movement agitates an adjoining
volcanic region; but these may be considered as mere vibrations,
propagated mechanically through the external covering of the globe, as
sounds travel almost to indefinite distances through the air. Shocks of
this kind have been felt in England, Scotland, Northern France, and
Germany--particularly during the Lisbon earthquake. But these countries
cannot, on this account, be supposed to constitute parts of the southern
volcanic region, any more than the Shetland and Orkney islands can be
considered as belonging to the Icelandic circle, because the sands
ejected from Hecla have been wafted thither by the winds.

Besides the continuous spaces of subterranean disturbance, of which we
have merely sketched the outline, there are other disconnected volcanic
groups, of which several will be mentioned hereafter.

_Lines of active and extinct Volcanoes not to be confounded._--We must
always be careful to distinguish between lines of extinct and active
volcanoes, even where they appear to run in the same direction; for
ancient and modern systems may interfere with each other. Already,
indeed, we have proof that this is the case; so that it is not by
geographical position, but by reference to the species of organic beings
alone, whether aquatic or terrestrial, whose remains occur in beds
interstratified with lavas, that we can clearly distinguish the relative
age of volcanoes of which no eruptions are recorded. Had Southern Italy
been known to civilized nations for as short a period as America, we
should have had no record of eruptions in Ischia; yet we might have
assured ourselves that the lavas of that isle had flowed since the
Mediterranean was inhabited by the species of testacea now living in the
Neapolitan seas. With this assurance, it would not have been rash to
include the numerous vents of that island in the modern volcanic group
of Campania.

On similar grounds we may infer, without much hesitation, that the
eruptions of Etna, and the modern earthquakes of Calabria, are a
continuation of that action which, at a somewhat earlier period,
produced the submarine lavas of the Val di Noto in Sicily. But on the
other hand, the lavas of the Euganean hills and the Vicentin, although
not wholly beyond the range of earthquakes in Northern Italy, must not
be confounded with any existing volcanic system; for when they flowed,
the seas were inhabited by animals almost all of them distinct from
those now known to live, whether in the Mediterranean or other parts of
the globe.




CHAPTER XXIII.

VOLCANIC DISTRICT OF NAPLES.


  History of the volcanic eruptions in the district round
    Naples--Early convulsions in the island of Ischia--Numerous cones
    thrown up there--Lake Avernus--The Solfatara--Renewal of the
    eruptions of Vesuvius, A.D. 79--Pliny's description of the
    phenomena--His silence respecting the destruction of Herculaneum and
    Pompeii--Subsequent history of Vesuvius--Lava discharged in Ischia
    in 1302--Pause in the eruptions of Vesuvius--Monte Nuovo thrown
    up--Uniformity of the volcanic operations of Vesuvius and Phlegræan
    Fields in ancient and modern times.


I shall next give a sketch of the history of some of the volcanic vents
dispersed throughout the great regions before described, and consider
the composition and arrangement of their lavas and ejected matter. The
only volcanic region known to the ancients was that of the
Mediterranean; and even of this they have transmitted to us very
imperfect records relating to the eruptions of the three principal
districts, namely, that round Naples, that of Sicily and its isles, and
that of the Grecian Archipelago. By far the most connected series of
records throughout a long period relates to the first of these
provinces; and these cannot be too attentively considered, as much
historical information is indispensable in order to enable us to obtain
a clear view of the connection and alternate mode of action of the
different vents in a single volcanic group.

_Early convulsions in the Island of Ischia._---The Neapolitan volcanoes
extend from Vesuvius, through the Phlegræan Fields, to Procida and
Ischia, in a somewhat linear arrangement, ranging from the northeast to
the southwest, as will be seen in the annexed map of the volcanic
district of Naples (fig. 40). Within the space above limited, the
volcanic force is sometimes developed in single eruptions from a
considerable number of irregularly scattered points; but a great part of
its action has been confined to one principal and habitual vent,
Vesuvius or Somma. Before the Christian era, from the remotest periods
of which we have any tradition, this principal vent was in a state of
inactivity. But terrific convulsions then took place from time to time
in Ischia (Pithecusa), and seem to have extended to the neighboring isle
of Procida (Prochyta); for Strabo[490] mentions a story of Procida
having been torn asunder from Ischia; and Pliny[491] derives its name
from its having been poured forth by an eruption from Ischia.

The present circumference of Ischia along the water's edge is eighteen
miles, its length from west to east about five, and its breadth from
north to south three miles. Several Greek colonies which settled there
before the Christian era were compelled to abandon it in consequence of
the violence of the eruptions. First the Erythræans, and afterwards the
Chalcidians, are mentioned as having been driven out by earthquakes and
igneous exhalations. A colony was afterwards established by Hiero, king
of Syracuse, about 380 years before the Christian era; but when they had
built a fortress, they were compelled by an eruption to fly, and never
again returned. Strabo tells us that Timæus recorded a tradition, that,
a little before his time, Epomeus, the principal mountain in the centre
of the island, vomited fire during great earthquakes; that the land
between it and the coast had ejected much fiery matter, which flowed
into the sea, and that the sea receded for the distance of three stadia,
and then returning, overflowed the island. This eruption is supposed by
some to have been that which formed the crater of Monte Corvo on one of
the higher flanks of Epomeo, above Foria, the lava-current of which may
still be traced, by aid of the scoriæ on its surface, from the crater to
the sea.

[Illustration: Fig. 40.

VOLCANIC DISTRICT OF NAPLES.

A. Astroni. B. Monte Barbaro. M. Monte Nuovo. S. The Solfatara.]

To one of the subsequent eruptions in the lower parts of the isle, which
caused the expulsion of the first Greek colony, Monte Rotaro has been
attributed, and it bears every mark of recent origin. The cone, which I
examined in 1828, is remarkably perfect, and has a crater on its summit
precisely resembling that of Monte Nuovo near Naples; but the hill is
larger, and resembles some of the more considerable cones of single
eruption near Clermont in Auvergne, and, like some of them, it has given
vent to a lava-stream at its base, instead of its summit. A small ravine
swept out by a torrent exposes the structure of the cone, which is
composed of innumerable inclined and slightly undulating layers of
pumice, scoriæ, white lapilli, and enormous angular blocks of trachyte.
These last have evidently been thrown out by violent explosions, like
those which in 1822 launched from Vesuvius a mass of augitic lava, of
many tons' weight, to the distance of three miles, which fell in the
garden of Prince Ottajano. The cone of Rotaro is covered with the
arbutus, and other beautiful evergreens. Such is the strength of the
virgin soil, that the shrubs have become almost arborescent; and the
growth of some of the smaller wild plants has been so vigorous, that
botanists have scarcely been able to recognize the species.

The eruption which dislodged the Syracusan colony is supposed to have
given rise to that mighty current which forms the promontory of Zaro and
Caruso. The surface of these lavas is still very arid and bristling, and
is covered with black scoriæ; so that it is not without great labor that
human industry has redeemed some small spots, and converted them into
vineyards. Upon the produce of these vineyards the population of the
island is almost entirely supported. It amounted when I was there, in
1828, to about twenty-five thousand, and was on the increase.

[Illustration: Fig 41.

Part of Ischia seen from the West.

_a._ Monte Epomeo or San Niccola.

_b._ Monte Vico.

_c._ Another of the minor cones with a crater.[492]]

From the date of the great eruption last alluded to, down to our own
time, Ischia has enjoyed tranquillity, with the exception of one
emission of lava hereafter to be described, which, although it
occasioned much local damage, does not appear to have devastated the
whole country, in the manner of more ancient explosions. There are, upon
the whole, on different parts of Epomeo, or scattered through the lower
tracts of Ischia, twelve considerable volcanic cones which have been
thrown up since the island was raised above the surface of the deep; and
many streams of lava may have flowed, like that of "Arso" in 1302,
without cones having been produced; so that this island may, for ages
before the period of the remotest traditions, have served as a
safety-valve to the whole Terra di Lavoro, while the fires of Vesuvius
were dormant.

_Lake Avernus._--It seems also clear that Avernus, a circular lake near
Puzzuoli, about half a mile in diameter, which is now a salubrious and
cheerful spot, once exhaled mephitic vapors, such as are often emitted
by craters after eruptions. There is no reason for discrediting the
account of Lucretius, that birds could not fly over it without being
stifled, although they may now frequent it uninjured.[493] There must
have been a time when this crater was in action; and for many centuries
afterwards it may have deserved the appellation of "atri jauna Ditis,"
emitting, perhaps, gases as destructive of animal life as those
suffocating vapors given out by Lake Quilotoa, in Quito, in 1797, by
which whole herds of cattle on its shores were killed,[494] or as those
deleterious emanations which annihilated all the cattle in the island of
Lancerote, one of the Canaries, in 1730.[495] Bory St. Vincent mentions,
that in the same isle birds fell lifeless to the ground; and Sir William
Hamilton informs us that he picked up dead birds on Vesuvius during an
eruption.

_Solfatara._--The Solfatara, near Puzzuoli, which may be considered as a
nearly extinguished crater, appears, by the accounts of Strabo and
others, to have been before the Christian era in very much the same
state as at present, giving vent continually to aqueous vapor, together
with sulphureous and muriatic acid gases, like those evolved by
Vesuvius.

_Ancient history of Vesuvius._--Such, then, were the points where the
subterranean fires obtained vent, from the earliest period to which
tradition reaches back, down to the first century of the Christian era;
but we then arrive at a crisis in the volcanic action of this
district--one of the most interesting events witnessed by man during the
brief period throughout which he has observed the physical changes on
the earth's surface. From the first colonization of Southern Italy by
the Greeks, Vesuvius afforded no other indications of its volcanic
character than such as the naturalist might infer, from the analogy of
its structure to other volcanoes. These were recognized by Strabo, but
Pliny did not include the mountain in his list of active vents. The
ancient cone was of a very regular form, terminating not as at present
in two peaks, but with a summit which presented, when seen from a
distance, the even outline of an abruptly truncated cone. On the summit,
as we learn from Plutarch, there was a crater with steep cliffs, and
having its interior overgrown with wild vines, and with a sterile plain
at the bottom. On the exterior, the flanks of the mountain were clothed
with fertile fields richly cultivated, and at its base were the populous
cities of Herculaneum and Pompeii. But the scene of repose was at length
doomed to cease, and the volcanic fire was recalled to the main channel,
which at some former unknown period had given passage to repeated
streams of melted lava, sand, and scoriæ.

_Renewal of its eruptions._--The first symptom of the revival of the
energies of this volcano was the occurrence of an earthquake in the year
63 after Christ, which did considerable injury to the cities in its
vicinity. From that time to the year 79 slight shocks were frequent; and
in the month of August of that year they became more numerous and
violent, till they ended at length in an eruption. The elder Pliny, who
commanded the Roman fleet, was then stationed at Misenum; and in his
anxiety to obtain a near view of the phenomena, he lost his life, being
suffocated by sulphureous vapors. His nephew, the younger Pliny,
remained at Misenum, and has given us, in his Letters, a lively
description of the awful scene. A dense column of vapor was first seen
rising vertically from Vesuvius, and then spreading itself out
laterally, so that its upper portion resembled the head, and its lower
the trunk of the pine, which characterizes the Italian landscape. This
black cloud was pierced occasionally by flashes of fire, as vivid as
lightning, succeeded by darkness more profound than night. Ashes fell
even upon the ships at Misenum, and caused a shoal in one part of the
sea--the ground rocked, and the sea receded from the shores, so that
many marine animals were seen on the dry sand. The appearances above
described agree perfectly with those witnessed in more recent eruptions,
especially those of Monte Nuovo, in 1538, and of Vesuvius in 1822.

The younger Pliny, although giving a circumstantial detail of so many
physical facts, and describing the eruption and earthquake, and the
shower of ashes which fell at Stabiæ, makes no allusion to the sudden
overwhelming of two large and populous cities, Herculaneum and Pompeii.
In explanation of this omission, it has been suggested that his chief
object was simply to give Tacitus a full account of the particulars of
his uncle's death. It is worthy, however, of remark, that had the buried
cities never been discovered, the accounts transmitted to us of their
tragical end might well have been discredited by the majority, so vague
and general are the narratives, or so long subsequent to the event.
Tacitus, the friend and contemporary of Pliny, when adverting in general
terms to the convulsions, says merely that "cities were consumed or
buried."[496]

Suetonius, although he alludes to the eruption incidentally, is silent
as to the cities. They are mentioned by Martial, in an epigram, as
immersed in cinders; but the first historian who alludes to them by name
is Dion Cassius,[497] who flourished about a century and a half after
Pliny. He appears to have derived his information from the traditions of
the inhabitants, and to have recorded, without discrimination, all the
facts and fables which he could collect. He tells us, "that during the
eruption a multitude of men of superhuman stature, resembling giants,
appeared, sometimes on the mountain, and sometimes in the environs--that
stones and smoke were thrown out, the sun was hidden, and then the
giants seemed to rise again, while the sounds of trumpets were heard,
&c., &c.; and finally," he relates, "two entire cities, Herculaneum and
Pompeii, were buried under showers of ashes, while all the people were
sitting in the theatre." That many of these circumstances were invented,
would have been obvious, even without the aid of Pliny's letters; and
the examination of Herculaneum and Pompeii enables us to prove, that
none of the people were destroyed in the theatres, and indeed that there
were very few of the inhabitants who did not escape from both cities.
Yet some lives were lost, and there was ample foundation for the tale in
its most essential particulars.

It does not appear that in the year 79 any lava flowed from Vesuvius;
the ejected substances, perhaps, consisted entirely of lapilli, sand,
and fragments of older lava, as when Monte Nuovo was thrown up in 1538.
The first era at which we have authentic accounts of the flowing of a
stream of lava, is the year 1036, which is the seventh eruption from the
revival of the fires of the volcano. A few years afterwards, in 1049,
another eruption is mentioned, and another in 1138 (or 1139), after
which a great pause ensued of 168 years. During this long interval of
repose, two minor vents opened at distant points. First, it is on
tradition that an eruption took place from the Solfatara, in the year
1198, during the reign of Frederick II., Emperor of Germany; and
although no circumstantial detail of the event has reached us from those
dark ages, we may receive the fact without hesitation.[498] Nothing
more, however, can be attributed to this eruption, as Mr. Scrope
observes, than the discharge of a light and scoriform trachytic lava, of
recent aspect, resting upon the strata of loose tuff which covers the
principal mass of trachyte.[499]

_Volcanic eruption in Ischia_, 1302.--The other occurrence is well
authenticated--the eruption, in the year 1302, of a lava-stream from a
new vent on the southeast end of the Island of Ischia. During part of
1301, earthquakes had succeeded one another with fearful rapidity; and
they terminated at last with the discharge of a lava-stream from a point
named the Campo del Arso, not far from the town of Ischia. This lava ran
quite down to the sea--a distance of about two miles; in color it varies
from iron-gray to reddish black, and is remarkable for the glassy
felspar which it contains. Its surface is almost as sterile, after a
period of five centuries, as if it had cooled down yesterday. A few
scantlings of wild thyme, and two or three other dwarfish plants, alone
appear in the interstices of the scoriæ, while the Vesuvian lava of 1767
is already covered with a luxuriant vegetation. Pontanus, whose
country-house was burnt and overwhelmed, describes the dreadful scene as
having lasted two months.[500] Many houses were swallowed up, and a
partial emigration of the inhabitants followed. This eruption produced
no cone, but only a slight depression, hardly deserving the name of a
crater, where heaps of black and red scoriæ lie scattered around. Until
this eruption, Ischia is generally believed to have enjoyed an interval
of rest for about seventeen centuries; but Julius Obsequens,[501] who
flourished A. D. 214, refers to some volcanic convulsions in the year
662 after the building of Rome (91 B. C.) As Pliny, who lived a century
before Obsequens, does not enumerate this among other volcanic
eruptions, the statement of the latter author is supposed to have been
erroneous; but it would be more consistent, for reasons before stated,
to disregard the silence of Pliny, and to conclude, that some kind of
subterranean commotion, probably of no great violence, happened at the
period alluded to.

_History of Vesuvius after_ 1138.--To return to Vesuvius:--the next
eruption occurred in 1306; between which era and 1631 there was only one
other (in 1500), and that a slight one. It has been remarked, that
throughout this period Etna was in a state of such unusual activity, as
to lend countenance to the idea that the great Sicilian volcano may
sometimes serve as a channel of discharge to elastic fluids and lava
that would otherwise rise to the vents in Campania.

_Formation of Monte Nuovo_, 1538.--The great pause was also marked by a
memorable event in the Phlegræan Fields--the sudden formation of a new
mountain in 1538, of which we have received authentic accounts from
contemporary writers.


  [Illustration: Fig. 42.

  Monte Nuovo, formed in the Bay of Baiæ, Sept. 29th, 1538.

  1. Cone of Monte Nuovo.
  2. Brim of crater of ditto.
  3. Thermal spring, called Baths of Nero, or Stufe di Tritoli.


]

The height of this mountain, called ever since Monte Nuovo, has been
determined by the Italian mineralogist Pini, to be 440 English feet
above the level of the bay; its base is about eight thousand feet, or
more than a mile and a half in circumference. According to Pini, the
depth of the crater is 421 English feet from the summit of the hill, so
that its bottom is only nineteen feet above the level of the sea. The
cone is declared, by the best authorities, to stand partly on the site
of the Lucrine Lake (4, fig. 43),[502] which was nothing more than the
crater of a pre-existent volcano, and was almost entirely filled during
the explosion of 1538. Nothing now remains but a shallow pool, separated
from the sea by an elevated beach, raised artificially.

[Illustration: Fig. 43.

The Phlegræan Fields.


  1. Monte Nuovo.
  2. Monte Barbaro.
  3. Lake Avernus.
  4. Lucrine Lake.
  5. The Solfatara.
  6. Puzzuoli.
  7. Bay of Baiæ.


]

Sir William Hamilton has given us two original letters describing this
eruption. The first, by Falconi, dated 1538, contains the following
passages.[503] "It is now two years since there have been frequent
earthquakes at Puzzuoli, Naples, and the neighboring parts. On the day
and in the night before the eruption (of Monte Nuovo), above twenty
shocks, great and small, were felt. The eruption began on the 29th of
September, 1538. It was on a Sunday, about one o'clock in the night,
when flames of fire were seen between the hot baths and Tripergola. In a
short time the fire increased to such a degree, that it burst open the
earth in this place, and threw up so great a quantity of ashes and
pumice-stones, mixed with water, as covered the whole country. The next
morning (after the formation of Monte Nuovo) the poor inhabitants of
Puzzuoli quitted their habitations in terror, covered with the muddy and
black shower which continued the whole day in that country--flying from
death, but with death painted in their countenances. Some with their
children in their arms, some with sacks full of their goods; others
leading an ass, loaded with their frightened family, towards Naples;
others carrying quantities of birds, of various sorts, that had fallen
dead at the beginning of the eruption; others, again, with fish which
they had found, and which were to be met with in plenty on the shore,
the sea having left them dry for a considerable time. I accompanied
Signor Moramaldo to behold the wonderful effects of the eruption. The
sea had retired on the side of Baiæ, abandoning a considerable tract,
and the shore appeared almost entirely dry, from the quantity of ashes
and broken pumice-stones thrown up by the eruption. I saw two springs in
the newly discovered ruins; one before the house that was the queen's,
of hot and salt water," &c.

So far Falconi: the other account is by Pietro Giacomo di Toledo, which
begins thus:--"It is now two years since this province of Campagna has
been afflicted with earthquakes, the country about Puzzuoli much more so
than any other parts; but the 27th and the 28th of the month of
September last, the earthquakes did not cease day or night in the town
of Puzzuoli: that plain which lies between Lake Avernus, the Monte
Barbaro, and the sea, was _raised a little_, and many cracks were made
in it, from some of which issued water; at the same time the sea,
immediately joining the plain, _dried up about two hundred paces_, so
that the fish were left on the sand a prey to the inhabitants of
Puzzuoli. At last, on the 29th of the same month, about two o'clock in
the night, the earth opened near the lake, and discovered a horrid
mouth, from which were vomited furiously smoke, fire, stones, and mud,
composed of ashes, making at the time of its opening a noise like the
loudest thunder. The stones which followed were by the flames converted
to pumice, and some of these were _larger than an ox_. The stones went
about as high as a cross-bow can carry, and then fell down, sometimes on
the edge, and sometimes into the mouth itself. The mud was of the color
of ashes, and at first very liquid, then by degrees less so, and in such
quantities, that in less than twelve hours, with the help of the
above-mentioned stones, a mountain was raised of 1000 paces in height.
Not only Puzzuoli and the neighboring country was full of this mud, but
the city of Naples also; so that many of its palaces were defaced by it.
Now this eruption lasted two nights and two days without intermission,
though, it is true, not always with the same force; the third day the
eruption ceased, and I went up with many people to the top of the new
hill, and saw down into its mouth, which was a round cavity about a
quarter of a mile in circumference, in the middle of which, the stones
which had fallen were boiling up, just as a caldron of water boils on
the fire. The fourth day it began to throw up again, and the seventh
much more, but still with less violence than the first night. At this
time many persons who were on the hill were knocked down by the stones
and killed, or smothered with the smoke. In the day the smoke still
continues, and you often see fire in the midst of it in the
nighttime."[504]

It will be seen that both these accounts, written immediately after the
birth of Monte Nuovo, agree in stating that the sea retired; and one
mentions that its bottom was upraised; but they attribute the origin of
the new hill exclusively to the jets of mud, showers of scoriæ, and
large fragments of rock, cast out from a central orifice, for several
days and nights. Baron Von Buch, however, in his excellent work on the
Canary Islands, and volcanic phenomena in general, has declared his
opinion that the cone and crater of Monte Nuovo were formed, not in the
manner above described, but by the upheaval of solid beds of white tuff,
which were previously horizontal, but which were pushed up in 1538, so
as to dip away in all directions from the centre, with the same
inclination as the sloping surface of the cone itself. "It is an error,"
he says, "to imagine that this hill was formed by eruption, or by the
ejection of pumice, scoriæ, and other incoherent matter; for the solid
beds of upraised tuff are visible all round the crater, and it is merely
the superficial covering of the cone which is made up of ejected
scoriæ."[505]

In confirmation of this view, M. Dufrénoy has cited a passage from the
works of Porzio, a celebrated physician of that period, to prove that in
1538 the ground where Monte Nuovo stands was pushed up in the form of a
great bubble or blister, which on bursting, gave origin to the present
deep crater. Porzio, says, "that after two days and nights of violent
earthquakes, the sea retired for nearly 200 yards; so that the
inhabitants could collect great numbers of fish on this part of the
shore, and see some springs of fresh water which rose up there. At
length, on the third day of the calends of October (September 29), they
saw a large tract of ground intervening between the foot of Monte
Barbaro, and part of the sea, near the Lake Avernus, rise, and suddenly
assume the form of an incipient hill; and at two o'clock at night, this
heap of earth, opening as it were its mouth, vomited, with a loud noise,
flames, pumice-stones, and ashes."[506]

So late as the year 1846 a fourth manuscript (written immediately after
the eruption) was discovered and published in Germany. It was written in
1538 by Francesco del Nero,[507] who mentions the drying up of the bed
of the sea near Puzzuoli, which enabled the inhabitants of the town to
carry off loads of fish. About eight o'clock in the morning of the 29th
September, the earth sunk down about 14 feet in that place where the
volcanic orifice now appears, and there issued forth a small stream of
water, at first cold, and afterwards tepid. At noon, on the same day,
the earth began to swell up in the same spot where it had sunk down 14
feet, so as to form a hill. About this time fire issued forth, and gave
rise to the great gulf, "with such a force, noise, and shining light,
that I, who was standing in my garden, was seized with terror. Forty
minutes afterwards, although unwell, I got upon a neighboring height,
from which I saw all that took place, and by my troth it was a splendid
fire, that threw up for a long time much earth and many stones, which
fell back again all round the gulf, in a semicircle of from one to three
bow-shots in diameter, and, filling up part of the sea, formed a hill
nearly of the height of Monte Morello. Masses of earth and stones, as
large as an ox, were shot up from the fiery gulf into the air, to a
height which I estimate at a mile and a half. When they descended, some
were dry, others in a soft muddy state." He concludes by alluding again
to the sinking of the ground, and the elevation of it which followed,
and says that to him it was inconceivable how such a mass of stones and
ashes could have been poured forth from the gulf. He also refers to the
account which Porzio was to draw up for the Viceroy.

On comparing these four accounts, recorded by eye-witnesses, there
appears to be no real discrepancy between them. It seems clear that the
ground first sunk down 14 feet on the site of the future volcano, and
after having subsided it was again propelled upwards by the lava mingled
with steam and gases, which were about to burst forth. Jets of red-hot
lava, fragments of fractured rock, and occasionally mud composed of a
mixture of pumice, tuff, and sea-water, were hurled into the air. Some
of the blocks of stone were very large, leading us to infer that the
ground which sank and rose again was much shattered and torn to pieces
by the elastic vapors. The whole hill was not formed at once, but by an
intermittent action extending over a week or more. It seems that the
chasm opened between Tripergola and the baths in its suburbs, and that
the ejected materials fell and buried that small town. A considerable
part, however, of the hill was formed in less than twenty-four hours,
and in the same manner as on a smaller scale the mud cones of the air
volcanoes are produced, with a cavity in the middle. There is no
difficulty in conceiving that the pumiceous mud, if so thrown out, may
have set into a kind of stone on drying, just as some cements, composed
of volcanic ashes, are known to consolidate with facility.

I am informed that Baron Von Buch discovered some marine shells of
existing species, such as occur fossil in the tuff of the neighborhood,
in beds exposed low down in the walls of the crater of Monte Nuovo.
These may have been ejected in the mud mixed with sea-water which was
cast out of the boiling gulf; or, as Signor Arcangelo Scacchi has
suggested,[508] they may have been derived from the older tuff, which
contains marine shells of recent species. The same observer remarks that
Porzio's account upon the whole corroborates the doctrine of the cone
having been formed by eruption, in proof of which he cites the
following passage:--"But what was truly astonishing, a hill of
pumice-stones and ashes was heaped up round the gulf to the height of a
mile in a single night."[509] Signor Scacchi also adds that the ancient
temple of Apollo, now at the foot of Monte Nuovo, and the walls of which
still retain their perfect perpendicularity, could not possibly have
maintained that position had the cone of Monte Nuovo really been the
result of upheaval.

Tripergola was much frequented as a watering-place, and contained a
hospital for those who resorted there for the benefit of the thermal
springs; and it appears that there were no fewer than three inns in the
principal street. Had Porzio stated that any of these buildings, or the
ruins of them, were seen by himself or others raised up above the plain,
a short time before the first eruption, so as to stand on the summit or
slope of a newly-raised hillock, we might have been compelled, by so
circumstantial a narrative, to adopt M. Dufrénoy's interpretation.

But in the absence of such evidence, we must appeal to the crater
itself, where we behold a section of the whole mountain, without being
able to detect any original nucleus of upheaved rock distinct from the
rest; on the contrary, the whole mass is similar throughout in
composition, and the cone very symmetrical in form; nor are there any
clefts, such as might be looked for, as the effect of the sudden upthrow
of stony masses. M. C. Prevost has well remarked, that if beds of solid
and non-elastic materials had yielded to a violent pressure directed
from below upward, we should find not simply a deep empty cavity, but an
irregular opening, where many rents converged; and these rents would be
now seen breaking through the walls of the crater, widening as they
approach the centre. (See Fig. 44, _a_, _b_.)[510] Not a single fissure
of this kind is observable in the interior of Monte Nuovo, where the
walls of the crater are continuous and entire; nor are there any dikes
implying that rents had existed, which were afterwards filled with lava
or other matter.

[Illustration: Fig. 44.]

It has moreover been often urged by Von Buch, De Beaumont, and others,
who ascribe the conical form of volcanoes chiefly to upheaval from
below, that in such mountains there are a great number of deep rents and
ravines, which diverge on all sides like the spokes of a wheel, from
near the central axis to the circumference or base of the cone, as in
the case of Palma, Cantal, and Teneriffe. Yet the entire absence of such
divergent fissures or ravines, in such cases as Monte Nuovo, Somma, or
Etna, is passed by unnoticed, and appears to have raised in their minds
no objection to their favorite theory.

It is, indeed, admitted by M. Dufrénoy that there are some facts which
it is very difficult to reconcile with his own view of Porzio's record.
Thus, for example, there are certain Roman monuments at the base of
Monte Nuovo, and on the borders of Lake Avernus, such as the temples of
Apollo (before mentioned) and Pluto, which do not seem to have suffered
in the least degree by the supposed upheaval. "The walls which still
exist have preserved their vertical position, and the vaults are in the
same state as other monuments on the shores of the Bay of Baiæ. The long
gallery which led to the Sibyl's Cave, on the other side of Lake
Avernus, has in like manner escaped injury, the roof of the gallery
remaining perfectly horizontal, the only change being that the soil of
the chamber in which the Sibyl gave out her oracles is now covered by a
few inches of water, which merely indicates a slight alteration in the
level of Lake Avernus."[511] On the supposition, then, that pre-existing
beds of pumiceous tuff were upraised in 1538, so as to form Monte Nuovo,
it is acknowledged that the perfectly undisturbed state of the
contiguous soil on which these ancient monuments stand, is very
different from what might have been expected.

Mr. Darwin, in his "Volcanic Islands," has described several crateriform
hills in the Galapagos Archipelago as composed of tuff which has
evidently flowed like mud, and yet on consolidating has preserved an
inclination of twenty and even thirty degrees. The tuff does not fold in
continuous sheets round the hills as would have happened if they had
been formed by the upheaval of horizontal layers. The author describes
the composition of the tuff as very similar to that of Monte Nuovo, and
the high angles at which the beds slope, both those which have flowed
and those which have fallen in the form of ashes, entirely removes the
difficulty supposed by M. Dufrénoy to exist in regard to the slope of
Monte Nuovo, where it exceeds an angle of 18° to 20°.[512] Mr. Dana,
also, in his account of the Sandwich Islands,[513] shows that in the
"cinder cones" of that region, the strata have an original inclination
of between 35° and 40°, while in the "tufa cones" formed near the sea,
the beds slope at about an angle of 30°. The same naturalist also
observed in the Samoan or Navigator Islands in Polynesia, that fragments
of fresh coral had been thrown up together with volcanic matter to the
height of 200 feet above the level of the sea in cones of tufa.[514]

I shall again revert to the doctrine of the origin of volcanic cones by
upheaval, when speaking of Vesuvius, Etna, and Santorin, and shall now
merely add, that, in 1538, the whole coast, from Monte Nuovo to beyond
Puzzuoli, was upraised to the height of many feet above the bed of the
Mediterranean, and has since retained the greater part of the elevation
then acquired. The proofs of these remarkable changes of level will be
considered at length when the phenomena of the temple of Serapis are
described.[515]

_Volcanoes of the Phlegræan Fields._--Immediately adjoining Monte Nuovo
is the larger volcanic cone of Monte Barbaro (2, fig. 43, p. 367), the
"Gaurus inanis" of Juvenal--an appellation given to it probably from its
deep circular crater, which is about a mile in diameter. Large as is
this cone, it was probably produced by a single eruption; and it does
not, perhaps, exceed in magnitude some of the largest of those formed in
Ischia, within the historical era. It is composed chiefly of indurated
tufa like Monte Nuovo, stratified conformably to its conical surface.
This hill was once very celebrated for its wines, and is still covered
with vineyards; but when the vine is not in leaf it has a sterile
appearance, and, late in the year, when seen from the beautiful Bay of
Baiæ, it often contrasts so strongly in verdure with Monte Nuovo, which
is always clothed with arbutus, myrtle, and other wild evergreens, that
a stranger might well imagine the cone of older date to be that thrown
up in the sixteenth century.[516]

There is nothing, indeed, so calculated to instruct the geologist as the
striking manner in which the recent volcanic hills of Ischia, and that
now under consideration, blend with the surrounding landscape. Nothing
seems wanting or redundant; every part of the picture is in such perfect
harmony with the rest, that the whole has the appearance of having been
called into existence by a single effort of creative power. Yet what
other result could we have anticipated if nature has ever been governed
by the same laws? Each new mountain thrown up--each new tract of land
raised or depressed by earthquakes--should be in perfect accordance with
those previously formed, if the entire configuration of the surface has
been due to a long series of similar disturbances. Were it true that the
greater part of the dry land originated simultaneously in its present
state, at some era of paroxysmal convulsion, and that additions were
afterwards made slowly and successively during a period of comparative
repose; then, indeed, there might be reason to expect a strong line of
demarcation between the signs of the ancient and modern changes. But the
very continuity of the plan, and the perfect identity of the causes, are
to many a source of deception; since by producing a unity of effect,
they lead them to exaggerate the energy of the agents which operated in
the earlier ages. In the absence of all historical information, they are
as unable to separate the dates of the origin of different portions of
our continents, as the stranger is to determine, by their physical
features alone, the distinct ages of Monte Nuovo, Monte Barbara,
Astroni, and the Solfatara.

The vast scale and violence of the volcanic operations in Campania, in
the olden time, has been a theme of declamation, and has been contrasted
with the comparative state of quiescence of this delightful region in
the modern era. Instead of inferring, from analogy, that the ancient
Vesuvius was always at rest when the craters of the Phlegræan Fields
were burning--that each cone rose in succession,--and that many years,
and often centuries, of repose intervened between different
eruptions,--geologists seem to have generally conjectured that the whole
group sprung up from the ground at once, like the soldiers of Cadmus
when he sowed the dragon's teeth. As well might they endeavor to
persuade us that on these Phlegræan Fields, as the poets feigned, the
giants warred with Jove, ere yet the puny race of mortals were in being.

_Modern eruptions of Vesuvius._--For nearly a century after the birth of
Monte Nuovo, Vesuvius continued in a state of tranquillity. There had
been no violent eruption for 492 years; and it appears that the crater
was then exactly in the condition of the present extinct volcano of
Astroni, near Naples. Bracini, who visited Vesuvius not long before the
eruption of 1631, gives the following interesting description of the
interior:--"The crater was five miles in circumference, and about a
thousand paces deep: its sides were covered with brushwood, and at the
bottom there was a plain on which cattle grazed. In the woody parts wild
boars frequently harbored. In one part of the plain, covered with ashes,
were three small pools, one filled with hot and bitter water, another
salter than the sea, and a third hot, but tasteless."[517] But at length
these forests and grassy plains were consumed, being suddenly blown into
the air, and their ashes scattered to the winds. In December, 1631,
seven streams of lava poured at once from the crater, and overflowed
several villages, on the flanks and at the foot of the mountain. Resina,
partly built over the ancient site of Herculaneum, was consumed by the
fiery torrent. Great floods of mud were as destructive as the lava
itself,--no uncommon occurrence during these catastrophes; for such is
the violence of rains produced by the evolutions of aqueous vapor, that
torrents of water descend the cone, and becoming charged with impalpable
volcanic dust, and rolling along loose ashes, acquire sufficient
consistency to deserve their ordinary appellation of "aqueous lavas."

A brief period of repose ensued, which lasted only until the year 1666,
from which time to the present there has been a constant series of
eruptions, with rarely an interval of rest exceeding ten years. During
these three centuries, no irregular volcanic agency has convulsed other
points in this district. Brieslak remarked, that such irregular
convulsions had occurred in the Bay of Naples in every second century;
as, for example, the eruption of the Solfatara, in the twelfth; of the
lava of Arso, in Ischia, in the fourteenth; and of Monte Nuovo in the
sixteenth; but the eighteenth has formed an exception to this rule, and
this seems accounted for by the unprecedented number of eruptions of
Vesuvius during that period; whereas, when the new vents opened, there
had always been, as we have seen, a long intermittence of activity in
the principal volcano.





CHAPTER XXIV.

VOLCANIC DISTRICT OF NAPLES--_continued_.


  Dimensions and structure of the cone of Vesuvius--Fluidity and
    motion of lava--Dikes--Alluviums called "aqueous lavas"--Origin and
    composition of the matter enveloping Herculaneum and
    Pompeii--Condition and contents of the buried cities--Small number
    of skeletons--State of preservation of animal and vegetable
    substances--Rolls of papyrus--Stabiæ--Torre del Greco--Concluding
    remarks on the Campanian volcanoes.


_Structure of the cone of Vesuvius._--Between the end of the eighteenth
century and the year 1822, the great crater of Vesuvius had been
gradually filled by lava boiling up from below, and by scoriæ falling
from the explosions of minor mouths which were formed at intervals on
its bottom and sides. In place of a regular cavity, therefore, there was
a rough and rocky plain, covered with blocks of lava and scoriæ, and cut
by numerous fissures, from which clouds of vapor were evolved. But this
state of things was totally changed by the eruption of October, 1822,
when violent explosions, during the space of more than twenty days,
broke up and threw out all this accumulated mass, so as to leave an
immense gulf or chasm, of an irregular, but somewhat elliptical shape,
about three miles in circumference when measured along the very sinuous
and irregular line of its extreme margin, but somewhat less than three
quarters of a mile in its longest diameter, which was directed from N.
E. to S. W.[518] The depth of this tremendous abyss has been variously
estimated; for from the hour of its formation it increased daily by the
dilapidation of its sides. It measured, at first, according to the
account of some authors, two thousand feet in depth from the extreme
part of the existing summit;[519] but Mr. Scrope, when he saw it, soon
after the eruption, estimated its depth at less than half that amount.
More than eight hundred feet of the cone was carried away by the
explosions, so that the mountain was reduced in height from about 4200
to 3400 feet.[520]

As we ascend the sloping sides, the volcano appears a mass of loose
materials--a mere heap of rubbish, thrown together without the slightest
order; but on arriving at the brim of the crater, and obtaining a view
of the interior, we are agreeably surprised to discover that the
conformation of the whole displays in every part the most perfect
symmetry and arrangement. The materials are disposed in regular strata,
slightly undulating, appearing, when viewed in front, to be disposed in
horizontal planes. But, as we make the circuit of the edge of the
crater, and observe the cliffs by which it is encircled projecting or
receding in salient or retiring angles, we behold transverse sections of
the currents of lava and beds of sand and scoriæ, and recognize their
true dip. We then discover that they incline outwards from the axis of
the cone, at angles varying from 30° to 40°. The whole cone, in fact, is
composed of a number of concentric coatings of alternating lavas, sand,
and scoriæ. Every shower of ashes which has fallen from above, and every
stream of lava descending from the lips of the crater, have conformed to
the outward surface of the hill, so that one conical envelope may be
said to have been successively folded round another, until the
aggregation of the whole mountain was completed. The marked separation
into distinct beds results from the different colors and degrees of
coarseness in the sands, scoriæ, and lava, and the alternation of these
with each other. The greatest difficulty, on the first view, is to
conceive how so much regularity can be produced, notwithstanding the
unequal distribution of sand and scoriæ, driven by prevailing winds in
particular eruptions, and the small breadth of each sheet of lava as it
first flows out from the crater.

But, on a closer examination, we find that the appearance of extreme
uniformity is delusive; for when a number of beds thin out gradually,
and at different points, the eye does not without difficulty recognize
the termination of any one stratum, but usually supposes it continuous
with some other, which at a short distance may lie precisely in the same
plane. The slight undulations, moreover, produced by inequalities on the
sides of the hill on which the successive layers were moulded, assist
the deception. As countless beds of sand and scoriæ constitute the
greater part of the whole mass, these may sometimes mantle continuously
round the whole cone; and even lava streams may be of considerable
breadth when first they overflow, and since, in some eruptions, a
considerable part of the upper portion of the cone breaks down at once,
may form a sheet extending as far as the space which the eye usually
takes in, in a single section.

The high inclination of some of the beds, and the firm union of the
particles even where there is evidently no cement, is another striking
feature in the volcanic tuffs and breccias, which seems at first not
very easy of explanation. But the last great eruption afforded ample
illustration of the manner in which these strata are formed. Fragments
of lava, scoriæ, pumice, and sand, when they fall at slight distances
from the summit, are only half cooled down from a state of fusion, and
are afterwards acted upon by the heat from within, and by fumeroles or
small crevices in the cone through which hot vapors are disengaged. Thus
heated, the ejected fragments cohere together strongly; and the whole
mass acquires such consistency in a few days, that fragments cannot be
detached without a smart blow of the hammer. At the same time sand and
scoriæ, ejected to a greater distance, remain incoherent.[521]

Sir William Hamilton, in his description of the eruption of 1779, says
that jets of liquid lava, mixed with stones and scoriæ, were thrown up
to the height of at least ten thousand feet, having the appearance of a
column of fire.[522] Some of these were directed by the winds towards
Ottajano, and some of them falling almost perpendicularly, still red-hot
and liquid, on Vesuvius, covered its whole cone, part of the mountain of
Somma, and the valley between them. The falling matter being nearly as
vividly inflamed as that which was continually issuing fresh from the
crater, formed with it one complete body of fire, which could not be
less than two miles and a half in breadth, and of the extraordinary
height above mentioned, casting a heat to the distance of at least six
miles round it. Dr. Clarke, also, in his account of the eruption of
1793, says that millions of red-hot stones were shot into the air full
half the height of the cone itself, and then bending, fell all round in
a fine arch. On another occasion he says that, as they fell, they
covered nearly half the cone with fire.

The same author has also described the different appearance of the lava
at its source, and at some distance from it, when it had descended into
the plains below. At the point where it issued, in 1793, from an arched
chasm in the side of the mountain, the vivid torrent rushed with the
velocity of a flood. It was in perfect fusion, unattended with any
scoriæ on its surface, or any gross materials not in a state of complete
solution. It flowed with the translucency of honey, "in regular
channels, cut finer than art can imitate, and glowing with all the
splendor of the sun."--"Sir William Hamilton," he continues, "had
conceived that no stones thrown upon a current of lava would make any
impression. I was soon convinced of the contrary. Light bodies, indeed,
of five, ten, and fifteen pounds' weight, made little or no impression
even at the source; but bodies of sixty, seventy, and eighty pounds were
seen to form a kind of bed on the surface of the lava, and float away
with it. A stone of three hundred weight, that had been thrown out by
the crater, lay near the source of the current of lava: I raised it upon
one end, and then let it fall in upon the liquid lava; when it gradually
sunk beneath the surface, and disappeared. If I wished to describe the
manner in which it acted upon the lava, I should say that it was like a
loaf of bread thrown into a bowl of very thick honey, which gradually
involves itself in the heavy liquid, and then slowly sinks to the
bottom.

"The lava, at a small distance from its source, acquires a darker tint
upon its surface, is less easily acted upon, and, as the stream widens,
the surface, having lost its state of perfect solution, grows harder and
harder, and cracks into innumerable fragments of very porous matter, to
which they give the name of scoriæ, and the appearance of which has led
many to suppose that it proceeded thus from the mountain. There is,
however, no truth in this. All lava, at its first exit from its native
volcano, flows out in a liquid state, and all equally in fusion. The
appearance of the scoriæ is to be attributed only to the action of the
external air, and not to any difference in the materials which compose
it, since any lava whatever, separated from its channel, and exposed to
the action of the external air, immediately cracks, becomes porous, and
alters its form. As we proceeded downwards, this became more and more
evident; and the same lava which at its original source flowed in
perfect solution, undivided, and free from incumbrances of any kind, a
little farther down had its surface loaded with scoriæ in such a manner,
that, upon its arrival at the bottom of the mountain, the whole current
resembled nothing so much as a heap of unconnected cinders from an
iron-foundry." In another place he says that "the rivers of lava in the
plain resembled a vast heap of cinders, or the scoriæ of an
iron-foundry, rolling slowly along, and falling with a rattling noise
over one another."[523] Von Buch, who was in company with MM. de
Humboldt and Gay-Lussac, describes the lava of 1805 (the most fluid on
record) as shooting suddenly before their eyes from top to bottom of the
cone in one single instant. Professor J. D. Forbes remarks that the
length of the slope of the cone proper being about 1300 feet, this
motion must correspond to a velocity of many hundred feet in a few
seconds, without interpreting Von Buch's expression literally. The same
lava, when it reached the level road at Torre del Greco, moved at the
rate of only eighteen inches per minute, or three-tenths of an inch per
second.[524] "Although common lava," observes Professor Forbes, "is
nearly as liquid as melted iron, when it issues from the orifice of the
crater, its fluidity rapidly diminishes, and as it becomes more and more
burdened by the consolidated slag through which it has to force its way,
its velocity of motion diminishes in an almost inconceivable degree; and
at length, when it ceases to present the slightest external trace of
fluidity, its movement can only be ascertained by careful and repeated
observations, just as in the case of a glacier."[525]

It appears that the intensity of the light and heat of the lava varies
considerably at different periods of the same eruption, as in that of
Vesuvius in 1819 and 1820, when Sir H. Davy remarked different degrees
of vividness in the white heat at the point where the lava
originated.[526]

When the expressions "flame" and "smoke" are used in describing volcanic
appearances, they must generally be understood in a figurative sense. We
are informed, indeed, by M. Abich, that he distinctly saw, in the
eruption of Vesuvius in 1834, the flame of burning hydrogen;[527] but
what is usually mistaken for flame consists of vapor or scoriæ, and
impalpable dust illuminated by that vivid light which is emitted from
the crater below, where the lava is said to glow with the splendor of
the sun. The clouds of apparent smoke are formed either of aqueous and
other vapor, or of finely comminuted scoriæ.

_Dikes in the recent cone, how formed._--The inclined strata before
mentioned which dip outwards in all directions from the axis of the cone
of Vesuvius, are intersected by veins or dikes of compact lava, for the
most part in a vertical position. In 1828 these were seen to be about
seven in number, some of them not less than four or five hundred feet in
height, and thinning out before they reached the uppermost part of the
cone. Being harder than the beds through which they pass, they have
decomposed less rapidly, and therefore stand out in relief. When I
visited Vesuvius, in November, 1828, I was prevented from descending
into the crater by the constant ejections then thrown out; so that I got
sight of three only of the dikes; but Signor Monticelli had previously
had drawings made of the whole, which he showed me. The dikes which I
saw were on that side of the cone which is encircled by Somma. The
eruption before mentioned, of 1828, began in March, and in the November
following the ejected matter had filled up nearly one-third of the deep
abyss formed at the close of the eruption of 1822. In November I found a
single black cone at the bottom of the crater continually throwing out
scoriæ, while on the exterior of the cone I observed the lava of 1822,
which had flowed out six years before, not yet cool, and still evolving
much heat and vapor from crevices.

Hoffmann, in 1832, saw on the north side of Vesuvius, near the peak
called Palo, a great many parallel bands of lava, some from six to eight
feet thick, alternating with scoriæ and conglomerate. These beds, he
says, were cut through by many dikes, some of them five feet broad. They
resemble those of Somma, the stone being composed of grains of leucite
and augite.[528]

There can be no doubt that the dikes above mentioned have been produced
by the filling up of open fissures with liquid lava; but of the date of
their formation we know nothing farther than that they are all
subsequent to the year 79, and, relatively speaking, that they are more
modern than all the lavas and scoriæ which they intersect. A
considerable number of the upper strata are not traversed by them. That
the earthquakes, which almost invariably precede eruptions, occasion
rents in the mass, is well known; and, in 1822, three months before the
lava flowed out, open fissures, evolving hot vapors, were numerous. It
is clear that such rents must be ejected with melted matter when the
column of lava rises, so that the origin of the dikes is easily
explained, as also the great solidity and crystalline nature of the rock
composing them, which has been formed by lava cooling slowly under great
pressure.

It has been suggested that the frequent rending of volcanic cones during
eruptions may be connected with the gradual and successive upheaval of
the whole mass in such a manner as to increase the inclination of the
beds composing the cone; and in accordance with the hypothesis before
proposed for the origin of Monte Nuovo, Von Buch supposes that the
present cone of Vesuvius was formed in the year 79, not by eruption, but
by upheaval. It was not produced by the repeated superposition of scoriæ
and lava cast out or flowing from a central source, but by the uplifting
of strata previously horizontal. The entire cone rose at once, such as
we now see it, from the interior and middle of Somma, and has since
received no accession of height, but, on the contrary, has ever since
been diminishing in elevation.[529]

Although I consider this hypothesis of Von Buch to be quite untenable, I
may mention some facts which may at first sight seem to favor it. These
are recorded by M. Abich in his account of the Vesuvian eruptions of
1833 and 1834, a work illustrated by excellent engravings of the
volcanic phenomena which he witnessed.[530] It appears that, in the year
1834, the great crater of Vesuvius had been filled up nearly to the top
with lava, which had consolidated and formed a level and unbroken plain,
except that a small cone thrown up by the ejection of scoriæ rose in the
middle of it like an island in a lake. At length this plain of lava was
broken by a fissure which passed from N. E. to S. W., and along this
line a great number of minute cones emitting vapor were formed. The
first act of formation of these minor cones is said to have consisted of
a partial upheaval of beds of lava previously horizontal, and which had
been rendered flexible by the heat and tension of elastic fluids, which,
rising from below, escaped from the centre of each new monticule. There
would be considerable analogy between this mode of origin and that
ascribed by Von Buch to Vesuvius and Somma, if the dimensions of the
upraised masses were not on so different a scale, and if it was safe to
reason from the inflation of bladders of half-fused lava, from fifteen
to twenty-five feet in height, to mountains attaining an altitude of
several thousand feet, and having their component strata strengthened by
intersecting dikes of solid lava.

At the same time M. Abich mentions, that when, in August, 1834, a great
subsidence took place in the platform of lava within the great crater,
so that the structure of the central cone was laid open, it was seen to
have been evidently formed, _not by upheaval_, but by the fall of
cinders and scoriæ which had been thrown out during successive
eruptions.[531]

Previous to the year 79, Vesuvius appears, from the description of its
figure given by Strabo, to have been a truncated cone, having a level
and even outline as seen from a distance. That it had a crater on its
summit, we may infer from a passage in Plutarch, on which Dr. Daubeny
has judiciously commented in his treatise on volcanoes.[532] The walls
of the crater were evidently entire, except on one side, where there was
a single narrow breach. When Spartacus, in the year 72, encamped his
gladiators in this hollow, Clodius, the prætor, besieged him there,
keeping the single outlet carefully guarded, and then let down his
soldiers by scaling-ladders over the steep precipices which surrounded
the crater, at the bottom of which the insurgents were encamped. On the
side towards the sea, the walls of this original cavity, which must have
been three miles in diameter, have been destroyed, and Brieslak was the
first to announce the opinion, that this destruction happened during the
tremendous eruption which occurred in 79, when the new cone, now called
Vesuvius, was thrown up, which stands encircled on three sides by the
ruins of the ancient cone, called Monte Somma.

[Illustration: Fig. 45.

Supposed section of Vesuvius and Somma.

_a_, Monte Somma, or the remains of the ancient cone of Vesuvius.

_b_, The Pedamentina, a terrace-like projection, encircling the base of
the recent cone of Vesuvius on the south side.

_c_, Atrio del Cavallo.[533]

_d_, _e_, Crater left by eruption of 1822.

_f_, Small cone thrown up in 1828, at the bottom of the great crater.

_g_, _g_, Dikes intersecting Somma.

_h_, _h_, Dikes intersecting the recent cone of Vesuvius.]

In the annexed diagram (fig. 45) it will be seen that on the side of
Vesuvius opposite to that where a portion of the ancient cone of Somma
(_a_) still remains, is a projection (_b_) called the Pedamentina, which
some have supposed to be part of the circumference of the ancient crater
broken down towards the sea, and over the edge of which the lavas of the
modern Vesuvius have poured; the axis of the present cone of Vesuvius
being, according to Visconti, precisely equidistant from the escarpment
of Somma and the Pedamentina.

In the same diagram I have represented the slanting beds of the cone of
Vesuvius as becoming horizontal in the Atrio del Cavallo (at _c_), where
the base of the new cone meets the precipitous escarpment of Somma; for
when the lava flows down to this point, as happened in 1822, its
descending course is arrested, and it then runs in another direction
along this small valley, circling round the base of the cone. Sand and
scoriæ, also, blown by the winds, collect at the base of the cone, and
are then swept away by torrents; so that there is always here a flatish
plain, as represented. In the same manner, the small interior cone
(_f_) must be composed of sloping beds, terminating in a horizontal
plain; for, while this monticule was gradually gaining height by
successive ejections of lava and scoriæ, in 1828, it was always
surrounded by a flat pool of semi-fluid lava, into which scoriæ and sand
were thrown.

In the steep simicircular escarpment of Somma, which faces the modern
Vesuvius, we see a great number of sheets of lava inclined at an angle
of about 26°. They alternate with scoriæ, and are intersected by
numerous dikes, which, like the sheets of lava, are composed chiefly of
augite, with crystals of leucite, but the rock in the dikes is more
compact, having cooled and consolidated under greater pressure. Some of
the dikes cut through and shift others, so that they have evidently been
formed during successive eruptions. While the higher region of Somma is
made up of these igneous products, there appear on its flanks, for some
depth from the surface, as seen in a ravine called the "Fossa Grande,"
beds of white pumiceous tuff, resembling the tuff which, at Pausilippo,
and other places, near Naples, contain shells of living Mediterranean
species. It is supposed by Pilla, Von Buch, and others, that the
tufaceous beds, which rise in Somma to more than half the height of that
mountain, are, in like manner, of submarine origin, because a few
sea-shells have been found in them, here and there, together with
serpulæ of recent species attached to included blocks of limestone.[534]

It is contended, therefore, that as these strata were once accumulated
beneath the sea, they may have been subjected as they rose to such an
upward movement as may have given rise to a conical hill; and this
hypothesis, it is said, acquires confirmation from the fact, that the
sheets of lava near the summit of Somma are so compact and crystalline,
and of such breadth individually, as would not have been the case had
they run down a steep slope. They must, therefore, have consolidated on
a nearly level surface, and have been subsequently uplifted into their
present inclined position.

Unfortunately there are no sections of sufficient depth and continuity
on the flanks of Somma, to reveal to us clearly the relations of the
lava, scoriæ, and associated dikes, forming the highest part of the
mountain, with the marine tuffs observed on its declivity. Both may,
perhaps, have been produced contemporaneously when Somma raised its
head, like Stromboli, above the sea, its sides and base being then
submerged. Such a state of things may be indicated by a fact noticed by
Von Buch, namely, that the pumiceous beds of Naples, when they approach
Somma, contain fragments of the peculiar leucitic lava proper to that
mountain, which are not found in the same tuff at a greater
distance.[535] Portions, therefore, of this lava were either thrown out
by explosions, or torn off by the waves, during the deposition of the
pumiceous strata beneath the sea.

We have as yet but a scanty acquaintance with the laws which regulate
the flow of lava beneath water, or the arrangement of scoriæ and
volcanic dust on the sides of a submarine cone. There can, however, be
little doubt that showers of ejected matter may settle on a steep slope,
and may include shells and the remains of aquatic animals, which
flourish in the intervals between eruptions. Lava under the pressure of
water would be less porous; but, as Dr. Daubeny suggests, it may retain
its fluidity longer than in the open air; for the rapidity with which
heated bodies are cooled by being plunged into water arises chiefly from
the conversion of the lower portions of water into steam, which steam
absorbing much heat, immediately ascends, and is reconverted into water.
But under the pressure of a deep ocean, the heat of the lava would be
carried off more slowly, and only by the circulation of ascending and
descending currents of water, those portions nearest the source of heat
becoming specifically light, and consequently displacing the water
above. This kind of circulation would take place with much less rapidity
than in the atmosphere, inasmuch as the expansion of water by equal
increments of heat is less considerable than that of air.[536]

We learn from the valuable observations made by Mr. Dana on the active
volcanoes of the Sandwich Islands, that large sheets of compact basaltic
lava have been poured out of craters at the top or near the summits of
flattened domes higher than Etna, as in the case of Mount Loa for
example, where a copious stream two miles broad and twenty-five miles
long proceeded from an opening 13,000 feet above the level of the sea.
The usual slope of these sheets of lava is between 5° and 10°; but Mr.
Dana convinced himself that, owing to the suddenness with which they
cool in the air, some lavas may occasionally form on slopes equalling
25°, and still preserve a considerable compactness of texture. It is
even proved, he says, from what he saw in the great lateral crater of
Kilauea, on the flanks of Mount Loa, that a mass of such melted rock may
consolidate at an inclination of 30°, and be continuous for 300 or 400
feet. Such masses are narrow, he admits, "but if the source had been
more generous, they would have had a greater breadth, and by a
succession of ejections overspreading each cooled layer, a considerable
thickness might have been attained."[537] The same author has also
shown, as before mentioned, that in the "cinder cones" of the Sandwich
Islands, the strata have an original inclination of between 35° and
40°.[538]

Mr. Scrope, writing in 1827, attributed the formation of a volcanic cone
chiefly to matter ejected from a central orifice, but partly to the
injection of lava into dikes, and "to that force of gaseous expansion,
the intensity of which, in the central parts of the cone, is attested
by local earthquakes, which so often accompany eruptions.[539] It is the
opinion of MM. Von Buch, De Beaumont, and Dufrénoy, that the sheets of
lava on Somma are so uniform and compact, that their original
inclination did not exceed four or five degrees, and that four-fifths,
therefore, of their present slope is due to their having been
subsequently tilted and upraised. Notwithstanding the light thrown by M.
de Beaumont on the laws regulating the flow and consolidation of lava, I
do not conceive that these laws are as yet sufficiently determined to
warrant us in assigning so much of the inclined position of the beds of
Somma to the subsequent rending and dislocation of the cone. Even if
this were admitted, it is far more in harmony with the usual mode of
development of volcanic forces to suppose the movement which modified
the shape of the cone to have been intermittent and gradual, and not to
have consisted of a single effort, or one sudden and violent
convulsion.[540]

_Vesuvian lavas._--The lavas of Somma are characterized by containing
disseminated crystals of leucite (called, by the French, amphigène), a
mineral said to be very rare in the modern lavas of Vesuvius, which are
in general much more scoriaceous and less crystalline than those of
Somma.[541]

At the fortress near Torre del Greco a section is exposed, fifteen feet
in height, of a current which ran into the sea; and it evinces,
especially in the lower part, a decided tendency to divide into rude
columns. A still more striking example may be seen to the west of Torre
del Annunziata, near Forte Scassato, where the mass is laid open to the
depth of twenty feet. In both these cases, however, the rock may rather
be said to be divided into numerous perpendicular fissures, than to be
prismatic, although the same picturesque effect is produced. In the
lava-currents of Central France (those of the Vivarais, in particular),
the uppermost portion, often forty feet or more in thickness, is an
amorphous mass passing downwards into lava irregularly prismatic; and
under this there is a foundation of regular and vertical columns; but
these lavas are often one hundred feet or more in thickness. We can
scarcely expect to discover the same phenomenon in the shallow currents
of Vesuvius, where the lowest part has cooled more rapidly, although it
may be looked for in modern streams in Iceland, which exceed even those
of ancient France in volume.

Mr. Scrope mentions that, in the cliffs encircling the modern crater of
Vesuvius, he saw many currents offering a columnar division, and some
almost as regularly prismatic as any ranges of the older basalts; and he
adds, that in some the spheroidal concretionary structure, on a large
scale, was equally conspicuous.[542] Brieslak[543] also informs us that,
in the siliceous lava of 1737, which contains augite, leucite, and
crystals of felspar, he found very regular prisms in a quarry near Torre
del Greco; an observation confirmed by modern authorities.[544]

_Effects of decomposition on lavas._--The decomposition of some of the
felspathic lavas, either by simple weathering, or by gaseous emanations,
converts them from a hard to a soft clayey state, so that they no longer
retain the smallest resemblance to rocks cooled down from a state of
fusion. The exhalations of sulphuretted hydrogen and muriatic acid,
which are disengaged continually from the Solfatara, also produce
curious changes on the trachyte of that nearly extinct volcano: the rock
is bleached, and becomes porous, fissile, and honey-combed, till at
length it crumbles into a white siliceous powder.[545] Numerous globular
concretions, composed of concentric laminæ, are also formed by the same
vapors in this decomposed rock.[546]

_Vesuvian minerals._--A great variety of minerals are found in the lavas
of Vesuvius and Somma; augite, leucite, felspar, mica, olivine, and
sulphur are most abundant. It is an extraordinary fact, that in an area
of three square miles round Vesuvius, a greater number of simple
minerals have been found than in any spot of the same dimensions on the
surface of the globe. Häuy enumerated only 380 species of simple
minerals as known to him; and no less than eighty-two had been found on
Vesuvius and in the tuffs on the flanks of Somma before the end of the
year 1828.[547] Many of these are peculiar to that locality. Some
mineralogists have conjectured that the greater part of these were not
of Vesuvian origin, but thrown up in fragments from some older
formation, through which the gaseous explosions burst. But none of the
older rocks in Italy, or elsewhere, contain such an assemblage of
mineral products; and the hypothesis seems to have been prompted by a
disinclination to admit that, in times so recent in the earth's history,
the laboratory of nature could have been so prolific in the creation of
new and rare compounds. Had Vesuvius been a volcano of high antiquity,
formed when nature


  Wanton'd as in her prime, and play'd at will
  Her virgin fancies,


it would have been readily admitted that these, or a much greater
variety of substances, had been sublimed in the crevices of lava, just
as several new earthy and metallic compounds are known to have been
produced by fumeroles, since the eruption of 1822.

_Mass enveloping Herculaneum and Pompeii._--In addition to the ejections
which fall on the cone, and that much greater mass which finds its way
gradually to the neighboring sea, there is a third portion, often of no
inconsiderable thickness, composed of alluviums, spread over the valleys
and plains at small distances from the volcano. Aqueous vapors are
evolved copiously from volcanic craters during eruptions, and often for
a long time subsequently to the discharge of scoriæ and lava: these
vapors are condensed in the cold atmosphere surrounding the high
volcanic peak, and heavy rains are thus caused. The floods thus
occasioned, sweep along the impalpable dust and light scoriæ, till a
current of mud is produced, which is called in Campania "lava d' acqua,"
and is often more dreaded than an igneous stream (lava di fuoco), from
the greater velocity with which it moves. So late as the 27th of
October, 1822, one of these alluviums descended the cone of Vesuvius,
and, after overspreading much cultivated soil, flowed suddenly into the
villages of St. Sebastian and Massa, where, filling the streets and
interior of some of the houses, it suffocated seven persons. It will,
therefore, happen very frequently that, towards the base of a volcanic
cone, alternations will be found of lava, alluvium, and showers of
ashes.

To which of these two latter divisions the mass enveloping Herculaneum
and Pompeii should be referred, has been a question of the keenest
controversy; but the discussion might have been shortened, if the
combatants had reflected that, whether volcanic sand and ashes were
conveyed to the towns by running water, or through the air, during an
eruption, the interior of buildings, so long as the roofs remain entire,
together with all underground vaults and cellars, could be filled only
by an alluvium. We learn from history, that a heavy shower of sand,
pumice, and lapilli, sufficiently great to render Pompeii and
Herculaneum uninhabitable, fell for eight successive days and nights in
the year 79, accompanied by violent rains.[548] We ought, therefore, to
find a very close resemblance between the strata covering these towns
and those composing the minor cones of the Phlegræan Fields, accumulated
rapidly, like Monte Nuovo, during a continued shower of ejected matter;
with this difference however, that the strata incumbent on the cities
would be horizontal, whereas those on the cones are highly inclined; and
that large angular fragments of rock, which are thrown out near the
vent, would be wanting at a distance where small lapilli only can be
found. Accordingly, with these exceptions, no identity can be more
perfect than the form, and distribution of the matter at the base of
Monte Nuovo, as laid open by the encroaching sea, and the appearance of
the beds superimposed on Pompeii. That city is covered with numerous
alternations of different horizontal beds of tuff and lapilli, for the
most part thin, and subdivided into very fine layers. I observed the
following section near the amphitheatre, in November, 1828--(descending
series):--


                                                           Feet Inches.

  1. Black sparkling sand from the eruption of 1822,
       containing minute regularly formed crystals of augite
       and tourmaline                                         0   2½

  2. Vegetable mould                                          3   0

  3. Brown incoherent tuff, full of _pisolitic globules_
       in layers, from half an inch to three inches in
       thickness                                              1   6

  4. Small scoriæ and white lapilli                           0   3

  5. Brown earthy tuff, with numerous pisolitic globules      0   9

  6. Brown earthy tuff, with lapilli divided into layers      4   0

  7. Layer of whitish lapilli                                 0   1

  8. Gray solid tuff                                          0   3

  9. Pumice and white lapilli                                 0   3
                                                             -------
                                                             10   3½
                                                             -------


Many of the ashes in these beds are vitrified, and harsh to the touch.
Crystals of leucite, both fresh and farinaceous, have been found
intermixed.[549] The depth of the bed of ashes above the houses is
variable, but seldom exceeds twelve or fourteen feet, and it is said
that the higher part of the amphitheatre always projected above the
surface; though if this were the case, it seems inexplicable that the
city should never have been discovered till the year 1750. It will be
observed in the above section that two of the brown, half-consolidated
tuffs are filled with small pisolitic globules. This circumstance is not
alluded to in the animated controversy which the Royal Academy of Naples
maintained with one of their members, Signor Lippi, as to the origin of
the strata incumbent on Pompeii. The mode of aggregation of these
globules has been fully explained by Mr. Scrope, who saw them formed in
great numbers in 1822, by rain falling during the eruption on fine
volcanic sand, and sometimes also produced like hail in the air, by the
mutual attraction of the minutest particles of fine damp sand. Their
occurrence, therefore, agrees remarkably well with the account of heavy
rain, and showers of sand and ashes recorded in history.[550]

Lippi entitled his work, "Fù il fuoco o l' acqua che sotterò Pompei ed
Ercolano?"[551] and he contended that neither were the two cities
destroyed in the year 79, nor by a volcanic eruption, but purely by the
agency of water charged with transported matter. His letters, wherein he
endeavored to dispense, as far as possible, with igneous agency, even at
the foot of the volcano, were dedicated, with great propriety, to
Werner, and afford an amusing illustration of the polemic style in which
geological writers of that day indulged themselves. His arguments were
partly of an historical nature, derived from the silence of contemporary
historians, respecting the fate of the cities, which, as we have already
stated, is most remarkable, and partly drawn from physical proofs. He
pointed out with great clearness the resemblance of the tufaceous matter
in the vaults and cellars at Herculaneum and Pompeii to aqueous
alluviums, and its distinctness from ejections which had fallen through
the air. Nothing, he observes, but moist pasty matter could have
received the impression of a woman's breast, which was found in a vault
at Pompeii, or have given the cast of a statue discovered in the
theatre at Herculaneum. It was objected to him, that the heat of the
tuff in Herculaneum and Pompeii was proved by the carbonization of the
timber, corn, papyrus-rolls, and other vegetable substances there
discovered; but Lippi replied with truth, that the papyri would have
been burnt up if they had come in contact with fire, and that their
being only carbonized was a clear demonstration of their having been
enveloped, like fossil wood, in a sediment deposited from water. The
Academicians, in their report on his pamphlet, assert, that when the
amphitheatre was first cleared out, the matter was arranged on the steps
in a succession of concave layers, accommodating themselves to the
interior form of the building, just as snow would lie if it had fallen
there. This observation is highly interesting, and points to the
difference between the stratification of ashes in an open building and
of mud derived from the same in the interior of edifices and cellars.
Nor ought we to call the allegation in question, because it could not be
substantiated at the time of the controversy after the matter had been
all removed; although Lippi took advantage of this removal, and met the
argument of his antagonists by requiring them to prove the fact. There
is decisive evidence that no stream of lava has ever reached Pompeii
since it was first built, although the foundations of the town stand
upon the old leucitic lava of Somma; several streams of which, with tuff
interposed, had been cut through in excavations.

_Infusorial beds covering Pompeii._--A most singular and unexpected
discovery has been recently made (1844-5) by Professor Ehrenberg,
respecting the remote origin of many of the layers of ashes and pumice
enveloping Pompeii. They are, he says, in great part, of organic and
freshwater origin, consisting of the siliceous cases of microscopic
infusoria. What is still more surprising, this fact proves to be by no
means an isolated or solitary example of an intimate relation between
organic life and the results of volcanic activity. On the Rhine, several
beds of tuff and pumiceous conglomerate, resembling the mass incumbent
upon Pompeii and closely connected with extinct volcanoes, are now
ascertained to be made up to a great extent of the siliceous cases of
infusoria (or Diatomaceæ), invisible to the naked eye, and often half
fused.[552] No less than 94 distinct species have already been detected
in one mass of this kind, more than 150 feet thick, at Hochsimmer, on
the left bank of the Rhine, near the Laacher-see. Some of these Rhenish
infusorial accumulations appear to have fallen in showers, others to
have been poured out of lake-craters in the form of mud, as in the Brohl
valley.

In Mexico, Peru, the Isle of France, and several other volcanic regions,
analogous phenomena have been observed, and everywhere the species of
infusoria belong to freshwater and terrestrial genera, except in the
case of the Patagonian pumiceous tuffs, specimens of which, brought
home by Mr. Darwin, are found to contain the remains of marine
animalcules. In various kinds of pumice ejected by volcanoes, the
microscope has revealed to Professor Ehrenberg the siliceous cases of
infusoria often half obliterated by the action of heat, and the fine
dust thrown out into the air during eruptions, is sometimes referable to
these most minute organic substances, brought up from considerable
depths, and sometimes mingled with small particles of vegetable matter.

In what manner did the solid coverings of these most minute plants and
animalcules, which can only originate and increase at the surface of the
earth, sink down and penetrate into subterranean cavities, so as to be
ejected from the volcanic orifices? We have of late years become
familiar with the fact, in the process of boring Artesian wells, that
the seeds of plants, the remains of insects, and even small fish, with
other organic bodies, are carried in an uninjured state by the
underground circulation of waters, to the depth of many hundred feet.
With still greater facility in a volcanic region we may conjecture, that
water and mud full of invisible infusoria may be sucked down, from time
to time, into subterranean rents and hollows in cavernous lava which has
been permeated by gases, or in rocks dislocated by earthquakes. It often
happens that a lake which has endured for centuries in a volcanic
crater, disappears suddenly on the approach of a new eruption. Violent
shocks agitate the surrounding region, and ponds, rivers, and wells are
dried up. Large cavities far below may thus become filled with fen-mud
chiefly composed of the more indestructible and siliceous portions of
infusoria, destined perhaps to be one day ejected in a fragmentary or
half-fused state, yet without the obliteration of all traces of organic
structure.[553]

_Herculaneum._--It was remarked that no lava has flowed over the site of
Pompeii, since that city was built, but with Herculaneum the case is
different. Although the substance which fills the interior of the houses
and the vaults must have been introduced in a state of mud, like that
found in similar situations in Pompeii; yet the superincumbent mass
differs wholly in composition and thickness. Herculaneum was situated
several miles nearer to the volcano, and has, therefore, been always
more exposed to be covered, not only by showers of ashes, but by
alluviums and streams of lava. Accordingly, masses of both have
accumulated on each other above the city, to a depth of nowhere less
than 70, and in many places of 112 feet.[554]

The tuff which envelops the buildings consists of comminuted volcanic
ashes, mixed with pumice. A mask imbedded in this matrix has left a
cast, the sharpness of which was compared by Hamilton to those in
plaster of Paris; nor was the mask in the least degree scorched, as if
it had been imbedded in heated matter. This tuff is porous; and, when
first excavated, is soft and easily worked, but acquires a considerable
degree of induration on exposure to the air. Above this lowest stratum
is placed, according to Hamilton, "the matter of six eruptions," each
separated from the other by veins of good soil. In these soils Lippi
states that he collected a considerable number of land shells--an
observation which is no doubt correct; for many snails burrow in soft
soils, and some Italian species descend, when they hybernate, to the
depth of five feet and more from the surface. Della Torre also informs
us that there is in one part of this superimposed mass a bed of true
siliceous lava (_lava di pietra dura_); and, as no such current is
believed to have flowed till near one thousand years after the
destruction of Herculaneum, we must conclude, that the origin of a large
part of the covering of Herculaneum was long subsequent to the first
inhumation of the place. That city, as well as Pompeii, was a seaport.
Herculaneum is still very near the shore, but a tract of land, a mile in
length, intervenes between the borders of the Bay of Naples and Pompeii.
In both cases the gain of land is due to the filling up of the bed of
the sea with volcanic matter, and not to elevation by earthquakes, for
there has been no change in the relative level of land and sea. Pompeii
stood on a slight eminence composed of the lavas of the ancient
Vesuvius, and flights of steps led down to the water's edge. The
lowermost of these steps are said to be still on an exact level with the
sea.

_Condition and contents of the buried cities._--After these observations
on the nature of the strata enveloping and surrounding the cities, we
may proceed to consider their internal condition and contents, so far at
least as they offer facts of geological interest. Notwithstanding the
much greater depth at which Herculaneum was buried, it was discovered
before Pompeii, by the accidental circumstance of a well being sunk, in
1713, which came right down upon the theatre, where the statues of
Hercules and Cleopatra were soon found. Whether this city or Pompeii,
both of them founded by Greek colonies, was the more considerable, is
not yet determined; but both are mentioned by ancient authors as among
the seven most flourishing cities in Campania. The walls of Pompeii were
three miles in circumference; but we have, as yet, no certain knowledge
of the dimensions of Herculaneum. In the latter place the theatre alone
is open for inspection; the Forum, Temple of Jupiter, and other
buildings, having been filled up with rubbish as the workmen proceeded,
owing to the difficulty of removing it from so great a depth below
ground. Even the theatre is only seen by torch-light, and the most
interesting information, perhaps, which the geologist obtains there, is
the continual formation of stalactite in the galleries cut through the
tuff; for there is a constant percolation of water charged with
carbonate of lime mixed with a small portion of magnesia. Such mineral
waters must, in the course of time, create great changes in many rocks;
especially in lavas, the pores of which they may fill with calcareous
spar, so as to convert them into amygdaloids. Some geologists,
therefore, are unreasonable when they expect that volcanic rocks of
remote eras should accord precisely with those of modern date; since it
is obvious that many of those produced in our own time will not long
retain the same aspect and internal composition.

Both at Herculaneum and Pompeii, temples have been found with
inscriptions commemorating the rebuilding of the edifices after they had
been thrown down by an earthquake.[555] This earthquake happened in the
reign of Nero, sixteen years before the cities were overwhelmed. In
Pompeii, one-fourth of which is now laid open to the day, both the
public and private buildings bear testimony to the catastrophe. The
walls are rent, and in many places traversed by fissures still open.
Columns are lying on the ground only half hewn from huge blocks of
travertin, and the temple for which they were designed is seen half
repaired. In some few places the pavement had sunk in, but in general it
was undisturbed, consisting of large irregular flags of lava joined
neatly together, in which the carriage wheels have often worn ruts an
inch and a half deep. In the wider streets, the ruts are numerous and
irregular; in the narrower, there are only two, one on each side, which
are very conspicuous. It is impossible not to look with some interest
even on these ruts, which were worn by chariot wheels more than
seventeen centuries ago; and, independently of their antiquity, it is
remarkable to see such deep incisions so continuous in a stone of great
hardness.

_Small number of skeletons._--A very small number of skeletons have been
discovered in either city; and it is clear that most of the inhabitants
not only found time to escape, but also to carry with them the principal
part of their valuable effects. In the barracks at Pompeii were the
skeletons of two soldiers chained to the stocks, and in the vaults of a
country-house in the suburbs were the skeletons of seventeen persons,
who appear to have fled there to escape from the shower of ashes. They
were found inclosed in an indurated tuff, and in this matrix was
preserved a perfect cast of a woman, perhaps the mistress of the house,
with an infant in her arms. Although her form was imprinted on the rock,
nothing but the bones remained. To these a chain of gold was suspended,
and on the fingers of the skeletons were rings with jewels. Against the
sides of the same vault was ranged a long line of earthen amphoræ.

The writings scribbled by the soldiers on the walls of their barracks,
and the names of the owners of each house written over the doors, are
still perfectly legible. The colors of fresco paintings on the stuccoed
walls in the interior of buildings are almost as vivid as if they were
just finished. There are public fountains decorated with shells laid out
in patterns in the same fashion as those now seen in the town of Naples;
and in the room of a painter, who was perhaps a naturalist, a large
collection of shells was found, comprising a great variety of
Mediterranean species, in as good a state of preservation as if they had
remained for the same number of years in a museum. A comparison of these
remains, with those found so generally in a fossil state would not
assist us in obtaining the least insight into the time required to
produce a certain degree of decomposition or mineralization; for,
although under favorable circumstances much greater alteration might
doubtless have been brought about in a shorter period, yet the example
before us shows that an inhumation of seventeen centuries may sometimes
effect nothing towards the reduction of shells to the state in which
fossils are usually found.

The wooden beams in the houses at Herculaneum are black on the exterior,
but, when cleft open, they appear to be almost in the state of ordinary
wood, and the progress made by the whole mass towards the state of
lignite is scarcely appreciable. Some animal and vegetable substances of
more perishable kinds have of course suffered much change and decay, yet
the state of preservation of these is truly remarkable. Fishing-nets are
very abundant in both cities, often quite entire; and their number at
Pompeii is the more interesting from the sea being now, as we stated, a
mile distant. Linen has been found at Herculaneum, with the texture well
defined; and in a fruiterer's shop in that city were discovered vessels
full of almonds, chestnuts, walnuts, and fruit of the "carubiere," all
distinctly recognizable from their shape. A loaf, also, still retaining
its form, was found in a baker's shop, with his name stamped upon it. On
the counter of an apothecary was a box of pills converted into a fine
earthy substance; and by the side of it a small cylindrical roll
evidently prepared to be cut into pills. By the side of these was a jar
containing medicinal herbs. In 1827, moist olives were found in a square
glass-case, and "caviare," or roe of a fish, in a state of wonderful
preservation. An examination of these curious condiments has been
published by Covelli of Naples, and they are preserved hermetically
sealed in the museum there.[556]

_Papyri._--There is a marked difference in the condition and appearance
of the animal and vegetable substances found at Pompeii and Herculaneum;
those of Pompeii being penetrated by a gray pulverulent tuff, those in
Herculaneum seeming to have been first enveloped by a paste which
consolidated round them, and then allowed them to become slowly
carbonized. Some of the rolls of papyrus at Pompeii still retain their
form; but the writing, and indeed almost all the vegetable matter,
appear to have vanished, and to have been replaced by volcanic tuff
somewhat pulverulent. At Herculaneum the earthy matter has scarcely ever
penetrated; and the vegetable substance of the papyrus has become a thin
friable black matter, almost resembling in appearance the tinder which
remains when stiff paper has been burnt, in which the letters may still
be sometimes traced. The small bundles of papyri, composed of five or
six rolls tied up together, had sometimes lain horizontally, and were
pressed in that direction, but sometimes they had been placed in a
vertical position. Small tickets were attached to each bundle, on which
the title of the work was inscribed. In one case only have the sheets
been found with writing on both sides of the pages. So numerous are the
obliterations and corrections, that many must have been original
manuscripts. The variety of handwritings is quite extraordinary: nearly
all are written in Greek, but there are a few in Latin. They were almost
all found in a suburban villa in the library of one private individual;
and the titles of four hundred of those least injured, which have been
read, are found to be unimportant works, but all entirely new, chiefly
relating to music, rhetoric, and cookery. There are two volumes of
Epicurus "On Nature," and the others are mostly by writers of the same
school, only one fragment having been discovered, by an opponent of the
Epicurean system, Chrysippus.[557]

_Probability of future discoveries of MSS._--In the opinion of some
antiquaries, not one-hundredth part of the city has yet been explored:
and the quarters hitherto cleared out at a great expense, are those
where there was the least probability of discovering manuscripts. As
Italy could already boast her splendid Roman amphitheatres and Greek
temples, it was a matter of secondary interest to add to their number
those in the dark and dripping galleries of Herculaneum; and having so
many of the masterpieces of ancient art, we could have dispensed with
the inferior busts and statues which could alone have been expected to
reward our researches in the ruins of a provincial town. But from the
moment that it was ascertained that rolls of papyrus preserved in this
city could still be deciphered, every exertion ought to have been
steadily and exclusively directed towards the discovery of other
libraries. Private dwellings should have been searched, before so much
labor and expense were consumed in examining public edifices. A small
portion of that zeal and enlightened spirit which prompted the late
French and Tuscan expedition to Egypt might long ere this, in a country
nearer home, have snatched from oblivion some of the lost works of the
Augustan age, or of eminent Greek historians and philosophers. A single
roll of papyrus might have disclosed more matter of intense interest
than all that was ever written in hieroglyphics.

_Stabiæ._--Besides the cities already mentioned, Stabiæ, a small town
about six miles from Vesuvius, and near the site of the modern
Castel-a-Mare (see map of volcanic district of Naples), was overwhelmed
during the eruption of 79. Pliny mentions that, when his uncle was
there, he was obliged to make his escape, so great was the quantity of
falling stones and ashes. In the ruins of this place, a few skeletons
have been found buried in volcanic ejections, together with some
antiquities of no great value, and rolls of papyrus, which, like those
of Pompeii, were illegible.

_Torre del Greco overflowed by lava._--Of the towns hitherto mentioned,
Herculaneum alone has been overflowed by a stream of melted matter; but
this did not, as we have seen, enter or injure the buildings, which were
previously enveloped or covered over with tuff. But burning torrents
have often taken their course through the streets of Torre del Greco,
and consumed or inclosed a large portion of the town in solid rock. It
seems probable that the destruction of three thousand of its inhabitants
in 1631, which some accounts attribute to boiling water, was principally
due to one of those alluvial floods which we before mentioned: but, in
1737, the lava itself flowed through the eastern side of the town, and
afterwards reached the sea; and, in 1794, another current, rolling over
the western side, filled the streets and houses, and killed more than
four hundred persons. The main street is now quarried through this lava,
which supplied building stones for new houses erected where others had
been annihilated. The church was half buried in a rocky mass, but the
upper portion served as the foundation of a new edifice.

The number of the population at present is estimated at fifteen
thousand; and a satisfactory answer may readily be returned to those who
inquire how the inhabitants can be so "inattentive to the voice of time
and the warnings of nature,"[558] as to rebuild their dwellings on a
spot so often devastated. No neighboring site unoccupied by a town, or
which would not be equally insecure, combines the same advantages of
proximity to the capital, to the sea, and to the rich lands on the
flanks of Vesuvius. If the present population were exiled, they would
immediately be replaced by another, for the same reason that the Maremma
of Tuscany and the Campagna di Roma will never be depopulated, although
the malaria fever commits more havoc in a few years than the Vesuvian
lavas in as many centuries. The district around Naples supplies one
amongst innumerable examples, that those regions where the surface is
most frequently renewed, and where the renovation is accompanied, at
different intervals of time, by partial destruction of animal and
vegetable life, may nevertheless be amongst the most habitable and
delightful on our globe.

I have already made a similar remark when speaking of tracts where
aqueous causes are now most active; and the observation applies as well
to parts of the surface which are the abode of aquatic animals, as to
those which support terrestrial species. The sloping sides of Vesuvius
give nourishment to a vigorous and healthy population of about eighty
thousand souls; and the surrounding hills and plains, together with
several of the adjoining isles, owe the fertility of their soil to
matter ejected by prior eruptions. Had the fundamental limestone of the
Apennines remained uncovered throughout the whole area, the country
could not have sustained a twentieth part of its present inhabitants.
This will be apparent to every geologist who has marked the change in
the agricultural character of the soil the moment he has passed the
utmost boundary of the volcanic ejections, as when, for example, at the
distance of about seven miles from Vesuvius, he leaves the plain and
ascends the declivity of the Sorrentine Hills.

Yet, favored as this region has been by Nature from time immemorial, the
signs of the changes imprinted on it during the period that it has
served as the habitation of man may appear in after-ages to indicate a
series of unparalleled disasters. Let us suppose that at some future
time the Mediterranean should form a gulf of the great ocean, and that
the waves and tidal current should encroach on the shores of Campania,
as it now advances upon the eastern coast of England; the geologist will
then behold the towns already buried, and many more which will evidently
be entombed hereafter, laid open in the steep cliffs, where he will
discover buildings superimposed above each other, with thick intervening
strata of tuff or lava--some unscathed by fire, like those of
Herculaneum and Pompeii; others half melted down, as in Torre del Greco;
and many shattered and thrown about in strange confusion, as in
Tripergola, beneath Monte Nuovo. Among the ruins will be seen skeletons
of men, and impressions of the human form stamped in solid rocks of
tuff. Nor will the signs of earthquakes be wanting. The pavement of part
of the Domitian Way, and the temple of the Nymphs, submerged at high
tide, will be uncovered at low water, the columns remaining erect and
uninjured. Other temples which had once sunk down, like that of Serapis,
will be found to have been upraised again by subsequent movements. If
they who study these phenomena, and speculate on their causes, assume
that there were periods when the laws of Nature or the whole course of
natural events differed greatly from those observed in their own time,
they will scarcely hesitate to refer the wonderful monuments in question
to those primeval ages. When they consider the numerous proofs of
reiterated catastrophes to which the region was subject, they may,
perhaps, commiserate the unhappy fate of beings condemned to inhabit a
planet during its nascent and chaotic state, and feel grateful that
their favored race has escaped such scenes of anarchy and misrule.

Yet what was the real condition of Campania during those years of dire
convulsion? "A climate where heaven's breath smells sweet and
wooingly--a vigorous and luxuriant nature unparalleled in its
productions--a coast which was once the fairy-land of poets, and the
favorite retreat of great men. Even the tyrants of the creation loved
this alluring region, spared it, adorned it, lived in it, died in
it."[559] The inhabitants, indeed, have enjoyed no immunity from the
calamities which are the lot of mankind; but the principal evils which
they have suffered must be attributed to moral, not to physical,
causes--to disastrous events over which man might have exercised a
control, rather than to the inevitable catastrophes which result from
subterranean agency. When Spartacus encamped his army of ten thousand
gladiators in the old extinct crater of Vesuvius, the volcano was more
justly a subject of terror to Campania, than it has ever been since the
rekindling of its fires.




CHAPTER XXV.

ETNA.


  External physiognomy of Etna--Lateral cones--Their successive
    obliteration--Early eruptions--Monti Rossi in 1669--Towns overflowed
    by lava--Part of Catania overflowed--Mode of advance of a current of
    lava--Subterranean caverns--Marine strata at base of Etna--Val del
    Bove not an ancient crater--Its scenery--Form, composition, and
    origin of the dikes--Linear direction of cones formed in 1811 and
    1819--Lavas and breccias--Flood produced by the melting of snow by
    lava--Glacier covered by a lava stream--Val del Bove how
    formed--Structure and origin of the cone of Etna--Whether the
    inclined sheets of lava were originally horizontal--Antiquity of
    Etna--Whether signs of diluvial waves are observable on Etna.


_External physiognomy of Etna._--After Vesuvius, our most authentic
records relate to Etna, which rises near the sea in solitary grandeur to
the height of nearly eleven thousand feet.[560] The base of the cone is
almost circular, and eighty-seven English miles in circumference; but if
we include the whole district over which its lavas extend, the circuit
is probably twice that extent.

_Divided into three regions._--The cone is divided by nature into three
distinct zones, called the _fertile_, the _woody_, and the _desert_
regions. The first of these, comprising the delightful country around
the skirts of the mountain, is well cultivated, thickly inhabited, and
covered with olives, vines, corn, fruit-trees, and aromatic herbs.
Higher up, the woody region encircles the mountain--an extensive forest
six or seven miles in width, affording pasturage for numerous flocks.
The trees are of various species, the chestnut, oak, and pine being most
luxuriant; while in some tracts are groves of cork and beech. Above the
forest is the desert region, a waste of black lava and scoriæ; where, on
a kind of plain, rises a cone of eruption to the height of about eleven
hundred feet, from which sulphureous vapors are continually evolved.

_Cones produced by lateral eruption._--The most grand and original
feature in the physiognomy of Etna is the multitude of minor cones which
are distributed over its flanks, and which are most abundant in the
woody region. These, although they appear but trifling irregularities
when viewed from a distance as subordinate parts of so imposing and
colossal a mountain, would, nevertheless, be deemed hills of
considerable altitude in almost any other region. Without enumerating
numerous monticules of ashes thrown out at different points, there are
about eighty of these secondary volcanoes, of considerable dimensions;
fifty-two on the west and north, and twenty-seven on the east side of
Etna. One of the largest, called Monte Minardo, near Bronte, is upwards
of 700 feet in height, and a double hill near Nicolosi, called Monti
Rossi, formed in 1669, is 450 feet high, and the base two miles in
circumference; so that it somewhat exceeds in size Monte Nuovo, before
described. Yet it ranks only as a cone of the second magnitude amongst
those produced by the lateral eruptions of Etna. On looking down from
the lower borders of the desert region, these volcanoes present us with
one of the most delightful and characteristic scenes in Europe. They
afford every variety of height and size, and are arranged in beautiful
and picturesque groups. However uniform they may appear when seen from
the sea, or the plains below, nothing can be more diversified than their
shape when we look from above into their craters, one side of which is
generally broken down. There are, indeed, few objects in nature more
picturesque than a wooded volcanic crater. The cones situated in the
higher parts of the forest zone are chiefly clothed with lofty pines;
while those at a lower elevation are adorned with chestnuts, oaks,
beech, and holm.

_Successive obliteration of these cones._--The history of the eruptions
of Etna, imperfect and interrupted as it is, affords us, nevertheless,
much insight into the manner in which the whole mountain has
successively attained its present magnitude and internal structure. The
principal cone has more than once fallen in and been reproduced. In 1444
it was 320 feet high, and fell in after the earthquakes of 1537. In the
year 1693, when a violent earthquake shook the whole of Sicily, and
killed sixty thousand persons, the cone lost so much of its height, says
Boccone, that it could not be seen from several places in Valdemone,
from which it was before visible. The greater number of eruptions happen
either from the great crater, or from lateral openings in the desert
region. When hills are thrown up in the middle zone, and project beyond
the general level, they gradually lose their height during subsequent
eruptions; for when lava runs down from the upper parts of the mountain,
and encounters any of these hills, the stream is divided, and flows
round them so as to elevate the gently sloping grounds from which they
rise. In this manner a deduction is often made at once of twenty or
thirty feet, or even more, from their height. Thus, one of the minor
cones, called Monte Peluso, was diminished in altitude by a great lava
stream which encircled it in 1444; and another current has recently
taken the same course--yet this hill still remains four or five hundred
feet high.

There is a cone called Monte Nucilla near Nicolosi, round the base of
which several successive currents have flowed, and showers of ashes have
fallen, since the time of history, till at last, during an eruption in
1536, the surrounding plain was so raised, that the top of the cone
alone was left projecting above the general level. Monte Nero, situated
above the Grotta dell' Capre, was in 1766 almost submerged by a current:
and Monte Capreolo afforded, in the year 1669, a curious example of one
of the last stages of obliteration; for a lava stream, descending on a
high ridge which had been built up by the continued superposition of
successive lavas, flowed directly into the crater, and nearly filled it.
The lava, therefore, of each new lateral cone tends to detract from the
relative height of lower cones above their base: so that the flanks of
Etna, sloping with a gentle inclination, envelop in succession a great
multitude of minor volcanoes, while new ones spring up from time to
time.

_Early eruptions of Etna._--Etna appears to have been in activity from
the earliest times of tradition; for Diodorus Siculus mentions an
eruption which caused a district to be deserted by the Sicani before the
Trojan war. Thucydides informs us, that in the sixth year of the
Peloponnesian war, or in the spring of the year 425 B. C., a lava stream
ravaged the environs of Catania, and this he says was the third eruption
which had happened in Sicily since the colonization of that island by
the Greeks.[561] The second of the three eruptions alluded to by the
historian took place in the year 475 B. C., and was that so poetically
described by Pindar, two years afterwards, in his first Pythian ode:--

              κιον
  Δ' ουρανια συνεχει
  Νιφοεσς' Αιτνα, πανετες
  Χιονος οξειας τιθηνα.

In these and the seven verses which follow, a graphic description is
given of Etna, such as it appeared five centuries before the Christian
era, and such as it has been seen when in eruption in modern times. The
poet is only making a passing allusion to the Sicilian volcano, as the
mountain under which Typhoeus lay buried, yet by a few touches of his
master-hand every striking feature of the scene has been faithfully
portrayed. We are told of "the snowy Etna, the pillar of heaven--the
nurse of everlasting frost, in whose deep caverns lie concealed the
fountains of unapproachable fire--a stream of eddying smoke by day--a
bright and ruddy flame by night; and burning rocks rolled down with loud
uproar into the sea."

[Illustration: Fig. 46.

Minor cones on the flanks of Etna.

1. Monti Rossi, near Nicolosi, formed in 1669. 2. Vampeluso?[562]]

_Eruption of 1669--Monti Rossi formed._--The great eruption which
happened in the year 1669 is the first which claims particular
attention. An earthquake had levelled to the ground all the houses in
Nicolosi, a town situated near the lower margin of the woody region,
about twenty miles from the summit of Etna, and ten from the sea at
Catania. Two gulfs then opened near that town, from whence sand and
scoriæ were thrown up in such quantity, that in the course of three or
four months a double cone was formed, called Monti Rossi, about 450 feet
high. But the most extraordinary phenomenon occurred at the commencement
of the convulsion in the plain of S. Lio. A fissure six feet broad, and
of unknown depth, opened with a loud crash, and ran in a somewhat
tortuous course to within a mile of the summit of Etna. Its direction
was from north to south, and its length twelve miles. It emitted a most
vivid light. Five other parallel fissures of considerable length
afterwards opened, one after the other, and emitted smoke, and gave out
bellowing sounds which were heard at the distance of forty miles. This
case seems to present the geologist with an illustration of the manner
in which those continuous dikes of vertical porphyry were formed, which
are seen to traverse some of the older lavas of Etna; for the light
emitted from the great rent of S. Lio appears to indicate that the
fissure was filled to a certain height with incandescent lava, probably
to the height of an orifice not far distant from Monti Rossi, which at
that time opened and poured out a lava current. When the melted matter
in such a rent has cooled, it must become a solid wall or dike,
intersecting the older rocks of which the mountain is composed; similar
rents have been observed during subsequent eruptions, as in 1832, when
they ran in all directions from the centre of the volcano. It has been
justly remarked by M. Elie de Beaumont, that such star-shaped fractures
may indicate a slight upheaval of the whole of Etna. They may be the
signs of the stretching of the mass, which may thus be raised gradually
by a force from below.[563]

The lava current of 1669, before alluded to, soon reached in its course
a minor cone called Mompiliere, at the base of which it entered a
subterranean grotto, communicating with a suite of those caverns which
are so common in the lavas of Etna. Here it appears to have melted down
some of the vaulted foundations of the hill, so that the whole of that
cone became slightly depressed and traversed by numerous open fissures.

_Part of Catania destroyed._--The lava, after overflowing fourteen towns
and villages, some having a population of between three and four
thousand inhabitants, arrived at length at the walls of Catania. These
had been purposely raised to protect the city; but the burning flood
accumulated till it rose to the top of the rampart, which was sixty feet
in height, and then it fell in a fiery cascade and overwhelmed part of
the city. The wall, however, was not thrown down, but was discovered
long afterwards by excavations made in the rock by the Prince of
Biscari; so that the traveller may now see the solid lava curling over
the top of the rampart as if still in the very act of falling.

This great current performed the first thirteen miles of its course in
twenty days, or at the rate of 162 feet per hour, but required
twenty-three days for the last two miles, giving a velocity of only
twenty-two feet per hour; and we learn from Dolomieu that the stream
moved during part of its course at the rate of 1500 feet an hour, and in
others it took several days to cover a few yards.[564] When it entered
the sea it was still six hundred yards broad, and forty feet deep. It
covered some territories in the environs of Catania which had never
before been visited by the lavas of Etna. While moving on, its surface
was in general a mass of solid rock; and its mode of advancing, as is
usual with lava streams, was by the occasional fissuring of the solid
walls. A gentleman of Catania, named Pappalardo, desiring to secure the
city from the approach of the threatening torrent, went out with a party
of fifty men whom he had dressed in skins to protect them from the heat,
and armed with iron crows and hooks. They broke open one of the solid
walls which flanked the current near Belpasso, and immediately forth
issued a rivulet of melted matter which took the direction of Paternó;
but the inhabitants of that town, being alarmed for their safety, took
up arms and put a stop to farther operations.[565]

As another illustration of the solidity of the walls of an advancing
lava stream, I may mention an adventure related by Recupero, who, in
1766, had ascended a small hill formed of ancient volcanic matter, to
behold the slow and gradual approach of a fiery current, two miles and a
half broad; when suddenly two small threads of liquid matter issuing
from a crevice detached themselves from the main stream, and ran rapidly
towards the hill. He and his guide had just time to escape, when they
saw the hill, which was fifty feet in height, surrounded, and in a
quarter of an hour melted down into the burning mass, so as to flow on
with it.

But it must not be supposed that this complete fusion of rocky matter
coming in contact with lava is of universal, or even common, occurrence.
It probably happens when fresh portions of incandescent matter come
successively in contact with fusible materials. In many of the dikes
which intersect the tuffs and lavas of Etna, there is scarcely any
perceptible alteration effected by heat on the edges of the horizontal
beds, in contact with the vertical and more crystalline mass. On the
side of Mompiliere, one of the towns overflowed in the great eruption
above described, an excavation was made in 1704; and by immense labor
the workmen reached, at the depth of thirty-five feet, the gate of the
principal church, where there were three statues, held in high
veneration. One of these, together with a bell, some money, and other
articles, were extracted in a good state of preservation from beneath a
great arch formed by the lava. It seems very extraordinary that any
works of art, not encased with tuff, like those in Herculaneum, should
have escaped fusion in hollow spaces left open in this lava-current,
which was so hot at Catania eight years after it entered the town, that
it was impossible to hold the hand in some of the crevices.

_Subterranean caverns on Etna._--Mention was made of the entrance of a
lava-stream into a subterranean grotto, whereby the foundations of a
hill were partially undermined. Such underground passages are among the
most curious features on Etna, and appear to have been produced by the
hardening of the lava, during the escape of great volumes of elastic
fluids, which are often discharged for many days in succession, after
the crisis of the eruption is over. Near Nicolosi, not far from Monti
Rossi, one of these great openings may be seen, called the Fossa della
Palomba, 625 feet in circumference at its mouth, and seventy-eight deep.
After reaching the bottom of this, we enter another dark cavity, and
then others in succession, sometimes descending precipices by means of
ladders. At length the vaults terminate in a great gallery ninety feet
long, and from fifteen to fifty broad, beyond which there is still a
passage, never yet explored; so that the extent of these caverns remains
unknown.[566] The walls and roofs of these great vaults are composed of
rough and bristling scoriæ, of the most fantastic forms.

_Marine strata at base of Etna._--If we skirt the fertile region at the
base of Etna on its southern and eastern sides, we behold marine strata
of clay sand, and volcanic tuff, cropping out from beneath the modern
lavas. The marine fossil shells occurring in these strata are all of
them, or nearly all, identical with species now inhabiting the
Mediterranean; and as they appear at the height of from 600 to 800 feet
above the sea near Catania, they clearly prove that there has been in
this region, as in other parts of Sicily farther to the south, an upward
movement of the ancient bed of the sea. It is fair, therefore, to infer
that the whole mountain, with the exception of those parts which are of
very modern origin, has participated in this upheaval.

If we view Etna from the south, we see the marine deposits above alluded
to, forming a low line of hills (_e_, _e_, Fig. 47), or a steep inland
slope or cliff (_f_), as in the annexed drawing taken from the limestone
platform of Primosole. It should be observed however, in reference to
this view, that the height of the volcanic cone is ten times greater
than the hills at its base (_e_, _e_), although it appears less
elevated, because the summit of the cone is ten or twelve times more
distant from the plain of Catania than is Licodia.

[Illustration: Fig. 47.

View of Etna from the summit of the limestone platform of Primosole.

_a_, Highest cone.

_b_, Montagnuola.

_c_, Monte Minardo, with smaller lateral cones above.

_d_, Town of Licodia dei Monaci.

_e_, Marine formation called creta, argillaceous and sandy beds with a
few shells, and associated volcanic rocks.

_f_, Escarpment of stratified subaqueous volcanic tuff, &c., northwest
of Catania.

_g_, Town of Catania.

_h i_, Dotted line expressing the highest boundary along which the
marine strata are occasionally seen.

_k_, Plain of Catania.

_l_, Limestone platform of Primosole of the Newer Pliocene period.

_m_, La Motta di Catania.]

The mountain is in general of a very symmetrical form, a flattened cone
broken on its eastern side, by a deep valley, called the Val del Bove,
or in the provincial dialect of the peasants, "Val di Bué," for here the
herdsman


    ---- "in reducta valle mugientium
  Prospectat errantes greges."


Dr. Buckland was, I believe, the first English geologist who examined
this valley with attention, and I am indebted to him for having
described it to me, before I visited Sicily, as more worthy of attention
than any single spot in that island, or perhaps in Europe.

[Illustration: PLATE III

VIEW LOOKING UP THE VAL DEL BOVE, ETNA]

The Val del Bove commences near the summit of Etna, and descending
into the woody region, is farther continued on one side by a second and
narrower valley, called the Val di Calanna. Below this another, named
the Val di St. Giacomo, begins,--a long narrow ravine, which is
prolonged to the neighborhood of Zaffarana (_e_, fig. 48), on the
confines of the fertile region. These natural incisions into the side of
the volcano are of such depth that they expose to view a great part of
the structure of the entire mass, which, in the Val del Bove, is laid
open to the depth of from 3000 to above 4000 feet from the summit of
Etna. The geologist thus enjoys an opportunity of ascertaining how far
the internal conformation of the cone corresponds with what he might
have anticipated as the result of that mode of increase which has been
witnessed during the historical era.

[Illustration: Fig. 48.

Great valley on the east side of Etna.

_a_, Highest cone.

_b_, Montagnuola.

_c_, Head of Val del Bove.

_d_, _d_, Serre del Solfizio.

_e_, Village of Zaffarana on the lower border of the woody region.

_f_, One of the lateral cones.

_g_, Monti Rossi.]

_Description of Plate III._--The accompanying view (Pl. III.) is part of
a panoramic sketch which I made in November, 1828, and may assist the
reader in comprehending some topographical details to be alluded to in
the sequel, although it can convey no idea of the picturesque grandeur
of the scene.

The great lava-currents of 1819 and 1811 are seen pouring down from the
higher parts of the valley, overrunning the forests of the great plain,
and rising up in the foreground on the left with a rugged surface, on
which many hillocks and depressions appear, such as often characterize a
lava-current immediately after its consolidation.

The small cone, No. 7, was formed in 1811, and was still smoking when I
saw it in 1828. The other small volcano to the left, from which vapor is
issuing, was, I believe, one of those formed in 1819.

The following are the names of some of the other points indicated in the
sketch:--

   1, Montagnuola.
   2, Torre del Filosofo.
   3, Highest cone.
   4, Lepra.
   5, Finocchio.
   6, Capra.
   7, Cone of 1811.
   8, Cima del Asino.
   9, Musara.
  10, Zocolaro.
  11, Rocca di Calanna.

DESCRIPTION OF PLATE IV.--The second view (Pl. IV.) represents the same
valley as seen from above, or looking directly down the Val del Bove,
from the summit of the principal crater formed in 1819.[567] I am
unable to point out the precise spot which this crater would occupy in
the view represented in Plate III.; but I conceive that it would appear
in the face of the great precipice, near which the smoke issuing from
the cone No. 7 is made to terminate. There are many ledges of rock on
the face of that precipice where eruptions have occurred.

The circular form of the Val del Bove is well shown in this view. (Pl.
IV.) To the right and left are the lofty precipices which form the
southern and northern sides of the great valley, and which are
intersected by dikes projecting in the manner afterwards to be
described. In the distance appears the "fertile region" of Etna,
extending like a great plain along the sea-coast.

The spots particularly referred to in the plate are the following:--


  _a_, Cape Spartivento, in Italy, of which the outline is seen
         in the distance.

  _b_, The promontory of Taormino, on the Sicilian coast.

  _c_, The river Alcantra.

  _d_, The small village of Riposto.

  _f_, The town of Aci Reale.

  _g_, Cyclopian islands, or "Faraglioni," in the Bay of Trezza.

  _h_, The great harbor of Syracuse.

  _k_, The Lake of Lentini.

  _i_, The city of Catania, near which is marked the course of
         the lava which flowed from the Monti Rossi in 1669,
         and destroyed part of the city.

  _l_, To the left of the view is the crater of 1811, which is
         also shown at No. 7 in Plate III.

  _m_, Rock of Musara, also seen at No. 9 in Plate III.

  _e_, Valley of Calanna.


The Val del Bove is of truly magnificent dimensions, a vast amphitheatre
four or five miles in diameter, surrounded by nearly vertical
precipices, varying from 1000 to above 3000 feet in height, the loftiest
being at the upper end, and the height gradually diminishing on both
sides. The feature which first strikes the geologist as distinguishing
the boundary cliffs of this valley, is the prodigious multitude of
verticle dikes which are seen in all directions traversing the volcanic
beds. The circular form of this great chasm, and the occurrence of these
countless dikes, amounting perhaps to several thousands in number, so
forcibly recalled to my mind the phenomena of the Atrio del Cavallo, on
Vesuvius, that I at first imagined that I had entered a vast crater, on
a scale as far exceeding that of Somma, as Etna surpasses Vesuvius in
magnitude.

But I was soon undeceived when I had attentively explored the different
sides of the great amphitheatre, in order to satisfy myself whether the
semicircular wall of the Val del Bove had ever formed the boundary of a
crater, and whether the beds had the same quâquâ-versal dip which is so
beautifully exhibited in the escarpment of Somma. Had the supposed
analogy between Somma and the Val del Bove held true, the tufts and
lavas at the head of the valley would have dipped to the west, those on
the north side towards the north, and those on the southern side to the
south. But such I did not find to be the inclination of the beds; they
all dip towards the sea, or nearly east, as in the valleys of St.
Giacomo and Calanna below.

[Illustration: PLATE IV

VIEW OF THE VAL DEL BOVE, ETNA, AS SEEN FROM ABOVE, OR FROM THE CRATER
OF 1819]

_Scenery of the Val del Bove._--Let the reader picture to himself a
large amphitheatre, five miles in diameter, and surrounded on three
sides by precipices from 2000 to 3000 feet in height. If he has beheld
that most picturesque scene in the chain of the Pyrenees, the celebrated
"cirque of Gavarnie," he may form some conception of the magnificent
circle of precipitous rocks which inclose, on three sides, the great
plain of the Val del Bove. This plain has been deluged by repeated
streams of lava; and although it appears almost level, when viewed from
a distance, it is, in fact, more uneven than the surface of the most
tempestuous sea. Besides the minor irregularities of the lava, the
valley is in one part interrupted by a ridge of rocks, two of which,
Musara and Capra, are very prominent. It can hardly be said that they


      ----"like giants stand
  To sentinel enchanted land;"


for although, like the Trosachs, in the Highlands of Scotland, they are
of gigantic dimensions, and appear almost isolated, as seen from many
points, yet the stern and severe grandeur of the scenery which they
adorn is not such as would be selected by a poet for a vale of
enchantment. The character of the scene would accord far better with
Milton's picture of the infernal world; and if we imagine ourselves to
behold in motion, in the darkness of the night, one of those fiery
currents which have so often traversed the great valley, we may well
recall


  ----"yon dreary plain, forlorn and wild,
  The seat of desolation, void of light,
  Save what the glimmering of these livid flames
  Casts pale and dreadful."


The face of the precipices already mentioned is broken in the most
picturesque manner by the vertical walls of lava which traverse them.
These masses visually stand out in relief, are exceedingly diversified
in form, and of immense altitude. In the autumn, their black outline may
often be seen relieved by clouds of fleecy vapor which settle behind
them, and do not disperse until mid-day, continuing to fill the valley
while the sun is shining on every other part of Sicily, and on the
higher regions of Etna.

As soon as the vapors begin to rise, the changes of scene are varied in
the highest degree, different rocks being unveiled and hidden by turns,
and the summit of Etna often breaking through the clouds for a moment
with its dazzling snows, and being then as suddenly withdrawn from the
view.

An unusual silence prevails; for there are no torrents dashing from the
rocks, nor any movement of running water in this valley such as may
almost invariably be heard in mountainous regions. Every drop of water
that falls from the heavens, or flows from the melting ice and snow, is
instantly absorbed by the porous lava; and such is the dearth of
springs, that the herdsman is compelled to supply his flocks, during
the hot season, from stores of snow laid up in hollows of the mountain
during winter.

The strips of green herbage and forest land, which have here and there
escaped the burning lavas, serve, by contrast, to heighten the
desolation of the scene. When I visited the valley, nine years after the
eruption of 1819, I saw hundreds of trees, or rather the white skeletons
of trees, on the borders of the black lava, the trunks and branches
being all leafless, and deprived of their bark by the scorching heat
emitted from the melted rock; an image recalling those beautiful
lines:--


  ----"As when heaven's fire
  Hath scath'd the forest oaks, or mountain pines,
  With singed top their stately growth, though bare,
  Stands on the blasted heath."


[Illustration: Fig. 49.

Dikes at the base of the Serre del Solfizio, Etna.]

_Form, composition, and origin of the dikes._--But without indulging the
imagination any longer in descriptions of scenery, I may observe that
the dikes before mentioned form unquestionably the most interesting
geological phenomenon in the Val del Bove. Some of these are composed of
trachyte, others of compact blue basalt with olivine. They vary in
breadth from two to twenty feet and upwards, and usually project from
the face of the cliffs, as represented in the annexed drawing (fig. 49).
They consist of harder materials than the strata which they traverse,
and therefore waste away less rapidly under the influence of that
repeated congelation and thawing to which the rocks in this zone of
Etna are exposed. The dikes are for the most part vertical, but
sometimes they run in a tortuous course through the tuffs and breccias,
as represented in fig. 50. In the escarpment of Somma, where similar
walls of lava cut through alternating beds of sand and scoriæ, a coating
of coal-black rock, approaching in its nature and appearance to
pitchstone, is seen at the contact of the dike with the intersected
beds. I did not observe such parting layers at the junction of the
Etnean dikes which I examined, but they may perhaps be discoverable.

[Illustration: Fig. 50.

Tortuous veins of lava at Punto di Giumento, Etna.]

The geographical position of these dikes is most interesting, as they
are very numerous near the head of the Val del Bove, where the cones of
1811 and 1819 were thrown up, as also in that zone of the mountain where
lateral eruptions are frequent; whereas in the valley of Calanna, which
is below that parallel, and in a region where lateral eruptions are
extremely rare, scarcely any dikes are seen, and none whatever still
lower in the valley of St. Giacomo. This is precisely what we might have
expected, if we consider the vertical fissures now filled with rock to
have been the feeders of lateral cones, or, in other words, the channels
which gave passage to the lava-currents and scoriæ that have issued from
vents in the forest zone. In other parts of Etna there may be numerous
dikes at as low a level as the Valley of Calanna, because the line of
lateral eruptions is not everywhere at the same height above the sea;
but in the section above alluded to, there appeared to me an obvious
connection between the frequency of dikes and of lateral eruptions.

Some fissures may have been filled from above, but I did not see any
which, by terminating downwards, gave proof of such an origin. Almost
all the isolated masses in the Val del Bove, such as Capra, Musara, and
others, are traversed by dikes, and may, perhaps, have partly owed their
preservation to that circumstance, if at least the action of occasional
floods has been one of the destroying causes in the Val del Bove; for
there is nothing which affords so much protection to a mass of strata
against the undermining action of running water as a perpendicular dike
of hard rock.

In the accompanying drawing (fig. 51), the flowing of the lavas of 1811
and 1819, between the rocks Finochio, Capra, and Musara, is represented.
The height of the two last-mentioned isolated masses has been much
diminished by the elevation of their base, caused by these currents.
They may, perhaps, be the remnants of lateral cones which existed before
the Val del Bove was formed, and may hereafter be once more buried by
the lavas that are now accumulating in the valley.

[Illustration: Fig. 51.

View of the rocks Finochio, Capra, and Musara, Val del Bove.]

From no point of view are the dikes more conspicuous than from the
summit of the highest cone of Etna; a view of some of them is given in
the annexed drawing. (Fig. 52.)

_Eruption of 1811._--I have alluded to the streams of lava which were
poured forth in 1811 and 1819. Gemmellaro, who witnessed these
eruptions, informs us that the great crater in 1811 first testified by
its loud detonations that a column of lava had ascended to near the
summit of the mountain. A violent shock was then felt, and a stream
broke out from the side of the cone, at no great distance from its apex.
Shortly after this had ceased to flow, a second stream burst forth at
another opening, considerably below the first; then a third still lower,
and so on till seven different issues had been thus successively formed,
all lying upon the same straight line. It has been supposed that this
line was a perpendicular rent in the internal framework of the mountain,
which rent was probably not produced at one shock, but prolonged
successively downwards, by the lateral pressure and intense heat of the
internal column of lava, as it subsided by gradual discharge through
each vent.[568]

_Eruption of 1819._--In 1819 three large mouths or caverns opened very
near those which were formed in the eruptions of 1811, from which
flames, red-hot cinders, and sand were thrown up with loud explosions. A
few minutes afterwards another mouth opened below, from which flames
and smoke issued; and finally a fifth, lower still, whence a torrent of
lava flowed, which spread itself with great velocity over the deep and
broad valley called "Val del Bove." This stream flowed two miles in the
first twenty-four hours, and nearly as far in the succeeding day and
night. The three original mouths at length united into one large crater,
and sent forth lava, as did the inferior apertures, so that an enormous
torrent poured down the "Val del Bove." When it arrived at a vast and
almost perpendicular precipice, at the head of the Valley of Calanna, it
poured over in a cascade, and, being hardened in its descent, made an
inconceivable crash as it was dashed against the bottom. So immense was
the column of dust raised by the abrasion of the tufaceous hill over
which the hardened mass descended, that the Catanians were in great
alarm, supposing a new eruption to have burst out in the woody region,
exceeding in violence that near the summit of Etna.

[Illustration: Fig. 52.

View from the summit of Etna into the Val del Bove.[569]]

_Mode of advance of the lava._--Of the cones thrown up during this
eruption, not more than two are of sufficient magnitude to be numbered
among those eighty which were before described as adorning the flanks of
Etna. The surface of the lava which deluged the "Val del Bove," consists
of rocky and _angular blocks_, tossed together in the utmost disorder.
Nothing can be more rugged, or more unlike the smooth and even
superficies, which those who are unacquainted with volcanic countries
may have pictured to themselves, in a mass of matter which had
consolidated from a liquid state. Mr. Scrope observed this current in
the year 1819, slowly advancing down a considerable slope, at the rate
of about a yard an hour, nine months after its emission. The lower
stratum being arrested by the resistance of the ground, the upper or
central part gradually protruded itself, and, being unsupported, fell
down. This in its turn was covered by a mass of more liquid lava, which
swelled over it from above. The current had all the appearance of a huge
heap of rough and large cinders rolling over and over upon itself by the
effect of an extremely slow propulsion from behind. The contraction of
the crust as it solidified, and the friction of the scoriform cakes
against one another, produced a crackling sound. Within the crevices a
dull red heat might be seen by night, and vapor issuing in considerable
quantity was visible by day.[570]

It was stated that when the lava of 1819 arrived at the head of the
Valley of Calanna, after flowing down the Val del Bove, it descended in
a cascade. This stream, in fact, like many previous currents of lava
which have flowed down successively from the higher regions of Etna, was
turned by a great promontory projecting from the southern side of the
Val del Bove. This promontory consists of the hills called Zocolaro and
Calanna, and of a ridge of inferior height which connects them. (See
fig. 53.)

[Illustration: Fig. 53.


  A, Zocolaro.
  B, Monte di Calanna.
  C, Plain at the head of the Valley of Calanna.
 _a_, Lava of 1819 descending the precipice and flowing through
         the valley.
 _b_, Lavas of 1811 and 1819 flowing round the hill of Calanna.]


It happened in 1811 and 1819 that the flows of lava overtopped the ridge
intervening between the hills of Zocolaro and Calanna, so that they fell
in a cascade over a lofty precipice, and began to fill up the valley of
Calanna (_a_, fig. 53). Other portions of the same lava-current (_b_)
flowed round the promontory, and they exhibit one of the peculiar
characteristics of such streams, namely that of becoming solid
externally, even while yet in motion. Instead of thinning out gradually
at their edges, their sides may often be compared to two rocky walls
which are sometimes inclined at an angle of between thirty and forty
degrees. When such streams are turned from their course by a projecting
rock, they move right onwards in a new direction; and in the Valley of
Calanna a considerable space has thus been left between the steep sides
of the lavas _b b_, so deflected, and the precipitous escarpment of
Zocolaro, A, which bounds the plain C.

_Lavas and breccias._--In regard to the volcanic masses which are
intersected by dikes in the Val del Bove, they consist in great part of
graystone lavas, of an intermediate character between basalt and
trachyte, and partly of porphyritic lava resembling trachyte, but to
which that name cannot, according to Von Buch and G. Rose, be in
strictness applied, because the felspar belongs to the variety called
Labradorite. There is great similarity in the composition of the ancient
and modern lavas of Etna, both consisting of felspar, augite, olivine,
and titaniferous iron. The alternating breccias are made up of scoriæ,
sand, and angular blocks of lava. Many of these fragments may have been
thrown out by volcanic explosions, which, falling on the hardened
surface of moving lava-currents, may have been carried to a considerable
distance. It may also happen that when lava advances very slowly, in the
manner of the flow of 1819, the angular masses resulting from the
frequent breaking of the mass as it rolls over upon itself, may produce
these breccias. It is at least certain that the upper portion of the
lava-currents of 1811 and 1819 now consist of angular masses to the
depth of many yards. D'Aubuisson has compared the surface of one of the
ancient lavas of Auvergne to that of a river suddenly frozen over by the
stoppage of immense fragments of drift-ice, a description perfectly
applicable to these modern Etnean flows. The thickness of the separate
beds of conglomerate or breccia which are seen in the same vertical
section, is often extremely different, varying from 3 to nearly 50 feet,
as I observed in the hill of Calanna.

_Flood produced by the melting of snow by lava._--It is possible that
some of the breccias or conglomerates may be referred to aqueous causes,
as great floods occasionally sweep down the flanks of Etna, when
eruptions take place in winter, and when the snows are melted by lava.
It is true that running water in general exerts no power on Etna, the
rain which falls being immediately imbibed by the porous lavas; so that,
vast as is the extent of the mountain, it feeds only a few small
rivulets, and these, even, are dry throughout the greater portion of the
year. The enormous rounded boulders, therefore, of felspar-porphyry and
basalt, a line of which can be traced from the sea, from near Giardini,
by Mascali, and Zafarana, to the "Val del Bove," would offer a
perplexing problem to the geologist, if history had not preserved the
memorials of a tremendous flood which happened in this district in the
year 1755. It appears that two streams of lava flowed in that year, on
the 2d of March, from the highest crater; they were immediately
precipitated upon an enormous mass of snow which then covered the whole
mountain, and was extremely deep near the summit. The sudden melting of
this frozen mass, by a fiery torrent three miles in length, produced a
frightful inundation, which devastated the sides of the mountain for
eight miles in length, and afterwards covered the lower flanks of Etna,
where they were less steep, together with the plains near the sea, with
great deposits of sand, scoriæ, and blocks of lava.

Many absurd stories circulated in Sicily respecting this event; such as
that the water was boiling, and that it was vomited from the highest
crater; that it was as salt as the sea, and full of marine shells; but
these were mere inventions, to which Recupero, although he relates them
as tales of the mountaineers, seems to have attached rather too much
importance.

Floods of considerable violence have also been produced on Etna by the
fall of heavy rains, aided, probably, by the melting of snow. By this
cause alone, in 1761, sixty of the inhabitants of Acicatena were killed,
and many of their houses swept away.[571]

_Glacier covered by a lava-stream._--A remarkable discovery was made on
Etna in 1828 of a great mass of ice, preserved for many years, perhaps
for centuries, from melting, by the singular accident of a current of
red-hot lava having flowed over it. The following are the facts in
attestation of a phenomenon which must at first sight appear of so
paradoxical a character. The extraordinary heat experienced in the South
of Europe, during the summer and autumn of 1828, caused the supplies of
snow and ice which had been preserved in the spring of that year, for
the use of Catania and the adjoining parts of Sicily and the island of
Malta, to fail entirely. Great distress was consequently felt for want
of a commodity regarded in those countries as one of the necessaries of
life rather than an article of luxury, and the abundance of which
contributes in some of the larger cities to the salubrity of the water
and the general health of the community. The magistrates of Catania
applied to Signor M. Gemmellaro, in the hope that his local knowledge of
Etna might enable him to point out some crevice or natural grotto on the
mountain, where drift-snow was still preserved. Nor were they
disappointed; for he had long suspected that a small mass of perennial
ice at the foot of the highest cone was part of a large and continuous
glacier covered by a lava-current. Having procured a large body of
workmen, he quarried into this ice, and proved the superposition of the
lava for several hundred yards, so as completely to satisfy himself that
nothing but the subsequent flowing of the lava over the ice could
account for the position of the glacier. Unfortunately for the
geologist, the ice was so extremely hard, and the excavation so
expensive, that there is no probability of the operations being renewed.

On the first of December, 1828, I visited this spot, which is on the
southeast side of the cone, and not far above the Casa Inglese; but the
fresh snow had already nearly filled up the new opening, so that it had
only the appearance of the mouth of a grotto. I do not, however,
question the accuracy of the conclusion of Signer Gemmellaro, who, being
well acquainted with all the appearances of drift-snow in the fissures
and cavities of Etna, had recognized, even before the late excavations,
the peculiarity of the position of the ice in this locality. We may
suppose that, at the commencement of the eruption, a deep mass of
drift-snow had been covered by volcanic sand showered down upon it
before the descent of the lava. A dense stratum of this fine dust mixed
with scoriæ is well known to be an extremely bad conductor of heat; and
the shepherds in the higher regions of Etna are accustomed to provide
water for their flocks during summer, by strewing a layer of volcanic
sand a few inches thick over the snow, which effectually prevents the
heat of the sun from penetrating.

Suppose the mass of snow to have been preserved from liquefaction until
the lower part of the lava had consolidated, we may then readily
conceive that a glacier thus protected, at the height of ten thousand
feet above the level of the sea, would endure as long as the snows of
Mont Blanc, unless melted by volcanic heat from below. When I visited
the great crater in the beginning of winter (December 1st, 1828), I
found the crevices in the interior incrusted with thick ice, and in some
cases hot vapors were actually streaming out between masses of ice and
the rugged and steep walls of the crater.[572]

After the discovery of Signor Gemmellaro, it would not be surprising to
find in the cones of the Icelandic volcanoes, which are covered for the
most part with perpetual snow, repeated alternations of lava-streams and
glaciers. We have, indeed, Lieutenant Kendall's authority for the fact
that Deception Island, in New South Shetland, lat. 62° 55' S., is
principally composed of alternate layers of volcanic ashes and ice.[573]

_Origin of the Val del Bove._--It is recorded, as will be stated in the
history of earthquakes (ch. 29), that in the year 1772 a great
subsidence took place on Papandayang, the largest volcano in the island
of Java; an extent of ground _fifteen miles in length_, _and six in
breadth_, covered by no less than forty villages, was engulphed, and the
cone lost 4000 feet of its height. In like manner the summit of
Carguairazo, one of the loftiest of the Andes of Quito, fell in on the
19th July, 1698; and another mountain of still greater altitude in the
same chain, called Capac Urcu, a short time before the conquest of
America by the Spaniards.

It will also be seen in the next chapter that, so late as the year
1822, during a violent earthquake and volcanic eruption in Java, one
side of the mountain called Galongoon, which was covered by a dense
forest, became an enormous gulf in the form of a semicircle. The new
cavity was about midway between the summit and the plain, and surrounded
by steep rocks.

Now we might imagine a similar event, or a series of subsidences to have
formerly occurred on the eastern side of Etna, although such
catastrophes have not been witnessed in modern times, or only on a very
trifling scale. A narrow ravine, about a mile long, twenty feet wide,
and from twenty to thirty-six in depth, has been formed, within the
historical era, on the flanks of the volcano, near the town of
Mascalucia; and a small circular tract, called the Cisterna, near the
summit, sank down in the year 1792, to the depth of about forty feet,
and left on all sides of the chasm a vertical section of the beds,
exactly resembling those which are seen in the precipices of the Val del
Bove. At some remote periods, therefore, we might suppose more extensive
portions of the mountain to have fallen in during great earthquakes.

But we ought not to exclude entirely from our speculations another
possible agency, by which the great cavity may in part at least have
been excavated, namely, the denuding action of the sea. Whether its
waves may once have had access to the great valley before the ancient
portion of Etna was upheaved to its present elevation, is a question
which will naturally present itself to every geologist. Marine shells
have been traced to a height of 800 feet above the base of Etna, and
would doubtless be seen to ascend much higher, were not the structure of
the lower region of the mountain concealed by floods of lava. We cannot
ascertain to what extent a change in the relative level of land and sea
may have been carried in this spot, but we know that some of the
tertiary strata in Sicily of no ancient date reach a height of 3000
feet, and the marine deposits on the flanks of Etna, full of recent
species of shells, may ascend to equal or greater heights. The narrow
Valley of Calanna leading out of the Val del Bove, and that of San
Giacomo lower down, have much the appearance of ravines swept out by
aqueous action.

_Structure and origin of the cone of Etna._--Our data for framing a
correct theory of the manner in which the cone of Etna has acquired its
present dimensions and internal structure are very imperfect, because it
is on its eastern side only, in the Val del Bove above described, that
we see a deep section exposed. Even here we obtain no insight into the
interior composition of the mountain beyond a depth of between three and
four thousand feet below the base of that highest cone, which has been
several times destroyed and renewed. The precipices seen at the head of
the Val del Bove, in the escarpment called the Serre del Solfizio,
exhibit merely the same series of alternating lavas and breccias, which,
descending with a general dip towards the sea, form the boundary cliffs
of all other parts of the Val del Bove. If then we estimate the height
of Etna at about 11,000 feet, we may say that we know from actual
observation less than one-half of its component materials, assuming it
to extend downwards to the level of the sea; namely, first, the highest
cone, which is about 1000 feet above its base; and, secondly, the
alternations of lava, tuff, and volcanic breccia, which constitute the
rocks between the Cisterna, near the base of the upper cone, and the
foot of the precipices at the head of the Val del Bove. At the lowest
point to which the vertical section extends, there are no signs of any
approach to a termination of the purely volcanic mass, which may perhaps
penetrate many thousand feet farther downwards. There is, indeed, a rock
called Rocca Gianicola, near the foot of the great escarpment, which
consists of a large mass between 150 and 200 feet wide, not divided into
beds, and almost resembling granite in its structure, although agreeing
very closely in mineral composition with the lavas of Etna in
general.[574] This mass may doubtless be taken as a representative of
those crystalline or plutonic formations which would be met with in
abundance if we could descend to greater depths in the direction of the
central axis of the mountain. For a great body of geological evidence
leads us to conclude, that rocks of this class result from the
consolidation, under great pressure, of melted matter, which has risen
up and filled rents and chasms, such, for example, as may communicate
with the principal and minor vents of eruption in a volcano like Etna.

But, if we speculate on the nature of the formation which the lava may
have pierced in its way upwards, we may fairly presume that a portion of
these consist of marine tertiary rocks, like those of the neighboring
Val di Noto, or those which skirt the borders of the Etnean cone, on its
southern and eastern sides. Etna may, in fact, have been at first an
insular volcano, raising its summit but slightly above the level of the
sea; but we have no grounds for concluding that any of the beds exposed
in the deep section of the Val del Bove have formed a part of such a
marine accumulation. On the contrary, all the usual signs of subaqueous
origin are wanting; and even if we believe the foundations of the
mountain to have been laid in the sea, we could not expect this portion
to be made visible in sections which only proceed downwards from the
summit through one-half the thickness of the mountain, especially as the
highest points attained by the tertiary strata in other parts of Sicily
very rarely exceed 3000 feet above the sea.

On the eastern and southern base of Etna, a marine deposit, already
alluded to, is traced up to the height of 800 or 1000 feet, before it
becomes concealed beneath that covering of modern lavas which is
continually extending its limits during successive eruptions, and
prevents us from ascertaining how much higher the marine strata may
ascend. As the imbedded shells belong almost entirely to species now
inhabiting the Mediterranean, it is evident that there has been here an
upheaval of the region at the base of Etna at a very modern period. It
is fair, therefore, to infer that the volcanic nucleus of the mountain,
partly perhaps of submarine, and partly of subaerial origin,
participated in this movement, and was carried up bodily. Now, in
proportion as a cone gains height by such a movement, combined with the
cumulative effects of eruptions, throwing out matter successively from
one or more central vents, the hydrostatic pressure of the columns of
lava augments with their increasing height, until the time arrives when
the flanks of the cone can no longer resist the increased pressure; and
from that period they give way more readily, lateral outbursts becoming
more frequent. Hence, independently of any local expansion of the
fractured volcanic mass, those general causes by which the modern
tertiary strata of a great part of Sicily have been raised to the height
of several thousand feet above their original level, would tend
naturally to render the discharge of lava and scoriæ from the summit of
Etna less copious, and the lateral discharge greater.

If, then, a conical or dome-shaped mass of volcanic materials was
accumulated to the height of 4000, or perhaps 7000 feet, before the
upward movement began, or, what is much more probable, during the
continuance of the upward movement, that ancient mass would not be
buried under the products of newer eruptions, because these last would
then be poured out chiefly at a lower level.

Since I visited Etna in 1828, M. de Beaumont has published a most
valuable memoir on the structure and origin of that mountain, which he
examined in 1834;[575] and an excellent description of it has also
appeared in the posthumous work of Hoffmann.[576]

In M. de Beaumont's essay, in which he has explained his views with
uncommon perspicuity and talent, he maintains that all the alternating
stony and fragmentary beds, more than 3000 feet thick, which are exposed
in the Val del Bove, were formed originally on a surface so nearly flat
that the slope never exceeded three degrees. From this horizontal
position they were at length heaved up suddenly (d'un seul coup) into a
great mountain, to which no important additions have since been made.
Prior to this upthrow, a platform is supposed to have existed above the
level of the sea, in which various fissures opened; and from these
melted matter was poured forth again and again, which spread itself
around in thin sheets of uniform thickness. From the same rents issued
showers of scoriæ and fragmentary matter, which were spread out so as to
form equally uniform and horizontal beds, intervening between the sheets
of lava. But although, by the continued repetition of these operations,
a vast pile of volcanic matter, 4000 feet or more in thickness, was
built up precisely in that region where Etna now rises, and to which
nothing similar was produced elsewhere in Sicily, still we are told that
Etna was not yet a mountain. No hypothetical diagram has been given to
help us to conceive how this great mass of materials of supramarine
origin could have been disposed of in horizontal beds, so as not to
constitute an eminence towering far above the rest of Sicily; but it is
assumed that a powerful force from below at length burst suddenly
through the horizontal formation, uplifted it to a considerable height,
and caused the beds to be, in many places, highly inclined. This
elevatory force was not all expended on a single central point as Von
Buch has imagined in the case of Palma, Teneriffe, or Somma, but rather
followed for a short distance a linear direction.[577]

Among other objections that may be advanced against the theory above
proposed, I may mention, first, that the increasing number of dikes as
we approach the head of the Val del Bove, or the middle of Etna, and the
great thickness of lava, scoriæ, and conglomerates in that region, imply
that the great centre of eruption was always where it now is, or nearly
at the same point, and there must, therefore, have been a tendency, from
the beginning, to a conical or dome-shaped arrangement in the ejected
materials. Secondly, were we to admit a great number of separate points
of eruption, scattered over a plain or platform, there must have been a
great number of cones thrown up over these different vents; and these
hills, some of which would probably be as lofty as those now seen on the
flanks of Etna, or from 300 to 750 feet in height, would break the
continuity of the sheets of lava, while they would become gradually
enveloped by them. The ejected materials, moreover, would slope at a
high angle on the sides of these cones, and where they fell on the
surrounding plain, would form strata thicker near the base of each cone
than at a distance.

What then are the facts, it will be asked, to account for which this
hypothesis of original horizontality, followed by a single and sudden
effort of upheaval, which gave to the beds their present slope, has been
invented? M. de Beaumont observes, that in the boundary precipices of
the Val del Bove, sheets of lava and intercalated beds of cinders, mixed
with pulverulent and fragmentary matter evidently cast out during
eruptions, are sometimes inclined at steep angles, varying from 15° to
27°. It is impossible, he says, that the lavas could have flowed
originally on planes so steeply inclined, for streams which descend a
slope even of 10° form narrow stripes, and never acquire such a compact
texture. Their thickness, moreover, always inconsiderable, varies with
every variation of steepness, in the declivity down which they flow;
whereas, in several parts of the Val del Bove, the sheets of lava are
continuous for great distances, in spite of their steep inclination, and
are often compact, and perfectly parallel one to the other, even where
there are more than 100 beds of interpolated fragmentary matter.

The intersecting dikes also terminate upwards in many instances, at
different elevations, and blend (or, as M. de Beaumont terms it,
articulate) with sheets of lava, which they meet at right angles. It is
therefore assumed that such dikes were the feeders of the streams of
lava with which they unite, and they are supposed to prove that the
platform, on the surface of which the melted matter was poured out, was
at first so flat, that the fluid mass spread freely and equally in every
direction, and not towards one point only of the compass, as would
happen if it had descended the sloping sides of a cone. This argument is
ingeniously and plainly put in the following terms:--"Had the melted
matter poured down an inclined plane, after issuing from a rent, the
sheet of lava would, after consolidation, have formed an elbow with the
dike, like the upper bar of the letter F, instead of extending itself on
both sides like that of a T."[578] It is also contended that a series of
sheets of lava, formed on a conical or dome-shaped mountain, would have
been more numerous at points farthest from the central axis, since every
dike which had been the source of a lava-stream, must have poured its
contents downwards, and never upwards.

[Illustration: Fig. 54.

Dikes as they would now appear had they been originally perpendicular.]

In reference to the facts here stated, I may mention that the dikes
which I saw in the Val del Bove were either vertical, or made almost all
of them a near approach to the perpendicular, which could not have been
the case had they been the feeders of horizontal beds of lava, and had
they consequently joined them originally at right angles, for then the
dikes, as at _a_, _b_, _c_, fig. 54, ought subsequently to have acquired
a considerable slope, like the beds which they intersect. I may also
urge another objection to the views above set forth, namely, that had
the dikes been linear vents, or orifices of eruption, we must suppose
the inter-stratified scoriæ and lapilli, as well as the lavas, to have
come out of them, and in that case the irregular heaping up of
fragmentary matter around the vents would, as before hinted, have
disturbed that uniform thickness and parallelism of the beds which M. de
Beaumont describes.

If, however, some of the sheets of lava join the dikes in such a manner,
as to imply that they were in a melted state simultaneously with the
contents of the fissures,--a point not easily ascertained, where the
precipices are for the most part inaccessible,--the fact may admit of a
different interpretation from that proposed by the French geologists.
Rents like those before alluded to (p. 399), which opened in the plain
of S. Lio in 1669, filled below with incandescent lava, may have lain in
the way of currents of melted matter descending from higher openings. In
that case, the matter of the current would have flowed into the fissure
and mixed with the lava at its bottom. Numerous open rents of this kind
are described by Mr. Dana as having been caused, during a late eruption,
in one of the volcanic domes of the Sandwich Islands. They remained open
at various heights on the slopes of the great cone, running in different
directions, and demonstrate the possibility of future junctions of
slightly inclined lava-streams with perpendicular walls of lava.

To me, therefore, it appears far more easy to explain the uniform
thickness and parallelism of so many lavas and beds of fragmentary
matter seen in the Val del Bove, by supposing them to have issued
successively out of one or more higher vents near the summit of a great
dome, than to imagine them to have proceeded from lateral dikes or rents
opening in a level plain. In the Sandwich Islands, we have examples of
volcanic domes 15,000 feet high, produced by successive outpourings from
vents at or near the summit. One of these, Mount Loa, has a slope in all
directions of 6° 30'; another, Mount Kea, a mean inclination of 7° 46'.
That their lavas may occasionally consolidate on slopes of 25°, and even
more, and still preserve considerable solidity of texture, has been
already stated; see above, p. 383.

We know not how large a quantity of modern lava may have been poured
into the bottom of the Val del Bove, yet we perceive that eruptions
breaking forth near the centre of Etna have already made some progress
in filling up this great hollow. Even within the memory of persons now
living, the rocks of Musara and Capra have, as before stated, lost much
of their height and picturesque grandeur by the piling up of recent
lavas round their base (see fig. 51, p. 408), and the great chasm has
intercepted many streams which would otherwise have deluged the fertile
region below, as has happened on the side of Catania. The volcanic
forces are now laboring, therefore, to repair the breach which
subsidence has caused on one side of the great cone; and unless their
energy should decline, or a new sinking take place, they may in time
efface this inequality. In that event, the restored portion will always
be unconformable to the more ancient part, yet it will consist, like it,
of alternating beds of lava, scoriæ;, and conglomerates, which, with all
their irregularities, will have a general slope from the centre and
summit of Etna towards the sea.

I shall conclude, then, by remarking that I conceive the general
inclination of the alternating stony and fragmentary beds of the Val del
Bove, from the axis of Etna towards its circumference or base, and the
greater thickness of the volcanic pile as we approach the central parts
of the mountain, to be due to the preponderance of eruptions from that
centre. These gave rise, from the first, to a dome-shaped mass, which
has ever since been increasing in height and area, being fractured again
and again by the expansive force of vapors, and the several parts made
to cohere together more firmly after the solidification of the lava with
which every open fissure and chasm has been filled. At the same time the
cone may have gained a portion of its height by the elevatory effect of
such dislocating movements, and the sheets of lava may have acquired in
some places a greater, in others a less, inclination than that which at
first belonged to them.

[Illustration: Fig. 55.

Non-volcanic protuberance and valley of elevation.]

But had the mountain been due solely, or even principally, to upheaval,
its structure would have resembled that which geologists have so often
recognized in dome-shaped hills, or certain elevated regions, which all
consider as having been thrust up by a force from below. In this case
there is often an elliptical cavity at the summit, due partly to the
fracture of the upraised rocks, but still more to aqueous denudation, as
they rose out of the sea. The central cavity, or valley, exposes to view
the subjacent formation _c_, fig. 55, and the incumbent mass dips away
on all sides from the axis, but has no tendency to thin out near the
base of the dome, or at _x_, _x_; whereas at this point the volcanic
mass terminates (see fig. 56) and allows the fundamental rock _c_ to
appear at the surface. In the last diagram, the more ordinary case is
represented of a great hollow or crater at the summit of the volcanic
cone; but instead of this, we have seen that in the case of Etna there
is a deep lateral depression, called the Val del Bove, the upper part of
which approaches near to the central axis, and the origin of which we
have attributed to subsidence.

[Illustration: Fig. 56.

Volcanic mountain and crater.]

_Antiquity of the cone of Etna._--It was before remarked that confined
notions in regard to the quantity of past time have tended, more than
any other prepossessions, to retard the progress of sound theoretical
views in geology;[579] the inadequacy of our conceptions of the earth's
antiquity having cramped the freedom of our speculations in this
science, very much in the same way as a belief in the existence of a
vaulted firmament once retarded the progress of astronomy. It was not
until Descartes assumed the indefinite extent of the celestial spaces,
and removed the supposed boundaries of the universe, that just opinions
began to be entertained of the relative distances of the heavenly
bodies; and until we habituate ourselves to contemplate the possibility
of an indefinite lapse of ages having been comprised within each of the
modern periods of the earth's history, we shall be in danger of forming
most erroneous and partial views in geology.

If history had bequeathed to us a faithful record of the eruptions of
Etna, and a hundred other of the principal active volcanoes of the
globe, during the last three thousand years,--if we had an exact account
of the volume of lava and matter ejected during that period, and the
times of their production,--we might, perhaps, be able to form a correct
estimate of the average rate of the growth of a volcanic cone. For we
might obtain a mean result from the comparison of the eruptions of so
great a number of vents, however irregular might be the development of
the igneous action in any one of them, if contemplated singly during a
brief period.

It would be necessary to balance protracted periods of inaction against
the occasional outburst of paroxysmal explosions. Sometimes we should
have evidence of a repose of seventeen centuries, like that which was
interposed in Ischia, between the end of the fourth century B.C., and
the beginning of the fourteenth century of our era.[580] Occasionally a
tremendous eruption, like that of Jorullo, would be recorded, giving
rise, at once, to a considerable mountain.

If we desire to approximate to the age of a cone such as Etna, we ought
first to obtain some data in regard to the thickness of matter which has
been added during the historical era, and then endeavor to estimate the
time required for the accumulation of such alternating lavas and beds of
sand and scoriæ as are superimposed upon each other in the Val del Bove;
afterwards we should try to deduce, from observations on other
volcanoes, the more or less rapid increase of burning mountains in all
the different stages of their growth.

There is a considerable analogy between the mode of increase of a
volcanic cone and that of trees of _exogenous_ growth. These trees
augment, both in height and diameter, by the successive application
externally of cone upon cone of new ligneous matter; so that if we make
a transverse section near the base of the trunk, we intersect a much
greater number of layers than nearer to the summit. When branches
occasionally shoot out from the trunk, they first pierce the bark, and
then, after growing to a certain size, if they chance to be broken off,
they may become inclosed in the body of the tree, as it augments in
size, forming knots in the wood, which are themselves composed of layers
of ligneous matter, cone within cone.

In like manner, a volcanic mountain, as we have seen, consists of a
succession of conical masses enveloping others, while lateral cones,
having a similar internal structure, often project, in the first
instance, like branches from the surface of the main cone, and then
becoming buried again, are hidden like the knots of a tree.

We can ascertain the age of an oak or pine by counting the number of
concentric rings of annual growth seen in a transverse section near the
base, so that we may know the date at which the seedling began to
vegetate. The Baobab-tree of Senegal (_Adansonia digitata_) is supposed
to exceed almost any other in longevity. Adanson inferred that one which
he measured, and found to be thirty feet in diameter, had attained the
age of 5150 years. Having made an incision to a certain depth, he first
counted three hundred rings of annual growth, and observed what
thickness the tree had gained in that period. The average rate of growth
of younger trees, of the same species, was then ascertained, and the
calculation made according to a supposed mean rate of increase. De
Candolle considers it not improbable that the celebrated Taxodium of
Chapultepec, in Mexico (_Cupressus disticha_, Linn.), which is 117 feet
in circumference, may be still more aged.[581]

It is, however, impossible, until more data are collected respecting the
average intensity of the volcanic action, to make any thing like an
approximation to the age of a cone like Etna; because, in this case, the
successive envelopes of lava and scoriæ are not continuous, like the
layers of wood in a tree, and afford us no definite measure of time.
Each conical envelope is made up of a great number of distinct
lava-currents and showers of sand and scoriæ, differing in quantity, and
which may have been accumulated in unequal periods of time. Yet we
cannot fail to form the most exalted conception of the antiquity of this
mountain, when we consider that its base is about ninety miles in
circumference; so that it would require ninety flows of lava, each a
mile in breadth at their termination, to raise the present foot of the
volcano as much as the average height of one lava-current.

There are no records within the historical era which lead to the opinion
that the altitude of Etna has materially varied within the last two
thousand years. Of the eighty most conspicuous minor cones which adorn
its flanks, only one of the largest, Monti Rossi, has been produced
within the times of authentic history. Even this hill, thrown up in the
year 1669, although 450 feet in height, only ranks as a cone of second
magnitude. Monte Minardo, near Bronte, rises, even now, to the height of
750 feet, although its base has been elevated by more modern lavas and
ejections. The dimensions of these larger cones appear to bear testimony
to _paroxysms_ of volcanic activity, after which we may conclude, from
analogy, that the fires of Etna remained dormant for many years--since
nearly a century of rest has sometimes followed a violent eruption in
the historical era. It must also be remembered, that of the small number
of eruptions which occur in a century, one only is estimated to issue
from the summit of Etna for every two that proceed from the sides. Nor
do all the lateral eruptions give rise to such cones as would be
reckoned amongst the smallest of the eighty hills above enumerated; some
of them produce merely insignificant monticules, which are soon
afterwards buried by showers of ashes.

How many years then must we not suppose to have been expended in the
formation of the eighty cones? It is difficult to imagine that a fourth
part of them have originated during the last thirty centuries. But if we
conjecture the whole of them to have been formed in twelve thousand
years, how inconsiderable an era would this portion of time constitute
in the history of the volcano! If we could strip off from Etna all the
lateral monticules now visible, together with the lavas and scoriæ that
have been poured out from them, and from the highest crater, during the
period of their growth, the diminution of the entire mass would be
extremely slight: Etna might lose, perhaps, several miles in diameter at
its base, and some hundreds of feet in elevation; but it would still be
the loftiest of Sicilian mountains, studded with other cones, which
would be recalled, as it were, into existence by the removal of the
rocks under which they are now buried.

There seems nothing in the deep sections of the Val del Bove to indicate
that the lava-currents of remote periods were greater in volume than
those of modern times; and there are abundant proofs that the countless
beds of solid rock and scoriæ were accumulated, as now, in succession.
On the grounds, therefore, already explained, we must infer that a mass
so many thousand feet in thickness must have required an immense series
of ages anterior to our historical periods for its growth; yet the whole
must be regarded as the product of a modern portion of the tertiary
epoch. Such, at least, is the conclusion that seems to follow from
geological data, which show that the oldest parts of the mountain, if
not of posterior date to the marine strata around its base, were at
least of coeval origin.

Some geologists contend, that the sudden elevation of large continents
from beneath the waters of the sea have again and again produced waves
which have swept over vast regions of the earth.[582] But it is clear
that no devastating wave has passed over the forest zone of Etna since
any of the lateral cones before mentioned were thrown up; for none of
these heaps of loose sand and scoriæ could have resisted for a moment
the denuding action of a violent flood. To some, perhaps, it may appear
that hills of such incoherent materials cannot be of very great
antiquity, because the mere action of the atmosphere must, in the course
of several thousand years, have obliterated their original forms. But
there is no weight in this objection; for the older hills are covered
with trees and herbage, which protect them from waste; and, in regard to
the newer ones, such is the porosity of their component materials, that
the rain which falls upon them is instantly absorbed; and for the same
reason that the rivers on Etna have a subterranean course, there are
none descending the sides of the minor cones.

No sensible alteration has been observed in the form of these cones
since the earliest periods of which there are memorials; and there seems
no reason for anticipating that in the course of the next ten thousand
or twenty thousand years they will undergo any great alteration in their
appearance, unless they should be shattered by earthquakes or covered by
volcanic ejections.

In other parts of Europe, as in Auvergne and Velay, in France, similar
loose cones of scoriæ, probably of as high antiquity as the whole mass
of Etna, stand uninjured at inferior elevations above the level of the
sea.




CHAPTER XXVI.


  Volcanic eruption in Iceland in 1783--New island thrown up--Lava
    currents of Skaptár Jokul, in same year--their immense
    volume--Eruption of Jorullo in Mexico--Humboldt's theory of the
    convexity of the plain of Malpais--Eruption of Galongoon in
    Java--Submarine volcanoes--Graham island, formed in 1831--Volcanic
    archipelagoes--Submarine eruptions in mid-Atlantic--The
    Canaries--Teneriffe--Cones thrown up in Lancerote, 1730-36--Santorin
    and its contiguous isles--Barren island in the Bay of Bengal--Mud
    volcanoes--Mineral composition of volcanic products.


_Volcanic eruptions in Iceland._--With the exception of Etna and
Vesuvius, the most complete chronological records of a series of
eruptions are those of Iceland, for their history reaches as far back as
the ninth century of our era; and, from the beginning of the twelfth
century, there is clear evidence that, during the whole period, there
has never been an interval of more than forty, and very rarely one of
twenty years, without either an eruption or a great earthquake. So
intense is the energy of the volcanic action in this region, that some
eruptions of Hecla have lasted six years without ceasing. Earthquakes
have often shaken the whole island at once, causing great changes in the
interior, such as the sinking down of hills, the rending of mountains,
the desertion by rivers of their channels, and the appearance of new
lakes.[583] New islands have often been thrown up near the coast, some
of which still exist; while others have disappeared, either by
subsidence or the action of the waves.

In the interval between eruptions, innumerable hot springs afford vent
to subterranean heat, and solfataras discharge copious streams of
inflammable matter. The volcanoes in different parts of this island are
observed, like those of the Phlegræan Fields, to be in activity by
turns, one vent often serving for a time as a safety-valve to the rest.
Many cones are often thrown up in one eruption, and in this case they
take a linear direction, running generally from northeast to southwest,
from the northeastern part of the island, where the volcano Krabla lies,
to the promontory Reykianas.

_New island thrown up in 1783._--The convulsions of the year 1783 appear
to have been more tremendous than any recorded in the modern annals of
Iceland; and the original Danish narrative of the catastrophe, drawn up
in great detail, has since been substantiated by several English
travellers, particularly in regard to the prodigious extent of country
laid waste, and the volume of lava produced.[584] About a month previous
to the eruption on the mainland, a submarine volcano burst forth in the
sea in lat. 63° 25' N., long. 23° 44' W., at a distance of thirty miles
in a southwest direction from Cape Reykianas, and ejected so much
pumice, that the ocean was covered with that substance to the distance
of 150 miles, and ships were considerably impeded in their course. A new
island was thrown up, consisting of high cliffs, within which fire,
smoke, and pumice were emitted from two or three different points. This
island was claimed by his Danish Majesty, who denominated it Nyöe, or
the New Island; but before a year had elapsed, the sea resumed its
ancient domain, and nothing was left but a reef of rocks from five to
thirty fathoms under water.

_Great eruption of Skaptár Jokul._--Earthquakes which had long been felt
in Iceland, became violent on the 11th of June, 1783, when Skaptár
Jokul, distant nearly 200 miles from Nyöe, threw out a torrent of lava
which flowed down into the river Skaptâ, and completely dried it up. The
channel of the river was between high rocks, in many places from four
hundred to six hundred feet in depth, and near two hundred in breadth.
Not only did the lava fill up this great defile to the brink, but it
overflowed the adjacent fields to a considerable extent. The burning
flood, on issuing from the confined rocky gorge, was then arrested for
some time by a deep lake, which formerly existed in the course of the
river, between Skaptardal and Aa, which it entirely filled. The current
then advanced again, and reaching some ancient lava full of
subterraneous caverns, penetrated and melted down part of it; and in
some places, where the steam could not gain vent, it blew up the rock,
throwing fragments to the height of more than 150 feet. On the 18th of
June another ejection of liquid lava rushed from the volcano, which
flowed down with amazing velocity over the surface of the first stream.
By the damming up of the mouths of some of the tributaries of the
Skaptâ, many villages were completely overflowed with water, and thus
great destruction of property was caused. The lava, after flowing for
several days, was precipitated down a tremendous cataract called
Stapafoss, where it filled a profound abyss, which that great waterfall
had been hollowing out for ages, and after this, the fiery current
again continued its course.

On the third of August, fresh floods of lava still pouring from the
volcano, a new branch was sent off in a different direction; for the
channel of the Skaptâ was now so entirely choked up, and every opening
to the west and north so obstructed, that the melted matter was forced
to take a new course, so that it ran in a southeast direction, and
discharged itself into the bed of the river Hverfisfliot, where a scene
of destruction scarcely inferior to the former was occasioned. These
Icelandic lavas (like the ancient streams which are met with in
Auvergne, and other provinces of Central France), are stated by
Stephenson to have accumulated to a prodigious depth in narrow rocky
gorges; but when they came to wide alluvial plains, they spread
themselves out into broad burning lakes, sometimes from twelve to
fifteen miles wide, and one hundred feet deep. When the "fiery lake"
which filled up the lower portion of the valley of the Skaptâ, had been
augmented by new supplies, the lava flowed up the course of the river to
the foot of the hills from whence the Skaptâ takes its rise. This
affords a parallel case to one which can be shown to have happened at a
remote era in the volcanic region of the Vivarais in France, where lava
issued from the cone of Thueyts, and while one branch ran down, another
more powerful stream flowed up the channel of the river Ardêche.

The sides of the valley of the Skaptâ present superb ranges of basaltic
columns of older lava, resembling those which are laid open in the
valleys descending from Mont Dor, in Auvergne, where more modern
lava-currents, on a scale very inferior in magnitude to those of
Iceland, have also usurped the beds of the existing rivers. The eruption
of Skaptár Jokul did not entirely cease till the end of two years; and
when Mr. Paulson visited the tract eleven years afterwards, in 1794, he
found columns of smoke still rising from parts of the lava, and several
rents filled with hot water.[585]

Although the population of Iceland was very much scattered, and did not
exceed fifty thousand, no less than twenty villages were destroyed,
besides those inundated by water; and more than nine thousand human
beings perished, together with an immense number of cattle, partly by
the depredations of the lava, partly by the noxious vapors which
impregnated the air, and, in part, by the famine caused by showers of
ashes throughout the island, and the desertion of the coasts by the
fish.

_Immense volume of the lava._--But the extraordinary volume of melted
matter produced in this eruption deserves the particular attention of
the geologist. Of the two branches, which flowed in nearly opposite
directions, the greatest was fifty, and the lesser forty miles in
length. The extreme breadth which the Skaptâ branch attained in the low
countries was from twelve to fifteen miles, that of the other about
seven. The ordinary height of both currents was one hundred feet, but in
narrow defiles it sometimes amounted to six hundred. Professor Bischoff
has calculated that the mass of lava brought up from the subterranean
regions by this single eruption "surpassed in magnitude the bulk of Mont
Blanc."[586] But a more distinct idea will be formed of the dimensions
of the two streams, if we consider how striking a feature they would now
form in the geology of England, had they been poured out on the bottom
of the sea after the deposition and before the elevation of our
secondary and tertiary rocks. The same causes which have excavated
valleys through parts of our marine strata, once continuous, might have
acted with equal force on the igneous rocks, leaving, at the same time,
a sufficient portion undestroyed to enable us to discover their former
extent. Let us, then, imagine the termination of the Skaptá branch of
lava to rest on the escarpment of the inferior and middle oolite, where
it commands the vale of Gloucester. The great platform might be one
hundred feet thick, and from ten to fifteen miles broad, exceeding any
which can be found in Central France. We may also suppose great tabular
masses to occur at intervals, capping the summit of the Cotswold Hills
between Gloucester and Oxford, by Northleach, Burford, and other towns.
The wide valley of the Oxford clay would then occasion an interruption
for many miles; but the same rocks might recur on the summit of Cumnor
and Shotover Hills, and all the other oolitic eminences of that
district. On the chalk of Berkshire, extensive plateaus, six or seven
miles wide, would again be formed; and lastly, crowning the highest
sands of Highgate and Hampstead, we might behold some remnants of the
current five or six hundred feet in thickness, causing those hills to
rival, or even to surpass, in height, Salisbury Craigs and Arthur's
Seat.

The distance between the extreme points here indicated would not exceed
ninety miles in a direct line; and we might then add, at the distance of
nearly two hundred miles from London, along the coast of Dorsetshire and
Devonshire, for example, a great mass of igneous rocks, to represent
those of contemporary origin, which were produced beneath the level of
the sea, where the island of Nyöe rose up.

_Volume of ancient and modern flows of lava compared._--Yet, gigantic as
must appear the scale of these modern volcanic operations, we must be
content to regard them as perfectly insignificant in comparison to
currents of the primeval ages, if we embrace the theoretical views of
many geologists, which were not inaccurately expressed by the late
Professor Alexander Brongniart, when he declared that "aux époques
géognostiques anciennes, tous les phénomènes géologiques se passoient
dans des dimensions _centuples_ de celles qu'ils présentent
aujourd'hui."[587] Had Skaptár Jokul, therefore, been a volcano of the
olden time, it would have poured forth lavas at a single eruption a
hundred times more voluminous than those which were witnessed by the
present generation in 1783. But it may, on the contrary, be affirmed
that, among the older formations, no igneous rock of such colossal
magnitude has yet been met with; nay, it would be most difficult to
point out a mass of ancient date (distinctly referable to a single
eruption) which would even rival in volume the matter poured out from
Skaptár Jokul in 1783.

_Eruption of Jorullo in 1759._--As another example of the stupendous
scale of modern volcanic eruptions, I may mention that of Jorullo in
Mexico, in 1759. The great region to which this mountain belongs has
already been described. The plain of Malpais forms part of an elevated
platform, between two and three thousand feet above the level of the
sea, and is bounded by hills composed of basalt, trachyte, and volcanic
tuff, clearly indicating that the country had previously, though
probably at a remote period, been the theatre of igneous action. From
the era of the discovery of the New World to the middle of the last
century, the district had remained undisturbed, and the space, now the
site of the volcano, which is thirty-six leagues distant from the
nearest sea, was occupied by fertile fields of sugar-cane and indigo,
and watered by the two brooks Cuitimba and San Pedro. In the month of
June, 1759, hollow sounds of an alarming nature were heard, and
earthquakes succeeded each other for two months, until, at the end of
September, flames issued from the ground, and fragments of burning rocks
were thrown to prodigious heights. Six volcanic cones, composed of
scoriæ and fragmentary lava, were formed on the line of a chasm which
ran in the direction from N. N. E. to S. S. W. The least of these cones
was 300 feet in height; and Jorullo, the central volcano, was elevated
1600 feet above the level of the plain. It sent forth great streams of
basaltic lava, containing included fragments of granitic rocks, and its
ejections did not cease till the month of February, 1760.[588]

[Illustration: Fig. 57.

_a_, Summit of Jorullo. _b_, _c_, Inclined plane sloping at an angle of
6° from the base of the cones.]

Humboldt visited the country more than forty years after this
occurrence, and was informed by the Indians, that when they returned,
long after the catastrophe, to the plain, they found the ground
uninhabitable from the excessive heat. When he himself visited the
place, there appeared, around the base of the cones, and spreading from
them, as from a centre, over an extent of four square miles, a mass of
matter of a convex form, about 550 feet high at its junction with the
cones, and gradually sloping from them in all directions towards the
plain. This mass was still in a heated state, the temperature in the
fissures being on the decrease from year to year, but in 1780 it was
still sufficient to light a cigar at the depth of a few inches. On this
slightly convex protuberance, the slope of which must form an angle of
about 6° with the horizon, were thousands of flattish conical mounds,
from six to nine feet high, which, as well as large fissures traversing
the plain, acted as fumeroles, giving out clouds of sulphurous acid and
hot aqueous vapor. The two small rivers before mentioned disappeared
during the eruption, losing themselves below the eastern extremity of
the plain, and reappearing as hot springs at its western limit.

_Cause of the convexity of the plain of Malpais._--Humboldt attributed
the convexity of the plain to inflation from below; supposing the
ground, for four square miles in extent, to have risen up in the shape
of a bladder to the elevation of 550 feet above the plain in the highest
part. But Mr. Scrope has suggested that the phenomena may be accounted
for far more naturally, by supposing that lava flowing simultaneously
from the different orifices, and principally from Jorullo, united into a
sort of pool or lake. As they were poured forth on a surface previously
flat, they would, if their liquidity was not very great, remain thickest
and deepest near their source, and diminish in bulk from thence towards
the limits of the space which they covered. Fresh supplies were probably
emitted successively during the course of an eruption which lasted more
than half a year; and some of these, resting on those first emitted,
might only spread to a small distance from the foot of the cone, where
they would necessarily accumulate to a great height. The average slope
of the great dome-shaped volcanoes of the Sandwich Islands, formed
almost exclusively of lava, with scarce any scoriæ, is between 6° 30'
and 7° 46', so that the inclination of the convex mass around Jorullo,
if we adopt Mr. Scrope's explanation (see fig. 57), is quite in
accordance with the known laws which govern the flow of lava.

The showers, also, of loose and pulverulent matter from the six craters,
and principally from Jorullo, would be composed of heavier and more
bulky particles near the cones, and would raise the ground at their
base, where, mixing with rain, they might have given rise to the stratum
of black clay, which is described as covering the lava. The small
conical mounds (called "hornitos," or little ovens) may resemble those
five or six small hillocks which existed in 1823 on the Vesuvian lava,
and sent forth columns of vapor, having been produced by the
disengagement of elastic fluids heaping up small dome-shaped masses of
lava. The fissures mentioned by Humboldt as of frequent occurrence, are
such as might naturally accompany the consolidation of a thick bed of
lava, contracting as it congeals; and the disappearance of rivers is the
usual result of the occupation of the lower part of a valley or plain by
lava, of which there are many beautiful examples in the old
lava-currents of Auvergne. The heat of the "hornitos" is stated to have
diminished from the first; and Mr. Bullock, who visited the spot many
years after Humboldt, found the temperature of the hot spring very
low,--a fact which seems clearly to indicate the gradual congelation of
a subjacent bed of lava, which from its immense thickness may have been
enabled to retain its heat for half a century. The reader may be
reminded, that when we thus suppose the lava near the volcano to have
been, together with the ejected ashes, more than five hundred feet in
depth, we merely assign a thickness which the current of Skaptár Jokul
attained in some places in 1783.

_Hollow sound of the plain when struck._--Another argument adduced in
support of the theory of inflation from below, was, the hollow sound
made by the steps of a horse upon the plain; which, however, proves
nothing more than that the materials of which the convex mass is
composed are light and porous. The sound called "rimbombo" by the
Italians is very commonly returned by _made ground_ when struck sharply;
and has been observed not only on the sides of Vesuvius and other
volcanic cones where there is a cavity below, but in such regions as the
Campagna di Roma, composed in a great measure of tuff and porous
volcanic rocks. The reverberation, however, may perhaps be assisted by
grottoes and caverns, for these may be as numerous in the lavas of
Jorullo as in many of those of Etna; but their existence would lend no
countenance to the hypothesis of a great arched cavity, four square
miles in extent, and in the centre 550 feet high.[589]

_No recent eruptions of Jorullo._--In a former edition I stated that I
had been informed by Captain Vetch, that in 1819 a tower at Guadalaxara
was thrown down by an earthquake, and that ashes, supposed to have come
from Jorullo, fell at the same time at Guanaxuato, a town situated 140
English miles from the volcano. But Mr. Burkhardt, a German director of
mines, who examined Jorullo in 1827, ascertained that there had been no
eruption there since Humboldt's visit in 1803. He went to the bottom of
the crater, and observed a slight evolution of sulphurous acid vapors,
but the "hornitos" had entirely ceased to send forth steam. During the
twenty-four years intervening between his visit and that of Humboldt,
vegetation had made great progress on the flanks of the new hills; the
rich soil of the surrounding country was once more covered with
luxuriant crops of sugar-cane and indigo, and there was an abundant
growth of natural underwood on all the uncultivated tracts.[590]

_Galongoon, Java_, 1822.--The mountain of Galongoon (or Galung Gung) was
in 1822 covered by a dense forest, and situated in a fruitful and
thickly-peopled part of Java. There was a circular hollow at its summit,
but no tradition existed of any former eruption. In July, 1822, the
waters of the river Kunir, one of those which flowed from its flanks,
became for a time hot and turbid. On the 8th of October following a loud
explosion was heard, the earth shook, and immense columns of hot water
and boiling mud, mixed with burning brimstone, ashes, and lapilli, of
the size of nuts, were projected from the mountain like a waterspout,
with such prodigious violence that large quantities fell beyond the
river Tandoi, which is forty miles distant. Every valley within the
range of this eruption became filled with a burning torrent, and the
rivers, swollen with hot water and mud, overflowed their banks, and
carried away great numbers of the people, who were endeavoring to
escape, and the bodies of cattle, wild beasts, and birds. A space of
twenty-four miles between the mountain and the river Tandoi was covered
to such a depth with bluish mud that people were buried in their houses,
and not a trace of the numerous villages and plantations throughout that
extent was visible. Within this space the bodies of those who perished
were buried in mud and concealed, but near the limits of the volcanic
action they were exposed, and strewed over the ground in great numbers,
partly boiled and partly burnt.

It was remarked, that the boiling mud and cinders were projected with
such violence from the mountain, that while many remote villages were
utterly destroyed and buried, others much nearer the volcano were
scarcely injured.

The first eruption lasted nearly five hours, and on the following days
the rain fell in torrents, and the rivers, densely charged with mud,
deluged the country far and wide. At the end of four days (October 12th)
a second eruption occurred more violent than the first, in which hot
water and mud were again vomited, and great blocks of basalt were thrown
to the distance of seven miles from the volcano. There was at the same
time a violent earthquake, and in one account it is stated that the face
of the mountain was utterly changed, its summits broken down, and one
side, which had been covered with trees, became an enormous gulf in the
form of a semicircle. This cavity was about midway between the summit
and the plain, and surrounded by steep rocks, said to be newly heaped up
during the eruption. New hills and valleys are said to have been formed,
and the rivers Banjarang and Wulan changed their course, and in one
night (October 12th) 2000 persons were killed.

The first intimation which the inhabitants of Bandong received of this
calamity on the 8th of October, was the news that the river Wulna was
bearing down into the sea the dead bodies of men, and the carcasses of
stags, rhinoceroses, tigers, and other animals. The Dutch painter Payen
determined to travel from thence to the volcano, and he found that the
quantity of the ashes diminished as he approached the base of the
mountain. He alludes to the altered form of the mountain after the 12th,
but does not describe the new semicircular gulf on its side.

The official accounts state that 114 villages were destroyed, and above
4000 persons killed.[591]

_Submarine volcanoes._--Although we have every reason to believe that
volcanic eruptions as well as earthquakes are common in the bed of the
sea, it was not to be expected that many opportunities would occur to
scientific observers of witnessing the phenomena. The crews of vessels
have sometimes reported that they have seen in different places
sulphurous smoke, flame, jets of water, and steam, rising up from the
sea, or they have observed the waters greatly discolored, and in a state
of violent agitation as if boiling. New shoals have also been
encountered, or a reef of rocks just emerging above the surface, where
previously there was always supposed to have been deep water. On some
few occasions the gradual formation of an island by a submarine eruption
has been observed, as that of Sabrina, in the year 1811, off St.
Michael's in the Azores. The throwing up of ashes in that case, and the
formation of a cone about three hundred feet in height, with a crater in
the centre, closely resembled the phenomena usually accompanying a
volcanic eruption on land. Sabrina was soon washed away by the waves.
Previous eruptions in the same part of the sea were recorded to have
happened in 1691 and 1720. The rise of Nyöe, also, a small island off
the coast of Iceland, in 1783, has already been alluded to; and another
volcanic isle was produced by an eruption near Reikiavig, on the same
coast, in June, 1830.[592]

_Graham Island_[593], 1831.--We have still more recent and minute
information respecting the appearance, in 1831, of a new volcanic island
in the Mediterranean, between the S. W. coast of Sicily and that
projecting part of the African coast where ancient Carthage stood. The
site of the island was not any part of the great shoal, or bank, called
"Nerita," as was first asserted, but a spot where Captain W. H. Smyth
had found, in his survey a few years before, a depth of more than one
hundred fathoms water.[594]

[Illustration: Fig. 58. Form of the cliffs of Graham Island, as seen
from S. S. E., distant one mile, 7th August, 1831.[596]]

[Illustration: Fig. 59. View of the interior of Graham Island, 29th
Sept., 1831.]

[Illustration: Fig. 60. Graham Island, 29th Sept., 1831.[597]]

The position of the island (lat. 37° 8' 30" N., long. 12° 42' 15" E.)
was about thirty miles S. W. of Sciacca, in Sicily, and thirty-three
miles N. E. of Pantellaria.[595] On the 28th of June, about a fortnight
before the eruption was visible, Sir Pulteney Malcolm, in passing over
the spot in his ship, felt the shocks of an earthquake, as if he had
struck on a sand-bank; and the same shocks were felt on the west coast
of Sicily, in a direction from S. W. to N. E. About the 10th of July,
John Corrao, the captain of a Sicilian vessel, reported that, as he
passed near the place, he saw a column of water like a water-spout,
sixty feet high, and 800 yards in circumference, rising from the sea,
and soon afterwards a dense steam in its place, which ascended to the
height of 1800 feet. The same Corrao, on his return from Girgenti, on
the 18th of July, found a small island, twelve feet high with a crater
in its centre, ejecting volcanic matter, and immense columns of vapor;
the sea around being covered with floating cinders and dead fish. The
scoriæ were of a chocolate color, and the water which boiled in the
circular basin was of a dingy red. The eruption continued with great
violence to the end of the same month; at which time the island was
visited by several persons, and among others by Capt. Swinburne, R. N.,
and M. Hoffmann, the Prussian geologist. It was then from fifty to
ninety feet in height, and three-quarters of a mile in circumference. By
the 4th of August it became, according to some accounts, above 200 feet
high, and three miles in circumference; after which it began to diminish
in size by the action of the waves, and it was only two miles round on
the 25th of August; and on the 3d of September, when it was carefully
examined by Captain Wodehouse, only three-fifths of a mile in
circumference; its greatest height being then 107 feet. At this time the
crater was about 780 feet in circumference. On the 29th of September,
when it was visited by Mons. C. Prevost, its circumference was reduced
to about 700 yards. It was composed entirely of incoherent ejected
matter, scoriæ, pumice, and lapilli, forming regular strata, some of
which are described as having been parallel to the steep inward slope of
the crater, while the rest were inclined outwards, like those of
Vesuvius.[598] When the arrangement of the ejected materials has been
determined by their falling continually on two steep slopes, that of the
external cone and that of the crater, which is always a hollow inverted
cone, a transverse section would probably resemble that given in the
annexed figure (61). But when I visited Vesuvius, in 1828, I saw no beds
of scoriæ inclined towards the axis of the cone. (See fig. 45, p. 381.)
Such may have once existed; but the explosions or subsidences, or
whatever causes produced the great crater of 1822, had possibly
destroyed them.

[Illustration: Fig. 61.]

Few of the pieces of stone thrown out from Graham Island exceeded a foot
in diameter. Some fragments of dolomitic limestone were intermixed; but
these were the only non-volcanic substances. During the month of August,
there occurred on the S. W. side of the new island a violent ebullition
and agitation of the sea, accompanied by the constant ascension of a
column of dense white steam, indicating the existence of a second vent
at no great depth from the surface. Towards the close of October, no
vestige of the crater remained, and the island was nearly levelled with
the surface of the ocean, with the exception, at one point, of a small
monticule of sand and scoriæ. It was reported that, at the commencement
of the year following (1832), there was a depth of 150 feet where the
island had been: but this account was quite erroneous; for in the early
part of that year Captain Swinburne found a shoal and discolored water
there, and towards the end of 1833 a dangerous reef existed of an oval
figure, about three-fifths of a mile in extent. In the centre was a
black rock, of the diameter of about twenty-six fathoms, from nine to
eleven feet under water; and round this rock are banks of black volcanic
stones and loose sand. At the distance of sixty fathoms from this
central mass, the depth increased rapidly. There was also a second shoal
at the distance of 450 feet S. W. of the great reef, with fifteen feet
water over it, also composed of rock, surrounded by deep sea. We can
scarcely doubt that the rock in the middle of the larger reef is solid
lava, which rose up in the principal crater, and that the second shoal
marks the site of the submarine eruption observed in August, 1831, to
the S. W. of the island.

From the whole of the facts above detailed, it appears that a hill eight
hundred feet or more in height was formed by a submarine volcanic vent,
of which the upper part (only about two hundred feet high) emerged above
the waters, so as to form an island. This cone must have been equal in
size to one of the largest of the lateral volcanoes on the flanks of
Etna, and about half the height of the mountain Jorullo in Mexico, which
was formed in the course of nine months, in 1759. In the centre of the
new volcano a large cavity was kept open by gaseous discharges, which
threw out scoriæ; and fluid lava probably rose up in this cavity. It is
not uncommon for small subsidiary craters to open near the summit of a
cone, and one of these may have been formed in the case of Graham
Island; a vent, perhaps, connected with the main channel of discharge
which gave passage in that direction to elastic fluids, scoriæ, and
melted lava. It does not appear that, either from this duct, or from the
principal vent, there was any overflowing of lava; but melted rock may
have flowed from the flanks or base of the cone (a common occurrence on
land), and may have spread in a broad sheet over the bottom of the sea.

[Illustration: Fig. 62.

Supposed section of Graham Island. (C. Maclaren.[599])]

The dotted lines in the annexed figure are an imaginary restoration of
the upper part of the cone, now removed by the waves: the strong lines
represent the part of the volcano which is still under water: in the
centre is a great column, or dike, of solid lava, two hundred feet in
diameter, supposed to fill the space by which the gaseous fluids rose;
and on each side of the dike is a stratified mass of scoriæ and
fragmentary lava. The solid nucleus of the reef, where the black rock is
now found, withstands the movements of the sea; while the surrounding
loose tuffs are cut away to a somewhat lower level. In this manner the
lava, which was the lowest part of the island, or, to speak more
correctly, which scarcely ever rose above the level of the sea when the
island existed, has now become the highest point in the reef.

No appearances observed, either during the eruption or since the island
disappeared, gave the least support to the opinion promulgated by some
writers, that part of the ancient bed of the sea had been lifted up
bodily.

The solid products, says Dr. John Davy, whether they consisted of sand,
light cinders, or vesicular lava, differed more in form than in
composition. The lava contained augite; and the specific gravity was
2·07 and 2·70. When the light spongy cinder, which floated on the sea,
was reduced to fine powder by trituration, and the greater part of the
entangled air got rid of, it was found to be of the specific gravity
2·64; and that of some of the sand which fell in the eruption was
2·75;[600] so that the materials equalled ordinary granites in weight
and solidity. The only gas evolved in any considerable quantity was
carbonic acid.[601]

_Submarine eruptions in mid-Atlantic._--In the Nautical Magazine for
1835, p. 642, and for 1838, p. 361, and in the Comptes Rendus, April,
1838, accounts are given of a series of volcanic phenomena, earthquakes,
troubled water, floating scoriæ and columns of smoke, which have been
observed at intervals since the middle of the last century, in a space
of open sea between longitudes 20° and 22° west, about half a degree
south of the equator. These facts, says Mr. Darwin, seem to show, that
an island or an archipelago is in process of formation in the middle of
the Atlantic; a line joining St. Helena and Ascension would, if
prolonged, intersect this slowly nascent focus of volcanic action.[602]
Should land be eventually formed here, it will not be the first that has
been produced by igneous action in this ocean since it was inhabited by
the existing species of testacea. At Porto Praya in St. Jago, one of the
Azores, a horizontal, calcareous stratum occurs, containing shells of
recent marine species, covered by a great sheet of basalt eighty feet
thick.[603] It would be difficult to estimate too highly the commercial
and political importance which a group of islands might acquire, if in
the next two or three thousand years they should rise in mid-ocean
between St. Helena and Ascension.


CANARY ISLANDS.

_Eruption in Lancerote, 1730 to 1736._--The effects of an eruption which
happened in Lancerote, one of the Canary Islands, between the years 1730
and 1736, were very remarkable; and a detailed description has been
published by Von Buch, who had an opportunity, when he visited that
island in 1815, of comparing the accounts transmitted to us of the
event, with the present state and geological appearances of the
country.[604] On the 1st of September, 1730, the earth split open on a
sudden two leagues from Yaira. In one night a considerable hill of
ejected matter was thrown up; and, a few days later, another vent
opened, and gave out a lava-stream, which overran Chinanfaya and other
villages. It flowed first rapidly, like water, but became afterwards
heavy and slow, like honey. On the 7th of September an immense rock was
protruded from the bottom of the lava with a noise like thunder, and the
stream was forced to change its course from N. to N. W., so that St.
Catalina and other villages were overflowed.

Whether this mass was protruded by an earthquake, or was a mass of
ancient lava, blown up like that before mentioned in 1783 in Iceland, is
not explained.

On the 11th of September more lava flowed out, and covered the village
of Maso entirely, and for the space of eight days precipitated itself
with a horrible roar into the sea. Dead fish floated on the waters in
indescribable multitudes, or were thrown dying on the shore. After a
brief interval of repose, three new openings broke forth immediately
from the site of the consumed St. Catalina, and sent out an enormous
quantity of lapilli, sand, and ashes. On the 28th of October the cattle
throughout the whole country dropped lifeless to the ground, suffocated
by putrid vapors, which condensed and fell down in drops. On the 1st of
December a lava-stream reached the sea, and formed an island, round
which dead fish were strewed.

_Number of cones thrown up._--It is unnecessary here to give the details
of the overwhelming of other places by fiery torrents, or of a storm
which was equally new and terrifying to the inhabitants, as they had
never known one in their country before. On the 10th of January, 1731, a
high hill was thrown up, which, on the same day, precipitated itself
back again into its own crater; fiery brooks of lava flowed from it to
the sea. On the 3d of February a new cone arose. Others were thrown up
in March, and poured forth lava-streams. Numerous other volcanic cones
were subsequently formed in succession, till at last their number
amounted to about thirty. In June, 1731, during a renewal of the
eruptions, all the banks and shores in the western part of the island
were covered with dying fish, of different species, some of which had
never before been seen. Smoke and flame arose from the sea, with loud
detonations. These dreadful commotions lasted without interruption for
_five successive years_, so that a great emigration of the inhabitants
became necessary.

_Their linear direction._--As to the height of the new cones, Von Buch
was assured that the formerly great and flourishing St. Catalina lay
buried under hills 400 feet in height; and he observes that the most
elevated cone of the series rose 600 feet above its base, and 1378 feet
above the sea, and that several others were nearly as high. The new
vents were all arranged _in one line_, about two geographical miles
long, and in a direction nearly east and west. If we admit the
probability of Von Buch's conjecture, that these vents opened along the
line of a cleft, it seems necessary to suppose that this subterranean
fissure was only prolonged upwards to the surface by degrees, and that
the rent was narrow at first, as is usually the case with fissures
caused by earthquakes. Lava and elastic fluids might escape from some
point on the rent where there was least resistance, till, the first
aperture becoming obstructed by ejections and the consolidation of lava,
other orifices burst open in succession along the line of the original
fissure. Von Buch found that each crater was lowest on that side on
which lava had issued; but some craters were not breached, and were
without any lava streams. In one of these were open fissures, out of
which hot vapors rose, which in 1815 raised the thermometer to 145°
Fahrenheit, and was probably at the boiling point lower down. The
exhalations seemed to consist of aqueous vapor; yet they could not be
pure steam, for the crevices were incrusted on either side by siliceous
sinter (an opal-like hydrate of silica of a white color), which extended
almost to the middle. This important fact attests the length of time
during which chemical processes continue after eruptions, and how open
fissures may be filled up laterally by mineral matter, sublimed from
volcanic exhalations. The lavas of this eruption covered nearly a third
of the whole island, often forming on slightly inclined planes great
horizontal sheets several square leagues in area, resembling very much
the basaltic platforms of Auvergne.

_Pretended distinction between ancient and modern lavas._--One of the
new lavas was observed to contain masses of olivine of an olive-green
color, resembling those which occur in one of the lavas of the Vivarais.
Von Buch supposes the great crystals of olivine to have been derived
from a previously existing basalt melted up by the new volcanoes; but we
have scarcely sufficient data to bear out such a conjecture. The older
rocks of the island consist, in a great measure, of that kind of
basaltic lava called dolerite, sometimes columnar, and partly of common
basalt and amygdaloid. Some recent lavas assumed, on entering the sea, a
prismatic form, and so much resembled the older lavas of the Canaries,
that the only geological distinction which Von Buch appears to have been
able to draw between them was, that they did not alternate with
conglomerates, like the ancient basalts. Some modern writers have
endeavored to discover, in the abundance of these conglomerates, a proof
of the dissimilarity of the volcanic action in ancient and modern times;
but this character is more probably attributable to the difference
between submarine operations and those on the land. All the blocks and
imperfectly rounded fragments of lava, transported during the intervals
of eruption, by rivers and torrents, into the adjoining sea, or torn by
the continued action of the waves from cliffs which are undermined, must
accumulate in stratified breccias and conglomerates, and be covered
again and again by other lavas. This is now taking place on the shores
of Sicily, between Catania and Trezza, where the sea breaks down and
covers the shore with blocks and pebbles of the modern lavas of Etna;
and on parts of the coast of Ischia, where numerous currents of trachyte
are in like manner undermined in lofty precipices. So often, then, as an
island is raised in a volcanic archipelago by earthquakes from the deep,
the fundamental and (relatively to all above) the oldest lava will often
be distinguishable from those formed by subsequent eruptions on dry
land, by their alternation with beds of sandstone and fragmentary rocks.

The supposed want of identity, then, between the volcanic phenomena of
different epochs resolves itself partly at least into the marked
difference between the operations simultaneously in progress, above and
below the waters. Such, indeed, is the source, as was before stated in
the First Book (Chap. V.), of many of our strongest theoretical
prejudices in geology. No sooner do we study and endeavor to explain
submarine appearances, than we feel, to use a common expression, out of
our element; and unwilling to concede that our extreme ignorance of
processes now continually going on can be the cause of our perplexity,
we take refuge in a "pre-existent order of nature."

_Recent formation of oolitic travertin in Lancerote._--Throughout a
considerable part of Lancerote, the old lavas are covered by a thin
stratum of limestone, from an inch to two feet in thickness. It is of a
hard stalactitic nature, sometimes oolitic, like the Jura limestone, and
contains fragments of lava and terrestrial shells, chiefly helices and
spiral bulimi. It sometimes rises to the height of 800 feet above the
level of the sea. Von Buch imagines that this remarkable superstratum
has been produced by the furious northwest storms, which in winter drive
the spray of the sea in clouds over the whole island; from whence
calcareous particles may be deposited stalactitically. Mr. Darwin
informs me that he found a limestone in St. Helena, the harder parts of
which correspond precisely to the stone of Lancerote. He attributes the
origin of this rock in St. Helena not to the spray of the sea, but to
drifting by violent winds of the finer particles of shells from the
sea-beach. Some parts of this drift are subsequently dissolved by
atmospheric moisture, and redeposited, so as to convert calcareous sand
into oolite.

_Recent eruption in Lancerote._--From the year 1736 to 1815, when Von
Buch visited Lancerote, there had been no eruption; but, in August,
1824, a crater opened near the port of Rescif, and formed by its
ejections, in the space of twenty-four hours, a considerable hill.
Violent earthquakes preceded and accompanied this eruption.[605]

_Teneriffe._--The Peak of Teneriffe is about 12,000 feet high, and
stands, says Von Buch, like a tower encircled by its fosse and bastion.
The bastion consists, like the semicircular escarpment of Somma turned
towards Vesuvius, of precipitous cliffs, composed of trachyte, basalt,
coarse conglomerates, and tuffs, traversed by volcanic dikes, mostly
vertical, and of basalt. These cliffs vary in height from 1000 to 1800
feet, and are supposed by Von Buch to have been heaved up into their
present position by a force exerted from below, in accordance with the
theory proposed by the same author for the origin of the cones of
Vesuvius and Etna. According to the observations of M. Deville in
1839[606], the trachytes are often granitoid in their aspect, and
contain instead of glassy felspar the allied mineral called oligoclase,
which had been previously considered as characteristic of more ancient
igneous rocks. The same traveller supposes, although he found no
limestone or trace of fossils in any of the rocks of Teneriffe, that the
alternating trachytes and trachytic conglomerates originated beneath the
sea. If this opinion be correct, and it is at least very probable,
geologists may still speculate on two modes in which the mass of the
island acquired its present form and elevation above the sea. 1st, The
advocates of Von Buch's crater-of-elevation hypothesis may imagine that
a succession of horizontally superimposed beds were upheaved by a sudden
movement, and tilted so as to dip in all directions outwards from the
centre of a new dome-shaped eminence, in the middle of which a large
opening or bowl-shaped cavity was produced. 2dly, Or according to the
theory which to me appears preferable, a submarine hill in the form of a
flattened dome may have gradually accumulated, partly below the waters
and partly above by the continued outpourings of sheets of lava and the
ejection of ashes from a central orifice. In this case the dikes would
represent the fissures, which were filled during successive eruptions,
and the original inclination of the beds may have been increased by the
distension and upheaval of the mass during reiterated convulsions,
acting most forcibly at or near the channel of discharge, which would
become partially sealed up with lava from time to time, and then be
burst open again during eruptions. At length the whole island may have
been raised bodily out of the sea by a gradual upward movement.

Whatever theory we adopt, we must always explain the abrupt termination
of the dikes and layers of trachyte and basalt in the steep walls of the
escarpments surrounding the great crater by supposing the removal of
part of the materials once prolonged farther inward towards the centre.
If, according to the elevation-crater hypothesis, a series of sheets of
lava and ashes originally spread over a level and even surface have been
violently broken and uplifted, why do not the opposite walls of the
chasm correspond in such a manner as to imply by their present outline
that they were formerly united? It is evident that the precipices on
opposite sides of the crateriform hollow would not fit if brought
together, there being no projecting masses in one wall to enter into
indentations in the other, as would happen with the sides of many
mineral veins, trap-dikes, and faults, could we extract the intrusive
matter now separating them, and reunite the rocks which have been
fractured and disjoined.

The highest crater of the peak has merely disengaged sulphureous vapors
ever since it has been known to Europeans; but an eruption happened in
June, 1798, not far from the summit, and others are recorded, which
poured out streams of lava from great heights, besides many which have
broken out nearer the level of the sea. All these, however, seem to be
dependent on one great centre of eruption, or on that open channel
communicating between the interior of the earth and the atmosphere,
which terminates in the highest crater of the peak.

We may consider Teneriffe, then, as having been from a remote period the
principal and habitual vent of the volcanic archipelago of the Canaries.
The discharges which have taken place in the contiguous isles of Palma,
Lancerote, and the rest, may be of a subsidiary kind, and have probably
been most frequent and violent when the greater crater has been
partially sealed up, just as the violent eruptions of Ischia or that of
Monte Nuovo coincided with the dormant state of Vesuvius.


SANTORIN.

The Gulf of Santorin, in the Grecian Archipelago, has been for two
thousand years a scene of active volcanic operations. The largest of the
three outer islands of the group (to which the general name of Santorin
is given) is called Thera (or sometimes Santorin), and forms more than
two-thirds of the circuit of the gulf (see Map, fig. 63, p. 442). The
length of the exterior coast-line of this and the other two islands
named Therasia and Aspronisi, taken together, amounts to about thirty
miles, and that of the inner coast-line of the same islands to about
eighteen miles. In the middle of the gulf are three other islands,
called the Little, the New, and the Old "Kaimenis," or "Burnt Islands."
The accompanying map has been reduced from a recent survey executed in
1848 by Captain Graves, R. N., and shortly to be published by the
Admiralty.

[Illustration: Fig. 63.

Map of Santorin in the Grecian Archipelago, from a Survey in 1848, by
Captain Graves, R. N.


  _The soundings are given in fathoms._

  A, Shoal formed by submarine volcanic eruption in 1650.
  B, Northern entrance.
  C, Mansell's Rock.
  D, Mount St. Elias, 1887 feet high.

]

[Illustration: Fig. 64.

Section of Santorin, in a N. E. and S. W. direction, from Thera through
the Kaimenia to Aspronisi.]

[Illustration: Fig. 65.

Part of the section, fig. 64, enlarged.]

Pliny informs us that the year 186, B. C., gave birth to the Old
Kaimeni, also called Hiera, or the "Sacred Isle," and in the year 19 of
our era "Thia" (the Divine) made its appearance above water, and was
soon joined by subsequent eruptions to the older island, from which it
was only 250 paces distant. The Old Kaimeni also increased successively
in size in 726 and in 1427. A century and a half later, in 1573, another
eruption produced the cone and crater called Micra-Kaimeni, or "the
Small Burnt Island." The next great event which we find recorded
occurred in 1650, when a submarine outbreak violently agitated the sea,
at a point three and a half miles to the N. E. of Thera, and which gave
rise to a shoal (see A in the map) carefully examined during the late
survey in 1848 by Captain Graves, and found to have ten fathoms water
over it, the sea deepening around it in all directions. This eruption
lasted three months, covering the sea with floating pumice. At the same
time an earthquake destroyed many houses in Thera, while the sea broke
upon the coast and overthrew two churches, exposing to view two
villages, one on each side of the mountain of St. Stephen, both of
which must have been overwhelmed by showers of volcanic matter during
some previous eruptions of unknown date.[607] The accompanying evolution
of sulphur and hydrogen issuing from the sea killed more than fifty
persons, and above 1000 domestic animals. A wave, also, 50 feet high,
broke upon the rocks of the Isle of Nia, about four leagues distant, and
advanced 450 yards into the interior of the Island of Sikino. Lastly, in
1707 and 1709, Nea-Kaimeni, or the New Burnt Island, was formed between
the two others, Palaia and Micra, the Old and Little isles. This isle
was composed originally of two distinct parts; the first which rose was
called the White Island, composed of a mass of pumice, extremely porous.
Gorce, the Jesuit, who was then in Santorin, says that the rock "cut
like bread," and that, when the inhabitants landed on it, they found a
multitude of full-grown fresh oysters adhering to it, which they
ate.[608] This mass was afterwards covered, in great part, by the matter
ejected from the crater of a twin-island formed simultaneously, and
called Black Island, consisting of brown trachyte. The trachytic lava
which rose on this spot appears to have been a long time in an
intumescent state, for the New Kaimeni was sometimes lowered on one side
while it gained height on the other, and rocks rose up in the sea at
different distances from the shore and then disappeared again. The
eruption was renewed at intervals during the years 1711 and 1712, and at
length a cone was piled up to the height of 330 feet above the level of
the sea, its exterior slope forming an angle of 33° with the horizon,
and the crater on its summit being 80 yards in diameter. In addition to
the two points of subaerial eruption on the New and Little Kaimenis, two
other cones, indicating the sites of submarine outbursts of unknown
date, were discovered under water near the Kaimenis during the late
survey.

In regard to the "White Island," which was described and visited by
Gorce in 1707, we are indebted to Mr. Edward Forbes for having, in 1842,
carefully investigated the layer of pumiceous ash of which it is
constituted. He obtained from it many shells of marine genera,
Pectunculus, Arca, Cardita, Trochus, and others, both univalve and
bivalve, all of recent Mediterranean species. They were in a fine state
of preservation, the bivalves with the epidermis remaining, and valves
closed, showing that they had been suddenly destroyed. Mr. Forbes, from
his study of the habits of the mollusca living at different depths in
the Mediterranean, was able to decide that such an assemblage of species
could not have lived at a less depth than 220 feet, so that a bodily
upheaval of the mass to that amount must have taken place in order to
bring up this bed of ashes and shells to the level of the sea, and they
now rise five or six feet above that level.[609]

We may compare this partial elevation of solid matter to the rise of a
hardened crust of scoriæ, such as is usually formed on the surface of
lava-currents, even while they are in motion, and which, although stony
and capable of supporting heavy weights, may be upraised without
bursting by the intumescence of the melted matter below. That the
upheaval was merely local is proved by the fact that the neighboring
Kaimenis did not participate in the movement, still less the three more
distant or outer islands before mentioned. The history, therefore, of
the Kaimenis shows that they have been the result of intermittent
action, and it lends no support to the hypothesis of the sudden
distension of horizontal beds blown up like a bladder by a single
paroxysmal effort of expansive gases.

It will be seen by the accompanying map and sections, that the Kaimenis
are arranged in a linear direction, running N. E. and S. W., in a manner
different from that represented in the older charts. In their longest
diameter they form at their base a ridge nearly bisecting the gulf or
crater (see sections, figs. 64, 65).

On considering these facts we are naturally led to compare the smaller
and newer islands in the centre of the gulf to the modern cone of
Vesuvius, surrounded by the older semicircular escarpment of Somma, or
to liken them to the Peak of Teneriffe before described, as surrounded
by its "fosse and bastion." This idea will appear to be still more fully
confirmed when we study the soundings taken during the late
hydrographical survey. Thera, which constitutes alone more than
two-thirds of the outer circuit, presents everywhere towards the gulf,
high and steep precipices composed of rocks of volcanic origin. In all
places near the base of its cliffs, a depth of from 800 to 1000 feet of
water was found, and Lieut. Leycester informs us[610] that if the gulf,
which is six miles in diameter, could be drained, a bowl-shaped cavity
would appear with walls 2449 feet high in some places, and even on the
southwest side, where it is lowest, nowhere less than 1200 feet high;
while the Kaimenis would be seen to form in the centre a huge mountain
five and a half miles in circumference at its base, with three principal
summits (the Old, the New, and the Little Burnt Islands) rising
severally to the heights of 1251, 1629, and 1158 feet above the bottom
of the abyss. The rim of the great caldron thus exposed would be
observed to be in all parts perfect and unbroken, except at one point
where there is a deep and long chasm or channel, known by mariners as
"the northern entrance" (B, fig. 63) between Thera and Therasia, and
called by Lieut. Leycester "the door into the crater." It is no less
than 1170 feet deep, and constitutes, as will appear by the soundings
(see map), a remarkable feature in the bed of the sea. There is no
corresponding channel passing out from the gulf into the Mediterranean
at any other point in the circuit between the outer islands, the
greatest depth there ranging from 7 to 66 feet.

We may conceive, therefore, if at some former time the whole mass of
Santorin stood at a higher level by 1200 feet, that this single ravine
or narrow valley now forming "the northern entrance," was the passage by
which the sea entered a circular bay and swept out in the form of mud
and pebbles, the materials derived by denudation from wasting cliffs. In
this manner the original crater may have been slowly widened and
deepened, after which the whole archipelago may have been partially
submerged to its present depth.

That such oscillations of level may in the course of ages have taken
place, will be the more readily admitted when we state that part of
Thera has actually sunk down in modern times, as, for example, during
the great earthquake before alluded to, which happened in 1650. The
subsidence alluded to is proved not only by tradition, but by the fact
that a road which formerly led between two places on the east coast of
Thera is now twelve fathoms under water.

MM. Boblaye and Virlet mention,[611] that the waves are constantly
undermining and encroaching on the cliffs of Therasia and Aspronisi, and
shoals or submarine ledges were found, during the late survey, to occur
round a great part of these islands, attesting the recent progress of
denudation. M. Virlet also remarks, in regard to the separation of the
three islands forming the walls of the crater, that the channels between
them are all to the W. and N. W., the quarter most exposed to the waves
and currents.

Mr. Darwin, in his work on volcanic islands, has shown that in the
Mauritius and in Santiago, there is an external circle of basaltic rocks
of vast diameter, in the interior of which more modern eruptions have
taken place, the older rocks dipping away from the central space in
every direction, as in the outer islands of Santorin. He refers the
numerous breaches, some of them very wide in the external ramparts of
those islands, to the denuding action of the sea. Every geologist,
therefore, will be prepared to call in the aid of the same powerful
cause, to account for the removal of a large part of the rocks which
must once have occupied the interior space, in the same manner as they
attribute the abstraction of matter from elliptical "valleys of
elevation," such as those of Woolhope and the Wealden in England, to the
waves and currents of the sea.

Thera, Therasia, and Aspronisi are all composed of volcanic matter,
except the southern part of Thera, where Mount St. Elias rises to three
times the height of the loftiest of the igneous rocks, reaching an
elevation of 1887 feet above the sea.[612] This mountain is formed of
granular limestone and argillaceous schist, and must have been
originally a submarine eminence in the bed of the Mediterranean, before
the volcanic cone, one side of the base of which now abuts against it,
was formed. The inclination, strike, and fractures of the calcareous and
argillaceous strata of St. Elias have no relation to the great cone,
but, according to M. Bory St. Vincent, have the same direction as those
of the other isles of the Grecian Archipelago, namely, from N. N. W. to
S. S. E. Each of the three islands, Thera, Therasia, and Aspronisi, is
capped by an enormous mass of white tufaceous conglomerate, from forty
to fifty feet thick, beneath which are beds of trachytic lava and tuff,
having a gentle inclination of only 3° or 4°. Each bed is usually very
narrow and discontinuous, the successive layers being moulded or
dove-tailed, as M. Virlet expresses it, into the inequalities of the
previously existing surface, on which showers of cinders or streams of
melted matter have been poured. Nothing, therefore, seems more evident
than that we have in Santorin the basal remains of a great ruined cone,
or flattened dome; and the absence of dikes in the cliffs surrounding
the gulf would indicate that the eruptions took place originally, as
they have done in the last two thousand years, not near the margin but
in the centre of the space now occupied by the gulf. The central
portions of the dome have since been removed by engulfment, or
denudation, or by both these causes.

An important fact is adduced by M. Virlet, to show that the gentle dip
of the lava-streams in the three outer islands towards all points of the
compass, away from the centre of the gulf, has not been due to the
upheaval of horizontal beds, as conjectured by Von Buch, who had not
visited Santorin.[613] The French geologist found that the vesicles or
pores of the trachytic masses were lengthened out in the several
directions in which they would have flowed if they had descended from
the axis of a cone once occupying the centre of the crater. For it is
well known that the bubbles of confined gas in a fluid in motion assume
an oval form, and the direction of their longer axis coincides always
with that of the stream.

On a review, therefore, of all the facts now brought to light respecting
Santorin, I attribute the moderate slope of the beds in Thera and the
other external islands to their having originally descended the inclined
flanks of a large volcanic cone, the principal orifice or vents of
eruption having been always situated where they are now, in or near the
centre of the space occupied by the gulf or crater--in other words,
where the outburst of the Kaimenis has been witnessed in historical
times. The single long and deep opening into the crater is a feature
common to all those remnants of ancient volcanoes, the central portions
of which have been removed, and is probably connected with aqueous
denudation. This denuding process has been the work of ages when the sea
was admitted into an original crater, and has taken place during the
gradual emergence of the island from the sea, or during various
oscillations in its level.

The volcanic island of St. Paul in the midst of the Indian Ocean, lat.
38° 44' S., long. 77° 37' E., surveyed by Capt. Blackwood in 1842, seems
to exemplify the first stage in the formation of such an archipelago as
that of Santorin. We have there a crater one mile in diameter,
surrounded by steep and lofty cliffs on every side save one, where the
sea enters by a single passage nearly dry at low water. In the interior
of the small circular bay or crater there is a depth of 30 fathoms, or
180 feet. The surface of the island slopes away on all sides from the
crest of the rocks encircling the crater.[614]

[Illustration: Fig. 66.

Cone and crater of Barren Island, in the Bay of Bengal. Height of the
central cone (according to Capt Miller, in 1834), 500 feet.]

_Barren Island._--There is great analogy between the structure of Barren
Island in the Bay of Bengal, lat. 12° 15', and that of Santorin last
described. When seen from the ocean, this island presents, on almost all
sides, a surface of bare rocks, rising, with a moderate acclivity,
towards the interior; but at one point there is a cleft by which we can
penetrate into the centre, and there discover that it is occupied by a
great circular basin, filled by the waters of the sea, and bordered all
around by steep rocks, in the midst of which rises a volcanic cone, very
frequently in eruption. The summit of this cone is about 500 feet in
height, corresponding to that of the circular border which incloses the
basin; so that it can be seen from the sea only through the ravine. It
is most probable that the exterior inclosure of Barren Island (_c_, _d_,
fig. 67) is nothing more than the remains of a truncated cone _c_, _a_,
_b_, _d_, a great portion of which has been removed by engulfment,
explosion, or denudation, which may have preceded the formation of the
new interior cone, _f_, _e_, _g_.[615]

[Illustration: Fig. 67.

Supposed section of Barren Island, in the Bay of Bengal.]


MUD VOLCANOES.

_Iceland._--Mr. R. Bunsen, in his account of the pseudo-volcanic
phenomena of Iceland, describes many valleys where sulphurous and
aqueous vapors burst forth with a hissing sound, from the hot soil
formed of volcanic tuff. In such spots a pool of boiling water is seen,
in which a bluish-black argillaceous paste rises in huge bubbles. These
bubbles on bursting throw the boiling mud to a height of fifteen feet
and upwards, accumulating it in ledges round the crater or basin of the
spring.

_Baku on the Caspian._--The formation of a new mud volcano was witnessed
on the 27th of November, 1827, at Tokmali, on the peninsula of
Abscheron, east of Baku. Flames blazed up to an extraordinary height for
a space of three hours, and continued for twenty hours to rise about
three feet above a crater, from which mud was ejected. At another point
in the same district where flames issued, fragments of rock of large
size were hurled up into the air, and scattered around.[616]

[Illustration: Fig. 68.

Mud cones and craters of Hinglaj near Beila, district of Lus, 120 miles
northwest of mouth of Indus. From original drawing by Capt. Robertson.
(See Map, p. 460.)]

_Sicily._--At a place called Macaluba, near Girgenti in Sicily, are
several conical mounds from ten to thirty feet in height, with small
craters at their summits, from which cold water, mixed with mud and
bitumen, is cast out. Bubbles of carbonic acid and carburetted hydrogen
gas are also disengaged from these springs, and at certain periods with
such violence, as to throw the mud to the height of 200 feet. These "air
volcanoes," as they are sometimes termed, are known to have been in the
same state of activity for the last fifteen centuries; and Dr. Daubeny
imagines that the gases which escape may be generated by the slow
combustion of beds of sulphur, which is actually in progress in the blue
clay, out of which the springs rise.[617] But as the gases are similar
to those disengaged in volcanic eruptions, and as they have continued to
stream out for so long a period, they may perhaps be derived from a more
deep-seated source.

_Beila in India._--In the district of Luss or Lus, south of Beila, about
120 miles N. W. of Cutch and the mouths of the Indus (see Map, fig. 71,
p. 460), numerous mud volcanoes are scattered over an area of probably
not less than 1000 square miles. Some of these have been well described
by Captain Hart, and subsequently by Captain Robertson, who has paid a
visit to that region, and made sketches of them, which he has kindly
placed at my disposal. From one of these the annexed view has been
selected. These conical hills occur to the westward of the Hara
mountains and the river Hubb. (See Map, p. 460.) One of the cones is 400
feet high, composed of light-colored earth, and having at its summit a
crater thirty yards in diameter. The liquid mud which fills the crater
is continually disturbed by air-bubbles, and here and there is cast up
in small jets.[618]

_Mineral composition of volcanic products._--The mineral called felspar
forms in general more than half of the mass of modern lavas. When it is
in great excess, lavas are called trachytic: they consist generally of a
base of compact felspar, in which crystals of glassy felspar are
disseminated.[619] When augite (or pyroxene) predominates, lavas are
termed basaltic. They contain about 50 per cent. of silica, or much less
than the trachytes, in which there is usually about 75 per cent. of that
mineral. They also contain about 11 per cent. of protoxide of iron, and
as much of lime, both of which are wanting, or only in insignificant
quantities in the trachytic rocks.[620] But lavas occur of an
intermediate composition between the trachytic and basaltic, which from
their color have been called graystones. The abundance of quartz,
forming distinct crystals or concretions, characterizes the granitic and
other ancient rocks, now generally considered by geologists as of
igneous origin; whereas that mineral is rarely exhibited in a separate
form in recent lavas, although silica enters so largely into their
composition. Hornblende, so common in hypogene rocks, or those commonly
called "primary," is rare in modern lava; nor does it enter largely into
rocks of any age in which augite abounds. It should, however, be stated,
that the experiments of Mr. Gustav Rose have made it very questionable,
whether the minerals called hornblende and augite can be separated as
distinct species, as their different varieties seem to pass into each
other, whether we consider the characters derived from their angles of
crystallization, their chemical composition, or their specific gravity.
The difference in form of the two substances may be explained by the
different circumstances under which they have been produced, the form
of hornblende being the result of slower cooling. Crystals of augite
have been met with in the scoriæ of furnaces, but never those of
hornblende; and crystals of augite have been obtained by melting
hornblende in a platina crucible; but hornblende itself has not been
formed artificially.[621] Mica occurs plentifully in some recent
trachytes, but is rarely present where augite is in excess.

_Frequency of eruptions, and nature of subterranean igneous
rocks._--When we speak of the igneous rocks of our own times, we mean
that small portion which, in violent eruptions, is forced up by elastic
fluids to the surface of the earth,--the sand, scoriæ, and lava, which
cool in the open air. But we cannot obtain access to that which is
congealed far beneath the surface under great pressure, equal to that of
many hundred, or many thousand atmospheres.

During the last century, about fifty eruptions are recorded of the five
European volcanic districts, of Vesuvius, Etna, Volcano, Santorin, and
Iceland; but many beneath the sea in the Grecian archipelago and near
Iceland may doubtless have passed unnoticed. If some of them produced no
lava, others, on the contrary, like that of Skaptár Jokul, in 1783,
poured out melted matter for five or six years consecutively; which
cases, being reckoned as single eruptions, will compensate for those of
inferior strength. Now, if we consider the active volcanoes of Europe to
constitute about a fortieth part of those already known on the globe,
and calculate that, one with another, they are about equal in activity
to the burning mountains in other districts, we may then compute that
there happen on the earth about 2000 eruptions in the course of a
century, or about twenty every year.

However inconsiderable, therefore, may be the superficial rocks which
the operations of fire produce on the surface, we must suppose the
subterranean changes now constantly in progress to be on the grandest
scale. The loftiest volcanic cones must be as insignificant, when
contrasted to the products of fire in the nether regions, as are the
deposits formed in shallow estuaries when compared to submarine
formations accumulating in the abysses of the ocean. In regard to the
characters of these volcanic rocks, formed in our own times in the
bowels of the earth, whether in rents and caverns, or by the cooling of
lakes of melted lava, we may safely infer that the rocks are heavier and
less porous than ordinary lavas, and more crystalline, although composed
of the same mineral ingredients. As the hardest crystals produced
artificially in the laboratory require the longest time for their
formation, so we must suppose that where the cooling down of melted
matter takes place by insensible degrees, in the course of ages, a
variety of minerals will be produced far harder than any formed by
natural processes within the short period of human observation.

These subterranean volcanic rocks, moreover, cannot be stratified in the
same manner as sedimentary deposits from water, although it is evident
that when great masses consolidate from a state of fusion, they may
separate into natural divisions; for this is seen to be the case in
many lava-currents. We may also expect that the rocks in question will
often be rent by earthquakes, since these are common in volcanic
regions; and the fissures will be often injected with similar matter, so
that dikes of crystalline rock will traverse masses of similar
composition. It is also clear, that no organic remains can be included
in such masses, as also that these deep-seated igneous formations
considered in mass must underlie all the strata containing organic
remains, because the heat proceeds from below upwards, and the intensity
required to reduce the mineral ingredients to a fluid state must destroy
all organic bodies in rocks included in the midst of them.

If by a continued series of elevatory movements, such masses shall
hereafter be brought up to the surface, in the same manner as
sedimentary marine strata have, in the course of ages, been upheaved to
the summit of the loftiest mountains, it is not difficult to foresee
what perplexing problems may be presented to the geologist. He may then,
perhaps, study in some mountain-chain the very rocks produced at the
depth of several miles beneath the Andes, Iceland, or Java, in the time
of Leibnitz, and draw from them the same conclusion which that
philosopher derived from certain igneous products of high antiquity; for
he conceived our globe to have been, for an indefinite period, in the
state of a comet, without an ocean, and uninhabitable alike by aquatic
or terrestrial animals.




CHAPTER XXVII.

EARTHQUAKES AND THEIR EFFECTS.


  Earthquakes and their effects--Deficiency of ancient
    accounts--Ordinary atmospheric phenomena--Changes produced by
    earthquakes in modern times considered in chronological
    order--Earthquake in Syria, 1837--Earthquakes in Chili in 1837 and
    1835--Isle of Santa Maria raised ten feet--Chili, 1822--Extent of
    country elevated--Aleppo and Ionian Isles--Earthquake of Cutch in
    1819--Subsidence in the Delta of the Indus--Island of Sumbawa in
    1815--Earthquake of Caraccas in 1812--Shocks at New Madrid in 1811
    in the valley of the Mississippi--Aleutian Islands in
    1806--Reflections on the earthquakes of the nineteenth
    century--Earthquake in Quito, Quebec, &c.--Java, 1786--Sinking down
    of large tracts.


In the sketch before given of the geographical boundaries of volcanic
regions, I stated, that although the points of eruption are but thinly
scattered, constituting mere spots on the surface of those vast
districts, yet the subterranean movements extend simultaneously over
immense areas. We may now proceed to consider the changes which these
movements produce on the surface, and in the internal structure of the
earth's crust.

_Deficiency of ancient accounts._--It is only within the last century
and a half, since Hooke first promulgated, in 1688, his views respecting
the connection between geological phenomena and earthquakes, that the
permanent changes affected by these convulsions have excited attention.
Before that time, the narrative of the historian was almost exclusively
confined to the number of human beings who perished, the number of
cities laid in ruins, the value of property destroyed, or certain
atmospheric appearances which dazzled or terrified the observers. The
creation of a new lake, the engulfing of a new city, or the raising of a
new island, are sometimes, it is true, adverted to, as being too
obvious, or of too much geographical or political interest to be passed
over in silence. But no researches were made expressly with a view of
ascertaining the amount of depression or elevation of the ground, or any
particular alterations in the relative position of sea and land; and
very little distinction was made between the raising of soil by volcanic
ejections, and the upheaving of it by forces acting from below. The same
remark applies to a very large proportion of modern accounts: and how
much reason we have to regret this deficiency of information appears
from this, that in every instance where a spirit of scientific inquiry
has animated the eye-witnesses of these events, facts calculated to
throw light on former modifications of the earth's structure are
recorded.

_Phenomena attending earthquakes._--As I shall confine myself almost
entirely, in the following notice of earthquakes, to the changes brought
about by them in the configuration of the earth's crust, I may mention,
generally, some accompaniments of these terrible events which are almost
uniformly commemorated in history, that it may be unnecessary to advert
to them again. Irregularities in the seasons preceding or following the
shocks; sudden gusts of wind, interrupted by dead calms; violent rains
at unusual seasons, or in countries where such phenomena are almost
unknown; a reddening of the sun's disk, and a haziness in the air, often
continued for months; an evolution of electric matter, or of inflammable
gas from the soil, with sulphurous and mephitic vapors; noises
underground, like the running of carriages, or the discharge of
artillery, or distant thunder; animals uttering cries of distress, and
evincing extraordinary alarm, being more sensitive than men of the
slightest movement; a sensation like sea-sickness, and a dizziness in
the head, experienced by men:--these, and other phenomena, less
connected with our present subject as geologists, have recurred again
and again at distant ages, and in all parts of the globe.

I shall now begin the enumeration of earthquakes with the latest
authentic narratives, and so carry back the survey retrospectively, that
I may bring before the reader, in the first place, the minute and
circumstantial details of modern times, and thus enable him, by
observing the extraordinary amount of change within the last 150 years,
to perceive how great must be the deficiency in the meager annals of
earlier eras.


EARTHQUAKES OF THE NINETEENTH CENTURY.[622]

_Syria_, January, 1837.--It has been remarked that earthquakes affect
elongated areas. The violent shock which devastated Syria in 1837 was
felt on a line 500 miles in length by 90 in breadth:[623] more than 6000
persons perished; deep rents were caused in solid rocks, and new hot
springs burst out at Tabereah.

_Chili--Valdivia_, 1837.--One of the latest earthquakes by which the
position of solid land is known to have been permanently altered is that
which occurred in Chili, on November 7th, 1837. On that day Valdivia was
destroyed by an earthquake, and a whaler, commanded by Captain Coste,
was violently shaken at sea, and lost her masts, in lat. 43° 38' S. in
sight of the land. The captain went on the 11th of December following to
a spot near the island of Lemus, one of the Chonos archipelago, where he
had anchored two years before, and found that the bottom of the sea had
been raised more than eight feet. Some rocks formerly covered at all
times by the sea were now constantly exposed, and an enormous quantity
of shells and fish in a decaying state, which had been thrown there by
the waves, or suddenly laid dry during the earthquake, attested the
recent date of the occurrence. The whole coast was strewed with uprooted
trees.[624]

_Chili--Conception_, 1835.--Fortunately we have a still more detailed
account of the geographical changes produced in the same country on the
20th of February, 1835. An earthquake was then felt at all places
between Copiapo and Chiloe, from north to south, and from Mendoza to
Juan Fernandez, from east to west. "Vessels," says Mr. Caldcleugh,
"navigating the Pacific, within 100 miles of the coast, experienced the
shock with considerable force."[625] Conception, Talcahuano, Chillan,
and other towns were thrown down. From the account of Captain Fitz Roy,
R. N., who was then employed in surveying the coast, we learn that after
the shock the sea retired in the Bay of Conception, and the vessels
grounded, even those which had been lying in seven fathoms water: all
the shoals were visible, and soon afterwards a wave rushed in and then
retreated, and was followed by two other waves. The vertical height of
these waves does not appear to have been much greater than from sixteen
to twenty feet, although they rose to much greater heights when they
broke upon a sloping beach.

[Illustration: Fig. 69.]

According to Mr. Caldcleugh and Mr. Darwin, the whole volcanic chain of
the Chilian Andes, a range 150 miles in length, was in a state of
unusual activity, both during the shocks and for some time preceding and
after the convulsion, and lava was seen to flow from the crater of
Osorno. (See Map, fig. 69.) The island of Juan Fernandez, distant 365
geographical miles from Chili, was violently shaken at the same time,
and devastated by a great wave. A submarine volcano broke out there
near Bacalao Head, about a mile from the shore, in sixty-nine fathoms
water, and illumined the whole island during the night.[626]

"At Conception," says Captain Fitz Roy, "the earth opened and closed
rapidly in numerous places. The direction of the cracks was not uniform,
though generally from southeast to northwest. The earth was not quiet
for three days after the great shock, and more than 300 shocks were
counted between the 20th February and the 4th of March. The loose earth
of the valley of the Biobio was everywhere parted from the solid rocks
which bound the plain, there being an opening between them from an inch
to a foot in width.

[Illustration: Fig. 70.]

"For some days after the 20th of February, the sea at Talcahuano," says
Captain Fitz Roy, "did not rise to the usual marks by four or five feet
vertically. When walking on the shore, even at high water, beds of dead
mussels, numerous chitons, and limpets, and withered seaweed, still
adhering, though lifeless, to the rocks on which they had lived,
everywhere met the eye." But this difference in the relative level of
the land and sea gradually diminished, till in the middle of April the
water rose again to within two feet of the former high-water mark. It
might be supposed that these changes of level merely indicated a
temporary disturbance in the set of the currents or in the height of the
tides at Talcahuano; but, on considering what occurred in the
neighboring island of Santa Maria, Captain Fitz Roy concluded that the
land had been raised four or five feet in February, and that it had
returned in April to within two or three feet of its former level.

Santa Maria, the island just alluded to, is about seven miles long and
two broad, and about twenty-five miles southwest of Conception. (See
Map, fig. 70.) The phenomena observed there are most important. "It
appeared," says Captain Fitz Roy, who visited Santa Maria twice, the
first time at the end of March, and afterwards in the beginning of
April, "that the southern extremity of the island had been raised eight
feet, the middle nine, and the northern end upwards of ten feet. On
steep rocks, where vertical measures could be correctly taken, beds of
dead mussels were found ten feet above high-water mark. One foot lower
than the highest bed of mussels, a few limpets and chitons were seen
adhering to the rock where they had grown. Two feet lower than the same,
dead mussels, chitons, and limpets were abundant.

"An extensive rocky flat lies around the northern parts of Santa Maria.
Before the earthquake this flat was covered by the sea, some projecting
rocks only showing themselves. Now, the whole flat is exposed, and
square acres of it are covered with dead shell-fish, the stench arising
from which is abominable. By this elevation of the land the southern
port of Santa Maria has been almost destroyed; little shelter remaining
there, and very bad landing." The surrounding sea is also stated to have
become shallower in exactly the same proportion as the land had risen;
the soundings having diminished a fathom and a half everywhere around
the island.

At Tubal, also, to the southeast of Santa Maria, the land was raised six
feet, at Mocha two feet, but no elevation could be ascertained at
Valdivia.

Among other effects of the catastrophe, it is stated that cattle
standing on a steep slope, near the shore, were rolled down into the
sea, and many others were washed off by the great wave from low land and
drowned.[627]

In November of the same year (1835), Conception was shaken by a severe
earthquake, and on the same day Osorno, at the distance of 400 miles,
renewed its activity. These facts prove not only the connection of
earthquakes with volcanic eruptions in this region, but also the vast
extent of the subterranean areas over which the disturbing cause acts
simultaneously.

_Ischia_, 1828.--On the 2d of February the whole island of Ischia was
shaken by an earthquake, and in the October following I found all the
houses in Casamicciol still without their roofs. On the sides of a
ravine between that town and Forio, I saw masses of greenish tuff which
had been thrown down. The hot-spring of Rita, which was nearest the
centre of the movement, was ascertained by M. Covelli to have increased
in temperature, showing, as he observes, that the explosion took place
below the reservoirs which heat the thermal waters.[628]

_Bogota_, 1827.--On the 16th of November, 1827, the plain of Bogota, in
New Granada, or Colombia, was convulsed by an earthquake, and a great
number of towns were thrown down. Torrents of rain swelled the
Magdalena, sweeping along vast quantities of mud and other substances,
which emitted a sulphurous vapor and destroyed the fish. Popayan, which
is distant 200 geographical miles S. S. W. of Bogota, suffered greatly.
Wide crevices appeared in the road of Guanacas, leaving no doubt that
the whole of the Cordilleras sustained a powerful shock. Other fissures
opened near Costa, in the plains of Bogota, into which the river Tunza
immediately began to flow.[629] It is worthy of remark, that in all such
cases the ancient gravel bed of a river is deserted and a new one formed
at a lower level; so that a want of relation in the position of alluvial
beds of the existing water-courses may be no test of the high antiquity
of such deposits, at least in countries habitually convulsed by
earthquakes. Extraordinary rains accompanied the shocks before
mentioned; and two volcanoes are said to have been in eruption in the
mountain-chain nearest to Bogota.

_Chili_, 1822.--On the 19th of November, 1822, the coast of Chili was
visited by a most destructive earthquake. The shock was felt
simultaneously throughout a space of 1200 miles from north to south. St.
Jago, Valparaiso, and some other places, were greatly injured. When the
district round Valparaiso was examined on the morning after the shock,
it was found that the coast for a considerable distance was raised above
its former level.[630] At Valparaiso the elevation was three feet, and
at Quintero about four feet. Part of the bed of the sea, says Mrs.
Graham, remained bare and dry at high water, "with beds of oysters,
mussels, and other shells adhering to the rocks on which they grew, the
fish being all dead, and exhaling most offensive effluvia.[631]

An old wreck of a ship, which before could not be approached, became
accessible from the land, although its distance from the original
sea-shore had not altered. It was observed that the water-course of a
mill, at the distance of about a mile from the sea, gained a fall of
fourteen inches, in little more than one hundred yards; and from this
fact it is inferred that the rise in some parts of the inland country
was far more considerable than on the borders of the ocean.[632] Part of
the coast thus elevated consisted of granite, in which parallel fissures
were caused, some of which were traced for a mile and a half inland.
Cones of earth about four feet high were thrown up in several districts,
by the forcing up of water mixed with sand through funnel-shaped
hollows,--a phenomenon very common in Calabria, and the explanation of
which will hereafter be considered. Those houses in Chili of which the
foundations were on rock were less damaged than such as were built on
alluvial soil.

Mr. Cruickshanks, an English botanist, who resided in the country
during the earthquake, has informed me that some rocks of greenstone at
Quintero, a few hundred yards from the beach, which had always been
under water till the shock of 1822, have since been uncovered when the
tide is at half-ebb: and he states that, after the earthquake, it was
the general belief of the fishermen and inhabitants of the Chilian
coast, _not_ that the land had risen, but that the ocean had permanently
retreated.

Dr. Meyen, a Prussian traveller, who visited Valparaiso in 1831, says
that on examining the rocks both north and south of the town, nine years
after the event, he found, in corroboration of Mrs. Graham's account,
that remains of animals and sea-weed, the _Lessonia_ of Bory de St.
Vincent, which has a firm ligneous stem, still adhered to those rocks
which in 1822 had been elevated above high-water mark.[633] According to
the same author, the whole coast of Central Chili was raised about four
feet, and banks of marine shells were laid dry on many parts of the
coast. He observed similar banks, elevated at unknown periods, in
several places, especially at Copiapo, where the species all agree with
those now living in the ocean. Mr. Freyer also, who resided some years
in South America, has confirmed these statements;[634] and Mr. Darwin
obtained evidence that the remains of an ancient wall, formerly washed
by the sea, and now 11½ feet above high-water mark, acquired several
feet of this additional elevation during the earthquake of 1822.[635]

The shocks continued up to the end of September, 1823; even then,
forty-eight hours seldom passed without one, and sometimes two or three
were felt during twenty-four hours. Mrs. Graham observed, after the
earthquake of 1822, that besides a beach newly raised above high-water
mark, there were several older elevated lines of beach, one above the
other, consisting of shingle mixed with shells extending in a parallel
direction to the shore, to the height of fifty feet above the sea.[636]

_Extent of country elevated._--By some observers it has been supposed
that the whole country from the foot of the Andes to a great distance
under the sea was upraised in 1822, the greatest rise being at the
distance of about two miles from the shore. "The rise upon the coast was
from two to four feet:--at the distance of a mile inland it must have
been from five to six or seven feet."[637] It has also been conjectured
by the same eye-witnesses to the convulsion, that the area over which
this permanent alteration of level extended may have been equal to
100,000 square miles. Although the increased fall of certain
water-courses may have afforded some ground for this conjecture, it must
be considered as very hypothetical, and the estimate may have exceeded
or greatly fallen short of the truth. It may nevertheless be useful to
reflect on the enormous amount of change which this single convulsion
occasioned, if the extent of country moved upward really amounted to
100,000 square miles,--an extent just equal to half the area of France,
or about five-sixths of the area of Great Britain and Ireland. If we
suppose the elevation to have been only three feet on an average, it
will be seen that the mass of rock added to the continent of America by
the movement, or, in other words, the mass previously below the level of
the sea, and after the shocks permanently above it, must have contained
fifty-seven cubic miles in bulk; which would be sufficient to form a
conical mountain two miles high (or about as high as Etna), with a
circumference at the base of nearly thirty-three miles. We may take the
mean specific gravity of the rock at 2·655,--a fair average, and a
convenient one in such computations, because at such a rate a cubic yard
weighs two tons. Then, assuming the great pyramid of Egypt, if solid, to
weigh, in accordance with an estimate before given, six million tons, we
may state the rock added to the continent by the Chilian earthquake to
have more than equalled 100,000 pyramids.

But it must always be borne in mind that the weight of rock here alluded
to constituted but an insignificant part of the whole amount which the
volcanic forces had to overcome. The whole thickness of rock between the
surface of Chili and the subterranean foci of volcanic action may be
many miles or leagues deep. Say that the thickness was only two miles,
even then the mass which changed place and rose three feet being 200,000
cubic miles in volume, must have exceeded in weight 363 million
pyramids.

It may be instructing to consider these results in connection with
others already obtained from a different source, and to compare the
working of two antagonistic forces--the levelling power of running
water, and the expansive energy of subterranean heat. How long, it may
be asked, would the Ganges require, according to data before explained
(p. 283), to transport to the sea a quantity of solid matter equal to
that which may have been added to the land by the Chilian earthquake?
The discharge of mud in one year by the Ganges was estimated at 20,000
million cubic feet. According to that estimate it would require about
four centuries (or 418 years) before the river could bear down from the
continent into the sea a mass equal to that gained by the Chilian
earthquake. In about half that time, perhaps, the united waters of the
Ganges and Burrampooter might accomplish the operation.

_Cutch_, 1819.--A violent earthquake occurred at Cutch, in the delta of
the Indus, on the 16th of June, 1819. (See Map, fig. 71.) The principal
town, Bhooj, was converted into a heap of ruins, and its stone buildings
were thrown down. The movement was felt over an area having a radius of
1000 miles from Bhooj, and extending to Kbatmandoo, Calcutta, and
Pondicherry.[638] The vibrations were felt in Northwest India, at a
distance of 800 miles, after an interval of about fifteen minutes after
the earthquake at Bhooj. At Ahmedabad the great mosque, erected by
Sultan Ahmed nearly 450 years before, fell to the ground, attesting how
long a period had elapsed since a shock of similar violence had visited
that point. At Anjar, the fort, with its tower and guns, was hurled to
the ground in one common mass of ruin. The shocks continued until the
20th; when, thirty miles northwest from Bhooj, the volcano called
Denodur is said by some to have sent forth flames, but Capt. Grant was
unable to authenticate this statement.

[Illustration: Fig. 71. MAP of THE COUNTRIES at THE MOUTH OF THE
INDUS.]

_Subsidence in the delta of the Indus._--Although the ruin of towns was
great, the face of nature in the inland country, says Captain Macmurdo,
was not visibly altered. In the hills some large masses only of rock and
soil were detached from the precipices; but the eastern and almost
deserted channel of the Indus, which bounds the province of Cutch, was
greatly changed. This estuary, or inlet of the sea, was, before the
earthquake, fordable at Luckput, being only about a foot deep when the
tide was at ebb, and at flood-tide never more than six feet; but it was
deepened at the fort of Luckput, after the shock, to more than _eighteen
feet at low water_.[639] On sounding other parts of the channel, it was
found, that where previously the depth of the water at flood never
exceeded one or two feet, it had become from four to ten feet deep. By
these and other remarkable changes of level, a part of the inland
navigation of that country, which had been closed for centuries, became
again practicable.

[Illustration: Fig. 72.

Fort of Sindree, on the eastern branch of the Indus, before it was
submerged by the earthquake of 1819, from a sketch of Capt. Grindlay,
made in 1808.]

_Fort and village submerged._[640]--The fort and village of Sindree, on
the eastern arm of the Indus, above Luckput, are stated by the same
writer to have been overflowed; and, after the shock, the tops of the
houses and wall were alone to be seen above the water, for the houses,
although submerged, were not cast down. Had they been situated,
therefore, in the interior, where so many forts were levelled to the
ground, their site would, perhaps, have been regarded as having remained
comparatively unmoved. Hence we may suspect that great permanent
upheavings and depressions of soil may be the result of earthquakes,
without the inhabitants being in the least degree conscious of any
change of level.

A more recent survey of Cutch, by Sir A. Burnes, who was not in
communication with Capt. Macmurdo, confirms the facts above enumerated,
and adds many important details.[641] That officer examined the delta of
the Indus in 1826 and 1828, and from his account it appears that, when
Sindree subsided in June, 1819, the sea flowed in by the eastern mouth
of the Indus, and in a few hours converted a tract of land, 2000 square
miles in area, into an inland sea, or lagoon. Neither the rush of the
sea into this new depression, nor the movement of the earthquake, threw
down entirely the small fort of Sindree, one of the four towers, the
northwestern, still continuing to stand; and, the day after the
earthquake, the inhabitants who had ascended to the top of this tower,
saved themselves in boats.[642]

_Elevation of the Ullah Bund._--Immediately after the shock, the
inhabitants of Sindree saw, at the distance of five miles and a half
from their village, a long elevated mound, where previously there had
been a low and perfectly level plain. (See Map, fig. 71.) To this
uplifted tract they gave the name of "Ullah Bund," or the "Mound of
God," to distinguish it from several artificial dams previously thrown
across the eastern arm of the Indus.

_Extent of country raised._--It has been ascertained that this
new-raised country is _upwards of fifty miles_ in length from east to
west, running parallel to that line of subsidence before mentioned,
which caused the grounds around Sindree to be flooded. The range of this
elevation extends from Puchum Island towards Gharee; its breadth from
north to south is conjectured to be in some parts _sixteen miles_, and
its greatest ascertained height above the original level of the delta is
ten feet,--an elevation which appears to the eye to be very uniform
throughout.

For several years after the convulsion of 1819, the course of the Indus
was very unsettled, and at length, in 1826, the river threw a vast body
of water into its eastern arm, that called the Phurraun, above Sindree;
and forcing its way in a more direct course to the sea, burst through
all the artificial dams which had been thrown across its channel, and at
length cut right through the "Ullah Bund," whereby a natural section was
obtained. In the perpendicular cliffs thus laid open Sir A. Burnes found
that the upraised lands consisted of clay filled with shells. The new
channel of the river where it intersected the "bund" was eighteen feet
deep, and forty yards in width; but in 1828 the channel was still
farther enlarged. The Indus, when it first opened this new passage,
threw such a body of water into the new mere, or salt lagoon, of
Sindree, that it became fresh for many months; but it had recovered its
saltness in 1828, when the supply of river-water was less copious, and
finally it became more salt than the sea, in consequence, as the natives
suggested to Sir A. Burnes, of the saline particles with which the "Runn
of Cutch" is impregnated.

In 1828 Sir A. Burnes went in a boat to the ruins of Sindree, where a
single remaining tower was seen in the midst of a wide expanse of sea.
The tops of the ruined walls still rose two or three feet above the
level of the water; and standing on one of these, he could behold
nothing in the horizon but water, except in one direction, where a blue
streak of land to the north indicated the Ullah Bund. This scene
presents to the imagination a lively picture of the revolutions now in
progress on the earth--a waste of waters where a few years before all
was land, and the only land visible consisting of ground uplifted by a
recent earthquake.

Ten years after the visit of Sir A. Burnes above alluded to, my friend,
Captain Grant, F. G. S., of the Bombay Engineers, had the kindness to
send at my request a native surveyor to make a plan of Sindree and Ullah
Bund, in March, 1838. From his description it appears that, at that
season, the driest of the whole year, he found the channel traversing
the Bund to be 100 yards wide, without water, and incrusted with salt.
He was told that it has now only four or five feet of water in it after
rains. The sides or banks were nearly perpendicular, and nine feet in
height. The lagoon has diminished both in area and depth, and part near
the fort was dry land. The annexed drawing, made by Captain Grant from
the surveyor's plan, shows the appearance of the fort in the midst of
the lake, as seen in 1838 from the west, or from the same point as that
from which Captain Grindlay's sketch (see fig. 72) was taken in 1808,
before the earthquake.

[Illustration: Fig. 73.

View of the Fort of Sindree, from the west, in March, 1838.]

The Runn of Cutch is a flat region of a very peculiar character, and no
less than 7000 square miles in area: a greater superficial extent than
Yorkshire, or about one-fourth the area of Ireland. It is not a desert
of moving sand, nor a marsh, but evidently the dried-up bed of an inland
sea, which for a great part of every year has a hard and dry bottom
uncovered by weeds or grass, and only supporting here and there a few
tamarisks. But during the monsoons, when the sea runs high, the
salt-water driven up from the Gulf of Cutch and the creeks at Luckput
overflows a large part of the Runn, especially after rains, when the
soaked ground permits the sea-water to spread rapidly. The Runn is also
liable to be overflowed occasionally in some parts by river-water: and
it is remarkable that the only portion which was ever highly cultivated
(that anciently called Sayra) is now permanently submerged. The surface
of the Runn is sometimes incrusted with salt about an inch in depth, in
consequence of the evaporation of the sea-water. Islands rise up in some
parts of the waste, and the boundary lands form bays and promontories.
The natives have various traditions respecting the former separation of
Cutch and Sinde by a bay of the sea, and the drying up of the district
called the Runn. But these tales, besides the usual uncertainty of oral
tradition, are farther obscured by mythological fictions. The conversion
of the Runn into land is chiefly ascribed to the miraculous powers of a
Hindoo saint, by name Damorath (or Dhoorunnath), who had previously done
penance for twelve years on the summit of Denodur hill. Captain Grant
infers, on various grounds, that this saint flourished about the
eleventh or twelfth century of our era. In proof of the drying up of
the Runn, some towns far inland are still pointed out as having once
been ancient ports. It has, moreover, been always said that ships were
wrecked and engulphed by the great catastrophe; and in the jets of black
muddy water thrown out of fissures in that region, in 1819, there were
cast up numerous pieces of wrought-iron and ship nails.[643] Cones of
sand six or eight feet in height were at the same time thrown up on
these lands.[644]

We must not conclude without alluding to a _moral_ phenomenon connected
with this tremendous catastrophe, which we regard as highly deserving
the attention of geologists. It is stated by Sir A. Burnes, that "these
wonderful events passed _unheeded_ by the inhabitants of Cutch;" for the
region convulsed, though once fertile, had for a long period been
reduced to sterility by want of irrigation, so that the natives were
indifferent as to its fate. Now it is to this profound apathy which all
but highly civilized nations feel, in regard to physical events not
having an immediate influence on their worldly fortunes, that we must
ascribe the extraordinary dearth of historical information concerning
changes of the earth's surface, which modern observations show to be by
no means of rare occurrence in the ordinary course of nature.

Since the above account was written, a description has been published of
more recent geographical changes in the district of Cutch, near the
mouth of the Koree, or eastern branch of the Indus, which happened in
June, 1845. A large area seems to have subsided, and the Sindree lake
had become a salt marsh.[645]

_Island of Sumbawa_, 1815.--In April, 1815, one of the most frightful
eruptions recorded in history occurred in the province of Tomboro, in
the island of Sumbawa (see Map, fig. 39, p. 351), about 200 miles from
the eastern extremity of Java. In April of the year preceding the
volcano had been observed in a state of considerable activity, ashes
having fallen upon the decks of vessels which sailed past the
coast.[646] The eruption of 1815 began on the 5th of April, but was most
violent on the 11th and 12th, and did not entirely cease till July. The
sound of the explosions was heard in Sumatra, at the distance of 970
geographical miles in a direct line; and at Ternate, in an opposite
direction, at the distance of 720 miles. Out of a population of 12,000,
in the province of Tomboro, only twenty-six individuals survived.
Violent whirlwinds carried up men, horses, cattle, and whatever else
came within their influence into the air; tore up the largest trees by
the roots, and covered the whole sea with floating timber.[647] Great
tracts of land were covered by lava, several streams of which, issuing
from the crater of the Tomboro mountain, reached the sea: So heavy was
the fall of ashes, that they broke into the Resident's house at Bima,
forty miles east of the volcano, and rendered it as well as many other
dwellings in the town uninhabitable. On the side of Java the ashes were
carried to the distance of 300 miles, and 217 towards Celebes, in
sufficient quantity to darken the air. The floating cinders to the
westward of Sumatra formed, on the 12th of April, a mass two feet thick,
and several miles in extent, through which ships with difficulty forced
their way.

The darkness occasioned in the daytime by the ashes in Java was so
profound, that nothing equal to it was ever witnessed in the darkest
night. Although this volcanic dust when it fell was an impalpable
powder, it was of considerable weight when compressed, a pint of it
weighing twelve ounces and three quarters. "Some of the finest
particles," says Mr. Crawfurd, "were transported to the islands of
Amboyna and Banda, which last is about 800 miles east from the site of
the volcano, although the southeast monsoon was then at its height."
They must have been projected, therefore, into the upper regions of the
atmosphere, where a counter-current prevailed.

Along the sea-coast of Sumbawa and the adjacent isles, the sea rose
suddenly to the height of from two to twelve feet, a great wave rushing
up the estuaries, and then suddenly subsiding. Although the wind at Bima
was still during the whole time, the sea rolled in upon the shore, and
filled the lower parts of the houses with water a foot deep. Every prow
and boat was forced from the anchorage, and driven on shore.

The town called Tomboro, on the west side of Sumbawa, was overflowed by
the sea, which encroached upon the shore so that the water remained
permanently eighteen feet deep in places where there was land before.
Here we may observe, that the amount of subsidence of land was apparent,
in spite of the ashes, which would naturally have caused the limits of
the coast to be extended.

The area over which tremulous noises and other volcanic effects
extended, was 1000 English miles in circumference, including the whole
of the Molucca Islands, Java, a considerable portion of Celebes,
Sumatra, and Borneo. In the island of Amboyna, in the same month and
year, the ground opened, threw out water, and then closed again.[648]

In conclusion, I may remind the reader, that but for the accidental
presence of Sir Stamford Raffles, then Governor of Java, we should
scarcely have heard in Europe of this tremendous catastrophe. He
required all the residents in the various districts under his authority
to send in a statement of the circumstances which occurred within their
own knowledge; but, valuable as were their communications, they are
often calculated to excite rather than to satisfy the curiosity of the
geologist. They mention that similar effects, though in a less degree,
had, about seven years before, accompanied an eruption of Carang Assam,
a volcano in the island of Bali, west of Sumatra; but no particulars of
that great catastrophe are recorded.[649]

_Caraccas_, 1812.--On the 26th of March, 1812, several violent shocks of
an earthquake were felt in Caraccas. The surface undulated like a
boiling liquid, and terrific sounds were heard underground. The whole
city with its splendid churches was in an instant a heap of ruins,
under which 10,000 of the inhabitants were buried. On the 5th of April,
enormous rocks were detached from the mountains. It was believed that
the mountain Silla lost from 300 to 360 feet of its height by
subsidence; but this was an opinion not founded on any measurement. On
the 27th of April, a volcano in St. Vincent's threw out ashes; and, on
the 30th, lava flowed from its crater into the sea, while its explosions
were heard at a distance equal to that between Vesuvius and Switzerland,
the sound being transmitted, as Humboldt supposes, through the ground.
During the earthquake which destroyed Caraccas, an immense quantity of
water was thrown out at Valecillo, near Valencia, as also at Porto
Cabello, through openings in the earth; and in the Lake Maracaybo the
water sank. Humboldt observed that the Cordilleras, composed of gneiss
and mica slate, and the country immediately at their feet, were more
violently shaken than the plains.[650]

_South Carolina and New Madrid, Missouri_, 1811-12.--Previous to the
destruction of La Guayra and Caraccas, in 1812, earthquakes were felt in
South Carolina; and the shocks continued till those cities were
destroyed. The valley also of the Mississippi, from the village of New
Madrid to the mouth of the Ohio in one direction, and to the St. Francis
in another, was convulsed in such a degree as to create new lakes and
islands. It has been remarked by Humboldt in his Cosmos, that the
earthquake of New Madrid presents one of the few examples on record of
the incessant quaking of the ground for several successive months _far
from any volcano_. Flint, the geographer, who visited the country seven
years after the event, informs us, that a tract of many miles in extent,
near the Little Prairie, became covered with water three or four feet
deep; and when the water disappeared a stratum of sand was left in its
place. Large lakes of twenty miles in extent were formed in the course
of an hour, and others were drained. The grave-yard at New Madrid was
precipitated into the bed of the Mississippi; and it is stated that the
ground whereon the town is built, and the river-bank for fifteen miles
above, sank eight feet below their former level.[651] The neighboring
forest presented for some years afterwards "a singular scene of
confusion; the trees standing inclined in every direction, and many
having their trunks and branches broken."[652]

The inhabitants relate that the earth rose in great undulations; and
when these reached a certain fearful height, the soil burst, and vast
volumes of water, sand, and pit-coal were discharged as high as the tops
of the trees. Flint saw hundreds of these deep chasms remaining in an
alluvial soil, seven years after. The people in the country, although
inexperienced in such convulsions, had remarked that the chasms in the
earth were in a direction from S. W. to N. E.; and they accordingly
felled the tallest trees, and laying them at right angles to the chasms,
stationed themselves upon them. By this invention, when chasms opened
more than once under these trees, several persons were prevented from
being swallowed up.[653] At one period during this earthquake, the
ground not far below New Madrid swelled up so as to arrest the
Mississippi in its course, and to cause a temporary reflux of its waves.
The motion of some of the shocks is described as having been horizontal,
and of others perpendicular; and the vertical movement is said to have
been much less desolating than the horizontal.

The above account has been reprinted exactly as it appeared in former
editions of this work, compiled from the authorities which I have cited;
but having more recently (March, 1846) had an opportunity myself of
visiting the disturbed region of the Mississippi, and conversing with
many eye-witnesses of the catastrophe, I am able to confirm the truth of
those statements, and to add some remarks on the present face and
features of the country. I skirted, as was before related (p. 270), part
of the territory immediately west of New Madrid, called "the sunk
country," which was for the first time permanently submerged during the
earthquake of 1811-12. It is said to extend along the course of the
White Water and its tributaries for a distance of between 70 and 80
miles north and south, and 30 miles east and west. I saw on its borders
many full-grown trees still standing leafless, the bottoms of their
trunks several feet under water, and a still greater number lying
prostrate. An active vegetation of aquatic plants is already beginning
to fill up some of the shallows, and the sediment washed in by
occasional floods when the Mississippi rises to an extraordinary height
contributes to convert the sunk region into marsh and forest land. Even
on the dry ground along the confines of the submerged area, I observed
in some places that all the trees of prior date to 1811 were dead and
leafless, though standing erect and entire. They are supposed to have
been killed by the loosening of their roots during the repeated
undulations which passed through the ground for three months in
succession.

Mr. Bringier, an experienced engineer of New Orleans, who was on
horseback near New Madrid when some of the severest shocks were
experienced, related to me (in 1846), that "as the waves advanced the
trees bent down, and the instant afterwards, while recovering their
position, they often met those of other trees similarly inclined, so
that their branches becoming interlocked, they were prevented from
righting themselves again. The transit of the wave through the woods was
marked by the crashing noise of countless boughs, first heard on one
side and then on the other. At the same time powerful jets of water,
mixed with sand, mud, and fragments of coaly matter, were cast up,
endangering the lives of both horse and rider."

I was curious, to ascertain whether any vestiges still remained of these
fountains of mud and water, and carefully examined between New Madrid
and the Little Prairie several "sink holes," as they are termed. They
consist of cavities from 10 to 30 yards in width, and 20 feet or more in
depth, and are very conspicuous, interrupting the level surface of a
flat alluvial plain. I saw abundance of sand, which some of the present
inhabitants saw spouting from these deep holes, also fragments of
decayed wood and black bituminous shale, probably drifted down at some
former period in the main channel of the Mississippi, from the
coal-fields farther north. I also found numerous rents in the soil left
by the earthquake, some of them still several feet wide, and a yard or
two in depth, although the action of rains, frost, and occasional
inundations, and especially the leaves of trees blown into them in
countless numbers every autumn, have done much to fill them up. I
measured the direction of some of the fissures, which usually varied
from 10 to 45 degrees W. of north, and were often parallel to each
other; I found, however, a considerable diversity in their direction.
Many of them are traceable for half a mile and upwards, but they might
easily be mistaken for artificial trenches if resident settlers were not
there to assure us that within their recollection they were "as deep as
wells." Fragments of coaly shale were strewed along the edges of some of
these open fissures, together with white sand, in the same manner as
round the "sink holes."[654]

Among other monuments of the changes wrought in 1811-12, I explored the
bed of the lake called Eulalie, near New Madrid, 300 yards long by 100
yards in width, which was suddenly drained during the earthquake. The
parallel fissures by which the waters escaped are not yet entirely
closed, and all the trees growing on its bottom were at the time of my
visit less than 34 years old. They consisted of cotton-wood, willows,
and honey-locust, and other species, differing from those clothing the
surrounding higher grounds, which are more elevated by 12 or 15 feet. On
them the hickory, the black and white oak, the gum and other trees, many
of them of ancient date, were flourishing.

_Aleutian Islands_, 1806.--In the year 1806, a new island, in the form
of a peak, with some low conical hills upon it, is said to have risen
from the sea among the Aleutian Islands, east of Kamtschatka. According
to Langsdorf,[655] it was four geographical miles in circumference; and
Von Buch infers from its magnitude, and from its not having again
subsided below the level of the sea, that it did not consist merely of
ejected matter, but of a solid rock of trachyte upheaved.[656] Another
extraordinary eruption happened in the spring of the year 1814, in the
sea near Unalaschka, in the same archipelago. A new isle was then
produced of considerable size, and with a peak three thousand feet high,
which remained standing for a year afterwards, though with somewhat
diminished height.

Although it is not improbable that earthquakes accompanying these
tremendous eruptions may have heaved up part of the bed of the sea, yet
the circumstance of the islands not having disappeared like Sabrina (see
p. 416), may have arisen from the emission of lava. If Jorullo, for
example, in 1759, had risen from a shallow sea to the height of 1600
feet, instead of attaining that elevation above the Mexican plateau, the
massive current of basaltic lava which poured out from its crater would
have enabled it to withstand, for a long period, the action of a
turbulent sea.

_Reflections on the earthquakes of the nineteenth century._--We are now
about to pass on to the events of the eighteenth century; but before we
leave the consideration of those already enumerated, let us pause for a
moment, and reflect how many remarkable facts of geological interest are
afforded by the earthquakes above described, though they constitute but
a small part of the convulsions even of the last forty years. New rocks
have risen from the waters; new hot springs have burst out, and the
temperature of others has been raised; the coast of Chili has been
thrice permanently elevated; a considerable tract in the delta of the
Indus has sunk down, and some of its shallow channels have become
navigable; an adjoining part of the same district, upwards of fifty
miles in length and sixteen in breadth, has been raised about ten feet
above its former level; part of the great plain of the Mississippi, for
a distance of eighty miles in length by thirty in breadth, has sunk down
several feet; the town of Tomboro has been submerged, and twelve
thousand of the inhabitants of Sumbawa have been destroyed. Yet, with a
knowledge of these terrific catastrophes, witnessed during so brief a
period by the present generation, will the geologist declare with
perfect composure that the earth has at length settled into a state of
repose? Will he continue to assert that the changes of relative level of
land and sea, so common in former ages of the world, have now ceased?
If, in the face of so many striking facts, he persists in maintaining
this favorite dogma, it is in vain to hope that, by accumulating the
proofs of similar convulsions during a series of antecedent ages, we
shall shake his tenacity of purpose:--


  Si fractus illabatur orbis
  Impavidum ferient ruinæ.



EARTHQUAKES OF THE EIGHTEENTH CENTURY.

_Quito_, 1797.--On the morning of February 4th, 1797, the volcano of
Tunguragua in Quito, and the surrounding district, for forty leagues
from south to north, and twenty leagues from west to east, experienced
an undulating movement, which lasted four minutes. The same shock was
felt over a tract of 170 leagues from south to north, from Piura to
Popayan; and 140 from west to east, from the sea to the river Napo. In
the smaller district first mentioned, where the movement was more
intense, every town was levelled to the ground; and Riobamba, Quero, and
other places, were buried under masses detached from the mountains. At
the foot of Tunguragua the earth was rent open in several places; and
streams of water and fetid mud, called "moya," poured out, overflowing
and wasting every thing. In valleys 1000 feet broad, the water of these
floods reached to the height of 600 feet; and the mud deposit barred up
the course of the river, so as to form lakes, which in some places
continued for more than eighty days. Flames and suffocating vapors
escaped from the lake Quilotoa, and killed all the cattle on its shores.
The shocks continued all February and March; and on the 5th of April
they recurred with almost as much violence as at first. We are told that
the form of the surface in the district most shaken was entirely
altered, but no exact measurements are given whereby we may estimate the
degree of elevation or subsidence.[657] Indeed it would be difficult,
except in the immediate neighborhood of the sea, to obtain any certain
standard of comparison if the levels were really as much altered as the
narrations imply.

_Cumana_, 1797.--In the same year, on the 14th of December, the small
Antilles experienced subterranean movements, and four-fifths of the town
of Cumana was shaken down by a vertical shock. The form of the shoal of
Mornerouge, at the mouth of the river Bourdones, was changed by an
upheaving of the ground.[658]

_Canada--Quebec_, 1791.--We learn from Captain Bayfield's memoirs, that
earthquakes are very frequent on the shore of the estuary of the St.
Lawrence, of force sufficient at times to split walls and throw down
chimneys. Such were the effects experienced in December, 1721, in St.
Paul's Bay, about fifty miles N. E. from Quebec; and the inhabitants
say, that about every twenty-five years a violent earthquake returns,
which lasts forty days. In the History of Canada, it is stated that, in
1663, a tremendous convulsion lasted six months, extending from Quebec
to Tadeausac,--a distance of about 130 miles. The ice on the river was
broken up, and many landslips caused.[659]

_Caraccas_, 1790.--In the Caraccas, near where the Caura joins the
Orinoco, between the towns San Pedro de Alcantara and San Francisco de
Aripao, an earthquake, on St. Matthew's day 1790, caused a sinking in of
the granitic soil, and left a lake 800 yards in diameter, and from
eighty to one hundred in depth. It was a portion of the forest of Aripao
which subsided, and the trees remained green for several months under
water.[660]

_Sicily_, 1790.--On the 18th of March in the same year, at S. Maria di
Niscemi, some miles from Terranuova, near the south coast of Sicily, the
ground gradually sunk down for a circumference of three Italian miles,
during seven shocks; and, in one place, to the depth of thirty feet. It
continued to subside to the end of the month. Several fissures sent
forth sulphur, petroleum, steam, and hot water, and a stream of mud,
which flowed for two hours, and covered a space sixty feet long and
thirty broad. This happened far from both the ancient and modern
volcanic district, in a group of strata consisting chiefly of blue
clay.[661]

_Java_, 1786.--About the year 1786, an earthquake was felt at intervals,
for the period of four months, in the neighborhood of Batur, in Java,
and an eruption followed. Various rents were formed, which emitted a
sulphurous vapor; separate tracts sunk away, and were swallowed by the
earth. Into one of these the rivulet Dotog entered, and afterwards
continued to follow a subterraneous course. The village of Jampang was
buried in the ground, with thirty-eight of its inhabitants, who had not
time to escape. We are indebted to Dr. Horsfield for having verified the
above-mentioned facts.[662]




CHAPTER XXVIII.

EARTHQUAKE IN CALABRIA, 1783.


  Earthquake in Calabria, February 5, 1783--Shocks continued to the
    end of the year 1786--Authorities--Area convulsed--Geological
    structure of the district--Difficulty of ascertaining changes of
    level--Subsidence of the quay at Messina--Movement in the stones of
    two obelisks--Shift or fault in the Round Tower of
    Terranuova--Opening and closing of fissures--Large edifices
    engulfed--Dimensions of new caverns and fissures--Gradual closing in
    of rents--Bounding of detached masses into the
    air--Landslips--Buildings transported entire to great distances--New
    lakes--Funnel-shaped hollows in alluvial plains--Currents of
    mud--Fall of cliffs, and shore near Scilla inundated--State of
    Stromboli and Etna during the shocks--How earthquakes contribute to
    the formation of valleys--Concluding remarks.


_Calabria_, 1783.--Of the numerous earthquakes which have occurred in
different parts of the globe, during the last 100 years, that of
Calabria, in 1783, is almost the only one of which the geologist can be
said to have such a circumstantial account as to enable him fully to
appreciate the changes which this cause is capable of producing in the
lapse of ages. The shocks began in February, 1783, and lasted for nearly
four years, to the end of 1786. Neither in duration, nor in violence,
nor in the extent of territory moved, was this convulsion remarkable,
when contrasted with many experienced in other countries, both during
the last and present century; nor were the alterations which it
occasioned in the relative level of hill and valley, land and sea, so
great as those effected by some subterranean movements in South America,
in later times. The importance of the earthquake in question arises from
the circumstance, that Calabria is the only spot hitherto visited, both
during and after the convulsions, by men possessing sufficient leisure,
zeal, and scientific information, to enable them to collect and describe
with accuracy the physical facts which throw light on geological
questions.

[Illustration: Fig. 42.]

_Authorities._--Among the numerous authorities, Vivenzio, physician to
the king of Naples, transmitted to the court a regular statement of his
observations during the continuance of the shocks; and his narrative is
drawn up with care and clearness.[663] Francesco Antonio Grimaldi, then
secretary of war, visited the different provinces at the king's command,
and published a most detailed description of the permanent changes in
the surface.[664] He measured the length, breadth, and depth of the
different fissures and gulfs which opened, and ascertained their number
in many provinces. His comments, moreover, on the reports of the
inhabitants, and his explanations of their relations, are judicious and
instructive. Pignataro, a physician residing at Monteleone, a town
placed in the very centre of the convulsions, kept a register of the
shocks, distinguishing them into four classes, according to their degree
of violence. From his work, it appears that, in the year 1783, the
number was 949, of which 501 were shocks of the first degree of force;
and in the following year there were 151, of which 98 were of the first
magnitude.

Count Ippolito, also, and many others, wrote descriptions of the
earthquake; and the Royal Academy of Naples, not satisfied with these
and other observations, sent a deputation from their own body into
Calabria, before the shocks had ceased, who were accompanied by artists
instructed to illustrate by drawings the physical changes of the
district, and the state of ruined towns and edifices. Unfortunately
these artists were not very successful in their representations of the
condition of the country, particularly when they attempted to express,
on a large scale, the extraordinary revolutions which many of the great
and minor river-courses underwent. But many of the plates published by
the Academy are valuable; and as they are little known, I shall
frequently avail myself of them to illustrate the facts about to be
described.[665]

In addition to these Neapolitan sources of information, our countryman,
Sir William Hamilton, surveyed the district, not without some personal
risk, before the shocks had ceased; and his sketch, published in the
Philosophical Transactions, supplies many facts that would otherwise
have been lost. He has explained, in a rational manner, many events
which, as related in the language of some eye-witnesses, appeared
marvellous and incredible. Dolomieu also examined Calabria during the
catastrophe, and wrote an account of the earthquake, correcting a
mistake into which Hamilton had fallen, who supposed that a part of the
tract shaken had consisted of volcanic tuff. It is, indeed, a
circumstance which enhances the geological interest of the commotions
which so often modify the surface of Calabria, that they are confined to
a country where there are neither ancient nor modern rocks of volcanic
or trappean origin; so that at some future time, when the era of
disturbance shall have passed by, the cause of former revolutions will
be as latent as in parts of Great Britain now occupied exclusively by
ancient marine formations.

_Extent of the area convulsed._--The convulsion of the earth, sea, and
air extended over the whole of Calabria Ultra, the southeast part of
Calabria Citra, and across the sea to Messina and its environs; a
district lying between the 38th and 39th degrees of latitude. The
concussion was perceptible over a great part of Sicily, and as far north
as Naples; but the surface over which the shocks acted so forcibly as to
excite intense alarm did not generally exceed 500 square miles in area.
The soil of that part of Calabria is composed chiefly, like the southern
part of Sicily, of calcareo-argillaceous strata of great thickness,
containing marine shells. This clay is sometimes associated with beds of
sand and limestone. For the most part these formations resemble in
appearance and consistency the Subapennine marls, with their
accompanying sands and sandstones; and the whole group bears
considerable resemblance, in the yielding nature of its materials, to
most of our tertiary deposits in France and England. Chronologically
considered, however, the Calabrian formations are comparatively of
modern date, often abounding in fossil shells referable to species now
living in the Mediterranean.

We learn from Vivencio, that on the 20th and 26th of March, 1783,
earthquakes occurred in the islands of Zante, Cephalonia, and St. Maura;
and in the last-mentioned island several public edifices and private
houses were overthrown, and many people destroyed.

If the city of Oppido, in Calabria Ultra, be taken as a centre, and
round that centre a circle be described, with a radius of twenty-two
miles, this space will comprehend the surface of the country which
suffered the greatest alteration, and where all the towns and villages
were destroyed. The first shock, of February 5th, 1783, threw down, in
two minutes, the greater part of the houses in all the cities, towns,
and villages, from the western flanks of the Apennines in Calabria Ultra
to Messina in Sicily, and convulsed the whole surface of the country.
Another occurred on the 28th of March, with almost equal violence. The
granitic chain which passes through Calabria from north to south, and
attains the height of many thousand feet, was shaken but slightly by the
first shock, but more rudely by some which followed.

Some writers have asserted that the wave-like movements which were
propagated through the recent strata, from west to east, became very
violent when they reached the point of junction with the granite, as if
a reaction was produced where the undulatory movement of the soft strata
was suddenly arrested by the more solid rocks. But the statement of
Dolomieu on this subject is most interesting, and perhaps, in a
geological point of view, the most important of all the observations
which are recorded.[666] The Apennines, he says, which consist in great
part of hard and solid granite, with some micaceous and argillaceous
schists, form bare mountains with steep sides, and exhibit marks of
great degradation. At their base newer strata are seen of sand and clay,
mingled with shells; a marine deposit containing such ingredients as
would result from the decomposition of granite. The surface of this
newer (_tertiary_) formation constitutes what is called the plain of
Calabria--a platform which is flat and level, except where intersected
by narrow valleys or ravines, which rivers and torrents have excavated
sometimes to the depth of six hundred feet. The sides of these ravines
are almost perpendicular; for the superior stratum, being bound together
by the roots of trees, prevents the formation of a sloping bank. The
usual effect of the earthquake, he continues, was to disconnect all
those masses which either had not sufficient bases for their bulk, or
which was supported only by lateral adherence. Hence it follows that
throughout almost the whole length of the chain, the soil which adhered
to the granite at the base of the mountains Caulone, Esope, Sagra, and
Aspramonte, slid over the solid and steeply inclined nucleus, and
descended somewhat lower, leaving almost uninterruptedly from St. George
to beyond St. Christina, a distance of from nine to ten miles, a chasm
between the solid granitic nucleus and the sandy soil. Many lands
slipping thus were carried to a considerable distance from their former
position, so as entirely to cover others; and disputes arose as to whom
the property which had thus shifted its place should belong.

From this account of Dolomieu we might anticipate, as the result of a
continuance of such earthquakes, first, a longitudinal valley following
the line of junction of the older and newer rocks; secondly, greater
disturbance in the newer strata near the point of contact than at a
greater distance from the mountains; phenomena very common in other
parts of Italy at the junction of the Apennine and Subapennine
formations.

Mr. Mallet, in his valuable essay on the Dynamics of Earthquakes,[667]
offers the following explanation of the fact to which Dolomieu has
called attention. When a wave of elastic compression, of which he
considers the earth-wave to consist, passes abruptly from a body having
an extremely low elasticity, such as clay and gravel, into another like
granite, whose elasticity is remarkably high, it changes not only its
velocity but in part also its course, a portion being reflected and a
portion refracted. The wave being thus sent back again produces a shock
in the opposite direction, doing great damage to buildings on the
surface by thus returning upon itself. At the same time, the shocks are
at once eased when they get into the more elastic materials of the
granitic mountains.

The surface of the country during the Calabrian earthquakes often heaved
like the billows of a swelling sea, which produced a swimming in the
head, like sea-sickness. It is particularly stated, in almost all the
accounts, that just before each shock the clouds appeared motionless;
and, although no explanation is offered of this phenomenon, it is
obviously the same as that observed in a ship at sea when it pitches
violently. The clouds seem arrested in their career as often as the
vessel rises in a direction contrary to their course; so that the
Calabrians must have experienced precisely the same motion on the land.

Trees, supported by their trunks, sometimes bent during the shocks to
the earth, and touched it with their tops. This is mentioned as a
well-known fact by Dolomieu; and he assures us that he was always on his
guard against the spirit of exaggeration in which the vulgar are ever
ready to indulge when relating these wonderful occurrences.

It is impossible to suppose that these waves, which are described in
Italy and other regions of earthquakes as passing along the solid
surface of the earth in a given direction like a billow on the sea, have
any strict analogy with the undulations of a fluid. They are doubtless
the effects of vibrations, radiating from some deep-seated point, each
of which on reaching the surface lifts up the ground, and then allows it
again to subside. As the distance between the source of the subterranean
movement and the surface must vary according to the outline of the
country, so the vibratory jar will reach different points in succession.

[Illustration: Fig. 75.

Shifts in the stones of two obelisks in the Convent of St Bruno.]

The Academicians relate that in some of the cities of Calabria effects
were produced seeming to indicate a whirling or vorticose movement.
Thus, for example, two obelisks (fig. 75) placed at the extremities of a
magnificent façade in the convent of S. Bruno, in a small town called
Stefano del Bosco, were observed to have undergone a movement of a
singular kind. The shock which agitated the building is described as
having been horizontal and vorticose. The pedestal of each obelisk
remained in its original place; but the separate stones above were
turned partially round, and removed sometimes nine inches from their
position without falling.

It has been suggested by Mr. Darwin that this kind of displacement may
be due to a vibratory rather than a whirling motion;[668] and more
lately Mr. Mallet, in the paper already cited, has offered a very
ingenious solution of the problem. He refers the twisting simply to an
elastic wave, which has moved the pedestal forwards and back again, by
an alternate horizontal motion within narrow limits, and he has
succeeded in showing that a rectilinear movement in the ground may have
sufficed to cause an incumbent body to turn partially round upon its
bed, provided a certain relation exist between the position of the
centre of gravity of the body and its centre of adherence.[669]

I shall now consider, in the first place, that class of physical changes
produced by the earthquake which are connected with alterations in the
relative level of the different parts of the land; and afterwards
describe those which are more immediately connected with the derangement
of the regular drainage of the country, and where the force of running
water co-operated with that of the earthquake.

_Difficulty of ascertaining changes of level._--In regard to alterations
of relative level, none of the accounts establish that they were on a
considerable scale; but it must always be remembered that, in proportion
to the area moved is the difficulty of proving that the general level
has undergone any change, unless the sea-coast happens to have
participated in the principal movement. Even then it is often impossible
to determine whether an elevation or depression even of several feet has
occurred, because there is nothing to attract notice in a band of
shingle and sand of unequal breadth above the level of the sea running
parallel to a coast; such bands generally marking the point reached by
the waves during spring tides, or the most violent tempests. The
scientific investigator has not sufficient topographical knowledge to
discover whether the extent of beach has diminished or increased; and he
who has the necessary local information, scarcely ever feels any
interest in ascertaining the amount of the rise or fall of the ground.
Add to this the great difficulty of making correct observations, in
consequence of the enormous waves which roll in upon a coast during an
earthquake, and efface every landmark near the shore.

_Subsidence of the quay at Messina._--It is evidently in seaports alone
that we can look for very accurate indications of slight changes of
level; and when we find them, we may presume that they would not be rare
at other points, if equal facilities of comparing relative altitudes
were afforded. Grimaldi states (and his account is confirmed by Hamilton
and others), that at Messina, in Sicily, the shore was rent; and the
soil along the port, which before the shock was perfectly level, was
found afterwards to be inclined towards the sea,--the sea itself near
the "Banchina" becoming deeper, and its bottom in several places
disordered. The quay also sunk down about fourteen inches below the
level of the sea, and the houses in its vicinity were much fissured.
(_Phil. Trans._ 1783.)

Among various proofs of partial elevation and depression in the
interior, the Academicians mention, in their Survey, that the ground was
sometimes on the same level on both sides of new ravines and fissures,
but sometimes there had been a considerable shifting, either by the
upheaving of one side, or the subsidence of the other. Thus, on the
sides of long rents in the territory of Soriano, the stratified masses
had altered their relative position to the extent of from eight to
fourteen palms (six to ten and a half feet).

_Polistena._--Similar shifts in the strata are alluded to in the
territory of Polistena, where there appeared innumerable fissures in the
earth. One of these was of great length and depth; and in parts the
level of the corresponding sides was greatly changed. (See fig. 76.)

_Terranuova._--In the town of Terranuova some houses were seen uplifted
above the common level, and others adjoining sunk down into the earth.
In several streets the soil appeared thrust up, and abutted against the
walls of houses: a large circular tower of solid masonry, part of which
had withstood the general destruction, was divided by a vertical rent,
and one side was upraised, and the foundations heaved out of the ground.
It was compared by the Academicians to a great tooth half extracted
from the alveolus, with the upper part of the fangs exposed. (See fig.
77.)

[Illustration: Fig. 76.

Deep fissure, near Polistena, caused by the earthquake of 1783.]

Along the line of this shift, or "fault," as it would be termed
technically by miners, the walls were found to adhere firmly to each
other, and to fit so well, that the only signs of their having been
disunited was the want of correspondence in the courses of stone on
either side of the rent.

[Illustration: Fig. 77.

Shift or "fault" in the Round Tower of Terranuova in Calabria,
occasioned by the earthquake of 1783.]

Dolomieu saw a stone well in the convent of the Augustins at Terranuova,
which had the appearance of having been driven out of the earth. It
resembled a small tower eight or nine feet in height, and a little
inclined. This effect, he says, was produced by the consolidation and
consequent sinking of the sandy soil in which the well was dug.

In some walls which had been thrown down, or violently shaken, in
Monteleone, the separate stones were parted from the mortar, so as to
leave an exact mould where they had rested; whereas in other cases the
mortar was ground to dust between the stones.

It appears that the wave-like motions often produced effects of the most
capricious kind. Thus, in some streets of Monteleone, every house was
thrown down but one; in others, all but two; and the buildings which
were spared were often scarcely in the least degree injured. In many
cities of Calabria, all the most solid buildings were thrown down, while
those which were slightly built escaped; but at Rosarno, as also at
Messina in Sicily, it was precisely the reverse, the massive edifices
being the only ones that stood.

_Fissures._--It appears evident that a great part of the rending and
fissuring of the ground was the effect of a violent motion from below
upwards; and in a multitude of cases where the rents and chasms opened
and closed alternately, we must suppose that the earth was by turns
heaved up, and then let fall again.[670] We may conceive the same effect
to be produced on a small scale, if, by some mechanical force, a
pavement composed of large flags of stone should be raised up, and then
allowed to fall suddenly, so as to resume its original position. If any
small pebbles happened to be lying on the line of contact of two flags,
they would fall into the opening when the pavement rose, and be
swallowed up, so that no trace of them would appear after the subsidence
of the stones. In the same manner, when the earth was upheaved, large
houses, trees, cattle, and men were engulfed in an instant in chasms and
fissures; and when the ground sank down again, the earth closed upon
them, so that no vestige of them was discoverable on the surface. In
many instances, individuals were swallowed up by one shock, and then
thrown out again alive, together with large jets of water, by the shock
which immediately succeeded.

[Illustration: Fig. 78.

Fissures near Jerocarne, in Calabria, caused by the earthquake of 1783.]


At Jerocarne, a country which, according to the Academicians, was
_lacerated_ in a most extraordinary manner, the fissures ran in every
direction, "like cracks on a broken pane of glass" (see fig. 78); and as
a great portion of them remained open after the shocks, it is very
possible that this country was permanently upraised. It was usual, as we
learn from Dolomieu, for the chasms and fissures throughout Calabria, to
ran parallel to the course of some pre-existing gorges in their
neighborhood.

_Houses engulfed._--In the vicinity of Oppido, the central point from
which the earthquake diffused its violent movements, many houses were
swallowed up by the yawning earth, which closed immediately over them.
In the adjacent district, also, of Cannamaria four farm-houses, several
oil-stores, and some spacious dwelling-houses were so completely
engulfed in one chasm, that not a vestige of them was afterwards
discernible. The same phenomena occurred at Terranuova, S. Christina,
and Sinopoli. The Academicians state particularly, that when deep
abysses had opened in the argillaceous strata of Terranuova, and houses
had sunk into them, the sides of the chasms closed with such violence,
that, on excavating afterwards to recover articles of value, the workmen
found the contents and detached parts of the buildings jammed together
so as to become one compact mass. It is unnecessary to accumulate
examples of similar occurrences; but so many are well authenticated
during this earthquake in Calabria, that we may, without hesitation,
yield assent to the accounts of catastrophes of the same kind repeated
again and again in history, where whole towns are declared to have been
engulfed, and nothing but a pool of water or tract of sand left in their
place.

_Chasm formed near Oppido._--On the sloping side of a hill near Oppido a
great chasm opened; and, although a large quantity of soil was
precipitated into the abyss, together with a considerable number of
olive-trees and part of a vineyard, a great gulf remained after the
shock, in the form of an amphitheatre, 500 feet long and 200 feet deep.
(See fig. 79.)

[Illustration: Fig. 79.

Chasm formed by the earthquake of 1783, near Oppido in Calabria.]

_Dimensions of new fissures and chasms._--According to Grimaldi, many
fissures and chasms, formed by the first shock of February 5th, were
greatly widened, lengthened, and deepened by the violent convulsions of
March 28th. In the territory of San Fili this observer found a new
ravine, half a mile in length, two feet and a half broad, and
twenty-five feet deep; and another of similar dimensions in the
territory of Rosarno. A ravine _nearly a mile long_, 105 feet broad and
thirty feet deep, opened in the district of Plaisano, where, also, two
gulfs were caused--one in a place called Cerzulle, three-quarters of a
mile long, 150 feet broad, and above _one hundred feet deep_; and
another at La Fortuna, nearly a quarter of a mile long, above thirty
feet in breadth, and no less than 225 feet deep.

[Illustration: Fig. 80.

Chasm in the hill of St. Angelo, near Soriano, in Calabria, caused by
the earthquake of 1783.]

In the district of Fosolano three gulfs opened: one of these measured
300 feet square, and above thirty feet deep; another was nearly half a
mile long, fifteen feet broad, and above thirty-feet deep; the third was
750 feet square. Lastly, a calcareous mountain, called Zefirio, at the
southern extremity of the Italian peninsula, was cleft in two for the
length of nearly half a mile, and an irregular breadth of many feet.
Some of these chasms were in the form of a crescent. The annexed cut
(fig. 80) represents one by no means remarkable for its dimensions,
which remained open by the side of a small pass over the hill of St.
Angelo, near Soriano. The small river Mesima is seen in the foreground.

_Formation of circular hollows and new lakes._--In the report of the
Academy, we find that some plains were covered with circular hollows,
for the most part about the size of carriage-wheels, but often somewhat
larger or smaller. When filled with water to within a foot or two of the
surface, they appeared like wells; but, in general, they were filled
with dry sand, sometimes with a concave surface, and at other times
convex. (See fig. 81.) On digging down, they found them to be
funnel-shaped, and the moist loose sand in the centre marked the tube up
which the water spouted. The annexed cut (fig. 82) represents a section
of one of these inverted cones when the water had disappeared, and
nothing but dry micaceous sand remained.

[Illustration: Fig. 81.

Circular hollows in the plain of Rosarno, formed by the earthquake of
1783.]

[Illustration: Fig. 82.

Section of one of the circular hollows formed in the plain of Rosarno.]

A small circular pond of similar character was formed not far from
Polistena (see fig. 83); and in the vicinity of Seminara, a lake was
suddenly caused by the opening of a great chasm, from the bottom of
which water issued. This lake was called Lago del Tolfilo. It extended
1785 feet in length, by 937 in breadth, and 52 in depth. The
inhabitants, dreading the miasma of this stagnant pool, endeavored, at
great cost, to drain it by canals, but without success, as it was fed by
springs issuing from the bottom of the deep chasm.

Vivenzio states, that near Sitizzano a valley was nearly filled up to a
level with the high grounds on each side, by the enormous masses
detached from the boundary hills, and cast down into the course of two
streams. By this barrier a lake was formed of great depth, about two
miles long and a mile broad. The same author mentions that, upon the
whole, there were fifty lakes occasioned during the convulsions: and he
assigns localities to all of these. The government surveyors enumerated
215 lakes; but they included in this number many small ponds.

[Illustration: Fig. 83.

Circular pond near Polistena, in Calabria, caused by the earthquake in
1783.]

_Cones of sand thrown up._--Many of the appearances exhibited in the
alluvial plains, such as springs spouting up their water like fountains
at the moment of the shock, have been supposed to indicate the alternate
rising and sinking of the ground. The first effect of the more violent
shocks was usually to dry up the rivers, but they immediately afterwards
overflowed their banks. In marshy places, an immense number of cones of
sand were thrown up. These appearances Hamilton explains, by supposing
that the first movement raised the fissured plain from below upwards, so
that the rivers and stagnant waters in bogs sank down, or at least were
not upraised with the soil. But when the ground returned with violence
to its former position, the water was thrown up in jets through
fissures.[671]

The phenomenon, according to Mr. Mallet, may be simply an accident
contingent on the principal cause of disturbance, the rapid transit of
the earth-wave. "The sources," he says, "of copious springs usually lie
in flat plates or fissures filled with water, whether issuing from solid
rock, or from loose materials; now, if a vein, or thin flat cavity
filled with water, be in such a position that the plane of the plate of
water or fissure be transverse to the line of transit of the earth-wave,
the effect of the arrival of the earth-wave at the watery fissure will
be, at the instant, to compress its walls more or less together, and so
squeeze out the water, which will, for a moment, gush up at the
spring-head like a fountain, and again remain in repose after the
transit of the wave."

_Gradual closing in of fissures._--Sir W. Hamilton was shown several
deep fissures in the vicinity of Mileto, which, although not one of
them was above a foot in breadth, had opened so wide during the
earthquake as to swallow an ox and nearly one hundred goats. The
Academicians also found, on their return through districts which they
had passed at the commencement of their tour, that many rents had, in
that short interval, gradually closed in, so that their width had
diminished several feet, and the opposite walls had sometimes nearly
met. It is natural that this should happen in argillaceous strata,
while, in more solid rocks, we may expect that fissures will remain open
for ages. Should this be ascertained to be a general fact in countries
convulsed by earthquakes, it may afford a satisfactory explanation of a
common phenomenon in mineral veins. Such veins often retain their full
size so long as the rocks consist of limestone, granite, or other
indurated materials; but they contract their dimensions, become mere
threads, or are even entirely cut off, where masses of an argillaceous
nature are interposed. If we suppose the filling up of fissures with
metallic and other ingredients to be a process requiring ages for its
completion, it is obvious that the opposite walls of rents, where strata
consist of yielding materials, must collapse or approach very near to
each other before sufficient time is allowed for the accretion of a
large quantity of veinstone.

_Thermal waters augmented._--It is stated by Grimaldi, that the thermal
waters of St. Eufemia, in Terra di Amato, which first burst out during
the earthquake of 1638, acquired, in February, 1783, an augmentation
both in quantity and degree of heat. This fact appears to indicate a
connection between the heat of the interior and the fissures caused by
the Calabrian earthquakes, notwithstanding the absence of volcanic
rocks, either ancient or modern, in that district.

_Bounding of detached masses into the air._--The violence of the
movement of the ground upwards was singularly illustrated by what the
Academicians call the "sbalzo," or bounding into the air, to the height
of several yards, of masses slightly adhering to the surface. In some
towns a great part of the pavement stones were thrown up, and found
lying with their lower sides uppermost. In these cases, we must suppose
that they were propelled upwards by the momentum which they had
acquired; and that the adhesion of one end of the mass being greater
than that of the other, a rotatory motion had been communicated to them.
When the stone was projected to a sufficient height to perform somewhat
more than a quarter of a revolution in the air, it pitched down on its
edge, and fell with its lower side uppermost.

_Effects of earthquakes on the excavations of valleys._--The next class
of effects to be considered, are those more immediately connected with
the formation of valleys, in which the action of water was often
combined with that of the earthquake. The country agitated was composed,
as before stated, chiefly of argillaceous strata, intersected by deep
narrow valleys, sometimes from 500 to 600 feet deep. As the boundary
cliffs were in great part vertical, it will readily be conceived that,
amidst the various movements of the earth, the precipices overhanging
rivers, being without support on one side, were often thrown down. We
find, indeed, that inundations produced by obstructions in river-courses
are among the most disastrous consequences of great earthquakes in all
parts of the world, for the alluvial plains in the bottoms of valleys
are usually the most fertile and well-peopled parts of the whole
country; and whether the site of a town is above or below a temporary
barrier in the channel of a river, it is exposed to injury by the waters
either of a lake or flood.

_Landslips._--From each side of the deep valley or ravine of Terranuova
enormous masses of the adjoining flat country were detached, and cast
down into the course of the river, so as to give rise to great lakes.
Oaks, olive-trees, vineyards, and corn, were often seen growing at the
bottom of the ravine, as little injured as their former companions,
which still continued to flourish in the plain above, at least 500 feet
higher, and at the distance of about three-quarters of a mile. In one
part of this ravine was an enormous mass, 200 feet high and about 400
feet at its base, which had been detached by some former earthquake. It
is well attested, that this mass travelled down the ravine nearly four
miles, having been put in motion by the earthquake of the 5th of
February. Hamilton, after examining the spot, declared that this
phenomenon might be accounted for by the declivity of the valley, the
great abundance of rain which fell, and the great weight of the alluvial
matter which pressed behind it. Dolomieu also alludes to the fresh
impulse derived from other masses falling, and pressing upon the rear of
those first set in motion.

The first account sent to Naples of the two great slides or landslips
above alluded to, which caused a great lake near Terranuova, was couched
in these words:--"Two mountains on the opposite sides of a valley walked
from their original position until they met in the middle of the plain,
and there joining together, they intercepted the course of a river," &c.
The expressions here used resemble singularly those applied to
phenomena, probably very analogous, which are said to have occurred at
Fez, during the great Lisbon earthquake, as also in Jamaica and Java at
other periods.

Not far from Soriano, which was levelled to the ground by the great
shock of February, a small valley, containing a beautiful olive-grove,
called Fra Ramondo, underwent a most extraordinary revolution.
Innumerable fissures first traversed the river-plain in all directions,
and absorbed the water until the argillaceous substratum became soaked,
so that a great part of it was reduced to a state of fluid paste.
Strange alterations in the outline of the ground were the consequence,
as the soil to a great depth was easily moulded into any form. In
addition to this change, the ruins of the neighboring hills were
precipitated into the hollow; and while many olives were uprooted,
others remained growing on the fallen masses, and inclined at various
angles (see fig. 84). The small river Caridi was entirely concealed for
many days; and when at length it reappeared, it had shaped for itself an
entirely new channel.

_Buildings transported entire to great distances._--Near Seminara an
extensive olive-ground and orchard were hurled to a distance of two
hundred feet, into a valley sixty feet in depth. At the same time a deep
chasm was riven in another part of the high platform from which the
orchard had been detached, and the river immediately entered the
fissure, leaving its former bed completely dry. A small inhabited house,
standing on the mass of earth carried down into the valley, went along
with it entire, and without injury to the inhabitants. The olive-trees,
also, continued to grow on the land which had slid into the valley, and
bore the same year an abundant crop of fruit.

[Illustration: Fig. 84.

Changes of the surface at Fra Ramondo, near Soriano, in Calabria.


  1, Portion of a hill covered with olives thrown down.
  2, New bed of the river Caridi.   3, Town of Soriano.

]

Two tracts of land on which a great part of the town of Polistena stood,
consisting of some hundreds of houses, were detached into a contiguous
ravine, and nearly across it, about half a mile from their original
site; and what is most extraordinary, several of the inhabitants were
dug out from the ruins alive and unhurt.

Two tenements, near Mileto, called the Macini and Vaticano, occupying an
extent of ground about a mile long and half a mile broad, were carried
for a mile down a valley. A thatched cottage, together with large olive
and mulberry trees, most of which remained erect, were carried uninjured
to this extraordinary distance. According to Hamilton, the surface
removed had been long undermined by rivulets, which were afterwards in
full view on the bare spot deserted by the tenements. The earthquake
seems to have opened a passage in the adjoining argillaceous hills,
which admitted water charged with loose soil into the subterranean
channels of the rivulets immediately under the tenements, so that the
foundations of the ground set in motion by the earthquake were loosened.
Another example of subsidence, where the edifices were not destroyed,
is mentioned by Grimaldi, as having taken place in the city of
Catanzaro, the capital of the province of that name. The houses in the
quarter called San Giuseppe subsided with the ground to various depths
from two to four feet, but the buildings remained uninjured.

[Illustration: Fig. 85.

Landslips near Cinquefrondi, caused by the earthquake of 1783.]

It would be tedious, and our space would not permit us, to follow the
different authors through their local details of landslips produced in
minor valleys; but they are highly interesting, as showing to how great
an extent the power of rivers to widen valleys, and to carry away large
portions of soil towards the sea, is increased where earthquakes are of
periodical occurrence. Among other territories, that of Cinquefrondi,
was greatly convulsed, various portions of soil being raised or sunk,
and innumerable fissures traversing the country in all directions (see
fig. 85). Along the flanks of a small valley in this district there
appears to have been an almost uninterrupted line of landslips.

_Currents of mud._--Near S. Lucido, among other places, the soil is
described as having been "dissolved," so that large torrents of mud
inundated all the low grounds, like lava. Just emerging from this mud,
the tops only of trees and of the ruins of farm-houses were seen. Two
miles from Laureana, the swampy soil in two ravines became filled with
calcareous matter, which oozed out from the ground immediately before
the first great shock. This mud, rapidly accumulating, began, ere long,
to roll onward, like a flood of lava, into the valley, where the two
streams uniting, moved forward with increased impetus from east to west.
It now presented a breadth of 225 feet by 15 in depth, and, before it
ceased to move, covered a surface equal in length to an Italian mile. In
its progress it overwhelmed a flock of thirty goats, and tore up by the
roots many olive and mulberry trees, which floated like ships upon its
surface. When this calcareous lava had ceased to move, it gradually
became dry and hard, during which process the mass was lowered seven
feet and a half. It contained fragments of earth of a ferruginous
color, and emitting a sulphureous smell.

_Fall of the sea-cliffs._--Along the sea-coast of the Straits of
Messina, near the celebrated rock of Scilla, the fall of huge masses
detached from the bold and lofty cliffs overwhelmed many villas and
gardens. At Gian Greco, a continuous line of cliff, for a mile in
length, was thrown down. Great agitation was frequently observed in the
bed of the sea during the shocks, and, on those parts of the coast where
the movement was most violent, all kinds of fish were taken in
abundance, and with unusual facility. Some rare species, as that called
Cicirelli, which usually lie buried in the sand, were taken on the
surface of the waters in great quantity. The sea is said to have boiled
up near Messina, and to have been agitated as if by a copious discharge
of vapors from its bottom.

_Shore near Scilla inundated._--The prince of Scilla had persuaded a
great part of his vassals to betake themselves to their fishing-boats
for safety, and he himself had gone on board. On the night of the 5th of
February, when some of the people were sleeping in the boats, and others
on a level plain slightly elevated above the sea, the earth rocked, and
suddenly a great mass was torn from the contiguous Mount Jaci, and
thrown down with a dreadful crash upon the plain. Immediately
afterwards, the sea, rising more than twenty feet above the level of
this low tract, rolled foaming over it, and swept away the multitude. It
then retreated, but soon rushed back again with greater violence,
bringing with it some of the people and animals it had carried away. At
the same time every boat was sunk or dashed against the beach, and some
of them were swept far inland. The aged prince, with 1430 of his people,
was destroyed.

_State of Stromboli and Etna during the shocks._--The inhabitants of
Pizzo remarked that on the 5th of February, 1783, when the first great
shock afflicted Calabria, the volcano of Stromboli, which is in full
view of that town, and at the distance of about fifty miles, smoked
less, and threw up a less quantity of inflamed matter than it had done
for some years previously. On the other hand, the great crater of Etna
is said to have given out a considerable quantity of vapor towards the
beginning, and Stromboli towards the close, of the commotions. But as no
eruption happened from either of these great vents during the whole
earthquake, the sources of the Calabrian convulsions, and of the
volcanic fires of Etna and Stromboli, appear to be very independent of
each other; unless, indeed, they have the same mutual relation as
Vesuvius and the volcanoes of the Phlegræan Fields and Ischia, a violent
disturbance in one district serving as a safety-valve to the other, and
both never being in full activity at once.

_Excavation of valleys._--It is impossible for the geologist to consider
attentively the effect of this single earthquake of 1783, and to look
forward to the alterations in the physical condition of the country to
which a continued series of such movements will hereafter give rise,
without perceiving that the formation of valleys by running water can
never be understood, if we consider the question independently of the
agency of earthquakes. It must not be imagined that rivers only begin to
act when a country is already elevated far above the level of the sea,
for their action must of necessity be most powerful while land is
_rising_ and _sinking_ by successive movements. Whether Calabria is now
undergoing any considerable change of relative level, in regard to the
sea, or is, upon the whole, nearly stationary, is a question which our
observations, confined almost entirely to the last half century, cannot
possibly enable us to determine. But we know that strata, containing
species of shells identical with those now living in the contiguous
parts of the Mediterranean, have been raised in that country, as they
have in Sicily, to the height of several thousand feet.

Now, those geologists who grant that the present course of Nature in the
inanimate world has continued the same since the existing species of
animals were in being, will not feel surprised that the Calabrian
streams and rivers have cut out of such comparatively modern strata a
great system of valleys, varying in depth from fifty to six hundred
feet, and often several miles wide, if they consider how numerous may
have been the shocks which accompanied the uplifting of those recent
marine strata to so prodigious a height. Some speculators, indeed, who
disregard the analogy of existing nature, and who are always ready to
assume that her forces were more energetic in by-gone ages, may dispense
with a long series of movements, and suppose that Calabria "rose like an
exhalation" from the deep, after the manner of Milton's Pandemonium. But
such an hypothesis would deprive them of that peculiar removing force
required to form a regular system of deep and wide valleys; for _time_,
which they are so unwilling to assume, is essential to the operation.
Time must be allowed in the intervals between distinct convulsions, for
running water to clear away the ruins caused by landslips, otherwise the
fallen masses will serve as buttresses, and prevent the succeeding
earthquake from exerting its full power. The sides of the valley must be
again cut away by the stream, and made to form precipices and
over-hanging cliffs, before the next shock can take effect in the same
manner.

Possibly the direction of the succeeding shock may not coincide with
that of the valley, a great extent of adjacent country being equally
shaken. Still it will usually happen that no permanent geographical
change will be produced except in valleys. In them alone will occur
landslips from the boundary cliffs, and these will frequently divert the
stream from its accustomed course, causing the original ravine to become
both wider and more tortuous in its direction.

If a single convulsion of extreme violence should agitate at once an
entire hydrographical basin, or if the shocks should follow each other
too rapidly, the previously existing valleys would be annihilated,
instead of being modified and enlarged. Every stream might in that case
be compelled to begin its operations anew, and to shape out new
channels, instead of continuing to deepen and widen those already
excavated. But if the subterranean movements have been intermittent, and
if sufficient periods have always intervened between the severer shocks
to allow the drainage of the country to be nearly restored to its
original state, then are both the kind and degree of force supplied by
which running water may hollow out valleys of any depth or size
consistent with the elevation above the sea which the districts drained
by them may have attained.

When we read of the drying up and desertion of the channels of rivers,
the accounts most frequently refer to their deflection into some other
part of the same alluvial plain, perhaps several miles distant. Under
certain circumstances a change of level may undoubtedly force the water
to flow over into some distinct hydrographical basin; but even then it
will fall immediately into some other system of valleys already formed.

We learn from history that, ever since the first Greek colonists settled
in Calabria, that region has been subject to devastation by earthquakes;
and, for the last century and a half, ten years have seldom elapsed
without a shock; but the severer convulsions have not only been
separated by intervals of twenty, fifty, or one hundred years, but have
not affected precisely the same points when they recurred. Thus the
earthquake of 1783, although confined within the same geographical
limits as that of 1638, and not very inferior in violence, visited,
according to Grimaldi, very different districts. The points where the
local intensity of the force is developed being thus perpetually varied,
more time is allowed for the removal of separate mountain masses thrown
into river-channels by each shock.

_Number of persons who perished during the earthquake._--The number of
persons who perished during the earthquake in the two Calabrias and
Sicily, is estimated by Hamilton at about forty thousand; and about
twenty thousand more died by epidemics, which were caused by
insufficient nourishment, exposure to the atmosphere, and malaria,
arising from the new stagnant lakes and pools.

By far the greater number were buried under the ruins of their houses;
but many were burnt to death in the conflagrations which almost
invariably followed the shocks. These fires raged the more violently in
some cities, such as Oppido, from the immense magazines of oil which
were consumed.

Many persons were engulfed in deep fissures, especially the peasants
when flying across the open country, and their skeletons may perhaps be
buried in the earth to this day, at the depth of several hundred feet.

When Dolomieu visited Messina after the shock of Feb. 5th, he describes
the city as still presenting, at least at a distance, an imperfect image
of its ancient splendor. Every house was injured, but the walls were
standing; the whole population had taken refuge in wooden huts in the
neighborhood, and all was solitude and silence in the streets: it seemed
as if the city had been desolated by the plague, and the impression made
upon his feelings was that of melancholy and sadness. "But when I passed
over to Calabria, and first beheld Polistena, the scene of horror almost
deprived me of my faculties; my mind was filled with mingled compassion
and terror; nothing had escaped; all was levelled with the dust; not a
single house or piece of wall remained; on all sides were heaps of stone
so destitute of form, that they gave no conception of there ever having
been a town on the spot. The stench of the dead bodies still rose from
the ruins. I conversed with many persons who had been buried for three,
four, and even for five days; I questioned them respecting their
sensations in so dreadful a situation, and they agreed that of all the
physical evils they endured, thirst was the most intolerable; and that
their mental agony was increased by the idea that they were abandoned by
their friends, who might have rendered them assistance."[672]

It is supposed that about a fourth part of the inhabitants of Polistena,
and of some other towns, were buried alive, and might have been saved
had there been no want of hands; but in so general a calamity, where
each was occupied with his own misfortunes or those of his family, aid
could rarely be obtained. Neither tears, nor supplications, nor promises
of high rewards were listened to. Many acts of self-devotion, prompted
by parental and conjugal tenderness, or by friendship, or the gratitude
of faithful servants, are recorded; but individual exertions were, for
the most part, ineffectual. It frequently happened, that persons in
search of those most dear to them could hear their moans,--could
recognize their voices--were certain of the exact spot where they lay
buried beneath their feet, yet could afford them no succor. The piled
mass resisted all their strength, and rendered their efforts of no
avail.

At Terranuova, four Augustin monks, who had taken refuge in a vaulted
sacristy, the arch of which continued to support an immense pile of
ruins, made their cries heard for the space of four days. One only of
the brethren of the whole convent was saved, and "of what avail was his
strength to remove the enormous weight of rubbish which had overwhelmed
his companions?" He heard their voices die away gradually; and when
afterwards their four corpses were disinterred, they were found clasped
in each other's arms. Affecting narratives are preserved of mothers
saved after the fifth, sixth, and even seventh day of their interment,
when their infants or children had perished with hunger.

It might have been imagined that the sight of sufferings such as these
would have been sufficient to awaken sentiments of humanity and pity in
the most savage breasts; but while some acts of heroism are related,
nothing could exceed the general atrocity of conduct displayed by the
Calabrian peasants: they abandoned the farms, and flocked in great
numbers into the towns--not to rescue their countrymen from a lingering
death, but to plunder. They dashed through the streets, fearless of
danger, amid tottering walls and clouds of dust, trampling beneath their
feet the bodies of the wounded and half-buried, and often stripping
them, while yet living, of their clothes.[673]

_Concluding remarks._--But to enter more fully into these details would
be foreign to the purpose of the present work, and several volumes
would be required to give the reader a just idea of the sufferings
which the inhabitants of many populous districts have undergone during
the earthquakes of the last 150 years. A bare mention of the loss of
life--as that fifty or a hundred thousand souls perished in one
catastrophe--conveys to the reader no idea of the extent of misery
inflicted: we must learn, from the narratives of eye-witnesses, the
various forms in which death was encountered, the numbers who escaped
with loss of limbs or serious bodily injuries, and the multitude who
were suddenly reduced to penury and want. It has been often remarked,
that the dread of earthquakes is strongest in the minds of those who
have experienced them most frequently; whereas, in the case of almost
every other danger, familiarity with peril renders men intrepid. The
reason is obvious--scarcely any part of the mischief apprehended in this
instance is imaginary; the first shock is often the most destructive;
and, as it may occur in the dead of the night, or if by day, without
giving the least warning of its approach, no forethought can guard
against it; and when the convulsion has begun, no skill, or courage, or
presence of mind, can point out the path of safety. During the
intervals, of uncertain duration, between the more fatal shocks, slight
tremors of the soil are not unfrequent; and as these sometimes precede
more violent convulsions, they become a source of anxiety and alarm. The
terror arising from this cause alone is of itself no inconsiderable
evil.

Although sentiments of pure religion are frequently awakened by these
awful visitations, yet we more commonly find that an habitual state of
fear, a sense of helplessness, and a belief in the futility of all human
exertions, prepare the minds of the vulgar for the influence of a
demoralizing superstition.

Where earthquakes are frequent, there can never be perfect security of
property under the best government; industry cannot be assured of
reaping the fruits of its labor; and the most daring acts of outrage may
occasionally be perpetrated with impunity, when the arm of the law is
paralyzed by the general consternation. It is hardly necessary to add,
that the progress of civilization and national wealth must be retarded
by convulsions which level cities to the ground, destroy harbors, render
roads impassable, and cause the most cultivated valley-plains to be
covered with lakes, or the ruins of adjoining hills.

Those geologists who imagine that, at remote periods ere man became a
sojourner on earth, the volcanic agency was more energetic than now,
should be careful to found their opinion on strict geological evidence,
and not permit themselves to be biased, as they have often been, by a
notion, that the disturbing force would probably be mitigated for the
sake of man.

I shall endeavor to point out in the sequel, that the general tendency
of subterranean movements, when their effects are considered for a
sufficient lapse of ages, is eminently beneficial, and that they
constitute an essential part of that mechanism by which the integrity of
the habitable surface is preserved, and the very existence and
perpetuation of dry land secured. Why the working of this same
machinery should be attended with so much evil, is a mystery far beyond
the reach of our philosophy, and must probably remain so until we are
permitted to investigate, not our planet alone and its inhabitants, but
other parts of the moral and material universe with which they may be
connected. Could our survey embrace other worlds, and the events, not of
a few centuries only, but of periods as indefinite as those with which
geology renders us familiar, some apparent contradictions might be
reconciled, and some difficulties would doubtless be cleared up. But
even then, as our capacities are finite, while the scheme of the
universe may be infinite, both in time and space, it is presumptuous to
suppose that all sources of doubt and perplexity would ever be removed.
On the contrary, they might, perhaps, go on augmenting in number,
although our confidence in the wisdom of the plan of Nature should
increase at the same time; for it has been justly said, that the greater
the circle of light, the greater the boundary of darkness by which it is
surrounded.[674]




CHAPTER XXIX.

EARTHQUAKES--_continued_.


  Earthquake of Java, 1772--Truncation of a lofty cone--St. Domingo,
    1770--Lisbon, 1755--Great area over which the shocks
    extended--Retreat of the sea--Proposed explanations--Conception Bay,
    1750--Permanent elevation--Peru, 1746--Java, 1699--Rivers obstructed
    by landslips--Subsidence in Sicily, 1693--Moluccas, 1693--Jamaica,
    1692--Large tracts engulfed--Portion of Port Royal sunk--Amount of
    change in the last 150 years--Elevation and subsidence of land in
    Bay of Baiæ--Evidence of the same afforded by the Temple of Serapis.


In the preceding chapters we have considered a small part only of those
earthquakes which have occurred during the last seventy years, of which
accurate and authentic descriptions happen to have been recorded. In
examining those of earlier date, we find their number so great that
allusion can be made to a few only respecting which information of
peculiar geological interest has been obtained.

_Java_, 1772.--_Truncation of a lofty cone._--In the year 1772,
Papandayang, formerly one of the loftiest volcanoes in the island of
Java, was in eruption. Before all the inhabitants on the declivities of
the mountain could save themselves by flight, the ground began to give
way, and a great part of the volcano fell in and disappeared. It is
estimated that an extent of ground of the mountain itself and its
immediate environs, fifteen miles long and full six broad, was by this
commotion swallowed up in the bowels of the earth. Forty villages were
destroyed, some being engulfed and some covered by the substances thrown
out on this occasion, and 2957 of the inhabitants perished. A
proportionate number of cattle were also killed, and most of the
plantations of cotton, indigo, and coffee in the adjacent districts were
buried under the volcanic matter. This catastrophe appears to have
resembled, although on a grander scale, that of the ancient Vesuvius in
the year 79. The cone was reduced in height from 9000 to about 5000
feet; and, as vapors still escape from the crater on its summit, a new
cone may one day rise out of the ruins of the ancient mountain, as the
modern Vesuvius has risen from the remains of Somma.[675]

_St. Domingo_, 1770.--During a tremendous earthquake which destroyed a
great part of St. Domingo, innumerable fissures were caused throughout
the island, from which mephitic vapors emanated and produced an
epidemic. _Hot springs_ burst forth in many places where there had been
no water before; but after a time they ceased to flow.[676]

In a previous earthquake, in November, 1751, a violent shock destroyed
the capital, Port au Prince, and part of the coast, twenty leagues in
length, sank down, and has ever since formed a bay of the sea.[677]

_Hindostan_, 1762.--The town of Chittagong, in Bengal, was violently
shaken by an earthquake, on the 2d of April, 1762, the earth opening in
many places, and throwing up water and mud of a sulphureous smell. At a
place called Bardavan, a large river was dried up; and at Bar Charra,
near the sea, a tract of ground sunk down, and 200 people, with all
their cattle, were lost. It is said, that sixty square miles of the
Chittagong coast suddenly and permanently subsided during this
earthquake, and that Ces-lung-Toom, one of the Mug mountains, entirely
disappeared, and another sank so low, that its summit only remained
visible. Four hills are also described as having been variously rent
asunder, leaving open chasms from thirty to sixty feet in width. Towns
which subsided several cubits, were overflowed with water; among others,
Deep Gong, which was submerged to the depth of seven cubits. Two
volcanoes are said to have opened in the Secta Cunda hills. The shock
was also felt at Calcutta.[678] While the Chittagong coast was sinking,
a corresponding rise of the ground took place at the island of Ramree,
and at Cheduba (see Map, fig. 39, p. 351).[679]

_Lisbon_, 1755.--In no part of the volcanic region of southern Europe
has so tremendous an earthquake occurred in modern times, as that which
began on the 1st of November, 1755, at Lisbon. A sound of thunder was
heard underground, and immediately afterwards a violent shock threw down
the greater part of that city. In the course of about six minutes, sixty
thousand persons perished. The sea first retired and laid the bar dry;
it then rolled in, rising fifty feet or more above its ordinary level.
The mountains of Arrabida, Estrella, Julio, Marvan, and Cintra, being
some of the largest in Portugal, were impetuously shaken, as it were,
from their very foundations; and some of them opened at their summits,
which were split and rent in a wonderful manner, huge masses of them
being thrown down into the subjacent valleys.[680] Flames are related to
have issued from these mountains, which are supposed to have been
electric; they are also said to have smoked; but vast clouds of dust may
have given rise to this appearance.

The area over which this convulsion extended is very remarkable. It has
been computed, says Humboldt,[681] that on the 1st November, 1755, a
portion of the earth's surface four times greater than the extent of
Europe was simultaneously shaken. The shock was felt in the Alps, and on
the coast of Sweden, in small inland lakes on the shores of the Baltic,
in Thuringia, and in the flat country of northern Germany. The thermal
springs of Toplitz dried up, and again returned, inundating every thing
with water discolored by ochre. In the islands of Antigua, Barbadoes,
and Martinique in the West Indies, where the tide usually rises little
more than two feet, it suddenly rose above twenty feet, the water being
discolored and of an inky blackness. The movement was also sensible in
the great lakes of Canada. At Algiers and Fez, in the north of Africa,
the agitation of the earth was as violent as in Spain and Portugal; and
at the distance of eight leagues from Morocco, a village with the
inhabitants, to the number of about 8000 or 10,000 persons, are said to
have been swallowed up; the earth soon afterwards closing over them.

_Subsidence of the quay._--Among other extraordinary events related to
have occurred at Lisbon during the catastrophe was the subsidence of a
new quay, built entirely of marble at an immense expense. A great
concourse of people had collected there for safety, as a spot where they
might be beyond the reach of falling ruins; but suddenly the quay sank
down with all the people on it, and not one of the dead bodies ever
floated to the surface. A great number of boats and small vessels
anchored near it, all full of people, were swallowed up, as in a
whirlpool.[682] No fragments of these wrecks ever rose again to the
surface, and the water in the place where the quay had stood is stated,
in many accounts, to be unfathomable; but Whitehurst says he ascertained
it to be one hundred fathoms.[683]

Circumstantial as are the contemporary narratives, I learn from a
correspondent, Mr. F. Freeman, in 1841, that no part of the Tagus was
then more than thirty feet deep at high tide, and an examination of the
position of the new quay, and the memorials preserved of the time and
manner in which it was built, rendered the statement of so great a
subsidence in 1755 quite unintelligible. Perhaps a deep narrow chasm,
such as was before described in Calabria (p. 481), opened and closed
again in the bed of the Tagus, after swallowing up some incumbent
buildings and vessels. We have already seen that such openings may
collapse after the shock suddenly, or, in places where the strata are of
soft and yielding materials, very gradually. According to the
observations made at Lisbon, in 1837, by Mr. Sharpe, the destroying
effects of this earthquake were confined to the tertiary strata, and
were most violent on the blue clay, on which the lower part of the city
is constructed. Not a building, he says, on the secondary limestone or
the basalt was injured.[684]

_Shocks felt at sea._--The shock was felt at sea, on the deck of a ship
to the west of Lisbon, and produced very much the same sensation as on
dry land. Off St. Lucar, the captain of the ship Nancy felt his vessel
so violently shaken, that he thought she had struck the ground; but, on
heaving the lead, found a great depth of water. Captain Clark, from
Denia, in latitude 36° 24' N., between nine and ten in the morning, had
his ship shaken and strained as if she had struck upon a rock, so that
the seams of the deck opened, and the compass was overturned in the
binnacle. Another ship, forty leagues west of St. Vincent, experienced
so violent a concussion, that the men were thrown a foot and a half
perpendicularly up from the deck.

_Rate at which the movement travelled._--The agitation of lakes, rivers,
and springs, in Great Britain, was remarkable. At Loch Lomond, in
Scotland, for example, the water, without, the least apparent cause,
rose against its banks, and then subsided below its usual level. The
greatest perpendicular height of this swell was two feet four inches. It
is said that the movement of this earthquake was undulatory, and that it
travelled at the rate of twenty miles a minute, its velocity being
calculated by the intervals between the time when the first shock was
felt at Lisbon, and its time of occurrence at other distant places.[685]

_Great wave and retreat of the sea._--A great wave swept over the coast
of Spain, and is said to have been sixty feet high at Cadiz. At Tangier,
in Africa, it rose and fell eighteen times on the coast. At Funchal, in
Madeira, it rose full fifteen feet perpendicular above high-water mark,
although the tide, which ebbs and flows there seven feet, was then at
half-ebb. Besides entering the city, and committing great havoc, it
overflowed other seaports in the island. At Kinsale, in Ireland, a body
of water rushed into the harbor, whirled round several vessels, and
poured into the market-place.

It was before stated that the sea first retired at Lisbon; and this
retreat of the ocean from the shore, at the commencement of an
earthquake, and its subsequent return in a violent wave, is a common
occurrence. In order to account for the phenomenon, Michell imagined a
subsidence at the bottom of the sea, from the giving way of the roof of
some cavity in consequence of a vacuum produced by the condensation of
steam. Such condensation, he observes, might be the first effect of the
introduction of a large body of water into fissures and cavities already
filled with steam, before there has been sufficient time for the heat of
the incandescent lava to turn so large a supply of water into steam,
which being soon accomplished causes a greater explosion.

Another proposed explanation is, the sudden rise of the land, which
would cause the sea to abandon immediately the ancient line of coast;
and if the shore, after being thus heaved up, should fall again to its
original level, the ocean would return. This theory, however, will not
account for the facts observed during the Lisbon earthquake; for the
retreat preceded the wave, not only on the coast of Portugal, but also
at the island of Madeira, and several other places. If the upheaving of
the coast of Portugal had caused the retreat, the motion of the waters,
when propagated to Madeira, would have produced a wave previous to the
retreat. Nor could the motion of the waters at Madeira have been caused
by a different local earthquake; for the shock travelled from Lisbon to
Madeira in two hours, which agrees with the time which it required to
reach other places equally distant.[686]

The following is another solution of the problem, which has been
offered:--Suppose a portion of the bed of the sea to be suddenly
upheaved; the first effect will be to raise over the elevated part a
body of water, the momentum of which will carry it much above the level
it will afterwards assume, causing a draught or receding of the water
from the neighboring coasts, followed immediately by the return of the
displaced water, which will also be impelled by its momentum much
farther and higher on the coast than its former level.[687]

Mr. Darwin, when alluding to similar waves on the coast of Chili, states
his opinion, that "the whole phenomenon is due to a common undulation in
the water, proceeding from a line or point of disturbance some little
way distant. If the waves," he says, "sent off from the paddles of a
steam-vessel be watched breaking on the sloping shore of a still river,
the water will be seen first to retire two or three feet, and then to
return in little breakers, precisely analogous to those consequent on an
earthquake." He also adds, that "the earthquake-wave occurs some time
after the shock, the water at first retiring both from the shores of the
mainland and of outlying islands, and then returning in mountainous
breakers. Their size is modified by the form of the neighboring coast;
for it is ascertained in South America, that places situated at the
head of shoaling bays have suffered most, whereas towns like Valparaiso,
seated close on the border of a profound ocean, have never been
inundated, though severely shaken by earthquakes."[688]

More recently (February, 1846), Mr. Mallet, in his memoir above cited
(p. 475), has endeavored to bring to bear on this difficult subject the
more advanced knowledge obtained of late years respecting the true
theory of waves. He conceives that when the origin of the shock is
beneath the deep ocean, one wave is propagated through the land, and
another moving with inferior velocity is formed on the surface of the
ocean. This last rolls in upon the land long after the earth-wave has
arrived and spent itself. However irreconcilable it may be to our common
notions of solid bodies, to imagine them capable of transmitting, with
such extreme velocity, motions analogous to tidal waves, it seems
nevertheless certain that such undulations are produced, and it is
supposed that when the shock passes a given point, each particle of the
solid earth describes an ellipse in space. The facility with which all
the particles of a solid mass can be made to vibrate may be illustrated,
says Gay Lussac, by many familiar examples. If we apply the ear to one
end of a long wooden beam, and listen attentively when the other end is
struck by a pin's head, we hear the shock distinctly; which shows that
every fibre throughout the whole length has been made to vibrate. The
rattling of carriages on the pavement shakes the largest edifices; and
in the quarries underneath some quarters in Paris, it is found that the
movement is communicated through a considerable thickness of rock.[689]

The great sea-wave originating directly over the centre of disturbance
is propagated, as Michell correctly stated, in every direction, like the
circle upon a pond when a pebble is dropped into it, the different rates
at which it moves depending (as he also suggested) on variations in the
depth of the water. This wave of the sea, says Mr. Mallet, is raised by
the impulse of the shock immediately below it, which in great
earthquakes lifts up the ground two or three feet perpendicularly. The
velocity of the shock, or earth-wave, is greater because it "depends
upon a function of the elasticity of the crust of the earth, whereas the
velocity of the sea-wave depends upon a function of the depth of the
sea."

"Although the shock in its passage under the deep ocean gives no trace
of its progress, it no sooner gets into soundings or shallow water, than
it gives rise to another and smaller wave of the sea. It carries, as it
were, upon its back, this lesser aqueous undulation; a long narrow ridge
of water which corresponds in form and velocity to itself, being pushed
up by the partial elevation of the bottom. It is this small wave, called
technically the 'forced sea-wave,' which communicates the
earthquake-shock to ships at sea, as if they had struck upon a rock. It
breaks upon a coast at the same moment that the shock reaches it, and
sometimes it may cause an apparent slight recession from the shore,
followed by its flowing up somewhat higher than the usual tide mark:
this will happen where the beach is very sloping, as is usual where the
sea is shallow, for then the velocity of the low flat earth-wave is
such, that it slips as it were, from under the undulation in the fluid
above. It does this at the moment of reaching the beach, which it
elevates by a vertical height equal to its own, and as instantly lets
drop again to its former level."

"While the shock propagated through the solid earth has thus travelled
with extra rapidity to the land, the great sea-wave has been following
at a slower pace, though advancing at the rate of several miles in a
minute. It consists, in the deep ocean, of a long low swell of enormous
volume, having an equal slope before and behind, and that so gentle that
it might pass under a ship without being noticed. But when it reaches
the edge of soundings, its front slope, like that of a tidal wave under
similar circumstances, becomes short and steep, while its rear slope is
long and gentle. If there be water of some depth close into shore, this
great wave may roll in long after the shock, and do little damage; but
if the shore be shelving, there will be first a retreat of the water,
and then the wave will break upon the beach and roll in far upon the
land."[690]

The various opinions which have been offered by Michell and later
writers, respecting the remote causes of earthquake shocks in the
interior of the earth, will more properly be discussed in the
thirty-second chapter.

_Chili_, 1751.--On the 24th of May, 1751, the ancient town of
Conception, otherwise called Penco, was totally destroyed by an
earthquake, and the sea rolled over it. (See plan of the bay, fig. 70,
p. 455.) The ancient port was rendered entirely useless, and the
inhabitants built another town about ten miles from the sea-coast, in
order to be beyond the reach of similar inundations. At the same time, a
colony recently settled on the sea-shore of Juan Fernandez was almost
entirely overwhelmed by a wave which broke upon the shore.

It has been already stated, that in 1835, or eighty-four years after the
destruction of Penco, the same coast was overwhelmed by a similar flood
from the sea during an earthquake; and it is also known that twenty-one
years before (or in 1730), a like wave rolled over these fated shores,
in which many of the inhabitants perished. A series of similar
catastrophes has also been tracked back as far as the year 1590,[691]
beyond which we have no memorials save those of oral tradition. Molina,
who has recorded the customs and legends of the aborigines, tells us,
that the Araucanian Indians, a tribe inhabiting the country between the
Andes and the Pacific, including the part now called Chili, "had among
them a tradition of a great deluge, in which only a few persons were
saved, who took refuge upon a high mountain called Thegtheg, "the
thundering," which had three points. Whenever a violent earthquake
occurs, these people fly for safety to the mountains, assigning as a
reason, that they are fearful, after the shock, that the sea will again
return and deluge the world.[692]

Notwithstanding the tendency of writers in his day to refer all
traditionary inundations to one remote period, Molina remarks that this
flood of the Araucanians "was probably very different from that of
Noah." We have, indeed, no means of conjecturing how long this same
tribe had flourished in Chili, but we can scarcely doubt, that if its
experience reached back even for three or four centuries, several
inroads of the ocean must have occurred within that period. But the
memory of a succession of physical events, similar in kind, though
distinct in time, can never be preserved by a people destitute of
written annals. Before two or three generations have passed away all
dates are forgotten, and even the events themselves, unless they have
given origin to some customs, or religious rites and ceremonies.
Oftentimes the incidents of many different earthquakes and floods become
blended together in the same narrative; and in such cases the single
catastrophe is described in terms so exaggerated, or is so disguised by
mythological fictions, as to be utterly valueless to the antiquary or
philosopher.

_Proofs of elevation of twenty-four feet._--During a late survey of
Conception Bay, Captain Beechey and Sir E. Belcher discovered that the
ancient harbor, which formerly admitted all large merchant vessels which
went round the Cape, is now occupied by a reef of sandstone, certain
points of which project above the sea at low water, the greater part
being very shallow. A tract of a mile and a half in length, where,
according to the report of the inhabitants, the water was formerly four
or five fathoms deep, is now a shoal; consisting, as our hydrographers
found, of hard sandstone, so that it cannot be supposed to have been
formed by recent deposits of the river Biobio, an arm of which carries
down loose micaceous sand into the same bay.

It is impossible at this distance of time to affirm that the bed of the
sea was uplifted at once to the height of twenty-four feet, during the
single earthquake of 1751, because other movements may have occurred
subsequently; but it is said, that ever since the shock of 1751, no
vessels have been able to approach within a mile and a half of the
ancient port of Penco. (See Map, p. 455.) In proof of the former
elevation of the coast near Penco our surveyors found above high-water
mark an enormous bed of shells of the same species as those now living
in the bay, filled with micaceous sand like that which the Biobio now
conveys to the bay. These shells, as well as others, which cover the
adjoining hills of mica-schist to the height of several hundred feet,
have lately been examined by experienced conchologists in London, and
identified with those taken at the same time in a living state from the
bay and its neighborhood.[693]

Ulloa, therefore, was perfectly correct in his statement that, at
various heights above the sea between Talcahuano and Conception, "mines
were found of various sorts of shells used for lime of the very same
kinds as those found in the adjoining sea." Among them he mentions the
great mussel called Choros, and two others which he describes. Some of
these, he says, are entire, and others broken; they occur at the bottom
of the sea, in four, six, ten, or twelve fathom water, where they adhere
to a sea-plant called Cochayuyo. They are taken in dredges, and have no
resemblance to those found on the shore or in shallow water; yet beds of
them occur at various heights on the hills. "I was the more pleased with
the sight," he adds, "as it appeared to me a convincing proof of the
universality of the deluge, although I am not ignorant that some have
attributed their position to other causes."[694] It has, however, been
ascertained that the foundation of the Castle of Penco was so low in
1835, or at so inconsiderable an elevation above the highest spring
tides, as to discountenance the idea of any permanent upheaval in modern
times, on the site of that ancient port; but no exact measurements or
levellings appear as yet to have been made to determine this point,
which is the more worthy of investigation, because it may throw some
light on an opinion often promulgated of late years, that there is a
tendency in the Chilian coast, after each upheaval, to sink gradually
and return towards its former position.

_Peru_, 1746.--Peru was visited, on the 28th of October, 1746, by a
tremendous earthquake. In the first twenty-four hours, two hundred
shocks were experienced. The ocean twice retired and returned
impetuously upon the land: Lima was destroyed, and part of the coast
near Callao was converted into a bay: four other harbors, among which
were Cavalla and Guanape, shared the same fate. There were twenty-three
ships and vessels, great and small, in the harbor of Callao, of which
nineteen were sunk; and the other four, among which was a frigate called
St. Fermin, were carried by the force of the waves to a great distance
up the country, and left on dry ground at a considerable height above
the sea. The number of inhabitants in this city amounted to four
thousand. Two hundred only escaped, twenty-two of whom were saved on a
small fragment of the fort of Vera Cruz, which remained as the only
memorial of the town after this dreadful inundation. Other portions of
its site were completely covered with heaps of sand and gravel.

A volcano in Lucanas burst forth the same night, and such quantities of
water descended from the cone that the whole country was overflowed; and
in the mountain near Pataz, called Conversiones de Caxamarquilla,
three other volcanoes burst out, and frightful torrents of water swept
down their sides.[695]

There are several records of prior convulsions in Peru, accompanied by
similar inroads in the sea, one of which happened fifty-nine years
before (in 1687), when the ocean, according to Ulloa, first retired and
then returned in a mountainous wave, overwhelming Callao and its
environs, with the miserable inhabitants.[696] This same wave, according
to Lionel Wafer, carried ships a league into the country, and drowned
man and beast for fifty leagues along the shore.[697] Inundations of
still earlier dates are carefully recorded by Ulloa, Wafer, Acosta, and
various writers, who describe them as having expended their chief fury,
some on one part of the coast and some on another.

But all authentic accounts cease when we ascend to the era of the
conquest of Peru by the Spaniards. The ancient Peruvians, although far
removed from barbarism, were without written annals, and therefore
unable to preserve a distinct recollection of a long series of natural
events. They had, however, according to Antonio de Herrera, who, in the
beginning of the seventeenth century, investigated their antiquities, a
tradition, "that many years before the reign of the Incas, at a time
when the country was very populous, there happened a great flood; the
sea breaking out beyond its bounds, so that the land was covered with
water and all the people perished. To this the Guacas, inhabiting the
vale of Xausca, and the natives of Chiquito, in the province of Callao,
add that some persons remained in the hollows and caves of the highest
mountains, who again peopled the land. Others of the mountain people
affirm that all perished in the deluge, only six persons being saved on
a float, from whom descended all the inhabitants of that country."[698]

On the mainland near Lima, and on the neighboring island of San Lorenzo,
Mr. Darwin found proofs that the ancient bed of the sea had been raised
to the height of more than eighty feet above water within the human
epoch, strata having been discovered at that altitude, containing pieces
of cotton thread and plaited rush, together with sea-weed and marine
shells.[699] The same author learnt from Mr. Gill, a civil engineer,
that he discovered in the interior near Lima, between Casma and Huaraz,
the dried-up channel of a large river, sometimes worn through solid
rock, which, instead of continually ascending towards its source, has,
in one place, a steep downward slope in that direction, for a ridge or
line of hills has been uplifted directly across the bed of the stream,
which is now arched. By these changes the water has been turned into
some other course; and a district, once fertile, and still covered with
ruins, and bearing the marks of ancient cultivation, has been converted
into a desert.[700]

_Java_, 1699.--On the 5th of January, 1699, a terrible earthquake
visited Java, and no less than 208 considerable shocks were reckoned.
Many houses in Batavia were overturned, and the flame and noise of a
volcanic eruption were seen and heard in that city, which were
afterwards found to proceed from Mount Salek,[701] a volcano six days'
journey distant. Next morning the Batavian river, which has its rise
from that mountain, became very high and muddy, and brought down
abundance of bushes and trees, half burnt. The channel of the river
being stopped up, the water overflowed the country round the gardens
about the town, and some of the streets, so that fishes lay dead in
them. All the fish in the river, except the carps, were killed by the
mud and turbid water. A great number of drowned buffaloes, tigers,
rhinoceroses, deer, apes, and other wild beasts, were brought down by
the current; and, "notwithstanding," observes one of the writers, "that
a crocodile is amphibious, several of them were found dead among the
rest."[702]

It is stated that seven hills bounding the river sank down; by which is
merely meant, as by similar expressions in the description of the
Calabrian earthquakes, seven great landslips. These hills, descending
some from one side of the valley and some from the other, filled the
channel, and the waters then finding their way under the mass, flowed
out thick and muddy. The Tangaran river was also dammed up by nine
hills, and in its channel were large quantities of drift trees. Seven of
its tributaries also are said to have been "covered up with earth." A
high tract of forest land, between the two great rivers before
mentioned, is described as having been changed into an open country,
destitute of trees, the surface being spread over with fine red clay.
This part of the account may, perhaps, merely refer to the sliding down
of woody tracts into the valleys, as happened to so many extensive
vineyards and olive-grounds in Calabria, in 1783. The close packing of
large trees in the Batavian river is represented as very remarkable, and
it attests in a striking manner the destruction of soil bordering the
valleys which had been caused by floods and landslips.[703]

_Quito_, 1698.--In Quito, on the 19th of July, 1698, during an
earthquake, a great part of the crater and summit of the volcano
Carguairazo fell in, and a stream of water and mud issued from the
broken sides of the hill.[704]

_Sicily_, 1693.--Shocks of earthquakes spread over all Sicily in 1693,
and on the 11th of January the city of Catania and forty-nine other
places were levelled to the ground, and about one hundred thousand
people killed. The bottom of the sea, says Vicentino Bonajutus, sank
down considerably, both in ports, inclosed bays, and open parts of the
coast, and water bubbled up along the shores. Numerous long fissures of
various breadths were caused, which threw out sulphurous water; and one
of them, in the plain of Catania (the delta of the Simeto), at the
distance of four miles from the sea, sent forth water as salt as the
sea. The stone buildings of a street in the city of Noto, for the length
of half a mile, sank into the ground, and remained hanging on one side.
In another street, an opening large enough to swallow a man and horse
appeared.[705]

_Moluccas_, 1693.--The small Isle of Sorea, which consists of one great
volcano, was in eruption in the year 1693. Different parts of the cone
fell, one after the other, into a deep crater, until almost half the
space of the island was converted into a fiery lake. Most of the
inhabitants fled to Banda; but great pieces of the mountain continued to
fall down, so that the lake of lava became wider; and finally the whole
population was compelled to emigrate. It is stated that, in proportion
as the burning lake increased in size, the earthquakes were less
vehement.[706]

_Jamaica_, 1692.--In the year 1692, the island of Jamaica was visited by
a violent earthquake; the ground swelled and heaved like a rolling sea,
and was traversed by numerous cracks, two or three hundred of which were
often seen at a time, opening and then closing rapidly again. Many
people were swallowed up in these rents; some the earth caught by the
middle, and squeezed to death; the heads of others only appeared above
ground; and some were first engulfed, and then cast up again with great
quantities of water. Such was the devastation, that even in Port Royal,
then the capital, where more houses are said to have been left standing
than in the whole island besides, three-quarters of the buildings,
together with the ground they stood on, sank down with their inhabitants
entirely under water.

_Subsidence in the harbor._--The large storehouses on the harbor side
subsided, so as to be twenty-four, thirty-six, and forty-eight feet
under water; yet many of them appear to have remained standing, for it
is stated that, after the earthquake, the mast-heads of several ships
wrecked in the harbor, together with the chimney-tops of houses, were
just seen projecting above the waves. A tract of land round the town,
about a thousand acres in extent, sank down in less than one minute,
during the first shock, and the sea immediately rolled in. The Swan
frigate, which was repairing in the wharf, was driven over the tops of
many buildings, and then thrown upon one of the roofs, through which it
broke. The breadth of one of the streets is said to have been doubled by
the earthquake.

According to Sir H. De la Beche, the part of Port Royal described as
having sunk was built upon newly formed land, consisting of sand, in
which piles had been driven; and the _settlement_ of this loose sand,
charged with the weight of heavy houses, may, he suggests, have given
rise to the subsidence alluded to.[707]

There have undoubtedly been instances in Calabria and elsewhere of
slides of land on which the houses have still remained standing; and it
is possible that such may have been the case at Port Royal. The fact at
least of submergence is unquestionable, for I was informed by the late
Admiral Sir Charles Hamilton that he frequently saw the submerged houses
of Port Royal in the year 1780, in that part of the harbor which lies
between the town and the usual anchorage of men-of-war. Bryan Edwards
also says, in his history of the West Indies, that in 1793 the _ruins_
were visible in clear weather from the boats which sailed over
them.[708] Lastly, Lieutenant B. Jeffery, R. N., tells me that, being
engaged in a survey between the years 1824 and 1835, he repeatedly
visited the site in question, where the depth of the water is from four
to six fathoms, and whenever there was but little wind perceived
distinct traces of houses. He saw these more clearly when he used the
instrument called the "diver's eye," which is let down below the ripple
of the wave.[709]

At several thousand places in Jamaica the earth is related to have
opened. On the north of the island several plantations, with their
inhabitants, were swallowed up, and a lake appeared in their place,
covering above a thousand acres, which afterwards dried up, leaving
nothing but sand and gravel, without the least sign that there had ever
been a house or a tree there. Several tenements at Yallows were buried
under land-slips; and one plantation was removed half a mile from its
place, the crops continuing to grow upon it uninjured. Between Spanish
Town and Sixteen-mile Walk, the high and perpendicular cliffs bounding
the river fell in, stopped the passage of the river and flooded the
latter place for nine days, so that the people "concluded it had been
sunk as Port Royal was." But the flood at length subsided, for the river
had found some new passage at a great distance.

_Mountains shattered._--The Blue and other of the highest mountains are
declared to have been strangely torn and rent. They appeared shattered
and half-naked, no longer affording a fine green prospect, as before,
but stripped of their woods and natural verdure. The rivers on these
mountains first ceased to flow for about twenty-four hours, and then
brought down into the sea, at Port Royal and other places, several
hundred thousand tons of timber, which looked like floating islands on
the ocean. The trees were in general barked, most of their branches
having been torn off in the descent. It is particularly remarked in
this, as in the narratives of so many earthquakes, that fish were taken
in great numbers on the coast during the shocks. The correspondents of
Sir Hans Sloane, who collected with care the accounts of eye-witnesses
of the catastrophe, refer constantly to _subsidences_, and some supposed
the whole of Jamaica to have sunk down.[710]

_Reflections on the amount of change in the last one hundred and sixty
years._--I have now only enumerated some few of the earthquakes of the
last 160 years, respecting which facts illustrative of geological
inquiries are on record. Even if my limits permitted, it would be an
unprofitable task to examine all the obscure and ambiguous narratives
of similar events of earlier epochs; although, if the places were now
examined by geologists well practised in the art of interpreting the
monuments of physical changes, many events which have happened within
the historical era might doubtless be still determined with precision.
It must not be imagined that, in the above sketch of the occurrences of
a short period, I have given an account of all, or even the greater
part, of the mutations which the earth has undergone by the agency of
subterranean movements. Thus, for example, the earthquake of Aleppo, in
the present century, and of Syria, in the middle of the eighteenth,
would doubtless have afforded numerous phenomena, of great geological
importance, had those catastrophes been described by scientific
observers. The shocks in Syria in 1759, were protracted for three
months, throughout a space of ten thousand square leagues: an area
compared to which that of the Calabrian earthquake in 1783 was
insignificant. Accon, Saphat, Balbeck, Damascus, Sidon, Tripoli, and
many other places, were almost entirely levelled to the ground. Many
thousands of the inhabitants perished in each; and, in the valley of
Balbeck alone, 20,000 men are said to have been victims to the
convulsion. In the absence of scientific accounts, it would be as
irrelevant to our present purpose to enter into a detailed account of
such calamities, as to follow the track of an invading army, to
enumerate the cities burnt or rased to the ground, and reckon the number
of individuals who perished by famine or the sword.

_Deficiency of historical records._--If such, then, be the amount of
ascertained changes in the last 160 years, notwithstanding the extreme
deficiency of our records during that brief period, how important must
we presume the physical revolutions to have been in the course of thirty
or forty centuries, during which some countries habitually convulsed by
earthquakes have been peopled by civilized nations! Towns engulfed
during one earthquake may, by repeated shocks, have sunk to great depths
beneath the surface, while the ruins remain as imperishable as the
hardest rocks in which they are inclosed. Buildings and cities,
submerged, for a time, beneath seas or lakes, and covered with
sedimentary deposits, must, in some places, have been re-elevated to
considerable heights above the level of the ocean. The signs of these
events have, probably, been rendered visible by subsequent mutations, as
by the encroachments of the sea upon the coast, by deep excavations made
by torrents and rivers, by the opening of new ravines, and chasms, and
other effects of natural agents, so active in districts agitated by
subterranean movements.

If it be asked why, if such wonderful monuments exist, so few have
hitherto been brought to light, we reply--because they have not been
searched for. In order to rescue from oblivion the memorials of former
occurrences, the inquirer must know what he may reasonably expect to
discover, and under what peculiar local circumstances. He must be
acquainted with the action and effect of physical causes, in order to
recognize, explain, and describe correctly the phenomena when they
present themselves.

The best known of the great volcanic regions, of which the boundaries
were sketched in the twenty-second chapter, is that which includes
Southern Europe, Northern Africa, and Central Asia; yet nearly the
whole, even of this region, must be laid down, in a geological map, as
"Terra Incognita." Even Calabria may be regarded as unexplored, as also
Spain, Portugal, the Barbary States, the Ionian Isles, Asia Minor,
Cyprus, Syria, and the countries between the Caspian and Black seas. We
are, in truth, beginning to obtain some insight into one small spot of
that great zone of volcanic disturbance, the district around Naples; a
tract by no means remarkable for the violence of the earthquakes which
have convulsed it.

If, in this part of Campania, we are enabled to establish that
considerable changes in the relative level of land and sea have taken
place since the Christian era, it is all that we could have expected;
and it is to recent antiquarian and geological research, not to history,
that we are principally indebted for the information. I shall now
proceed to lay before the reader some of the results of modern
investigations in the Bay of Baiæ and the adjoining coast.


PROOFS OF ELEVATION AND SUBSIDENCE IN THE BAY OF BAIÆ.

[Illustration: Fig. 86.

Ground plan of the coast of the Bay of Baiæ, in the environs of
Puzzuoli.]

_Temple of Jupiter Serapis._--This celebrated monument of antiquity, a
representation of which is given in the frontispiece,[711] affords in
itself alone, unequivocal evidence that the relative level of land and
sea has changed twice at Puzzuoli since the Christian era; and each
movement, both of elevation and subsidence, has exceeded twenty feet.
Before examining these proofs, I may observe, that a geological
examination of the coast of Baiæ, both on the north and south of
Puzzuoli, establishes, in the most satisfactory manner, an elevation, at
no remote period, of more than twenty feet, and, at one point, of more
than thirty feet; and the evidence of this change would have been
complete, if even the temple had, to this day, remained undiscovered.

_Coast south of Puzzuoli._--If we coast along the shore from Naples to
Puzzuoli, we find, on approaching the latter place, that the lofty and
precipitous cliffs of indurated tuff, resembling that of which Naples is
built, retire slightly from the sea; and that a low level tract of
fertile land, of a very different aspect, intervenes between the present
sea-beach and what was evidently the ancient line of coast.

The inland cliff may be seen opposite the small island of Nisida, about
two miles and a half southeast of Puzzuoli (see Map, fig. 40, p. 361),
where, at the height of thirty-two feet above the level of the sea, Mr.
Babbage observed an ancient mark, such as might have been worn by the
waves; and, upon farther examination, discovered that, along that line,
the face of the perpendicular rock, consisting of very hard tuff, was
covered with barnacles (_Balanus sulcatus_, Lamk.), and drilled by
boring testacea. Some of the hollows of the lithodomi contained the
shells; while others were filled with the valves of a species of
Area.[712] Nearer to Puzzuoli, the inland cliff is eighty feet high, and
as perpendicular as if it was still undermined by the waves. At its
base, a new deposit, constituting the fertile tract above alluded to,
attains a height of about twenty feet above the sea; and, since it is
composed of regular sedimentary deposits, containing marine shells, its
position proves that, subsequently to its formation, there has been a
change of more than twenty feet in the relative level of land and sea.

[Illustration: Fig. 87.

_a_, Antiquities on hill S. E. of Puzzuoli (see ground plan, fig. 86).

_b_, Ancient cliff now inland.

_c_, Terrace composed of recent submarine deposit.]

The sea encroaches on these new incoherent strata; and as the soil is
valuable, a wall has been built for its protection; but when I visited
the spot in 1828, the waves had swept away part of this rampart, and
exposed to view a regular series of strata of tuff, more or less
argillaceous, alternating with beds of pumice and lapilli, and
containing great abundance of marine shells, of species now common on
this coast, and amongst them _Cardium rusticum_, _Ostrea edulis_, _Donax
trunculus_, Lamk., and others. The strata vary from about a foot to a
foot and a half in thickness, and one of them contains abundantly
remains of works of art, tiles, squares of mosaic pavement of different
colors, and small sculptured ornaments, perfectly uninjured.
Intermixed with these I collected some teeth of the pig and ox. These
fragments of building occur below as well as above strata containing
marine shells. Puzzuoli itself stands chiefly on a promontory of the
older tufaceous formation, which cuts off the new deposit, although I
detected a small patch of the latter in a garden under the town.

[Illustration: Fig. 88.

VIEW OF BAY OF BAIÆ.

  1. Puzzuoli. 2. Temple of Serapis. 3. Caligula's Bridge
  4. Monte Barbaro. 5. Monte Nuovo. 6. Baths of Nero. 7. Baiæ.
  8. Castle of Baiæ. 9. Bauli. 10. Cape Misenum. 11. Mount Epomeo in
  Ischia. 12. South Part of Ischia.

]

From the town the ruins of a mole, called Caligula's Bridge, run out
into the sea (see fig. 88, p. 509).[713] This mole, which is believed to
be eighteen centuries old, consists of a number of piers and arches,
thirteen of which are now standing, and two others appear to have been
overthrown. Mr. Babbage found, on the sixth pier, perforations of
lithodomi four feet above the level of the sea; and, near the
termination of the mole on the last pier but one, marks of the same, ten
feet above the level of the sea, together with great numbers of balani
and flustra. The depth of the sea, at a very small distance from most of
the piers, is from thirty to fifty feet.

[Illustration: Fig. 89.


  _a_, Remains of Cicero's villa, N. side of Puzzuoli.[714]
  _b_, Ancient cliff now inland.
  _c_, Terrace (called La Starza) composed of recent submarine deposits.
  _d_, Temple of Serapis.

]

_Coast north of Puzzuoli._--If we then pass to the north of Puzzuoli,
and examine the coast between that town and Monte Nuovo, we find a
repetition of analogous phenomena. The sloping sides of Monte Barbaro
slant down within a short distance of the coast, and terminate in an
inland cliff of moderate elevation, to which the geologist perceives at
once that the sea must, at some former period, have extended. Between
this cliff and the sea is a low plain or terrace, called La Starza (_c_,
fig. 89), corresponding to that before described on the southeast of the
town; and as the sea encroaches rapidly, fresh sections of the strata
may readily be obtained, of which the annexed is an example.

Section on the shore north of the town of Puzzuoli:--

                                                                  Ft. In.

  1. Vegetable soil                                                1   0

  2. Horizontal beds of pumice and scoriæ, with broken fragments
       of unrolled bricks, bones of animals, and marine shells     1   6

  3. Beds of lapilli, containing abundance of marine shells,
       principally _Cardium rusticum_, _Donax trunculus_, Lam.,
      _Ostrea edulis_, _Triton cutaceum_, Lam., and
      _Buccinum serratum_, Brocchi, the beds varying in
       thickness from one to eighteen inches                      10   0

  4. Argillaceous tuff, containing bricks and fragments
       of buildings not rounded by attrition.                      1   6


The thickness of many of these beds varies greatly as we trace them
along the shore, and sometimes the whole group rises to a greater height
than at the point above described. The surface of the tract which they
compose appears to slope gently upwards towards the base of the old
cliffs.

Now, if such appearances presented themselves on the coast of England, a
geologist might endeavor to seek an explanation in some local change in
the set of the tides and currents: but there are scarce any tides in the
Mediterranean; and, to suppose the sea to have sunk generally from
twenty to twenty-five feet since the shores of Campania were covered
with sumptuous buildings is an hypothesis obviously untenable. The
observations, indeed, made during modern surveys on the moles and
cothons (docks) constructed by the ancients in various ports of the
Mediterranean, have proved that there has been no sensible variation of
level in that sea during the last two thousand years.[715]

Thus we arrive, without the aid of the celebrated temple, at the
conclusion, that the recent marine deposit at Puzzuoli was upraised in
modern times above the level of the sea, and that not only this change
of position, but the accumulation of the modern strata, was posterior to
the destruction of many edifices, of which they contain the imbedded
remains. If we next examine the evidence afforded by the temple itself,
it appears, from the most authentic accounts, that the three pillars now
standing erect continued, down to the middle of the last century, almost
buried in the new marine strata (_c_, fig. 89). The upper part of each
protruding several feet above the surface was concealed by bushes, and
had not attracted, until the year 1749, the notice of antiquaries; but,
when the soil was removed in 1750, they were seen to form part of the
remains of a splendid edifice, the pavement of which was still
preserved, and upon it lay a number of columns of African breccia and of
granite. The original plan of the building could be traced distinctly:
it was of a quadrangular form, seventy feet in diameter, and the roof
had been supported by forty-six noble columns, twenty-four of granite
and the rest of marble. The large court was surrounded by apartments,
supposed to have been used as bathing-rooms; for a thermal spring, still
used for medicinal purposes, issues just behind the building, and the
water of this spring appears to have been originally conveyed by a
marble duct, still extant, into the chambers, and then across the
pavement by a groove an inch or two deep, to a conduit made of Roman
brickwork, by which it gained the sea.

Many antiquaries have entered into elaborate discussions as to the deity
to which this edifice was consecrated. It is admitted that, among other
images found in excavating the ruins, there was one of the god Serapis;
and at Puzzuoli a marble column was dug up, on which was carved an
ancient inscription, of the date of the building of Rome 648 (or B. C.
105), entitled "Lex parieti faciundo." This inscription, written in
very obscure Latin, sets forth a contract, between the municipality of
the town, and a company of builders who undertook to keep in repair
certain public edifices, the Temple of Serapis being mentioned amongst
the rest, and described as being near or towards the sea, "mare vorsum."
Sir Edmund Head, after studying, in 1828, the topography and antiquities
of this district, and the Greek, Roman, and Italian writers on the
subject, informed me, that at Alexandria, on the Nile, the chief seat of
the worship of Serapis, there was a Serapeum of the same form as this
temple at Puzzuoli, and surrounded in like manner by chambers, in which
the devotees were accustomed to pass the night, in the hope of receiving
during sleep a revelation from the god, as to the nature and cure of
their diseases. Hence it was very natural that the priests of Serapis, a
pantheistic divinity, who, among other usurpations, had appropriated to
himself the attributes of Esculapius, should regard the hot spring as a
suitable appendage to the temple, although the original Serapeum of
Alexandria could boast no such medicinal waters. Signor Carelli[716] and
others, in objecting to these views, have insisted on the fact, that the
worship of Serapis, which we know prevailed at Rome in the days of
Catullus (in the first century before Christ), was prohibited by the
Roman Senate, during the reign of the Emperor Tiberius. But there is
little doubt that, during the reigns of that emperor's successors, the
shrines of the Egyptian god were again thronged by zealous votaries; and
in no place more so than at Puteoli (now Puzzuoli), one of the principal
marts for the produce of Alexandria.

Without entering farther into an inquiry which is not strictly
geological, I shall designate this valuable relic of antiquity by its
generally received name, and proceed to consider the memorials of
physical changes inscribed on the three standing columns in most legible
characters by the hand of Nature. (See Frontispiece.) These pillars,
which have been carved each out of a single block of marble, are forty
feet three inches and a half in height. A horizontal fissure nearly
intersects one of the columns; the other two are entire. They are all
slightly out of the perpendicular, inclining somewhat to the southwest,
that is, towards the sea.[717] Their surface is smooth and uninjured to
the height of about twelve feet above their pedestals. Above this is a
zone, about nine feet in height, where the marble has been pierced by a
species of marine perforating bivalve--_Lithodomus_, Cuv.[718] The holes
of these animals are pear-shaped, the external opening being minute, and
gradually increasing downwards. At the bottom of the cavities, many
shells are still found, notwithstanding the great numbers that have been
taken out by visitors; in many the valves of a species of arca, an
animal which conceals itself in small hollows, occur. The perforations
are so considerable in depth and size, that they manifest a
long-continued abode of the lithodomi in the columns, for, as the
inhabitant grows older and increases in size, it bores a larger cavity,
to correspond with the increased magnitude of its shell. We must,
consequently, infer a long-continued immersion of the pillars in
sea-water, at a time when the lower part was covered up and protected by
marine, fresh-water, and volcanic strata, afterwards to be described,
and by the rubbish of buildings; the highest part, at the same time,
projecting above the waters, and being consequently weathered, but not
materially injured. (See fig. 90, p. 514.)

On the pavement of the temple lie some columns of marble, which are also
perforated in certain parts; one, for example, to the length of eight
feet, while, for the length of four feet, it is uninjured. Several of
these broken columns are eaten into, not only on the exterior, but on
the cross fracture, and, on some of them, other marine animals (serpulæ,
&c.) have fixed themselves.[719] All the granite pillars are untouched
by lithodomi. The platform of the temple, which is not perfectly even,
was, when I visited it in 1828, about one foot below high-water mark
(for there are small tides in the bay of Naples); and the sea, which was
only one hundred feet distant, soaked through the intervening soil. The
upper part of the perforations, therefore, were at least twenty-three
feet above high-water mark; and it is clear that the columns must have
continued for a long time in an erect position, immersed in salt water,
and then the submerged portion must have been upraised to the height of
about twenty-three feet above the level of the sea.

By excavations carried on in 1828, below the marble pavement on which
the columns stand, another costly pavement of mosaic was found, at the
depth of about five feet below the upper one (_a_, _b_, fig. 90). The
existence of these two pavements, at different levels, clearly implies
some subsidence previously to the building of the more modern temple
which had rendered it necessary to construct the new floor at a higher
level.

[Illustration: Fig. 90.

Temple of Serapis at its period of greatest depression.


  _a b_, Ancient mosaic pavement.
  _c c_, Dark marine incrustation.
  _d d_, First filling up, shower of ashes.
  _e e_, Freshwater calcareous deposit.
  _f f_, Second filling up.
  _A_, Stadium.

]

We have already seen (p. 512) that a temple of Serapis existed long
before the Christian era. The change of level just mentioned must have
taken place some time before the end of the second century, for
inscriptions have been found in the temple, from which we learn that
Septimius Severus adorned its walls with precious marbles, between the
years 194 and 211 of our era, and the emperor Alexander Severus
displayed the like munificence between the years 222 and 235.[720] From
that era there is an entire dearth of historical information for a
period of more than twelve centuries, except the significant fact that
Alaric and his Goths sacked Puzzuoli in 456, and that Genseric did the
like in 545, A. D. Yet we have fortunately a series of natural archives
self-registered during the dark ages, by which many events which
occurred in and about the temple are revealed to us. These natural
records consist partly of deposits, which envelop the pillars below the
zone of lithodomous perforations, and partly of those which surround the
outer walls of the temple. Mr. Babbage, after a minute examination of
these, has shown (see p. 507, note) that incrustations on the walls of
the exterior chambers and on the floor of the building demonstrate that
the pavement did not sink down suddenly, but was depressed by a gradual
movement. The sea first entered the court or atrium and mingled its
waters partially with those of the hot spring. From this brackish medium
a dark calcareous precipitate (_c c_, fig. 90) was thrown down, which
became, in the course of time, more than two feet thick, including some
serpulæ in it. The presence of these annelids teaches us that the water
was salt or brackish. After this period the temple was filled up with an
irregular mass of volcanic tuff (_d d_, fig. 90), probably derived from
an eruption of the neighboring crater of the Solfatara, to the height of
from five to nine feet above the pavement. Over this again a purely
freshwater deposit of carbonate of lime (_e e_, fig. 90) accumulated
with an _uneven_ bottom since it necessarily accommodated itself to the
irregular outline of the upper surface of the volcanic shower before
thrown down. The top of the same deposit (a freshwater limestone) was
perfectly even and flat, bespeaking an ancient water level. It is
suggested by Mr. Babbage that this freshwater lake may have been caused
by the fall of ashes which choked up the channel previously
communicating with the sea, so that the hot spring threw down calcareous
matter in the atrium, without any marine intermixture. To the freshwater
limestone succeeded another irregular mass of volcanic ashes and rubbish
(_f f_, fig. 90), some of it perhaps washed in by the waves of the sea
during a storm, its surface rising to ten or eleven feet above the
pavement. And thus we arrive at the period of greatest depression
expressed in the accompanying diagram, when the lower half of the
pillars were enveloped in the deposits above enumerated, and the
uppermost twenty feet were exposed in the atmosphere, the remaining or
middle portion, about nine feet long, being for years immersed in salt
water and drilled by perforating bivalves. After this period other
strata, consisting of showers of volcanic ashes and materials washed in
during storms, covered up the pillars to the height in some places of
thirty-five feet above the pavement. The exact time when these
enveloping masses were heaped up, and how much of them were formed
during submergence, and how much after the re-elevation of the temple,
cannot be made out with certainty.

The period of deep submergence was certainly antecedent to the close of
the fifteenth century. Professor James Forbes[721] has reminded us of a
passage in an old Italian writer Loffredo, who says that in 1530, or
fifty years before he wrote, which was in 1580, the sea washed the base
of the hills which rise from the flat land called La Starza, as
represented in fig. 90, so that, to quote his words, "a person might
then have fished from the site of those ruins which are now called the
stadium" (A, fig. 90).

But we know from other evidence that the upward movement had begun
before 1530, for the Canonico Andrea di Jorio cites two authentic
documents in illustration of this point. The first, dated Oct. 1503, is
a deed written in Italian, by which Ferdinand and Isabella grant to the
University of Puzzuoli a portion of land, "where the sea is drying up"
(che va seccando el mare); the second, a document in Latin, dated May
23, 1511, or nearly eight years after, by which Ferdinand grants to the
city a certain territory around Puzzuoli, where the ground _is dried up_
from the sea (desiccatum).[722]

The principal elevation, however, of the low tract unquestionably took
place at the time of the great eruption of Monte Nuovo in 1538. That
event and the earthquakes which preceded it have been already described
(p. 368); and we have seen that two of the eye-witnesses of the
convulsion, Falconi and Giacomo di Toledo, agree in declaring that the
sea abandoned a considerable tract of the shore, so that fish were taken
by the inhabitants; and, among other things, Falconi mentions that he
saw two springs _in the newly discovered ruins_.

The flat land, when first upraised, must have been more extensive than
now, for the sea encroaches somewhat rapidly, both to the north and
southeast of Puzzuoli. The coast had, when I examined it in 1828, given
way more than a foot in a twelvemonth; and I was assured, by fishermen
in the bay, that it has lost ground near Puzzuoli, to the extent of
thirty feet, within their memory.

It is, moreover, very probable that the land rose to a greater height at
first before it ceased to move upwards, than the level at which it was
observed to stand when the temple was rediscovered in 1749, for we learn
from a memoir, of Niccolini, published in 1838, that since the beginning
of the nineteenth century, the temple of Serapis has subsided more than
two feet. That learned architect visited the ruins frequently, for the
sake of making drawings, in the beginning of the year 1807, and was in
the habit of remaining there throughout the day, yet never saw the
pavement overflowed by the sea, except occasionally when the south wind
blew violently. On his return, sixteen years after, to superintend some
excavations ordered by the king of Naples, he found the pavement covered
by sea-water twice every day at high tide, so that he was obliged to
place there a line of stones to stand upon. This induced him to make a
series of observations from Oct. 1822 to July 1838, by which means he
ascertained that the ground had been and was sinking, at the average
rate of about seven millimetres a year, or about one inch in four years;
so that, in 1838, fish were caught every day on that part of the
pavement where, in 1807, there was never a drop of water in calm
weather.[723]

On inquiring still more recently as to the condition of the temple and
the continuance of the sinking of the ground, I learn from Signor
Scacchi in a letter, dated June 1852, that the downward movement has
ceased for several years, or has at least become almost inappreciable.
During an examination undertaken by him at my request in the summer of
that year (1852), he observed that the rising tide spread first over the
seaward side of the flat surface of the pedestals of each column
(confirming the fact previously noticed by others, that they are out of
the perpendicular); and he also remarked that the water gained unequally
on the base of each pillar, in such a manner as to prove that they have
neither the same amount of inclination, nor lean precisely in the same
direction.

From what was said before (p. 510), we saw that the marine shells in the
strata forming the plain called La Starza, considered separately,
establish the fact of an upheaval of the ground to the height of
twenty-three feet and upwards. The temple proves much more, because it
could not have been built originally under water, and must therefore
first have sunk down twenty feet at least below the waves, to be
afterwards restored to its original position. Yet if such was the order
of events we ought to meet with other independent signs of a like
subsidence round the margin of a bay once so studded with buildings as
the Bay of Baiæ. Accordingly memorials of such submergence are not
wanting. About a mile northwest of the temple of Serapis, and about 500
feet from the shore, are the ruins of a temple of Neptune and others of
a temple of the Nymphs, now underwater. The columns of the former
edifice stand erect in five feet of water, their upper portions just
rising to the surface of the sea. The pedestals are doubtless buried in
the sand or mud; so that, if this part of the bottom of the bay should
hereafter be elevated, the exhumation of these temples might take place
after the manner of that of Serapis. Both these buildings probably
participated in the movement which raised the Starza; but either they
were deeper under water than the temple of Serapis, or they were not
raised up again to so great a height. There are also two Roman roads
under water in the bay, one reaching from Puzzuoli to the Lucrine Lake,
which may still be seen, and the other near the castle of Baiæ (No. 8,
fig. 88, p. 509). The ancient mole, too, of Puzzuoli (No. 4, ibid.)
before alluded to, has the water up to a considerable height of the
arches; whereas Brieslak justly observes, it is next to certain that the
piers must formerly have reached the surface before the springing of the
arches;[724] so that, although the phenomena before described prove that
this mole has been uplifted ten feet above the level at which it once
stood, it is still evident that it has not yet been restored to its
original position.

A modern writer also reminds us, that these effects are not so local as
some would have us to believe; for on the opposite side of the Bay of
Naples, on the Sorrentine coast, which, as well as Puzzuoli, is subject
to earthquakes, a road, with some fragments of Roman buildings, is
covered to some depth by the sea. In the island of Capri, also, which is
situated some way out at sea, in the opening of the Bay of Naples, one
of the palaces of Tiberius is now covered with water.[725]

That buildings should have been submerged, and afterwards upheaved,
without being entirely reduced to a heap of ruins, will appear no
anomaly, when we recollect that, in the year 1819, when the delta of the
Indus sank down, the houses within the fort of Sindree subsided beneath
the waves without being overthrown. In like manner, in the year 1692,
the buildings round the harbor of Port Royal, in Jamaica, descended
suddenly to the depth of between thirty and fifty feet under the sea
without falling. Even on small portions of land transported to a
distance of a mile down a declivity, tenements, like those near Mileto,
in Calabria, were carried entire. At Valparaiso buildings were left
standing in 1822, when their foundations, together with a long tract of
the Chilian coast, were permanently upraised to the height of several
feet. It is still more easy to conceive that an edifice may escape
falling during the upheaval or subsidence of land, if the walls are
supported on the exterior and interior with a deposit like that which
surrounded and filled to the height of ten or eleven feet the temple of
Serapis all the time it was sinking, and which enveloped it to more than
twice that height when it was rising again to its original level.

We can scarcely avoid the conclusion, as Mr. Babbage has hinted, "that
the action of heat is in some way or other the cause of the phenomena of
the change of level of the temple. Its own hot spring, its immediate
contiguity to the Solfatara, its nearness to the Monte Nuovo, the hot
spring at the baths of Nero (No. 6, fig. 88), on the opposite side of
the Bay of Baiæ; the boiling springs and ancient volcanoes of Ischia on
one side and Vesuvius on the other, are the most prominent of a
multitude of facts which point to that conclusion."[726] And when we
reflect on the dates of the principal oscillations of level, and the
volcanic history of the country before described (chap. 23), we seem to
discover a connection between each era of upheaval and a local
development of volcanic heat, and again between each era of depression
and the local quiescence or dormant condition of the subterranean
igneous causes. Thus for example, before the Christian era, when so many
vents were in frequent eruption in Ischia, and when Avernus and other
points in the Phlegræan Fields were celebrated for their volcanic aspect
and character, the ground on which the temple stood was several feet
above water. Vesuvius was then regarded as a spent volcano; but when,
after the Christian era, the fires of that mountain were rekindled,
scarcely a single outburst was ever witnessed in Ischia, or around the
Bay of Baiæ. Then the temple was sinking. Vesuvius, at a subsequent
period, became nearly dormant for five centuries preceding the great
outbreak of 1631 (see p. 374), and in that interval the Solfatara was in
eruption A. D. 1198, Ischia in 1302, and Monte Nuovo was formed in 1538.
Then the foundations on which the temple stood were rising again.
Lastly, Vesuvius once more became a most active vent, and has been so
ever since, and during the same lapse of time the area of the temple, so
far as we know any thing of its history, has been subsiding.

These phenomena would agree well with the hypothesis, that when the
subterranean heat is on the increase, and when lava is forming without
obtaining an easy vent, like that afforded by a great habitual chimney,
such as Vesuvius, the incumbent surface is uplifted; but when the heated
rocks below are cooling and contracting, and sheets of lava are slowly
consolidating and diminishing in volume, then the incumbent land
subsides.

Signor Niccolini, when he ascertained in 1838 that the relative levels
of the floor of the temple and of the sea were slowly changing from year
to year, embraced the opinion that it was the sea which was rising. But
Signor Capocci successfully controverted this view, appealing to many
appearances which attest the local character of the movements of the
adjoining country, besides the historical fact that in 1538, when the
sea retired permanently 200 yards from the ancient shore at Puzzuoli,
there was no simultaneous retreat of the waters from Naples,
Castelamare, and Ischia.[727]

_Permanence of the ocean's level._--In concluding this subject I may
observe, that the interminable controversies to which the phenomena of
the Bay of Baiæ gave rise, have sprung from an extreme reluctance to
admit that the land, rather than the sea, is subject alternately to rise
and fall. Had it been assumed that the level of the ocean was
invariable, on the ground that no fluctuations have as yet been clearly
established, and that, on the other hand, the continents are inconstant
in their level, as has been demonstrated by the most unequivocal proofs
again and again, from the time of Strabo to our own times, the
appearances of the temple at Puzzuoli could never have been regarded as
enigmatical. Even if contemporary accounts had not distinctly attested
the upraising of the coast, this explanation should have been proposed
in the first instance as the most natural, instead of being now adopted
unwillingly when all others have failed.

To the strong prejudices still existing in regard to the mobility of the
land, we may attribute the rarity of such discoveries as have been
recently brought to light in the Bay of Baiæ and the Bay of Conception.
A false theory, it is well known, may render us blind to facts which are
opposed to our prepossessions, or may conceal from us their true import
when we behold them. But it is time that the geologist should, in some
degree, overcome those first and natural impressions, which induced the
poets of old to select the rock as the emblem of firmness--the sea as
the image of inconstancy. Our modern poet, in a more philosophical
spirit, saw in the sea "The image of eternity," and has finely
contrasted the fleeting existence of the successive empires which have
flourished and fallen on the borders of the ocean with its own unchanged
stability.


                         ------Their decay
    Has dried up realms to deserts:--not so thou,
    Unchangeable, save to thy wild wave's play:
    Time writes no wrinkle on thine azure brow;
  Such as creation's dawn beheld, thou rollest now.

  CHILDE HAROLD, Canto iv.




CHAPTER XXX.

ELEVATION AND SUBSIDENCE OF LAND WITHOUT EARTHQUAKES.


  Changes in the relative level of land and sea in regions not
    volcanic--Opinion of Celsius that the waters of the Baltic Sea and
    Northern Ocean were sinking--Objections raised to his
    opinion--Proofs of the stability of the sea level in the
    Baltic--Playfair's hypothesis that the land was rising in
    Sweden--Opinion of Von Buch--Marks cut on the rocks--Survey of these
    in 1820--Facility of detecting slight alterations of level on coast
    of Sweden--Shores of the ocean also rising--Area upheaved--Shelly
    deposits of Uddevalla--Of Stockholm, containing fossil shells
    characteristic of the Baltic--Subsidence in south of Sweden--Fishing
    hut buried under marine strata--Upheaval in Sweden not always in
    horizontal planes--Sinking of land in Greenland--Bearing of these
    facts on geology.


We have now considered the phenomena of volcanoes and earthquakes
according to the division of the subject before proposed (p. 345), and
have next to turn our attention to those slow and insensible changes in
the relative level of land and sea which take place in countries remote
from volcanoes, and where no violent earthquakes have occurred within
the period of human observation. Early in the last century the Swedish
naturalist, Celsius, expressed his opinion that the waters, both of the
Baltic and Northern Ocean, were gradually subsiding. From numerous
observations, he inferred that the rate of depression was about fifty
Swedish inches in a century.[728] In support of this position, he
alleged that there were many rocks both on the shores of the Baltic and
the ocean known to have been once sunken reefs, and dangerous to
navigators, but which were in his time above water--that the waters of
the Gulf of Bothnia had been gradually converted into land, several
ancient ports having been changed into inland cities, small islands
joined to the continent, and old fishing-grounds deserted as being too
shallow, or entirely dried up. Celsius also maintained, that the
evidence of the change rested not only on modern observations, but on
the authority of the ancient geographers, who had stated that
Scandinavia was formerly an island. This island, he argued, must in the
course of centuries, by the gradual retreat of the sea, have become
connected with the continent; an event which he supposed to have
happened after the time of Pliny, and before the ninth century of our
era.

To this argument it was objected that the ancients were so ignorant of
the geography of the most northern parts of Europe, that their authority
was entitled to no weight; and that their representation of Scandinavia
as an island, might with more propriety be adduced to prove the
scantiness of their information, than to confirm so bold an hypothesis.
It was also remarked that if the land which connected Scandinavia with
the main continent was laid dry between the time of Pliny and the ninth
century, to the extent to which it is known to have risen above the sea
at the latter period, the rate of depression could not have been
uniform, as was pretended; for it ought to have fallen much more rapidly
between the ninth and eighteenth centuries.

Many of the proofs relied on by Celsius and his followers were
immediately controverted by several philosophers, who saw clearly that a
fall of the sea in any one region could not take place without a general
sinking of the waters over the whole globe: they denied that this was
the fact, or that the depression was universal, even in the Baltic. In
proof of the stability of the level of that sea, they appealed to the
position of the island of Saltholm, not far from Copenhagen. This island
is so low, that in autumn and winter it is permanently overflowed; and
it is only dry in summer, when it serves for pasturing cattle. It
appears, from the documents of the year 1280, that Saltholm was then
also in the same state, and exactly on a level with the mean height of
the sea, instead of having been about twenty feet under water, as it
ought to have been, according to the computation of Celsius. Several
towns, also, on the shores of the Baltic, as Lubeck, Wismar, Rostock,
Stralsund, and others, after six and even eight hundred years, are as
little elevated above the sea as at the era of their foundation, being
now close to the water's edge. The lowest part of Dantzic was no higher
than the mean level of the sea in the year 1000; and after eight
centuries its relative position remains exactly the same.[729]

Several of the examples of the gain of land and shallowing of the sea
pointed out by Celsius, and afterwards by Linnæus, who embraced the same
opinions, were ascribed by others to the deposition of sediment at
points where rivers entered; and, undoubtedly, Celsius had not
sufficiently distinguished between changes due to these causes and such
as would arise if the waters of the ocean itself were diminishing. Many
large rivers descending from a mountainous country, at the head of the
Gulf of Bothnia, enter the sea charged with sand, mud, and pebbles; and
it was said that in these places the low land had advanced rapidly,
especially near Torneo. At Piteo also, half a mile had been gained in
forty-five years; at Luleo,[730] no less than a mile in twenty-eight
years; facts which might all be admitted consistently with the
assumption that the level of the Baltic has remained unchanged, like
that of the Adriatic, during a period when the plains of the Po and the
Adige have greatly extended their area.

It was also alleged that certain insular rocks, once entirely covered
with water, had at length protruded themselves above the waves, and
grown, in the course of a century and a half, to be eight feet high. The
following attempt was made to explain away this phenomenon:--In the
Baltic, large erratic blocks, as well as sand and smaller stones which
lie on shoals, are liable every year to be frozen into the ice, where
the sea freezes to the depth of five or six feet. On the melting of the
snow in spring, when the sea rises about half a fathom, numerous
ice-islands float away, bearing up these rocky fragments so as to convey
them to a distance; and if they are driven by the waves upon shoals,
they may convert them into islands by depositing the blocks; if stranded
upon low islands, they may considerably augment their height.

Browallius, also, and some other Swedish naturalists, affirmed that some
islands were lower than formerly; and that, by reference to this kind of
evidence, there was equally good reason for contending that the level of
the Baltic was gradually rising. They also added another curious proof
of the permanency of the water level, at some points at least, for many
centuries. On the Finland coast were some large pines, growing close to
the water's edge; these were cut down, and, by counting the concentric
rings of annual growth, as seen in a transverse section of the trunk, it
was demonstrated that they had stood there for four hundred years. Now,
according to the Celsian hypothesis, the sea had sunk about fifteen feet
during that period, in which case the germination and early growth of
these pines must have been, for many seasons, below the level of the
water. In like manner it was asserted, that the lower walls of many
ancient castles, such as those of Sonderburg and Åbo, reached then to
the water's edge, and must, therefore, according to the theory of
Celsius, have been originally constructed below the level of the sea.

[Illustration: Fig. 91.]

In reply to this last argument, Colonel Hällstrom, a Swedish engineer,
well acquainted with the Finland coast, assured me, that the base of the
walls of the castle of Åbo is now ten feet above the water, so that
there may have been a considerable rise of the land at that point since
the building was erected.

Playfair, in his "Illustrations of the Huttonian Theory," in 1802,
admitted the sufficiency of the proofs adduced by Celsius, but
attributed the change of level to the movement of the land, rather than
to a diminution of the waters. He observed, "that in order to depress or
elevate the absolute level of the sea, by a given quantity, in any one
place, we must depress or elevate it by the same quantity over the whole
surface of the earth; whereas no such necessity exists with respect to
the elevation or depression of the land."[731] The hypothesis of the
rising of the land he adds, "agrees well with the Huttonian theory,
which holds, that our continents are subject to be acted upon by the
expansive forces of the mineral regions; that by these forces they have
been actually raised up, and are sustained by them in their present
situation.[732]

In the year 1807, Von Buch, after returning from a tour in Scandinavia,
announced his conviction, "that the whole country, from Frederickshall
in Norway to Åbo in Finland, and perhaps as far as St. Petersburg, was
slowly and insensibly rising." He also suggested "that Sweden may rise
more than Norway, and the northern more than the southern part."[733] He
was led to these conclusions principally by information obtained from
the inhabitants and pilots, and in part by the occurrence of marine
shells of recent species, which he had found at several points on the
coast of Norway above the level of the sea. He also mentions the marks
set on the rocks. Von Buch, therefore, has the merit of being the first
geologist who, after a personal examination of the evidence, declared in
favor of the rise of land in Scandinavia.

The attention excited by this subject in the early part of the last
century, induced many philosophers in Sweden to endeavor to determine,
by accurate observations, whether the standard level of the Baltic was
really subject to periodical variations; and under their direction,
lines or grooves, indicating the ordinary level of the water on a calm
day, together with the date of the year, were chiselled out upon the
rocks. In 1820-21, all the marks made before those years were examined
by the officers of the pilotage establishment of Sweden; and in their
report to the Royal Academy of Stockholm they declared, that on
comparing the level of the sea at the time of their observations with
that indicated by the ancient marks, they found that the Baltic was
lower relatively to the land in certain places, but the amount of change
during equal periods of time had not been everywhere the same. During
their survey, they cut new marks for the guidance of future observers,
several of which I had an opportunity of examining fourteen years after
(in the summer of 1834), and in that interval the land appeared to me to
have risen at certain places north of Stockholm four or five inches. I
also convinced myself, during my visit to Sweden, after conversing with
many civil engineers, pilots, and fishermen, and after examining some
of the ancient marks, that the evidence formerly adduced in favor of the
change of level, both on the coasts of Sweden and Finland, was full and
satisfactory.[734] The alteration of level evidently diminishes as we
proceed from the northern parts of the Gulf of Bothnia towards the
south, being very slight around Stockholm. Some writers have indeed
represented the rate of depression of the waters at Stockholm as very
considerable, because certain houses in that city which are built on
piles have sunk down within the memory of persons still living, so as to
be out of the perpendicular; and this in consequence of the tops of the
piles giving way and decaying, owing to a fall of the waters which has
exposed them to be alternately wet and dry. The houses alluded to are
situated on the borders of Lake Maeler, a large lake, the outlet of
which joins the Baltic, in the middle of Stockholm. This lake is
certainly lower than formerly; but the principal cause of the change is
not the elevation of the land, but the removal of two old bridges built
on piles, which formerly obstructed the discharge of the fresh water
into the sea. Another cause is the opening, in the year 1819, of a new
canal at Södertelje, a place south of Stockholm, by means of which a new
line of communication was formed between Lake Maeler and the
Baltic.[735]

It will naturally be asked, whether the mean level of a sea like the
Baltic can ever be determined so exactly as to permit us to appreciate a
variation of level, amounting only to one or two feet. In reply, I may
observe, that, except near the Cattegat, there are no tides in the
Baltic; and it is only when particular winds have prevailed for several
days in succession, or at certain seasons when there has been an
unusually abundant influx of river water, or when these causes have
combined, that this sea is made to rise two or three feet above its
standard level. The fluctuations due to these causes are nearly the same
from year to year; so that the pilots and fishermen believe and
apparently with reason, that they can mark a deviation, even of a few
inches, from the ordinary or mean height of the waters.

There are, moreover, peculiarities in the configuration of the shores of
Norway and Sweden, which facilitate in a remarkable degree the
appreciation of slight changes in the relative level of land and water.
It has often been said, that there are two coasts, an inner and an outer
one; the inner being the shore of the main land; the outer one, a fringe
of countless rocky islands of all dimensions, called the skär (_shair_).
Boats and small vessels make their coasting voyages within this skär:
for here they may sail in smooth water, even when the sea without is
strongly agitated. But the navigation is very intricate, and the pilot
must possess a perfect acquaintance with the breadth and depth of every
narrow channel, and the position of innumerable sunken rocks. If on such
a coast the land rises one or two feet in the course of half a century,
the minute topography of the skär is entirely altered. To a stranger,
indeed, who revisits it after an interval of many years, its general
aspect remains the same; but the inhabitant finds that he can no longer
penetrate with his boat through channels where he formerly passed, and
he can tell of countless other changes in the height and breadth of
isolated rocks, now exposed, but once only seen through the clear water.

The rocks of gneiss, mica-schist, and quartz are usually very hard on
this coast, slow to decompose, and, when protected from the breakers,
remaining for ages unaltered in their form. Hence it is easy to mark the
stages of their progressive emergence by the aid of natural and
artificial marks imprinted on them. Besides the summits of _fixed_
rocks, there are numerous erratic blocks of vast size strewed over the
shoals and islands in the skär, which have been probably drifted by ice
in the manner before suggested.[736] All these are observed to have
increased in height and dimension with the last half century. Some,
which were formerly known as dangerous sunken rocks, are now only hidden
when the water is highest. On their first appearance, they usually
present a smooth, bare, rounded protuberance, a few feet or yards in
diameter; and a single sea-gull often appropriates to itself this
resting-place, resorting there to devour its prey. Similar points, in
the mean time, have grown to long reefs, and are constantly whitened by
a multitude of sea-fowl; while others have been changed from a reef,
annually submerged, to a small islet, on which a few lichens, a
fir-seedling, and a few blades of grass, attest that the shoal has at
length been fairly changed into dry land. Thousands of wooded islands
around show the great alterations which time can work. In the course of
centuries also, the spaces intervening between the existing islands may
be laid dry, and become grassy plains encircled by heights well clothed
with lofty firs. This last step of the process, by which long fiords and
narrow channels, once separating wooded islands, are deserted by the
sea, has been exemplified within the memory of living witnesses on
several parts of the coast.

Had the apparent fall of the waters been observed in the Baltic only, we
might have endeavored to explain the phenomenon by local causes
affecting that sea alone. For instance, the channel by which the Baltic
discharges its surplus waters into the Atlantic, might be supposed to
have been gradually widened and deepened by the waves and currents, in
which case a fall of the water like that before alluded to in Lake
Maeler, might have occurred. But the lowering of level would in that
case have been uniform and universal, and the waters could not have sunk
at Torneo, while they retained their former level at Copenhagen. Such an
explanation is also untenable on other grounds; for it is a fact, as
Celsius long ago affirmed, that the alteration of level extends to the
western shores of Sweden, bordering the ocean. The signs of elevation
observed between Uddevalla and Gothenburg are as well established as
those on the shores of the Bothnian Gulf. Among the places where they
may be studied, are the islands of Marstrand and Gulholmen, the
last-mentioned locality being one of those particularly pointed out by
Celsius.

The inhabitants there and elsewhere affirm, that the rate of the sinking
of the sea (or elevation of land) varies in different and adjoining
districts, being greatest at points where the land is low. But in this
they are deceived; for they measure the amount of rise by the area
gained, which is most considerable where the land descends with a gentle
slope into the sea. In the same manner, some advocates of the Celsian
theory formerly appealed to the increase of lands near the mouths of
rivers, not sufficiently adverting to the fact, that if the bed of the
sea is rising, the change will always be most sensible where the bottom
has been previously rendered shallow; whereas, at a distance from these
points where the scarped granitic cliffs plunge at once into deep water,
a much greater amount of elevation is necessary to produce an equally
conspicuous change.

As to the area in northern Europe which is subject to this slow
upheaving movement, we have not as yet sufficient data for estimating it
correctly. It seems probable, however, that it reaches from Gothenburg
to Torneo, and from thence to the North Cape, the rate of elevation
increasing always as we proceed farther northwards. The two extremities
of this line are more than a thousand geographical miles distant from
each other; and as both terminate in the ocean, we know not how much
farther the motion may be prolonged under water. As to the breadth of
the tract, its limits are equally uncertain, though it evidently extends
across the widest parts of the Gulf of Bothnia, and may probably stretch
far into the interior, both of Sweden and Finland. Now if the elevation
continue, a larger part of the Gulf of Bothnia will be turned into land,
as also more of the ocean off the west coast of Sweden between
Gothenburg and Uddevalla; and on the other hand, if the change has been
going on for thousands of years at the rate of several feet in a
century, large tracts of what is now land must have been submarine at
periods comparatively modern. It is natural therefore to inquire whether
there are any signs of the recent sojourn of the sea on districts now
inland? The answer is most satisfactory.--Near Uddevalla and the
neighboring coastland, we find upraised deposits of shells belonging to
species such as now live in the ocean; while on the opposite or eastern
side of Sweden, near Stockholm, Gefle, and other places bordering the
Bothnian Gulf, there are analogous beds containing shells of species
characteristic of the Baltic.

Von Buch announced in 1807, that he had discovered in Norway and at
Uddevalla in Sweden, beds of shells of existing species, at considerable
heights above the sea. Since that time, other naturalists have
confirmed his observation; and, according to Ström, deposits occur at
an elevation of more than 400 feet above the sea in the northern part of
Norway. M. Alex. Brongniart, when he visited Uddevalla, ascertained that
one of the principal masses of shells, that of Capellbacken, is raised
more than 200 feet above the sea, resting on rocks of gneiss, all the
species being identical with those now inhabiting the contiguous ocean.
The same naturalist also stated, that on examining with care the surface
of the gneiss, immediately above the ancient shelly deposit, he found
barnacles (_balani_) adhering to the rocks, showing that the sea had
remained there for a long time. I was fortunate enough to be able to
verify this observation by finding in the summer of 1834, at Kured,
about two miles north of Uddevalla, and at the height of more than 100
feet above the sea, a surface of gneiss newly laid open by the partial
removal of a mass of shells used largely in the district for making lime
and repairing the roads. So firmly did these barnacles adhere to the
gneiss, that I broke off portions of the rock with the shells attached.
The face of the gneiss was also incrusted with small zoophytes
(_Cellepora?_ Lam.); but had these or the barnacles been exposed in the
atmosphere ever since the elevation of the rocks above the sea, they
would doubtless have decomposed and been obliterated.

The town of Uddevalla (see Map, p. 523) stands at the head of a narrow
creek overhung by steep and barren rocks of gneiss, of which all the
adjacent country is composed, except in the low grounds and bottoms of
valleys, where strata of sand, clay, and marl frequently hide the
fundamental rocks. To these newer and horizontal deposits the fossil
shells above mentioned belong, and similar marine remains are found at
various heights above the sea on the opposite island of Orust. The
extreme distance from the sea to which such fossils extend is as yet
unknown; but they have been already found at Trollhättan in digging the
canal there, and still farther inland on the northern borders of Lake
Wener, fifty miles from the sea, at an elevation of 200 feet near Lake
Rogvarpen.

To pass to the Baltic: I observed near its shores at Södertelje, sixteen
miles S. W. of Stockholm, strata of sand, clay, and marl, more than 100
feet high, and containing shells of species now inhabiting the Bothnian
Gulf. These consist partly of marine and partly of freshwater species;
but they are few in number, the brackishness of the water appearing to
be very unfavorable to the development of testacea. The most abundant
species are the common cockle and the common mussel and periwinkle of
our shores (_Cardium edule_, _Mytilus edulis_, and _Littorina
littorea_), together with a small tellina (_T. Baltica_) and a few
minute univalves allied to _Paludina ulva_. These live in the same water
as a _Lymneus_, a Neritina (_N. fluviatilis_), and some other
fresh-water shells.

But the marine mollusks of the Baltic above mentioned, although very
numerous in individuals, are dwarfish in size, scarcely ever attaining a
third of the average dimensions which they acquire in the salter waters
of the ocean. By this character alone a geologist would generally be
able to recognize an assemblage of Baltic fossils as distinguished from
those derived from a deposit in the ocean. The absence also of oysters,
barnacles, whelks, scallops, limpets (_ostrea_, _balanus_, _buccinum_,
_pecten_, _patella_), and many other forms abounding alike in the sea
near Uddevalla, and in the fossiliferous deposits of modern date on that
coast, supplies an additional negative character of the greatest value,
distinguishing assemblages of Baltic from those of oceanic shells. Now
the strata containing Baltic shells are found in many localities near
Stockholm, Upsala, and Gefle, and will probably be discovered everywhere
around the borders of the Bothnian Gulf; for I have seen similar remains
brought from Finland, in marl resembling that found near Stockholm. The
utmost distance to which these deposits have yet been traced inland, is
on the southern shores of Lake Maeler, at a place seventy miles from the
sea.[737] Hence it appears from the distinct assemblage of fossil shells
found on the eastern and western coasts of Sweden, that the Baltic has
been for a long period separated as now from the ocean, although the
intervening tract of land was once much narrower, even after both seas
had become inhabited by all the existing species of testacea.

As no accurate observations on the rise of the Swedish coast refer to
periods more remote than a century and a half from the present time, and
as traditional information, and that derived from ancient buildings on
the coast, do not enable the antiquary to trace back any monuments of
change for more than five or six centuries, we cannot declare whether
the rate of the upheaving force is uniform during very long periods. In
those districts where the fossil shells are found at the height of more
than 200 feet above the ocean, as at Uddevalla, Orust, and Lake
Rogvarpen, the present rate of rise seems less than four feet in a
century. Even at that rate it would have required five thousand years to
lift up those deposits. But as the movement is now very different in
different places, it may also have varied much in intensity at different
eras.

We have, moreover, yet to learn not only whether the motion proceeds
always at the same rate, but also whether it has been uniformly _in one
direction_. The level of the land may oscillate; and for centuries there
may be a depression, and afterwards a re-elevation, of the same
district. Some phenomena in the neighborhood of Stockholm appear to me
only explicable on the supposition of the alternate rising and sinking
of the ground since the country was inhabited by man. In digging a
canal, in 1819, at Södertelje, about sixteen miles to the south of
Stockholm, to unite Lake Maeler with the Baltic, marine strata,
containing fossil shells of Baltic species, were passed through. At a
depth of about sixty feet, they came down upon what seems to have been a
buried fishing-hut, constructed of wood in a state of decomposition,
which soon crumbled away on exposure to the air. The lowest part,
however, which had stood on a level with the sea, was in a more perfect
state of preservation. On the floor of this hut was a rude fireplace,
consisting of a ring of stones, and within this were cinders and charred
wood. On the outside lay boughs of the fir, cut as with an axe, with the
leaves or needles still attached. It seems very difficult to explain the
position of this buried hut, without imagining, as in the case of the
temple of Serapis (see p. 486), first a subsidence to the depth of more
than sixty feet, then a re-elevation. During the period of submergence,
the hut must have become covered over with gravel and shelly marl, under
which not only the hut, but several vessels also were found, of a very
antique form, and having their timbers fastened together by wooden pegs
instead of nails.[738]

Whether any of the land in Norway is now rising, must be determined by
future investigations. Marine fossil shells, of recent species, have
been collected from inland places near Drontheim; but Mr. Everest, in
his "Travels through Norway," informs us that the small island of
Munkholm, which is an insulated rock in the harbor of Drontheim, affords
conclusive evidence of the land having in that region remained
stationary for the last eight centuries. The area of this isle does not
exceed that of a small village, and by an official survey, its highest
point has been determined to be twenty-three feet above the mean
high-water mark, that is, the mean between neap and spring tides. Now,
a monastery was founded there by Canute the Great, A. D. 1028, and
thirty-three years before that time it was in use as a common place of
execution. According to the assumed average rate of rise in Sweden
(about forty inches in a century), we should be obliged to suppose that
this island had been three feet eight inches below high-water mark when
it was originally chosen as the site of the monastery.

Professor Keilhau of Christiania, after collecting the observations of
his predecessors respecting former changes of level in Norway, and
combining them with his own, has made the fact of a general change of
level at a modern period, that is to say, within the period of the
actual testaceous fauna, very evident. He infers that the whole country
from Cape Lindesnæs to Cape North, and beyond that as far as the
fortress of Vardhuus, has been gradually upraised, and on the southeast
coast the elevation has amounted to more than 600 feet. The marks which
denote the ancient coast-line are so nearly horizontal that the
deviation from horizontality, although the measurements have been made
at a great number of points, is too small to be appreciated.

More recently (1844), however, it appears from the researches of M.
Bravais, member of the French scientific commission of the North, that
in the Gulf of Alten in Finmark, the most northerly part of Norway,
there are two distinct lines of upraised ancient sea-coast, one above
the other, which are not parallel, and both of them imply that within a
distance of fifty miles a considerable slope can be detected in such a
direction as to show that the ancient shores have undergone a greater
amount of upheaval in proportion as we advance inland.[739]

It has been already stated, that, in proceeding from the North Cape to
Stockholm, the rate of upheaval diminishes from several feet to a few
inches in a century. To the south of Stockholm, the upward movement
ceases, and at length in Scania, or the southernmost part of Sweden, it
appears to give place to a movement in an opposite direction. In proof
of this fact, Professor Nilsson observes, in the first place, that there
are no elevated beds of recent marine shells in Scania like those
farther to the north. Secondly, Linnæus, with a view of ascertaining
whether the waters of the Baltic were retiring from the Scanian shore,
measured, in 1749, the distance between the sea and a large stone near
Trelleborg. This same stone was, in 1836, a hundred feet nearer the
water's edge than in Linnæus's time, or eighty-seven years before.
Thirdly, there is also a submerged peat moss, consisting of land and
freshwater plants, beneath the sea at a point to which no peat could
have been drifted down by any river. Fourthly, and what is still more
conclusive, it is found that in seaport towns, all along the coast of
Scania, there are streets below the high-water level of the Baltic, and
in some cases below the level of the lowest tide. Thus, when the wind is
high at Malmo, the water overflows one of the present streets, and some
years ago some excavations showed an ancient street in the same place
eight feet lower, and it was then seen that there had been an artificial
raising of the ground, doubtless in consequence of that subsidence.
There is also a street at Trelleborg, and another at Skanör, a few
inches below high-water mark, and a street at Ystad is exactly on a
level with the sea, at which it could not have been originally built.

The inferences deduced from the foregoing facts are in perfect harmony
with the proofs brought to light by two Danish investigators, Dr. Pingel
and Captain Graah, of the sinking down of part of the west coast of
Greenland, for a space of more than 600 miles from north to south. The
observations of Captain Graah were made during a survey of Greenland in
1823-24; and afterwards in 1828-29; those by Dr. Pingel were made in
1830-32. It appears from various signs and traditions, that the coast
has been subsiding for the last four centuries from the firth called
Igaliko, in lat. 60° 43' N. to Disco Bay, extending to nearly the 69th
degree of north latitude. Ancient buildings on low rocky islands and on
the shore of the main land have been gradually submerged, and experience
has taught the aboriginal Greenlander never to build his hut near the
water's edge. In one case the Moravian settlers have been obliged more
than once to move inland the poles upon which their large boats were
set, and the old poles still remain beneath the water as silent
witnesses of the change.[740]

The probable cause of the movements above alluded to, whether of
elevation or depression, will be more appropriately discussed in the
following chapters, when the origin of subterranean heat is considered.
But I may remark here, that the rise of Scandinavia has naturally been
regarded as a very singular and scarcely credible phenomenon, because no
region on the globe has been more free within the times of authentic
history from violent earthquakes. In common, indeed, with our own island
and with almost every spot on the globe, some movements have been, at
different periods, experienced, both in Norway and Sweden. But some of
these, as for example during the Lisbon earthquake in 1755, may have
been mere vibrations or undulatory movements of the earth's crust
prolonged from a great distance. Others, however, have been sufficiently
local to indicate a source of disturbance immediately under the country
itself. Notwithstanding these shocks, Scandinavia has, upon the whole,
been as tranquil in modern times, and as free from subterranean
convulsions, as any region of equal extent on the globe. There is also
another circumstance which has made the change of level in Sweden appear
anomalous, and has for a long time caused the proofs of the fact to be
received with reluctance. Volcanic action, as we have seen, is usually
intermittent: and the variations of level to which it has given rise
have taken place by starts, not by a prolonged and insensible movement
similar to that experienced in Sweden. Yet, as we enlarge our experience
of modern changes, we discover instances in which the volcanic eruption,
the earthquake, and the permanent rise or fall of land, whether slow or
sudden, are all connected. The union of these various circumstances was
exemplified in the case of the temple of Serapis, described in the last
chapter, and we might derive other illustrations from the events of the
present century in South America.

Some writers, indeed, have imagined that there is geological evidence in
Norway, of the sudden upheaval of land to a considerable height at
successive periods, since the era when the sea was inhabited by the
living species of testacea. They point in proof to certain horizontal
lines of inland cliffs and sea-beaches containing recent shells at
various heights above the level of the sea.[741] But these appearances,
when truly interpreted, simply prove that there have been long pauses in
the process of upheaval or subsidence. They mark eras at which the level
of the sea has remained stationary for ages, and during which new strata
were deposited near the shore in some places, while in others the waves
and currents had time to hollow out rocks, undermine cliffs, and throw
up long ranges of shingle. They undoubtedly show that the movement has
not been always uniform or continuous, but they do not establish the
fact of any sudden alterations of level.

When we are once assured of the reality of the gradual rise of a large
region, it enables us to account for many geological appearances
otherwise of very difficult explanation. There are large continental
tracts and high table-lands where the strata are nearly horizontal,
bearing no marks of having been thrown up by violent convulsions, nor by
a series of movements, such as those which occur in the Andes, and cause
the earth to be rent open, and raised or depressed from time to time,
while large masses are engulfed in subterranean cavities. The result of
a series of such earthquakes might be to produce in a great lapse of
ages a country of shattered, inclined, and perhaps vertical strata. But
a movement like that of Scandinavia would cause the bed of the sea, and
all the strata recently formed in it, to be upheaved so gradually, that
it would merely seem as if the ocean had formerly stood at a higher
level, and had slowly and tranquilly sunk down into its present bed.

The fact also of a very gradual and insensible elevation of land may
explain many geological movements of denudation, on a grand scale. If,
for example, instead of the hard granitic rocks of Norway and Sweden, a
large part of the bed of the Atlantic, consisting chiefly of soft
strata, should rise up century after century, at the rate of about half
an inch, or an inch, in a year, how easily might oceanic currents sweep
away the thin film of matter thus brought up annually within the sphere
of aqueous denudation! The tract, when it finally emerged, might present
table-lands and ridges of horizontal strata, with intervening valleys
and vast plains, where originally, and during its period of submergence,
the surface was level and nearly uniform.

These speculations relate to superficial changes; but others must be
continually in progress in the subterranean regions. The foundations of
the country, thus gradually uplifted in Sweden, must be undergoing
important modifications. Whether we ascribe these to the expansion of
solid matter by continually increasing heat, or to the liquefaction of
rock, or to the crystallization of a dense fluid, or the accumulation of
pent-up gases, in whatever conjectures we indulge, we can never doubt
for a moment, that at some unknown depth beneath Sweden and the Baltic,
the structure of the globe is in our own times becoming changed from day
to day, throughout a space probably more than a thousand miles in
length, and several hundred in breadth.




CHAPTER XXXI.

CAUSES OF EARTHQUAKES AND VOLCANOES.


  Intimate connection between the causes of volcanoes and
    earthquakes--Supposed original state of fusion of the
    planet--Universal fluidity not proved by spheroidal figure of the
    earth--Attempt to calculate the thickness of the solid crust of the
    earth by precessional motion--Heat in mines increasing with the
    depth--Objections to the supposed intense heat of a central
    fluid--Whether chemical changes may produce volcanic heat--Currents
    of electricity circulating in the earth's crust.


It will hardly be questioned, after the description before given of the
phenomena of earthquakes and volcanoes, that both of these agents have,
to a certain extent, a common origin; and I may now, therefore, proceed
to inquire into their probable causes. But first, it may be well to
recapitulate some of those points of relation and analogy which lead
naturally to the conclusion that they spring from a common source.

The regions convulsed by violent earthquakes include within them the
site of all the active volcanoes. Earthquakes, sometimes local,
sometimes extending over vast areas, often precede volcanic eruptions.
The subterranean movement and the eruption return again and again, at
irregular intervals of time, and with unequal degrees of force, to the
same spots. The action of either may continue for a few hours, or for
several consecutive years. Paroxysmal convulsions are usually followed,
in both cases, by long periods of tranquillity. Thermal and mineral
springs are abundant in countries of earthquakes and active volcanoes.
Lastly, hot springs situated in districts considerably distant from
volcanic vents have been observed to have their temperature suddenly
raised, and the volume of their water augmented, by subterranean
movements.

All these appearances are evidently more or less connected with the
passage of heat from the interior of the earth to the surface; and where
there are active volcanoes, there must exist, at some unknown depth
below, enormous masses of matter intensely heated, and, in many
instances, in a constant state of fusion. We have first, then, to
inquire, whence is this heat derived?

It has long been a favorite conjecture, that the whole of our planet was
originally in a state of igneous fusion, and that the central parts
still retain a great portion of their primitive heat. Some have
imagined, with the late Sir W. Herschel, that the elementary matter of
the earth may have been first in a gaseous state, resembling those
nebulæ which we behold in the heavens, and which are of dimensions so
vast, that some of them would fill the orbits of the remotest planets of
our system. The increased power of the telescope has of late years
resolved the greater number of these nebulous appearances into clusters
of stars, but so long as they were confidently supposed to consist of
aeriform matter it was a favorite conjecture that they might, if
concentrated, form solid spheres; and it was also imagined that the
evolution of heat, attendant on condensation, might retain the materials
of the new globes in a state of igneous fusion.

Without dwelling on such speculations, which can only have a distant
bearing on geology, we may consider how far the spheroidal form of the
earth affords sufficient ground for presuming that its primitive
condition was one of universal fluidity. The discussion of this question
would be superfluous, were the doctrine of original fluidity less
popular; for it may well be asked, why the globe should be supposed to
have had a pristine shape different from the present one?--why the
terrestrial materials, when first called into existence, or assembled
together in one place, should not have been subject to rotation, so as
to assume at once that form which alone could retain their several parts
in a state of equilibrium?

Let us, however, concede that the statical figure may be a modification
of some other pre-existing form, and suppose the globe to have been at
first a perfect and quiescent sphere, covered with a uniform ocean--what
would happen when it was made to turn round on its axis with its present
velocity? This problem has been considered by Playfair in his
Illustrations, and he has decided, that if the surface of the earth, as
laid down in Hutton's theory, has been repeatedly changed by the
transportation of the detritus of the land to the bottom of the sea, the
figure of the planet must in that case, whatever it may have been
originally, be brought at length to coincide with the spheroid of
equilibrium.[742] Sir John Herschel also, in reference to the same
hypothesis, observes, "a centrifugal force would in that case be
generated, whose general tendency would be to urge the water at every
point of the surface to _recede_ from the _axis_. A rotation might
indeed be conceived so swift as to flirt the whole ocean from the
surface, like water from a mop. But this would require a far greater
velocity than what we now speak of. In the case supposed, the _weight_
of the water would still keep it _on_ the earth; and the tendency to
recede from the axis _could_ only be satisfied therefore by the water
leaving the poles, and flowing towards the equator; there heaping itself
up in a ridge, and being retained in opposition to its weight or natural
tendency towards the centre by the pressure thus caused. This, however,
could not take place without laying dry the polar regions, so that
protuberant land would appear at the poles, and a zone of ocean be
disposed around the equator. This would be the first or immediate
effect. Let us now see what would afterwards happen if things were
allowed to take their natural course.

"The sea is constantly beating on the land, grinding it down, and
scattering its worn-off particles and fragments, in the state of sand
and pebbles, over its bed. Geological facts afford abundant proof that
the existing continents have all of them undergone this process even
more than once, and been entirely torn in fragments, or reduced to
powder, and submerged and reconstructed. Land, in this view of the
subject, loses its attribute of fixity. As a mass it might hold together
in opposition to forces which the water freely obeys; but in its state
of successive or simultaneous degradation, when disseminated through the
water, in the state of sand or mud, it is subject to all the impulses of
that fluid. In the lapse of time, then, the protuberant land would be
destroyed, and spread over the bottom of the ocean, filling up the lower
parts, and tending continually to remodel the surface of the solid
nucleus, in correspondence with the _form of equilibrium_. Thus after a
sufficient lapse of time, in the case of an earth in rotation, the polar
protuberances would gradually be cut down and disappear, being
transferred to the equator (as being _then_ the _deepest sea_), till the
earth would assume by degrees the form we observe it to have--that of a
flattened or _oblate_ ellipsoid.

"We are far from meaning here to trace the process _by which_ the earth
really assumed its actual form; all we intend is to show that this is
the form to which, under a condition of a rotation on its axis, it must
_tend_, and which it would attain even if originally and (so to speak)
perversely constituted otherwise."[743]

In this passage, the author has contemplated the superficial effects of
aqueous causes only; but neither he nor Playfair seem to have followed
out the same inquiry with reference to another part of Hutton's system;
namely, that which assumes the successive fusion by heat of different
parts of the solid earth. Yet the progress of geology has continually
strengthened the evidence in favor of the doctrine that local variations
of temperature have melted one part after another of the earth's crust,
and this influence has perhaps extended downwards to the very centre.
If, therefore, before the globe had assumed its present form, it was
made to revolve on its axis, all matter to which freedom of motion was
given by fusion, must before consolidating have been impelled towards
the equatorial regions in obedience to the centrifugal force. Thus lava
flowing out in superficial streams would have its motion retarded when
its direction was towards the pole, accelerated when towards the
equator; or if lakes and seas of lava existed beneath the earth's crust
in equatorial regions, as probably now beneath the Peruvian Andes, the
imprisoned fluid would force outwards and permanently upheave the
overlying rocks. The statical figure, therefore, of the terrestrial
spheroid (of which the longest diameter exceeds the shortest by about
twenty-five miles), may have been the result of gradual and even of
existing causes, and not of a primitive, universal, and simultaneous
fluidity.[744]

Experiments made with the pendulum, and observations on the manner in
which the earth attracts the moon, have shown that our planet is not an
empty sphere, but, on the contrary, that its interior, whether solid or
fluid, has a higher specific gravity than the exterior. It has also been
inferred, that there is a regular increase in density from the surface
towards the centre, and that the equatorial protuberance is continued
inwards; that is to say, that layers of equal density are arranged
elliptically, and symmetrically, from the exterior to the centre. These
conclusions, however, have been deduced rather as a consequence of the
hypothesis of primitive and simultaneous fluidity than proved by
experiment. The inequalities in the moon's motion, by which some have
endeavored to confirm them, are so extremely slight, that the opinion
can be regarded as little more than a probable conjecture.

The mean density of the earth has been computed by Laplace to be about
5½, or more than five times that of water. Now the specific gravity
of many of our rocks is from 2½ to 3, and the greater part of the
metals range between that density and 21. Hence some have imagined that
the terrestrial nucleus may be metallic--that it may correspond, for
example, with the specific gravity of iron, which is about 7. But here a
curious question arises in regard to the form which materials, whether
fluid or solid, might assume, if subjected to the enormous pressure
which must obtain at the earth's centre. Water, if it continued to
decrease in volume according to the rate of compressibility deduced from
experiment, would have its density doubled at the depth of ninety-three
miles, and be as heavy as mercury at the depth of 362 miles. Dr. Young
computed that, at the earth's centre, steel would be compressed into
one-fourth, and stone into one-eighth of its bulk.[745] It is more than
probable, however, that after a certain degree of condensation, the
compressibility of bodies may be governed by laws altogether different
from those which we can put to the test of experiment; but the limit is
still undetermined, and the subject is involved in such obscurity, that
we cannot wonder at the variety of notions which have been entertained
respecting the nature and conditions of the central nucleus. Some have
conceived it to be fluid, others solid; some have imagined it to have a
cavernous structure, and have even endeavored to confirm this opinion by
appealing to observed irregularities in the vibrations of the pendulum
in certain countries.

An attempt has recently been made by Mr. Hopkins to determine the least
thickness which can be assigned to the solid crust of the globe, if we
assume the whole to have been once perfectly fluid, and a certain
portion of the exterior to have acquired solidity by gradual
refrigeration. This result he has endeavored to obtain by a new solution
of the delicate problem of the processional motion of the pole of the
earth. It is well known that while the earth revolves round the sun the
direction of its axis remains very nearly the same, _i. e._ its
different positions in space are all nearly parallel to each other. This
parallelism, however, is not accurately preserved, so that the axis,
instead of coming exactly into the position which it occupied a year
before, becomes inclined to it at a very small angle, but always
retaining very nearly the same inclination to the plane of the earth's
orbit. This motion of the pole changes the position of the equinoxes by
about fifty seconds annually, and always in the same direction. Thus the
pole-star, after a certain time, will entirely lose its claim to that
appellation, until in the course of somewhat more than 25,000 years the
earth's axis shall again occupy its present angular position, and again
point very nearly as now to the pole-star. This motion of the axis is
called _precession_. It is caused by the attraction of the sun and moon,
and principally the moon, on the protuberant parts of the earth's
equator; and if these parts were solid to a great depth, the motion thus
produced would differ considerably from that which would exist if they
were perfectly fluid, and incrusted over with a thin shell only a few
miles thick. In other words, the disturbing action of the moon will not
be the same upon a globe all solid and upon one nearly all fluid, or it
will not be the same upon a globe in which the solid shell forms
one-half of the mass, and another in which it forms only one-tenth.

Mr. Hopkins has, therefore, calculated the amount of precessional motion
which would result if we assume the earth to be constituted as above
stated; _i. e._ fluid internally, and enveloped by a solid shell; and he
finds that the amount will not agree with the observed motion, unless
the crust of the earth be of a certain thickness. In calculating the
exact amount some ambiguity arises in consequence of our ignorance of
the effect of pressure in promoting the solidification of matter at high
temperatures. The hypothesis least favorable for a great thickness is
found to be that which assumes the pressure to produce no effect on the
process of solidification. Even on this extreme assumption the thickness
of the solid crust must be nearly _four hundred miles_, and this would
lead to the remarkable result that the proportion of the solid to the
fluid part would be as 49 to 51, or, to speak in round numbers, there
would be nearly as much solid as fluid matter in the globe. The
conclusion, however, which Mr. Hopkins announces as that to which his
researches have finally conducted him, is thus expressed: "Upon the
whole, then, we may venture to assert that the minimum thickness of the
crust of the globe, which can be deemed consistent with the observed
amount of precession, cannot be less than one-fourth or one-fifth of the
earth's radius." That is from 800 to 1000 miles.[746]

It will be remarked, that this is a _minimum_, and any still _greater_
amount would be quite consistent with the actual phenomena; the
calculations not being opposed to the supposition of the general
solidity of the entire globe. Nor do they preclude us from imagining
that great lakes or seas of melted matter may be distributed through a
shell 400 or 800 miles thick, provided they be so inclosed as to move
with it, whatever motion of rotation may be communicated by the
disturbing forces of the sun and moon.

_Central heat._--The hypothesis of internal fluidity calls for the more
attentive consideration, as it has been found that the heat in mines
augments in proportion as we descend. Observations have been made, not
only on the temperature of the air in mines, but on that of the rocks,
and on the water issuing from them. The mean rate of increase,
calculated from results obtained in six of the deepest coal mines in
Durham and Northumberland, is 1° Fahr. for a descent of forty-four
English feet.[747] A series of observations, made in several of the
principal lead and silver mines in Saxony, gave 1° Fahr. for every
sixty-five feet. In this case, the bulb of the thermometer was
introduced into cavities purposely cut in the solid rock at depths
varying from 200 to above 900 feet. But in other mines of the same
country, it was necessary to descend thrice as far for each degree of
temperature.[748]

A thermometer was fixed in the rock of the Dolcoath mine, in Cornwall,
by Mr. Fox, at the great depth of 1380 feet, and frequently observed
during eighteen months; the mean temperature was 68° Fahr., that of the
surface being 50°, which gives 1° for every seventy-five feet.

Kupffer, after an extensive comparison of the results in different
countries, makes the increase 1° F. for about every thirty-seven English
feet.[749] M. Cordier announces, as the result of his experiments and
observations on the temperature of the interior of the earth, that the
heat increases rapidly with the depth; but the increase does not follow
the same law over the whole earth, being twice or three times as much in
one country as in another, and these differences are not in constant
relation either with the latitudes or longitudes of places.[750] He is
of opinion, however, that the increase would not be overstated at 1°
Cent. for every twenty-five metres, or about 1° F. for every forty-five
feet.[751] The experimental well bored at Grenelle, near Paris, gave
about 1° F. for every sixty English feet, when they had reached a depth
of 1312 feet.

Some writers have endeavored to refer these phenomena (which, however
discordant as to the ratio of increasing heat, appear all to point one
way) to the condensation of air constantly descending from the surface
into the mines. For the air under pressure would give out latent heat,
on the same principle as it becomes colder when rarefied in the higher
regions of the atmosphere. But, besides that the quantity of heat is
greater than could be supposed to flow from this source, the argument
has been answered in a satisfactory manner by Mr. Fox, who has shown,
that in the mines of Cornwall the ascending have generally a higher
temperature than the descending aerial currents. The difference between
them was found to vary from 9° to 17° F.; a proof that, instead of
imparting heat, these currents actually carry off a large quantity from
the mines.[752]

If we adopt M. Cordier's estimate of 1° F. for every 45 feet of depth as
the mean result, and assume, with the advocates of central fluidity,
that the increasing temperature is continued downwards, we should reach
the ordinary boiling point of water at about two miles below the
surface, and at the depth of about twenty-four miles should arrive at
the melting point of iron, a heat sufficient to fuse almost every known
substance. The temperature of melted iron was estimated at 21,000° F.,
by Wedgwood; but his pyrometer gives, as is now demonstrated, very
erroneous results. Professor Daniell ascertained that the point of
fusion is 2786° F.[753]

[Illustration: Fig. 92.

Section of the earth, in which the breadth of the outer boundary line
represents a thickness of 25 miles; the space between the circles,
including the breadth of the lines, 200 miles.]

According to Mr. Daniell's scale, we ought to encounter the internal
melted matter before penetrating through a thickness represented by
that of the outer circular line in the annexed diagram (fig. 92);
whereas, if the other or less correct scale be adopted, we should meet
with it at some point between the two circles; the space between them,
together with the lines themselves, representing a crust of 200 miles in
depth. In either case, we must be prepared to maintain that a
temperature many times greater than that sufficient to melt the most
refractory substances known to us, is sustained at the centre of the
globe; while a comparatively thin crust, resting upon the fluid, remains
unmelted; or is even, according to M. Cordier, increasing in thickness,
by the continual addition of new internal layers solidified during the
process of refrigeration.

The mathematical calculations of Fourier, on the passage of heat through
conducting bodies, have been since appealed to in support of these
views; for he has shown that it is compatible with theory that the
present temperature of the surface might coexist with an intense heat at
a certain depth below. But his reasoning seems to be confined to the
conduction of heat through solid bodies; and the conditions of the
problem are wholly altered when we reason about a fluid nucleus, as we
must do if it be assumed that the heat augments from the surface to the
interior, according to the rate observed in mines. For when the heat of
the lower portion of a fluid is increased, a circulation begins
throughout the mass, by the ascent of hotter, and the descent of colder
currents. And this circulation, which is quite distinct from the mode in
which heat is propagated through solid bodies, must evidently occur in
the supposed central ocean, if the laws of fluids and of heat are the
same there as upon the surface.

In Mr. Daniell's experiments for obtaining a measure of the heat of
bodies at their point of fusion, he invariably found that it was
impossible to raise the heat of a large crucible of melted iron, gold,
or silver, a single degree beyond the melting point, so long as a bar of
the respective metals was kept immersed in the fluid portions. So in
regard to other substances, however great the quantities fused, their
temperature could not be raised while any solid pieces immersed in them
remained unmelted; every accession of heat being instantly absorbed
during their liquefaction. These results are, in fact, no more than the
extension of a principle previously established, that so long as a
fragment of ice remains in water, we cannot raise the temperature of the
water above 32° F.

If, then, the heat of the earth's centre amount to 450,000° F., as M.
Cordier deems highly probable, that is to say, about twenty times the
heat of melted iron, even according to Wedgwood's scale, and upwards of
160 times according to the improved pyrometer, it is clear that the
upper parts of the fluid mass could not long have a temperature only
just sufficient to melt rocks. There must be a continual tendency
towards a uniform heat; and until this were accomplished, by the
interchange of portions of fluid of different densities, the surface
could not begin to consolidate. Nor, on the hypothesis of primitive
fluidity, can we conceive any crust to have been formed until _the
whole_ planet had cooled down to about the temperature of incipient
fusion.

It cannot be objected that hydrostatic pressure would prevent a tendency
to equalization of temperature; for, as far as observations have yet
been made, it is found that the waters of deep lakes and seas are
governed by the same laws as a shallow pool; and no experiments indicate
that solids resist fusion under high pressure. The arguments, indeed,
now controverted, always proceed on the admission that the internal
nucleus is in a state of fusion.

It may be said that we may stand upon the hardened surface of a
lava-current while it is still in motion,--nay, may descend into the
crater of Vesuvius after an eruption, and stand on the scoriæ while
every crevice shows that the rock is red-hot two or three feet below us;
and at a somewhat greater depth, all is, perhaps, in a state of fusion.
May not, then, a much more intense heat be expected at the depth of
several hundred yards, or miles? The answer is,--that until a great
quantity of heat has been given off, either by the emission of lava, or
in a latent form by the evolution of steam and gas, the melted matter
continues to boil in the crater of a volcano. But ebullition ceases when
there is no longer a sufficient supply of heat from below, and then a
crust of lava may form on the top, and showers of scoriæ may then
descend upon the surface, and remain unmelted. If the internal heat be
raised again, ebullition will recommence, and soon fuse the superficial
crust. So in the case of the moving current, we may safely assume that
no part of the liquid beneath the hardened surface is much above the
temperature sufficient to retain it in a state of fluidity.

It may assist us in forming a clearer view of the doctrine now
controverted, if we consider what would happen were a globe of
homogeneous composition placed under circumstances analogous, in regard
to the distribution of heat, to those above stated. If the whole planet,
for example, were composed of water covered with a spheroidal crust of
ice fifty miles thick, and with an interior ocean having a central heat
about two hundred times that of the melting point of ice, or 6400° F.;
and if, between the surface and the centre, there was every intermediate
degree of temperature between that of melting ice and that of the
central nucleus--could such a state of things last for a moment? If it
must be conceded, in this case, that the whole spheroid would be
instantly in a state of violent ebullition, that the ice (instead of
being strengthened annually by new internal layers) would soon melt, and
form part of an atmosphere of steam--on what principle can it he
maintained that analogous effects would not follow, in regard to the
earth, under the conditions assumed in the theory of central heat?[754]


M. Cordier admits that there must be tides in the internal melted ocean;
but their effect, he says, has become feeble, although originally, when
the fluidity of the globe was perfect, "the rise and fall of these
ancient land tides could not have been less than from thirteen to
sixteen feet." Now, granting for a moment, that these tides have become
so feeble as to be incapable of causing the fissured shell of the earth
to be first uplifted and then depressed every six hours, still may we
not ask whether, during eruptions, the lava, which is supposed to
communicate with a great central ocean, would not rise and fall sensibly
in a crater such as Stromboli, where there is always melted matter in a
state of ebullition?

_Whether chemical changes may produce volcanic heat._--Having now
explained the reasons which have induced me to question the hypothesis
of central heat as the primary source of volcanic action, it remains to
consider what has been termed the chemical theory of volcanoes. It is
well known that many, perhaps all, of the substances of which the earth
is composed are continually undergoing chemical changes. To what depth
these processes may be continued downwards must, in a great degree, be
matter of conjecture; but there is no reason to suspect that, if we
could descend to a great distance from the surface, we should find
elementary substances differing essentially from those with which we are
acquainted.

All the solid, fluid, and gaseous bodies known to us consist of a very
small number of these elementary substances variously combined: the
total number of elements at present known is less than sixty; and not
half of these enter into the composition of the more abundant inorganic
productions. Some portions of such compounds are daily undergoing
decomposition, and their constituent parts being set free are passing
into new combinations. These processes are by no means confined to
minerals at the earth's surface, and are very often accompanied by the
evolution of heat, which is intense in proportion to the rapidity of the
combinations. At the same time there is a development of electricity.

The spontaneous combustion of beds of bituminous shale, and of refuse
coal thrown out of mines, is generally due to the decomposition of
pyrites; and it is the contact of air and water which brings about the
change. Heat results from the oxidation of the sulphur and iron, though
on what principle heat is generated, when two or more bodies having a
strong affinity for each other unite suddenly, is wholly unexplained.

_Electricity a source of volcanic heat._--It has already been stated,
that chemical changes develop electricity; which, in its turn, becomes a
powerful disturbing cause. As a chemical agent, says Davy, its silent
and slow operation in the economy of nature is much more important than
its grand and impressive operation in lightning and thunder. It may be
considered, not only as directly producing an infinite variety of
changes, but as influencing almost all which take place; it would seem,
indeed, that chemical attraction itself is only a peculiar form of the
exhibition of electrical attraction.[755]

Now that it has been demonstrated that magnetism and electricity are
always associated, and are perhaps only different conditions of the same
power, the phenomena of terrestrial magnetism have become of no ordinary
interest to the geologist. Soon after the first great discoveries of
Oersted in electro-magnetism, Ampère suggested that all the phenomena of
the magnetic needle might be explained by supposing currents of
electricity to circulate constantly in the shell of the globe in
directions parallel to the magnetic equator. This theory has acquired
additional consistency the farther we have advanced in science; and
according to the experiments of Mr. Fox, on the electro-magnetic
properties of metalliferous veins, some trace of electric currents seems
to have been detected in the interior of the earth.[756]

Some philosophers ascribe these currents to the chemical action going on
in the superficial parts of the globe to which air and water have the
readiest access; while others refer them, in part at least, to
thermo-electricity excited by the solar rays on the surface of the earth
during its rotation; successive parts of the atmosphere, land, and sea
being exposed to the influence of the sun, and then cooled again in the
night. That this idea is not a mere speculation, is proved by the
correspondence of the diurnal variations of the magnet with the apparent
motion of the sun; and by the greater amount of variation in summer than
in winter, and during the day than in the night. M. de la Rive, although
conceding that such minor variations of the needle may be due to
thermo-electricity, contends that the general phenomena of terrestrial
magnetism must be attributed to currents far more intense; which, though
liable to secular fluctuations, act with much greater constancy and
regularity than the causes which produce the diurnal variations.[757]
The remark seems just; yet it is difficult to assign limits to the
accumulated influence even of a very feeble force constantly acting on
the whole surface of the earth. This subject, however, must evidently
remain obscure, until we become acquainted with the causes which give a
determinate direction to the supposed electric currents. Already the
experiments of Faraday on the rotation of magnets have led him to
speculate on the manner in which the earth, when once it had become
magnetic, might produce electric currents within itself, in consequence
of its diurnal rotation.[758] We have seen also in a former chapter (p.
129) that the recent observations of Schwabe, 1852, have led Col. Sabine
to the discovery of a connection between certain periodical changes,
which take place in the spots on the sun, and a certain cycle of
variations in terrestrial magnetism. These seem to point to the
existence of a solar magnetic period, and suggest the idea of the sun's
magnetism exerting an influence on the mass of our planet.

In regard to thermo-electricity, I may remark, that it may be generated
by great inequalities of temperature, arising from a partial
distribution of volcanic heat. Wherever, for example, masses of rock
occur of great horizontal extent, and of considerable depth, which are
at one point in a state of fusion (as beneath some active volcano); at
another, red-hot; and at a third, comparatively cold--strong
thermo-electric action may be excited.

Some, perhaps, may object, that this is reasoning in a circle; first to
introduce electricity as one of the primary causes of volcanic heat, and
then to derive the same heat from thermo-electric currents. But there
must, in truth, be much reciprocal action between the agents now under
consideration; and it is very difficult to decide which should be
regarded as the prime mover, or to see where the train of changes, once
begun, would terminate. Whether subterranean electric currents if once
excited might sometimes possess the decomposing power of the voltaic
pile, is a question not perhaps easily answered in the present state of
science; but such a power, if developed, would at once supply us with a
never-failing source of chemical action from which volcanic heat might
be derived.

_Recapitulation._--Before entering, in the next chapter, still farther
into the inquiry, how far the phenomena of volcanoes and earthquakes
accord with the hypothesis of a continued generation of heat by chemical
action, it may be desirable to recapitulate, in a few words, the
conclusions already obtained.

1st. The primary causes of the volcano and the earthquake are, to a
great extent, the same, and must be connected with the passage of heat
from the interior to the surface.

2dly. This heat has been referred, by many, to a supposed state of
igneous fusion of the central parts of the planet when it was first
created, of which a part still remains in the interior, but is always
diminishing in intensity.

3dly. The spheroidal figure of the earth, adduced in support of this
theory, does not of necessity imply a universal and simultaneous
fluidity, in the beginning; for supposing the original figure of our
planet had been strictly spherical--which, however, is a gratuitous
assumption, resting on no established analogy--still the statical figure
must have been assumed, if sufficient time be allowed, by the gradual
operation of the centrifugal force, acting on the materials brought
successively within its action by aqueous and igneous causes.

4thly. It appears, from experiment, that the heat in mines increases
progressively with their depth; and if the ratio of increase be
continued uniformly from the surface to the interior, the whole globe,
with the exception of a small external shell, must be fluid, and the
central parts must have a temperature many times higher than that of
melted iron.

5thly. But the theory adopted by M. Cordier and others, which maintains
the actual existence of such a state of things, seems wholly
inconsistent with the laws which regulate the circulation of heat
through fluid bodies. For, if the central heat were as intense as is
represented, there must be a circulation of currents, tending to
equalize the temperature of the resulting fluids, and the solid crust
itself would be melted.

6thly. Instead of an original central heat, we may, perhaps, refer the
heat of the interior to chemical changes constantly going on in the
earth's crust; for the general effect of chemical combination is the
evolution of heat and electricity, which in their turn become sources of
new chemical changes.




CHAPTER XXXII.

CAUSES OF EARTHQUAKES AND VOLCANOES--_continued_.


  Review of the proofs of internal heat--Theory of an unoxidated
    metallic nucleus--Whether the decomposition of water may be a source
    of volcanic heat--Geysers of Iceland--Causes of
    earthquakes--Wavelike motion--Expansive power of liquid
    gases--Connection between the state of the atmosphere and
    earthquakes--Permanent upheaval and subsidence of land--Expansion of
    rocks by heat--The balance of dry land how preserved--Subsidence in
    excess--Conclusion.


When we reflect that the largest mountains are but insignificant
protuberances upon the surface of the earth, and that these mountains
are nevertheless composed of different parts which have been formed in
succession, we may well feel surprise that the central fluidity of the
planet should have been called in to account for volcanic phenomena. To
suppose the entire globe to be in a state of igneous fusion, with the
exception of a solid shell, not more than from thirty to one hundred
miles thick, and to imagine that the central heat of this fluid spheroid
exceeds by more than two hundred times that of liquid lava, is to
introduce a force altogether disproportionate to the effects which it is
required to explain.

The ordinary repose of the surface implies, on the contrary, an
inertness in the internal mass which is truly wonderful. When we
consider the combustible nature of the elements of the earth, so far as
they are known to us,--the facility with which their compounds may be
decomposed and made to enter into new combinations,--the quantity of
heat which they evolve during these processes; when we recollect the
expansive power of steam, and that water itself is composed of two gases
which, by their union, produce intense heat; when we call to mind the
number of explosive and detonating compounds which have been already
discovered, we may be allowed to share the astonishment of Pliny, that a
single day should pass without a general conflagration:--"Excedit
profectò omnia miracula, ullum diem fuisse quo non cuncta
conflagrarent."[759]

The signs of internal heat observable on the surface of the earth do not
necessarily indicate the permanent existence of subterranean heated
masses, whether fluid or solid, by any means so vast as our continents
and seas; yet how insignificant would these appear if distributed
through an external shell of the globe one or two hundred miles in
depth! The principal facts in proof of the accumulation of heat below
the surface may be summed up in a few words. Several volcanoes are
constantly in eruption, as Stromboli and Nicaragua; others are known to
have been active for periods of 60, or even 150 years, as those of
Sangay in Quito, Popocatepetl in Mexico, and the volcano of the Isle of
Bourbon. Many craters emit hot vapors in the intervals between
eruptions, and solfataras evolve incessantly the same gases as
volcanoes. Steam of high temperature has continued for more than twenty
centuries to issue from the "stufas," as the Italians call them; thermal
springs abound not only in regions of earthquakes, but are found in
almost all countries, however distant from active vents; and, lastly,
the temperature in the mines of various parts of the world is found to
increase in proportion as we descend.

The diagram (fig. 93) in the next page, may convey some idea of the
proportion which our continents and the ocean bear to the radius of the
earth.[760] If all the land were about as high as the Himalaya
mountains, and the ocean everywhere as deep as the Pacific, the whole of
both might be contained within a space expressed by the thickness of the
line _a b_; and masses of nearly equal volume might be placed in the
space marked by the line _c d_, in the interior. Seas of lava,
therefore, of the size of the Mediterranean, or even of the Atlantic,
would be as nothing if distributed through such an outer shell of the
globe as is represented by the shaded portion of the figure _a b c d_.
If throughout that space we imagine electro-chemical causes to be
continually in operation, even of very feeble power, they might give
rise to heat which, if accumulated at certain points, might melt or
render red-hot entire mountains, or sustain the temperature of stufas
and hot springs for ages.

_Theory of an unoxidated metallic nucleus._--When Sir H. Davy first
discovered the metallic basis of the earths and alkalies, he threw out
the idea that those metals might abound in an unoxidized state in the
subterranean regions to which water must occasionally penetrate.
Whenever this happened, gaseous matter would be set free, the metals
would combine with the oxygen of the water, and sufficient heat might be
evolved to melt the surrounding rocks. This hypothesis, although
afterwards abandoned by its author, was at first very favorably received
both by the chemist and the geologist: for silica, alumina, lime, soda,
and oxide of iron,--substances of which lavas are principally
composed,--would all result from the contact of the inflammable metals
alluded to with water. But whence this abundant store of unsaturated
metals in the interior? It was assumed that, in the beginning of things,
the nucleus of the earth was mainly composed of inflammable metals, and
that oxidation went on with intense energy at first; till at length,
when a superficial crust of oxides had been formed, the chemical action
became more and more languid.

[Illustration: Fig. 93.

Centre of the earth.]

This speculation, like all others respecting the primitive state of the
earth's nucleus, rests unavoidably on arbitrary assumptions. But we may
fairly inquire whether any existing causes may have the power of
deoxidating the earthy and alkaline compounds formed from time to time
by the action of water upon the metallic bases. If so, and if the
original crust or nucleus of the planet contained distributed through it
here and there some partial stores of potassium, sodium, and other
metallic bases, these might be oxidated and again deoxidated, so as to
sustain for ages a permanent chemical action. Yet even then we should be
unable to explain why such a continuous circle of operations, after
having been kept up for thousands of years in one district, should
entirely cease, and why another region, which had enjoyed a respite from
volcanic action for one or many geological periods, should become a
theatre for the development of subterranean heat.

It is well known to chemists, that the metallization of oxides, the most
difficult to reduce, may be effected by hydrogen brought into contact
with them at a red heat; and it is more than probable that the
production of potassium itself, in the common gun-barrel process, is due
to the power of nascent hydrogen derived from the water which the
hydrated oxide contains. According to the recent experiments, also, of
Faraday, it would appear that every case of metallic reduction by
voltaic agency, from saline solutions, in which water is present, is due
to the secondary action of hydrogen upon the oxide; both of these being
determined to the negative pole and then reacting upon one another.

It is admitted that intense heat would be produced by the occasional
contact of water with the metallic bases; and it is certain that, during
the process of saturation, vast volumes of hydrogen must be evolved. The
hydrogen, thus generated, might permeate the crust of the earth in
different directions, and become stored up for ages in fissures and
caverns, sometimes in a liquid form, under the necessary pressure.
Whenever, at any subsequent period, in consequence of the changes
effected by earthquakes in the shell of the earth, this gas happened to
come in contact with metallic oxides at a high temperature, the
reduction of these oxides might be the result.

No theory seems at first more startling than that which represents water
as affording an inexhaustible supply of fuel to the volcanic fires; yet
is it by no means visionary. It is a fact that must not be overlooked,
that while a great number of volcanoes are entirely submarine, the
remainder occur for the most part in islands or maritime tracts. There
are a few exceptions; but some of these, observes Dr. Daubeny, are near
inland salt lakes, as in Central Tartary; while others form part of a
train of volcanoes, the extremities of which are near the sea.

Sir H. Davy suggested that, when the sea is distant, as in the case of
some of the South American volcanoes, they may still be supplied with
water from subterranean lakes; since, according to Humboldt, large
quantities of fish are often thrown out during eruptions.[761] Mr. Dana
also, in his valuable and original observations on the volcanoes of the
Sandwich Islands, reminds us of the prodigious volume of atmospheric
water which must be absorbed into the interior of such large and lofty
domes, composed as they are entirely of porous lava. To this source
alone he refers the production of the steam by which the melted matter
is propelled upwards, even to the summit of cones three miles in
height.[762]

When treating of springs and overflowing wells, I have stated that
porous rocks are percolated by fresh water to great depths, and that
sea-water probably penetrates in the same manner through the rocks which
form the bed of the ocean. But, besides this universal circulation in
regions not far from the surface, it must be supposed that, wherever
earthquakes prevail, much larger bodies of water will be forced by the
pressure of the ocean into fissures at great depths, or swallowed up in
chasms; in the same manner as on the land, towns, houses, cattle, and
trees are sometimes engulfed. It will be remembered, that these chasms
often close again after houses have fallen into them; and for the same
reason, when water has penetrated to a mass of melted lava, the steam
into which it is converted may often rush out at a different aperture
from that by which the water entered.

The gases, it is said, exhaled from volcanoes, together with steam, are
such as would result from the decomposition of salt water, and the fumes
which escape from the Vesuvian lava have been observed to deposit common
salt.[763] The emission of free muriatic acid gas in great quantities is
also thought by many to favor the theory of the decomposition of the
salt contained in sea-water. It has been objected, however, that M.
Boussingault did not meet with this gas in his examination of the
elastic fluids evolved from the volcanoes of equatorial America; which
only give out aqueous vapor (in very large quantity), carbonic acid gas,
sulphurous acid gas, and sometimes fumes of sulphur.[764] In reply, Dr.
Daubeny has remarked, that muriatic acid may have ceased to be
disengaged, because the volcanic action has become languid in equatorial
America, and sea-water may no longer obtain admission.

M. Gay Lussac, while he avows his opinion that the decomposition of
water contributes largely to volcanic action, called attention,
nevertheless, to the supposed fact, that hydrogen had not been detected
in a separate form among the gaseous products of volcanoes; nor can it,
he says, be present; for, in that case, it would be inflamed in the air
by the red-hot stones thrown out during an eruption. Dr. Davy, in his
account of Graham Island, says, "I watched when the lightning was most
vivid, and the eruption of the greatest degree of violence, to see if
there was any inflammation occasioned by this natural electric
spark--any indication of the presence of inflammable gas; but in
vain."[765]

May not the hydrogen, Gay Lussac inquires, be combined with chlorine,
and produce muriatic acid? for this gas has been observed to be evolved
from Vesuvius--and the chlorine may have been derived from sea salt;
which was, in fact, extracted by simple washing from the Vesuvian lava
of 1822, in the proportion of nine per cent.[766] But it was answered,
that Sir H. Davy's experiments had shown, that hydrogen is not
combustible when mixed with muriatic acid gas; so that if muriatic gas
was evolved in large quantities, the hydrogen might be present without
inflammation.[767] M. Abich, on the other hand, assures us, "that
although it be true that vapor illuminated by incandescent lava has
often been mistaken for flame," yet he clearly detected in the eruption
of Vesuvius in 1834 the flame of hydrogen.[768]

M. Gay Lussac, in the memoir just alluded to, expressed doubt as to the
presence of sulphurous acid; but the abundant disengagement of this gas
during eruptions has been since ascertained: and thus all difficulty in
regard to the general absence of hydrogen in an inflammable state is
removed; for, as Dr. Daubeny suggests, the hydrogen of decomposed water
may unite with sulphur to form sulphuretted hydrogen gas, and this gas
will then be mingled with the sulphurous acid as it rises to the crater.
It is shown by experiment, that these gases mutually decompose each
other when mixed where steam is present; the hydrogen of the one
immediately uniting with the oxygen of the other to form water, while
the excess of sulphurous acid alone escapes into the atmosphere. Sulphur
is at the same time precipitated.

This explanation is sufficient; but it may also be observed that the
flame of hydrogen would rarely be visible during an eruption; as that
gas, when inflamed in a pure state, burns with a very faint blue flame,
which even in the night could hardly be perceptible by the side of
red-hot and incandescent cinders. Its immediate, conversion into water
when inflamed in the atmosphere, might also account for its not
appearing in a separate form.

Dr. Daubeny is of opinion that water containing atmospheric air may
descend from the surface of the earth to the volcanic foci, and that the
same process of combustion by which water is decomposed may deprive such
subterranean air of its oxygen. In this manner he explains the great
quantities of nitrogen evolved from volcanic vents and thermal waters,
and the fact that air disengaged from the earth in volcanic regions is
either wholly or in part deprived of its oxygen.

Sir H. Davy, in his memoir on the "Phenomena of Volcanoes," remarks,
that there was every reason to suppose in Vesuvius the existence of a
descending current of air; and he imagined that subterranean cavities
which threw out large volumes of steam during the eruption, might
afterwards, in the quiet state of the volcano, become filled with
atmospheric air.[769] The presence of ammoniacal salts in volcanic
emanations, and of ammonia (which is in part composed of nitrogen) in
lava, favors greatly the notion of air as well as water being deoxidated
in the interior of the earth.[770]

It has been alleged by Professor Bischoff that the slight specific
gravity of the metals of the alkalies is fatal to Davy's hypothesis, for
if the mean density of the earth, as determined by astronomers, surpass
that of all kinds of rocks, these metals cannot exist, at least not in
great quantities in the interior of the earth.[771] But Dr. Daubeny has
shown, that if we take the united specific gravity of potassium, sodium,
silicon, iron, and all the materials which, when united with oxygen,
constitute ordinary lava, and then compare their weight with lava of
equal bulk, the difference is not very material, the specific gravity of
the lava only exceeding by about one-fourth that of the unoxidized
metals. Besides, at great depths, the metallic bases of the earths and
alkalies may very probably be rendered heavier by pressure.[772] Nor is
it fair to embarrass the chemical theory of volcanoes with a doctrine so
purely gratuitous, as that which supposes the entire nucleus of the
planet to have been at first composed of unoxidated metals.

Professor Bunsen of Marburg, after analyzing the gases which escape from
the volcanic fumeroles and solfataras of Iceland, and after calculating
the quantity of hydrogen evolved between two eruptions, affirms, in
contradiction of opinions previously entertained, that the hydrogen
bears a perfect relation in quantity to the magnitude of the streams of
lava, assuming the fusion of these last to have been the result of the
heat evolved during the oxidation of alkaline and earthy metals, and
this to have been brought about by the decomposition of water. Yet after
having thus succeeded in removing the principal objection once so
triumphantly urged against Davy's hypothesis, Bunsen concludes by
declaring that the hydrogen evolved in volcanic regions cannot have been
generated by the decomposition of water coming in contact with alkaline
and earthy metallic bases. For, says the Professor, this process
presupposes the prevalence of a temperature in which carbonic acid
cannot exist in contact with hydrogen without suffering a partial
reduction to carbonic oxide; "and not a trace of carbonic oxide is ever
found in volcanic exhalations."[773] At the same time it will be seen,
by consulting the able memoirs of the Marburg chemist, that he supposes
many energetic kinds of chemical action to be continually going on in
the interior of the earth, capable of causing the disengagement of
hydrogen; and there can be no doubt that this gas may be a source of
innumerable new changes, capable of producing the local development of
internal heat.

_Cause of volcanic eruptions._--The most probable causes of a volcanic
outburst at the surface have been in a great degree anticipated in the
preceding speculations on the liquefaction of rocks and the generation
of gases. When a minute hole is bored in a tube filled with gas
condensed into a liquid, the whole becomes instantly aeriform, or, as
some writers have expressed it, "flashes into vapor," and often bursts
the tube. Such an experiment may represent the mode in which gaseous
matter may rush through a rent in the rocks, and continue to escape for
days or weeks through a small orifice, with an explosive power
sufficient to reduce every substance which opposes its passage into
small fragments or even dust. Lava may be propelled upwards at the same
time, and ejected in the form of scoriæ. In some places, where the fluid
lava lies at the bottom of a deep fissure, communicating on the one hand
with the surface, and on the other with a cavern in which a considerable
body of vapor has been formed, there may be an efflux of lava, followed
by the escape of gas. Eruptions often commence and close with the
discharge of vapor; and, when this is the case, the next outburst may be
expected to take place by the same vent, for the concluding evolution of
elastic fluids will keep open the duct, and leave it unobstructed.

The breaking out of lava from the side or base of a lofty cone, rather
than from the summit, may be attributed to the hydrostatic pressure to
which the flanks of the mountain are exposed, when the column of lava
has risen to a great height. Or if, before it has reached the top, there
should happen to be any stoppage in the main duct, the upward pressure
of the ascending column of gas and lava may burst a lateral opening.

In the case however of Mount Loa, in the Sandwich Islands, there appears
to be a singular want of connection or sympathy between the eruptions of
the central and the great lateral vent. The great volcanic cone alluded
to rises to the height of 13,760 feet above the level of the sea, having
a crater at its summit, from which powerful streams of lava have flowed
in recent times, and having another still larger crater, called Kilauea,
on its southeastern slope, about 4000 feet above the sea. This lateral
cavity resembles a huge quarry cut in the mountain's side, being about
1000 feet deep when in its ordinary state. It is seven miles and a half
in circuit, and scattered over its bottom, at different levels, are
lakes and pools of lava, always in a state of ebullition. The liquid in
one of these will sometimes sink 100 or 150 feet, while it is
overflowing in another at a higher elevation, there being, it should
seem, no communication between them. In like manner, lava overflows in
the summit crater of Mount Loa, nearly 14,000 feet high, while the great
lateral cauldron just alluded to (of Kilauea) continues as tranquil as
usual, affording no relief to any part of the gases or melted matter
which are forcing their way upwards in the centre of the mountain.
"How," asks Mr. Dana, "if there were any subterranean channel connecting
the two great vents, could this want of sympathy exist? How, according
to the laws of hydrostatic pressure, can a column of fluid stand 10,000
feet higher in one leg of the siphon than in the other?" The eruptions,
he observes, are not paroxysmal; on the contrary, the lava rises slowly
and gradually to the summit of the lofty cone, and then escapes there
without any commotion manifesting itself in Kilauea, a gulf always open
on the flanks of the same mountain. One conclusion, he says, is certain,
namely, _that volcanoes are no safety valves_ as they have been called;
for here two independent and apparently isolated centres of volcanic
activity, only sixteen miles distant from each other, are sustained in
one and the same cone.[774]

Without pretending to solve this enigma, I cannot refrain from
remarking, that the supposed independence of several orifices of
eruption in one crater like Kilauea, when adduced in confirmation of the
doctrine of two distinct sources of volcanic action underneath one
mountain, proves too much. No one can doubt, that the pools of lava in
Kilauea have been derived from some common reservoir, and have resulted
from a combination of causes commonly called volcanic, which are at work
in the interior at some unknown distance below. These causes have given
rise in Mount Loa to eruptions from many points, but principally from
one centre, so that a vast dome of ejected matter has been piled up. The
subsidiary crater has evidently never given much relief to the
imprisoned, heated, and liquefied matter, for Kilauea does not form a
lateral protuberance interfering with the general shape or uniform
outline of Mount Loa.

_Geysers of Iceland._--As aqueous vapor constitutes the most abundant of
the aeriform products of volcanoes in eruption, it may be well to
consider attentively a case in which steam is exclusively the moving
power--that of the Geysers of Iceland. These intermittent hot springs
occur in a district situated in the southwestern division of Iceland,
where nearly one hundred of them are said to break out within a circle
of two miles. That the water is of atmospheric origin, derived from rain
and melted snow, is proved, says Professor Bunsen, by the nitrogen which
rises from them either pure or mixed with other gases. The springs rise
through a thick current of lava, which may perhaps have flowed from
Mount Hecla, the summit of that volcano being seen from the spot at the
distance of more than thirty miles. In this district the rushing of
water is sometimes heard in chasms beneath the surface; for here, as on
Etna, rivers flow in subterranean channels through the porous and
cavernous lavas. It has more than once happened, after earthquakes, that
some of the boiling fountains have increased or diminished in violence
and volume, or entirely ceased, or that new ones have made their
appearance--changes which may be explained by the opening of new rents
and the closing of pre-existing fissures.

Few of the Geysers play longer than five or six minutes at a time,
although sometimes half an hour. The intervals between their eruptions
are for the most part very irregular. The Great Geyser rises out of a
spacious basin at the summit of a circular mound composed of siliceous
incrustations deposited from the spray of its waters. The diameter of
this basin, in one direction, is fifty-six feet, and forty-six in
another. (See fig. 94.) In the centre is a pipe seventy-eight feet in
perpendicular depth, and from eight to ten feet in diameter, but
gradually widening, as it rises into the basin. The inside of the basin
is whitish, consisting of a siliceous crust, and perfectly smooth, as
are likewise two small channels on the sides of the mound, down which
the water escapes when the bowl is filled to the margin. The circular
basin is sometimes empty, as represented in the following sketch; but is
usually filled with beautifully transparent water in a state of
ebullition. During the rise of the boiling water in the pipe, especially
when the ebullition is most violent, and when the water is thrown up in
jets, subterranean noises are heard, like the distant firing of cannon,
and the earth is slightly shaken. The sound then increases and the
motion becomes more violent, till at length a column of water is thrown
up, with loud explosions, to the height of one or two hundred feet.
After playing for a time like an artificial fountain, and giving off
great clouds of vapor, the pipe or tube is emptied; and a column of
steam, rushing up with amazing force and a thundering noise, terminates
the eruption.

[Illustration: Fig. 94.

View of the Crater of the Great Geyser in Iceland.[775]]

If stones are thrown into the crater, they are instantly ejected; and
such is the explosive force, that very hard rocks are sometimes shivered
by it into small pieces. Henderson found that by throwing a great
quantity of large stones into the pipe of Strockr, one of the Geysers,
he could bring on an eruption in a few minutes.[776] The fragments of
stone, as well as the boiling water, were thrown in that case to a much
greater height than usual. After the water had been ejected, a column of
steam continued to rush up with a deafening roar for nearly an hour; but
the Geyser, as if exhausted by this effort, did not send out a fresh
eruption when its usual interval of rest had elapsed. The account given
by Sir George Mackenzie of a Geyser which he saw in eruption in 1810
(see fig. 95), agrees perfectly with the above description by Henderson.
The steam and water rose for half an hour to the height of 70 feet, and
the white column remained perpendicular notwithstanding a brisk gale of
wind which was blowing against it. Stones thrown into the pipe were
projected to a greater height than the water. To leeward of the vapor a
heavy shower of rain was seen to fall.[777]

[Illustration: Fig. 95.

Eruption of the New Geyser in 1810. (Mackenzie.)]

Among the different theories proposed to account for these phenomena, I
shall first mention one suggested by Sir. J. Herschel. An imitation of
these jets, he says, may be produced on a small scale, by heating red
hot the stem of a tobacco pipe, filling the bowl with water, and so
inclining the pipe as to let the water run through the stem. Its escape,
instead of taking place in a continued stream, is then performed by a
succession of violent explosions, at first of steam alone, then of water
mixed with steam; and, as the pipe cools, almost wholly of water. At
every such paroxysmal escape of the water, a portion is driven back,
accompanied with steam, into the bowl. The intervals between the
explosions depend on the heat, length, and inclination of the pipe;
their continuance, on its thickness and conducting power.[778] The
application of this experiment to the Geysers merely requires that a
subterranean stream, flowing through the pores and crevices of lava,
should suddenly reach a fissure in which the rock is red hot or nearly
so. Steam would immediately be formed, which, rushing up the fissure,
might force up water along with it to the surface, while, at the same
time, part of the steam might drive back the water of the supply for a
certain distance towards its source. And when, after the space of some
minutes, the steam was all condensed, the water would return, and a
repetition of the phenomena take place.

[Illustration: Fig. 96.

Supposed reservoir and pipe of a Geyser in Iceland.[779]]

There is, however, another mode of explaining the action of the Geyser,
perhaps more probable than that above described. Suppose water
percolating from the surface of the earth to penetrate into the
subterranean cavity A D (fig. 96) by the fissures F F, while, at the
same time, steam at an extremely high temperature, such as is commonly
given out from the rents of lava currents during congelation, emanates
from the fissures C. A portion of the steam is at first condensed into
water, while the temperature of the water is raised by the latent heat
thus evolved, till, at last, the lower part of the cavity is filled with
boiling water and the upper with steam under high pressure. The
expansive force of the steam becomes, at length, so great, that the
water is forced up the fissure or pipe E B, and runs over the rim of the
basin. When the pressure is thus diminished, the steam in the upper part
of the cavity A expands, until all the water D is driven into the pipe;
and when this happens, the steam, being the lighter of the two fluids,
rushes up through the water with great velocity. If the pipe be choked
up artificially, even for a few minutes, a great increase of heat must
take place; for it is prevented from escaping in a latent form in steam;
so that the water is made to boil more violently, and this brings on an
eruption.

Professor Bunsen, before cited, adopts this theory to account for the
play of the "Little Geyser," but says it will not explain the phenomena
of the Great one. He considers this, like the others, to be a thermal
spring, having a narrow funnel-shaped tube in the upper part of its
course, where the walls of the channel have become coated over with
siliceous incrustations. At the mouth of this tube the water has a
temperature, corresponding to the pressure of the atmosphere, of about
212° Fahr., but at a certain depth below it is much hotter. This the
professor succeeded in proving by experiment; a thermometer suspended by
a string in the pipe rising to 266° Fahr., or no less than 48 degrees
above the boiling point. After the column of water has been expelled,
what remains in the basin and pipe is found to be much cooled.

Previously to these experiments of Bunsen and Descloizeaux, made in
Iceland in 1846, it would scarcely have been supposed possible that the
lower part of a free and open column of water could be raised so much in
temperature without causing a circulation of ascending and descending
currents, followed by an almost immediate equalization of heat. Such
circulation is no doubt impeded greatly by the sides of the well not
being vertical, and by numerous contractions of its diameter, but the
phenomenon may be chiefly due to another cause. According to recent
experiments on the cohesion of liquids by Mr. Donny of Ghent, it appears
that when water is freed from all admixture of air, its temperature can
be raised, even under ordinary atmospheric pressure, to 275° Fahr., so
much does the cohesion of its molecules increase[780] when they are not
separated by particles of air. As water long boiled becomes more and
more deprived of air, it is probably very free from such intermixture at
the bottom of the Geysers.

Among other results of the experiments of Bunsen and his companion, they
convinced themselves that the column of fluid filling the tube is
constantly receiving accessions of hot water from below, while it
becomes cooler above by evaporation on the broad surface of the basin.
They also came to a conclusion of no small interest, as bearing on the
probable mechanism of ordinary volcanic eruptions, namely that the tube
itself is the main seat or focus of mechanical force. This was proved by
letting down stones suspended by strings to various depths. Those which
were sunk to considerable distances from the surface were not cast up
again, whereas those nearer the mouth of the tube were ejected to great
heights. Other experiments also were made tending to demonstrate the
singular fact, that there is often scarce any motion below, when a
violent rush of steam and water is taking place above. It seems that
when a lofty column of water possesses a temperature increasing with the
depth, any slight ebullition or disturbance of equilibrium in the upper
portion may first force up water into the basin, and then cause it to
flow over the edge. A lower portion, thus suddenly relieved of part of
its pressure, expands and is converted into vapor more rapidly than the
first, owing to its greater heat. This allows the next subjacent
stratum, which is much hotter, to rise and flash into a gaseous form;
and this process goes on till the ebullition has descended from the
middle to near the bottom of the funnel.[781]

In speculating, therefore, on the mechanism of an ordinary volcanic
eruption, we may suppose that large subterranean cavities exist at the
depth of some miles below the surface of the earth, in which melted lava
accumulates; and when water containing the usual mixture of air
penetrates into these, the steam thus generated may press upon the lava
and force it up the duct of a volcano, in the same manner as a column of
water is driven up the pipe of a Geyser. In other cases we may suppose a
continuous column of liquid lava mixed with _red-hot water_ (for water
may exist in that state, as Professor Bunsen reminds us, under
pressure), and this column may have a temperature regularly increasing
downwards. A disturbance of equilibrium may first bring on an eruption
near the surface, by the expansion and conversion into gas of entangled
water and other constituents of what we call lava, so as to occasion a
diminution of pressure. More steam would then be liberated, carrying up
with it jets of melted rock, which being hurled up into the air may fall
in showers of ashes on the surrounding country, and at length, by the
arrival of lava and water more and more heated at the orifice of the
duct or the crater of the volcano, expansive power may be acquired
sufficient to expel a massive current of lava. After the eruption has
ceased, a period of tranquillity succeeds, during which fresh accessions
of heat are communicated from below, and additional masses of rock fused
by degrees, while at the same time atmospheric or sea water is
descending from the surface. At length the conditions required for a new
outburst are obtained, and another cycle of similar changes is renewed.

_Causes of earthquakes--wave-like motion._--I shall now proceed to
examine the manner in which the heat of the interior may give rise to
earthquakes. One of the most common phenomena attending subterranean
movements, is the undulatory motion of the ground. And this, says
Michell, will seem less extraordinary, if we call to mind the extreme
elasticity of the earth and the compressibility of even the most solid
materials. Large districts, he suggests, may rest on fluid lava; and,
when this is disturbed, its motions may be propagated through the
incumbent rocks. He also adds the following ingenious speculation:--"As
a small quantity of vapor almost instantly generated at some
considerable depth below the surface of the earth will produce a
vibratory motion, so a very large quantity (whether it be generated
almost instantly, or in any small portion of time) will produce a
wave-like motion. The manner in which this wave-like motion will be
propagated may, in some measure, be represented by the following
experiment:--Suppose a large cloth, or carpet (spread upon a floor), to
be raised at one edge, and then suddenly brought down again to the
floor; the air under it, being by this means propelled, will pass along
till it escapes at the opposite side, raising the cloth in a wave all
the way as it goes. In like manner, a large quantity of vapor may be
conceived to raise the earth in a wave, as it passes along between the
strata, which it may easily separate in a horizontal direction, there
being little or no cohesion between one stratum and another. The part of
the earth that is first raised being bent from its natural form, will
endeavor to restore itself by its elasticity; and the parts next to it
being to have their weight supported by the vapor, which will insinuate
itself under them, will be raised in their turn, till it either finds
some vent, or is again condensed by the cold into water, and by that
means prevented from proceeding any farther."[782] In a memoir published
in 1843, on the structure of the Appalachian chain, by the Professors
Rogers,[783] the following hypothesis is proposed as "simpler and more
in accordance with dynamical considerations, and the recorded
observations on earthquakes."--"In place," say they, "of supposing it
possible for a body of vapor or gaseous matter to pass horizontally
between the strata, or even between the crust and the fluid lava upon
which it floats, and with which it must be closely entangled, we are
inclined to attribute the movement to an _actual pulsation_, engendered
in the _molten matter itself_, by a linear disruption under enormous
tension, giving vent explosively to elastic vapors, escaping either to
the surface, or into cavernous spaces beneath. According to this
supposition, the movement of the subterranean vapors would be _towards_,
and not from, the disrupted belt, and the oscillation of the crust would
originate in the tremendous and sudden disturbance of the previous
pressure on the surface of the lava mass below, brought about by the
instantaneous and violent rending of the overlying strata."

This theory requires us to admit that the crust of the earth is so
flexible, that it can assume the form, and follow the motion of an
undulation in the fluid below. Even if we grant this, says Mr. Mallet,
another more serious objection presents itself, viz. the great velocity
attributed to the transit of the wave in the subterranean sea of lava.
We are called upon to admit that the speed of the wave below equals that
of the true earthquake shock at the surface, which is so immense, that
it is not inferior to the velocity of sound in the same solids. But the
undulation in the fluid below must follow the laws of a tidal wave, or
of the great sea-wave already spoken of. "Its velocity, like that of the
tidal wave of our seas, will be a function of its length and of the
depth of the fluid, diminished in this case by certain considerations as
to the density and degree of viscidity of the liquid; and although it
would be at present impossible, for want of data, to calculate the exact
velocity with which this subterraneous lava-wave could move, it may be
certainly affirmed that its velocity would be immeasurably short of the
observed or theoretic velocity of the great earth-wave, or true shock in
earthquakes."[784]

_Liquid gases._--The rending and upheaving of continental masses are
operations which are not difficult to explain, when we are once
convinced that heat, of sufficient power, not only to melt but to reduce
to a gaseous form a great variety of substances, is accumulated in
certain parts of the interior. We see that elastic fluids are capable of
projecting solid masses to immense heights in the air; and the volcano
of Cotopaxi has been known to throw out, to the distance of eight or
nine miles, a mass of rock about one hundred cubic yards in volume. When
we observe these aeriform fluids rushing out from particular vents for
months, or even years, continuously, what power may we not expect them
to exert in other places, where they happen to be confined under an
enormous weight of rock?

The experiments of Faraday and others have shown, within the last twelve
years, that many of the gases, including all those which are most
copiously disengaged from volcanic vents, as the carbonic, sulphurous,
and muriatic acids, may be condensed into liquids by pressure. At
temperatures of from 30° to 50° F., the pressure required for this
purpose varies from fifteen to fifty atmospheres; and this amount of
pressure we may regard as very insignificant in the operations of
nature. A column of Vesuvian lava that would reach from the lip of the
crater to the level of the sea, must be equal to about three hundred
atmospheres; so that, at depths which may be termed moderate in the
interior of the crust of the earth, the gases may be condensed into
liquids, even at very high temperatures. The method employed to reduce
some of these gases to a liquid state is, to confine the materials, from
the mutual action of which they are evolved, in tubes hermetically
sealed, so that the accumulated pressure of the vapor, as it rises and
expands, may force some part of it to assume the liquid state. A similar
process may, and indeed must, frequently take place in subterranean
caverns and fissures, or even in the pores and cells of many rocks; by
which means, a much greater store of expansive power may be _packed_
into a small space than could happen if these vapors had not the
property of becoming liquid. For, although the gas occupies much less
room in a liquid state, yet it exerts exactly the same pressure upon the
sides of the containing cavity as if it remained in the form of vapor.

If a tube, whether of glass or other materials, filled with condensed
gas, have its temperature slightly raised, it will often burst; for a
slight increment of heat causes the elasticity of the gas to increase in
a very high ratio. We have only to suppose certain rocks, permeated by
these liquid gases (as porous strata are sometimes filled with water),
to have their temperature raised some hundred degrees, and we obtain a
power capable of lifting superincumbent masses of almost any conceivable
thickness; while, if the depth at which the gas is confined be great,
there is no reason to suppose that any other appearances would be
witnessed by the inhabitants of the surface than vibratory movements and
rents, from which no vapor might escape. In making their way through
fissures a very few miles only in length, or in forcing a passage
through soft yielding strata, the vapors may be cooled and absorbed by
water. For water has a strong affinity to several of the gases, and will
absorb large quantities, with a very slight increase of volume. In this
manner, the heat or the volume of springs may be augmented, and their
mineral properties made to vary.

_Connection between the state of the atmosphere and earthquakes._--The
inhabitants of Stromboli, who are mostly fishermen, are said to make use
of that volcano as a weather-glass, the eruptions being comparatively
feeble when the sky is serene, but increasing in turbulence during
tempestuous weather, so that in winter the island often seems to shake
from its foundations. Mr. P. Scrope, after calling attention to these
and other analogous facts, first started the idea (as long ago as the
year 1825) that the diminished pressure of the atmosphere, the
concomitant of stormy weather, may modify the intensity of the volcanic
action. He suggests that where liquid lava communicates with the
surface, as in the crater of Stromboli, it may rise or fall in the vent
on the same principle as mercury in a barometer; because the ebullition
or expansive power of the steam contained in the lava would be checked
by every increase, and augmented by every diminution of weight. In like
manner, if a bed of liquid lava be confined at an immense depth below
the surface, its expansive force may be counteracted partly by the
weight of the incumbent rocks, and also in part by atmospheric pressure
acting contemporaneously on a vast superficial area. In that case, if
the upheaving force increase gradually in energy, it will at length be
restrained by only the slightest degree of superiority in the antagonist
or repressive power, and then the equilibrium may be suddenly destroyed
by any cause, such as an ascending draught of air, which is capable of
depressing the barometer. In this manner we may account for the
remarkable coincidence so frequently observed between the state of the
weather and subterranean commotions, although it must be admitted that
earthquakes and volcanic eruptions react in their turn upon the
atmosphere, so that disturbances of the latter are generally the
consequences rather than the forerunners of volcanic disturbances.[785]

From an elaborate catalogue of the earthquakes experienced in Europe and
Syria during the last fifteen centuries, M. Alexis Perrey has deduced
the conclusion that the number which happen in the winter season
preponderates over those which occur in any one of the other seasons of
the year, there being, however, some exceptions to this rule, as in the
Pyrenees. Curious and valuable as are these data, M. d'Archiac justly
remarks, in commenting upon them, that they are not as yet sufficiently
extensive or accordant in different regions, to entitle us to deduce any
general conclusions from them respecting the laws of subterranean
movements throughout the globe.[786]

_Permanent elevation and subsidence._--It is easy to conceive that the
shattered rocks may assume an arched form during a convulsion, so that
the country above may remain permanently upheaved. In other cases gas
may drive before it masses of liquid lava, which may thus be injected
into newly opened fissures. The gas having then obtained more room, by
the forcing up of the incumbent rocks, may remain at rest; while the
lava congealing in the rents may afford a solid foundation for the newly
raised district.

Experiments have recently been made in America, by Colonel Totten, to
ascertain the ratio according to which some of the stones commonly used
in architecture expand with given increments of heat.[787] It was found
impossible, in a country where the annual variation of temperature was
more than 90° F., to make a coping of stones, five feet in length, in
which the joints should fit so tightly as not to admit water between the
stone and the cement; the annual contraction and expansion of the stones
causing, at the junctions, small crevices, the width of which varied
with the nature of the rock. It was ascertained that fine-grained
granite expanded with 1° F. at the rate of ·000004825; while crystalline
marble ·000005668; and red sandstone ·000009532, or about twice as much
as granite.

Now, according to this law of expansion, a mass of sandstone a mile in
thickness, which should have its temperature raised 200° F., would lift
a superimposed layer of rock to the height of ten feet above its former
level. But, suppose a part of the earth's crust, one hundred miles in
thickness and equally expansive, to have its temperature raised 600° or
800°, this might produce an elevation of between two and three thousand
feet. The cooling of the same mass might afterwards cause the overlying
rocks to sink down again and resume their original position. By such
agency we might explain the gradual rise of Scandinavia or the
subsidence of Greenland, if this last phenomenon should also be
established as a fact on farther inquiry.

It is also possible that as the clay in Wedgwood's pyrometer contracts,
by giving off its water, and then, by incipient vitrification; so, large
masses of argillaceous strata on the earth's interior may shrink, when
subjected to heat and chemical changes, and allow the incumbent rocks to
subside gradually.

Moreover, if we suppose that lava cooling slowly at great depths may be
converted into various granitic rocks, we obtain another source of
depression; for, according to the experiments of Deville and the
calculations of Bischoff, the contraction of granite when passing from a
melted or plastic to a solid and crystalline state must be more than ten
per cent.[788] The sudden subsidence of land may also be occasioned by
subterranean caverns giving way, when gases are condensed, or when they
escape through newly-formed crevices. The subtraction, moreover, of
matter from certain parts of the interior, by the flowing of lava and of
mineral springs, must, in the course of ages, cause vacuities below, so
that the undermined surface may at length fall in.

_The balance of dry land, how preserved._--In the present state of our
knowledge, we cannot pretend to estimate the average number of
earthquakes which may happen in the course of a single year. As the area
of the ocean is nearly three times that of the land, it is probable that
about three submarine earthquakes may occur for one exclusively
continental; and when we consider the great frequency of slight
movements in certain districts, we can hardly suppose that a day, if,
indeed, an hour, ever passes without one or more shocks being
experienced in some part of the globe. We have also seen that in Sweden,
and other countries, changes in the relative level of sea and land may
take place without commotion, and these perhaps produce the most
important geographical and geological changes; for the position of land
may be altered to a greater amount by an elevation or depression of one
inch over a vast area, than by the sinking of a more limited tract, such
as the forest of Aripao, to the depth of many fathoms at once.[789]

It must be evident, from the historical details above given, that the
force of subterranean movement, whether intermittent or continuous,
whether with or without disturbance, does not operate at random, but is
developed in certain regions only; and although the alterations produced
during the time required for the occurrence of a few volcanic eruptions
may be inconsiderable, we can hardly doubt that, during the ages
necessary for the formation of large volcanic cones, composed of
thousands of lava currents, shoals might be converted into lofty
mountains, and low lands into deep seas.

In a former chapter (p. 198), I have stated that aqueous and igneous
agents may be regarded as antagonist forces; the aqueous laboring
incessantly to reduce the inequalities of the earth's surface to a
level, while the igneous are equally active in renewing the unevenness
of the surface. By some geologists it has been thought that the
levelling power of running water was opposed rather to the _elevating_
force of earthquakes than to their action generally. This opinion is,
however, untenable; for the sinking down of the bed of the ocean is one
of the means by which the gradual submersion of land is prevented. The
depth of the sea cannot be increased at any one point without a
universal fall of the waters, nor can any partial deposition of sediment
occur without the displacement of a quantity of water of equal volume,
which will raise the sea, though in an imperceptible degree, even to the
antipodes. The preservation, therefore, of the dry land may sometimes be
effected by the subsidence of part of the earth's crust (that part,
namely, which is covered by the ocean), and in like manner an upheaving
movement must often tend to destroy land; for if it render the bed of
the sea more shallow, it will displace a certain quantity of water, and
thus tend to submerge low tracts.

Astronomers having proved (see above, p. 129) that there has been no
change in the diameter of the earth during the last two thousand years,
we may assume it as probable, that the dimensions of the planet remain
uniform. If, then, we inquire in what manner the force of earthquakes
must be regulated, in order to restore perpetually the inequalities of
the surface which the levelling power of water tends to efface, it will
be found, that the amount of depression must exceed that of elevation.
It would be otherwise if the action of volcanoes and mineral springs
were suspended; for then the forcing outwards of the earth's envelope
ought to be no more than equal to its sinking in.

To understand this proposition more clearly, it must be borne in mind,
that the deposits of rivers and currents probably add as much to the
height of lands which are rising, as they take from those which have
risen. Suppose a large river to bring down sediment to a part of the
ocean two thousand feet deep, and that the depth of this part is
gradually reduced by the accumulation of sediment till only a shoal
remains, covered by water at high tides; if now an upheaving force
should uplift this shoal to the height of 2000 feet, the result would be
a mountain 2000 feet high. But had the movement raised the same part of
the bottom of the sea before the sediment of the river had filled it up;
then, instead of changing a shoal into a mountain 2000 feet high, it
would only have converted a deep sea into a shoal.

It appears, then, that the operations of the earthquake are often such
as to cause the levelling power of water to counteract itself; and,
although the idea may appear paradoxical, we may be sure, wherever we
find hills and mountains composed of stratified deposits, that such
inequalities of the surface would have had no existence if water, at
some former period, had not been laboring to reduce the earth's surface
to one level.

But, besides the transfer of matter by running water from the continents
to the ocean, there is a constant transportation from below upwards, by
mineral springs and volcanic vents. As mountain masses are, in the
course of ages, created by the pouring forth of successive streams of
lava, so stratified rocks, of great extent, originate from the
deposition of carbonate of lime, and other mineral ingredients, with
which springs are impregnated. The surface of the land, and portions of
the bottom of the sea, being thus raised, the external accessions due to
these operations would cause the dimensions of the planet to enlarge
continually, if the amount of depression of the earth's crust were no
more than equal to the elevation. In order, therefore, that the mean
diameter of the earth should remain uniform, and the unevenness of the
surface be preserved, it is necessary that the amount of subsidence
should be in excess. And such a predominance of depression is far from
improbable, on mechanical principles, since every upheaving movement
must be expected either to produce caverns in the mass below, or to
cause some diminution of its density. Vacuities must, also, arise from
the subtraction of the matter poured out from volcanoes and mineral
springs, or from the contraction of argillaceous masses by subterranean
heat; and the foundations having been thus weakened, the earth's crust,
shaken and rent by reiterated convulsions, must, in the course of time,
fall in.

If we embrace these views, important geological consequences will
follow; since, if there be, upon the whole, more subsidence than
elevation, the average depth to which former surfaces have sunk beneath
their original level must exceed the height which ancient marine strata
have attained above the sea. If, for example, marine strata, about the
age of our chalk and greensand, have been lifted up in Europe to an
extreme height of more than eleven thousand feet, and a mean elevation
of some hundreds, we may conclude that certain parts of the surface,
which existed when those strata were deposited, have sunk to an extreme
depth of _more than_ eleven thousand feet below their original level,
and to a mean depth of _more than_ a few hundreds.

In regard to faults, also, we must infer, according to the hypothesis
now proposed, that a greater number have arisen from the sinking down
than from the elevation of rocks.

To conclude: it seems to be rendered probable, by the views above
explained, that the constant repair of the land, and the subserviency of
our planet to the support of terrestrial as well as aquatic species, are
secured by the elevating and depressing power of causes acting in the
interior of the earth; which, although so often the source of death and
terror to the inhabitants of the globe--visiting in succession every
zone, and filling the earth with monuments of ruin and disorder--are
nevertheless the agents of a conservative principle above all others
essential to the stability of the system.




BOOK III.




CHAPTER XXXIII.

CHANGES OF THE ORGANIC WORLD NOW IN PROGRESS.


  Division of the subject--Examination of the question, Whether
    species have a real existence in nature?--Importance of this
    question in geology--Sketch of Lamarck's arguments in favor of the
    transmutation of species, and his conjectures respecting the origin
    of existing animals and plants--His theory of the transformation of
    the orang-outang into the human species.


The last book, from chapters fourteen to thirty-three inclusive, was
occupied with the consideration of the changes brought about on the
earth's surface, within the period of human observation, by inorganic
agents; such, for example, as rivers, marine currents, volcanoes, and
earthquakes. But there is another class of phenomena relating to the
organic world, which have an equal claim on our attention, if we desire
to obtain possession of all the preparatory knowledge respecting the
existing course of nature, which may be available in the interpretation
of geological monuments. It appeared from our preliminary sketch of the
progress of the science, that the most lively interest was excited among
its earlier cultivators, by the discovery of the remains of animals and
plants in the interior of mountains frequently remote from the sea. Much
controversy arose respecting the nature of these remains, the causes
which may have brought them into so singular a position, and the want of
a specific agreement between them and known animals and plants. To
qualify ourselves to form just views on these curious questions, we must
first study the present condition of the animate creation on the globe.

This branch of our inquiry naturally divides itself into two parts:
first, we may examine the vicissitudes to which species are subject;
secondly, the processes by which certain individuals of these species
occasionally become fossil. The first of these divisions will lead us,
among other topics, to inquire, first, whether species have a real and
permanent existence in nature? or whether they are capable, as some
naturalists pretend, of being indefinitely modified in the course of a
long series of generations? Secondly, whether, if species have a real
existence, the individuals composing them have been derived originally
from many similar stocks, or each from one only, the descendants of
which have spread themselves gradually from a particular point over the
habitable lands and waters? Thirdly, how far the duration of each
species of animal and plant is limited by its dependence on certain
fluctuating and temporary conditions in the state of the animate and
inanimate world? Fourthly, whether there be proofs of the successive
extermination of species in the ordinary course of nature, and whether
there be any reason for conjecturing that new animals and plants are
created from time to time, to supply their place?

_Whether species have a real existence in nature._--Before we can
advance a step in our proposed inquiry, we must be able to define
precisely the meaning which we attach to the term species. This is even
more necessary in geology than in the ordinary studies of the
naturalist; for they who deny that such a thing as a species exists,
concede nevertheless that a botanist or zoologist may reason as if the
specific character were constant, because they confine their
observations to a brief period of time. Just as the geographer, in
constructing his maps from century to century, may proceed as if the
apparent places of the fixed stars remained absolutely the same, and as
if no alteration were brought about by the precession of the equinoxes;
so, it is said, in the organic world, the stability of a species may be
taken as absolute, if we do not extend our views beyond the narrow
period of human history; but let a sufficient number of centuries
elapse, to allow of important revolutions in climate, physical
geography, and other circumstances, and the characters, say they, of the
descendants of common parents may deviate indefinitely from their
original type.

Now, if these doctrines be tenable, we are at once presented with a
principle of incessant change in the organic world; and no degree of
dissimilarity in the plants and animals which may formerly have existed,
and are found fossil, would entitle us to conclude that they may not
have been the prototypes and progenitors of the species now living.
Accordingly M. Geoffroy St. Hilaire has declared his opinion, that there
has been an uninterrupted succession in the animal kingdom, effected by
means of generation, from the earliest ages of the world up to the
present day, and that the ancient animals whose remains have been
preserved in the strata, however different, may nevertheless have been
the ancestors of those now in being. This notion is not very generally
received, but we are not warranted in assuming the contrary, without
fully explaining the data and reasoning by which it may be refuted.

I shall begin by stating as concisely as possible all the facts and
ingenious arguments by which the theory has been supported; and for this
purpose I cannot do better than offer the reader a rapid sketch of
Lamarck's statement of the proofs which he regards as confirmatory of
the doctrine, and which he has derived partly from the works of his
predecessors and in part from original investigations.

His proofs and inferences will be best considered in the order in which
they appear to have influenced his mind, and I shall then point out some
of the results to which he was led while boldly following out his
principles to their legitimate consequences.

_Lamarck's arguments in favor of the transmutation of species._--The
name of species, observes Lamarck, has been usually applied to "every
collection of similar individuals produced by other individuals like
themselves."[790] This definition, he admits, is correct; because every
living individual bears a very close resemblance to those from which it
springs. But this is not all which is usually implied by the term
species; for the majority of naturalists agree with Linnæus in supposing
that all the individuals propagated from one stock have certain
distinguishing characters in common, which will never vary, and which
have remained the same since the creation of each species.

In order to shake this opinion, Lamarck enters upon the following line
of argument:--The more we advance in the knowledge of the different
organized bodies which cover the surface of the globe, the more our
embarrassment increases, to determine what ought to be regarded as a
species, and still more how to limit and distinguish genera. In
proportion as our collections are enriched, we see almost every void
filled up, and all our lines of separation effaced! We are reduced to
arbitrary determinations, and are sometimes fain to seize upon the
slight differences of mere varieties, in order to form characters for
what we choose to call a species; and sometimes we are induced to
pronounce individuals but slightly differing, and which others regard as
true species, to be varieties.

The greater the abundance of natural objects assembled together, the
more do we discover proofs that every thing passes by insensible shades
into something else; that even the more remarkable differences are
evanescent, and that nature has, for the most part, left us nothing at
our disposal for establishing distinctions, save trifling, and, in some
respects, puerile particularities.

We find that many genera amongst animals and plants are of such an
extent, in consequence of the number of species referred to them, that
the study and determination of these last has become almost
impracticable. When the species are arranged in a series, and placed
near to each other, with due regard to their natural affinities, they
each differ in so minute a degree from those next adjoining, that they
almost melt into each other, and are in a manner confounded together. If
we see isolated species, we may presume the absence of some more closely
connected, and which have not yet been discovered. Already are there
genera, and even entire orders--nay, whole classes, which present an
approximation to the state of things here indicated.

If, when species have been thus placed in a regular series, we select
one, and then, making a leap over several intermediate ones, we take a
second, at some distance from the first, these two will, on comparison,
be seen to be very dissimilar; and it is in this manner that every
naturalist begins to study the objects which are at his own door. He
then finds it an easy task to establish generic and specific
distinctions; and it is only when his experience is enlarged, and when
he has made himself master of the intermediate links, that his
difficulties and ambiguities begin. But while we are thus compelled to
resort to trifling and minute characters in our attempt to separate the
species, we find a striking disparity between individuals which we know
to have descended from a common stock; and these newly acquired
peculiarities are regularly transmitted from one generation to another,
constituting what are called _races_.

From a great number of facts, continues the author, we learn that in
proportion as the individuals of one of our species change their
situation, climate, and manner of living, they change also, by little
and little, the consistence and proportions of their parts, their form,
their faculties, and even their organization, in such a manner that
every thing in them comes at last to participate in the mutations to
which they have been exposed. Even in the same climate, a great
difference of situation and exposure causes individuals to vary; but if
these individuals continue to live and to be reproduced under the same
difference of circumstances, distinctions are brought about in them
which become in some degree essential to their existence. In a word, at
the end of many successive generations, these individuals, which
originally belonged to another species, are transformed into a new and
distinct species.[791]

Thus, for example, if the seeds of a grass, or any other plant which
grows naturally in a moist meadow, be accidentally transported, first to
the slope of some neighboring hill, where the soil, although at a
greater elevation, is damp enough to allow the plant to live; and if,
after having lived there, and having been several times regenerated, it
reaches by degrees the drier and almost arid soil of a mountain
declivity, it will then, if it succeeds in growing, and perpetuates
itself for a series of generations, be so changed that botanists who
meet with it will regard it as a particular species.[792] The
unfavorable climate in this case, deficiency of nourishment, exposure to
the winds, and other causes, give rise to a stunted and dwarfish race,
with some organ more developed than others, and having proportions often
quite peculiar.

What nature brings about in a great lapse of time, we occasion suddenly
by changing the circumstances in which a species has been accustomed to
live. All are aware that vegetables taken from their birthplace, and
cultivated in gardens, undergo changes which render them no longer
recognizable as the same plants. Many which were naturally hairy become
smooth, or nearly so; a great number of such as were creepers and
trailed along the ground, rear their stalks and grow erect. Others lose
their thorns or asperities; others, again, from the ligneous state which
their stem possessed in hot climates, where they were indigenous, pass
to the herbaceous; and, among them, some which were perennials become
mere annuals. So well do botanists know the effects of such changes of
circumstances, that they are averse to describe species from garden
specimens, unless they are sure that they have been cultivated for a
very short period.

"Is not the cultivated wheat" (_Triticum sativum_), asks Lamarck, "a
vegetable brought by man into the state in which we now see it? Let any
one tell me in what country a similar plant grows wild, unless where it
has escaped from cultivated fields? Where do we find in nature our
cabbages, lettuces, and other culinary vegetables, in the state in which
they appear in our gardens? Is it not the same in regard to a great
quantity of animals which domesticity has changed or considerably
modified?"[793] Our domestic fowls and pigeons are unlike any wild
birds. Our domestic ducks and geese have lost the faculty of raising
themselves into the higher regions of the air, and crossing extensive
countries in their flight, like the wild ducks and wild geese from which
they were originally derived. A bird which we breed in a cage cannot,
when restored to liberty, fly like others of the same species which have
been always free. This small alteration of circumstances, however, has
only diminished the power of flight, without modifying the form of any
part of the wings. But when individuals of the same race are retained in
captivity during a considerable length of time, the form even of their
parts is gradually made to differ, especially if climate, nourishment,
and other circumstances be also altered.

The numerous races of dogs which we have produced by domesticity are
nowhere to be found in a wild state. In nature we should seek in vain
for mastiffs, harriers, spaniels, greyhounds, and other races, between
which the differences are sometimes so great that they would be readily
admitted as specific between wild animals; "yet all these have sprung
originally from a single race, at first approaching very near to a wolf,
if, indeed, the wolf be not the true type which at some period or other
was domesticated by man."

Although important changes in the nature of the places which they
inhabit modify the organization of animals as well as vegetables; yet
the former, says Lamarck, require more time to complete a considerable
degree of transmutation; and, consequently, we are less sensible of such
occurrences. Next to a diversity of the medium in which animals or
plants may live, the circumstances which have most influence in
modifying their organs are differences in exposure, climate, the nature
of the soil, and other local particulars. These circumstances are as
varied as are the characters of the species, and, like them, pass by
insensible shades into each other, there being every intermediate
gradation between the opposite extremes. But each locality remains for a
very long time the same, and is altered so slowly that we can only
become conscious of the reality of the change by consulting geological
monuments, by which we learn that the order of things which how reigns
in each place has not always prevailed, and by inference anticipate that
it will not always continue the same.[794]

Every considerable alteration in the local circumstances in which each
race of animals exists causes a change in their wants, and these new
wants excite them to new actions and habits. These actions require the
more frequent employment of some parts before but slightly exercised,
and then greater development follows as a consequence of their more
frequent use. Other organs no longer in use are impoverished and
diminished in size, nay, are sometimes entirely annihilated, while in
their place new parts are insensibly produced for the discharge of new
functions.[795]

I must here interrupt the author's argument, by observing, that no
positive fact is cited to exemplify the substitution of some _entirely
new_ sense, faculty, or organ, in the room of some other suppressed as
useless. All the instances adduced go only to prove that the dimensions
and strength of members and the perfection of certain attributes may, in
a long succession of generations, be lessened and enfeebled by disuse;
or, on the contrary, be matured and augmented by active exertion; just
as we know that the power of scent is feeble in the greyhound, while its
swiftness of pace and its acuteness of sight are remarkable--that the
harrier and stag-hound, on the contrary, are comparatively slow in their
movements, but excel in the sense of smelling.

It was necessary to point out to the reader this important chasm in the
chain of evidence, because he might otherwise imagine that I had merely
omitted the illustrations for the sake of brevity; but the plain truth
is, that there were no examples to be found; and when Lamarck talks "of
the efforts of internal sentiment," "the influence of subtle fluids,"
and "acts of organization," as causes whereby animals and plants may
acquire _new organs_, he substitutes names for things; and, with a
disregard to the strict rules of induction, resorts to fictions, as
ideal as the "plastic virtue," and other phantoms of the geologists of
the middle ages.

It is evident that, if some well-authenticated facts could have been
adduced to establish one complete step in the process of transformation,
such as the appearance, in individuals descending from a common stock,
of a sense or organ entirely new, and a complete disappearance of some
other enjoyed by their progenitors, time alone might then be supposed
sufficient to bring about any amount of metamorphosis. The gratuitous
assumption, therefore, of a point so vital to the theory of
transmutation, was unpardonable on the part of its advocate.

But to proceed with the system: it being assumed as an undoubted fact,
that a change of external circumstances may cause one organ to become
entirely obsolete, and a new one to be developed, such as never before
belonged to the species, the following proposition is announced, which,
however staggering and absurd it may seem, is logically deduced from the
assumed premises. It is not the organs, or, in other words, the nature
and form of the parts of the body of an animal, which have given rise to
its habits, and its particular faculties; but, on the contrary, its
habits, its manner of living, and those of its progenitors, have in the
course of time determined the form of its body, the number and condition
of its organs--in short, the faculties which it enjoys. Thus otters,
beavers, waterfowl, turtles, and frogs, were not made web-footed in
order that they might swim; but their wants having attracted them to the
water in search of prey, they stretched out the toes of their feet to
strike the water and move rapidly along its surface. By the repeated
stretching of their toes, the skin which united them at the base
acquired a habit of extension, until, in the course of time, the broad
membranes which now connect their extremities were formed.

In like manner, the antelope and the gazelle were not endowed with light
agile forms, in order that they might escape by flight from carnivorous
animals; but, having been exposed to the danger of being devoured by
lions, tigers, and other beasts of prey, they were compelled to exert
themselves in running with great celerity; a habit which, in the course
of many generations, gave rise to the peculiar slenderness of their
legs, and the agility and elegance of their forms.

The camelopard was not gifted with a long flexible neck because it was
destined to live in the interior of Africa, where the soil was arid and
devoid of herbage; but, being reduced by the nature of that country to
support itself on the foliage of lofty trees, it contracted a habit of
stretching itself up to reach the high boughs, until its neck became so
elongated that it could raise its head to the height of twenty feet
above the ground.

Another line of argument is then entered upon, in farther corroboration
of the instability of species. In order, it is said, that individuals
should perpetuate themselves unaltered by generation, those belonging to
one species ought never to ally themselves to those of another; but such
sexual unions do take place, both among plants and animals; and although
the offspring of such irregular connections are usually sterile, yet
such is not always the case. Hybrids have sometimes proved prolific,
where the disparity between the species was not too great; and by this
means alone, says Lamarck, varieties may gradually be created by near
alliances, which would become races, and in the course of time would
constitute what we term species.[796]

But if the soundness of all these arguments and inferences be admitted,
we are next to inquire, what were the original types of form,
organization, and instinct, from which the diversities of character, as
now exhibited by animals and plants, have been derived? We know that
individuals which are mere varieties of the same species would, if their
pedigree could be traced back far enough, terminate in a single stock;
so, according to the train of reasoning before described, the species of
a genus, and even the genera of a great family, must have had a common
point of departure. What, then, was the single stem from which so many
varieties of form have ramified? Were there many of these, or are we to
refer the origin of the whole animate creation, as the Egyptian priests
did that of the universe, to a single egg?

In the absence of any positive data for framing a theory on so obscure a
subject, the following considerations were deemed of importance to guide
conjecture.

In the first place, if we examine the whole series of known animals,
from one extremity to the other, when they are arranged in the order of
their natural relations, we find that we may pass progressively, or, at
least, with very few interruptions, from beings of more simple to those
of a more compound structure; and, in proportion as the complexity of
their organization increases, the number and dignity of their faculties
increase also. Among plants, a similar approximation to a graduated
scale of being is apparent, Secondly, it appears, from geological
observations, that plants and animals of more simple organization
existed on the globe before the appearance of those of more compound
structure, and the latter were successively formed at more modern
periods; each new race being more fully developed than the most perfect
of the preceding era.

Of the truth of the last-mentioned geological theory, Lamarck seems to
have been fully persuaded; and he also shows that he was deeply
impressed with a belief prevalent amongst the older naturalists, that
the primeval ocean invested the whole planet long after it became the
habitation of living beings; and thus he was inclined to assert the
priority of the types of marine animals to those of the terrestrial, so
as to fancy, for example, that the testacea of the ocean existed first,
until some of them, by gradual evolution, were _improved_ into those
inhabiting the land.

These speculative views had already been, in a great degree, anticipated
by Demaillet in his Telliamed, and by several modern writers; so that
the tables were completely turned on the philosophers of antiquity, with
whom it was a received maxim, that created things were always most
perfect when they came first from the hands of their Maker; and that
there was a tendency to progressive deterioration in sublunary things
when left to themselves--


        ----omnia fatis
  In pejus ruere, ac retrò sublapsa referri.


So deeply was the faith of the ancient schools of philosophy imbued with
this dóctrine, that, to check this universal proneness to degeneracy,
nothing less than the reintervention of the Deity was thought adequate;
and it was held, that thereby the order, excellence, and pristine energy
of the moral and physical world had been repeatedly restored.

But when the possibility of the indefinite modification of individuals
descending from common parents was once assumed, as also the geological
inference respecting the progressive development of organic life, it was
natural that the ancient dogma should be rejected, or rather reversed,
and that the most simple and imperfect forms and faculties should be
conceived to have been the originals whence all others were developed.
Accordingly, in conformity to these views, inert matter was supposed to
have been first endowed with life; until, in the course of ages,
sensation was superadded to mere vitality: sight, hearing, and the
other senses were afterwards acquired; then instinct and the mental
faculties; until, finally, by virtue of the tendency of things to
_progressive improvement_, the irrational was developed in the rational.

The reader, however, will immediately perceive that when all the higher
orders of plants and animals were thus supposed to be comparatively
modern, and to have been derived in a long series of generations from
those of more simple conformation, some farther hypothesis became
indispensable, in order to explain why, after an indefinite lapse of
ages, there were still so many beings of the simplest structure. Why
have the majority of existing creatures remained stationary throughout
this long succession of epochs, while others have made such prodigious
advances? Why are there such multitudes of infusoria and polyps, or of
confervæ and other cryptogamic plants? Why, moreover, has the process of
development acted with such unequal and irregular force on those classes
of beings which have been greatly perfected, so that there are wide
chasms in the series; gaps so enormous, that Lamarck fairly admits we
can never expect to fill them up by future discoveries?

The following hypothesis was provided to meet these objections. Nature,
we are told, is not an intelligence, nor the Deity; but a delegated
power--a mere instrument--a piece of mechanism acting by necessity--an
order of things constituted by the Supreme Being, and subject to laws
which are the expressions of his will. This Nature is _obliged_ to
proceed gradually in all her operations; she cannot produce animals and
plants of all classes at once, but must always begin by the formation of
the most simple kinds, and out of them elaborate the more compound,
adding to them, successively, different systems of organs, and
multiplying more and more their number and energy.

This nature is daily engaged in the formation of the elementary
rudiments of animal and vegetable existence, which correspond to what
the ancients termed _spontaneous generation_. She is always beginning
anew, day by day, the work of creation, by forming monads, or "rough
draughts" (ébauches), which are the only living things she gives birth
to _directly_.

There are distinct primary rudiments of plants and animals, and
_probably_ of each of the great divisions of the animal and vegetable
kingdoms.[797] These are gradually developed into the higher and more
perfect classes by the slow but unceasing agency of two influential
principles: first, _the tendency to progressive advancement_ in
organization, accompanied by greater dignity in instinct, intelligence,
&c.; secondly, _the force of external circumstances_, or of variations
in the physical condition of the earth, or the mutual relations of
plants and animals. For, as species spread themselves gradually over the
globe, they are exposed from time to time to variations in climate, and
to changes in the quantity and quality of their food; they meet with new
plants and animals which assist or retard their development, by
supplying them with nutriment, or destroying their foes. The nature,
also, of each locality, is in itself fluctuating; so that, even if the
relation of other animals and plants were invariable, the habits and
organization of species would be modified by the influence of local
revolutions.

Now, if the first of these principles, _the tendency to progressive
development_, were left to exert itself with perfect freedom, it would
give rise, says Lamarck, in the course of ages, to a graduated scale of
being, where the most insensible transition might be traced from the
simplest to the most compound structure, from the humblest to the most
exalted degree of intelligence. But, in consequence of the perpetual
interference of the _external causes_ before mentioned, this regular
order is greatly interfered with, and an approximation only to such a
state of things is exhibited by the animate creation, the progress of
some races being retarded by unfavorable, and that of others accelerated
by favorable, combinations of circumstances. Hence, all kinds of
anomalies interrupt the continuity of the plan; and chasms, into which
whole genera or families might be inserted, are seen to separate the
nearest existing portions of the series.

_Lamarck's theory of the transformation of the orang-outang into the
human species._--Such is the machinery of the Lamarckian system; but the
reader will hardly, perhaps, be able to form a perfect conception of so
complicated a piece of mechanism, unless it is exhibited in motion, so
that we may see in what manner it can work out, under the author's
guidance, all the extraordinary effects which we behold in the present
state of the animate creation. I have only space for exhibiting a small
part of the entire process by which a complete metamorphosis is
achieved, and shall therefore omit the mode by which, after a countless
succession of generations, a small gelatinous body is transformed into
an oak or an ape; passing on at once to the last grand step in the
progressive scheme, by which the orang-outang, having been already
evolved out of a monad, is made slowly to attain the attributes and
dignity of man.

One of the races of quadrumanous animals which had reached the highest
state of perfection, lost, by constraint of circumstances (concerning
the exact nature of which tradition is unfortunately silent), the habit
of climbing trees, and of hanging on by grasping the boughs with their
feet as with hands. The individuals of this race being obliged, for a
long series of generations, to use their feet exclusively for walking,
and ceasing to employ their hands as feet, were transformed into
bimanous animals, and what before were thumbs became mere toes, no
separation being required when their feet were used solely for walking.
Having acquired a habit of holding themselves upright, their legs and
feet assumed, insensibly, a conformation fitted to support them in an
erect attitude, till at last these animals could no longer go on
all-fours without much inconvenience.

The Angola orang (_Simia troglodytes_, Linn.) is the most perfect of
animals; much more so than the Indian orang (_Simia Satyrus_), which has
been called the orang-outang, although _both_ are _very inferior_ to man
in corporeal powers and intelligence. These animals frequently hold
themselves upright; but their organization has _not yet_ been
sufficiently modified to sustain them habitually in this attitude, so
that the standing posture is very uneasy to them. When the Indian orang
is compelled to take flight from pressing danger, he immediately falls
down upon all-fours, showing clearly that this was the original position
of the animal. Even in man, whose organization, in the course of a long
series of generations, has advanced so much farther, the upright posture
is fatiguing, and can be supported only for a limited time, and by aid
of the contraction of many muscles. If the vertebral column formed the
axis of the human body, and supported the head and all the other parts
in equilibrium, then might the upright position be a state of repose:
but, as the human head does not articulate in the centre of gravity, as
the chest, belly, and other parts press almost entirely forward with
their whole weight, and as the vertebral column reposes upon an oblique
base, a watchful activity is required to prevent the body from falling.
Children who have large heads and prominent bellies can hardly walk at
the end even of two years; and their frequent tumbles indicate the
natural tendency in man to resume the quadrupedal state.

Now, when so much progress had been made by the quadrumanous animals
before mentioned, that they could hold themselves habitually in an erect
attitude, and were accustomed to a wide range of vision, and ceased to
use their jaws for fighting and tearing, or for clipping herbs for food,
their snout became gradually shorter, their incisor teeth became
vertical, and the facial angle grew more open.

Among other ideas which the natural _tendency to perfection_ engendered,
the desire of ruling suggested itself, and this race succeeded at length
in getting the better of the other animals, and made themselves masters
of all those spots on the surface of the globe which best suited them.
They drove out the animals which approached nearest them in organization
and intelligence, and which were in a condition to dispute with them the
good things of this world, forcing them to take refuge in deserts,
woods, and wildernesses, where their multiplication was checked, and the
progressive development of their faculties retarded; while, in the mean
time, the dominant race spread itself in every direction, and lived in
large companies, where new wants were successively created, exciting
them to industry, and gradually perfecting their means and faculties.

In the supremacy and increased intelligence acquired by the ruling race,
we see an illustration of the natural tendency of the organic world to
grow more perfect; and, in their influence in repressing the advance of
others, an example of one of those disturbing causes before enumerated,
that _force of external circumstances_ which causes such wide chasms in
the regular series of animated being.

When the individuals of the dominant race became very numerous, their
ideas greatly increased in number, and they felt the necessity of
communicating them to each other, and of augmenting and varying the
signs proper for the communication of ideas. Meanwhile the inferior
quadrumanous animals, although most of them were gregarious, acquired no
new ideas, being persecuted and restless in the deserts, and obliged to
fly and conceal themselves, so that they conceived no new wants. Such
ideas as they already had remained unaltered, and they could dispense
with the communication of the greater part of these. To make themselves,
therefore, understood by their fellows, required merely a few movements
of the body or limbs--whistling, and the uttering of certain cries
varied by the inflexions of the voice.

On the contrary, the individuals of the ascendant race, animated with a
desire of interchanging their ideas, which became more and more
numerous, were prompted to multiply the means of communication, and were
no longer satisfied with mere pantomimic signs, nor even with all the
possible inflexions of the voice, but made continual efforts to acquire
the power of uttering articulate sounds, employing a few at first, but
afterwards varying and perfecting them according to the increase of
their wants. The habitual exercise of their throat, tongue, and lips,
insensibly modified the conformation of these organs, until they became
fitted for the faculty of speech.[798]

In effecting this mighty change, "the exigencies of the individuals were
the sole agents; they gave rise to efforts, and the organs proper for
articulating sounds were developed by their habitual employment." Hence,
in this peculiar race, the origin of the admirable faculty of speech;
hence also the diversity of languages, since the distance of places
where the individuals composing the race established themselves soon
favored the corruption of conventional signs.[799]

In conclusion, it may be proper to observe that the above sketch of the
Lamarckian theory is no exaggerated picture, and those passages which
have probably excited the greatest surprise in the mind of the reader
are literal translations from the original.




CHAPTER XXXIV.

TRANSMUTATION OF SPECIES--_Continued_.


  Recapitulation of the arguments in favor of the theory of
    transmutation of species--Their insufficiency--Causes of difficulty
    in discriminating species--Some varieties possibly more distinct
    than certain individuals of distinct species--Variability in a
    species consistent with a belief that the limits of deviation are
    fixed--No facts of transmutation authenticated--Varieties of the
    Dog--the Dog and Wolf distinct species--Mummies of various animals
    from Egypt identical in character with living individuals--Seeds and
    plants from the Egyptian tombs--Modifications produced in plants by
    agriculture and gardening.


The theory of the transmutation of species, considered in the last
chapter, has met with some degree of favor from many naturalists, from
their desire to dispense, as far as possible, with the repeated
intervention of a First Cause, as often as geological monuments attest
the successive appearance of new races of animals and plants, and the
extinction of those pre-existing. But, independently of a predisposition
to account, if possible, for a series of changes in the organic world by
the regular action of secondary causes, we have seen that in truth many
perplexing difficulties present themselves to one who attempts to
establish the nature and reality of the specific character. And if once
there appears ground of reasonable doubt, in regard to the constancy of
species, the amount of transformation which they are capable of
undergoing may seem to resolve itself into a mere question of the
quantity of time assigned to the past duration of animate existence.

Before entering upon the reasons which may be adduced for rejecting
Lamarck's hypothesis, I shall recapitulate, in a few words, the
phenomena, and the whole train of thought, by which I conceive it to
have been suggested, and which have gained for this and analogous
theories, both in ancient and modern times, a considerable number of
votaries.

In the first place, the various groups into which plants and animals may
be thrown seem almost invariably, to a beginner, to be so natural, that
he is usually convinced at first, as was Linnæus to the last, "that
genera are as much founded in nature as the species which compose
them."[800] When by examining the numerous intermediate gradations the
student finds all lines of demarcation to be in most instances
obliterated, even where they at first appeared most distinct, he grows
more and more sceptical as to the real existence of genera, and finally
regards them as mere arbitrary and artificial signs, invented, like
those which serve to distinguish the heavenly constellations, for the
convenience of classification, and having as little pretensions to
reality.

Doubts are then engendered in his mind as to whether species may not
also be equally unreal. The student is probably first struck with the
phenomenon, that some individuals are made to deviate widely from the
ordinary type by the force of peculiar circumstances, and with the still
more extraordinary fact, that the newly acquired peculiarities are
faithfully transmitted to the offspring. How far, he asks, may such
variations extend in the course of indefinite periods of time, and
during great vicissitudes in the physical condition of the globe? His
growing incertitude is at first checked by the reflection that nature
has forbidden the intermixture of the descendants of distinct original
stocks, or has, at least, entailed sterility on their offspring, thereby
preventing their being confounded together, and pointing out that a
multitude of distinct types must have been created in the beginning, and
must have remained pure and uncorrupted to this day.

Relying on this general law, he endeavors to solve each difficult
problem by direct experiment, until he is again astounded by the
phenomenon of a prolific hybrid, and still more by an example of a
hybrid perpetuating itself throughout several generations in the
vegetable world. He then feels himself reduced to the dilemma of
choosing between two alternatives; either to reject the test, or to
declare that the two species, from the union of which the fruitful
progeny has sprung, were mere varieties. If he prefer the latter, he is
compelled to question the reality of the distinctness of all other
supposed species which differ no more than the parents of such prolific
hybrids; for although he may not be enabled immediately to procure, in
all such instances, a fruitful offspring; yet experiments show, that
after repeated failures, the union of two recognized species may at
last, under very favorable circumstances, give birth to a fertile
progeny. Such circumstances, therefore, the naturalist may conceive to
have occurred again and again, in the course of a great lapse of ages.

His first opinions are now fairly unsettled, and every stay at which he
has caught has given way one after another; he is in danger of falling
into any new and visionary doctrine which may be presented to him; for
he now regards every part of the animate creation as void of stability,
and in a state of continual flux. In this mood he encounters the
Geologist, who relates to him how there have been endless vicissitudes
in the shape and structure of organic beings in former ages--how the
approach to the present system of things has been gradual--that there
has been a progressive development of organization subservient to the
purposes of life, from the most simple to the most complex state--that
the appearance of man is the last phenomenon in a long succession of
events--and, finally, that a series of physical revolutions can be
traced in the inorganic world, coeval and co-extensive with those of
organic nature.

These views seem immediately to confirm all his preconceived doubts as
to the stability of the specific character, and he begins to think there
may exist an inseparable connection between a series of changes in the
inanimate world, and the capability of the species to be indefinitely
modified by the influence of external circumstances. Henceforth his
speculations know no definite bounds; he gives the rein to conjecture,
and fancies that the outward form, internal structure, instinctive
faculties, nay, that reason itself may have been gradually developed
from some of the simplest states of existence--that all animals, that
man himself, and the irrational beings, may have had one common origin;
that all may be parts of one continuous and progressive scheme of
development, from the most imperfect to the more complex; in fine, he
renounces his belief in the high genealogy of his species, and looks
forward, as if in compensation, to the future perfectibility of man in
his physical, intellectual, and moral attributes.

Let us now proceed to consider what is defective in evidence, and what
fallacious in reasoning, in the grounds of these strange conclusions.
Blumenbach judiciously observes, that "no general rule can be laid down
for determining the distinctness of species, as there is no particular
class of characters which can serve as a criterion. In each case we must
be guided by _analogy_ and _probability_." The multitude, in fact, and
complexity of the proofs to be weighed is so great, that we can only
hope to obtain presumptive evidence, and we must, therefore, be the more
careful to derive our general views as much as possible from those
observations where the chances of deception are least. We must be on our
guard not to tread in the footsteps of the naturalists of the middle
ages, who believed the doctrine of spontaneous generation to be
applicable to all those parts of the animal and vegetable kingdoms which
they least understood, in direct contradiction to the analogy of all the
parts best known to them; and who, when at length they found that
insects and cryptogamous plants were also propagated from eggs or seeds,
still persisted in retaining their old prejudices respecting the
infusory animalcules and other minute beings, the generation of which
had not then been demonstrated by the microscope to be governed by the
same laws.

Lamarck has, indeed, attempted to raise an argument in favor of his
system, out of the very confusion which has arisen in the study of some
orders of animals and plants, in consequence of the slight shades of
difference which separate the new species discovered within the last
half century. That the embarrassment of those who attempt to classify
and distinguish the new acquisitions, poured in such multitudes into our
museums, should increase with the augmentation of their number, is quite
natural; since to obviate this, it is not enough that our powers of
discrimination should keep pace with the increase of the objects, but we
ought to possess greater opportunities of studying each animal and plant
in all stages of its growth, and to know profoundly their history, their
habits, and physiological characters, throughout several generations;
for, in proportion as the series of known animals grows more complete
none can doubt there is a nearer approximation to a graduated scale of
being; and thus the most closely allied species will be found to possess
a greater number of characters in common.

_Causes of the difficulty of discriminating species._--But, in point of
fact, our new acquisitions consist, more and more as we advance, of
specimens brought from foreign and often very distant and barbarous
countries. A large proportion have never even been seen alive by
scientific inquirers. Instead of having specimens of the young, the
adult, and the aged individuals of each sex, and possessing means of
investigating the anatomical structure, the peculiar habits, and
instincts of each, what is usually the state of our information? A
single specimen, perhaps, of a dried plant, or a stuffed bird or
quadruped; a shell, without the soft parts of the animal; an insect in
one stage of its numerous transformations;--these are the scanty and
imperfect data which the naturalist possesses. Such information may
enable us to separate species which stand at a considerable distance
from each other; but we have no right to expect any thing but difficulty
and ambiguity, if we attempt, from such imperfect opportunities, to
obtain distinctive marks for defining the characters of species which
are closely related.

If Lamarck could introduce so much certainty and precision into the
classification of several thousand species of recent and fossil shells,
notwithstanding the extreme remoteness of the organization of these
animals from the type of those vertebrated species which are best known,
and in the absence of so many of the living inhabitants of shells, we
are led to form an exalted conception of the degree of exactness to
which specific distinctions are capable of being carried, rather than to
call in question their reality.

When our data are so defective, the most acute naturalist must expect to
be sometimes at fault, and, like the novice, to overlook essential
points of difference, passing unconsciously from one species to another,
until, like one who is borne along in a current, he is astonished on
looking back, at observing that he has reached a point so remote from
that whence he set out.

It is by no means improbable, that, when the series of species of
certain genera is very full, they may be found to differ less widely
from each other than do the mere varieties or races of certain species.
If such a fact could be established, it would, undoubtedly, diminish the
chance of our obtaining certainty in our results; but it would by no
means overthrow our confidence in the reality of species.

_Some mere varieties possibly more distinct than certain individuals of
distinct species._--It is almost necessary, indeed, to suppose that
varieties will differ in some cases more decidedly than some species, if
we admit that there is a graduated scale of being, and assume that the
following laws prevail in the economy of the animate creation:--first,
that the organization of individuals is capable of being modified to a
limited extent, by the force of external causes; secondly, that these
modifications are, to a certain extent, transmissible to their
offspring; thirdly, that there are fixed limits, beyond which the
descendants from common parents can never deviate from a certain type;
fourthly, that each species springs from one original stock, and can
never be permanently confounded by intermixing with the progeny of any
other stock; fifthly, that each species shall endure for a considerable
period of time. Now, let us assume, for the present, these rules
hypothetically, and see what consequences may naturally be expected to
result from them.

We must suppose that when the Author of Nature creates an animal or
plant, all the possible circumstances in which its descendants are
destined to live are foreseen, and that an organization is conferred
upon it which will enable the species to perpetuate itself and survive
under all the varying circumstances to which it must be inevitably
exposed. Now, the range of variation of circumstances will differ
essentially in almost every case. Let us take, for example, any one of
the most influential conditions of existence, such as temperature. In
some extensive districts near the equator, the thermometer might never
vary, throughout several thousand centuries, for more than 20°
Fahrenheit; so that if a plant or animal be provided with an
organization fitting it to endure such a range, it may continue on the
globe for that immense period, although every individual might be liable
at once to be cut off by the least possible excess of heat or cold
beyond the determinate degree. But if a species be placed in one of the
temperate zones, and have a constitution conferred on it capable of
supporting a similar range of temperature only, it will inevitably
perish before a single year has passed away.

Humboldt has shown that, at Cumana, within the tropics, there is a
difference of only 4° Fahr. between the temperature of the warmest and
coldest months; whereas, in the temperate zones, the annual variation
amounts to about 60°, and the extreme range of the thermometer in Canada
is not less than 90°.

The same remark might be applied to any other condition, as food, for
example; it may be foreseen that the supply will be regular throughout
indefinite periods in one part of the world, and in another very
precarious and fluctuating both in kind and quantity. Different
qualifications may be required for enabling species to live for a
considerable time under circumstances so changeable. If, then,
temperature and food be among those external causes which, according to
certain laws of animal and vegetable physiology, modify the
organization, form, or faculties, of individuals, we instantly perceive
that the degrees of variability from a common standard must differ
widely in the two cases above supposed; since there is a necessity of
accommodating a species in one case to a much greater latitude of
circumstances than in the other.

If it be a law, for instance, that scanty sustenance should check those
individuals in their growth which are enabled to accommodate themselves
to privations of this kind, and that a parent, prevented in this manner
from attaining the size proper to its species, should produce a dwarfish
offspring, a stunted race will arise, as is remarkably exemplified in
some varieties of the horse and dog. The difference of stature in some
races of dogs, when compared to others, is as one to five in linear
dimensions, making a difference of a hundred-fold in volume.[801] Now,
there is a good reason to believe that species in general are by no
means susceptible of existing under a diversity of circumstances, which
may give rise to such a disparity in size, and, consequently, there will
be a multitude of distinct species, of which no two adult individuals
can ever depart so widely from a certain standard of dimensions as the
mere varieties of certain other species--the dog, for instance. Now, we
have only to suppose that what is true of size, may also hold in regard
to color and many other attributes; and it will at once follow, that the
degree of possible discordance between varieties of the same species
may, in certain cases, exceed the utmost disparity which can arise
between two individuals of many distinct species.

The same remarks may hold true in regard to instincts; for, if it be
foreseen that one species will have to encounter a great variety of
foes, it may be necessary to arm it with great cunning and
circumspection, or with courage or other qualities capable of developing
themselves on certain occasions; such, for example, as those migratory
instincts which are so remarkably exhibited at particular periods, after
they have remained dormant for many generations. The history and habits
of one variety of such a species may often differ more considerably from
some other than those of many distinct species which have no such
latitude of accommodation to circumstances.

_Extent of known variability in species._--Lamarck has somewhat
mis-stated the idea commonly entertained of a species; for it is not
true that naturalists in general assume that the organisation of an
animal or plant remains absolutely constant, and that it can never vary
in any of its parts.[802] All must be aware that circumstances influence
the habits, and that the habits may alter the state of the parts and
organs; but the difference of opinion relates to the extent to which
these modifications of the habits and organs of a particular species may
be carried.

Now, let us first inquire what positive facts can be adduced in the
history of known species, to establish a great and permanent amount of
change in the form, structure, or instinct of individuals descending
from some common stock. The best authenticated examples of the extent to
which species can be made to vary may be looked for in the history of
domesticated animals and cultivated plants. It usually happens, that
those species, both of the animal and vegetable kingdom, which have the
greatest pliability of organisation, those which are most capable of
accommodating themselves to a great variety of new circumstances, are
most serviceable to man. These only can be carried by him into different
climates, and can have their properties or instincts variously
diversified by differences of nourishment and habits. If the resources
of a species be so limited, and its habits and faculties be of such a
confined and local character, that it can only flourish in a few
particular spots, it can rarely be of great utility.

We may consider, therefore, that in the domestication of animals and the
cultivation of plants, mankind have first selected those species which
have the most flexible frames and constitutions, and have then been
engaged for ages in conducting a series of experiments, with much
patience and at great cost, to ascertain what may be the greatest
possible deviation from a common type which can be elicited in these
extreme cases.

_Varieties of the dog--no transmutation._--The modifications produced in
the different races of dogs exhibit the influence of man in the most
striking point of view. These animals have been transported into every
climate and placed in every variety of circumstances; they have been
made, as a modern naturalist observes, the servant, the companion, the
guardian, and the intimate friend of man, and the power of a superior
genius has had a wonderful influence not only on their forms, but on
their manners and intelligence.[803] Different races have undergone
remarkable changes in the quantity and color of their clothing; the dogs
of Guinea are almost naked, while those of the arctic circle are covered
with a warm coat both of hair and wool, which enables them to bear the
most intense cold without inconvenience. There are differences also of
another kind no less remarkable, as in size, the length of their
muzzles, and the convexity of their foreheads.

But, if we look for some of those essential changes which would be
required to lend even the semblance of a foundation for the theory of
Lamarck, respecting the growth of new organs and the gradual
obliteration of others, we find nothing of the kind. For, in all these
varieties of the dog, says Cuvier, the relation of the bones with each
other remains essentially the same; the form of the teeth never changes
in any perceptible degree, except that, in some individuals, one
additional false grinder occasionally appears, sometimes on the one
side, and sometimes on the other.[804] The greatest departure from a
common type--and it constitutes the maximum of variation as yet known in
the animal kingdom--is exemplified in those races of dogs which have a
supernumerary toe on the hind foot with the corresponding tarsal bones;
a variety analogous to one presented by six-fingered families of the
human race.[805]

Lamarck has thrown out as a conjecture, that the wolf may have been the
original of the dog; and eminent naturalists are still divided in
opinion on this subject. It seems now admitted that both species agree
in the period of gestation, and Mr. Owen has been unable to confirm the
alleged difference in the structure of a part of the intestinal
canal.[806] Mr. Bell inclines to the opinion that all the various races
of dogs have descended from one common stock, of which the wolf is the
original source.

It is well known that the horse, the ox, the boar, and other domestic
animals which have been introduced into South America, and have run wild
in many parts, have entirely lost all marks of domesticity, and have
reverted to the original characters of their species. But dogs have also
become wild in Cuba, Hayti, and in all the Caribbean islands. In the
course of the seventeenth century, they hunted in packs from twelve to
fifty, or more, in number, and fearlessly attacked herds of wild boars
and other animals. It is natural, therefore, to inquire to what form
they reverted? Now, they are said by many travellers to have resembled
very nearly the shepherd's dog; but it is certain that they were never
turned into wolves. They were extremely savage, and their ravages appear
to have been as much dreaded as those of wolves; but when any of their
whelps were caught, and brought from the woods to the towns, they grew
up in the most perfect submission to man.[807]

Many examples might be adduced to prove that the extent to which the
alteration of species can be pushed in the domestic state depends on the
original capacity of the species to admit of variation. The horse has
been as long domesticated as the dog, yet its different races depart
much less widely from a common type; the ass has been still less
changed, the camel scarcely at all; yet these species have probably been
subjected to the influence of domestication as long as the horse.

_Mummies of animals in Egyptian tombs identical with species still
living._--As the advocates of the theory of transmutation trust much to
the slow and insensible changes which time may work, they are accustomed
to lament the absence of accurate descriptions, and figures of
particular animals and plants, handed down from the earliest periods of
history, such as might have afforded data for comparing the condition of
species, at two periods considerably remote. But, fortunately, we are in
some measure independent of such evidence: for, by a singular accident,
the priests of Egypt have bequeathed to us, in their cemeteries, that
information which the museums and works of the Greek philosophers have
failed to transmit.

For the careful investigation of these documents, we are greatly
indebted to the skill and diligence of those naturalists who accompanied
the French armies during their brief occupation of Egypt: that conquest
of four years, from which we may date the improvement of the modern
Egyptians in the arts and sciences, and the rapid progress which has
been made of late in our knowledge of the arts and sciences of their
remote predecessors. Instead of wasting their whole time, as so many
preceding travellers had done, in exclusively collecting human mummies,
M. Geoffrey and his associates examined diligently, and sent home great
numbers of embalmed bodies of consecrated animals, such as the bull, the
dog, the cat, the ape, the ichneumon, the crocodile, and the ibis.

To those who have never been accustomed to connect the facts of Natural
History with philosophical speculations, who have never raised their
conceptions of the end and import of such studies beyond the mere
admiration of isolated and beautiful objects, or the exertion of skill
in detecting specific differences, it will seem incredible that amidst
the din of arms, and the stirring excitement of political movements, so
much enthusiasm could have been felt in regard to these precious
remains.

In the official report drawn up by the Professors of the Museum at
Paris, on the value of these objects, there are some eloquent passages,
which may appear extravagant, unless we reflect how fully these
naturalists could appreciate the bearing of the facts thus brought to
light on the past history of the globe.

"It seems," say they, "as if the superstition of the ancient Egyptians
had been inspired by Nature, with a view of transmitting to after ages a
monument of her history. That extraordinary and eccentric people, by
embalming with so much care the brutes which were the objects of their
stupid adoration, have left us in their secret grottoes, cabinets of
zoology almost complete. The climate has conspired with the art of
embalming to preserve the bodies from corruption, and we can now assure
ourselves by our own eyes what was the state of a great number of
species three thousand years ago. We can scarcely restrain the
transports of our imagination, on beholding thus preserved, with their
minutest bones, with the smallest portions of their skin, and in every
particular most perfectly recognizable, many an animal, which at Thebes
or Memphis, two or three thousand years ago, had its own priests and
altars."[808]

Among the Egyptian mummies thus procured were not only those of numerous
wild quadrupeds, birds, and reptiles; but what was perhaps of still
higher importance in deciding the great question under discussion, there
were the mummies of domestic animals, among which those above mentioned,
the bull, the dog, and the cat, were frequent. Now, such was the
conformity of the whole of these species to those now living, that there
was no more difference, says Cuvier, between them than between the human
mummies and the embalmed bodies of men of the present day. Yet some of
these animals have since that period been transported by man to almost
every climate, and forced to accommodate their habits to the greatest
variety of circumstances. The cat, for example, has been carried over
the whole earth, and within the last three centuries, has been
naturalized in every part of the new world,--from the cold regions of
Canada to the tropical plains of Guiana; yet it has scarcely undergone
any perceptible mutation, and is still the same animal which was held
sacred by the Egyptians.

Of the ox, undoubtedly, there are many very distinct races; but the bull
Apis, which was led in solemn processions by the Egyptian priests, did
not differ from some of those now living. The black cattle that have run
wild in America, where there were many peculiarities in the climate not
to be found, perhaps, in any part of the old world, and where scarcely a
single plant on which they fed was of precisely the same species,
instead of altering their form and habits, have actually reverted to the
exact likeness of the aboriginal wild cattle of Europe.

In answer to the arguments drawn from the Egyptian mummies, Lamarck said
they were identical with their living descendants in the same country,
because the climate and physical geography of the banks of the Nile have
remained unaltered for the last thirty centuries. But why, it may be
asked, have other individuals of these species retained the same
characters in many different quarters of the globe, where the climate
and many other conditions are so varied?

_Seeds and plants from the Egyptian tombs._--The evidence derived from
the Egyptian monuments was not confined to the animal kingdom; the
fruits, seeds, and other portions of twenty different plants, were
faithfully preserved in the same manner; and among these the common
wheat was procured by Delille, from closed vessels in the sepulchres of
the kings, the grain of which retained not only their form but even
their color; so effectual has proved the process of embalming with
bitumen in a dry and equable climate. No difference could be detected
between this wheat and that which now grows in the East and elsewhere;
and in regard to the barley, I am informed by Mr. Brown, the celebrated
botanist, that its identity with the grain of our own times can be
tested by the closest comparison. On examining, for example, one of the
seeds from Mr. Sam's Egyptian collection in the British Museum, it is
found that "the structure of the husks or that part of the flower which
is persistent, agrees precisely with the barley of the present day, in
having one perfect flower and the filiform rudiments of a second." Some
naturalists believe that the perfect identification of the ancient
Egyptian cerealia with the varieties now cultivated has been carried
still further, by sowing the seeds taken out of the catacombs, and
raising plants from them; but we want more evidence of this fact.
Certain it is, that when the experiment was recently made in the botanic
garden at Kew, with 100 seeds of wheat, barley, and lentils, from the
Egyptian collection before mentioned of the British Museum, not one of
them would germinate.[809]

_Native country of the common wheat._--And here I may observe that there
is an obvious answer to Lamarck's objection, that the botanist cannot
point out a country where the common wheat grows wild, unless in places
where it may have been derived from neighboring cultivation.[810] All
naturalists are well aware that the geographical distribution of a great
number of species is extremely limited; that it was to be expected that
every useful plant should first be cultivated successfully in the
country where it was indigenous; and that, probably, every station which
it partially occupied, when growing wild, would be selected by the
agriculturist as best suited to it when artificially increased.
Palestine has been conjectured, by a late writer on the cerealia, to
have been the original habitation of wheat and barley; a supposition
which is rendered the more plausible by Hebrew and Egyptian traditions,
and by tracing the migrations of the worship of Ceres, as indicative of
the migrations of the plant.[811]

If we are to infer that some one of the wild grasses has been
transformed into the common wheat, and that some animal of the genus
_Canis_, still unreclaimed, has been metamorphosed into the dog, merely
because we cannot find the domestic dog, or the cultivated wheat, in a
state of nature, we may be next called upon to make similar admissions
in regard to the camel; for it seems very doubtful whether any race of
this species of quadruped is now wild.

_Changes in plants produced by cultivation._--But if agriculture, it
will be said, does not supply examples of extraordinary changes of form
and organization, the horticulturist can, at least, appeal to facts
which may confound the preceding train of reasoning. The crab has been
transformed into the apple; the sloe into the plum; flowers have changed
their color, and become double; and these new characters can be
perpetuated by seed; a bitter plant, with wavy sea-green leaves, has
been taken from the sea-side, where it grew like wild charlock; has been
transplanted into the garden, lost its saltness, and has been
metamorphosed into two distinct vegetables, as unlike each other as is
each to the parent plant--the red cabbage and the cauliflower. These,
and a multitude of analogous facts, are undoubtedly among the wonders of
nature, and attest more strongly, perhaps, the extent to which species
may be modified, than any examples derived from the animal kingdom. But
in these cases we find that we soon reach certain limits, beyond which
we are unable to cause the individuals descending from the same stock to
vary; while, on the other hand, it is easy to show that these
extraordinary varieties could seldom arise, and could never be
perpetuated in a wild state for many generations, under any imaginable
combination of accidents. They may be regarded as extreme cases,
brought about by human interference, and not as phenomena which indicate
a capability of indefinite modification in the natural world.

The propagation of a plant by buds or grafts, and by cuttings, is
obviously a mode which nature does not employ; and this multiplication,
as well as that produced by roots and layers, seems merely to operate as
an extension of the life of an individual, and not as a reproduction of
the species such as happens by seed. All plants increased by grafts or
layers retain precisely the peculiar qualities of the individual to
which they owe their origin, and, like an individual, they have only a
determinate existence; in some cases longer, and in others shorter.[812]
It seems now admitted by horticulturists, that none of our garden
varieties of fruit are entitled to be considered strictly permanent, but
that they wear out after a time;[813] and we are thus compelled to
resort again to seeds; in which case there is so decided a tendency in
the seedlings to revert to the original type, that our utmost skill is
sometimes baffled in attempting to recover the desired variety.

_Varieties of the cabbage._--The different races of cabbages afford, as
was admitted, an astonishing example of deviation from a common type;
but we can scarcely conceive them to have originated, much less to have
lasted for several generations, without the intervention of man. It is
only by strong manures that these varieties have been obtained, and in
poorer soils they instantly degenerate. If, therefore, we suppose in a
state of nature the seed of the wild _Brassica oleracea_ to have been
wafted from the sea-side to some spot enriched by the dung of animals,
and to have there become a cauliflower, it would soon diffuse its seed
to some comparatively sterile soils around, and the offspring would
relapse to the likeness of the parent stock.

But if we go so far as to imagine the soil, in the spot first occupied,
to be constantly manured by herds of wild animals, so as to continue as
rich as that of a garden, still the variety could not be maintained;
because we know that each of these races is prone to fecundate others,
and gardeners are compelled to exert the utmost diligence to prevent
cross-breeds. The intermixture of the pollen of varieties growing in the
poorer soil around would soon destroy the peculiar characters of the
race which occupied the highly manured tract; for, if these accidents so
continually happen, in spite of our care, among the culinary varieties,
it is easy to see how soon this cause might obliterate every marked
singularity in a wild state.

Besides, it is well known that, although the pampered races which we
rear in our gardens for use or ornament may often be perpetuated by
seed, yet they rarely produce seed in such abundance, or so prolific in
quality, as wild individuals; so that if the care of man were withdrawn,
the most fertile variety would always, in the end, prevail over the more
sterile.

Similar remarks may be applied to the double flowers, which present
such strange anomalies to the botanist. The ovarium, in such cases, is
frequently abortive; and the seeds, when prolific, are generally much
fewer than where the flowers are single.

_Changes caused by soil._--Some curious experiments, recently made on
the production of blue instead of red flowers in the _Hydrangea
hortensis_, illustrate the immediate effect of certain soils on the
colors of the calyx and petals. In garden-mould or compost, the flowers
are invariably red; in some kinds of bog-earth they are blue; and the
same change is always produced by a particular sort of yellow loam.

_Varieties of the primrose._--Linnæus was of opinion that the primrose,
oxlip, cowslip, and polyanthus, were only varieties of the same species.
The majority of the modern botanists, on the contrary, consider them to
be distinct, although some conceived that the oxlip might be a cross
between the cowslip and the primrose. Mr. Herbert has lately recorded
the following experiment:--"I raised from the natural seed of one umbel
of a highly manured red cowslip a primrose, a cowslip, oxlips of the
usual and other colors, a black polyanthus, a hose-in-hose cowslip, and
a natural primrose bearing its flower on a polyanthus stalk. From the
seed of that very hose-in-hose cowslip I have since raised a
hose-in-hose primrose. I therefore consider all these to be only local
varieties, depending upon soil and situation."[814] Professor Henslow,
of Cambridge, has since confirmed this experiment of Mr. Herbert; so
that we have an example, not only of the remarkable varieties which the
florist can obtain from a common stock, but of the distinctness of
analogous races found in a wild state.[815]

On what particular ingredient, or quality in the earth, these changes
depend, has not yet been ascertained.[816] But gardeners are well aware
that particular plants, when placed under the influence of certain
circumstances, are changed in various ways, according to the species;
and as often as the experiments are repeated, similar results are
obtained. The nature of these results, however, depends upon the
species, and they are, therefore, part of the specific character; they
exhibit the same phenomena, again and again, and indicate certain fixed
and invariable relations between the physiological peculiarities of the
plant, and the influence of certain external agents. They afford no
ground for questioning the instability of species, but rather the
contrary; they present us with a class of phenomena, which, when they
are more thoroughly understood, may afford some of the best tests for
identifying species, and proving that the attributes originally
conferred endure so long as any issue of the original stock remains upon
the earth.




CHAPTER XXXV.

WHETHER SPECIES HAVE A REAL EXISTENCE IN NATURE--_continued_.


  Limits of the variability of species--Species susceptible of
    modification may be altered greatly in a short time, and in a few
    generations; after which they remain stationary--The animals now
    subject to man had originally an aptitude to domesticity--Acquired
    peculiarities which become hereditary have a close connexion with
    the habits or instincts of the species in a wild state--Some
    qualities in certain animals have been conferred with a view of
    their relation to man--Wild elephant domesticated in a few years,
    but its faculties incapable of further development.


_Variability of a species compared to that of an individual._--I
endeavored, in the last chapter, to show, that a belief in the reality
of species is not inconsistent with the idea of a considerable degree of
variability in the specific character. This opinion, indeed, is little
more than an extension of the idea which we must entertain of the
identity of an individual, throughout the changes which it is capable of
undergoing.

If a quadruped, inhabiting a cold northern latitude, and covered with a
warm coat of hair or wool, be transported to a southern climate, it will
often, in the course of a few years, shed a considerable portion of its
coat, which it gradually recovers on being again restored to its native
country. Even there the same changes are, perhaps, superinduced to a
certain extent by the return of winter and summer. We know that the
Alpine hare (_Lepus variabilis_, Pal.) and the ermine, or stoat,
(_Mustela erminea_, Linn.) become white during winter, and again obtain
their full color during the warmer season; that the plumage of the
ptarmigan undergoes a like metamorphosis in color and quantity, and that
the change is equally temporary. We are aware that, if we reclaim some
wild animal, and modify its habits and instincts by domestication, it
may, if it escapes, become in a few years nearly as wild and untractable
as ever; and if the same individual be again retaken, it may be reduced
to its former tame state. A plant is sown in a prepared soil, in order
that the petals of its flowers may multiply, and their color be
heightened or changed: if we then withhold our care, the flowers of this
same species become again single. In these, and innumerable other
instances, we must suppose that the species was produced with a certain
number of qualities; and, in the case of animals, with a variety of
instincts, some of which may or may not be developed according to
circumstances, or which, after having been called forth, may again
become latent when the exciting causes are removed.

Now, the formation of races seems the necessary consequence of such a
capability in species to vary, if it be a general law that the offspring
should very closely resemble the parent. But, before we can infer that
there are no limits to the deviation from an original type which may be
brought about in the course of an indefinite number of generations, we
ought to have some proof that, in each successive generation,
individuals may go on acquiring an equal amount of new peculiarities,
under the influence of equal changes of circumstances. The balance of
evidence, however, inclines most decidedly on the opposite side; for in
all cases we find that the quantity of divergence diminishes after a few
generations in a very rapid ratio.

_Species susceptible of modification may be greatly altered in a few
generations._--It cannot be objected, that it is out of our power to go
on varying the circumstances in the same manner as might happen in the
natural course of events during some great geological cycle. For in the
first place, where a capacity is given to individuals to adapt
themselves to new circumstances, it does not generally require a very
long period for its development: if, indeed, such were the case, it is
not easy to see how the modification would answer the ends proposed, for
all the individuals would die before new qualities, habits, or instincts
were conferred.

When we have succeeded in naturalizing some tropical plant in a
temperate climate, nothing prevents us from attempting gradually to
extend its distribution to higher latitudes, or to greater elevations
above the level of the sea, allowing equal quantities of time, or an
equal number of generations, for habituating the species to successive
increments of cold. But every husbandman and gardener is aware that such
experiments will fail; and we are more likely to succeed in making some
plants, in the course of the first two generations, support a
considerable degree of difference of temperature, than a very small
difference afterwards, though we persevere for many centuries.

It is the same if we take any other cause instead of temperature; such
as the quality of the food, or the kind of dangers to which an animal is
exposed, or the soil in which a plant lives. The alteration in habits,
form, or organization, is often rapid during a short period; but when
the circumstances are made to vary farther, though in ever so slight a
degree, all modification ceases, and the individual perishes. Thus some
herbivorous quadrupeds may be made to feed partially on fish or flesh;
but even these can never be taught to live on some herbs which they
reject, and which would even poison them, although the same may be very
nutritious to other species of the same natural order. So when man uses
force or stratagem against wild animals, the persecuted race soon
becomes more cautious, watchful, and cunning; new instincts seem often
to be developed, and to become hereditary in the first two or three
generations: but let the skill and address of man increase, however
gradually, no farther variation can take place, no new qualities are
elicited by the increasing dangers. The alteration of the habits of the
species has reached a point beyond which no ulterior modification is
possible, however indefinite the lapse of ages during which the new
circumstances operate. Extirpation then follows, rather than such a
transformation as could alone enable the species to perpetuate itself
under the new state of things.

_Animals now subject to man had originally an aptitude to
domesticity._--It has been well observed by M. F. Cuvier and M. Dureau
de la Malle, that unless some animals had manifested in a wild state an
aptitude to second the efforts of man, their domestication would never
have been attempted. If they had all resembled the wolf, the fox, and
the hyæna, the patience of the experimentalist would have been exhausted
by innumerable failures before he at last succeeded in obtaining some
imperfect results; so if the first advantages derived from the
cultivation of plants had been elicited by as tedious and costly a
process as that by which we now make some slight additional improvements
in certain races, we should have remained to this day in ignorance of
the greater number of their useful qualities.

_Acquired instincts of some animals become hereditary._--It is
undoubtedly true, that many new habits and qualities have not only been
acquired in recent times by certain races of dogs, but have been
transmitted to their offspring. But in these cases it will be observed,
that the new peculiarities have an intimate relation to the habits of
the animal in a wild state, and therefore do not attest any tendency to
a departure to an indefinite extent from the original type of the
species. A race of dogs employed for hunting deer in the platform of
Sante Fé, in Mexico, affords a beautiful illustration of a new
hereditary instinct. The mode of attack, observes M. Roulin, which they
employ consists in seizing the animal by the belly and overturning it by
a sudden effort, taking advantage of the moment when the body of the
deer rests only upon the fore-legs. The weight of the animal thus thrown
over is often six times that of its antagonist. The dog of pure breed
inherits a disposition to this kind of chase, and never attacks a deer
from before while running. Even should the deer, not perceiving him,
come directly upon him, the dog steps aside and makes his assault on the
flank; whereas other hunting dogs, though of superior strength, and
general sagacity, which are brought from Europe, are destitute of this
instinct. For want of similar precautions, they are often killed by the
deer on the spot, the vertebræ of their neck being dislocated by the
violence of the shock.[817]

A new instinct has also become hereditary in a mongrel race of dogs
employed by the inhabitants of the banks of the Magdalena almost
exclusively in hunting the white-lipped pecari. The address of these
dogs consists in restraining their ardor, and attaching themselves to no
animal in particular, but keeping the whole herd in check. Now, among
these dogs some are found, which the very first time they are taken to
the woods, are acquainted with this mode of attack; whereas, a dog of
another breed starts forward at once, is surrounded by the pecari, and,
whatever may be his strength, is destroyed in a moment.

Some of our countrymen, engaged of late in conducting one of the
principal mining associations in Mexico, that of Real del Monte, carried
out with them some English greyhounds of the best breed, to hunt the
hares which abound in that country. The great platform which is the
scene of sport is at an elevation of about nine thousand feet above the
level of the sea, and the mercury in the barometer stands habitually at
the height of about nineteen inches. It was found that the greyhounds
could not support the fatigues of a long chase in this attenuated
atmosphere, and before they could come up with their prey, they lay down
gasping for breath; but these same animals have produced whelps which
have grown up, and are not in the least degree incommoded by the want of
density in the air, but run down the hares with as much ease as the
fleetest of their race in this country.

The fixed and deliberate stand of the pointer has with propriety been
regarded as a mere modification of a habit, which may have been useful
to a wild race accustomed to wind game, and steal upon it by surprise,
first pausing for an instant, in order to spring with unerring aim. The
faculty of the retriever, however, may justly be regarded as more
inexplicable and less easily referable to the instinctive passions of
the species. M. Majendie, says a French writer in a recently published
memoir, having learnt that there was a race of dogs in England which
stopped and brought back game of their own accord, procured a pair, and
having obtained a whelp from them, kept it constantly under his eyes,
until he had an opportunity of assuring himself that, without having
received any instruction, and on the very first day that it was carried
to the chase, it brought back game with as much steadiness as dogs which
had been schooled into the same manoeuvre by means of the whip and
collar.

_Attributes of animals in their relation to man._--Such attainments, as
well as the habits and dispositions which the shepherd's dog and many
others inherit, seem to be of a nature and extent which we can hardly
explain by supposing them to be modifications of instincts necessary for
the preservation of the species in a wild state. When such remarkable
habits appear in races of this species we may reasonably conjecture that
they were given with no other view than for the use of man and the
preservation of the dog, which thus obtains protection.

As a general rule, I fully agree with M. F. Cuvier, that, in studying
the habits of animals, we must attempt, as far as possible, to refer
their domestic qualities to modifications of instincts which are
implanted in them in a state of nature; and that writer has successfully
pointed out, in an admirable essay on the domestication of the
mammalia[818], the true origin of many dispositions which are vulgarly
attributed to the influence of education alone. But we should go too far
if we did not admit that some of the qualities of particular animals and
plants may have been given solely with a view to the connection which it
was foreseen would exist between them and man--especially when we see
that connexion to be in many cases so intimate, that the greater number,
and sometimes, as in the case of the camel, all the individuals of the
species which exist on the earth are in subjection to the human race.

We can perceive in a multitude of animals, especially in some of the
parasitic tribes, that certain instincts and organs are conferred for
the purpose of defence or attack against some other species. Now if we
are reluctant to suppose the existence of similar relations between man
and the instincts of many of the inferior animals, we adopt an
hypothesis no less violent, though in the opposite extreme to that which
has led some to imagine the whole animate and inanimate creation to have
been made solely for the support, gratification, and instruction of
mankind.

Many species, most hostile to our persons or property, multiply, in
spite of our efforts to repress them; others, on the contrary, are
intentionally augmented many hundred fold in number by our exertions. In
such instances, we must imagine the relative resources of man, and of
species friendly or inimical to him, to have been prospectively
calculated and adjusted. To withhold assent to this supposition, would
be to refuse what we must grant in respect to the economy of nature in
every other part of the organic creation; for the various species of
contemporary plants and animals have obviously their relative forces,
nicely balanced, and their respective tastes, passions, and instincts so
contrived, that they are all in perfect harmony with each other. In no
other manner could it happen that each species, surrounded, as it is, by
countless dangers, should be enabled to maintain its ground for periods
of considerable duration.

The docility of the individuals of some of our domestic species,
extending, as it does, to attainments foreign to their natural habits
and faculties, may, perhaps, have been conferred with a view to their
association with man. But, lest species should be thereby made to vary
indefinitely, we find that such habits are never transmissible by
generation.

A pig has been trained to hunt and point game with great activity and
steadiness[819]; and other learned individuals, of the same species,
have been taught to spell; but such fortuitous acquirements never become
hereditary, for they have no relation whatever to the exigencies of the
animal in a wild state, and cannot, therefore, be developments of any
instinctive propensities.

_Influence of domestication._--An animal in domesticity, says M. F.
Cuvier, is not essentially in a different situation, in regard to the
feeling of restraint, from one left to itself. It lives in society
without constraint, because, without doubt, it was a social animal; and
it conforms itself to the will of man, because it had a chief, to which,
in a wild state, it would have yielded obedience. There is nothing in
its new situation that is not conformable to its propensities; it is
satisfying its wants by submission to a master, and makes no sacrifice
of its natural inclinations. All the social animals, when left to
themselves, form herds more or less numerous; and all the individuals of
the same herd know each other, are mutually attached, and will not allow
a strange individual to join them. In a wild state, moreover, they obey
some individual, which, by its superiority, has become the chief of the
herd. Our domestic species had, originally, this sociability of
disposition; and no solitary species, however easy it may be _to tame
it_, has yet afforded true domestic races. We merely, therefore,
develope, to our own advantage, propensities which propel the
individuals of certain species to draw near to their fellows.

The sheep which we have reared is induced to follow us, as it would be
led to follow the flock among which it was brought up; and, when
individuals of gregarious species have been accustomed to one master, it
is he alone whom they acknowledge as their chief--he only whom they
obey. "The elephant allows himself to be directed only by the carnac
whom he has adopted; the dog itself, reared in solitude with its master,
manifests a hostile disposition towards all others; and every body knows
how dangerous it is to be in the midst of a herd of cows, in pasturages
that are little frequented, when they have not at their head the keeper
who takes care of them.

"Every thing, therefore, tends to convince us, that formerly men were
only with regard to the domestic animals, what those who are
particularly charged with the care of them still are--namely, members of
the society which these animals form among themselves; and, that they
are only distinguished, in the general mass, by the authority which they
have been enabled to assume from their superiority of intellect. Thus,
every social animal which recognizes man as a member, and as the chief
of its herd, is a domestic animal. It might even be said, that, from the
moment when such an animal admits man as a member of its society, it is
domesticated, as man could not enter into such society without becoming
the chief of it."[820]

But the ingenious author whose observations I have here cited, admits
that the obedience which the individuals of many domestic species yield
indifferently to every person, is without analogy in any state of things
which could exist previously to their subjugation by man. Each troop of
wild horses, it is true, has some stallion for its chief, who draws
after him all the individuals of which the herd is composed; but when a
domesticated horse has passed from hand to hand, and has served several
masters, he becomes equally docile towards _any person_, and is
subjected to the whole human race. It seems fair to presume that the
capability in the instinct of the horse to be thus modified, was given
to enable the species to render greater services to man; and, perhaps,
the facility with which many other acquired characters become hereditary
in various races of the horse, may be explicable only on a like
supposition. The amble, for example, a pace to which the domestic races
in some parts of Spanish America are exclusively trained, has, in the
course of several generations, become hereditary, and is assumed by all
the young colts before they are broken in.[821]

It seems, also, reasonable to conclude, that the power bestowed on the
horse, the dog, the ox, the sheep, the cat, and many species of domestic
fowls, of supporting almost every climate, was given expressly to enable
them to follow man throughout all parts of the globe, in order that we
might obtain their services, and they our protection. If it be objected
that the elephant which, by the union of strength, intelligence, and
docility, can render the greatest services to mankind, is incapable of
living in any but the warmest latitudes, we may observe that the
quantity of vegetable food required by this quadruped would render its
maintenance in the temperate zones too costly, and in the arctic
impossible.

Among the changes superinduced by man, none appear, at first sight, more
remarkable than the perfect tameness of certain domestic races. It is
well known that, at however early an age we obtain possession of the
young of many unreclaimed races, they will retain, throughout life, a
considerable timidity and apprehensiveness of danger; whereas, after one
or two generations, the descendants of the same stock will habitually
place the most implicit confidence in man. There is good reason,
however, to suspect that such changes are not without analogy in a state
of nature; or, to speak more correctly, in situations where man has not
interfered.

We learn from Mr. Darwin, that in the Galapagos archipelago, placed
directly under the equator, and nearly 600 miles west of the American
continent, all the terrestrial birds, as the finches, doves, hawks, and
others, are so tame, that they may be killed with a switch. One day,
says this author, "a mocking bird alighted on the edge of a pitcher
which I held in my hand, and began quietly to sip the water, and allowed
me to lift it with the vessel from the ground." Yet formerly, when the
first Europeans landed, and found no inhabitants in these islands, the
birds were even tamer than now: already they are beginning to acquire
that salutary dread of man which in countries long settled is natural
even to young birds which have never received any injury. So in the
Falkland Islands, both the birds and foxes are entirely without fear of
man; whereas, in the adjoining mainland of South America, many of the
same species of birds are extremely wild; for there they have for ages
been persecuted by the natives.[822]

Dr. Richardson informs us, in his able history of the habits of the
North American animals, that, "in the retired parts of the mountains
where the hunters had seldom penetrated, there is no difficulty in
approaching the Rocky Mountain sheep, which there exhibit _the
simplicity of character so remarkable in the domestic species_; but
where they have been often fired at, they are exceedingly wild, alarm
their companions, on the approach of danger, by a hissing noise, and
scale the rocks with a speed and agility that baffle pursuit."[823]

It is probable, therefore, that as man, in diffusing himself over the
globe, has tamed many wild races, so, also, he has made many tame races
wild. Had some of the larger carnivorous beasts, capable of scaling the
rocks, made their way into the North American mountains before our
hunters, a similar alteration in the instincts of the sheep would
doubtless have been brought about.

_Wild elephants domesticated in a few years._--No animal affords a more
striking illustration of the principal points which I have been
endeavouring to establish than the elephant; for, in the first place,
the wonderful sagacity with which he accommodates himself to the society
of man, and the new habits which he contracts, are not the result of
time, nor of modifications produced in the course of many generations.
These animals will breed in captivity, as is now ascertained, in
opposition to the vulgar opinion of many modern naturalists, and in
conformity to that of the ancients Ælian and Columella[824]: yet it has
always been the custom, as the least expensive mode of obtaining them,
to capture wild individuals in the forests, usually when full grown;
and, in a few years after they are taken--sometimes, it is said, in the
space of a few months--their education is completed.

Had the whole species been domesticated from an early period in the
history of man, like the camel, their superior intelligence would,
doubtless, have been attributed to their long and familiar intercourse
with the lord of the creation; but we know that a few years is
sufficient to bring about this wonderful change of habits; and although
the same individual may continue to receive tuition for a century
afterwards, yet it makes no farther progress in the general development
of its faculties. Were it otherwise, indeed, the animal would soon
deserve more than the poet's epithet of "half-reasoning."

From the authority of our countrymen employed in the late Burmese war,
it appears, in corroboration of older accounts, that when elephants are
required to execute extraordinary tasks, they may be made to understand
that they will receive unusual rewards. Some favourite dainty is shown
to them, in the hope of acquiring which the work is done; and so
perfectly does the nature of the contract appear to be understood, that
the breach of it, on the part of the master, is often attended with
danger. In this case, a power has been given to the species to adapt
their social instincts to new circumstances with surprising rapidity;
but the extent of this change is defined by strict and arbitrary limits.
There is no indication of a tendency to continued divergence from
certain attributes with which the elephant was originally endued--no
ground whatever for anticipating that, in thousands of centuries, any
material alteration could ever be effected. All that we can infer from
analogy is, that some more useful and peculiar races might probably be
formed, if the experiment were fairly tried; and that some individual
characteristic, now only casual and temporary, might be perpetuated by
generation.

In all cases, therefore, where the domestic qualities exist in animals,
they seem to require no lengthened process for their developement; and
they appear to have been wholly denied to some classes, which, from
their strength and social disposition, might have rendered great
services to man; as, for example, the greater part of the quadrumana.
The orang-outang, indeed, which, for its resemblance in form to man, and
apparently for no other good reason, has been assumed by Lamarck to be
the most perfect of the inferior animals, has been tamed by the savages
of Borneo, and made to climb lofty trees, and to bring down the fruit.
But he is said to yield to his masters an unwilling obedience, and to be
held in subjection only by severe discipline. We know nothing of the
faculties of this animal which can suggest the idea that it rivals the
elephant in intelligence; much less anything which can countenance the
dreams of those who have fancied that it might have been transmuted into
the "dominant race." One of the baboons of Sumatra (_Simia carpolegus_)
appears to be more docile, and is frequently trained by the inhabitants
to ascend trees, for the purpose of gathering cocoa-nuts; a service in
which the animal is very expert. He selects, says Sir Stamford Raffles,
the ripe nuts, with great judgment, and pulls no more than he is
ordered.[825] The capuchin and cacajao monkeys are, according to
Humboldt, taught to ascend trees in the same manner, and to throw down
fruit on the banks of the lower Orinoco.[826]

It is for the Lamarckians to explain how it happens that those same
savages of Borneo have not themselves acquired, by dint of longing, for
many generations, for the power of climbing trees, the elongated arms of
the ourang, or even the prehensile tails of some American monkeys:
Instead of being reduced to the necessity of subjugating stubborn and
untractable brutes, we should naturally have anticipated "that their
wants would have excited them to efforts, and that continued efforts
would have given rise to new organs;" or rather to the re-acquisition of
organs which, in a manner irreconcileable with the principle of the
_progressive_ system, have grown obsolete in tribes of men which have
such constant need of them.

_Recapitulation._--It follows, then, from the different facts which have
been considered in this chapter, that a short period of time is
generally sufficient to effect nearly the whole change which an
alteration of external circumstances can bring about in the habits of a
species, and that such capacity of accommodation to new circumstances is
enjoyed in very different degrees, by different species.

Certain qualities appear to be bestowed exclusively with a view to the
relations which are destined to exist between different species, and,
among others, between certain species and man; but these latter are
always so nearly connected with the original habits and propensities of
each species in a wild state, that they imply no indefinite capacity of
varying from the original type. The acquired habits derived from human
tuition are rarely transmitted to the offspring; and when this happens,
it is almost universally the case with those merely which have some
obvious connexion with the attributes of the species when in a state of
independence.




CHAPTER XXXVI.

WHETHER SPECIES HAVE A REAL EXISTENCE IN NATURE--_continued_.


  Phenomena of hybrids--Hunter's opinions--Mules not strictly
    intermediate between parent species--Hybrid plants--Experiments of
    Kölreuter and Wiegmann--Vegetable hybrids prolific throughout
    several generations--Why rare in a wild state--Decundolle on hybrid
    plants--The phenomena of hybrids confirm the distinctness of
    species--Theory of the gradation in the intelligence of animals as
    indicated by the facial angle--Doctrine that certain organs of the
    foetus in mammalia assume successively the forms of fish, reptile,
    and bird--Recapitulation.


_Phenomena of hybrids._--We have yet to consider another class of
phenomena, those relating to the production of hybrids, which have been
regarded in a very different light with reference to their bearing on
the question of the permanent distinctness of species; some naturalists
considering them as affording the strongest of all proofs in favor of
the reality of species; others, on the contrary, appealing to them as
countenancing the opposite doctrine, that all the varieties of
organization and instinct now exhibited in the animal and vegetable
kingdoms may have been propagated from a small number of original types.

In regard to the mammifers and birds it is found that no sexual union
will take place between races which are remote from each other in their
habits and organization; and it is only in species that are very nearly
allied that such unions produce offspring. It may be laid down as a
general rule, admitting of very few exceptions among quadrupeds, that
the hybrid progeny is sterile; and there seem to be no well
authenticated examples of the continuance of the mule race beyond one
generation. The principal number of observations and experiments relate
to the mixed offspring of the horse and the ass; and in this case it is
well established that the he-mule can generate, and the she-mule
produce. Such cases occur in Spain and Italy, and much more frequently
in the West Indies and New Holland; but these mules have never bred in
cold climates, seldom in warm regions, and still more rarely in
temperate countries.

The hybrid offspring of the she-ass and the stallion, the γιννος of
Aristotle, and the hinnus of Pliny, differs from the mule, or the
offspring of the ass and mare. In both cases, says Buffon, these animals
retain more of the dam than of the sire, not only in the magnitude, but
in the figure of the body: whereas, in the form of the head, limbs, and
tail, they bear a greater resemblance to the sire. The same naturalist
infers, from various experiments respecting cross-breeds between the
he-goat and ewe, the dog and she-wolf, the goldfinch and canary-bird,
that the male transmits his sex to the greatest number, and that the
preponderance of males over females exceeds that which prevails where
the parents are of the same species.

_Hunter's opinion._--The celebrated John Hunter has observed, that the
true distinction of species must ultimately be gathered from their
incapacity of propagating with each other, and producing offspring
capable of again continuing itself. He was unwilling, however, to admit
that the horse and the ass were of the same species, because some rare
instances had been adduced of the breeding of mules, although he
maintained that the wolf, the dog, and the jackal were all of one
species; because he had found, by two experiments, that the dog would
breed both with the wolf and the jackal; and that the mule, in each
case, would breed again with the dog. In these cases, however, it may be
observed, that there was always one parent at least of pure breed, and
no proof was obtained that a true hybrid race could be perpetuated; a
fact of which I believe no examples are yet recorded, either in regard
to mixtures of the horse and ass, or any other of the mammalia.

Should the fact be hereafter ascertained, that two mules can propagate
their kind, we must still inquire whether the offspring may not be
regarded in the light of a monstrous birth, proceeding from some
accidental cause, or, rather, to speak more philosophically, from some
general law not yet understood, but which may not be permitted
permanently to interfere with those laws of generation by which species
may, in general, be prevented from becoming blended. If, for example, we
discovered that the progeny of a mule race degenerated greatly, in the
first generation, in force, sagacity, or any attribute necessary for its
preservation in a state of nature, we might infer that, like a monster,
it is a mere temporary and fortuitous variety. Nor does it seem probable
that the greater number of such monsters could ever occur unless
obtained by art; for, in Hunter's experiments, stratagem or force was,
in most instances, employed to bring about the irregular connexion.[827]

_Mules not strictly intermediate between the parent species._--It seems
rarely to happen that the mule offspring is truly intermediate in
character between the two parents. Thus Hunter mentions that, in his
experiments, one of the hybrid pups resembled the wolf much more than
the rest of the litter; and we are informed by Wiegmann, that, in a
litter lately obtained in the Royal Menagerie at Berlin, from a white
pointer and a she-wolf, two of the cubs resembled the common wolf-dog,
but the third was like a pointer with hanging ears.

There is undoubtedly a very close analogy between these phenomena and
those presented by the intermixture of distinct races of the same
species, both in the inferior animals and in man. Dr. Prichard, in his
"Physical History of Mankind," cites examples where the peculiarities of
the parents have been transmitted very unequally to the offspring; as
where children, entirely white, or perfectly black, have sprung from the
union of the European and the negro. Sometimes the colour or other
peculiarities of one parent, after having failed to show themselves in
the immediate progeny, reappear in a subsequent generation; as where a
white child is born of two black parents, the grandfather having been a
white.[828]

The same author judiciously observes that, if different species mixed
their breed, and hybrid races were often propagated, the animal world
would soon present a scene of confusion; its tribes would be every where
blended together, and we should perhaps find more hybrid creatures than
genuine and uncorrupted races.[829]

_Hybrid plants._--_Kölreuter's experiments_.--The history of the
vegetable kingdom has been thought to afford more decisive evidence in
favour of the theory of the formation of new and permanent species from
hybrid stocks. The first accurate experiments in illustration of this
curious subject appear to have been made by Kölreuter, who obtained a
hybrid from two species of tobacco, _Nicotiana rustica_ and _N.
paniculata_, which differ greatly in the shape of their leaves, the
colour of the corolla, and the height of the stem. The stigma of a plant
of _N. rustica_ was impregnated with the pollen of a plant of _N.
paniculata_. The seed ripened, and produced a hybrid which was
intermediate between the two parents, and which, like all the hybrids
which this botanist brought up, had imperfect stamens. He afterwards
impregnated this hybrid with the pollen of _N. paniculata_, and obtained
plants which much more resembled the last. This he continued through
several generations, until, by due perseverance, he actually changed the
_Nicotiana rustica_ into the _Nicotiana paniculata_.

The plan of impregnation adopted, was the cutting off of the anthers of
the plant intended for fructification before they had shed pollen, and
then laying on foreign pollen upon the stigma.

_Wiegmann's experiments._--The same experiment has since been repeated
with success by Wiegmann, who found that he could bring back the hybrids
to the exact likeness of either parent, by crossing them a sufficient
number of times.

The blending of the characters of the parent stocks, in many other of
Wiegmann's experiments, was complete; the colour and shape of the leaves
and flowers, and even the scent, being intermediate, as in the offspring
of the two species of verbascum. An intermarriage, also, between the
common onion and the leek (_Allium cepa_ and _A. porrum_) gave a mule
plant, which, in the character of its leaves and flowers, approached
most nearly to the garden onion, but had the elongated bulbous root and
smell of the leek.

The same botanist remarks, that vegetable hybrids, when not strictly
intermediate, more frequently approach the female than the male parent
species; _but they never exhibit characters foreign to both_. A re-cross
with one of the original stocks generally causes the mule plant to
revert towards that stock; but this is not always the case, the
offspring sometimes continuing to exhibit the character of a full
hybrid.

In general, the success attending the production and perpetuity of
hybrids among plants depends, as in the animal kingdom, on the degree of
proximity between the species intermarried. If their organization be
very remote, impregnation never takes place; if somewhat less distant,
seeds are formed, but always imperfect and sterile. The next degree of
relationship yields hybrid seedlings, but these are barren; and it is
only when the parent species are very nearly allied that the hybrid race
may be perpetuated for several generations. Even in this case the best
authenticated examples seem confined to the crossing of hybrids with
individuals of pure breed. In none of the experiments most accurately
detailed does it appear that both the parents were mules.

Wiegmann diversified as much as possible his mode of bringing about
these irregular unions among plants. He often sowed parallel rows, near
to each other, of the species from which he desired to breed; and,
instead of mutilating, after Kölreuter's fashion, the plants of one of
the parent stocks, he merely washed the pollen off their anthers. The
branches of the plants in each row were then gently bent towards each
other and intertwined; so that the wind, and numerous insects, as they
passed from the flowers of one to those of the other species, carried
the pollen and produced fecundation.

_Vegetable hybrids why rare in a wild slate._--The same observer saw a
good exemplification of the manner in which hybrids may be formed in a
state of nature. Some wallflowers and pinks had been growing in a
garden, in a dry sunny situation, and their stigmas had been ripened so
as to be moist, and to absorb pollen with avidity, although their
anthers were not yet developed. These stigmas became impregnated by
pollen blown from some other adjacent plants of the same species; but
had they been of different species, and not too remote in their
organization, mule races must have resulted.

When, indeed, we consider how busily some insects have been shown to be
engaged in conveying anther-dust from flower to flower, especially bees,
flower-eating beetles, and the like, it seems a most enigmatical problem
how it can happen that promiscuous alliances between distinct species
are not perpetually occurring.

How continually do we observe the bees diligently employed in collecting
the red and yellow powder by which the stamens of flowers are covered,
loading it on their hind legs, and carrying it to their hive for the
purpose of feeding their young! In thus providing for their own progeny,
these insects assist materially the process of fructification.[830] Few
persons need be reminded that the stamens in certain plants grow on
different blossoms from the pistils; and unless the summit of the pistil
be touched with the fertilizing dust, the fruit does not swell, nor the
seed arrive at maturity. It is by the help of bees chiefly, that the
development of the fruit of many such species is secured, the powder
which they have collected from the stamens being unconsciously left by
them in visiting the pistils.

How often, during the heat of a summer's day, do we see the males of
dioecious plants, such as the yew-tree, standing separate from the
females, and sending off into the air, upon the slightest breath of
wind, clouds of buoyant pollen! That the zephyr should so rarely
intervene to fecundate the plants of one species with the anther-dust of
others, seems almost to realize the converse of the miracle believed by
the credulous herdsmen of the Lusitanian mares--


  Ore omnes versæ in Zephyrum, stant rupibus altis
  Exceptantque leves auras: et sæpe sine ullis
  Conjugiis, vento gravidæ, mirabile dictu.[831]


But, in the first place, it appears that there is a natural aversion in
plants, as well as in animals, to irregular sexual unions; and in most
of the successful experiments in the animal and vegetable world, some
violence has been used in order to procure impregnation. The stigma
imbibes, slowly and reluctantly, the granules of the pollen of another
species, even when it is abundantly covered with it; and if it happen
that, during this period, ever so slight a quantity of the anther-dust
of its own species alight upon it, this is instantly absorbed, and the
effect of the foreign pollen destroyed. Besides, it does not often
happen that the male and female organs of fructification, in different
species, arrive at a state of maturity at precisely the same time. Even
where such synchronism does prevail, so that a cross impregnation is
effected, the chances are very numerous against the establishment of a
hybrid race.

If we consider the vegetable kingdom generally, it must be recollected
that even of the seeds which are well ripened, a great part are either
eaten by insects, birds, and other animals, or decay for want of room
and opportunity to germinate. Unhealthy plants are the first which are
cut off by causes prejudicial to the species, being usually stifled by
more vigorous individuals of their own kind. If, therefore, the relative
fecundity or hardiness of hybrids be in the least degree inferior, they
cannot maintain their footing for many generations, even if they were
ever produced beyond one generation in a wild state. In the universal
struggle for existence, the right of the strongest eventually prevails;
and the strength and durability of a race depend mainly on its
prolificness, in which hybrids are acknowledged to be deficient.

_Centaurea hybrida_, a plant which never bears seed, and is supposed to
be produced by the frequent intermixture of two well-known species of
Centaurea, grows wild upon a hill near Turin. _Ranunculus lacerus_, also
sterile, has been produced accidentally at Grenoble, and near Paris, by
the union of two Ranunculi; but this occurred in gardens.[832]

_Mr. Herbert's experiments._--Mr. Herbert, in one of his ingenious
papers on mule plants, endeavors to account for their non-occurrence in
a state of nature, from the circumstance that all the combinations that
were likely to occur have already been made many centuries ago, and have
formed the various species of botanists; but in our gardens, he says,
whenever species, having a certain degree of affinity to each other, are
transported from different countries, and brought for the first time
into contact, they give rise to hybrid species.[833] But we have no
data, as yet, to warrant the conclusion, that a single permanent hybrid
race has ever been formed, even in gardens, by the intermarriage of two
allied species brought from distant habitations. Until some fact of this
kind is fairly established, and a new species, capable of perpetuating
itself in a state of perfect independence of man, can be pointed out, it
seems reasonable to call in question entirely this hypothetical source
of new species. That varieties do sometimes spring up from
cross-breeds, in a natural way, can hardly be doubted; but they
probably die out even more rapidly than races propagated by grafts or
layers.

_Opinion of De Candolle._--De Candolle, whose opinion on a philosophical
question of this kind deserves the greatest attention, has observed, in
his Essay on Botanical Geography, that the _varieties_ of plants range
themselves under two general heads: those produced by external
circumstances, and those formed by hybridity. After adducing various
arguments to show that neither of these causes can explain the permanent
diversity of plants indigenous in different regions, he says, in regard
to the crossing of races, "I can perfectly comprehend without altogether
sharing the opinion, that, where many species of the same genera occur
near together, hybrid species may be formed, and I am aware that the
great number of species of certain genera which are found in particular
regions may be explained in this manner; but I am unable to conceive how
any one can regard the same explanation as applicable to species
which live naturally at great distances. If the three larches, for
example, now known in the world, lived in the same localities, I might
then believe that one of them was the produce of the crossing of the two
others; but I never could admit that the Siberian species has been
produced by the crossing of those of Europe and America. I see, then,
that there exist in organized beings, permanent differences which cannot
be referred to any one of the actual causes of variation, and these
differences are what constitute species."[834]

_Reality of species confirmed by the phenomena of hybrids._--The most
decisive arguments perhaps, amongst many others, against the probability
of the derivation of permanent species from cross-breeds, are to be
drawn from the fact alluded to by De Candolle, of species having a close
affinity to each other occurring in distinct botanical provinces, or
countries inhabited by groups of distinct species of indigenous plants;
for in this case naturalists, who are not prepared to go the whole
length of the transmutationists, are under the necessity of admitting
that, in some cases, species which approach very near to each other in
their characters, were so created from their origin; an admission fatal
to the idea of its being a general law of nature that a few original
types only should be formed, and that all intermediate races should
spring from the intermixture of those stocks.

This notion, indeed, is wholly at variance with all that we know of
hybrid generation; for the phenomena entitle us to affirm, that had the
types been at first somewhat distinct, _no cross-breeds would ever have
been produced_, much less those prolific races which we now recognize as
distinct species.

In regard, moreover, to the permanent propagation of hybrid races among
animals, insuperable difficulties present themselves, when we endeavor
to conceive the blending together of the different instincts and
propensities of two species, so as to insure the preservation of the
intermediate race. The common mule, when obtained by human art, may be
protected by the power of man; but, in a wild state, it would not have
precisely the same wants either as the horse or the ass; and if in
consequence of some difference of this kind, it strayed from the herd,
it would soon be hunted down by beasts of prey, and destroyed.

If we take some genus of insects, such as the bee, we find that each of
the numerous species has some difference in its habits, its mode of
collecting honey, or constructing its dwelling, or providing for its
young, and other particulars. In the case of the common hive bee, the
workers are described, by Kirby and Spence, as being endowed with no
less than thirty distinct instincts.[835] So also we find that, amongst
a most numerous class of spiders, there are nearly as many different
modes of spinning their webs as there are species. When we recollect how
complicated are the relations of these instincts with co-existing
species, both of the animal and vegetable kingdoms, it is scarcely
possible to imagine that a bastard race could spring from the union of
two of these species, and retain just so much of the qualities of each
parent stock as to preserve its ground in spite of the dangers which
surround it.

We might also ask, if a few generic types alone have been _created_
among insects, and the intermediate species have proceeded from
hybridity, where are those original types, combining, as they ought to
do, the elements of all the instincts which have made their appearance
in the numerous derivative races? So also in regard to animals of all
classes, and of plants; if species are in general of hybrid origin,
where are the stocks which combine in themselves the habits, properties,
and organs, of which all the intervening species ought to afford us mere
modifications?

_Recapitulation of the arguments from hybrids._--I shall now conclude
this subject by summing up, in a few words, the results to which I have
been led by the consideration of the phenomena of hybrids. It appears
that the aversion of individuals of distinct species to the sexual union
is common to animals and plants; and that it is only when the species
approach near to each other in their organization and habits, that any
offspring are produced from their connexion. Mules are of extremely rare
occurrence in a state of nature, and no examples are yet known of their
having procreated in a wild state. But it has been proved, that hybrids
are not universally sterile, provided the parent stocks have a near
affinity to each other, although the continuation of the mixed race, for
several generations, appears hitherto to have been obtained only by
crossing the hybrids with individuals of pure species; an experiment
which by no means bears out the hypothesis that a true hybrid race could
ever be permanently established.

Hence we may infer, that aversion to sexual intercourse is, in general,
a good test of the distinctness of original stocks, or of _species_; and
the procreation of hybrids is a proof of the near affinity of species.
Perhaps, hereafter, the number of generations for which hybrids may be
continued, before the race dies out (for it seems usually to degenerate
rapidly), may afford the zoologist and botanist an experimental test of
the difference in the degree of affinity of allied species.

I may also remark, that if it could have been shown that a single
permanent species had ever been produced by hybridity (of which there is
no satisfactory proof), it might certainly have lent some countenance to
the notions of the ancients respecting the gradual deterioration of
created things, but none whatever to Lamarck's theory of their
progressive perfectibility, for observations have hitherto shown that
there is a tendency in mule animals and plants to degenerate in
organization.

It was before remarked, that the theory of progressive development arose
partly from an attempt to ingraft the doctrines of the transmutationists
upon one of the most popular generalizations in geology. But we have
seen in the ninth chapter, that the modern researches of geologists have
broken at many points the chain of evidence once supposed to exist in
favor of the doctrine, that, at each successive period in the earth's
history, animals and plants of a higher grade, or more complex
organization, have been created. The recent origin of man, and the
absence of all signs of any rational being holding an analogous relation
to former states of the animate world, affords one, and perhaps in the
present state of science the only argument of much weight in support of
the hypothesis of a progressive scheme; but none whatever in favor of
the fancied evolution of one species out of another.

_Theory of the gradation of intellect as shown by the facial
angle._--When the celebrated anatomist, Camper, first attempted to
estimate the degrees of sagacity of different animals, and of the races
of man, by the measurement of the facial angle, some speculators were
bold enough to affirm that certain Simiæ, or apes, differed as little
from the more savage races of men, as those do from the human race in
general; and that a scale might be traced from "apes with foreheads
villanous low" to the African variety of the human species, and from
that to the European. The facial angle was measured by drawing a line
from the prominent centre of the forehead to the most advanced part of
the lower jaw-bone, and observing the angle which it made with the
horizontal line; and it was affirmed, that there was a regular series of
such angles from birds to the mammalia.

The gradation from the dog to the monkey was said to be perfect, and
from that again to man. One of the ape tribe has a facial angle of 42°;
and another, which approximated nearest to man in figure, an angle of
50°. To this succeeds (longo sed proximus intervallo) the head of the
African negro, which, as well as that of the Calmuck, forms an angle of
70°; while that of the European contains 80°. The Roman painters
preferred the angle of 95°; and the character of beauty and sublimity so
striking in some works of Grecian sculpture, as in the head of the
Apollo, and in the Medusa of Sisocles, is given by an angle which
amounts to 100°.[836]

A great number of valuable facts and curious analogies in comparative
anatomy were brought to light during the investigations which were made
by Camper, John Hunter, and others, to illustrate this scale of
organization; and their facts and generalizations must not be confounded
with the fanciful systems which White and others deduced from them.[837]

That there is some connexion between an elevated and capacious forehead,
in certain races of men, and a large developement of the intellectual
faculties, seems highly probable; and that a low facial angle is
frequently accompanied with inferiority of mental powers, is certain;
but the attempt to trace a gradual scale of intelligence through the
different species of animals accompanying the modifications of the form
of the scull, is a mere visionary speculation. It has been found
necessary to exaggerate the sagacity of the ape tribe at the expense of
the dog; and strange contradictions have arisen in the conclusions
deduced from the structure of the elephant; some anatomists being
disposed to deny the quadruped the intelligence which he really
possesses, because they found that the volume of his brain was small in
comparison to that of the other mammalia; while others were inclined to
magnify extravagantly the superiority of his intellect, because the
vertical height of his skull is so great when compared to its horizontal
length.

_Different races of men are all of one species._--It would be irrelevant
to our subject if we were to enter into a farther discussion on these
topics; because, even if a graduated scale of organization and
intelligence could have been established, it would prove nothing in
favor of a tendency, in each species, to attain a higher state of
perfection. I may refer the reader to the writings of Blumenbach,
Prichard, Lawrence, and more recently Latham[838], for convincing proofs
that the varieties of form, color, and organization of different races
of men, are perfectly consistent with the generally received opinion,
that all the individuals of the species have originated from a single
pair; and, while they exhibit in man as many diversities of a
physiological nature as appear in any other species, they confirm also
the opinion of the slight deviation from a common standard of which
species are capable.

The power of existing and multiplying in every latitude, and in every
variety of situation and climate, which has enabled the great human
family to extend itself over the habitable globe, is partly, says
Lawrence, the result of physical constitution, and partly of the mental
prerogative of man. If he did not possess the most enduring and flexible
corporeal frame, his arts would not enable him to be the inhabitant of
all climates, and to brave the extremes of heat and cold, and the other
destructive influences of local situation.[839] Yet, notwithstanding
this flexibility of bodily frame, we find no signs of indefinite
departure from a common standard, and the intermarriages of individuals
of the most remote varieties are not less fruitful than between those of
the same tribe.

_Tiedemann on the brain of the foetus in vertebrated animals._--There
is yet another department of anatomical discovery to which I must
allude, because it has appeared to some persons to afford a distant
analogy, at least, to that progressive development by which some of the
inferior species may have been gradually perfected into those of more
complex organization. Tiedemann found, and his discoveries have been
most fully confirmed and elucidated by M. Serres, that the brain of the
foetus, in the highest class of vertebrated animals, assumes, in
succession, forms, bearing a certain degree of resemblance to those
which belong to fishes, reptiles, and birds, before it acquires the
additions and modifications which are peculiar to the mammiferous tribe;
so that, in the passage from the embryo to the perfect mammifer, there
is a typical representation, it is said, of all those transformations
which the primitive species are supposed to have undergone, during a
long series of generations, between the present period and the remotest
geological era.

"If you examine the brain of the mammalia," says M. Serres, "at an early
stage of uterine life, you perceive the cerebral hemispheres
consolidated, as in fish, in two vesicles, isolated one from the other;
at a later period, you see them affect the configuration of the cerebral
hemispheres of reptiles; still later again, they present you with the
forms of those of birds; finally they acquire, at the era of birth, and
sometimes later, the permanent forms which the adult mammalia present.

"The cerebral hemispheres, then, arrive at the state which we observe in
the higher animals only by a series of successive metamorphoses. If we
reduce the whole of these evolutions to four periods, we shall see, that
in the first are born the cerebral lobes of fishes; and this takes place
homogeneously in all classes. The second period will give us the
organization of reptiles; the third, the brain of birds; and the fourth,
the complex hemispheres of mammalia.

"If we could develop the different parts of the brain of the inferior
classes, we should make, in succession, a reptile out of a fish, a bird
out of a reptile, and a mammiferous quadruped out of a bird. If, on the
contrary, we could starve this organ in the mammalia, we might reduce it
successively to the condition of the brain of the three inferior
classes.

"Nature often presents us with this last phenomenon in monsters, but
never exhibits the first. Among the various deformities which organized
beings may experience, they never pass the limits of their own classes
to put on the forms of the class above them. Never does a fish elevate
itself so as to assume the form of the brain of a reptile; nor does the
latter ever attain that of birds; nor the bird that of the mammifer. It
may happen that a monster may have two heads; but the conformation of
the brain always remains circumscribed narrowly within the limits of its
class."[840]

Dr. Clark of Cambridge, in a memoir on "Foetal Development" (1845),
has shown that the concurrent labours of Valentin, Ratké, and Bischoff
disprove the reality of the supposed anatomical analogy between the
embryo condition of certain organs in the higher orders, and the perfect
structure of the same organs in animals of an inferior class. The hearts
and brains, for example, of birds and mammals do not pass through forms
which are permanent in fishes and reptiles; there is only just so much
resemblance as may point to a unity of plan running through the
organization of the whole series of vertebrated animals; but which lends
no support whatever to the notion of a gradual transmutation of one
species into another; least of all of the passage, in the course of many
generations, from an animal of a more simple to one of a more complex
structure.

_Recapitulation._--For the reasons, therefore, detailed in this and the
two preceding chapters, we may draw the following inferences in regard
to the reality of _species_ in nature:--

1st. That there is a capacity in all species to accommodate themselves,
to a certain extent, to a change of external circumstances, this extent
varying greatly, according to the species.

2ndly. When the change of situation which they can endure is great, it
is usually attended by some modifications of the form, colour, size,
structure, or other particulars; but the mutations thus superinduced are
governed by constant laws, and the capability of so varying, forms part
of the permanent specific character.

3dly. Some acquired peculiarities, of form, structure, and instinct, are
transmissible to the offspring; but these consist of such qualities and
attributes only as are intimately related to the natural wants and
propensities of the species.

4thly. The entire variation from the original type, which any given kind
of change can produce, may usually be effected in a brief period of
time, after which no farther deviation can be obtained by continuing to
alter the circumstances, though ever so gradually; indefinite
divergence, either in the way of improvement or deterioration, being
prevented, and the least possible excess beyond the defined limits being
fatal to the existence of the individual.

5thly. The intermixture of distinct species is guarded against by the
aversion of the individuals composing them to sexual union, or by the
sterility of the mule offspring. It does not appear that true hybrid
races have ever been perpetuated for several generations, even by the
assistance of man; for the cases usually cited relate to the crossing of
mules with individuals of pure species, and not to the intermixture of
hybrid with hybrid.

6thly. From the above considerations, it appears that species have a
real existence in nature; and that each was endowed, at the time of its
creation, with the attributes and organization by which it is now
distinguished.




CHAPTER XXXVII.

LAWS WHICH REGULATE THE GEOGRAPHICAL DISTRIBUTION OF SPECIES.


  Analogy of climate not attended with identity of species--Botanical
    geography--Stations--Habitations--Distinct provinces of indigenous
    plants--Vegetation of islands--Marine vegetation--In what manner
    plants become diffused--Effects of wind, rivers, marine
    currents--Agency of animals--Many seeds pass through the stomachs of
    animals and birds undigested--Agency of man in the dispersion of
    plants, both voluntary and involuntary--Its analogy to that of the
    inferior animals.


Next to determining the question whether species have a real existence,
the consideration of the laws which regulate their geographical
distribution is a subject of primary importance to the geologist. It is
only by studying these laws with attention, by observing the positions
which groups of species occupy at present, and inquiring how these may
be varied in the course of time by migrations, by changes in physical
geography, and other causes, that we can hope to learn whether the
duration of species be limited, or in what manner the state of the
animate world is affected by the endless vicissitudes of the inanimate.

_Different regions inhabited by distinct species._--That different
regions of the globe are inhabited by entirely distinct animals and
plants, is a fact which has been familiar to all naturalists since
Buffon first pointed out the want of _specific_ identity between the
land quadrupeds of America and those of the Old World. The same
phenomenon has, in later times, been forced in a striking manner upon
our attention, by the examination of New Holland, where the indigenous
species of animals and plants were found to be, almost without
exception, distinct from those known in other parts of the world.

But the extent of this parcelling out of the globe amongst different
_nations_, as they have been termed, of plants and animals--the
universality of a phenomenon so extraordinary and unexpected, may be
considered as one of the most interesting facts clearly established by
the advance of modern science.

Scarcely fourteen hundred species of plants appear to have been known
and described by the Greeks, Romans, and Arabians. At present, more than
three thousand species are enumerated, as natives of our own
island.[841] In other parts of the world there have been now collected
(1846) upwards of 100,000 species, specimens of which are preserved in
European herbariums. It was not to be supposed, therefore, that the
ancients should have acquired any correct notions respecting what may be
called the geography of plants, although the influence of climate on the
character of the vegetation could hardly have escaped their observation.


Antecedently to investigation, there was no reason for presuming that
the vegetable productions, growing wild in the eastern hemisphere,
should be unlike those of the western, in the same latitude; nor that
the plants of the Cape of Good Hope should be unlike those of the south
of Europe; situations where the climate is little dissimilar. The
contrary supposition would have seemed more probable, and we might have
anticipated an almost perfect identity in the animals and plants which
inhabit corresponding parallels of latitude. The discovery, therefore,
that each separate region of the globe, both of the land and water, is
occupied by distinct groups of species, and that most of the exceptions
to this general rule may be referred to disseminating causes now in
operation, is eminently calculated to excite curiosity, and to stimulate
us to seek some hypothesis respecting the first introduction of species
which may be reconcileable with such phenomena.

_Botanical geography._--A comparison of the _plants_ of different
regions of the globe affords results more to be depended upon in the
present state of our knowledge than those relating to the animal
kingdom, because the science of botany is more advanced, and probably
comprehends a great proportion of the total number of the vegetable
productions of the whole earth. Humboldt, in several eloquent passages
of his Personal Narrative, was among the first to promulgate
philosophical views on this subject. Every hemisphere, says this
traveller, produces plants of different species; and it is not by the
diversity of climates that we can attempt to explain why equinoctial
Africa has no Laurinæ, and the New World no Heaths; why the Calceolariæ
are found only in the southern hemisphere; why the birds of the
continent of India glow with colors less splendid than the birds of the
hot parts of America: finally, why the tiger is peculiar to Asia, and
the ornithorhynchus to New Holland.[842]

"We can conceive," he adds, "that a small number of the families of
plants, for instance, the Musaceæ and the Palms, cannot belong to very
cold regions, on account of their internal structure and the importance
of certain organs; but we cannot explain why no one of the family of
Melastomas vegetates north of the parallel of thirty degrees; or why no
rose-tree belongs to the southern hemisphere. Analogy of climates is
often found in the two continents without identity of productions."[843]

The luminous essay of De Candolle on "Botanical Geography" presents us
with the fruits of his own researches and those of Humboldt, Brown, and
other eminent botanists, so arranged, that the principal phenomena of
the distribution of plants are exhibited in connexion with the causes to
which they are chiefly referrible.[844] "It might not, perhaps, be
difficult," observes this writer, "to find two points, in the United
States and in Europe, or in Equinoctial America and Africa, which
present all the same circumstances: as, for example, the same
temperature, the same height above the sea, a similar soil, an equal
dose of humidity; yet nearly all, _perhaps all_, the plants in these two
similar localities shall be distinct. A certain degree of analogy,
indeed, of aspect, and even of structure, might very possibly be
discoverable between the plants of the two localities in question; but
the _species_ would in general be different. Circumstances, therefore,
different from those which now determine the _stations_, have had an
influence on the _habitations_ of plants."

_Stations and habitations of plants._--As I shall frequently have
occasion to speak of the _stations_ and _habitations_ of plants in the
technical sense in which the terms are used in the above passage, I may
remind the geologist that station indicates the peculiar nature of the
locality where each species is accustomed to grow, and has reference to
climate, soil, humidity, light, elevation above the sea, and other
analogous circumstances; whereas, by habitation is meant a general
indication of the country where a plant grows wild. Thus the _station_
of a plant may be a salt-marsh, a hill-side, the bed of the sea, or a
stagnant pool. Its _habitation_ may be Europe, North America, or New
Holland, between the tropics. The study of stations has been styled the
topography, that of habitations the geography, of botany. The terms thus
defined, express each a distinct class of ideas, which have been often
confounded together, and which are equally applicable in zoology.

In farther illustration of the principle above alluded to, that
difference of longitude, independently of any influence of temperature,
is accompanied by a great, and sometimes a complete, diversity in the
species of plants, De Candolle observes, that, out of 2891 species of
phænogamous plants described by Pursh, in the United States, there are
only 385 which are found in northern or temperate Europe. MM. Humboldt
and Bonpland, in all their travels through equinoctial America, found
only twenty-four species (these being all Cyperaceæ and Gramineæ) common
to America and any part of the Old World. They collected, it is true,
chiefly on the mountains, or the proportion would have been larger; for
Dr. J. Hooker informs me that many tropical plants of the New World are
identical with African species. Nevertheless, the general discordance of
these Floras is very striking. On comparing New Holland with Europe, Mr.
Brown ascertained that, out of 4100 species, discovered in Australia,
there were only 166 common to Europe, and of this small number there
were some few which may have been transported thither by man. Almost all
of the 166 species were cryptogamic, and the rest consist, in nearly
every case, of phænogamous plants which also inhabit intervening
regions.

But what is still more remarkable, in the more widely separated parts of
the ancient continent, notwithstanding the existence of an uninterrupted
land-communication, the diversity in the specific character of the
respective vegetations is almost as striking. Thus there is found one
assemblage of species in China, another in the countries bordering the
Black Sea and the Caspian, a third in those surrounding the
Mediterranean, a fourth in the great platforms of Siberia and Tartary,
and so forth.

The distinctness of the groups of indigenous plants, in the same
parallel of latitude, is greatest where continents are disjoined by a
wide expanse of ocean. In the northern hemisphere, near the pole, where
the extremities of Europe, Asia, and America unite or approach near to
one another, a considerable number of the same species of plants are
found, common to the three continents. But it has been remarked, that
these plants, which are thus so widely diffused in the arctic regions,
are also found in the chain of the Aleutian islands, which stretch
almost across from America to Asia, and which may probably have served
as the channel of communication for the partial blending of the Floras
of the adjoining regions. It has, indeed, been observed to be a general
rule, that plants found at two points very remote from each other occur
also in places intermediate.

Dr. J. Hooker informs me that in high latitudes in the southern ocean,
in spite of the great extent of the sea, Floras of widely disconnected
islands contain many species in common. Perhaps icebergs, transporting
to vast distances not only stones, but soil with the seeds of plants,
may explain this unusually wide diffusion of insular plants.

In islands very distant from continents the total number of plants is
comparatively small; but a large proportion of the species are such as
occur nowhere else. In so far as the Flora of such islands is not
peculiar to them, it contains, in general, species common to the nearest
main lands.[845] The islands of the great southern ocean exemplify these
rules; the easternmost containing more American, and the western more
Indian plants.[846] Madeira and Teneriffe contain many species, and even
entire genera, peculiar to them; but they have also plants in common
with Portugal, Spain, the Azores, and the north-west coast of
Africa.[847]

In the Canaries, out of 533 species of phænogamous plants, it is said
that 310 are peculiar to these islands, and the rest identical with
those of the African continent; but in the Flora of St. Helena, which is
so far distant even from the western shores of Africa, there have been
found, out of thirty native species of the phænogamous class, only _one
or two_ which are to be found in any other part of the globe. On the
other hand, of sixty cryptogamic plants, collected by Dr. J. Hooker in
the same island, twelve only were peculiar.

The natural history of the Galapagos archipelago, described by Mr.
Darwin, affords another very instructive illustration of the laws
governing the geographical distribution of plants and animals in
islands. This group consists of ten principal islands, situated in the
Pacific Ocean, under the equator, about 600 miles westward of the coast
of South America. As they are all formed of volcanic rocks, many of the
craters, of which there are about 2000 in number, having a very fresh
aspect, we may regard the whole as much more modern in origin than the
mass of the adjoining continent; yet neither has the Flora nor Fauna
been derived from South America, but consist of species for the most
part indigenous, yet stamped with a character decidedly South American.

What is still more singular, there is a difference between the species
inhabiting the different islands. Of flowering plants, for example,
there are 185 species at present known, and forty cryptogamic, making
together 225. One hundred of the former class are new species, probably
confined to this archipelago; and of the rest, ten at least have been
introduced by man. Of twenty-one species of _Compositæ_, all but one are
peculiar, and they belong to twelve genera, no less than ten of which
genera are confined to the Galapagos. Dr. Hooker observes, that the type
of this Flora has an undoubted relation to that of the western side of
South America, and he detects in it no affinity with that of the
numerous islands scattered over other parts of the Pacific. So in regard
to the birds, reptiles, land-shells, and insects, this archipelago,
standing as it does in the Pacific Ocean, is zoologically part of
America. Although each small island is not more than fifty or sixty
miles apart, and most of them are in sight of each other, formed of
precisely the same rocks, rising nearly to an equal height, and placed
under a similar climate, they are tenanted each by a different set of
beings, the tortoises, mocking-thrushes, finches, beetles, scarcely any
of them ever ranging over the whole, and often not even common to any
two of the islands.

"The archipelago," says Mr. Darwin, "is a little world within itself, or
rather a satellite attached to America; whence it has derived a few
stray colonists, and has received the general character of its
indigenous productions. One is astonished," he adds, "at the amount of
creative force displayed on so many small, barren, and rocky islands,
and still more so, at its diverse, yet analogous action on points so
near each other. I have said that the Galapagos archipelago might be
called a satellite attached to America, but it should rather be called a
group of satellites physically similar, organically distinct, yet
intimately related to each other, and all related in a marked, though
much lesser degree, to the great American continent."[848]

_Number of botanical provinces._--De Candolle has enumerated twenty
great botanical provinces inhabited by indigenous or aboriginal plants;
and although many of these contain a variety of species which are common
to several others, and sometimes to places very remote, yet the lines of
demarcation are, upon the whole, astonishingly well defined.[849] Nor is
it likely that the bearing of the evidence on which these general views
are founded will ever be materially affected, since they are already
confirmed by the examination of nearly one hundred thousand species of
plants.

The entire change of opinion which the contemplation of those phenomena
has brought about is worthy of remark. The first travellers were
persuaded that they should find, in distant regions, the plants of their
own country, and they took a pleasure in giving them the same names. It
was some time before this illusion was dissipated; but so fully sensible
did botanists at last become of the extreme smallness of the number of
phænogamous plants common to different continents, that the ancient
Floras fell into disrepute. All grew diffident of the pretended
identifications; and we now find that every naturalist is inclined to
examine each supposed exception with scrupulous severity.[850] If they
admit the fact, they begin to speculate on the mode whereby the seeds
may have been transported from one country into the other, or enquire on
which of two continents the plant was indigenous, assuming that a
species, like an individual, cannot have two birthplaces.

_Marine vegetation._--The marine vegetation is divisible into different
systems, like those prevailing on the land; but they are much fewer, as
we might have expected, the temperature of the ocean being more uniform
than that of the atmosphere, and consequently the dispersion of species
from one zone to another being less frequently checked by the
intervention of uncongenial climates. The proportion also of land to sea
throughout the globe being small, the migration of marine plants is not
so often stopped by barriers of land, as is that of the terrestrial
species by the ocean. The number of hydrophytes, as they are termed, is
very considerable, and their stations are found to be infinitely more
varied than could have been anticipated; for while some plants are
covered and uncovered daily by the tide, others live at the depth of
several hundred feet. Among the known provinces of Algæ, we may mention,
1st, The north circumpolar, from lat 60° N. to the pole; 2dly, The North
Atlantic or the region of Fucus proper and Delesseriæ, extending from
lat. 40° N. to lat. 60° N.; 3dly, That of the Mediterranean, which may
be regarded as a sub-region of the _fourth_ or warmer temperate zone of
the Atlantic, between lat. 23° N. and lat. 40° N.; 5thly, The Tropical
Atlantic, in which Sargassum, Rhodomelia, Corallinea, and Siphonia
abound; 6thly, The South Atlantic, where the Fucus reappears; 7thly, The
Antarctic American, comprehending from Chili to Cape Horn, the Falkland
Islands, and thence round the world south of latitude 50° S.; 8thly, The
Australian and New Zealand, which is very peculiar, being characterized,
among other generic forms, by Cystoseiriæ and Fuceæ; 9thly, The Indian
Ocean and Red Sea; and, 10thly, The Chinese and Japanese seas.[851] In
addition to the above provinces, there are several others not yet well
determined in the Pacific Ocean and elsewhere. There are, however, many
species which range through several of these geographical regions of
subaqueous vegetation, being common to very remote countries; as, for
example, to the coasts of

Europe and the United States, and others, to Cape Horn and Van Diemen's
Land, the same plants extending also for the most part to the New
Zealand sea. Of the _species_ strictly antarctic (excluding the New
Zealand and Tasmanian groups) Dr. Hooker has identified not less than a
fifth part of the whole with British Algæ! Yet is there a much smaller
proportion of cosmopolite species among the Algæ than among the
terrestrial cellular plants, such as lichens, mosses, and Hepaticæ.

It must always be borne in mind, that the distinctness alluded to
between the provinces, whether of subaqueous or terrestrial plants,
relates strictly to _species_, and not to forms. In regard to the
numerical preponderance of certain forms, and many peculiarities of
internal structure, there is usually a marked agreement in the vegetable
productions of districts placed in corresponding latitudes, and under
similar physical circumstances, however remote their position. Thus
there are innumerable points of analogy between the vegetation of the
Brazils, equinoctial Africa, and India; and there are also points of
difference wherein the plants of these regions are distinguishable from
all extra-tropical groups. But there is a very small proportion of the
entire number of species common to the three continents. The same may be
said, if we compare the plants of the United States with that of the
middle of Europe; the species are distinct, but the forms are often so
analogous, as to have been styled "geographical representatives." There
are very few _species_ of phænogamous plants, says Dr. J. Hooker, common
to Van Diemen's Land, New Zealand, and Fuegia, but a great many
_genera_, and some of them are confined to those three distant regions
of the southern hemisphere, being in many instances each severally
represented by a single species. The same naturalist also observes that
the southern temperate as well as the antarctic regions, possess each of
them representatives of some of the genera of the analogous climates of
the opposite hemisphere; but very few of the species are identical
unless they be such as are equally diffused over other countries, or
which inhabit the Andes, by the aid of which they have evidently
effected their passage southwards.

_Manner in which plants become diffused.--Winds._--Let us now consider
what means of diffusion, independently of the agency of man, are
possessed by plants, whereby, in the course of ages, they may be enabled
to stray from one of the botanical provinces above mentioned to another,
and to establish new colonies at a great distance from their birthplace.

The principal of the inanimate agents provided by nature for scattering
the seeds of plants over the globe, are the movements of the atmosphere
and of the ocean, and the constant flow of water from the mountains to
the sea. To begin with the winds: a great number of seeds, are furnished
with downy and feathery appendages, enabling them, when ripe, to float
in the air, and to be wafted easily to great distances by the most
gentle breeze. Other plants are fitted for dispersion by means of an
attached wing, as in the case of the fir tree, so that they are caught
up by the wind as they fall from the cone, and are carried to a
distance. Amongst the comparatively small number of plants known to
Linnæus, no less than 138 genera are enumerated as having winged seeds.

As winds often prevail for days, weeks, or even months together, in the
same direction, these means of transportation may sometimes be without
limits; and even the heavier grains may be borne through considerable
spaces, in a very short time, during ordinary tempests; for strong
gales, which can sweep along grains of sand, often move at the rate of
about forty miles an hour, and if the storm be very violent, at the rate
of fifty-six miles.[852] The hurricanes of tropical regions, which root
up trees and throw down buildings, sweep along at the rate of ninety
miles an hour; so that, for however short a time they prevail, they may
carry even the heavier fruits and seeds over friths and seas of
considerable width, and doubtless are often the means of introducing
into islands the vegetation of adjoining continents. Whirlwinds are also
instrumental in bearing along heavy vegetable substances to considerable
distances. Slight ones may frequently be observed in our fields, in
summer carrying up haycocks into the air, and then letting fall small
tufts of hay far and wide over the country; but they are sometimes so
powerful as to dry up lakes and ponds, and to break off the boughs of
trees, and carry them up in a whirling column of air.

Franklin tells us, in one of his letters, that he saw, in Maryland, a
whirlwind which began by taking up the dust which lay in the road, in
the form of a sugar loaf with the pointed end downwards, and soon after
grew to the height of forty or fifty feet, being twenty or thirty in
diameter. It advanced in a direction contrary to the wind; and although
the rotary motion of the column was surprisingly rapid, its onward
progress was sufficiently slow to allow a man to keep pace with it on
foot. Franklin followed it on horseback, accompanied by his son, for
three quarters of a mile, and saw it enter a wood, where it twisted and
turned round large trees with surprising force. These were carried up in
a spiral line, and were seen flying in the air, together with boughs and
innumerable leaves, which, from their height, appeared reduced to the
apparent size of flies. As this cause operates at different intervals of
time throughout a great portion of the earth's surface, it may be the
means of bearing not only plants but insects, land testacea and their
eggs, with many other species of animals, to points which they could
never otherwise have reached, and from which they may then begin to
propagate themselves again as from a new centre.

_Distribution of cryptogamous plants._--It has been found that a great
numerical proportion of the exceptions to the limitation of species to
certain quarters of the globe occur in the various tribes of cryptogamic
plants. Linnæus observed that, as the germs of plants of this class,
such as mosses, fungi, and lichens, consist of an impalpable powder, the
particles of which are scarcely visible to the naked eye, there is no
difficulty to account for their being dispersed throughout the
atmosphere, and carried to every point of the globe, where there is a
station fitted for them.
Lichens in particular ascend to great elevations, sometimes growing two
thousand feet above the line of perpetual snow, at the utmost limits of
vegetation, and where the mean temperature is nearly at the freezing
point. This elevated position must contribute greatly to facilitate the
dispersion of those buoyant particles of which their fructification
consists.[853]

Some have inferred, from the springing up of mushrooms whenever
particular soils and decomposed organic matter are mixed together, that
the production of fungi is accidental, and not analogous to that of
perfect plants. But Fries, whose authority on these questions is
entitled to the highest respect, has shown the fallacy of this argument
in favor of the old doctrine of equivocal generation. "The sporules of
fungi," says this naturalist, "are so infinite, that in a single
individual of _Reticularia maxima_, I have counted above ten millions,
and so subtile as to be scarcely visible, often resembling thin smoke;
so light that they may be raised perhaps by evaporation into the
atmosphere, and dispersed in so many ways by the attraction of the sun,
by insects, wind, elasticity, adhesion, &c., that it is difficult to
conceive a place from which they may be excluded."[854]

The club-moss called _Lycopodium cernuum_ affords a striking example of
a cryptogamous plant universally distributed over all equinoctial
countries. It scarcely ever passes beyond the northern tropic, except in
one instance, where it appears around the hot-springs in the Azores,
although it is neither an inhabitant of the Canaries nor Madeira.
Doubtless its microscopic sporules are everywhere present, ready to
germinate on any spot where they can enjoy throughout the year the
proper quantity of warmth, moisture, light, and other conditions
essential to the species.

Almost every lichen brought home from the southern hemisphere by the
antarctic expedition under Sir James Ross, amounting to no less than 200
species, was ascertained to be also an inhabitant of the northern
hemisphere, and almost all of them European.

_Agency of rivers and currents._--In considering, in the next place, the
instrumentality of the aqueous agents of dispersion, I cannot do better
than cite the words of one of our ablest botanical writers. "The
mountain stream or torrent," observes Keith, "washes down to the valley
the seeds which may accidentally fall into it, or which it may happen to
sweep from its banks when it suddenly overflows them. The broad and
majestic river, winding along the extensive plain, and traversing the
continents of the world, conveys to the distance of many hundreds of
miles the seeds that may have vegetated at its source. Thus the southern
shores of the Baltic are visited by seeds which grew in the interior of
Germany, and the western shores of the Atlantic by seeds that have been
generated in the interior of America."[855] Fruits, moreover, indigenous
to America and the West Indies, such as that of the _Mimosa scandens_,
the cashewnut and others, have been known to be drifted across the
Atlantic by the Gulf stream, on the western coasts of Europe, in such a
state that they might have vegetated had the climate and soil been
favourable. Among these the _Guilandina Bonduc_, a leguminous plant, is
particularly mentioned, as having been raised from a seed found on the
west coast of Ireland.[856]

Sir Hans Sloane states, that several kinds of beans cast ashore on the
Orkney Isles, and Ireland, but none of which appear to have naturalized
themselves, are derived from trees which grow in the West Indies, and
many of them in Jamaica. He conjectures that they might have been
conveyed by rivers into the sea, and then by the Gulf stream to greater
distances, in the same manner as the sea-weed called _Lenticula marina_,
or Sargasso, which grows on the rocks about Jamaica, is known to be
"carried by the winds and current towards the coast of Florida, and
thence into the North American ocean, where it lies very thick on the
surface of the sea."[857]

The absence of liquid matter in the composition of seeds renders them
comparatively insensible to heat and cold, so that they may be carried
without detriment through climates where the plants themselves would
instantly perish. Such is their power of resisting the effects of heat,
that Spallanzani mentions some seeds that germinated after having been
boiled in water.[858] Sir John Herschel informs me that he has sown at
the Cape of Good Hope the seeds of the _Acacia lophanta_ after they had
remained for twelve hours in water of 140° Fahrenheit, and they
germinated far more rapidly than unboiled seeds. He also states that an
eminent botanist, Baron Ludwig, could not get the seeds of a species of
cedar to grow at the Cape till they were thoroughly boiled.

When therefore, a strong gale, after blowing violently off the land for
a time, dies away, and the seeds alight upon the surface of the waters,
or wherever the ocean, by eating away the sea-cliffs, throws down into
its waves plants which would never otherwise reach the shores, the tides
and currents become active instruments in assisting the dissemination of
almost all classes of the vegetable kingdom. The pandanus and many other
plants have been distributed in this way over the islands of the
Pacific. I have before called attention (p. 618.) to the interesting
fact that one-fifth of all the algæ found in the antarctic regions in
1841-3, by Dr. J. Hooker, were of species common to the British seas. He
has suggested that cold currents which prevail from Cape Horn to the
equator, and are there met by other cold water, may by their direct
influence, as well as by their temperature, facilitate the passage of
antarctic species to the Arctic Ocean. In like manner the migration of
certain marine animals from the southern to the northern hemisphere may
have been brought about by the same cause.

In a collection of six hundred plants from the neighborhood of the river
Zaire, in Africa, Mr. Brown found that thirteen species were also met
with on the opposite shores of Guiana and Brazil. He remarked that most
of these plants were found only on the lower parts of the river Zaire,
and were chiefly such as produced seeds capable of retaining their
vitality a long time in the currents of the ocean. Dr. J. Hooker informs
me that after an examination of a great many insular floras, he has
found that no one of the large natural orders is so rich in species
common to other countries, as the Leguminosæ. The seeds in this order,
which comprises the largest proportion of widely diffused littoral
species, are better adapted than those of any other plants for
water-carriage.

_The migration of plants aided by islands._--Islands, moreover, and even
the smallest rocks, play an important part in aiding such migrations;
for when seeds alight upon them from the atmosphere, or are thrown up by
the surf, they often vegetate, and supply the winds and waves with a
repetition of new and uninjured crops of fruit and seeds. These may
afterwards pursue their course through the atmosphere, or along the
surface of the sea, in the same direction. The number of plants found at
any given time on an islet affords us no test whatever of the extent to
which it may have co-operated towards this end, since a variety of
species may first thrive there and then perish, and be followed by other
chance-comers like themselves. If neither St. Helena nor Ascension have
promoted the botanical intercourse between the Old and New Worlds, we
may easily account for the fact by remembering that they are not only
extremely minute and isolated spots, but are also bounded by lofty and
precipitous shores without beaches, where the seeds of foreign species
could readily establish themselves.

Currents and winds in the arctic regions drift along icebergs covered
with an alluvial soil, on which herbs and pine-saplings are seen
growing, which may often continue to vegetate on some distant shore
where the ice-island is stranded.

_Dispersion of marine plants._--With respect to marine vegetation, the
seeds, being in their native element, may remain immersed in water
without injury for indefinite periods, so that there is no difficulty in
conceiving the diffusion of species wherever uncongenial climates,
contrary currents, and other causes do not interfere. All are familiar
with the sight of the floating sea-weed,


  "Flung from the rock on ocean's foam to sail,
  Where'er the surge may sweep, the tempest's breath prevail."


Remarkable accumulations of that species of sea-weed generally known as
gulf-weed, or sargasso, occur on each side of the equator in the
Atlantic, Pacific, and Indian Oceans. Columbus and other navigators, who
first encountered these banks of algæ in the Northern Atlantic, compared
them to vast inundated meadows, and state that they retarded the
progress of their vessels. The most extensive bank is a little west of
the meridian of Fayal, one of the Azores, between latitudes 35° and 36°:
violent north-winds sometimes prevail in this space, and drive the
sea-weed to low latitudes, as far as the 24th or even the 20th
degree.[859] Along the northern edge of the Gulf stream Dr. Hooker found
_Fucus nodosus_, and _F. serratus_, which he traced all the way from
lat. 36° N. to England.

The hollow pod-like receptacle in which the seeds of many algæ are
lodged, and the filaments attached to the seed-vessels of others, seem
intended to give buoyancy; and I may observe that these hydrophytes are
in general _proliferous_, so that the smallest fragment of a branch can
be developed into a perfect plant. The seeds, moreover, of the greater
number of species are enveloped with a mucous matter like that which
surrounds the eggs of some fish, and which not only protects them from
injury, but serves to attach them to floating bodies or to rocks.

_Agency of animals in the distribution of plants._--But we have as yet
considered part only of the fertile resources of nature for conveying
seeds to a distance from their place of growth. The various tribes of
animals are busily engaged in furthering an object whence they derive
such important advantages. Sometimes an express provision is found in
the structure of seeds to enable them to adhere firmly by prickles,
hooks, and hairs, to the coats of animals, or feathers of the winged
tribe, to which they remain attached for weeks, or even months, and are
borne along into every region whither birds or quadrupeds may migrate.
Linnæus enumerates fifty genera of plants, and the number now known to
botanists is much greater, which are armed with hooks, by which, when
ripe, they adhere to the coats of animals. Most of these vegetables, he
remarks, require a soil enriched with dung. Few have failed to mark the
locks of wool hanging on the thorn-bushes, wherever the sheep pass, and
it is probable that the wolf or lion never give-chase to herbivorous
animals without being unconsciously subservient to this part of the
vegetable economy.

A deer has strayed from the herd when browsing on some rich pasture,
when he is suddenly alarmed by the approach of his foe. He instantly
takes to flight, dashing through many a thicket, and swimming across
many a river and lake. The seeds of the herbs and shrubs which have
adhered to his smoking flanks are washed off again by the waters. The
thorny spray is torn off, and fixes itself in its hairy coat, until
brushed off again in other thickets and copses. Even on the spot where
the victim is devoured many of the seeds which he had swallowed
immediately before the chase may be left on the ground uninjured, and
ready to spring up in a new soil.

The passage, indeed, of undigested seeds through the stomachs of animals
is one of the most efficient causes of the dissemination of plants, and
is of all others, perhaps, the most likely to be overlooked. Few are
ignorant that a portion of the oats eaten by a horse preserve their
germinating faculty in the dung. The fact of their being still
nutritious is not lost on the sagacious rook. To many, says Linnæus, it
seems extraordinary, and something of a prodigy, that when a field is
well tilled and sown with the best wheat, it frequently produces darnel
or the wild oat, especially if it be manured with new dung; they do not
consider that the fertility of the smaller seeds is not destroyed in the
stomachs of animals.[860]

_Agency of birds._--Some birds of the order Passeres devour the seeds of
plants in great quantities, which they eject again in very distant
places, without destroying its faculty of vegetation: thus a flight of
larks will fill the cleanest field with a great quantity of various
kinds of plants, as the melilot trefoil (_Medicago lupulina_), and
others whose seeds are so heavy that the wind is not able to scatter
them to any distance.[861] In like manner, the blackbird and
misselthrush, when they devour berries in too great quantities, are
known to consign them to the earth undigested in their excrement.[862]

Pulpy fruits serve quadrupeds and birds as food, while their seeds,
often hard and indigestible, pass uninjured through the intestines, and
are deposited far from their original place of growth in a condition
peculiarly fit for vegetation.[863] So well are the farmers, in some
parts of England, aware of this fact, that when they desire to raise a
quickset hedge in the shortest possible time, they feed turkeys with the
haws of the common white-thorn (_Cratægus Oxyacantha_), and then sow the
stones which are ejected in their excrement, whereby they gain an entire
year in the growth of the plant.[864] Birds, when they pluck cherries,
sloes, and haws, fly away with them to some convenient place; and when
they have devoured the fruit, drop the stone into the ground. Captain
Cook, in his account of the volcanic island of Tanna, one of the New
Hebrides, which he visited in his second voyage, makes the following
interesting observation:--"Mr. Forster, in his botanical excursion this
day, shot a pigeon, in the craw of which was a wild nutmeg."[865] It is
easy, therefore, to perceive, that birds in their migrations to great
distances, and even across seas, may transport seeds to new isles and
continents.

The sudden deaths to which great numbers of frugivorous birds are
annually exposed must not be omitted as auxiliary to the transportation
of seeds to new habitations. When the sea retires from the shore, and
leaves fruits and seeds on the beach, or in the mud of estuaries, it
might, by the returning tide, wash them away again, or destroy them by
long immersion; but when they are gathered by land birds which frequent
the sea side, or by waders and water-fowl, they are often borne inland;
and if the bird to whose crop they have been consigned is killed, they
may be left to grow up far from the sea. Let such an accident happen but
once in a century, or a thousand years, it will be sufficient to spread
many of the plants from one continent to another; for in estimating the
activity of these causes, we must not consider whether they act slowly
in relation to the period of our observation, but in reference to the
duration of species in general.

Let us trace the operation of this cause in connection with others. A
tempestuous wind bears the seeds of a plant many miles through the air,
and then delivers them to the ocean; the oceanic current drifts them to
a distant continent; by the fall of the tide they become the food of
numerous birds, and one of these is seized by a hawk or eagle, which,
soaring across hill and dale to a place of retreat, leaves, after
devouring its prey, the unpalatable seeds to spring up and flourish in a
new soil.

The machinery before adverted to, is so capable of disseminating seeds
over almost unbounded spaces, that were we more intimately acquainted
with the economy of nature, we might probably explain all the instances
which occur of the aberration of plants to great distances from their
native countries. The real difficulty which must present itself to every
one who contemplates the present geographical distribution of species,
is the small number of exceptions to the rule of the non-intermixture of
different groups of plants. Why have they not, supposing them to have
been ever so distinct originally, become more blended and confounded
together in the lapse of ages?

_Agency of man in the dispersion of plants._--But in addition to all the
agents already enumerated as instrumental in diffusing plants over the
globe, we have still to consider man--one of the most important of all.
He transports with him, into every region, the vegetables which he
cultivates for his wants, and is the involuntary means of spreading a
still greater number which are useless to him, or even noxious. "When
the introduction of cultivated plants," says De Candolle, "is of recent
date, there is no difficulty in tracing their origin; but when it is of
high antiquity, we are often ignorant of the true country of the plants
on which we feed. No one contests the American origin of the maize or
the potatoe; nor the origin, in the Old World, of the coffee-tree, and
of wheat. But there are certain objects of culture, of very ancient
date, between the tropics, such for example as the banana, of which the
origin cannot be verified. Armies, in modern times, have been known to
carry, in all directions, grain and cultivated vegetables from one
extremity of Europe to the other; and thus have shown us how, in more
ancient times, the conquests of Alexander, the distant expeditions of
the Romans, and afterwards the crusades, may have transported many
plants from one part of the world to the other."[866]

But, besides the plants used in agriculture, the numbers which have been
naturalized by accident, or which man has spread unintentionally, is
considerable. One of our old authors, Josselyn, gives a catalogue of
such plants as had, in his time, sprung up in the colony since the
English planted and kept cattle in New England. They were two-and-twenty
in number. The common nettle was the first which the settlers noticed;
and the plantain was called by the Indians "Englishman's foot," as if it
sprung from their footsteps.[867]

"We have introduced every where," observes De Candolle, "some weeds
which grow among our various kinds of wheat, and which have been
received, perhaps, originally from Asia along with them. Thus, together
with the Barbary wheat, the inhabitants of the south of Europe have
sown, for many ages, the plants of Algiers and Tunis. With the wools and
cottons of the East, or of Barbary, there are often brought into France
the grains of exotic plants, some of which naturalize themselves. Of
this I will cite a striking example. There is, at the gate of
Montpellier, a meadow set apart for drying foreign wool, _after it has
been washed_. There hardly passes a year without foreign plants being
found naturalized in this drying-ground. I have gathered there
_Centaurea parviflora_, _Psoralea palæstina_, and _Hypericum crispum_."
This fact is not only illustrative of the aid which man lends
inadvertently to the propagation of plants, but it also demonstrates the
multiplicity of seeds which are borne about in the woolly and hairy
coats of wild animals.

The same botanist mentions instances of plants naturalized in seaports
by the ballast of ships; and several examples of others which have
spread through Europe from botanical gardens, so as to have become more
common than many indigenous species.

It is scarcely a century, says Linnæus, since the Canadian erigeron, or
flea-bane, was brought from America to the botanical garden at Paris;
and already the seeds have been carried by the winds so that it is
diffused over France, the British islands, Italy, Sicily, Holland, and
Germany.[868] Several others are mentioned by the Swedish naturalist, as
having been dispersed by similar means. The common thorn-apple (_Datura
Stramonium_), observes Willdenow, now grows as a noxious weed throughout
all Europe, with the exception of Sweden, Lapland and Russia. It came
from the East Indies and Abyssinia to us, and was thus universally
spread by certain quacks, who used its seeds as an emetic.[869] The same
plant is now abundant throughout the greater part of the United States,
along road-sides and about farm-yards. The yellow monkey-flower,
_Mimulus luteus_, a plant from the north-west region of America, has now
established itself in various parts of England, and is spreading
rapidly.

In hot and ill-cultivated countries, such naturalization takes place
more easily. Thus the _Chenopodium ambrosioides_, sown by Mr. Burchell
on a point of St. Helena, multiplied so fast in four years as to become
one of the commonest weeds in the island, and it has maintained its
ground ever since 1845.[870]

The most remarkable proof, says De Candolle, of the extent to which man
is unconsciously the instrument of dispersing and naturalizing species,
is found in the fact, that in New Holland, America, and the Cape of Good
Hope, the aboriginal European species exceed in number all the others
which have come from any distant regions; so that, in this instance, the
influence of man has surpassed that of all the other causes which tend
to disseminate plants to remote districts. Of nearly 1600 British
flowering plants, it is supposed that about 300 species are naturalized;
but a large proportion of these would perish with the discontinuance of
agriculture.

Although we are but slightly acquainted, as yet, with the extent of our
instrumentality in naturalizing species, yet the facts ascertained
afford no small reason to suspect that the number which we introduce
unintentionally exceeds all those transported by design. Nor is it
unnatural to suppose that the functions, which the inferior beings,
extirpated by man, once discharged in the economy of nature, should
devolve upon the human race. If we drive many birds of passage from
different countries, we are probably required to fulfil their office of
carrying seeds, eggs of fish, insects, mollusks, and other creatures, to
distant regions: if we extirpate quadrupeds, we must replace them not
merely as consumers of the animal and vegetable substances which they
devour, but as disseminators of plants, and of the inferior classes of
the animal kingdom. I do not mean to insinuate that the very same
changes which man brings about, would have taken place by means of the
agency of other species, but merely that he supersedes a certain number
of agents; and so far as he disperses plants unintentionally, or against
his will, his intervention is strictly analogous to that of the species
so extirpated.

I may observe, moreover, that if, at former periods, the animals
inhabiting any given district have been partially altered by the
extinction of some species, and the introduction of others, whether by
new creations or by immigration, a change must have taken place in
regard to the particular plants conveyed about with them to foreign
countries. As, for example, when one set of migratory birds is
substituted for another, the countries from and to which seeds are
transported are immediately changed. Vicissitudes, therefore, analogous
to those which man has occasioned, may have previously attended the
springing up of new relations between species in the vegetable and
animal worlds.

It may also be remarked, that if man is the most active agent in
enlarging, so also is he in circumscribing the geographical boundaries
of particular plants. He promotes the migration of some, he retards that
of other species; so that, while in many respects he appears to be
exerting his power to blend and confound the various provinces of
indigenous species, he is, in other ways, instrumental in obstructing
the fusion into one group of the inhabitants of contiguous provinces.

Thus, for example, when two botanical regions exist in the same great
continent, such as _the European region_, comprehending the central
parts of Europe, and those surrounding the Mediterranean, and _the
Oriental region_, as it has been termed, embracing the countries
adjoining the Black Sea and the Caspian, the interposition between these
of thousands of square miles of cultivated lands, opposes a new and
powerful barrier against the mutual interchange of indigenous plants.
Botanists are well aware that garden plants naturalize and diffuse
themselves with great facility in comparatively unreclaimed countries,
but spread themselves slowly and with difficulty in districts highly
cultivated. There are many obvious causes for this difference; by
drainage and culture the natural variety of stations is diminished, and
those stray individuals by which the passage of a species from one fit
station to another is effected, are no sooner detected by the
agriculturist, than they are uprooted as weeds. The larger shrubs and
trees, in particular, can scarcely ever escape observation, when they
have attained a certain size, and will rarely fail to be cut down if
unprofitable.

The same observations are applicable to the interchange of the insects,
birds, and quadrupeds of two regions situated like those above alluded
to. No beasts of prey are permitted to make their way across the
intervening arable tracts. Many birds, and hundreds of insects, which
would have found some palatable food amongst the various herbs and trees
of the primeval wilderness, are unable to subsist on the olive, the
vine, the wheat, and a few trees and grasses favored by man. In
addition, therefore, to his direct intervention, man, in this case,
operates indirectly to impede the dissemination of plants, by
intercepting the migration of animals, many of which would otherwise
have been active in transporting seeds from one province to another.

Whether, in the vegetable kingdom, the influence of man will tend, after
a considerable lapse of ages, to render the geographical range of
_species in general_ more extended, as De Candolle seems to anticipate,
or whether the compensating agency above alluded to will not
counterbalance the exceptions caused by our naturalizations, admits at
least of some doubt. In the attempt to form an estimate on this subject,
we must be careful not to underrate, or almost overlook, as some appear
to have done, the influence of man in checking the diffusion of plants,
and restricting their distribution to narrower limits.




CHAPTER XXXVIII.

LAWS WHICH REGULATE THE GEOGRAPHICAL DISTRIBUTION OF
SPECIES--_continued_.


  Geographical distribution of animals--Buffon on specific
    distinctness of quadrupeds of Old and New World--Doctrine of
    "natural barriers"--Different regions of indigenous
    mammalia--Europe--Africa--India, and Indian
    Archipelago--Australia--North and South America--Quadrupeds in
    islands--Range of the Cetacea--Dispersion of quadrupeds--Their
    powers of swimming--Migratory instincts--Drifting of animals on
    ice-floes--On floating islands of drift-timber--Migrations of
    Cetacea--Habitations of birds--Their migrations and facilities of
    diffusion--Distribution of reptiles, and their power of
    dissemination.


_Geographical distribution of animals._--Although in speculating on
"philosophical possibilities," said Buffon, "the same temperature might
have been expected, all other circumstances being equal, to produce the
same beings in different parts of the globe, both in the animal and
vegetable kingdoms, yet it is an undoubted fact, that when America was
discovered, its indigenous quadrupeds were all dissimilar to those
previously known in the Old World. The elephant, the rhinoceros, the
hippopotamus, the camelopard, the camel, the dromedary, the buffalo, the
horse, the ass, the lion, the tiger, the apes, the baboons, and a number
of other mammalia, were nowhere to be met with on the new continent;
while in the old, the American species, of the same great class, were
nowhere to be seen--the tapir, the lama, the pecari, the jaguar, the
couguar, the agouti, the paca, the coati, and the sloth."

These phenomena, although few in number relatively to the whole animate
creation, were so striking and so positive in their nature, that the
great French naturalist caught sight at once of a general law in the
geographical distribution of organic beings, namely, the limitation of
groups of distinct species to regions separated from the rest of the
globe by certain natural barriers. It was, therefore, in a truly
philosophical spirit that, relying on the clearness of the evidence
obtained respecting the larger quadrupeds, he ventured to call in
question the identifications announced by some contemporary naturalists
of species of animals said to be common to the southern extremities of
America and Africa.[871]

The migration of quadrupeds from one part of the globe to another,
observes Dr. Prichard, is prevented by uncongenial climates and the
branches of the ocean which intersect continents. "Hence, by a
reference to the geographical site of countries, we may divide the
earth into a certain number of regions fitted to become the abodes of
particular groups of animals, and we shall find, on inquiry, that each
of these provinces, thus conjecturally marked out, is actually inhabited
by a distinct nation of quadrupeds."[872] It will be observed that the
language of Buffon respecting "natural barriers," which has since been
so popular, would be wholly without meaning if the geographical
distribution of organic beings had not led naturalists to adopt very
generally _the doctrine of specific centres_, or, in other words, to
believe that each species, whether of plant or animal, originated in a
single birth-place. Reject this view, and the fact that not a single
native quadruped is common to Australia, the Cape of Good Hope, and
South America, can in no ways be explained by adverting to the wide
extent of intervening ocean, or to the sterile deserts, or the great
heat or cold of the climates, through which each species must have
passed, before it could migrate from one of those distant regions to
another. It might fairly be asked of one who talked of impassable
barriers, why the same kangaroos, rhinoceroses, or lamas, should not
have been created simultaneously in Australia, Africa, and South
America! The horse, the ox, and the dog, although foreign to these
countries until introduced by man, are now able to support themselves
there in a wild state, and we can scarcely doubt that many of the
quadrupeds at present peculiar to Australia, Africa, and South America,
might have continued in like manner to inhabit each of the three
continents had they been indigenous or could they once have got a
footing there as new colonists.

At the same time every zoologist will be willing to concede, that even
if the departure of each species from a single centre had not appeared
to be part of the plan of Nature, the range of species in general must
have become limited, under the influence of a variety of causes,
especially in the class of terrestrial mammalia. Scarcely any one of
these could be expected to retain as fair a claim to the title of
cosmopolite as man, although even the human race, fitted as it is by its
bodily constitution and intellectual resources to spread very widely
over the earth, is far from being strictly cosmopolite. It is excluded
both from the arctic and antarctic circles, from many a wide desert and
the summits of many mountain-chains; and lastly, from three-fourths of
the globe covered by water, where there are large areas very prolific in
animal life, even in the highest order of the vertebrate class. But the
_habitations_ of species are, as before stated, in reference to plants
(see above, p. 614), circumscribed by causes different from those which
determine their _stations_, and these causes are clearly connected with
the time and place of the original creation of each species.

As the names and characters of land quadrupeds are much better known to
the general reader than those of other great families of the animal
kingdom, I shall select this class to exemplify the zoological provinces
into which species are divisible, confining myself, however, to those
facts which may help to elucidate some principle, or rule apparently
followed by the Author of Nature, in regard to that "mystery of
mysteries," the first peopling of the earth with living beings.[873]
First, then, the _European region_ comprehends, besides Europe, the
borders of the Mediterranean, and even the north of Africa, and extends
into Asia, beyond the Oural mountains and the Caspian. Although the
species are almost all peculiar, the number of characteristic _genera_
is remarkably small. The bear, the fox, the hare, the rabbit, the deer,
and almost every European form is found equally in several of the other
large provinces of mammalia, where the species are distinct. Even the
mole (_Talpa_), although confined to the northern parts of the old
world, ranges eastwards, as far as the Himalaya mountains.

2dly. The _African_ Fauna, on the other hand, is singularly rich in
generic forms, not met with in a living state in any other region. The
hippopotamus, for example, of which two very distinct species are known,
the giraffe, the Chimpanzee, the blue-faced baboon, the four-fingered
monkeys (_Colubus_), many carnivora, such as _Proteles_, allied to the
hyæna, and a multitude of other forms, are exclusively African. A few of
the species inhabiting the northern confines of this continent, such as
the dromedary, lion, and jackall, are also common to Asia; and a much
larger number of _forms_ belong equally to the great Asiatic province,
the species being distinct. The elephant, for example, of Africa is
smaller, has a rounder head, and larger ears than the Indian one, and
has only three instead of four nails on each hind foot. In like manner,
not one of three African species of Rhinoceros agrees with one of the
three Indian kinds.

3dly. The _Southern_ region of _Africa_, where that continent extends
into the temperate zone, constitutes another separate zoological
province, surrounded as it is on three sides by the ocean, and cut off
from the countries of milder climate in the northern hemisphere, by the
intervening torrid zone. In many instances, this region contains the
same genera which are found in temperate climates to the northward of
the line: but then the southern are different from the northern species.
Thus, in the south we find the quagga and the zebra; in the north, the
horse, the ass, and the jiggetai of Asia.

The south of Africa is spread out into fine level plains from the tropic
to the Cape. In this region, says Pennant, besides the horse genus, of
which five species have been found, there are also peculiar species of
rhinoceros, the hog, and the hyrax, among pachydermatous races; and
amongst the ruminating, the Cape buffalo, and a variety of remarkable
antelopes, as the springbok, the oryx, the gnou, the leucophoë, the
pygarga, and several others.[874]

4thly. The assemblage of quadrupeds in _Madagascar_ affords a striking
illustration of the laws before alluded to, as governing the
distribution of species in islands. Separated from Africa by the
Mozambique channel, which is 300 miles wide, Madagascar forms, with two
or three small islands in its immediate vicinity, a zoological province
by itself, all the species except one, and nearly all the genera, being
peculiar. The only exception consists of a small insectivorous quadruped
(_Centetes_), found also in the Mauritius, to which place it is supposed
to have been taken in ships. The most characteristic feature of this
remarkable fauna consists in the number of quadrumana of the Lemur
family, no less than six genera of these monkeys being exclusively met
with in this island, and a seventh genus of the same, called _Galago_,
which alone has any foreign representative, being found, as we might
from analogy have anticipated, in the nearest main land. Had the species
of quadrupeds in Madagascar agreed with those of the contiguous parts of
Africa, as do those of England with the rest of Europe, the naturalist
would have inferred that there had been a land communication since the
period of the coming in of the existing quadrupeds, whereas we may now
conclude that the Mozambique channel has constituted an insuperable
barrier to the fusion of the continental fauna with that of the great
island during the whole period that has elapsed since the living species
were created.

5thly. Another of the great nations of terrestrial mammalia is that of
_India_, containing a great variety of peculiar forms, such as the
sloth-bear (_Prochilus_), the musk-deer (_Moscus_), the nylghau, the
gibbon or long-armed ape, and many others.

6thly. A portion of the islands of the _Indian archipelago_ might,
perhaps, be considered by some geologists as an appendage of the same
province. In fact, we find in the large islands of Java, Sumatra, and
Borneo, the same genera, for the most part, as on the continent of
India, and some of the same species, _e. g._ the tapir (_Tapirus
Malayanus_), the rhinoceros of Sumatra, and some others. Most of the
species, however, are distinct, and each island has many, and even a few
genera, peculiar to itself. Between eighty and ninety species are known
to inhabit Java, and nearly the same number occur in Sumatra. Of these,
more than half are common to the two islands. Borneo, which is much less
explored, has yielded already upwards of sixty species, more than half
of which are met with either in Java or Sumatra. Of the species
inhabiting Sumatra and not found in Java, Borneo contains the greater
portion. Upon the whole, if these three large islands were united, and a
fusion of their respective indigenous mammalia should take place, they
would present a fauna related to that of continental India, and
comprising about as many species as we might expect from analogy to
discover in an area of equal extent. The Philippine Islands are peopled
with another assemblage of species generically related to the great
Indian type.

7thly. But the islands of Celebes, Amboina, Timor, and _New Guinea_,
constitute a different region of mammalia more allied to the Australian
type, as having an intermixture of marsupial quadrupeds, yet showing an
affinity also to the Indian in such forms as the deer (_Cervus_), the
weasel (_Viverra_), the pig (_Sus_), the Macaque monkey
(_Cercopithecus_), and others. As we proceed in a south-westerly
direction, from Celebes to Amboina and thence to New Guinea, we find the
Indian types diminishing in number, and the Australian (_i. e._
marsupial forms) increasing. Thus in New Guinea seven species of pouched
quadrupeds have been detected, and among them two singular
tree-kangaroos; yet only one species of the whole seven, viz. the flying
opossum (_Petauris ariel_), is common to the Indian archipelago and the
main land of Australia. The greater the zoological affinity, therefore,
between the latter and the New Guinea fauna, although it seems in some
way connected with geographical proximity, is not to be explained simply
by the mutual migration of species from the one to the other.

8thly. When _Australia_ was discovered, its land quadrupeds, belonging
almost exclusively to the marsupial or pouched tribe, such as the
kangaroos, wombats, flying opossums, kangaroo-rats, and others, some
feeding on herbs and fruits, others carnivorous, were so novel in their
structure and aspect, that they appeared to the naturalist almost as
strange as if they were the inhabitants of some other planet. We learn
from the recent investigations of Mr. Waterhouse,[875] that no less than
170 species of marsupial quadrupeds have now been determined, and of the
whole number all but thirty-two are exclusively restricted to Australia.
Of these thirty-two, nine belong to the islands in the Indian
archipelago before mentioned, and the other twenty-three are all species
of opossum inhabiting the tropical parts of South America, or a few of
them extending into Mexico and California, and one, the Virginian
opossum, into the United States.

9thly. It only remains for me to say something of the mammiferous fauna
of _North_ and _South America_. It has often been said that, where the
three continents of Asia, Europe, and North America, approach very near
to each other towards the pole, the whole arctic region forms one
zoological and botanical province. The narrow straits which separate the
old and new world are frozen over in winter, and the distance is farther
lessened by intervening islands. Many plants and animals of various
classes have accordingly spread over all the arctic lands, being
sometimes carried in the same manner as the polar bear, when it is
drifted on floating ice from Greenland to Iceland. But on a close
inspection of the arctic mammalia, it has been found of late years that
a very small number of the American species are identical with those of
Europe or Asia. The genera are, in great part, the same or nearly
allied; but the species are rarely identical, and are often very unlike,
as in the case of the American badger and that of Europe. Some of the
_genera_ of arctic America, such as the musk ox (_Ovibos_), are quite
peculiar, and the distinctness of the fauna of the great continents goes
on increasing in proportion as we trace them southwards, or as they
recede farther from each other, and become more and more separated by
the ocean. At length we find that the three groups of tropical mammalia,
belonging severally to America, Africa, and India, have not a single
species in common.

The predominant influence of climate over all the other causes which
limit the range of species in the mammalia is perhaps nowhere so
conspicuously displayed as in North America. The arctic fauna, so
admirably described by Sir John Richardson, has scarcely any species in
common with the fauna of the state of New York, which is 600 miles
farther south, and comprises about forty distinct mammifers. If again we
travel farther south about 600 miles, and enter another zone, running
east and west, in South Carolina, Georgia, Alabama, and the contiguous
states, we again meet with a new assemblage of land quadrupeds, and this
again differs from the fauna of Texas, where frosts are unknown. It will
be observed that on this continent there are no great geographical
barriers running east and west, such as high snow-clad mountains, barren
deserts, or wide arms of the sea, capable of checking the free migration
of species from north to south. But notwithstanding the distinctness of
those zones of indigenous mammalia, there are some species, such as the
buffalo (_Bison Americanus_), the racoon (_Procyon lotor_), and the
Virginian opossum (_Didelphis Virginiana_), which have a wider
habitation, ranging almost from Canada to the Gulf of Mexico; but they
form exceptions to the general rule. The opossum of Texas (_Didelphis
carnivora_) is different from that of Virginia, and other species of the
same genus inhabit westward of the Rocky Mountains, in California, for
example, where almost all the mammalia differ from those of the United
States.

10thly. The _West Indian_ land quadrupeds are not numerous, but several
of them are peculiar; and 11thly, _South America_ is the most distinct,
with the exception of Australia, of all the provinces into which the
mammalia can be classed geographically. The various genera of monkeys,
for example, belong to the family Platyrrhini, a large natural division
of the quadrumana, so named from their widely separated nostrils. They
have a peculiar dentition, and many of them prehensile tails, and are
entirely unknown in other quarters of the globe. The sloths and
armadillos, the true blood-sucking bats or vampyres (_Phyllostomidæ_),
the capybara, the largest of the rodents, the carnivorous coatimondi
(_Nasua_), and a great many other forms, are also exclusively
characteristic of South America.

"In Peru and Chili," says Humboldt, "the region of the grasses, which is
at an elevation of from 12,300 to 15,400 feet, is inhabited by crowds
of lama, guanaco, and alpaca. These quadrupeds, which here represent the
genus camel of the ancient continent, have not extended themselves
either to Brazil or Mexico; because, during their journey, they must
necessarily have descended into regions that were too hot for
them."[876] In this passage it will be seen that the doctrine of
"specific centres" is tacitly assumed.

_Quadrupeds in Islands._--Islands remote from continents, especially
those of small size, are either destitute of quadrupeds, except such as
have been conveyed to them by man, or contain species peculiar to them.
In the Galapagos archipelago no indigenous quadrupeds were found except
one mouse, which is supposed to be distinct from any hitherto found
elsewhere. A peculiar species of fox is indigenous in the Falkland
Islands, and a rat in New Zealand, which last country, notwithstanding
its magnitude, is destitute of other mammalia, except bats, and these,
says Dr. Prichard, may have made their way along the chain of islands
which extend from the shores of New Guinea far into the Southern
Pacific. The same author remarks, that among the various groups of
fertile islands in the Pacific, no quadrupeds have been met with except
the rat and a few bats as above mentioned, and the dog and hog, which
appear to have been conveyed thither by the natives from New Guinea.
"Rats are to be found even on some desert islands, whither they may have
been conveyed by canoes which have occasionally approached the shore. It
is known, also, that rats occasionally swim in large numbers to
considerable distances."[877]

_Geographical range of the Cetacea._--It is natural to suppose that the
geographical range of the different species of Cetacea should be less
correctly ascertained than that of the terrestrial mammifers. It is,
however, well known that the whales which are obtained by our fishers in
the South Seas are distinct from those of the North; and the same
dissimilarity has been found in all the other marine animals, of the
same class, so far as they have yet been studied by naturalists.

_Dispersion of quadrupeds._--Let us now inquire what facilities the
various land quadrupeds enjoy of spreading themselves over the surface
of the earth. In the first place, as their numbers multiply, all of
them, whether they feed on plants, or prey on other animals, are
disposed to scatter themselves gradually over as wide an area as is
accessible to them. But before they have extended their migrations over
a large space, they are usually arrested either by the sea, or a zone of
uncongenial climate, or some lofty and unbroken chain of mountains, or a
tract already occupied by a hostile and more powerful species.

_Their powers of swimming._--Rivers and narrow friths can seldom
interfere with their progress; for the greater part of them swim well,
and few are without this power when urged by danger and pressing want.
Thus, amongst beasts of prey, the tiger is seen swimming about among
the islands and creeks in the delta of the Ganges, and the jaguar
traverses with ease the largest streams in South America.[878] The bear,
also, and the bison, cross the current of the Mississippi. The popular
error, that the common swine cannot escape by swimming when thrown into
the water, has been contradicted by several curious and
well-authenticated instances during the floods in Scotland of 1829. One
pig, only six months old, after having been carried down from Garmouth
to the bar at the mouth of the Spey, a distance of a quarter of a mile,
swam four miles eastward to Port Gordon, and landed safe. Three others,
of the same age and litter, swam, at the same time, five miles to the
west, and landed at Blackhill.[879]

In an adult and wild state, these animals would doubtless have been more
strong and active, and might, when hard pressed, have performed a much
longer voyage. Hence islands remote from the continent may obtain
inhabitants by casualties which, like the late storms in Morayshire, may
only occur once in many centuries, or thousands of years, under all the
same circumstances. It is obvious that powerful tides, winds, and
currents may sometimes carry along quadrupeds capable, in like manner,
of preserving themselves for hours in the sea, to very considerable
distances; and in this way, perhaps, the tapir (_Tapir Indicus_) may
have become common to Sumatra and the Malayan peninsula.

To the elephant, in particular, the power of crossing rivers is
essential in a wild state, for the quantity of food which a herd of
these animals consumes renders it necessary that they should be
constantly moving from place to place. The elephant crosses the stream
in two ways. If the bed of the river be hard, and the water not of too
great a depth, he fords it. But when he crosses great rivers, such as
the Ganges and the Niger, the elephant swims deep, so deep, that the end
of his trunk only is out of the water; for it is a matter of
indifference to him whether his body be completely immersed, provided he
can bring the tip of his trunk to the surface, so as to breathe the
external air.

Animals of the deer kind frequently take to the water, especially in the
rutting season, when the stags are seen, swimming for several leagues at
a time, from island to island, in search of the does, especially in the
Canadian lakes; and in some countries where there are islands near the
sea-shore, they fearlessly enter the sea and swim to them. In hunting
excursions, in North America, the elk of that country is frequently
pursued for great distances through the water.

The large herbivorous animals, which are gregarious, can never remain
long in a confined region, as they consume so much vegetable food. The
immense herds of bisons (_Bos Americanus_) which often, in the great
valleys of the Mississippi and its tributaries blacken the surface of
the prairie lands, are continually shifting their quarters, followed by
wolves, which prowl about in their rear. "It is no exaggeration," says
Mr. James, "to assert, that in one place, on the banks of the Platte, at
least ten thousand bisons burst on our sight in an instant. In the
morning, we again sought the living picture; but upon all the plain,
which last evening was so teeming with noble animals, not one
remained."[880]

_Migratory instincts._--Besides the disposition common to the
individuals of every species slowly to extend their range in search of
food, in proportion as their numbers augment, a migratory instinct often
developes itself in an extraordinary manner, when, after an unusually
prolific season, or upon a sudden scarcity of provisions, great
multitudes are threatened by famine. It may be useful to enumerate some
examples of these migrations, because they may put us upon our guard
against attributing a high antiquity to a particular species merely
because it is diffused over a great space; they show clearly how soon,
in a state of nature, a newly created species might spread itself, in
every direction, from a single point.

In very severe winters, great numbers of the black bears of America
migrate from Canada into the United States; but in milder seasons, when
they have been well fed, they remain and hybernate in the north.[881]
The rein-deer, which, in Scandinavia, can scarcely exist to the south of
the sixty-fifth parallel, descends, in consequence of the greater
coldness of the climate, to the fiftieth degree in Chinese Tartary, and
often roves into a country of more southern latitude than any part of
England.

In Lapland, and other high latitudes, the common squirrels, whenever
they are compelled, by want of provisions, to quit their usual abodes,
migrate in amazing numbers, and travel directly forwards, allowing
neither rocks nor forests, nor the broadest waters, to turn them from
their course. Great numbers are often drowned in attempting to pass
friths and rivers. In like manner the small Norway rat sometimes pursues
its migrations in a straight line across rivers and lakes; and Pennant
informs us, that when the rats, in Kamtschatka, become too numerous,
they gather together in the spring, and proceed in great bodies
westward, swimming over rivers, lakes, and arms of the sea. Many are
drowned or destroyed by water-fowl or fish. As soon as they have crossed
the river Penginsk, at the head of the gulf of the same name, they turn
southward, and reach the rivers Judoma and Okotsk by the middle of July;
a district more than 800 miles distant from their point of departure.

The lemings, also, a small kind of rat, are described as natives of the
mountains of Kolen, in Lapland; and once or twice in a quarter of a
century they appear in vast numbers, advancing along the ground, and
"devouring every green thing." Innumerable bands march from the Kolen,
through Nordland and Finmark, to the Western Ocean, which they
immediately enter; and after swimming about for some time, perish. Other
bands take their route through Swedish Lapland, to the Bothnian Gulf,
where they are drowned in the same manner. They are followed in their
journeys by bears, wolves, and foxes, which prey upon them incessantly.
They generally move in lines, which are about three feet from each
other, and exactly parallel, going directly forward through rivers and
lakes; and when they meet with stacks of hay or corn, gnawing their way
through them instead of passing round.[882] These excursions usually
precede a rigorous winter, of which the lemings seem in some way
forewarned.

[Illustration: Fig. 97.

The Leming, or Lapland Marmot (Mus Lemmus, Linn.)]

Vast troops of the wild ass, or _onager_ of the ancients, which inhabit
the mountainous deserts of Great Tartary, feed, during the summer, in
the tracts east and north of Lake Aral. In the autumn they collect in
herds of hundreds, and even thousands, and direct their course towards
Persia, to enjoy a warm retreat during winter.[883] Bands of two or
three hundred quaggas, a species of wild ass, are sometimes seen to
migrate from the tropical plains of southern Africa to the vicinity of
the Malaleveen River. During their migrations they are followed by
lions, who slaughter them night by night.[884]

The migratory swarms of the springbok, or Cape antelope, afford another
illustration of the rapidity with which a species under certain
circumstances may be diffused over a continent. When the stagnant pools
of the immense deserts south of the Orange River dry up, which often
happens after intervals of three or four years, myriads of these animals
desert the parched soil, and pour down like a deluge on the cultivated
regions near the Cape. The havoc committed by them resembles that of the
African locusts; and so crowded are the herds, that "the lion has been
seen to walk in the midst of the compressed phalanx with only as much
room between him and his victims as the fears of those immediately
around could procure by pressing outwards."[885]

[Illustration: Fig. 98.

Mydaus meliceps, or badger-headed Mydaus. Length, including the tail, 16
inches.]

Dr. Horsfield mentions a singular fact in regard to the geographical
distribution of the _Mydaus meliceps_, an animal intermediate between
the polecat and badger. It inhabits Java, and is "confined exclusively
to those mountains which have an elevation of more than seven thousand
feet above the level of the ocean; on these it occurs with the same
regularity as many plants. The long extended surface of Java, abounding
with conical points which exceed this elevation, affords many places
favorable for its resort. On ascending these mountains, the traveller
scarcely fails to meet with this animal, which, from its peculiarities,
is universally known to the inhabitants of these elevated tracts, while
to those of the plains it is as strange to an animal from a foreign
county. In my visits to the mountainous districts, I uniformly met with
it; and, as far as the information of the natives can be relied on, it
is found on all the mountains."[886]

Now, if asked to conjecture how the Mydaus arrived at the elevated
regions of each of these isolated mountains, we might say that, before
the island was peopled by man, by whom their numbers are now thinned,
they may occasionally have multiplied so as to be forced to collect
together and migrate: in which case notwithstanding the slowness of
their motions, some few would succeed in reaching another mountain, some
twenty, or even, perhaps, fifty miles distant; for although the climate
of the hot intervening plains would be unfavourable to them, they might
support it for a time, and would find there abundance of insects on
which they feed. Volcanic eruptions, which, at different times have
covered the summits of some of those lofty cones with sterile sand and
ashes, may have occasionally contributed to force on these migrations.

_Drifting of animals on ice-floes._--The power of the terrestrial
mammalia to cross the sea is very limited, and it was before stated that
the same species is scarcely ever common to districts widely separated
by the ocean. If there be some exceptions to this rule, they generally
admit of explanation; for there are natural means whereby some animals
may be floated across the water, and the sea may in the course of ages
wear a wide passage through a neck of land, leaving individuals of a
species on each side of the new channel. Polar bears are known to have
been frequently drifted on the ice from Greenland to Iceland; they can
also swim to considerable distances, for Captain Parry, on the return of
his ships through Barrow's Straits, met with a bear swimming in the
water about midway between the shores, which were about forty miles
apart, and where no ice was in sight.[887] "Near the east coast of
Greenland," observes Scoresby, "they have been seen on the ice in such
quantities, that they were compared to flocks of sheep on a common; and
they are often found on field-ice, above two hundred miles from the
shore."[888] Wolves, in the arctic regions, often venture upon the ice
near the shore, for the purpose of preying upon young seals which they
surprise when asleep. When these ice-floes get detached, the wolves are
often carried out to sea; and though some may be drifted to islands or
continents, the greater part of them perish, and have been often heard
in this situation howling dreadfully, as they die by famine.[889]

During the short summer which visits Melville Island, various plants
push forth their leaves and flowers the moment the snow is off the
ground, and form a carpet spangled with the most lively colours. These
secluded spots are reached annually by herds of musk-oxen and reindeer,
which travel immense distances over dreary and desolate regions, to
graze undisturbed on these luxuriant pastures.[890] The rein-deer often
pass along in the same manner, by the chain of the Aleutian Islands,
from Behring's Straits to Kamtschatka, subsisting on the moss found in
these islands during their passage.[891] But the musk-ox,
notwithstanding its migratory habits, and its long journeys over the
ice, does not exist, either in Asia or Greenland.[892]

_On floating islands of drift-wood._--Within the tropics there are no
ice-floes; but, as if to compensate for that mode of transportation,
there are floating islets of matted trees, which are often borne along
through considerable spaces. These are sometimes seen sailing at the
distance of fifty or one hundred miles from the mouth of the Ganges,
with living trees standing erect upon them. The Amazon, the Congo, and
the Orinoco, also produce these verdant rafts, which are formed in the
manner already described when speaking of the great raft of the
Atchafalaya, an arm of the Mississippi, where a natural bridge of
timber, ten miles long, and more than two hundred yards wide, existed
for more than forty years, supporting a luxuriant vegetation, and rising
and sinking with the water which flowed beneath it.

On these green islets of the Mississippi, observes Malte-Brun, young
trees take root, and the pistia and nenuphar display their yellow
flowers: serpents, birds, and the cayman alligator, come to repose
there, and all are sometimes carried to the sea and engulphed in its
waters.[893]

Spix and Martius relate that, during their travels in Brazil, they were
exposed to great danger while ascending the Amazon in a canoe, from the
vast quantity of drift-wood constantly propelled against them by the
current; so much so, that their safety depended on the crew being always
on the alert to turn aside the trunks of trees with long poles. The tops
alone of some trees appeared above water, others had their roots
attached to them with so much soil that they might be compared to
floating islets. On these, say the travellers, we saw some very singular
assemblages of animals, pursuing peacefully their uncertain way in
strange companionship. On one raft were several grave-looking storks,
perched by the side of a party of monkeys, who made comical gestures,
and burst into loud cries, on seeing the canoe. On another was seen a
number of ducks and divers, sitting by a group of squirrels. Next came
down upon the stem of a large rotten cedar tree, an enormous crocodile,
by the side of a tiger-cat, both animals regarding each other with
hostility and mistrust, but the saurian being evidently most at his
ease, as conscious of his superior strength.[894]

Similar green rafts, principally composed of canes and brushwood, are
called "camelotes" on the Parana in South America; and they are
occasionally carried down by inundations, bearing on them the tiger,
cayman, squirrels, and other quadrupeds, which are said to be always
terror-stricken on their floating habitation. No less than four tigers
(pumas) were landed in this manner in one night at Monte Video, lat. 35°
S., to the great alarm of the inhabitants, who found them prowling about
the streets in the morning.[895]

In a memoir lately published, a naval officer relates that, as he
returned from China by the eastern passage, he fell in, among the
Moluccas, with several small floating islands of this kind, covered with
mangrove trees interwoven with underwood. The trees and shrubs retained
their verdure, receiving nourishment from a stratum of soil which formed
a white beach round the margin of each raft, where it was exposed to the
washing of the waves and the rays of the sun.[896] The occurrence of
soil in such situations may easily be explained; for all the natural
bridges of timber which occasionally connect the islands of the Ganges,
Mississippi, and other rivers, with their banks, are exposed to floods
of water, densely charged with sediment.

Captain W. H. Smyth informs me, that, when cruising in the Cornwallis
amidst the Philippine Islands, he has more than once seen, after those
dreadful hurricanes called typhoons, floating masses of wood, with
trees growing upon them, and ships have sometimes been in imminent
peril, as often as these islands were mistaken for terra firma, when, in
fact, they were in rapid motion.

It is highly interesting to trace, in imagination, the effects of the
passage of these rafts from the mouth of a large river to some
archipelago, such as those in the South Pacific, raised from the deep,
in comparatively modern times, by the operations of the volcano and the
earthquake, and the joint labours of coral animals and testacea. If a
storm arise, and the frail vessel be wrecked, still many a bird and
insect may succeed in gaining, by flight, some island of the newly
formed group, while the seeds and berries of herbs and shrubs, which
fall into the waves, may be thrown upon the strand. But if the surface
of the deep be calm, and the rafts are carried along by a current, or
wafted by some slight breath of air fanning the foliage of the green
trees, it may arrive, after a passage of several weeks, at the bay of an
island, into which its plants and animals may be poured out as from an
ark, and thus a colony of several hundred new species may at once be
naturalized.

The reader should be reminded, that I merely advert to the
transportation of these rafts as of extremely rare and accidental
occurrence; but it may account, in tropical countries, for some of the
rare exceptions to the general law of the confined range of mammiferous
species.

_Migrations of the Cetacea._--Many of the Cetacea, the whales of the
northern seas for example, are found to desert one tract of the sea, and
to visit another very distant, when they are urged by want of food, or
danger. The seals also retire from the coast of Greenland in July,
return again in September, and depart again in March, to return in June.
They proceed in great droves northwards, directing their course where
the sea is most free from ice, and are observed to be extremely fat when
they set out on this expedition, and very lean when they come home
again.[897]

_Species of the Mediterranean, Black Sea, and Caspian identical._--Some
naturalists have wondered that the sea-calves, dolphins, and other
marine mammalia of the Mediterranean and Black Sea, should be identical
with those found in the Caspian: and among other fanciful theories, they
have suggested that they may dive through subterranean conduits, and
thus pass from one sea into the other. But as the occurrence of wolves
and other noxious animals, on both sides of the British Channel, was
adduced, by Verstegan and Desmarest, as one of many arguments to prove
that England and France were once united; so the correspondence of the
aquatic species of the inland seas of Asia with those of the Black Sea
tend to confirm the hypothesis, for which there are abundance of
independent geological data, that those seas were connected together by
straits at no remote period of the earth's history.


_Geographical Distribution and Migrations of Birds._

I shall now offer a few observations on some of the other divisions of
the animal kingdom. Birds, notwithstanding their great locomotive
powers, form no exception to the general rules already laid down; but,
in this class, as in plants and terrestrial quadrupeds, different groups
of species are circumscribed within definite limits. We find, for
example, one assemblage in the Brazils, another in the same latitudes in
Central Africa, another in India, and a fourth in New Holland. Of
twenty-six different species of land birds found in the Galapagos
archipelago, all, with the exception of one, are distinct from those
inhabiting other parts of the globe;[898] and in other archipelagos a
single island sometimes contains a species found in no other spot on the
whole earth; as is exemplified in some of the parrot tribes. In this
extensive family, which are, with few exceptions, inhabitants of
tropical regions, the American group has not one in common with the
African, nor either of these with the parrots of India.[899]

Another illustration is afforded by that minute and beautiful tribe, the
humming-birds. The whole of them are, in the first place, peculiar to
the new world; but some species are confined to Mexico, while others
exist only in some of the West India Islands, and have not been found
elsewhere in the western hemisphere. Yet there are species of this
family which have a vast range, as the _Trochilus flammifrons_ (or
_Mellisuga Kingii_), which is found over a space of 2500 miles on the
west coast of South America, from the hot dry country of Lima to the
humid forests of Tierra del Fuego. Captain King, during his survey in
the years 1826-30, found this bird at the Straits of Magellan, in the
month of May--the depth of winter--sucking the flowers of a large
species of fuchsia, then in bloom, in the midst of a shower of snow.

The ornithology of our own country affords one well-known and striking
exemplification of the law of a limited specific range; for the common
grouse (_Tetra scoticus_) occurs nowhere in the known world except in
the British isles.

Some species of the vulture tribe are said to be cosmopolites; and the
common wild goose (_Anas anser_, Linn.), if we may believe some
ornithologists, is a general inhabitant of the globe, being met with
from Lapland to the Cape of Good Hope, frequent in Arabia, Persia,
China, and Japan, and in the American continent from Hudson's Bay to
South Carolina.[900] An extraordinary range has also been attributed to
the nightingale, which extends from western Europe to Persia, and still
farther. In a work entitled Specchio Comparativo,[901] by Charles
Bonaparte, many species of birds are enumerated as common to Rome and
Philadelphia: the greater part of these are migratory, but some of them,
such as the long-eared owl (_Strix otus_), are permanent in both
countries. The correspondence of the ornithological fauna of the eastern
and western hemispheres increases considerably, as might have been
anticipated, in high northern latitudes.[902]

_Their facilities of diffusion._--In parallel zones of the northern and
southern hemispheres, a great general correspondence of form is
observable, both in the aquatic and terrestrial birds; but there is
rarely any specific identity; and this phenomenon is truly remarkable,
when we recollect the readiness with which some birds, not gifted with
great powers of flight, shift their quarters to different regions, and
the facility with which others, possessing great strength of wing,
perform their aërial voyage. Some migrate periodically from high
latitudes, to avoid the cold of winter, and the accompaniments of
cold,--scarcity of insects and vegetable food; others, it is said, for
some particular kinds of nutriment required for rearing their young: for
this purpose they often traverse the ocean for thousands of miles, and
recross it at other periods, with equal security.

Periodical migrations, no less regular, are mentioned by Humboldt, of
many American water-fowl, from one part of the tropics to another, in a
zone where there is the same temperature throughout the year. Immense
flights of ducks leave the valley of the Orinoco, when the increasing
depth of its waters and the flooding of its shores prevent them from
catching fish, insects, and aquatic worms. They then betake themselves
to the Rio Negro and Amazon, having passed from the eighth and third
degrees of north latitude to the first and fourth of south latitude,
directing their course south-south-east. In September, when the Orinoco
decreases and re-enters its channel, these birds return
northwards.[903]

The insectivorous swallows which visit our island would perish during
winter, if they did not annually repair to warmer climes. It is supposed
that in these aerial excursions the average rapidity of their flight is
not less than fifty miles an hour; so that, when aided by the wind, they
soon reach warmer latitudes. Spallanzani calculated that the swallow can
fly at the rate of ninety-two miles an hour, and conceived that the
rapidity of the swift might be three times greater.[904] The rate of
flight of the eider duck (_Anas mollissima_) is said to be ninety miles
an hour; and Bachman says that the hawk, wild pigeon (_Columba
migratoria_), and several species of wild ducks, in North America, fly
at the rate of forty miles an hour, or nearly a thousand miles in
twenty-four hours.[905]

When we reflect how easily different species, in a great lapse of ages,
may be each overtaken by gales and hurricanes, and, abandoning
themselves to the tempest, be scattered at random through various
regions of the earth's surface, where the temperature of the atmosphere,
the vegetation, and the animal productions, might be suited to their
wants, we shall be prepared to find some species capriciously
distributed, and to be sometimes unable to determine the native
countries of each. Captain Smyth informs me, that, when engaged in his
survey of the Mediterranean, he encountered a gale in the Gulf of Lyons,
at the distance of between twenty and thirty leagues from the coast of
France, which bore along many land birds of various species, some of
which alighted on the ship, while others were thrown with violence
against the sails. In this manner islands become tenanted by species of
birds inhabiting the nearest mainland.


_Geographical Distribution and Dissemination of Reptiles._

A few facts respecting the third great class of vertebrated animals will
suffice to show that the plan of nature in regard to their location on
the globe is perfectly analogous to that already exemplified in other
parts of the organic creation, and has probably been determined by
similar causes.

_Habitations of reptiles._--Of the great saurians, the gavials which
inhabit the Ganges differ from the cayman of America, or the crocodile
of the Nile. The monitor of New Holland is specifically distinct from
the Indian species; these latter, again, from the African, and all from
their congeners in the new world. So in regard to snakes; we find the
boa of America represented by the python, a different though nearly
allied genus in India. America is the country of the rattlesnake;
Africa, of the cerastes; and Asia, of the hooded snake, or cobra di
capello. The amphibious genera Siren and Menopoma belong to North
America, possessing both lungs and gills, and respiring at pleasure
either air or water. The only analogous animal of the old world is the
_Proteus anguinus_ of the lakes of Lower Carniola, and the grotto of
Adelsberg between Trieste and Vienna.[906]

There is a legend that St. Patrick expelled all reptiles from Ireland;
and certain it is that none of the three species of snakes common in
England, nor the toad, have been observed there by naturalists. They
have our common frog, and our water-newt, and according to Ray (Quad.
264.), the green lizard (_Lacerta viridis_).

_Migrations of the larger reptiles._--The range of the large reptiles
is, in general, quite as limited as that of some orders of the
terrestrial mammalia. The great saurians sometimes cross a considerable
tract in order to pass from one river to another; but their motions by
land are generally slower than those of quadrupeds. By water, however,
they may transport themselves to distant situations more easily. The
larger alligator of the Ganges sometimes descends beyond the brackish
water of the delta into the sea; and in such cases it might chance to be
drifted away by a current, and survive till it reached a shore at some
distance; but such casualties are probably very rare.

Turtles migrate in large droves from one part of the ocean to another
during the ovipositing season; and they find their way annually to the
island of Ascension, from which the nearest land is about 800 miles
distant. Dr. Fleming mentions, that an individual of the hawk's bill
turtle (_Chelonia imbricata_), so common in the American seas, has been
taken at Papa Stour, one of the West Zetland Islands;[907] and,
according to Sibbald, "the same animal came into Orkney." Another was
taken, in 1774, in the Severn, according to Turton. Two instances, also,
of the occurrence of the leathern tortoise (_C. coriacea_), on the coast
of Cornwall, in 1756, are mentioned by Borlase. These animals of more
southern seas can be considered only as stragglers, attracted to our
shores during uncommonly warm seasons by an abundant supply of food, or
carried by the Gulf stream, or driven by storms to high latitudes.

Some of the smaller reptiles lay their eggs on aquatic plants; and these
must often be borne rapidly by rivers, and conveyed to distant regions
in a manner similar to the dispersion of seeds before adverted to. But
that the larger ophidians may be themselves transported across the seas,
is evident from the following most interesting account of the arrival of
one at the island of St. Vincent. It is worthy of being recorded, says
Mr. Guilding, "that a noble specimen of the _Boa constrictor_ was lately
conveyed to us by the currents, twisted round the trunk of a large sound
cedar tree, which had probably been washed out of the bank by the floods
of some great South American river, while its huge folds hung on the
branches, as it waited for its prey. The monster was fortunately
destroyed after killing a few sheep, and his skeleton now hangs before
me in my study, putting me in mind how much reason I might have had to
fear in my future rambles through the forests of St. Vincent, had this
formidable reptile been a pregnant female, and escaped to a safe
retreat."[908]




CHAPTER XXXIX.

LAWS WHICH REGULATE THE GEOGRAPHICAL DISTRIBUTION OF
SPECIES--_continued_.



  Geographical distribution and migration of Fish--of Testaoea--of
    Zoophytes--Distribution of Insects--Migratory instincts of some
    species--Certain types characterize particular countries--Their
    means of dissemination--Geographical distribution and diffusion of
    man--Speculations as to the birth-place of the human
    species--Progress of human population--Drifting of canoes to vast
    distances--On the involuntary influence of man in extending the
    range of many other species.


_Geographical Distribution and Migrations of Fish._


Although we are less acquainted with the habitations of marine animals
than with the grouping of the terrestrial species before described, yet
it is well ascertained that their distribution is governed by the same
general laws. The testimony borne by MM. Péron and Lesueur to this
important fact is remarkably strong. These eminent naturalists, after
collecting and describing many thousand species of marine animals which
they brought to Europe from the southern hemisphere, insist most
emphatically on their distinctness from those north of the equator; and
this remark they extend to animals of all classes, from those of a more
simple to those of a more complex organization--from the sponges and
Medusæ to the Cetacea. "Among all those which we have been able to
examine," say they, "with our own eyes, or with regard to which it has
appeared to us possible to pronounce with certainty, there is not a
single animal of the southern regions which is not distinguished by
essential characters from the analogous species in the northern
seas."[909]

On comparing the freshwater fish of Europe and North America, Sir John
Richardson remarks, that the only species which is unequivocally common
to the two continents is the pike (_Esox lucius_); and it is curious
that this fish is unknown to the westward of the Rocky Mountains, the
very coast which approaches nearest to the old continent.[910] According
to the same author the genera of freshwater fish in China agree closely
with those of the peninsula of India, but the species are not the same.
"As in the distribution," he adds, "of marine fish, the interposition of
a continent stretching from the tropics far into the temperate or colder
parts of the ocean, separate different ichthyological groups; so with
respect to the freshwater species, the intrusion of arms of the sea
running far to the northwards, or the interposition of a lofty
mountain-chain, effects the same thing. The freshwater fish of the Cape
of Good Hope and the South American ones, are different from those of
India and China, &c."[911]

Cuvier and Valenciennes, in their "Histoire des Poissons," observe, that
very few species of fish cross the Atlantic. Although their statement is
correct, it is found that a great many species are common to the
opposite sides of the Indian Ocean, inhabiting alike the Red Sea, the
eastern coast of Africa, Madagascar, the Mauritius, the Indian Ocean,
the southern seas of China, the Malay archipelago, the northern coasts
of Australia, and the whole of Polynesia![912] This very wide diffusion,
says Sir J. Richardson, may have been promoted by chains of islands
running east and west, which are wanting in the deep Atlantic. An
archipelago extending far in longitude, favours the migration of fish by
multiplying the places of deposit for spawn along the shores of islands,
and on intervening coral banks; and in such places, also, fish find
their appropriate food.

The flying fish are found (some stragglers excepted) only between the
tropics: in receding from the line, they never approach a higher
latitude than the fortieth parallel. The course of the Gulf stream,
however, and the warmth of its water, enable some tropical fish to
extend their habitations far into the temperate zone; thus the chætodons
which abound in the seas of hot climates, are found among the Bermudas
on the thirty-second parallel, where they are preserved in basins
inclosed from the sea, as an important article of food for the garrison
and inhabitants. Other fish, following the direction of the same great
current, range from the coast of Brazil to the banks of
Newfoundland.[913]

All are aware that there are certain fish of passage which have their
periodical migrations, like some tribes of birds. The salmon, towards
the season of spawning, ascends the rivers for hundreds of miles,
leaping up the cataracts which it meets in its course, and then retreats
again into the depths of the ocean. The herring and the haddock, after
frequenting certain shores, in vast shoals, for a series of years,
desert them again, and resort to other stations, followed by the species
which prey on them. Eels are said to descend into the sea for the
purpose of producing their young, which are seen returning into the
fresh water by myriads, extremely small in size, but possessing the
power of surmounting every obstacle which occurs in the course of a
river, by applying their slimy and glutinous bodies to the surface of
rocks, or the gates of a lock, even when dry, and so climbing over
it.[914] Before the year 1800 there were no eels in Lake Wener, the
largest inland lake in Sweden, which discharges its waters by the
celebrated cataracts of Trolhättan. But I am informed by Professor
Nilsson, that since the canal was opened uniting the river Gotha with
the lake by a series of nine locks, each of great height, eels have been
observed in abundance in the lake. It appears, therefore, that though
they were unable to ascend the falls, they have made their way by the
locks, by which in a very short space a difference of level of 114 feet
is overcome.

Gmelin says, that the Anseres (wild geese, ducks, and others) subsist,
in their migrations, on the spawn of fish; and that oftentimes, when
they void the spawn, two or three days afterwards, the eggs retain their
vitality unimpaired.[915] When there are many disconnected freshwater
lakes in a mountainous region, at various elevations, each remote from
the other, it has often been deemed inconceivable how they could all
become stocked with fish from one common source; but it has been
suggested, that the minute eggs of these animals may sometimes be
entangled in the feathers of water-fowl. These, when they alight to wash
and plume themselves in the water, may often unconsciously contribute to
propagate swarms of fish, which, in due season, will supply them with
food. Some of the water-beetles, also, as the Dyticidæ, are amphibious,
and in the evening quit their lakes and pools, and, flying in the air,
transport the minute ova of fishes to distant waters. In this manner
some naturalists account for the fry of fish appearing occasionally in
small pools caused by heavy rains; but the showers of small fish, stated
in so many accounts to have fallen from the atmosphere, require farther
investigation.


_Geographical Distribution and Migrations of Testacea._

The Testacea, of which so great a variety of species occurs in the sea,
are a class of animals of peculiar importance to the geologist; because
their remains are found in strata of all ages, and generally in a higher
state of preservation than those of other organic beings. Climate has a
decided influence on the geographical distribution of species in this
class; but as there is much greater uniformity of temperature in the
waters of the ocean, than in the atmosphere which invests the land, the
diffusion of marine mollusks is on the whole more extensive.

Some forms attain their fullest development in warm latitudes; and are
often exclusively confined to the torrid zone, as _Nautilus_, _Harpa_,
_Terebellum_, _Pyramidella_, _Delphinula_, _Aspergillum_, _Tridacna_,
_Cucullæa_, _Crassatella_, _Corbis_, _Perna_, and _Plicatula_. Other
forms are limited to one region of the sea, as the _Trigonia_ to parts
of Australia, and the _Concholepas_ to the western coast of South
America. The marine species inhabiting the ocean on the opposite sides
of the narrow isthmus of Panama, are found to differ almost entirely, as
we might have anticipated, since a West Indian mollusk cannot enter the
Pacific without coasting round South America, and passing through the
inclement climate of Cape Horn. The continuity of the existing lines of
continent from north to south, prevents any one species from belting the
globe, or from following the direction of the isothermal lines.

Currents also flowing permanently in certain directions, and the influx
at certain points of great bodies of fresh water, limit the extension of
many species. Those which love deep water are arrested by shoals;
others, fitted for shallow seas, cannot migrate across unfathomable
abysses. The nature also of the ground has an important influence on the
testaceous fauna, both on the land and beneath the waters. Certain
species prefer a sandy, others a gravelly, and some a muddy sea-bottom.
On the land, limestone is of all rocks the most favourable to the number
and propagation of species of the genera Helix, Clausilia, Bulimus, and
others. Professor E. Forbes has shown as the result of his labours in
dredging in the Ægean Sea, that there are eight well-marked regions of
depth, each characterized by its peculiar testaceous fauna. The first of
these, called the littoral zone, extends to a depth of two fathoms only;
but this narrow belt is inhabited by more than one hundred species. The
second region, of which ten fathoms is the inferior limit, is almost
equally populous; and a copious list of species is given as
characteristic of each region down to the seventh, which lies between
the depths of 80 and 105 fathoms, all the inhabited space below this
being included in the eighth province, where no less than 65 species of
Testacea have been taken. The majority of the shells in this lowest zone
are white or transparent. Only two species of Mollusca are common to
all the eight regions, namely, _Arca lactea_ and _Cerithium lima_.[916]

_Great range of some provinces and species._--In Europe conchologists
distinguish between the arctic fauna, the southern boundary of which
corresponds with the isothermal line of 32° F., and the Celtic, which,
commencing with that limit as its northern frontier, extends southwards
to the mouth of the English Channel and Cape Finisterre, in France. From
that point begins the Lusitanian fauna, which, according to the recent
observations of Mr. M'Andrew (1852), ranges to the Canary Islands. The
Mediterranean province is distinct from all those above enumerated,
although it has some species in common with each.

The Indo-Pacific region is by far the most extensive of all. It reaches
from the Red Sea and the eastern coast of Africa, to the Indian
Archipelago, and adjoining parts of the Pacific Ocean. To the geologist
it furnishes a fact of no small interest, by teaching us that one group
of living species of mollusca may prevail throughout an area exceeding
in magnitude the utmost limits we can as yet assign to any assemblage of
contemporaneous fossil species. Mr. Cuming obtained more than a hundred
species of shells from the eastern coast of Africa identical with those
collected by himself at the Philippines and in the eastern coral islands
of the Pacific Ocean, a distance equal to that from pole to pole.[917]

Certain species of the genus _Ianthina_ have a very wide range, being
common to seas north and south of the equator. They are all provided
with a beautifully contrived float, which renders them buoyant,
facilitating their dispersion, and enabling them to become active agents
in disseminating other species. Captain King took a specimen of
_Ianthina fragilis_, alive, a little north of the equator, so loaded
with barnacles (_Pentelasmis_) and their ova that the upper part of its
shell was invisible. The "Rock Whelk" (_Purpura lapillus_), a well-known
British univalve, inhabits both the North Atlantic and North Pacific.

_Helix putris_ (_Succinea putris_, Lam.), so common in Europe, where it
reaches from Norway to Italy, is also said to occur in the United States
and in Newfoundland. As this animal inhabits constantly the borders of
pools and streams where there is much moisture, it is not impossible
that different water-fowl have been the agents of spreading some of its
minute eggs, which may have been entangled in their feathers. The
freshwater snail, _Lymneus palustris_, so abundant in English ponds,
ranges uninterruptedly from Europe to Cashmere, and thence to the
eastern parts of Asia. _Helix aspersa_, one of the commonest of our
larger land-shells, is found in St. Helena and other distant countries.
Some conchologists have conjectured that it was accidentally imported
into St. Helena in some ship; for it is an eatable species, and these
animals are capable of retaining life during long voyages, without air
or nourishment.[918]

Perhaps no species has a better claim to be called cosmopolite than one
of our British bivalves, _Saxicava rugosa_. It is spread over all the
north-polar seas, and ranges in one direction through Europe to Senegal,
occurring on both sides of the Atlantic; while in another it finds its
way into the North Pacific, and thence to the Indian Ocean. Nor do its
migrations cease till it reaches the Australian seas.

A British brachiopod, named _Terebratula caput-serpentis_, is common,
according to Professor E. Forbes, to both sides of the North Atlantic,
and to the South African and Chinese seas.

_Confined range of other species._--Mr. Lowe, in a memoir published in
the Cambridge Transactions in 1834, enumerates seventy-one species of
land Mollusca, collected by him in the islands of Madeira and Porto
Santo, sixty of which belonged to the genus Helix alone, including as
sub-genera Bulimus and Achatina, and excluding Vitrina and Clausilia;
forty-four of these are new. It is remarkable that very few of the
above-mentioned species are common to the neighbouring archipelago of
the Canaries; but it is a still more striking fact, that of the sixty
species of the three genera above mentioned, thirty-one are natives of
Porto Santo; whereas, in Madeira, which contains ten times the
superficies, were found but twenty-nine. Of these only four were common
to the two islands, which are separated by a distance of only twelve
leagues; and two even of these four (namely _Helix rhodostoma_ and _H.
ventrosa_) are species of general diffusion, common to Madeira, the
Canaries, and the south of Europe.[919]

The confined range of these mollusks may easily be explained, if we
admit that species have only one birth-place; and the only problem to be
solved would relate to the exceptions--to account for the dissemination
of some species throughout several islands, and the European continent.
May not the eggs, when washed into the sea by the undermining of cliffs,
or blown by a storm from the land, float uninjured to a distant shore?

_Their mode of diffusion._--Notwithstanding the proverbially slow motion
of snails and mollusks in general, and although many aquatic species
adhere constantly to the same rock for their whole lives, they are by no
means destitute of provision for disseminating themselves rapidly over a
wide area. "Some Mollusca," says Professor E. Forbes, "migrate in their
larva state, for all of them undergo a metamorphosis either in the egg
or out of the egg. The gasteropoda commence life under the form of a
small spiral shell, and an animal furnished with ciliated wings, or
lobes, like a pteropod, by means of which it can swim freely, and in
this form can migrate with ease through the sea."[920]

We are accustomed to associate in our minds the idea of the greatest
locomotive powers with the most mature and perfect state of each species
of invertebrate animal, especially when they undergo a series of
transformations; but in all the Mollusca the reverse is true. The young
fry of the cockle, for example (_Cardium_), possess, when young or in
the larva state, an apparatus which enables them both to swim and to be
carried along easily by a marine current. (See fig. 99.)

[Illustration: Fig. 99.

Tne young fry of a cockle (Cardium pygmæum,) from Loven's Kongl.
Vetenskaps. Akadem. Handling, 1848.


   A, The young just hatched, magnified 100 diameters.
   B, the same farther advanced.

  _a_, The ciliated organ of locomotion with its filamentous
         appendage _b_.
  _c_, The rudimentary intestine.
  _d_, The rudimentary shell.

]

These small bodies here represented, which bear a considerable
resemblance to the fry of the univalve, or gasteropodous shells above
mentioned, are so minute at first as to be just visible to the naked
eye. They begin to move about from the moment they are hatched, by means
of the long cilia, _a_, _a_, placed on the edges of the locomotive disk
or velum. This disk shrinks up as they increase in size, and gradually
disappears, no trace of it being visible in the perfect animal.

Some species of shell-bearing Mollusca lay their eggs in a sponge-like
nidus, wherein the young remain enveloped for a time after their birth;
and this buoyant substance floats far and wide as readily as sea-weed.
The young of other viviparous tribes are often borne along entangled in
sea-weed. Sometimes they are so light, that, like grains of sand, they
can be easily moved by currents. Balani and Serpulæ are sometimes found
adhering to floating cocoa-nuts, and even to fragments of pumice. In
rivers and lakes, on the other hand, aquatic univalves usually attach
their eggs to leaves and sticks which have fallen into the water, and
which are liable to be swept away during floods, from tributaries to the
main streams, and from thence to all parts of the same basins.
Particular species may thus migrate during one season from the head
waters of the Mississippi, or any other great river, to countries
bordering the sea, at the distance of many thousand miles.

An illustration of the mode of attachment of these eggs will be seen in
the annexed cut. (Fig. 100.)

The habit of some Testacea to adhere to floating wood is proved by their
fixing themselves to the bottoms of ships. By this mode of conveyance
_Mytilus polymorphus_, previously known only in the Danube and Wolga,
may have been brought to the Commercial Docks in the Thames, and to
Hamburgh, where the species is now domiciled. But Mr. Gray suggests that
as the animal is known to have the faculty of living for a very long
time out of water, it is more probable that it was brought in Russian
timber, than borne uninjured through the salt water at the bottom of a
vessel.[921]

A lobster (_Astacus marinus_) was lately taken alive covered with living
mussels (_Mytilus edulis_)[922]; and a large female crab (_Cancer
pagurus_), covered with oysters, and bearing also _Anomia ephippium_,
and Actiniæ, was taken in April, 1832, off the English coast. The
oysters, seven in number, include individuals of six years' growth, and
the two largest are four inches long and three inches and a half broad.
Both the crab and the oysters were seen alive by Mr. Robert Brown.[923]

[Illustration: Fig. 100.

Eggs of Freshwater mollusks.


  Fig. 1. Eggs of _Ampullaria ovata_ (a fluviatile species) fixed to
            a small sprig which had fallen into the water.
  Fig. 2. Eggs of _Planorbis albus_, attached to a dead leaf lying
            under water.
  Fig. 3. Eggs of the common Limneus (_L. vulgaris_), adhering to
            a dead stick under water.

]

From this example we learn the manner in which oysters may be diffused
over every part of the sea where the crab wanders; and if they are at
length carried to a spot where there is nothing but fine mud, the
foundation of a new oyster-bank may be laid on the death of the crab. In
this instance the oysters survived the crab many days, and were killed
at last only by long exposure to the air.


_Geographical Distribution and Migrations of Zoophytes._

Zoophytes are very imperfectly known; but there can be little doubt that
each maritime region possesses species peculiar to itself. The
Madrepores, or lamelliferous Polyparia, are found in their fullest
development only in the tropical seas of Polynesia and the East and West
Indies; and this family is represented only by a few species in our
seas. The zoophytes of the Mediterranean, according to Ehrenberg, differ
almost entirely from those of the Red Sea, although only seventy miles
distant. Out of 120 species of Anthozoa, only two are common to both
seas.[924] Péron and Lesueur, after studying the Holothuriæ, Medusæ, and
other congeners of delicate and changeable forms, came to the conclusion
that each kind has its place of residence determined by the temperature
necessary to support its existence. Thus, for example, they found the
abode of _Pyrosoma Atlantica_ to be confined to one particular region of
the Atlantic Ocean.[925]

Let us now inquire how the transportation of zoophytes from one part of
the globe to another is effected. Many of them, as in the families
Flustra and Sertularia, attach themselves to sea-weed, and are
occasionally drifted along with it. Many fix themselves to the shells of
Mollusca, and are thus borne along by them to short distances. Others,
like some species of sea-pens, float about in the ocean, and are usually
believed to possess powers of spontaneous motion. But the most frequent
mode of transportation consists in the buoyancy of their eggs, or
certain small vesicles, which are detached, and are capable of becoming
the foundation of a new colony. These gems, as they are called, have, in
many instances, a locomotive power of their own, by which they proceed
in a determinate direction for several days after separation from the
parent. They are propelled by means of numerous short threads or
_ciliæ_, which are in constant and rapid vibration; and, when thus
supported in the water, they may be borne along by currents to a great
distance.

That some zoophytes adhere to floating bodies, is proved by their being
found attached to the bottoms of ships, like certain Testacea before
alluded to.


_Geographical Distribution and Migrations of Insects._

Before I conclude this sketch of the manner in which the habitable parts
of the earth are shared out among particular assemblages of organic
beings, I must offer a few remarks on insects, which, by their numbers
and the variety of their powers and instincts, exert a prodigious
influence in the economy of animate nature. As a large portion of these
minute creatures are strictly dependent for their subsistence on certain
species of vegetables, the entomological provinces must coincide in
considerable degree with the botanical.

All the insects, says Latreille, brought from the eastern parts of Asia
and China, whatever be their latitude and temperature, are distinct from
those of Europe and of Africa. The insects of the United States,
although often approaching very close to our own, are, with very few
exceptions, specifically distinguishable by some characters. In South
America, the equinoctial lands of New Granada and Peru on the one side,
and of Guiana on the other, contain for the most part distinct groups;
the Andes forming the division, and interposing a narrow line of severe
cold between climates otherwise very similar.[926]

_Migratory instincts._--Nearly all the insects of the United States and
Canada, differ specifically from the European; while those of Greenland
appear to be in a great measure identical with our own. Some insects are
very local; while a few, on the contrary, are common to remote
countries, between which the torrid zone and the ocean intervene. Thus
our painted lady butterfly (_Vanessa cardui_) re-appears at the Cape of
Good Hope and in New Holland and Japan with scarcely a varying
streak.[927] The same species is said to be one of the few insects which
are universally dispersed over the earth, being found in Europe, Asia,
Africa, and America; and its wide range is the more interesting, because
it seems explained by its migratory instinct, seconded, no doubt, by a
capacity, enjoyed by few species, of enduring a great diversity of
temperature.

A vast swarm of this species, forming a column from ten to fifteen feet
broad, was, a few years since, observed in the Canton de Vaud; they
traversed the country with great rapidity from north to south, all
flying onwards in regular order, close together, and not turning from
their course on the approach of other objects. Professor Bonelli, of
Turin, observed, in March of the same year, a similar swarm of the same
species, also directing their flight from north to south, in Piedmont,
in such immense numbers that at night the flowers were literally covered
with them. They had been traced from Coni, Raconi, Susa, &c. A similar
flight at the end of the last century is recorded by M. Louch in the
Memoirs of the Academy of Turin. The fact is the more worthy of notice,
because the caterpillars of this butterfly are not gregarious, but
solitary from the moment that they are hatched; and this instinct
remains dormant, while generation after generation passes away, till it
suddenly displays itself in full energy when their numbers happen to be
in excess.

Not only peculiar species, but certain types, distinguish particular
countries; and there are groups, observes Kirby, which represent each
other in distant regions, whether in their form, their functions, or in
both. Thus the honey and wax of Europe, Asia, and Africa, are in each
case prepared by bees congenerous with our common hive-bee (_Apis_,
Latr.); while, in America, this genus is nowhere indigenous, but is
replaced by Melipona, Trigona, and Euglossa; and in New Holland by
a still different but undescribed type.[928] The European bee (_Apis
mellifica_), although not a native of the new world, is now established
both in North and South America. It was introduced into the United
States by some of the early settlers, and has since overspread the vast
forests of the interior, building hives in the decayed trunks of trees.
"The Indians," says Irving, "consider them as the harbinger of the white
man, as the buffalo is of the red man, and say that in proportion as the
bee advances the Indian and the buffalo retire. It is said," continues
the same writer, "that the wild bee is seldom to be met with at any
great distance from the frontier, and that they have always been the
heralds of civilization, preceding it as it advanced from the Atlantic
borders. Some of the ancient settlers of the west even pretend to give
the very year when the honey-bee first crossed the Mississippi."[929]
The same species is now also naturalized in Van Diemen's Land and New
Zealand.

As almost all insects are winged, they can readily spread themselves
wherever their progress is not opposed by uncongenial climates, or by
seas, mountains, and other physical impediments; and these barriers they
can sometimes surmount by abandoning themselves to violent winds, which,
as I before stated, when speaking of the dispersion of seeds (p. 618.),
may in a few hours carry them to very considerable distances. On the
Andes some sphinxes and flies have been observed by Humboldt, at the
height of 19,180 feet above the sea, and which appeared to him to have
been involuntarily carried into these regions by ascending currents of
air.[930]

White mentions a remarkable shower of aphides which seem to have
emigrated, with an east wind, from the great hop plantations of Kent and
Sussex, and blackened the shrubs and vegetables where they alighted at
Selbourne, spreading at the same time in great clouds all along the vale
from Farnham to Alton. These aphides are sometimes accompanied by vast
numbers of the common lady-bird (_Coccinella septempunctata_), which
feed upon them.[931]

It is remarkable, says Kirby, that many of the insects which are
occasionally observed to emigrate, as, for instance, the Libellulæ,
Coccinellæ, Carabi, Cicadæ, &c. are not usually social insects; but seem
to congregate, like swallows, merely for the purpose of emigration.[932]
Here, therefore, we have an example of an instinct developing itself on
certain rare emergencies, causing unsocial species to become gregarious
and to venture sometimes even to cross the ocean.

The armies of locusts which darken the air in Africa, and traverse the
globe from Turkey to our southern counties in England, are well known to
all. When the western gales sweep over the Pampas they bear along with
them myriads of insects of various kinds. As a proof of the manner in
which species may be thus diffused, I may mention that when the Creole
frigate was lying in the outer roads off Buenos Ayres, in 1819, at the
distance of six miles from the land, her decks and rigging were suddenly
covered by thousands of flies and grains of sand. The sides of the
vessel had just received a fresh coat of paint, to which the insects
adhered in such numbers as to spot and disfigure the vessel, and to
render it necessary partially to renew the paint.[933] Captain W. H.
Smyth was obliged to repaint his vessel, the Adventure, in the
Mediterranean, from the same cause. He was on his way from Malta to
Tripoli, when a southern wind blowing from the coast of Africa, then one
hundred miles distant, drove such myriads of flies upon the fresh paint,
that not the smallest point was left unoccupied by insects.

To the southward of the river Plate, off Cape St. Antonio, and at the
distance of fifty miles from land, several large dragon-flies alighted
on the Adventure frigate, during Captain King's late expedition to the
Straits of Magellan. If the wind abates when insects are thus crossing
the sea, the most delicate species are not necessarily drowned; for many
can repose without sinking on the water. The slender long-legged tipulæ
have been seen standing on the surface of the sea, when driven out far
from our coast, and took wing immediately on being approached.[934]
Exotic beetles are sometimes thrown on our shore, which revive after
having been long drenched in salt water; and the periodical appearance
of some conspicuous butterflies amongst us, after being unseen some for
five others for fifty years, has been ascribed, not without probability,
to the agency of the winds.

Inundations of rivers, observes Kirby, if they happen at any season
except in the depths of winter, always carry down a number of insects,
floating on the surface of bits of stick, weeds, &c.; so that when the
waters subside, the entomologist may generally reap a plentiful harvest.
In the dissemination, moreover, of these minute beings, as in that of
plants, the larger animals play their part. Insects are, in numberless
instances, borne along in the coats of animals, or the feathers of
birds; and the eggs of some species are capable, like seeds, of
resisting the digestive powers of the stomach, and after they are
swallowed with herbage, may be ejected again unharmed in the dung.


_Geographical Distribution and Diffusion of Man._

I have reserved for the last some observations on the range and
diffusion of the human species over the earth, and the influence of man
in spreading other animals and plants, especially the terrestrial.

Many naturalists have amused themselves in speculating on the probable
birth-place of mankind, the point from which, if we assume the whole
human race to have descended from a single pair, the tide of emigration
must originally have proceeded. It has been always a favorite
conjecture, that this birth-place was situated within or near the
tropics, where perpetual summer reigns, and where fruits, herbs, and
roots are plentifully supplied throughout the year. The climate of these
regions, it has been said, is suited to a being born without any
covering, and who had not yet acquired the arts of building habitations
or providing clothes.

_Progress of Human Population._--"The hunter state," it has been argued,
"which Montesquieu placed the first, was probably only the second stage
to which mankind arrived; since so many arts must have been invented to
catch a salmon, or a deer, that society could no longer have been in its
infancy when they came into use."[935] When regions where the
spontaneous fruits of the earth abound became overpeopled, men would
naturally diffuse themselves over the neighboring parts of the temperate
zone; but a considerable time would probably elapse before this event
took place; and it is possible, as a writer before cited observes, that
in the interval before the multiplication of their numbers and their
increasing wants had compelled them to emigrate, some arts to take
animals were invented, but far inferior to what we see practised at this
day among savages. As their habitations gradually advanced into the
temperate zone, the new difficulties they had to encounter would call
forth by degrees the spirit of invention, and the probability of such
inventions always rises with the number of people involved in the same
necessity.[936]

A distinguished modern writer, who coincides for the most part in the
views above mentioned, has introduced one of the persons in his second
dialogue, as objecting to the theory of the human race having gradually
advanced from a savage to a civilized state, on the ground that "the
first man must have inevitably been destroyed by the elements or
devoured by savage beasts, so infinitely his superiors in physical
force."[937] He then contends against the difficulty here started by
various arguments, all of which were, perhaps, superfluous; for if a
philosopher is pleased to indulge in conjectures on this subject, why
should he not assign, as the original seat of man, some one of those
large islands within the tropics, which are as free from large beasts of
prey as Van Diemen's Land or Australia? Here man may have remained for a
period, peculiar to a single island, just as some of the large
anthropomorphous species are now limited to one island within the
tropics. In such a situation, the new-born race might have lived in
security, though far more helpless than the New Holland savages, and
might have found abundance of vegetable food. Colonies may afterwards
have been sent forth from this mother country, and then the peopling of
the earth may have proceeded according to the hypothesis before alluded
to.

To form a probable conjecture respecting the country from whence the
early civilization of India was derived, has been found almost as
difficult as to determine the original birth-place of the human race.
That the dawn of oriental civilization did not arise within the limits
of the tropics, is the conclusion to which Baron William von Humboldt
has come after much patient research into "the diversities of the
structure of language and their influence on the mental development of
the human race." According to him the ancient Zend country from whence
the spread of knowledge and the arts has been traced in a south-easterly
direction, lay to the north-west of the upper Indus.[938]

As to the time of the first appearance of man upon the earth, if we are
to judge from the discordance of opinion amongst celebrated
chronologers, not even a rude approximation has yet been made towards
determining a point of so much interest. The problem seems hitherto to
have baffled the curiosity of the antiquary, if possible, more
completely than the fixing on a geographical site for the original
habitation of the ancestors of the human race. The Chevalier Bunsen, in
his elaborate and philosophical work on Ancient Egypt,[939] has
satisfied not a few of the learned, by an appeal to monumental
inscriptions still extant, that the successive dynasties of kings may be
traced back without a break, to Menes, and that the date of his reign
would correspond with the year 3640 B. C. He supposes at the same time,
what is most reasonable, that the Egyptian people must have existed for
a long period (probably at least for five centuries), in their earlier
and less settled state, before they reached the point of civilization at
which Menes consolidated them into a great and united empire. This would
carry us back to upwards of 4000 years B. C., or to an epoch coincident
with that commonly set down for the creation of the world in accordance
with computations founded on the combined ages of the successive
antediluvian patriarchs. It follows that the same epoch of Menes is
anterior by a great many centuries to the most ancient of the dates
usually fixed upon for the Mosaic deluge. The fact that no record or
tradition of any great and overwhelming flood has been detected in the
mythology, or monumental annals of the Egyptians, will suggest many
reflections to a geologist who has weighed well the evidence we possess
of a variety of partial deluges which have happened in districts not
free like Egypt, for the last 3000 years, from earthquakes and other
causes of great aqueous catastrophes. The tales and legends of
calamitous floods preserved in Greece, Asia Minor, the southern shores
of the Baltic, China, Peru, and Chili, have, as we have seen, been all
of them handed down to us by the inhabitants of regions in which the
operation of natural causes in modern times, and the recurrence of a
succession of disastrous floods, afford us data for interpreting the
meaning of the obscure traditions of an illiterate age.[940]

In his learned treatise on ancient chronology, Dr. Hales has selected,
from a much greater number, a list of no less than 120 authors, all of
whom give a different period for the epoch of the creation of the world,
the extreme range of difference between them amounting to no less than
3268 years. It appears that even amongst authorities, who in England are
generally regarded, as orthodox, there is a variance, not of years or of
one or two centuries, but of upwards of a millennium, according as they
have preferred to follow the Hebrew, or the Samaritan, or the Greek
versions of the Mosaic writings. Can we then wonder that they who
decipher the monuments of Egypt, or the geologist who interprets the
earth's autobiography, should arrive at views respecting the date of an
ancient empire, or the age of our planet, irreconcilable with every one
of these numerous and conflicting chronologies? The want of agreement
amongst the learned in regard to the probable date of the deluge of Noah
is a source of far greater perplexity and confusion than our extreme
uncertainty as to the epoch of the creation,--the deluge being a
comparatively modern event, from which the repeopling of the earth and
the history of the present races of mankind is made to begin.

Naturalists have long felt that to render probable the received opinion
that all the leading varieties of the human family have originally
sprung from a single pair, (a doctrine against which there appears to me
to be no sound objection,) a much greater lapse of time is required for
the slow and gradual formation of races, (such as the Caucasian,
Mongolian, and Negro,) than is embraced in any of the popular systems of
chronology. The existence of two of those marked varieties above
mentioned can be traced back 3000 years before the present time, or to
the painting of pictures, preserved in the tombs or on the walls of
buried temples in Egypt. In these we behold the Negro and Caucasian
physiognomies portrayed as faithfully and in as strong contrast as if
the likenesses of those races had been taken yesterday. When we consider
therefore the extreme slowness of the changes, which climate and other
modifying causes have produced in modern times, we must allow for a vast
series of antecedent ages, in the course of which the long-continued
influence of similar external circumstances gave rise to peculiarities,
probably increased in many successive generations, until they were fixed
by hereditary transmission. The characteristic forms and features thus
acquired by certain tribes, may have been afterwards diffused by
migration from a few centres over wide continental spaces. The theory,
therefore, that all the races of man have come from one common stock
receives support from every investigation which forces us to expand our
ideas of the duration of past time, or which multiplies the number of
years that have passed away since the origin of man. Hitherto, geology
has neither enlarged nor circumscribed the "human period;" but simply
proved that in the history of animated nature it is comparatively
modern, or the last of a long series of antecedent epochs, in each of
which the earth has been successively peopled by distinct species of
animals and plants.

In an early stage of society the necessity of hunting acts as a
principle of repulsion, causing men to spread with the greatest rapidity
over a country, until the whole is covered with scattered settlements.
It has been calculated that eight hundred acres of hunting-ground
produce only as much food as half an acre of arable land. When the game
has been in a great measure exhausted, and a state of pasturage
succeeds, the several hunter tribes, being already scattered, may
multiply in a short time into the greatest number which the pastoral
state is capable of sustaining. The necessity, says Brand, thus imposed
upon the two savage states, of dispersing themselves far and wide over
the country, affords a reason why, at a very early period, the worst
parts of the earth may have become inhabited.

But this reason, it may be said, is only applicable in as far as regards
the peopling of a continuous continent; whereas the smallest islands,
however remote from continents, have almost always been found inhabited
by man. St. Helena, it is true, afforded an exception; for when that
island was discovered in 1501, it was only inhabited by sea-fowl, and
occasionally by seals and turtles, and was covered with a forest of
trees and shrubs, all of species peculiar to it, with one or two
exceptions, and which seem to have been expressly created for this
remote and insulated spot.[941]

The islands also of Mauritius, Bourbon, Pitcairns, and Juan Fernandez,
and those of the Galapagos archipelago, one of which is seventy miles
long, were inhabited when first discovered, and, what is more remarkable
than all, the Falkland Islands, which together are 120 miles in length
by 60 in breadth, and abounding in food fit for the support of man.

_Drifting of canoes to vast distances._--But very few of the numerous
coral islets and volcanoes of the vast Pacific, capable of sustaining a
few families of men, have been found untenanted; and we have, therefore,
to inquire whence and by what means, if all the members of the great
human family have had one common source, could those savages have
migrated. Cook, Forster, and others, have remarked that parties of
savages in their canoes must have often lost their way, and must have
been driven on distant shores, where they were forced to remain,
deprived both of the means and of the requisite intelligence for
returning to their own country. Thus Captain Cook found on the island of
Wateoo three inhabitants of Otaheite, who had been drifted thither in a
canoe, although the distance between the two isles is 550 miles. In
1696, two canoes, containing thirty persons, who had left Ancorso, were
thrown by contrary winds and storms on the island of Samar, one of the
Philippines, at a distance of 800 miles. In 1721, two canoes, one of
which contained twenty-four, and the other six persons, men, women, and
children, were drifted from an island called Farroilep to the island of
Guaham, one of the Marians, a distance of 200 miles.[942]

Kotzebue, when investigating the Coral Isles of Radack, at the eastern
extremity of the Caroline Isles, became acquainted with a person of the
name of Kadu, who was a native of Ulea, an isle 1500 miles distant, from
which he had been drifted with a party. Kadu and three of his
countrymen one day left Ulea in a sailing boat, when a violent storm
arose, and drove them out of their course: they drifted about the open
sea for eight months, according to their reckoning by the moon, making a
knot on a cord at every new moon. Being expert fishermen, they subsisted
entirely on the produce of the sea; and when the rain fell, laid in as
much fresh water as they had vessels to contain it. "Kadu," says
Kotzebue, "who was the best diver, frequently went down to the bottom of
the sea, where it is well known that the water is not so salt, with a
cocoa-nut shell, with only a small opening."[943] When these unfortunate
men reached the isles of Radack, every hope and almost every feeling had
died within them; their sail had long been destroyed, their canoe had
long been the sport of winds and waves, and they were picked up by the
inhabitants of Aur in a state of insensibility; but by the hospitable
care of those islanders they soon recovered, and were restored to
perfect health.[944]

Captain Beechey, in his voyage to the Pacific, fell in with some natives
of the Coral Islands, who had in a similar manner been carried to a
great distance from their native country. They had embarked, to the
number of 150 souls, in three double canoes, from Anaa, or Chain Island,
situated about three hundred miles to the eastward of Otaheite. They
were overtaken by the monsoon, which dispersed the canoes; and after
driving them about the ocean, left them becalmed, so that a great number
of persons perished. Two of the canoes were never heard of; but the
other was drifted from one uninhabited island to another, at each of
which the voyagers obtained a few provisions; and at length, after
having wandered for a distance of 600 miles, they were found and carried
to their home in the Blossom.[945]

Mr. Crawfurd informs me that there are several well-authenticated
accounts of canoes having been drifted from Sumatra to Madagascar, and
by such causes a portion of the Malayan language, with some useful
plants, have been transferred to that island, which is principally
peopled by negroes.

The space traversed in some of these instances was so great, that
similar accidents might suffice to transport canoes from various parts
of Africa to the shores of South America, or from Spain to the Azores,
and thence to North America; so that man, even in a rude state of
society, is liable to be scattered involuntarily by the winds and waves
over the globe, in a manner singularly analogous to that in which many
plants and animals are diffused. We ought not, then, to wonder, that
during the ages required for some tribes of the human race to attain
that advanced stage of civilization which empowers the navigator to
cross the ocean in all directions with security, the whole earth should
have become the abode of rude tribes of hunters and fishers. Were the
whole of mankind now cut off, with the exception of one family,
inhabiting the old or new continent, or Australia, or even some coral
islet of the Pacific, we might expect their descendants, though they
should never become more enlightened than the South Sea Islanders or the
Esquimaux, to spread in the course of ages over the whole earth,
diffused partly by the tendency of population to increase, in a limited
district, beyond the means of subsistence, and partly by the accidental
drifting of canoes by tides and currents to distant shores.


_Involuntary Influence of Man in diffusing Animals and Plants._

Many of the general remarks which have been made respecting the
influence of man in spreading or in checking the diffusion of plants
apply equally to his relations with the animal kingdom. On a future
occasion I shall be led to speak of the instrumentality of our species
in naturalizing useful animals and plants in new regions, when
explaining my views of the effects which the spreading and increase of
certain species exert in the extirpation of others. At present I shall
confine myself to a few remarks on the involuntary aid which man lends
to the dissemination of species.

In the mammiferous class our influence is chiefly displayed in
increasing the number of quadrupeds which are serviceable to us, and in
exterminating or reducing the number of those which are noxious.

Sometimes, however, we unintentionally promote the multiplication of
inimical species, as when we introduced the rat, which was not
indigenous in the new world, into all parts of America. They have been
conveyed over in ships, and now infest a great multitude of islands and
parts of that continent. In like manner the Norway rat (_Mus decumanus_)
has been imported into England, where it plunders our property in ships
and houses.

Among birds, the house sparrow may be cited as a species known to have
extended its range with the tillage of the soil. During the last century
it has spread gradually over Asiatic Russia towards the north and east,
always following the progress of cultivation. It made its first
appearance on the Irtisch in Tobolsk, soon after the Russians had
ploughed the land. It came in 1735 up the Obi to Beresow, and four years
after to Naryn, about fifteen degrees of longitude farther east. In
1710, it had been seen in the higher parts of the coast of the Lena, in
the government of Irkutzk. In all these places it is now common, but is
not yet found in the uncultivated regions of Kamtschatka.[946]

The great viper (_Fer de lance_), a species no less venomous than the
rattlesnake, which now ravages Martinique and St. Lucia, was
accidentally introduced by man, and exists in no other part of the West
Indies.

Many parasitic insects which attack our persons, and some of which are
supposed to be peculiar to our species, have been carried into all parts
of the earth, and have as high a claim as man to a _universal_
geographical distribution.

A great variety of insects have been transported in ships from one
country to another, especially in warmer latitudes. The European
house-fly has been introduced in this way into all the South Sea
Islands. Notwithstanding the coldness of our climate in England we have
been unable to prevent the cockroach (_Blatta orientalis_) from entering
and diffusing itself in our ovens and kneading troughs, and availing
itself of the artificial warmth which we afford. It is well known also,
that beetles, and many other kinds of ligniperdous insects, have been
introduced into Great Britain in timber; especially several North
American species. "The commercial relations," says Malte-Brun[947],
"between France and India have transported from the latter country the
aphis, which destroys the apple tree, and two sorts of Neuroptera, the
_Lucifuga_ and _Flavicola_, mostly confined to Provence and the
neighbourhood of Bourdeaux, where they devour the timber in the houses
and naval arsenals."

Among mollusks we may mention the _Teredo navalis_, which is a native of
equatorial seas, but which, by adhering to the bottom of ships, was
transported to Holland, where it has been most destructive to vessels
and piles. The same species has also become naturalized in England, and
other countries enjoying an extensive commerce. _Bulimus undatus_, a
land species of considerable size, native of Jamaica and other West
Indian islands, has been imported, adhering to tropical timber, into
Liverpool; and, as I learn from Mr. Broderip, is now naturalized in the
woods near that town.

In all these and innumerable other instances we may regard the
involuntary agency of man as strictly analogous to that of the inferior
animals. Like them, we unconsciously contribute to extend or limit the
geographical range and numbers of certain species, in obedience to
general rules in the economy of nature, which are for the most part
beyond our control.




CHAPTER XL.

THEORIES RESPECTING THE ORIGINAL INTRODUCTION OF SPECIES.


  Proposal of an hypothesis on this subject--Supposed centres or foci
    of creation--Why distinct provinces of animals and plants have not
    become more blended together--Brocchi's speculations on the loss of
    species--Stations of plants and animals--Causes on which they
    depend--Stations of plants how affected by animals--Equilibrium in
    the number of species how preserved--Peculiar efficacy of insects in
    this task--Rapidity with which certain insects multiply or decrease
    in numbers--Effect of omnivorous animals in preserving the
    equilibrium of species--Reciprocal influence of aquatic and
    terrestrial species on each other.


_Theory of Linnæus._--It would be superfluous to examine the various
attempts which were made to explain the phenomena of the distribution of
species alluded to in the preceding chapters, in the infancy of the
sciences of botany, zoology, and physical geography. The theories or
rather conjectures then indulged now stand refuted by a simple statement
of facts; and if Linnæus were living he would be the first to renounce
the notions which he promulgated. For he imagined the habitable world to
have been for a certain time limited to one small tract, the only
portion of the earth's surface that was as yet laid bare by the
subsidence of the primæval ocean. In this fertile spot he supposed the
originals of all the species of plants which exist on this globe to have
been congregated together with the first ancestors of all animals and of
the human race. "In quâ commodè habitaverint animalia omnia, et
vegetabilia lætè germinaverint." In order to accommodate the various
habitudes of so many creatures, and to provide a diversity of climate
suited to their several natures, the tract in which the creation took
place was supposed to have been situated in some warm region of the
earth, but to have contained a lofty mountain range, on the heights and
in the declivities of which were to be found all temperatures and every
climate, from that of the torrid to that of the frozen zone.[948]

That there never was a universal ocean since the planet was inhabited,
or, rather, since the oldest groups of strata yet known to contain
organic remains were formed, is proved by the presence of terrestrial
plants or by indications of shores in all the older formations; and if
this conclusion was not established, yet no geologist could deny that,
since the first small portion of the earth was laid dry, there have been
many entire changes in the species of plants and animals inhabiting the
land.

But, without dwelling on the above and other refuted theories, let us
inquire whether some hypothesis cannot be substituted as simple as that
of Linnæus, to which the phenomena now ascertained in regard to the
distribution both of aquatic and terrestrial species may be referred.
The following may, perhaps, be reconcileable with known facts:--Each
species may have had its origin in a single pair, or individual, where
an individual was sufficient, and species may have been created in
succession at such times and in such places as to enable them to
multiply and endure for an appointed period, and occupy an appointed
space on the globe.

In order to explain this theory, let us suppose every living thing to be
destroyed in the western hemisphere, both on the land and in the ocean,
and permission to be given to man to people this great desert, by
transporting into it animals and plants from the eastern hemisphere, a
strict prohibition being enforced against introducing two original
stocks of the same species.

Now it is easy to show that the result of such a mode of colonizing
would correspond exactly, so far as regards the grouping of animals and
plants, with that now observed throughout the globe. In the first place,
it would be necessary for naturalists, before they imported species into
particular localities, to study attentively the climate and other
physical conditions of each spot. It would be no less requisite to
introduce the different species in succession, so that each plant and
animal might have time and opportunity to multiply before the species
destined to prey upon it was admitted. Many herbs and shrubs, for
example, must spread far and wide before the sheep, the deer, and the
goat could be allowed to enter, lest they should devour and annihilate
the original stocks of many plants, and then perish themselves for want
of food. The above-mentioned herbivorous animals in their turn must be
permitted to make considerable progress before the entrance of the first
pair of wolves or lions. Insects must be allowed to swarm before the
swallow could be permitted to skim through the air, and feast on
thousands at one repast.

It is evident that, however equally in this case our original stocks
were distributed over the whole surface of land and water, there would
nevertheless arise distinct botanical and zoological provinces, for
there are a great many natural barriers which oppose common obstacles to
the advance of a variety of species. Thus, for example, almost all the
animals and plants naturalized by us, towards the extremity of South
America, would be unable to spread beyond a certain limit, towards the
east, west, and south; because they would be stopped by the ocean, and a
few of them only would succeed in reaching the cooler latitudes of the
northern hemisphere, because they would be incapable of bearing the heat
of the tropics, through which they must pass. In the course of ages,
undoubtedly, exceptions would arise, and some species might become
common to the temperate and polar regions, or both sides of the equator;
for I have before shown that the powers of diffusion conferred on some
classes are very great. But we might confidently predict that these
exceptions would never become so numerous as to invalidate the general
rule.

Some of the plants and animals transplanted by us to the coast of Chili
and Peru would never be able to cross the Andes, so as to reach the
eastern plains; nor, for a similar reason, would those first established
in the Pampas, or the valleys of the Amazon and the Orinoco, ever arrive
at the shores of the Pacific.

In the ocean an analogous state of things would prevail; for there,
also, climate would exert a great influence in limiting the range of
species, and the land would stop the migrations of aquatic tribes as
effectually as the sea arrests the dispersion of the terrestrial. As
certain birds, insects, and the seeds of plants, can never cross the
direction of prevailing winds, so currents form natural barriers to the
dissemination of many oceanic races. A line of shoals may be as
impassable to deep-water species, as are the Alps and the Andes to
plants and animals peculiar to plains; while deep abysses may prove
insuperable obstacles to the migrations of the inhabitants of shallow
waters.

_Supposed centres, or foci, of creation._--It is worthy of observation,
that one effect of the introduction of single pairs of each species must
be the confined range of certain groups in spots, which, like small
islands, or solitary inland lakes, have few means of interchanging their
inhabitants with adjoining regions. Now this congregating in a small
space of many peculiar species, would give an appearance of _centres_ or
_foci_ of creation, as they have been termed, as if they were favourite
points where the creative energy has been in greater action than in
others, and where the numbers of peculiar organic beings have
consequently become more considerable.

I do not mean to call in question the soundness of the inferences of
some botanists, as to the former existence of certain limited spots
whence species of plants have been propagated, radiating, as it were, in
all directions from a common centre. On the contrary, I conceive these
phenomena to be the necessary consequences of the plan of nature before
suggested, operating during the successive mutations of the surface,
some of which the geologist can prove to have taken place subsequently
to the period when many species now existing were created. In order to
exemplify how this arrangement of plants may have been produced, let us
imagine that, about three centuries before the discovery of St. Helena
(itself of submarine volcanic origin), a multitude of new islands had
been thrown up in the surrounding sea, and that these had each become
clothed with plants emigrating from St. Helena, in the same manner as
the wild plants of Campania have diffused themselves over Monte Nuovo.
Whenever the first botanist investigated the new archipelago, he would,
in all probability, find a different assemblage of plants in each of the
islands of recent formation; but in St. Helena itself, he would meet
with individuals of every species, belonging to all parts of the
archipelago, and some, in addition, peculiar to itself, viz., those
which had not been able to obtain a passage into any one of the
surrounding new-formed lands. In this case it might be truly said that
the original island was the primitive focus, or centre, of a certain
type of vegetation; whereas, in the surrounding islands, there would be
a smaller number of species, yet all belonging to the same group.

But this peculiar distribution of plants would not warrant the
conclusion that, in the space occupied by St. Helena, there had been a
greater exertion of creative power than in the spaces of equal area
occupied by the new adjacent lands; because, within the period in which
St. Helena had acquired its peculiar vegetation, each of the spots
supposed to be subsequently converted into land may have been the
birth-place of a great number of _marine_ animals and plants, which may
have had time to scatter themselves far and wide over the southern
Atlantic.

_Why distinct provinces not more blended._--Perhaps it may be objected
to some parts of the foregoing train of reasoning, that during the lapse
of past ages, especially during many partial revolutions of the globe of
comparatively modern date, different zoological and botanical provinces
ought to have become more confounded and blended together--that the
distribution of species approaches too nearly to what might have been
expected, if animals and plants had been introduced into the globe when
its physical geography had already assumed the features which it now
wears; whereas we know that, in certain districts, considerable
geographical changes have taken place since species identical with those
now in being were created.

_Brocchi's speculations on loss of species._--These and many kindred
topics cannot be fully discussed until we have considered, not merely
the general laws which may regulate the first introduction of species,
but those which may limit their _duration_ on the earth. Brocchi
remarked, when hazarding some interesting conjectures respecting "the
loss of species," that a modern naturalist had no small assurance, who
declared "that individuals alone were capable of destruction, and that
species were so perpetuated that nature could not annihilate them, so
long as the planet lasted, or at least that nothing less than the shock
of a comet, or some similar disaster, could put an end to their
existence."[949] The Italian geologist, on the contrary, had satisfied
himself that many species of Testacea, which formerly inhabited the
Mediterranean, had become extinct, although a great number of others,
which had been the contemporaries of those lost races, still survived.
He came to the opinion that about half the species which peopled the
waters when the Subapennine strata were deposited had gone out of
existence; and in this inference he does not appear to have been far
wrong.

But, instead of seeking a solution of this problem; like some other
geologists of his time, in a violent and general catastrophe, Brocchi
endeavoured to imagine some regular and constant law by which species
might be made to disappear from the earth gradually and in succession.
The death, he suggested, of a species might depend, like that of
individuals, on certain peculiarities of constitution conferred upon
them at their birth; and as the longevity of the one depends on a
certain force of vitality, which, after a period, grows weaker and
weaker, so the duration of the other may be governed by the quantity of
prolific power bestowed upon the species which, after a season, may
decline in energy, so that the fecundity and multiplication of
individuals may be gradually lessened from century to century, "until
that fatal term arrives when the embryo, incapable of extending and
developing itself, abandons, almost at the instant of its formation, the
slender principle of life by which it was scarcely animated,--and so all
dies with it."

Now we may coincide in opinion with the Italian naturalist, as to the
gradual extinction of species one after another, by the operation of
regular and constant causes, without admitting an inherent principle of
deterioration in their physiological attributes. We might concede, "that
many species are on the decline, and that the day is not far distant
when they will cease to exist;" yet deem it consistent with what we know
of the nature of organic beings, to believe that the last individuals of
each species retain their prolific powers in their full intensity.

Brocchi has himself speculated on the share which a change of climate
may have had in rendering the Mediterranean unfit for the habitation of
certain Testacea, which still continued to thrive in the Indian Ocean,
and of others which were now only represented by analogous forms within
the tropics. He must also have been aware that other extrinsic causes,
such as the progress of human population, or the increase of some one of
the inferior animals, might gradually lead to the extirpation of a
particular species, although its fecundity might remain to the last
unimpaired. If, therefore, amid the vicissitudes of the animate and
inanimate world, there are known causes capable of bringing about the
decline and extirpation of species, it became him thoroughly to
investigate the full extent to which these might operate, before he
speculated on any cause of so purely hypothetical a kind as "the
diminution of the prolific virtue."

If it could have been shown that some wild plant had insensibly dwindled
away and died out, as sometimes happens to cultivated varieties
propagated by cuttings, even though climate, soil, and every other
circumstance, should continue identically the same--if any animal had
perished while the physical condition of the earth, and the number and
force of its foes, with every other extrinsic cause, remain unaltered,
then might we have some ground for suspecting that the infirmities of
age creep on as naturally on species as upon individuals. But, in the
absence of such observations, let us turn to another class of facts, and
examine attentively the circumstances which determine the _stations_ of
particular animals and plants, and perhaps we shall discover, in the
vicissitudes to which these stations are exposed, a cause fully adequate
to explain the phenomena under consideration.

_Stations of plants and animals._--Stations comprehend all the
circumstances, whether relating to the animate or inanimate world, which
determine whether a given plant or animal can exist in a given place; so
that if it be shown that stations can become essentially modified by the
influence of known causes, it will follow that species, as well as
individuals, are mortal.

Every naturalist is familiar with the fact, that although in a
particular country, such as Great Britain, there may be more than three
thousand species of plants, ten thousand insects, and a great variety in
each of the other classes; yet there will not be more than a hundred,
perhaps not half that number, inhabiting any given locality. There may
be no want of space in the supposed tract: it may be a large mountain,
or an extensive moor, or a great river plain, containing room enough for
individuals of every species in our island; yet the spot will be
occupied by a few to the exclusion of many, and these few are enabled,
throughout long periods, to maintain their ground successfully against
every intruder, notwithstanding the facilities which species enjoy, by
virtue of their power of diffusion, of invading adjacent territories.

The principal causes which enable a certain assemblage of plants thus to
maintain their ground against all others depend, as is well known, on
the relations between the physiological nature of each species, and the
climate, exposure, soil, and other physical conditions of the locality.
Some plants live only on rocks, others in meadows, a third class in
marshes. Of the latter, some delight in a fresh-water morass,--others in
salt marshes, where their roots may copiously absorb saline particles.
Some prefer an alpine region in a warm latitude, where, during the heat
of summer, they are constantly irrigated by the cool waters of melting
snows. To others loose sand, so fatal to the generality of species,
affords the most proper station. The _Carex arenaria_ and the _Elymus
arenarius_ acquire their full vigor on a sandy dune, obtaining an
ascendancy over the very plants which in a stiff clay would immediately
stifle them.

Where the soil of a district is of so peculiar a nature that it is
extremely favorable to certain species, and agrees ill with every other,
the former get exclusive possession of the ground, and, as in the case
of heaths, live in societies. In like manner the bog moss (_Sphagnum_)
is fully developed in peaty swamps, and becomes, like the heath, in the
language of botanists, a social plant. Such monopolies, however, are not
common, for they are checked by various causes. Not only are many
species endowed with equal powers to obtain and keep possession of
similar stations, but each plant, for reasons not fully explained by the
physiologist, has the property of rendering the soil where it has grown
less fitted for the support of other individuals of its own species, or
even other species of the same family. Yet the same spot, so far from
being impoverished, is improved, for plants of _another_ family. Oaks,
for example, render the soil more fertile for the fir tribe, and firs
prepare the soil for oaks. Every agriculturist feels the force of this
law of the organic world, and regulates accordingly the rotation of his
crops.

_Equilibrium in the number of species, how preserved._--"All the plants
of a given country," says De Candolle, in his usual spirited style, "are
at war one with another. The first which establish themselves by chance
in a particular spot tend, by the mere occupancy of space, to exclude
other species--the greater choke the smaller; the longest livers replace
those which last for a shorter period; the more prolific gradually make
themselves masters of the ground, which species multiplying more slowly
would otherwise fill."

In this continual strife it is not always the resources of the plant
itself which enable it to maintain or extend its ground. Its success
depends, in a great measure, on the number of its foes or allies among
the animals and plants inhabiting the same region. Thus, for example, a
herb which loves the shade may multiply, if some tree with spreading
boughs and dense foliage flourish in the neighborhood. Another, which,
if unassisted, would be overpowered by the rank growth of some hardy
competitor, is secure because its leaves are unpalatable to cattle;
which, on the other hand, annually crop down its antagonist, and rarely
suffer it to ripen its seed.

Oftentimes we see some herb which has flowered in the midst of a thorny
shrub, when all the other individuals of the same species, in the open
fields around, are eaten down, and cannot bring their seed to maturity.
In this case, the shrub has lent his armor of spines and prickles to
protect the defenceless herb against the mouths of the cattle, and thus
a few individuals which occupied, perhaps, the most unfavorable station
in regard to exposure, soil, and other circumstances, may, nevertheless,
by the aid of an ally, become the principal source whereby the winds are
supplied with seeds which perpetuate the species throughout the
surrounding tract. Thus, in the New Forest in Hampshire, the young oaks
which are not consumed by the deer, or uprooted by the swine, are
indebted to the holly for their escape.

In the above examples we see one plant shielding another from the
attacks of animals; but instances are, perhaps, still more numerous,
where some animal defends a plant against the enmity of some other
subject of the vegetable kingdom.

Scarcely any beast, observes a Swedish naturalist, will touch the
nettle, but fifty different kinds of insects are fed by it.[950] Some of
these seize upon the root, others upon the stem; some eat the leaves,
others devour the seeds and flowers; but for this multitude of enemies,
the nettle (_Urtica dioica_), which is now found in all the four
quarters of the globe, would annihilate a great number of plants.
Linnæus tells us, in his "Tour in Scania," that goats were turned into
an island which abounded with the _Agrostis arundinacea_, where they
perished by famine; but horses which followed them grew fat on the same
plant. The goat, also, he says, thrives on the meadow-sweet and
water-hemlock, plants which are injurious to cattle.[951]

_Agency of insects._--Every plant, observes Wilcke, has its proper
insect allotted to it to curb its luxuriancy, and to prevent it from
multiplying to the exclusion of others. "Thus grass in meadows sometimes
flourishes so as to exclude all other plants; here the Phalæna graminis
(_Bombyx gram._), with her numerous progeny, finds a well-spread table;
they multiply in immense numbers, and the farmer, for some years,
laments the failure of his crop; but the grass being consumed, the moths
die with hunger, or remove to another place. Now the quantity of grass
being greatly diminished, the other plants, which were before choked by
it, spring up, and the ground becomes variegated with a multitude of
different species of flowers. Had not nature given a commission to this
minister for that purpose, the grass would destroy a great number of
species of vegetables, of which the equilibrium is now kept up."[952]

In the above passage allusion is made to the ravages committed in 1740,
and the two following years, in many provinces of Sweden, by a most
destructive insect. The same moth is said never to touch the foxtail
grass, so that it may be classed as a most active ally and benefactor of
that species, and as peculiarly instrumental in preserving it in its
present abundance.[953] A discovery of Rolander, cited in the treatise
of Wilcke above mentioned, affords a good illustration of the checks and
counter-checks which nature has appointed to preserve the balance of
power among species. "The _Phalæna strobilella_ has the fir cone
assigned to it to deposit its eggs upon; the young caterpillars coming
out of the shell consume the cone and superfluous seed; but, lest the
destruction should be too general, the _Ichneumon strobilellæ_ lays its
eggs in the caterpillar, inserting its long tail in the openings of the
cone till it touches the included insect, for its body is too large to
enter. Thus it fixes its minute egg upon the caterpillar, which being
hatched, destroys it."[954]

Entomologists enumerate many parallel cases where insects, appropriated
to certain plants, are kept down by other insects, and these again by
parasites expressly appointed to prey on them.[955] Few perhaps are in
the habit of duly appreciating the extent to which insects are active in
preserving the balance of species among plants, and thus regulating
indirectly the relative numbers of many of the higher orders of
terrestrial animals.

The peculiarity of their agency consists in their power of suddenly
multiplying their numbers to a degree which could only be accomplished
in a considerable lapse of time in any of the larger animals, and then
as instantaneously relapsing, without the intervention of any violent
disturbing cause, into their former insignificance.

If, for the sake of employing, on different but rare occasions, a power
of many hundred horses, we were under the necessity of feeding all these
animals at great cost in the intervals when their services were not
required, we should greatly admire the invention of a machine, such as
the steam-engine, which was capable at any moment of exerting the same
degree of strength without any consumption of food during periods of
inaction. The same kind of admiration is strongly excited when we
contemplate the powers of insect life, in the creation of which the
Author of nature has been so prodigal. A scanty number of minute
individuals, to be detected only by careful research, are ready in a few
days, weeks, or months, to give birth to myriads, which may repress any
degree of monopoly in another species, or remove nuisances, such as dead
carcases, which might taint the air. But no sooner has the destroying
commission been executed than the gigantic power becomes dormant--each
of the mighty host soon reaches the term of its transient existence, and
the season arrives when the whole species passes naturally into the egg,
and thence into the larva and pupa state. In this defenceless condition
it may be destroyed either by the elements, or by the augmentation of
some of its numerous foes which may prey upon it in the early stages of
its transformation: or it often happens that in the following year the
season proves unfavorable to the hatching of the eggs or the development
of the pupæ.

Thus the swarming myriads depart which may have covered the vegetation
like the aphides, or darkened the air like locusts. In almost every
season there are some species which in this manner put forth their
strength, and then, like Milton's spirits, which thronged the spacious
hall, "reduce to smallest forms their shapes immense"--


    ----So thick the aëry crowd
  Swarm'd and were straiten'd; till the signal given,
  Behold a wonder! they but how who seem'd
  In bigness to surpass earth's giant sons,
  Now less than smallest dwarfs.


A few examples will illustrate the mode in which this force operates. It
is well known that, among the countless species of the insect creation,
some feed on animal, others on vegetable matter; and upon considering a
catalogue of eight thousand British Insects and Arachnidæ, Mr. Kirby
found that these two divisions were nearly a counterpoise to each other,
the carnivorous being somewhat preponderant. There are also distinct
species, some appointed to consume living, others dead or putrid animal
and vegetable substances. One female, of _Musca carnaria_, will give
birth to twenty thousand young; and the larvæ of many flesh-flies devour
so much food in twenty-four hours, and grow so quickly, as to increase
their weight two hundred-fold! In five days after being hatched they
arrive at their full growth and size, so that there was ground, says
Kirby, for the assertion of Linnæus, that three flies of _M. vomitoria_
could devour a dead horse as quickly as a lion[956]; and another Swedish
naturalist remarks, that so great are the powers of propagation of a
single species even of the smallest insects, that each can commit, when
required, more ravages than the elephant.[957]

Next to locusts, the aphides, perhaps, exert the greatest power over the
vegetable world, and, like them, are so sometimes so numerous as to
darken the air. The multiplication of these little creatures is without
parallel, and almost every plant has its peculiar species. Reaumur has
proved that in five generations one aphis may be the progenitor of
5,904,900,000 descendants; and it is supposed that in one year there may
be twenty generations.[958] Mr. Curtis observes that, as among
caterpillars we find some that are constantly and unalterably attached
to one or more particular species of plants, and others that feed
indiscriminately on most sorts of herbage, so it is precisely with the
aphides: some are particular, others more general feeders; and as they
resemble other insects in this respect, so they do also in being more
abundant in some years than in others.[959] In 1793 they were the chief,
and in 1798 the sole, cause of the failure of the hops. In 1794, a
season, almost unparalleled for drought, the hop was perfectly free from
them; while peas and beans, especially the former, suffered very much
from their depredations.

The ravages of the caterpillars of some of our smaller moths afford a
good illustration of the temporary increase of a species. The oak-trees
of a considerable wood have been stripped of their leaves as bare as in
winter by the caterpillars of a small green moth (_Tortrix viridana_),
which has been observed the year following not to abound.[960] The
silver Y moth (_Plusia gamma_), although one of our common species, is
not dreaded by us for its devastations; but legions of their
caterpillars have at times created alarm in France, as in 1735. Reaumur
observes that the female moth lays about four hundred eggs; so that if
twenty caterpillars were distributed in a garden, and all lived through
the winter and became moths in the succeeding May, the eggs laid by
these, if half of them were female and all fertile, would in the next
generation produce 800,000 caterpillars.[961] A modern writer,
therefore, justly observes that, did not Providence put causes in
operation to keep them in due bounds, the caterpillars of this moth
alone, leaving out of consideration the two thousand other British
species, might soon destroy more than half of our vegetation.[962]

In the latter part of the last century an ant most destructive to the
sugar-cane (_Formica saccharivora_), appeared in such infinite hosts in
the island of Granada, as to put a stop to the cultivation of that
vegetable. Their numbers were incredible. The plantations and roads were
filled with them; many domestic quadrupeds, together with rats, mice,
and reptiles, and even birds, perished in consequence of this plague. It
was not till 1780 that they were at length annihilated by torrents of
rain, which accompanied a dreadful hurricane.[963]

_Devastations caused by locusts._--We may conclude by mentioning some
instances of the devastations of locusts in various countries. Among
other parts of Africa, Cyrenaica has been at different periods infested
by myriads of these creatures, which have consumed nearly every green
thing. The effect of the havoc committed by them may be estimated
by the famine they occasioned. St. Augustin mentions a plague of this
kind in Africa, which destroyed no less than 800,000 men in the kingdom
of Massinissa alone, and many more upon the territories bordering upon
the sea. It is also related, that in the year 591 an infinite army of
locusts migrated from Africa into Italy; and, after grievously ravaging
the country, were cast into the sea, when there arose a pestilence from
their stench, which carried off nearly a million of men and beasts.

In the Venetian territory, also, in 1748, more than thirty thousand
persons are said to have perished in a famine occasioned by this
scourge; and other instances are recorded of their devastations in
France, Spain, Italy, Germany, &c. In different parts of Russia also,
Hungary, and Poland, in Arabia and India, and other countries, their
visitations have been periodically experienced. Although they have a
preference for certain plants, yet, when these are consumed, they will
attack almost all the remainder. In the accounts of the invasion of
locusts, the statements which appear most marvellous relate to the
prodigious mass of matter which encumbers the sea wherever they are
blown into it, and the pestilence arising from its putrefaction. Their
dead bodies are said to have been, in some places, heaped one upon
another, to the depth of four feet, in Russia, Poland and Lithuania; and
when, in Southern Africa, they were driven into the sea, by a north-west
wind, they formed, says Barrow, along the shore, for fifty miles, a bank
three or four feet high.[964] But when we consider that forests are
stripped of their foliage, and the earth of its green garment for
thousands of square miles, it may well be supposed that the volume of
animal matter produced may equal that of great herds of quadrupeds and
flights of large birds suddenly precipitated into the sea.

The occurrence of such events, at certain intervals, in hot countries,
like the severe winters and damp summers returning after a series of
years in the temperate zone, may affect the proportional numbers of
almost all classes of animals and plants, and probably prove fatal to
the existence of many which would otherwise thrive there; while, on the
contrary, the same occurrences can scarcely fail to be favorable to
certain species which, if deprived of such aid, might not maintain their
ground.

Although it may usually be remarked that the extraordinary increase of
some one species is immediately followed and checked by the
multiplication of another, yet this does not always happen; partly
because many species feed in common on the same kinds of food, and
partly because many kinds of food are often consumed indifferently by
one and the same species. In the former case, where a variety of
different animals have precisely the same taste, as, for example, when
many insectivorous birds and reptiles devour alike some particular fly
or beetle, the unusual numbers of these insects may cause only a slight
and almost imperceptible augmentation of each of these species of bird
and reptile. In the other instances, where one animal preys on others
of almost every class, as for example, where our English buzzards devour
not only small quadrupeds, as rabbits and field-mice, but also birds,
frogs, lizards, and insects, the profusion of any one of these last may
cause all such general feeders to subsist more exclusively upon the
species thus in excess, by which means the balance may be restored.

_Agency of omnivorous animals._--The number of species which are nearly
omnivorous is considerable; and although every animal has, perhaps, a
predilection for some one description of food rather than another, yet
some are not even confined to one of the great kingdoms of the organic
world. Thus, when the raccoon of the West Indies can procure neither
fowls, fish, snails, nor insects, it will attack the sugar-canes, and
devour various kinds of grain. The civets, when animal food is scarce,
maintain themselves on fruits and roots.

Numerous birds, which feed indiscriminately on insects and plants, are
perhaps more instrumental than any other of the terrestrial tribes in
preserving a constant equilibrium between the relative numbers of
different classes of animals and vegetables. If the insects become very
numerous and devour the plants, these birds will immediately derive a
larger portion of their subsistence from insects, just as the Arabians,
Syrians, and Hottentots feed on locusts, when the locusts devour their
crops.

_Reciprocal influence of aquatic and terrestrial species._--The intimate
relation of the inhabitants of the water to those of the land, and the
influence exerted by each on the relative number of species, must not be
overlooked amongst the complicated causes which determine the existence
of animals and plants in certain regions. A large portion of the
amphibious quadrupeds and reptiles prey partly on aquatic plants and
animals, and in part on terrestrial; and a deficiency of one kind of
prey causes them to have immediate recourse to the other. The voracity
of certain insects, as the dragon-fly, for example, is confined to the
water during one stage of their transformations, and in their perfect
state to the air. Innumerable water-birds, both of rivers and seas,
derive in like manner their food indifferently from either element; so
that the abundance or scarcity of prey in one induces them either to
forsake or more constantly to haunt the other. Thus an intimate
connection between the state of the animate creation in a lake or river,
and in the adjoining dry land, is maintained; or between a continent,
with its lakes and rivers, and the ocean. It is well known that many
birds migrate, during stormy seasons, from the sea-shore into the
interior, in search of food; while others, on the contrary, urged by
like wants, forsake their inland haunts, and live on substances rejected
by the tide.

The migration of fish into rivers during the spawning season supplies
another link of the same kind. Suppose the salmon to be reduced in
numbers by some marine foes, as by seals and grampuses, the consequence
must often be, that in the course of a few years the otters at the
distance of several hundred miles inland will be lessened in number from
the scarcity of fish. On the other hand, if there be a dearth of food
for the young fry of the salmon in rivers and estuaries, so that few
return to the sea, the sand eels and other marine species, which are
usually kept down by the salmon, will swarm in greater profusion.

It is unnecessary to accumulate a greater number of illustrations in
order to prove that the stations of different plants and animals depend
on a great complication of circumstances,--on an immense variety of
relations in the state of the inanimate worlds. Every plant requires a
certain climate, soil, and other conditions, and often the aid of many
animals, in order to maintain its ground. Many animals feed on certain
plants, being often restricted to a small number, and sometimes to one
only; other members of the animal kingdom feed on plant-eating species,
and thus become dependent on the conditions of the _stations_ not only
of their prey, but of the plants consumed by them.

Having duly reflected on the nature and extent of these mutual relations
in the different parts of the organic and inorganic worlds, we may next
proceed to examine the results which may be anticipated from the
fluctuations now continually in progress in the state of the earth's
surface, and in the geographical distribution of its living productions.




CHAPTER XLI.

EXTINCTION OF SPECIES.--CHANGES IN THE STATIONS OF ANIMALS.


  Extension of the range of one species alters the condition of many
    others--The first appearance of a new species causes the chief
    disturbance--Changes known to have resulted from the advance of
    human population--Whether man increases the productive powers of the
    earth--Indigenous quadrupeds and birds extirpated in Great
    Britain--Extinction of the dodo--Rapid propagation of domestic
    quadrupeds in America--Power of exterminating species no prerogative
    of man--Concluding remarks.


We have seen that the stations of animals and plants depend not merely
on the influence of external agents in the inanimate world, and the
relations of that influence to the structure and habits of each species,
but also on the state of the contemporary living beings which inhabit
the same part of the globe. In other words, the possibility of the
existence of a certain species in a given place, or of its thriving more
or less therein, is determined not merely by temperature, humidity,
soil, elevation, and other circumstances of the like kind; but also by
the existence or non-existence, the abundance or scarcity, of a
particular assemblage of other plants and animals in the same region.

If it be shown that both these classes of circumstances, whether
relating to the animate or inanimate creation, are perpetually changing,
it will follow that species are subject to incessant vicissitudes; and
if the result of these mutations, in the course of ages, be so great as
materially to affect the general condition of _stations_, it will follow
that the successive destruction of species must now be part of the
regular and constant order of nature.

_Extension of the range of one species alters the condition of the
others._--It will be desirable, first, to consider the effects which
every extension of the numbers or geographical range of one species must
produce on the condition of others inhabiting the same regions. When the
necessary consequences of such extensions have been fully explained, the
reader will be prepared to appreciate the important influence which
slight modifications in the physical geography of the globe may exert on
the condition of organic beings.

In the first place, it is clear that when any region is stocked with as
great a variety of animals and plants as the productive powers of that
region will enable it to support, the addition of any new species, or
the _permanent_ numerical increase of one previously established, must
always be attended either by the local extermination or the numerical
decrease of some other species.

There may undoubtedly be considerable fluctuations from year to year,
and the equilibrium may be again restored without any permanent
alteration; for, in particular seasons, a greater supply of heat,
humidity, or other causes, may augment the total quantity of vegetable
produce, in which case all the animals subsisting on vegetable food, and
others which prey on them, may multiply without any one species giving
way: but whilst the aggregate quantity of vegetable produce remains
unaltered, the progressive increase of one animal or plant implies the
decline of another.

All agriculturists and gardeners are familiar with the fact that when
weeds intrude themselves into the space appropriated to cultivated
species, the latter are starved in their growth, or stifled. If we
abandon for a short time a field or garden, a host of indigenous plants,


  The darnel, hemlock, and rank fumitory,


pour in and obtain the mastery, extirpating the exotics, or putting an
end to the monopoly of some native plants.

If we inclose a park, and stock it with as many deer as the herbage will
support, we cannot add sheep without lessening the number of the deer;
nor can other herbivorous species be subsequently introduced, unless the
individuals of each species in the park become fewer in proportion.

So, if there be an island where leopards are the only beasts of prey,
and the lion, tiger, and hyæna afterwards enter, the leopards, if they
stand their ground, will be reduced in number. If the locusts then
arrive and swarm greatly, they may deprive a large number of
plant-eating animals of their food, and thereby cause a famine, not only
among them, but among the beasts of prey: certain species perhaps, which
had the weakest footing in the island, may thus be annihilated.

We have seen how many distinct geographical provinces there are of
aquatic and terrestrial species, and how great are the powers of
migration conferred on different classes, whereby the inhabitants of one
region may be enabled from time to time to invade another, and do
actually so migrate and diffuse themselves over new countries. Now,
although our knowledge of the history of the animate creation dates from
so recent a period, that we can scarcely trace the advance or decline of
any animal or plant, except in those cases where the influence of man
has intervened; yet we can easily conceive what must happen when some
new colony of wild animals or plants enters a region for the first time,
and succeeds in establishing itself.

_Supposed effects of the first entrance of the polar bear into
Iceland._--Let us consider how great are the devastations committed at
certain periods by the Greenland bears, when they are drifted to the
shores of Iceland in considerable numbers on the ice. These periodical
invasions are formidable even to man; so that when the bears arrive, the
inhabitants collect together, and go in pursuit of them with
fire-arms--each native who slays one being rewarded by the King of
Denmark. The Danes of old, when they landed in their marauding
expeditions upon our coast, hardly excited more alarm, nor did our
islanders muster more promptly for the defence of their lives and
property against the common enemy, than the modern Icelanders against
these formidable brutes. It often happens, says Henderson, that the
natives are pursued by the bear when he has been long at sea, and when
his natural ferocity has been heightened by the keenness of hunger; if
unarmed, it is frequently by stratagem only that they make their
escape.[965]

Let us cast our thoughts back to the period when the first polar bears
reached Iceland, before it was colonized by the Norwegians in 874: we
may imagine the breaking up of an immense barrier of ice like that
which, in 1816 and the following year, disappeared from the east coast
of Greenland, which it had surrounded for four centuries. By the aid of
such means of transportation a great number of these quadrupeds might
effect a landing at the same time, and the havoc which they would make
among the species previously settled in the island would be terrific.
The deer, foxes, seals, and even birds, on which these animals sometimes
prey, would be soon thinned down.

But this would be a part only, and probably an insignificant portion, of
the aggregate amount of change brought about by the new invader. The
plants on which the deer fed, being less consumed in consequence of the
lessened numbers of that herbivorous species, would soon supply more
food to several insects, and probably to some terrestrial testacea, so
that the latter would gain ground. The increase of these would furnish
other insects and birds with food, so that the numbers of these last
would be augmented. The diminution of the seals would afford a respite
to some fish which they had persecuted; and these fish, in their turn,
would then multiply and press upon their peculiar prey. Many
water-fowls, the eggs and young of which are devoured by foxes, would
increase when the foxes were thinned down by the bears; and the fish on
which the water-fowls subsisted would then, in their turn, be less
numerous. Thus the numerical proportions of a great number of the
inhabitants, both of the land and sea, might be permanently altered by
the settling of one new species in the region; and the changes caused
indirectly would ramify through all classes of the living creation, and
be almost endless.

An actual illustration of what we have here only proposed
hypothetically, is in some degree afforded by the selection of small
islands by the eider duck for its residence during the season of
incubation, its nest being seldom if ever found on the shores of the
main land, or even of a large island. The Icelanders are so well aware
of this, that they have expended a great deal of labor in forming
artificial islands, by separating from the main land certain
promontories, joined to it by narrow isthmuses. This insular position is
necessary to guard against the destruction of the eggs and young birds,
by foxes, dogs, and other animals. One year, says Hooker, it happened
that, in the small island of Vidoe, adjoining the coast of Iceland, a
fox got over _upon the ice_, and caused great alarm, as an immense
number of ducks were then sitting on their eggs or young ones. It was
long before he was taken, which was at last, however, effected by
bringing another fox to the island, and fastening it by a string near
the haunt of the former, by which he was allured within shot of the
hunter.[966]

_The first appearance of a new species causes the chief
disturbance._--It is usually the first appearance of an animal or plant,
in a region to which it was previously a stranger, that gives rise to
the chief alteration; since, after a time, an equilibrium is again
established. But it must require ages before such a new adjustment of
the relative forces of so many conflicting agents can be definitely
settled. The causes in simultaneous action are so numerous, that they
admit of an almost infinite number of combinations; and it is necessary
that all these should have occurred once before the total amount of
change, capable of flowing from any new disturbing force, can be
estimated.

Thus, for example, suppose that once in two centuries a frost of unusual
intensity, or a volcanic eruption of great violence accompanied by
floods from the melting of glaciers, should occur in Iceland; or an
epidemic disease, fatal to the larger number of individuals of some one
species, and not affecting others,--these, and a variety of other
contingencies, all of which may occur at once, or at periods separated
by different intervals of time, ought to happen before it would be
possible for us to declare what ultimate alteration the presence of any
new comer, such as the bear before mentioned, might occasion in the
animal population of the isle.

Every new condition in the state of the organic or inorganic creation, a
new animal or plant, an additional snow-clad mountain, any permanent
change, however slight in comparison to the whole, gives rise to a new
order of things, and may make a material change in regard to some one or
more species. Yet a swarm of locusts, or a frost of extreme intensity,
or an epidemic disease, may pass away without any great apparent
derangement; no species may be lost, and all may soon recover their
former relative numbers, because the same scourges may have visited the
region again and again, at preceding periods. Every plant that was
incapable of resisting such a degree of cold, every animal which was
exposed to be entirely cut off by an epidemic or by famine caused by the
consumption of vegetation by the locusts, may have perished already, so
that the subsequent recurrence of similar catastrophes is attended only
by a temporary change.


_Changes caused by Man_

We are best acquainted with the mutations brought about by the progress
of human population, and the growth of plants and animals favored by
man. To these, therefore, we should in the first instance turn our
attention. If we conclude, from the concurrent testimony of history and
of the evidence yielded by geological data, that man is, comparatively
speaking, of very modern origin, we must at once perceive how great a
revolution in the state of the animate world the increase of the human
race, considered merely as consumers of a certain quantity of organic
matter, must necessarily cause.

_Whether man increases the productive powers of the earth._--It may
perhaps, be said, that man has, in some degree, compensated for the
appropriation to himself of so much food, by artificially improving the
natural productiveness of soils, by irrigation, manure, and a judicious
intermixture of mineral ingredients conveyed from different localities.
But it admits of reasonable doubt whether, upon the whole, we fertilize
or impoverish the lands which we occupy. This assertion may seem
startling to many; because they are so much in the habit of regarding
the sterility or productiveness of land in relation to the wants of man,
and not as regards the organic world generally. It is difficult, at
first, to conceive, if a morass is converted into arable land, and made
to yield a crop of grain, even of moderate abundance, that we have not
improved the capabilities of the habitable surface--that we have not
empowered it to support a larger quantity of organic life. In such
cases, however, a tract, before of no utility to man, may be reclaimed,
and become of high agricultural importance, though it may, nevertheless,
yield a scantier vegetation. If a lake be drained, and turned into a
meadow, the space will provide sustenance to man, and many terrestrial
animals serviceable to him, but not, perhaps, so much food as it
previously yielded to the aquatic races.

If the pestiferous Pontine marshes were drained, and covered with corn,
like the plains of the Po, they might, perhaps, feed a smaller number of
animals than they do now; for these morasses are filled with herds of
buffaloes and swine, and they swarm with birds, reptiles, and insects.

The felling of dense and lofty forests, which covered, even within the
records of history, a considerable space on the globe, now tenanted by
civilized man, must generally have lessened the amount of vegetable food
throughout the space where these woods grew. We must also take into our
account the area covered by towns, and a still larger surface occupied
by roads.

If we force the soil to bear extraordinary crops one year, we are,
perhaps, compelled to let it lie fallow the next. But nothing so much
counterbalances the fertilizing effects of human art as the extensive
cultivation of foreign herbs and shrubs, which, although they are often
more nutritious to man, seldom thrive with the same rank luxuriance as
the native plants of a district. Man is, in truth, continually striving
to diminish the natural diversity of the _stations_ of animals and
plants in every country, and to reduce them all to a small number fitted
for species of economical use. He may succeed perfectly in attaining his
object, even though the vegetation be comparatively meagre, and the
total amount of animal life be greatly lessened.

Spix and Martius have given a lively description of the incredible
number of insects which lay waste the crops in Brazil, besides swarms of
monkeys, flocks of parrots, and other birds, as well as the paca,
agouti, and wild swine. They describe the torment which the planter and
the naturalist suffer from the musquitoes, and the devastation of the
ants and blattæ; they speak of the dangers to which they were exposed
from the jaguar, the poisonous serpents, crocodiles, scorpions,
centipedes, and spiders. But with the increasing population and
cultivation of the country, say these naturalists, these evils will
gradually diminish; when the inhabitants have cut down the woods,
drained the marshes, made roads in all directions, and founded villages
and towns, man will, by degrees, triumph over the rank vegetation and
the noxious animals, and all the elements will second and amply
recompense his activity.[967]

The number of human beings now peopling the earth is supposed to amount
to eight hundred millions, so that we may easily understand how great a
number of beasts of prey, birds, and animals of every class, this
prodigious population must have displaced, independently of the still
more important consequences which have followed from the derangement
brought about by man in the relative numerical strength of particular
species.

_Indigenous quadrupeds and birds extirpated in Great Britain._--Let us
make some inquiries into the extent of the influence which the progress
of society has exerted during the last seven or eight centuries, in
altering the distribution of indigenous British animals. Dr. Fleming has
prosecuted this inquiry with his usual zeal and ability; and in a memoir
on the subject has enumerated the best-authenticated examples of the
decrease or extirpation of certain species during a period when our
population has made the most rapid advances. I shall offer a brief
outline of his results.[968]

The stag, as well as the fallow deer and the roe, were formerly so
abundant in our island, that, according to Lesley, from five hundred to
a thousand were sometimes slain at a hunting match; but the native races
would already have been extinguished, had they not been carefully
preserved in certain forests. The otter, the marten, and the polecat,
were also in sufficient numbers to be pursued for the sake of their fur;
but they have now been reduced within very narrow bounds. The wild cat
and fox have also been sacrificed throughout the greater part of the
country, for the security of the poultry-yard or the fold. Badgers have
been expelled from nearly every district, which at former periods they
inhabited.

Besides these, which have been driven out from their favorite haunts,
and everywhere reduced in number, there are some which have been wholly
extirpated; such as the ancient breed of indigenous horses, and the wild
boar; of the wild oxen a few remains are still preserved in some of the
old English parks. The beaver, which is eagerly sought after for its
fur, had become scarce at the close of the ninth century; and, by the
twelfth century, was only to be met with, according to Giraldus de
Barri, in one river in Wales, and another in Scotland. The wolf, once so
much dreaded by our ancestors, is said to have maintained its ground in
Ireland so late as the beginning of the eighteenth century (1710),
though it had been extirpated in Scotland thirty years before, and in
England at a much earlier period. The bear, which, in Wales, was
regarded as a beast of the chase equal to the hare or the boar[969],
only perished, as a native of Scotland, in the year 1057.[970]

Many native birds of prey have also been the subjects of unremitting
persecution. The eagles, larger hawks, and ravens, have disappeared from
the more cultivated districts. The haunts of the mallard, the snipe, the
redshank, and the bittern, have been drained equally with the summer
dwellings of the lapwing and the curlew. But these species still linger
in some portion of the British isles; whereas the larger capercailzies
or wood grouse, formerly natives of the pine-forests of Ireland and
Scotland, have been destroyed within the last sixty years. The egret and
the crane, which appear to have been formerly very common in Scotland,
are now only occasional visitants.[971]

The bustard (_Otis tarda_), observes Graves, in his British
Ornithology[972], "was formerly seen in the downs and heaths of various
parts of our island, in flocks of forty or fifty birds; whereas it is
now a circumstance of rare occurrence to meet with a single individual."
Bewick also remarks, "that they were formerly more common in this island
than at present; they are now found only in the open counties of the
south and east--in the plains of Wiltshire, Dorsetshire, and some parts
of Yorkshire."[973] In the few years that have elapsed since Bewick
wrote, this bird has entirely disappeared from Wiltshire and
Dorsetshire.

These changes, it may be observed, are derived from very imperfect
memorials, and relate only to the larger and more conspicuous animals
inhabiting a small spot on the globe; but they cannot fail to exalt our
conception of the enormous revolutions which, in the course of several
thousand years, the whole human species must have effected.

_Extinction of the dodo._--The kangaroo and the emu are retreating
rapidly before the progress of colonization in Australia; and it
scarcely admits of doubt, that the general cultivation of that country
must lead to the extirpation of both. The most striking example of the
loss, even within the last two centuries, of a remarkable species, is
that of the dodo--a bird first seen by the Dutch, when they landed on
the Isle of France, at that time uninhabited, immediately after the
discovery of the passage to the East Indies by the Cape of Good Hope. It
was of a large size, and singular form; its wings short, like those of
an ostrich, and wholly incapable of sustaining its heavy body, even for
a short flight. In its general appearance it differed from the ostrich,
cassowary, or any known bird.[974]

Many naturalists gave figures of the dodo after the commencement of the
seventeenth century; and there is a painting of it in the British
Museum, which is said to have been taken from a living individual.
Beneath the painting is a leg, in a fine state of preservation, which
ornithologists are agreed cannot belong to any other known bird. In the
museum at Oxford, also, there is a foot and a head in an imperfect
state.

In spite of the most active search, during the last century, no
information respecting the dodo was obtained, and some authors have gone
so far as to pretend that it never existed; but a great mass of
satisfactory evidence in favor of its recent existence has now been
collected by Mr. Broderip,[975] and by Mr. Strickland and Dr. Melville.
Mr. Strickland, agreeing with Professor Reinhardt, of Copenhagen, in
referring the dodo to the Columbidæ, calls it a "vulture-like
frugivorous pigeon." It appears, also, that another short-winged bird of
the same order, called "The Solitaire," inhabited the small island of
Rodrigues, 300 miles east of the Mauritius, and has been exterminated by
man, as have one or two different but allied birds of the Isle of
Bourbon.[976]

_Rapid propagation of domestic quadrupeds over the American
continent._--Next to the direct agency of man, his indirect influence in
multiplying the numbers of large herbivorous quadrupeds of domesticated
races may be regarded as one of the most obvious causes of the
extermination of species. On this, and on several other grounds, the
introduction of the horse, ox, and other mammalia, into America, and
their rapid propagation over that continent within the last three
centuries, is a fact of great importance in natural history. The
extraordinary herds of wild cattle and horses which overran the plains
of South America sprung from a very few pairs first carried over by the
Spaniards; and they prove that the wide geographical range of large
species in great continents does not necessarily imply that they have
existed there from remote periods.

Humboldt observes, in his Travels, on the authority of Azzara, that it
is believed there exist, in the Pampas of Buenos Ayres, twelve million
cows and three million horses, without comprising, in this enumeration,
the cattle that have no acknowledged proprietor. In the Llanos of
Caraccas, the rich hateros, or proprietors of pastoral farms, are
entirely ignorant of the number of cattle they possess. The young are
branded with a mark peculiar to each herd, and some of the most wealthy
owners mark as many as fourteen thousand a year.[977] In the northern
plains, from the Orinoco to the lake of Maraycabo, M. Depons reckoned
that 1,200,000 oxen, 180,000 horses, and 90,000 mules, wandered at
large.[978] In some parts of the valley of the Mississippi, especially
in the country of the Osage Indians, wild horses are immensely numerous.

The establishment of black cattle in America dates from Columbus's
second voyage to St. Domingo. They there multiplied rapidly; and that
island presently became a kind of nursery from which these animals were
successively transported to various parts of the continental coast, and
from thence into the interior. Notwithstanding these numerous
exportations, in twenty-seven years after the discovery of the island,
herds of four thousand head, as we learn from Oviedo, were not uncommon,
and there were even some that amounted to eight thousand. In 1587, the
number of hides exported from St. Domingo alone, according to Acosta's
report, was 35,444; and in the same year there were exported 64,350 from
the ports of New Spain. This was in the sixty-fifth year after the
taking of Mexico, previous to which event the Spaniards, who came into
that country, had not been able to engage in anything else than
war.[979] Every one is aware that these animals are now established
throughout the American continent from Canada to the Straits of
Magellan.

The ass has thriven very generally in the New World; and we learn from
Ulloa, that in Quito they ran wild, and multiplied in amazing numbers,
so as to become a nuisance. They grazed together in herds, and when
attacked defended themselves with their mouths. If a horse happened to
stray into the places where they fed, they all fell upon him, and did
not cease biting and kicking till they left him dead.[980]

The first hogs were carried to America by Columbus, and established in
the Island of St. Domingo the year following its discovery, in November,
1493. In succeeding years they were introduced into other places where
the Spaniards settled; and, in the space of half a century, they were
found established in the New World, from the latitude of 25° north, to
the 40th degree of south latitude. Sheep, also, and goats have
multiplied enormously in the New World, as have also the cat and the
rat; which last, as before stated, has been imported unintentionally in
ships. The dogs introduced by man which have at different periods become
wild in America, hunted in packs, like the wolf and the jackall,
destroying not only hogs, but the calves and foals of the wild cattle
and horses.

Ulloa in his voyage, and Buffon on the authority of old writers, relate
a fact which illustrates very clearly the principle before explained, of
the check which the increase of one animal necessarily offers to that of
another. The Spaniards had introduced goats into the Island of Juan
Fernandez, where they became so prolific as to furnish the pirates who
infested those seas with provisions. In order to cut off this resource
from the buccaneers, a number of dogs were turned loose into the island;
and so numerous did they become in their turn, that they destroyed the
goats in every accessible part, after which the number of the wild dogs
again decreased.[981]

_Increase of rein-deer imported into Iceland._--As an example of the
rapidity with which a large tract may become peopled by the offspring of
a single pair of quadrupeds, it may be mentioned that in the year 1773
thirteen rein-deer were exported from Norway, only three of which
reached Iceland. These were turned loose into the mountains of
Guldbringè Syssel, where they multiplied so greatly, in the course of
forty years, that it was not uncommon to meet with herds, consisting of
from forty to one hundred, in various districts.

The rein-deer, observes a modern writer, is in Lapland a loser by his
connexion with man, but Iceland will be this creature's paradise. There
is, in the interior, a tract which Sir. G. Mackenzie computes at not
less than forty thousand square miles, without a single human
habitation, and almost entirely unknown to the natives themselves. There
are no wolves: the Icelanders will keep out the bears; and the
reindeer, being almost unmolested by man, will have no enemy whatever,
unless it has brought with it its own tormenting gad-fly.[982]

Besides the quadrupeds before enumerated, our domestic fowls have also
succeeded in the West Indies and America, where they have the common
fowl, the goose, the duck, the peacock, the pigeon, and the guinea-fowl.
As these were often taken suddenly from the temperate to very hot
regions, they were not reared at first without much difficulty: but
after a few generations, they became familiarized to the climate, which,
in many cases, approached much nearer than that of Europe to the
temperature of their original native countries.

The fact of so many millions of wild and tame individuals of our
domestic species, almost all of them the largest quadrupeds and birds,
having been propagated throughout the new continent within the short
period that has elapsed since the discovery of America, while no
appreciable improvement can have been made in the productive powers of
that vast continent, affords abundant evidence of the extraordinary
changes which accompany the diffusion and progressive advancement of the
human race over the globe. That it should have remained for us to
witness such mighty revolutions is a proof, even if there was no other
evidence, that the entrance of man into the planet is, comparatively
speaking, of extremely modern date, and that the effects of his agency
are only beginning to be felt.

_Population which the globe is capable of supporting._--A modern writer
has estimated, that there are in America upwards of four million square
miles of useful soil, each capable of supporting 200 persons; and nearly
six million, each mile capable of supporting 490 persons.[983] If this
conjecture be true, it will follow, as that author observes, that if the
natural resources of America were fully developed, it would afford
sustenance to five times as great a number of inhabitants as the entire
mass of human beings existing at present upon the globe. The new
continent, he thinks, though less than half the size of the old,
contains an equal quantity of useful soil, and much more than an equal
amount of productive power. Be this as it may, we may safely conclude
that the amount of human population now existing constitutes but a small
proportion of that which the globe is capable of supporting, or which it
is destined to sustain at no distant period, by the rapid progress of
society, especially in America, Australia, and certain parts of the old
continent.

_Power of exterminating species no prerogative of man._--But if we
reflect that many millions of square miles of the most fertile land,
occupied originally by a boundless variety of animal and vegetable
forms, have been already brought under the dominion of man, and
compelled, in a great measure, to yield nourishment to him, and to a
limited number of plants and animals which he has caused to increase, we
must at once be convinced, that the annihilation of a multitude of
species has already been effected, and will continue to go on hereafter,
in certain regions, in a still more rapid ratio, as the colonies of
highly civilized nations spread themselves over unoccupied lands.

Yet, if we wield the sword of extermination as we advance, we have no
reason to repine at the havoc committed, nor to fancy, with the Scottish
poet, that "we violate the social union of nature;" or complain, with
the melancholy Jacques, that we


  Are mere usurpers, tyrants, and what's worse,
  To fright the animals and to kill them up
  In their assign'd and native dwelling-place.


We have only to reflect, that in thus obtaining possession of the earth
by conquest, and defending our acquisitions by force, we exercise no
exclusive prerogative. Every species which has spread itself from a
small point over a wide area must, in like manner, have marked its
progress by the diminution or the entire extirpation of some other, and
must maintain its ground by a successful struggle against the
encroachments of other plants and animals. That minute parasitic plant,
called "the rust" in wheat, has, like the Hessian fly, the locust, and
the aphis, caused famines ere now amongst the "lords of the creation."
The most insignificant and diminutive species, whether in the animal or
vegetable kingdom, have each slaughtered their thousands, as they
disseminated themselves over the globe, as well as the lion, when first
it spread itself over the tropical regions of Africa.

_Concluding remarks._--Although we have as yet considered one class only
of the causes (the organic) by which species may become exterminated,
yet it cannot but appear evident that the continued action of these
alone, throughout myriads of future ages, must work an entire change in
the state of the organic creation, not merely on the continents and
islands, where the power of man is chiefly exerted, but in the great
ocean, where his control is almost unknown. The mind is prepared by the
contemplation of such future revolutions to look for the signs of
others, of an analogous nature, in the monuments of the past. Instead of
being astonished at the proofs there manifested of endless mutations in
the animate world, they will appear to one who has thought profoundly on
the fluctuations now in progress, to afford evidence in favor of the
uniformity of the system, unless, indeed, we are precluded from speaking
of _uniformity_ when we characterize a principle of endless variation.




CHAPTER XLII.

EXTINCTION OF SPECIES.--INFLUENCE OF INORGANIC CAUSES.


  Powers of diffusion indispensable, that each species may maintain
    its ground--How changes in physical geography affect the
    distribution of species--Rate of the change of species due to this
    cause cannot be uniform--Every change in the physical geography of
    large regions tends to the extinction of species--Effects of a
    general alteration of climate on the migration of species--Gradual
    refrigeration would cause species in the northern and southern
    hemispheres to become distinct--Elevation of temperature the
    reverse--Effects on the condition of species which must result from
    inorganic changes inconsistent with the theory of transmutation.


_Powers of diffusion indispensable, that each species may maintain its
ground._--Having shown in the last chapter, how considerably the
numerical increase or the extension of the geographical range of any one
species must derange the numbers and distribution of others, let us now
direct our attention to the influence which the inorganic causes
described in the second book are continually exerting on the habitations
of species.

So great is the instability of the earth's surface, that if nature were
not continually engaged in the task of sowing seeds and colonizing
animals, the depopulation of a certain portion of the habitable sea and
land would in a few years be considerable. Whenever a river transports
sediment into a lake or sea, so as materially to diminish its depth, the
aquatic animals and plants which delight in deep water are expelled: the
tract, however, is not allowed to remain useless; but is soon peopled by
species which require more light and heat, and thrive where the water is
shallow. Every addition made to the land by the encroachment of the
delta of a river banishes many subaqueous species from their native
abodes; but the new-formed plain is not permitted to lie unoccupied,
being instantly covered with terrestrial vegetation. The ocean devours
continuous lines of sea-coasts, and precipitates forests or rich pasture
land into the waves: but this space is not lost to the animate creation;
for shells and sea-weeds soon adhere to the new-made cliffs, and
numerous fish people the channel which the current has scooped out for
itself. No sooner has a volcanic island been thrown up than some lichens
begin to grow upon it, and it is sometimes clothed with verdure while
smoke and ashes are still occasionally thrown from the crater. The
cocoa, pandanus, and mangrove take root upon the coral reef before it
has fairly risen above the waves. The burning stream of lava that
descends from Etna rolls through the stately forest, and converts to
ashes every tree and herb which stands in its way; but the black strip
of land thus desolated is covered again in the course of time, with
oaks, pines, and chestnuts, as luxuriant as those which the fiery
torrent swept away.

Every flood and landslip, every wave which a hurricane or earthquake
throws upon the shore, every shower of volcanic dust and ashes which
buries a country far and wide to the depth of many feet, every advance
of the sand-flood, every conversion of salt water into fresh when rivers
alter their main channel of discharge, every permanent variation in the
rise or fall of tides in an estuary--these and countless other causes
displace, in the course of a few centuries, certain plants and animals
from stations which they previously occupied. If, therefore, the Author
of nature had not been prodigal of those numerous contrivances, before
alluded to, for spreading all classes of organic beings over the
earth--if he had not ordained that the fluctuations of the animate and
inanimate creation should be in perfect harmony with each other, it is
evident that considerable spaces, now the most habitable on the globe,
would soon be as devoid of life as are the Alpine snows, or the dark
abysses of the ocean, or the moving sands of the Sahara.

The powers, then, of migration and diffusion conferred on animals and
plants are indispensable to enable them to maintain their ground, and
would be necessary, even though it were never intended that a species
should gradually extend its geographical range. But a facility of
shifting their quarters being once given, it cannot fail to happen that
the inhabitants of one province should occasionally penetrate into some
other; since the strongest of those barriers which I before described as
separating distinct regions are all liable to be thrown down, one after
the other, during the vicissitudes of the earth's surface.

_How changes in physical Geography affect the distribution of
species._--The numbers and distribution of particular species are
affected in two ways, by changes in the physical geography of the
earth:--First, these changes promote or retard the migrations of
species; secondly, they alter the physical conditions of the localities
which species inhabit. If the ocean should gradually wear its way
through an isthmus, like that of Suez, it would open a passage for the
intermixture of the aquatic tribes of two seas previously disjoined, and
would, at the same time, close a free communication which the
terrestrial plants and animals of two continents had before enjoyed.
These would be, perhaps, the most important consequences, in regard to
the distribution of species, which would result from the breach made by
the sea in such a spot; but there would be others of a distinct nature,
such as the conversion of a certain tract of land, which formed the
isthmus, into sea. This space, previously occupied by terrestrial plants
and animals, would be immediately delivered over to the aquatic; a local
revolution which might have happened in innumerable other parts of the
globe, without being attended by any alteration in the blending together
of species of two distinct provinces.

_Rate of change of species cannot be uniform._--This observation leads
me to point out one of the most interesting conclusions to which we are
led by the contemplation of the vicissitudes of the inanimate world in
relation to those of the animate. It is clear that, if the agency of
inorganic causes be uniform, as I have supposed, they must operate very
irregularly on the state of organic beings, so that the rate according
to which these will change in particular regions will not be equal in
equal periods of time.

I am not about to advocate the doctrine of general catastrophes
recurring at certain intervals, as in the ancient Oriental cosmogonies,
nor do I doubt that, if very considerable periods of equal duration
could be compared one with another, the rate of change in the living, as
well as in the inorganic world, might be nearly uniform; but if we
regard each of the causes separately, which we know to be at present the
most instrumental in remodelling the state of the surface, we shall find
that we must expect each to be in action for thousands of years, without
producing any extensive alterations in the habitable surface, and then
to give rise, during a very brief period, to important revolutions.

_Illustration derived from subsidences._--I shall illustrate this
principle by a few of the most remarkable examples which present
themselves. In the course of the last century, as we have seen, a
considerable number of instances are recorded of the solid surface,
whether covered by water or not, having been permanently sunk or
upraised by subterranean movements. Most of these convulsions are only
accompanied by temporary fluctuations in the state of limited districts,
and a continued repetition of these events for thousands of years might
not produce any decided change in the state of many of those great
zoological or botanical provinces of which I have sketched the
boundaries.

When, for example, large parts of the ocean and even of inland seas are
a thousand fathoms or upwards in depth, it is a matter of no moment to
the animate creation that vast tracts should be heaved up many fathoms
at certain intervals, or should subside to the same amount. Neither can
any material revolution be produced in South America either in the
terrestrial or the marine plants or animals by a series of shocks on the
coast of Chili, each of which, like that of Penco, in 1751, should
uplift the coast about twenty-five feet. Nor if the ground sinks fifty
feet at a time, as in the harbor of Port Royal, in Jamaica, in 1692,
will such alterations of level work any general fluctuations in the
state of organic beings inhabiting the West Indian Islands, or the
Caribbean Sea.

It is only when the subterranean powers, by shifting gradually the
points where their principal force is developed, happen to strike upon
some particular region where a slight change of level immediately
affects the distribution of land and water, or the state of the climate,
or the barriers between distinct groups of species over extensive areas,
that the rate of fluctuation becomes accelerated, and may, in the course
of a few years or centuries, work mightier changes than had been
experienced in myriads of antecedent years.

Thus, for example, a repetition of subsidences causing the narrow
isthmus of Panama to sink down a few hundred feet, would, in a few
centuries, bring about a great revolution in the state of the animate
creation in the western hemisphere. Thousands of aquatic species would
pass, for the first time, from the Caribbean Sea into the Pacific; and
thousands of others, before peculiar to the Pacific Ocean, would make
their way into the Caribbean Sea, the Gulf of Mexico, and the Atlantic.
A considerable modification would probably be occasioned by the same
event in the direction or volume of the Gulf stream, and thereby the
temperature of the sea and the contiguous lands might be altered as far
as the influence of that current extends. A change of climate might thus
be produced in the ocean from Florida to Spitzbergen, and in many
countries of North America, Europe, and Greenland. Not merely the heat,
but the quantity of rain which falls, would be altered in certain
districts, so that many species would be excluded from tracts where they
before flourished: others would be reduced in number; and some would
thrive more and multiply. The seeds also and the fruits of plants would
no longer be drifted in precisely the same directions, nor the eggs of
aquatic animals; neither would species be any longer impeded in their
migrations towards particular stations before shut out from them by
their inability to cross the mighty current.

Let us take another example from a part of the globe which is at present
liable to suffer by earthquakes, namely, the low sandy tract which
intervenes between the sea of Azof and the Caspian. If there should
occur a sinking down to a trifling amount, and such ravines should be
formed as might be produced by a few earthquakes, not more considerable
than have fallen within our limited observation during the last 150
years, the waters of the Sea of Azof would pour rapidly into the
Caspian, which, according to the measurements lately made by the Academy
of St. Petersburg, is 84 feet below the level of the Black Sea.[984] The
Sea of Azof would immediately borrow from the Black Sea, that sea again
from the Mediterranean, and the Mediterranean from the Atlantic, so that
an inexhaustible current would pour down into the low tracts of Asia
bordering the Caspian, by which all the sandy salt steppes adjacent to
that sea would be inundated. An area of several thousand square leagues,
now below the level of the Mediterranean, would be converted from land
into sea.

_Illustration derived from the elevation of land._--Let us next imagine
a few cases of the elevation of land of small extent at certain critical
points, as, for example, in the shallowest part of the Straits of
Gibraltar, where the deepest soundings from the African to the European
side give only 220 fathoms. In proportion as this submarine barrier of
rock was upheaved, the whole channel would be contracted in width and
depth, and the volume of water which the current constantly flowing from
the Atlantic pours into the Mediterranean would be lessened. But the
loss of the inland sea by evaporation would remain the same; so that
being no longer able to draw on the ocean for a supply sufficient to
restore its equilibrium, it must sink, and leave dry a certain portion
of land around its borders. The current which now flows constantly out
of the Black Sea into the Mediterranean would then rush in more rapidly,
and the level of the Mediterranean would be thereby prevented from
falling so low; but the level of the Black Sea would, for the same
reason, sink; so that when, by a continued series of elevatory
movements, the Straits of Gibraltar had become completely closed up, we
might expect large and level sandy steppes to surround both the Black
Sea and Mediterranean, like those occurring at present on the skirts of
the Caspian and the Lake of Aral. The geographical range of hundreds of
aquatic species would be thereby circumscribed, and that of hundreds of
terrestrial plants and animals extended.

A line of submarine volcanos crossing the channel of some strait, and
gradually choking it up with ashes and lava, might produce a new barrier
as effectually as a series of earthquakes; especially if thermal
springs, charged with carbonate of lime, silica, and other mineral
ingredients, should promote the rapid multiplication of corals and
shells, and cement them together with solid matter precipitated during
the intervals between eruptions. Suppose in this manner a stoppage to be
caused of the Bahama channel between the bank of that name and the coast
of Florida. This insignificant revolution, confined to a mere spot in
the bottom of the ocean, would, by diverting the main current of the
Gulf stream, give rise to extensive changes in the climate and
distribution of animals and plants inhabiting the northern hemisphere.

_Illustration from the formation of new islands._--A repetition of
elevatory movements of earthquakes might continue over an area as
extensive as Europe, for thousands of ages, at the bottom of the ocean,
in certain regions, and produce no visible effects; whereas, if they
should operate in some shallow parts of the Pacific, amid the coral
archipelagos, they would soon give birth to a new continent. Hundreds of
volcanic islands may be thrown up, and become covered with vegetation,
without causing more than local fluctuations in the animate world; but
if a chain like the Aleutian archipelago, or the Kurile Isles, run for a
distance of many hundred miles, so as to form an almost uninterrupted
communication between two continents, or two distant islands, the
migrations of plants, birds, insects, and even of some quadrupeds, may
cause, in a short time, an extraordinary series of revolutions tending
to augment the range of some animals and plants, and to limit that of
others. A new archipelago might be formed in the Mediterranean, the Bay
of Biscay, and a thousand other places, and might produce less important
events than one rock which should rise up between Australia and Java, so
placed that winds and currents might cause an interchange of the plants,
insects, and birds.

_From the wearing through of an isthmus._--If we turn from the igneous
to the aqueous agents, we find the same tendency to an irregular rate of
change, naturally connected with the strictest uniformity in the energy
of those causes. When the sea, for example, gradually encroaches upon
both sides of a narrow isthmus, as that of Sleswick, separating the
North Sea from the Baltic, where, as before stated, the cliffs on both
the opposite coasts are wasting away[985], no material alteration
results for thousands of years, save only that there is a progressive
conversion of a small strip of land into water. A few feet only, or a
few yards, are annually removed; but if, at last, the partition should
be broken down, and the tides of the ocean should enter by a direct
passage into the inland sea, instead of going by a circuitous route
through the Cattegat, a body of salt water would sweep up as far as the
Gulfs of Bothnia and Finland, the waters of which are now brackish, or
almost fresh; and this revolution would be attended by the local
annihilation of many species.

Similar consequences must have resulted on a small scale, when the sea
opened its way through the Isthmus of Staveren in the thirteenth
century, forming a union between an inland lake and the ocean, and
opening, in the course of one century, a shallow strait, more than half
as wide as the narrowest part of that which divides England from France.

_Changes in physical geography which must occasion extinction of
species._--It will almost seem superfluous, after I have thus traced the
important modifications in the condition of living beings which flow
from changes of trifling extent, to argue that entire revolutions might
be brought about, if the climate and physical geography of the whole
globe were greatly altered. It has been stated, that species are in
general local, some being confined to extremely small spots, and
depending for their existence on a combination of causes, which, if they
are to be met with elsewhere, occur only in some very remote region.
Hence it must happen that, when the nature of these localities is
changed, the species will perish; for it will rarely happen that the
cause which alters the character of the district will afford new
facilities to the species to establish itself elsewhere.

_African deserts._--If we attribute the origin of a great part of the
desert of Africa to the gradual progress of moving sands driven eastward
by the westerly winds, we may safely infer that a variety of species
must have been annihilated by this cause alone. The sand-flood has been
inundating, from time immemorial, some of the rich lands on the west of
the Nile; and we have only to multiply this effect a sufficient number
of times in order to understand how, in the lapse of ages, a whole group
of terrestrial animals and plants may become extinct.

The African desert, without including Bornou and Darfour, extends,
according to the calculation of Humboldt, over 194,000 square leagues;
an area nearly three times as great as that of France. In a small
portion of so vast a space, we may infer from analogy that there were
many peculiar species of plants and animals which must have been
banished by the sand, and their habitations invaded by the camel, and by
birds and insects formed for the arid sands.

There is evidently nothing in the nature of the catastrophe to favor the
escape of the former inhabitants to some adjoining province; nothing to
weaken, in the bordering lands, that powerful barrier against
emigration--pre-occupancy. Nor, even if the exclusion of a certain group
of species from a given tract were compensated by an extension of their
range over a new country, would that circumstance tend to the
conservation of species in general; for the extirpation would merely
then be transferred to the region so invaded. If it be imagined, for
example, that the aboriginal quadrupeds, birds, and other animals of
Africa, emigrated in consequence of the advance of drift-sand, and
colonized Arabia, the indigenous Arabian species must have given way
before them, and have been reduced in number or destroyed.

Let us next suppose that, in some central or more elevated parts of the
great African desert, the upheaving power of subterranean movements
should be exerted throughout an immense series of ages, accompanied, at
certain intervals, by volcanic eruptions, such as gave rise at once, in
1755, to a mountain 1600 feet high, on the Mexican plateau. When the
continued repetition of these events had caused a mountain-chain, it is
obvious that a complete transformation in the state of the climate would
be brought about throughout a vast area.

We may imagine the summits of the new chain to rise so high as to be
covered, like Mount Atlas, for several thousand feet, with snow, during
a great part of the year. The melting of these snows, during the
greatest heat, would cause the rivers to swell in the season when the
greatest drought now prevails; the waters, moreover, derived from this
source, would always be of lower temperature than the surrounding
atmosphere, and would thus contribute to cool the climate. During the
numerous earthquakes and volcanic eruptions supposed to accompany the
gradual formation of the chain, there would be many floods caused by the
bursting of temporary lakes, and by the melting of snows by lava. These
inundations might deposit alluvial matter far and wide over the original
sands, as the country assumed varied shapes, and was modified again and
again by the moving power from below, and the aqueous erosion of the
surface above. At length the Sahara might be fertilized, irrigated by
rivers and streamlets intersecting it in every direction, and covered by
jungle and morasses; so that the animals and plants which now people
Northern Africa would disappear, and the region would gradually become
fitted for the reception of a population of species perfectly dissimilar
in their forms, habits, and organization.

There are always some peculiar and characteristic features in the
physical geography of each large division of the globe; and on these
peculiarities the state of animal and vegetable life is dependent. If,
therefore, we admit incessant fluctuations in the physical geography, we
must, at the same time, concede the successive extinction of terrestrial
and aquatic species to be part of the economy of our system. When some
great class of _stations_ is in excess in certain latitudes, as, for
example, in wide savannahs, arid sands, lofty mountains, or inland seas,
we find a corresponding development of species adapted for such
circumstances. In North America, where there is a chain of vast inland
lakes of fresh water, we find an extraordinary abundance and variety of
aquatic birds, fresh-water fish, testacea, and small amphibious
reptiles, fitted for such a climate. The greater part of these would
perish if the lakes were destroyed,--an event that might be brought
about by some of the least of those important revolutions contemplated
in geology. It might happen that no fresh-water lakes of corresponding
magnitude might then exist on the globe; or that, if they occurred
elsewhere, they might be situated in New Holland, Southern Africa,
Eastern Asia, or some region so distant as to be quite inaccessible to
the North American species; or they might be situated within the
tropics, in a climate uninhabitable by creatures fitted for a temperate
zone; or, finally, we may presume that they would be pre-occupied by
_indigenous_ tribes.

A vivid description has been given by Mr. Darwin and Sir W. Parish of
the great droughts which have sometimes visited the Pampas of South
America, for three or four years in succession, during which an
incredible number of wild animals, cattle, horses, and birds, have
perished from want of food and water. Several hundred thousand animals
were drowned in the Parana alone, having rushed into the river to drink,
and being too much exhausted by hunger to escape.[986] Such droughts are
often attended in South America and other hot climates by wide-spreading
conflagrations, caused by lightning, which fires the dried grass and
brush-wood. Thus quadrupeds, birds, insects, and other creatures, are
destroyed by myriads. How many species, both of the animal and vegetable
world, which once flourished in the country between the valley of the
Parana and the Straits of Magellan, may not have been annihilated, since
the first drought or first conflagration began!

To pursue this train of reasoning farther is unnecessary; the geologist
has only to reflect on what has been said of the habitations and
stations of organic beings in general, and to consider them in relation
to those effects which were contemplated in the second book, as
resulting from the igneous and aqueous causes now in action, and he will
immediately perceive that, amidst the vicissitudes of the earth's
surface, species cannot be immortal, but must perish, one after the
other, like the individuals which compose them. There is no possibility
of escaping from this conclusion, without resorting to some hypothesis
as violent as that of Lamarck, who imagined, as we have before seen,
that species are each of them endowed with indefinite powers of
modifying their organization, in conformity to the endless changes of
circumstances to which they are exposed.


_Effects of a general Alteration in Climate on the Distribution of
Species._

Some of the effects which must attend every general alteration of
_climate_ are sufficiently peculiar to claim a separate consideration
before concluding the present chapter.

I have before stated that, during seasons of extraordinary severity,
many northern birds, and in some countries many quadrupeds, migrate
southwards. If these cold seasons were to become frequent, in
consequence of a gradual and general refrigeration of the atmosphere,
such migrations would be more and more regular, until, at length, many
animals, now confined to the arctic regions, would become the tenants of
the temperate zone; while the inhabitants of the temperate zone would
approach nearer to the equator. At the same time, many species
previously established on high mountains would begin to descend, in
every latitude, towards the middle regions; and those which were
confined to the flanks of mountains would make their way into the
plains. Analogous changes would also take place in the vegetable
kingdom.

If, on the contrary, the heat of the atmosphere be on the increase, the
plants and animals of low grounds would ascend to higher levels, the
equatorial species would migrate into the temperate zone, and those of
the temperate into the arctic circle.

But although some species might thus be preserved, every great change of
climate must be fatal to many which can find no place of retreat when
their original habitations become unfit for them. For if the general
temperature be on the rise, then there is no cooler region whither the
polar species can take refuge; if it be on the decline, then the animals
and plants previously established between the tropics have no resource.
Suppose the general heat of the atmosphere to increase, so that even the
arctic region became too warm for the musk-ox, and rein-deer, it is
clear that they must perish; so if the torrid zone should lose so much
of its heat, by the progressive refrigeration of the earth's surface, as
to be an unfit habitation for apes, boas, bamboos, and palms, these
tribes of animals and plants, or, at least; most of the species now
belonging to them, would become extinct, for there would be no warmer
latitudes for their reception.

It will follow, therefore, that as often as the climates of the globe
are passing from the extreme of heat to that of cold--from the summer to
the winter of the great year before alluded to[987]--the migratory
movement will be directed constantly from the poles towards the equator;
and for this reason the species inhabiting parallel latitudes, in the
northern and southern hemispheres, must become widely different. For I
assume, on grounds before explained, that the original stock of each
species is introduced into one spot of the earth only, and,
consequently, no species can be at once indigenous in the arctic and
antarctic circles.

But when, on the contrary, a series of changes in the physical geography
of the globe, or any other supposed cause, occasions an elevation of the
general temperature,--when there is a passage from the winter to one of
the vernal or summer seasons of the great cycle of climate,--then the
order of the migratory movement is inverted. The different species of
animals and plants direct their course from the equator towards the
poles; and the northern and southern hemispheres may become peopled to
a certain limited extent by identical species.

I say limited, because we cannot speculate on the entire transposition
of a group of animals and plants from tropical to polar latitudes, or
the reverse, as a probable or even possible event. We may believe the
mean annual temperature of one zone to be transferable to another, but
we know that the same climate cannot be so transferred. Whatever be the
general temperature of the earth's surface, comparative equability of
heat will characterize the tropical regions; while great periodical
variations will belong to the temperate, and still more to the polar
latitudes. These, and many other peculiarities connected with heat and
light, depend on fixed astronomical causes, such as the motion of the
earth and its position in relation to the sun, and not on those
fluctuations of its surface which may influence the general temperature.

Among many obstacles to such extensive transference of habitations, we
must not forget the immense lapse of time required, according to the
hypothesis before suggested, to bring about a considerable change in
climate. During a period so vast, the other cause of extirpation, before
enumerated, would exert so powerful an influence as to prevent all, save
a very few hardy species, from passing from equatorial to polar regions,
or from the tropics to the pole.[988]

But the power of accommodation to new circumstances is great in certain
species, and might enable many to pass from one zone to another, if the
mean annual heat of the atmosphere and the ocean were greatly altered.
To the marine tribes, especially, such a passage would be possible; for
they are less impeded in their migrations by barriers of land, than are
the terrestrial by the ocean. Add to this, that the temperature of the
ocean is much more uniform than that of the atmosphere investing the
land; so that we may easily suppose that most of the testacea, fish, and
other classes, might pass from the equatorial into the temperate
regions, if the mean temperature of those regions were transposed,
although a second expatriation of these species of tropical origin into
the arctic and antarctic circles would probably be impossible.

Let us now consider more particularly the effect of vicissitudes of
climate in causing one species to give way before the increasing numbers
of some other.

When temperature forms the barrier which arrests the progress of an
animal or plant in a particular direction, the individuals are fewer and
less vigorous as they approach the extreme confines of the geographical
range of the species. But these stragglers are ready to multiply rapidly
on the slightest increase or diminution of heat that may be favorable to
them, just as particular insects increase during a hot summer, and
certain plants and animals gain ground after a series of congenial
seasons.

In almost every district, especially if it be mountainous, there are a
variety of species the limits of whose habitations are conterminous,
some being unable to proceed farther without encountering too much heat,
others too much cold. Individuals, which are thus on the borders of the
regions proper to their respective species, are like the outposts of
hostile armies, ready to profit by every slight change of circumstances
in their favor, and to advance upon the ground occupied by their
neighbors and opponents.

The proximity of distinct climates produced by the inequalities of the
earth's surface, brings species possessing very different constitutions
into such immediate contact, that their naturalizations are very speedy
whenever opportunities of advancing present themselves. Many insects and
plants, for example, are common to low plains within the arctic circle,
and to lofty mountains in Scotland and other parts of Europe. If the
climate, therefore, of the polar regions were transferred to our own
latitudes, the species in question would immediately descend from these
elevated stations to overrun the low grounds. Invasions of this kind,
attended by the expulsion of the pre-occupants, are almost
instantaneous, because the change of temperature not only places the one
species in a more favorable position, but renders the others sickly and
almost incapable of defence.

_These changes inconsistent with the theory of transmutation._--Lamarck,
when speculating on the transmutation of species, supposed every
modification in organization and instinct to be brought about slowly and
insensibly in an indefinite lapse of ages. But he does not appear to
have sufficiently considered how much every alteration in the physical
condition of the habitable surface changes the relations of a great
number of coexisting species, and that some of these would be ready
instantly to avail themselves of the slightest change in their favor,
and to multiply to the injury of others. Even if we thought it possible
that the palm or the elephant, which now flourish in equatorial regions,
could ever learn to bear the variable seasons of our temperate zone, or
the rigors of an arctic winter, we might with no less confidence affirm,
that they must perish before they had time to become habituated to such
new circumstances. That they would be displaced by other species as
often as the climate varied, may be inferred from the data before
explained respecting the local extermination of species produced by the
multiplication of others.

Suppose the climate of the highest part of the woody zone of Etna to be
transferred to the sea-shore of the base of the mountain, no botanist
would anticipate that the olive, lemon-tree, and prickly pear (_Cactus
Opuntia_) would be able to contend with the oak and chestnut, which
would begin forthwith to descend to a lower level; or that these last
would be able to stand their ground against the pine, which would also,
in the space of a few years, begin to occupy a lower position. We might
form some kind of estimate of the time which might be required for the
migrations of these plants; whereas we have no data for concluding that
any number of thousands of years would be sufficient for one step in
the pretended metamorphosis of one species into another, possessing
distinct attributes and qualities.

This argument is applicable not merely to _climate_, but to any other
cause of mutation. However slowly a lake may be converted into a marsh,
or a marsh into a meadow, it is evident that before the lacustrine
plants can acquire the power of living in marshes, or the marsh-plants
of living in a less humid soil, other species, already existing in the
region, and fitted for these several stations, will intrude and keep
possession of the ground. So, if a tract of salt water becomes fresh by
passing through every intermediate degree of brackishness, still the
marine mollusks will never be permitted to be gradually metamorphosed
into fluviatile species; because long before any such transformation can
take place by slow and insensible degrees, other tribes, already formed
to delight in brackish or fresh water, will avail themselves of the
change in the fluid, and will, each in their turn, monopolize the space.

It is idle, therefore, to dispute about the abstract possibility of the
conversion of one species into another, when there are known causes so
much more active in their nature, which must always intervene and
prevent the actual accomplishment of such conversions. A faint image of
the certain doom of a species less fitted to struggle with some new
condition in a region which it previously inhabited, and where it has to
contend with a more vigorous species, is presented by the extirpation of
savage tribes of men by the advancing colony of some civilized nation.
In this case the contest is merely between two different _races_--two
varieties, moreover, of a species which exceeds all others in its
aptitude to accommodate its habits to the most extraordinary variations
of circumstances. Yet few future events are more certain than the speedy
extermination of the Indians of North America and the savages of New
Holland in the course of a few centuries, when these tribes will be
remembered only in poetry or history.


_Concluding remarks._--We often hear astonishment expressed at the
disappearance from the earth in times comparatively modern of many small
as well as large animals, the remains of which have been found in a
fossil state, under circumstances implying that neither any great
geographical revolution, nor the exterminating influence of man has
intervened to account for their extinction. But in all such cases we
should inquire whether we are sufficiently acquainted with the numerous
and complicated conditions on which the perpetuation of each species
depends, to entitle us to wonder if it should be suddenly cut off.

Mr. Darwin, when calling attention to the fact that the horse,
megatherium, megalonyx, and many contemporary Mammalia, had perished in
South America after that continent had acquired its present
configuration, and when, if we may judge by the Testacea, the climate
very nearly resembled the present, observes, "that in the living
creation one species is often extremely rare in a given region, while
another of the same genus and with closely allied habits is exceedingly
common. A zoologist familiar with such phenomena, if asked to explain
them, usually replies, that some slight difference in climate, food, or
the number of its enemies, must determine the relative strength of the
two species in question, although we may be unable to point out the
precise manner of the action of the check. We are, therefore, driven to
the conclusion, that causes generally quite inappreciable by us
determine whether a given species shall be abundant or scanty in
numbers. Why, then, should we feel astonishment if the rarity is
occasionally carried a step farther,--to extinction?"[989]




CHAPTER XLIII.

EXTINCTION AND CREATION OF SPECIES.


  Theory of the successive extinction of species consistent with a
    limited geographical distribution--Opinions of botanists respecting
    the centres from which plants have been diffused--Whether there are
    grounds for inferring that the loss, from time to time, of certain
    animals and plants, is compensated by the introduction of new
    species?--Whether any evidence of such new creations could be
    expected within the historical era?--The question whether the
    existing species have been created in succession must be decided by
    geological monuments.


_Successive Extinction of Species consistent with their limited
Geographical Distribution._


In the preceding chapters I have pointed out the strict dependence of
each species of animal and plant on certain physical conditions in the
state of the earth's surface, and on the number and attributes of other
organic beings inhabiting the same region. I have also endeavored to
show that all these conditions are in a state of continual fluctuation,
the igneous and aqueous agents remodelling, from time to time, the
physical geography of the globe, and the migrations of species causing
new relations to spring up successively between different organic
beings. I have deduced as a corollary, that the species existing at any
particular period, must, in the course of ages, become extinct one after
the other. "They must die out," to borrow an emphatical expression from
Buffon, "because Time fights against them."

If the views which I have taken are just, there will be no difficulty in
explaining why the habitations of so many species are now restrained
within exceedingly narrow limits. Every local revolution, such as those
contemplated in the preceding chapter, tends to circumscribe the range
of some species, while it enlarges that of others; and if we are led to
infer that new species originate in one spot only, each must require
time to diffuse itself over a wide area. It will follow, therefore, from
the adoption of this hypothesis, that the recent origin of some species,
and the high antiquity of others, are equally consistent with the
general fact of their limited distribution; some being local, because
they have not existed long enough to admit of their wide dissemination;
others, because circumstances in the animate or inanimate world have
occurred to restrict the range which they may once have obtained. As a
general rule, however, species, common to many distant provinces, or
those now found to inhabit very distant parts of the globe, are to be
regarded as the most ancient. Numerically speaking, they may not perhaps
be largely represented, but their wide diffusion shows that they have
had a long time to spread themselves, and have been able to survive many
important revolutions in physical geography.

After so much evidence has been brought to light by the geologist, of
land and sea having changed places in various regions since the existing
species were in being, we can feel no surprise that the zoologist and
botanist have hitherto found it difficult to refer the geographical
distribution of species to any clear and determinate principles, since
they have usually speculated on the phenomena, upon the assumption that
the physical geography of the globe had undergone no material alteration
since the introduction of the species now living. So long as this
assumption was made, the facts relating to the geography of plants and
animals appeared capricious in the extreme, and by many the subject was
pronounced to be so full of mystery and anomalies, that the
establishment of a satisfactory theory was hopeless.[990]

_Centres from which plants have been diffused._--Some botanists
conceived, in accordance with the hypothesis of Wildenow, that mountains
were the centres of creation from which the plants now inhabiting large
continents have radiated; to which De Candolle and others, with much
reason, objected, that mountains, on the contrary, are often the
barriers between two provinces of distinct vegetation. The geologist who
is acquainted with the extensive modifications which the surface of the
earth has undergone in very recent geological epochs, may be able,
perhaps, to reconcile both these theories in their application to
different regions.

A lofty range of mountains, which is so ancient as to date from a period
when the species of animals and plants differed from those now living,
will naturally form a barrier between contiguous provinces; but a chain
which has been raised, in great part, within the epoch of existing
species, and around which new lands have arisen from the sea within that
period, will be a centre of peculiar vegetation.

"In France," observes De Candolle, "the Alps and Cevennes prevent a
great number of the plants of the south from spreading themselves to the
northward; but it has been remarked that some species have made their
way through the gorges of these chains, and are found on their northern
sides, principally in those places where they are lower and more
interrupted."[991] Now the chains here alluded to have probably been of
considerable height ever since the era when the existing vegetation
began to appear, and were it not for the deep fissures which divide
them, they might have caused much more abrupt terminations to the
extension of distinct assemblages of species.

Parts of the Italian peninsula, on the other hand, have gained a
considerable portion of their present height since a majority of the
marine species now inhabiting the Mediterranean, and probably, also,
since the terrestrial plants of the same region were in being. Large
tracts of land have been added, both on the Adriatic and Mediterranean
side, to what originally constituted a much narrower range of mountains,
if not a chain of islands running nearly north and south, like Corsica
and Sardinia. It may therefore be presumed that the Apennines have been
a centre whence species have diffused themselves over the contiguous
_lower_ and _newer_ regions. In this and all analogous situations, the
doctrine of Wildenow, that species have radiated from the mountains as
from centres, may be well founded.


_Introduction of New Species._

If the reader should infer, from the facts laid before him in the
preceding chapters, that the successive extinction of animals and plants
may be part of the constant and regular course of nature, he will
naturally inquire whether there are any means provided for the repair of
these losses? Is it part of the economy of our system that the habitable
globe should, to a certain extent, become depopulated both in the ocean
and on the land; or that the variety of species should diminish until
some new era arrives when a new and extraordinary effort of creative
energy is to be displayed? Or is it possible that new species can be
called into being from time to time, and yet that so astonishing a
phenomenon can escape the observation of naturalists?

Humboldt has characterized these subjects as among the mysteries which
natural science cannot reach; and he observes that the investigation of
the origin of beings does not belong to zoological or botanical
geography. To geology, however, these topics do strictly appertain; and
this science is chiefly interested in inquiries into the state of the
animate creation as it now exists, with a view of pointing out its
relations to antecedent periods when its condition was different.

Before offering any hypothesis towards the solution of so difficult a
problem, let us consider what kind of evidence we ought to expect, in
the present state of science, of the first appearance of new animals or
plants, if we could imagine the successive creation of species to
constitute, like their gradual extinction, a regular part of the economy
of nature.

In the first place it is obviously more easy to prove that a species,
once numerously represented in a given district, has ceased to be, than
that some other which did not pre-exist has made its
appearance--assuming always, for reasons before stated, that single
stocks only of each animal and plant are originally created, and that
individuals of new species do not suddenly start up in many different
places at once.

So imperfect has the science of natural history remained down to our own
times, that, within the memory of persons now living, the numbers of
known animals and plants have been doubled, or even quadrupled, in many
classes. New and often conspicuous species are annually discovered in
parts of the old continent, long inhabited by the most civilized
nations. Conscious, therefore, of the limited extent of our information,
we always infer, when such discoveries are made, that the beings in
question had previously eluded our research; or had at least existed
elsewhere, and only migrated at a recent period into the territories
where we now find them. It is difficult, even in contemplation, to
anticipate the time when we shall be entitled to make any other
hypothesis in regard to all the marine tribes, and to by far the greater
number of the terrestrial;--such as birds, which possess such unlimited
powers of migration; insects, which, besides the variability of each
species in number, are also so capable of being diffused to vast
distances; and cryptogamous plants, to which, as to many other classes,
both of the animal and vegetable kingdom, similar observations are
applicable.

_What kind of evidence of new creations could be expected?_--What kind
of proofs, therefore, could we reasonably expect to find of the origin
at a particular period of a new species?

Perhaps it may be said in reply that, within the last two or three
centuries, some forest tree or new quadruped might have been observed to
appear suddenly in those parts, of England or France which had been most
thoroughly investigated;--that naturalists might have been able to show
that no such living being inhabited any other region of the globe, and
that there was no tradition of anything similar having before been
observed in the district where it had made its appearance.

Now, although this objection may seem plausible, yet its force will be
found to depend entirely on the rate of fluctuation which we suppose to
prevail in the animate world, and on the proportion which such
conspicuous subjects of the animal and vegetable kingdoms bear to those
which are less known and escape our observation. There are, perhaps,
more than a million species of plants and animals, exclusive of the
microscopic and infusory animalcules, now inhabiting the terraqueous
globe. The terrestrial plants may amount, says De Candolle, to somewhere
between 110,000 and 120,000;[992] but the data on which this conjecture
is founded are considered by many botanists to be vague and
unsatisfactory. Sprengel only enumerated, in 1827, about 31,000 known
phænogamous, and 6000 cryptogamous plants; but that naturalist omitted
many, perhaps 7000 phænogamous, and 1000 cryptogamous species. Mr.
Lindley, in a letter to the author in 1836, expressed his opinion that
it would be rash to speculate on the existence of more than 80,000
phænogamous, and 10,000 cryptogamous plants. "If we take," he says, in a
letter to the author on this subject, "37,000 as the number of published
phænogamous species, and then add, for the undiscovered species in Asia
and New Holland, 15,000, in Africa 10,000, and in America 18,000, we
have 80,000 species; and if 7000 be the number of published cryptogamous
plants, and we allow 3000 for the undiscovered species (making 10,000),
there would then be, on the whole, 90,000 species." But since that
period one catalogue, as I learn from Dr. J. Hooker, contains a list of
the names of 78,000 phænogamous plants which had been published before
1841.

It was supposed by Linnæus that there were four or five species of
insects in the world for each phænogamous plant: but if we may judge
from the relative proportion of the two classes in Great Britain, the
number of insects must be still greater; for the total number of British
insects, "according to the last census," is about 12,500;[993] whereas
there are only 1500 phænogamous plants indigenous to our island. As the
insects are much more numerous in hot countries than in our temperate
latitudes, it seems difficult to avoid the conclusion that there are
more than half a million species in the world.

The number of known mammifers, when Temminck wrote, exceeded 800, and
Mr. Waterhouse informs me that more than 1200 are now (1850) ascertained
to exist. Baron Cuvier estimated the amount of known fishes at 6000; and
Mr. G. Gray, in his "Genera of Birds," enumerates 8000 species. We have
still to add the reptiles, and all the invertebrated animals, exclusive
of insects. It remains, in a great degree, mere matter of conjecture
what proportion the aquatic tribes may bear to the denizens of the land;
but the habitable surface beneath the waters can hardly be estimated at
less than double that of the continents and islands, even admitting that
a very considerable area is destitute of life, in consequence of great
depth, cold, darkness, and other circumstances. In the late polar
expedition it was found that, in some regions, as in Baffin's Bay, there
were marine animals inhabiting the bottom at great depths, where the
temperature of the water was below the freezing point. That there is
life at much greater profundities in warmer regions may be confidently
inferred.

The ocean teems with life--the class of _Polyps_ alone are conjectured
by Lamarck to be as strong in individuals as insects. Every tropical
reef is described as covered with Corals and Sponges, and swarming with
Crustacea, Echini, and Testacea; while almost every tide-washed rock in
the world is carpeted with Fuci, and supports some Corallines, Actiniæ,
and Mollusca. There are innumerable forms in the seas of the warmer
zones, which have scarcely begun to attract the attention of the
naturalist; and there are parasitic animals without number, three or
four of which are sometimes appropriated to one genus, as to the whale
(_Balæna_), for example. Even though we concede, therefore, that the
geographical range of marine species is more extensive in general than
that of the terrestrial (the temperature of the sea being more uniform,
and the land impeding less the migrations of the oceanic than the ocean
those of the terrestrial species), yet it seems probable that the
aquatic tribes far exceed in number the inhabitants of the land.

Without insisting on this point, it may be safe to assume, that,
exclusive of microscopic beings, there are between one and two millions
of species now inhabiting the terraqueous globe; so that if only one of
these were to become extinct annually, and one new one were to be every
year called into being, much more than a million of years might be
required to bring about a complete revolution in organic life.

I am not hazarding at present any hypothesis as to the probable rate of
change; but none will deny that when the _annual_ birth and the _annual_
death of one species on the globe is proposed as a mere speculation,
this at least is to imagine no slight degree of instability in the
animate creation. If we divide the surface of the earth into twenty
regions of equal area, one of these might comprehend a space of land and
water about equal in dimensions to Europe, and might contain a twentieth
part of the million of species which may be assumed to exist in the
animal kingdom. In this region one species only would, according to the
rate of mortality before assumed, perish in twenty years, or only five
out of fifty thousand in the course of a century. But as a considerable
proportion of the whole would belong to the aquatic classes, with which
we have a very imperfect acquaintance, we must exclude them from our
consideration; and if they constitute half of the entire number, then
one species only might be lost in forty years among the terrestrial
tribes. Now the Mammalia, whether terrestrial or aquatic, bear so small
a proportion to other classes of animals, forming less, perhaps, than
one thousandth part of the whole, that if the longevity of species in
the different orders were equal, a vast period must elapse before it
would come to the turn of this conspicuous class to lose one of their
number. If one species only of the whole animal kingdom died out in
forty years, no more than one mammifer might disappear in 40,000 years
in a region of the dimensions of Europe.

It is easy, therefore, to see, that in a small portion of such an area,
in countries, for example, of the size of England and France, periods
of much greater duration must elapse before it would be possible to
authenticate the first appearance of one of the larger plants and
animals, assuming the annual birth and death of one species to be the
rate of vicissitude in the animate creation throughout the world.

The observations of naturalists upon living species may, in the course
of future centuries, accumulate positive data, from which an insight
into the laws which govern this part of our terrestrial system may be
derived; but, in the present deficiency of historical records, we have
traced up the subject to that point where geological monuments alone are
capable of leading us on to the discovery of ulterior truths. To these,
therefore, we must appeal, carefully examining the strata of recent
formation wherein the remains of _living_ species, both animal and
vegetable, are known to occur. We must study these strata in strict
reference to their chronological order, as deduced from their
superposition, and other relations. From these sources we may learn
which of the species, now our contemporaries, have survived the greatest
revolutions of the earth's surface; which of them have co-existed with
the greatest number of animals and plants now extinct; and which have
made their appearance only when the animate world had nearly attained
its present condition.

From such data we may be enabled to infer, whether species have been
called into existence in succession, or all at one period; whether
singly, or by groups simultaneously; whether the antiquity of man be as
high as that of any of the inferior beings which now share the planet
with him, or whether the human species is one of the most recent of the
whole.

To some of these questions we can even now return a satisfactory answer;
and with regard to the rest, we have some data to guide conjecture, and
to enable us to speculate with advantage: but in order to be fully
qualified to enter upon such discussions the reader must study the ample
body of materials amassed by the industry of modern geologists.




CHAPTER XLIV.

EFFECTS PRODUCED BY THE POWERS OF VITALITY ON THE STATE OF THE EARTH'S
SURFACE.


  Modifications in physical geography caused by organic beings--Why
    the vegetable soil does not augment in thickness--The theory, that
    vegetation is an antagonist power counterbalancing the degradation
    caused by running water untenable--Conservative influence of
    vegetation--Rain diminished by felling of forests--Distribution of
    American forests dependent on direction of predominant
    winds--Influence of man in modifying the physical geography of the
    globe.


The second branch of our inquiry, respecting changes of the organic
world, relates to the processes by which the remains of animals and
plants become fossil, or, to speak still more generally, to all the
effects produced by the powers of vitality on the surface and shell of
the earth.

Before entering on the principal division of this subject, the imbedding
and preservation of animal and vegetable remains, I shall offer a few
remarks on the superficial modifications caused directly by the agency
of organic beings, as when the growth of certain plants covers the slope
of a mountain with peat, or converts a swamp into dry land; or when
vegetation prevents the soil, in certain localities, from being washed
away by running water.

In considering alterations of this kind, brought about in the physical
geography of particular tracts, we are too apt to think exclusively of
that part of the earth's surface which has emerged from beneath the
waters, and with which alone, as terrestrial beings, we are familiar.
Here the direct power of animals and plants to cause any important
variation is, of necessity, very limited, except in checking the
progress of that decay of which the land is the chief theatre. But if we
extend our views, and instead of contemplating the dry land, consider
that larger portion which is assigned to the aquatic tribes, we discover
the great influence of the living creation, in imparting varieties of
conformation to the solid exterior which the agency of inanimate causes
alone could not produce.

Thus, when timber is floated into the sea, it is often drifted to vast
distances, and subsides in spots where there might have been no deposit,
at that time and place, if the earth had not been tenanted by living
beings. If, therefore, in the course of ages, a hill of wood, or
lignite, be thus formed in the subaqueous regions, a change in the
submarine geography may be said to have resulted from the action of
organic powers. So in regard to the growth of coral reefs; it is
probable that a large portion of the matter of which they are composed
is supplied by mineral springs, which often rise up at the bottom of the
sea, and which, on land, abound throughout volcanic regions hundreds of
leagues in extent. The matter thus constantly given out could not go on
accumulating for ever in the waters, but would be precipitated in the
abysses of the sea, even if there were no polyps and testacea; but these
animals arrest and secrete the carbonate of lime on the summits of
submarine mountains, and form reefs many hundred feet in thickness, and
hundreds of miles in length, where, but for them, none might ever have
existed.

_Why the vegetable soil does not augment in thickness._--If no such
voluminous masses are formed on the land, it is not from the want of
solid matter in the structure of terrestrial animals and plants; but
merely because, as I have so often stated, the continents are those
parts of the globe where accessions of matter can scarcely ever take
place--where, on the contrary, the most solid parts already formed are,
each in their turn, exposed to gradual degradation. The quantity of
timber and vegetable matter which grows in a tropical forest in the
course of a century is enormous, and multitudes of animal skeletons are
scattered there during the same period, besides innumerable land shells
and other organic substances. The aggregate of these materials,
therefore, might constitute a mass greater in volume than that which is
produced in any coral-reef during the same lapse of years; but, although
this process should continue on the land for ever, no mountains of wood
or bone would be seen stretching far and wide over the country, or
pushing out bold promontories into the sea. The whole solid mass is
either devoured by animals, or decomposes, as does a portion of the rock
and soil on which the animals and plants are supported.

The waste of the strata themselves, accompanied by the decomposition of
their organic remains, and the setting free of their alkaline
ingredients, is one source from whence running water and the atmosphere
may derive the materials which are absorbed by the roots and leaves of
plants. Another source is the passage into a gaseous form of even the
hardest parts of animals and plants which die and putrefy in the air,
where they are soon resolved into the elements of which they are
composed: and while a portion of these constituents is volatilized, the
rest is taken up by rain-water, and sinks into the earth, or flows
towards the sea; so that they enter again and again into the composition
of different organic beings.

The principal elements found in plants are hydrogen, carbon, and oxygen;
so that water and the atmosphere contain all of them, either in their
own composition or in solution.[994] The constant supply of these
elements is maintained not only by the putrefaction of animal and
vegetable substances, and the decay of rocks, but also by the copious
evolution of carbonic acid and other gases from volcanoes and mineral
springs, and by the effects of ordinary evaporation, whereby aqueous
vapors are made to rise from the ocean, and to circulate round the
globe.

It is well known, that when two gases of different specific gravity are
brought into contact, even though the heavier be the lowermost, they
soon become uniformly diffused by mutual absorption through the whole
space which they occupy. By virtue of this law, the heavy carbonic acid
finds its way upwards through the lighter air of the atmosphere, and
conveys nourishment to the lichen which covers the mountain top.

If the quantity of food consumed by terrestrial animals, and the
elements imbibed by the roots and leaves of plants, were derived
entirely from that supply of hydrogen, carbon, oxygen, nitrogen, and
other elements, given out into the atmosphere and the waters by the
putrescence of organic substances, then we might imagine that the
vegetable mould would, after a series of years, neither gain nor lose a
single particle by the action of organic beings; and this conclusion is
not far from the truth; but the operation which renovates the vegetable
and animal mould is by no means so simple as that here supposed.
Thousands of carcases of terrestrial animals are floated down, every
century, into the sea; and, together with forests of drift-timber, are
imbedded in subaqueous deposits, where their elements are imprisoned in
solid strata, and may there remain locked up throughout whole geological
epochs before they again become subservient to the purposes of life.

On the other hand, fresh supplies are derived by the atmosphere and by
running water, as before stated, from the disintegration of rocks and
their organic contents, and through the agency of mineral springs from
the interior of the earth, from whence all the elements before
mentioned, which enter principally into the composition of animals and
vegetables, are continually evolved. Even nitrogen is found, by
chemists, to be contained very generally in the waters of mineral
springs.

_Vegetation not an antagonist power counterbalancing the action of
running water._--If we suppose that the copious supply from the nether
regions, by springs and volcanic vents, of carbonic acid and other
gases, together with the decomposition of rocks, may be just sufficient
to counterbalance that loss of matter which, having already served for
the nourishment of animals and plants, is annually carried down in
organized forms, and buried in subaqueous strata, we concede the utmost
that is consistent with probability. An opinion, however, has been
expressed, that the processes of vegetable life, by absorbing various
gases from the atmosphere, cause so large a mass of solid matter to
accumulate on the surface of the land, that this mass alone may
constitute a great counterpoise to all the matter transported to lower
levels by the aqueous agents of decay. "Torrents and rivers," it is
said--"the waves of the sea and marine currents--act upon lines only;
but the power of vegetation to absorb the elastic and non-elastic fluids
circulating round the earth, extends over the whole surface of the
continents. By the silent but universal action of this great antagonist
power, the spoliation and waste caused by running water on the land,
and by the movements of the ocean, are neutralized, and even
counterbalanced."[995]

In opposition to these views, I conceive that we shall form a juster
estimate of the influence of vegetation, if we consider it as being in a
slight degree conservative, and capable of retarding the waste of land,
but not of acting as an antagonist power. The vegetable mould is seldom
more than a few feet in thickness, and frequently does not exceed a few
inches; and we by no means find that its volume is more considerable on
those parts of our continents which we can prove, by geological data, to
have been elevated at more ancient periods, and where, consequently,
there has been the greatest time for the accumulation of vegetable
matter, produced throughout successive zoological epochs. On the
contrary, these higher and older regions are more frequently denuded, so
as to expose the bare rock to the action of the sun and air.

We find in the torrid zone, where the growth of plants is most rank and
luxurious, that accessions of matter due to their agency are by no means
the most conspicuous. Indeed it is in these latitudes, where the
vegetation is most active, that, for reasons to be explained in the next
chapter, even those superficial peat mosses are unknown which cover a
large area in some parts of our temperate zone. If the operation of
animal and vegetable life could restore to the general surface of the
continents a portion of the elements of those disintegrated rocks of
which such enormous masses are swept down annually into the sea, the
effects would long ere this have constituted one of the most striking
features in the structure and composition of our continents. All the
great steppes and table-lands of the world, where the action of running
water is feeble, would have become the grand repositories of organic
matter, accumulated without that intermixture of earthy sediment which
so generally characterizes the subaqueous strata.

I have already stated that, in the known operation of the _igneous_
causes, a real antagonist power is found, which may counterbalance the
levelling action of running water (p. 563); and there seems no good
reason for presuming that the upheaving and depressing force of
earthquakes, together with the ejection of matter by volcanoes, may not
be fully adequate to restore that inequality of the surface which rivers
and the waves and currents of the ocean annually tend to lessen. If a
counterpoise be derived from this source, the quantity and elevation of
land above the sea may for ever remain the same, in spite of the action
of the aqueous causes, which, if thus counteracted, may never be able to
reduce the surface of the earth more nearly to a state of equilibrium
than that which it has now attained; and, on the other hand, the force
of the aqueous agents themselves might thus continue for ever
unimpaired.

_Conservative influence of vegetation._--If, then, vegetation cannot act
as an antagonist power amid the mighty agents of change which are always
modifying the surface of the globe, let us next inquire how far its
influence is conservative,--how far it may retard the levelling effects
of running water, which it cannot oppose, much less counterbalance.

It is well known that a covering of herbage and shrubs may protect a
loose soil from being carried away by rain, or even by the ordinary
action of a river, and may prevent hills of loose sand from being blown
away by the wind; for the roots bind together the separate particles
into a firm mass, and the leaves intercept the rain-water, so that it
dries up gradually, instead of flowing off in a mass and with great
velocity. The old Italian hydrographers make frequent mention of the
increased degradation which has followed the clearing away of natural
woods in several parts of Italy. A remarkable example was afforded in
the Upper Val d' Arno, in Tuscany, on the removal of the woods clothing
the steep declivities of the hills by which that valley is bounded. When
the ancient forest laws were abolished by the Grand Duke Joseph, during
the last century, a considerable tract of surface in the Cassentina (the
Clausentinium of the Romans) was denuded, and immediately the quantity
of sand and soil washed down into the Arno increased enormously. Frisi,
alluding to such occurrences, observes, that as soon as the bushes and
plants were removed, the waters flowed off more rapidly, and, in the
manner of floods, swept away the vegetable soil.[996]

This effect of vegetation is of high interest to the geologist, when he
is considering the formation of those valleys which have been
principally due to the action of rivers. The spaces intervening between
valleys, whether they be flat or ridgy, when covered with vegetation,
may scarcely undergo the slightest waste, as the surface may be
protected by the green sward of grass; and this may be renewed, in the
manner before described, from elements derived from rain-water and the
atmosphere. Hence, while the river is continually bearing down matter in
the alluvial plain, and undermining the cliffs on each side of every
valley, the height of the intervening rising grounds may remain
stationary.

In this manner, a cone of loose scoriæ, sand, and ashes, such as Monte
Nuovo, may, when it has once become densely clothed with herbage and
shrubs, suffer scarcely any further dilapidation; and the perfect state
of the cones of hundreds of extinct volcanoes in France, the Neapolitan
territory, Sicily, and elsewhere, may prove nothing whatever, either as
to their relative or absolute antiquity. We may be enabled to infer,
from the integrity of such conical hills of incoherent materials, that
no flood can have passed over the countries where they are situated,
since their formation; but the atmospheric action alone, in spots where
there happen to be no torrents, and where the surface was clothed with
vegetation, could scarcely in any lapse of ages have destroyed them.

During a tour in Spain, in 1830, I was surprised to see a district of
gently undulating ground in Catalonia, consisting of red and gray
sandstone, and in some parts of red marl, almost entirely denuded of
herbage; while the roots of the pines, holm oaks, and some other trees,
were half exposed, as if the soil had been washed away by a flood. Such
is the state of the forests, for example, between Oristo and Vich, and
near San Lorenzo. But, being overtaken by a violent thunder-storm, in
the month of August, I saw the whole surface, even the highest levels of
some flat-topped hills, streaming with mud, while on every declivity the
devastation of torrents was terrific. The peculiarities in the
physiognomy of the district were at once explained; and I was taught
that, in speculating on the greater effects which the direct action of
rain may once have produced on the surface of certain parts of England,
we need not revert to periods when the heat of the climate was
_tropical_.

In the torrid zone the degradation of land is generally more rapid; but
the waste is by no means proportioned to the superior quantity of rain
or the suddenness of its fall, the transporting power of water being
counteracted by a greater luxuriance of vegetation. A geologist who is
no stranger to tropical countries observes, that the softer rocks would
speedily be washed away in such regions, if the numerous roots of plants
were not matted together in such a manner as to produce considerable
resistance to the destructive power of the rains. The parasitical and
creeping plants also entwine in every possible direction, so as to
render the forests nearly impervious, and the trees possess forms and
leaves best calculated to shoot off the heavy rains; which, when they
have thus been broken in their fall, are quickly absorbed by the ground
beneath, or, when thrown into the drainage depressions, give rise to
furious torrents.[997]


_Influence of Man in modifying the Physical Geography of the Globe._

Before concluding this chapter, I shall offer a few observations on the
influence of man in modifying the physical geography of the globe; for
we must class his agency among the powers of organic nature.

_Felling of forests._--The felling of forests has been attended, in many
countries, by a diminution of rain, as in Barbadoes and Jamaica.[998]
For in tropical countries, where the quantity of aqueous vapor in the
atmosphere is great, but where, on the other hand, the direct rays of
the sun are most powerful, any impediment to the free circulation of
air, or any screen which shades the earth from the solar rays, becomes a
source of humidity; and wherever dampness and cold have begun to be
generated by such causes, the condensation of vapor continues. The
leaves, moreover, of all plants are alembics, and some of those in the
torrid zone have the remarkable property of distilling water, thus
contributing to prevent the earth from becoming parched up.

_Distribution of the American forests._--There can be no doubt then,
that the state of the climate, especially the humidity of the
atmosphere, influences vegetation, and that, in its turn, vegetation
re-acts upon the climate: but some writers seem to have attributed too
much importance to the influence of forests, particularly those of
America, as if they were the primary cause of the moisture of the
climate.

The theory of a modern author on this subject "that forests exist in
those parts of America only where the predominant winds carry with them
a considerable quantity of moisture from the ocean," seems far more
rational. In all countries, he says, "having a summer heat exceeding
70°, the presence or absence of natural woods, and their greater or less
luxuriance, may be taken as a measure of the amount of humidity, and of
the fertility of the soil. Short and heavy rains in a warm country will
produce grass, which, having its roots near to the surface, springs up
in a few days, and withers when the moisture is exhausted; but
transitory rains, however heavy, will not nourish trees; because, after
the surface is saturated, the remainder of the water runs off, and the
moisture lodged in the soil neither sinks deep enough, nor is in
sufficient quantity, to furnish the giants of the forests with the
necessary sustenance. It may be assumed that twenty inches of rain
falling moderately or at intervals, will leave a greater permanent
supply in the soil than forty inches falling, as it sometimes does in
the torrid zone, in as many hours."[999]

"In all regions," he continues, "where ranges of mountains intercept the
course of the constant or predominant winds, the country on the windward
side of the mountains will be moist, and that on the leeward dry; and
hence parched deserts will generally be found on the west side of
countries within the tropics, and on the east side of those beyond them,
the prevailing winds in these cases being generally in opposite
directions. On this principle, the position of forests in North and
South America may be explained. Thus, for example, in the region within
the thirtieth parallel, the moisture swept up by the trade-wind from the
Atlantic is precipitated in part upon the mountains of Brazil, which are
but low, and so distributed as to extend far into the interior. The
portion which remains is borne westward, and, losing a little as it
proceeds, is at length arrested by the Andes, where it falls down in
showers on their summits. The aërial current, now deprived of all the
humidity with which it can part, arrives in a state of complete
exsiccation at Peru, where consequently no rain falls. But in the region
of America, beyond the thirtieth parallel, the Andes serve as a screen
to intercept the moisture brought by the prevailing winds from the
Pacific Ocean: rains are copious on their summits, and in Chili on their
_western_ declivities; but none falls on the plains to the _eastward_,
except occasionally when the wind blows from the Atlantic."[1000]

I have been more particular in explaining these views, because they
appear to place in a true light the dependence of vegetation on climate,
the humidity being increased, and more uniformly diffused throughout the
year, by the gradual spreading of wood.

It has been affirmed, that formerly, when France and England were
covered with wood, Europe was much colder than at present; that the
winters in Italy were longer, and that the Seine, and many other rivers,
froze more regularly every winter than now. M. Arago, in an essay on
this subject, has endeavored to show, by tables of observations on the
congelation of the Rhine, Danube, Rhone, Po, Seine, and other rivers, at
different periods, that there is no reason to believe the cold to have
been in general more intense in ancient times.[1001] He admits, however,
that the climate of Tuscany has been so far modified, by the removal of
wood, as that the winters are less cold; but the summers also, he
contends, are less hot than of old; and the summers, according to him,
were formerly hotter in France than in our own times. His evidence is
derived chiefly from documents showing that wine was made three
centuries ago in the Vivarais and several other provinces, at an earlier
season, at greater elevations, and in higher latitudes, than are now
found suitable to the vine.

There seems little doubt that in the United States of North America the
rapid _clearing_ of the country has rendered the winters less severe and
the summers less hot; in other words, the extreme temperatures of
January and July have been observed from year to year to approach
somewhat nearer to each other. Whether in this case, or in France, the
_mean_ temperature has been raised, seems by no means as yet decided;
but there is no doubt that the climate has become, as Buffon would have
said, "less excessive."

I have before shown, when treating of the excavation of new estuaries in
Holland by inroads of the ocean, as also of the changes on our own
coasts, that although the conversion of sea into land by artificial
labors may be great, yet it must always be in subordination to the power
of the tides and currents, or to the great movements which alter the
relative level of the land and sea, (Chap. XX.) If, in addition to the
assistance obtained by parliamentary grants for defending Dunwich from
the waves, all the resources of Europe had been directed to the same
end, the existence of that port might perhaps have been prolonged for
several centuries (p. 310.) But in the mean time, the current would have
continued to sweep away portions from the adjoining cliffs on each side,
giving to the whole line of coast its present form, until at length the
town, projecting as a narrow promontory, must have become exposed to the
irresistible fury of the waves.

It is scarcely necessary to observe, that the control which man can
obtain over the igneous agents is less even than that which he may exert
over the aqueous. He cannot modify the upheaving or depressing force of
earthquakes, or the periods or degree of violence of volcanic eruptions;
and on these causes the inequalities of the earth's surface, and,
consequently, the shape of the sea and land, appear mainly to depend.
The utmost that man can hope to effect in this respect is occasionally
to divert the course of a lava-stream, and to prevent the burning
matter, for a season, from overwhelming a city, or some other of the
proudest works of human industry.

If all the nations of the earth should attempt to quarry away the lava
which flowed during one eruption from the Icelandic volcanoes in 1783,
and the two following years, and should attempt to consign it to the
deepest abysses of the ocean, they might toil for thousands of years and
not accomplish their task. Yet the matter borne down to the sea by two
great rivers, the Ganges and Burrampooter, in each quarter of a century,
probably equals in weight and volume the mass of Icelandic lava produced
by that great eruption (p. 282). So insignificant is the aggregate force
exerted by man, when contrasted with the ordinary operations of aqueous
or igneous agents in the natural world.

No application, perhaps, of human skill and labor tends so greatly to
vary the state of the habitable surface, as that employed in the
drainage of lakes and marshes, since not only the _stations_ of many
animals and plants, but the general climate of a district, may thus be
modified. It is also a kind of alteration to which it is difficult to
find anything analogous in the agency of inferior beings; for we ought
always, before we decide that any part of the influence of man is novel
and anomalous, carefully to consider the powers of all other animated
agents which may be limited or superseded by him.[1002] Many who have
reasoned on these subjects seem to have forgotten that the human race
often succeeds to the discharge of functions previously fulfilled by
other species. Suppose the growth of some of the larger terrestrial
plants, or, in other words, the extent of forest, to be diminished by
man, and the climate to be thereby modified, it does not follow that
this kind of innovation is unprecedented. It is a change in the state of
vegetation, and such may often have been the result of the appearance of
new species upon the earth. The multiplication, for example, of certain
insects in parts of Germany, during the last century, destroyed more
trees than man, perhaps, could have felled during an equal period.

It would be rash, however, to affirm that the power of man to modify the
surface may not differ in kind or degree from that of other living
beings; although the problem is certainly more complex than many who
have speculated on such topics have imagined. If land be raised from the
sea, the greatest alteration in its physical condition, which could ever
arise from the influence of organic beings, would probably be produced
by the first immigration of terrestrial plants, whereby the new tract
would become covered with vegetation. The change next in importance
would seem to be when animals first enter, and modify the proportionate
numbers of certain species of plants. If there be any anomaly in the
intervention of man, in farther varying the relative numbers in the
vegetable kingdom, it may not so much consist in the kind or absolute
quantity of alteration, as in the circumstance that a _single species_,
in this case, would exert, by its superior power and universal
distribution, an influence equal to that of hundreds of other
terrestrial animals.

If we inquire whether man, by his direct power, or by the changes which
he may give rise to indirectly, tends, upon the whole, to lessen or
increase the inequalities of the earth's surface, we shall incline,
perhaps, to the opinion that he is a levelling agent. In mining
operations he conveys upwards a certain quantity of materials from the
bowels of the earth; but, on the other hand, much rock is taken annually
from the land, in the shape of ballast, and afterwards thrown into the
sea, and by this means, in spite of prohibitory laws, many harbors, in
various parts of the world, have been blocked up. We rarely transport
heavy materials to higher levels, and our pyramids and cities are
chiefly constructed of stone brought down from more elevated situations.
By ploughing up thousands of square miles, and exposing a surface for
part of the year to the action of the elements, we assist the abrading
force of rain, and diminish the conservative effects of vegetation.




CHAPTER XLV.

INCLOSING OF FOSSILS IN PEAT, BROWN SAND, AND VOLCANIC EJECTIONS.


  Division of the subject--Imbedding of organic remains in deposits on
    emerged land--Growth of peat--Site of ancient forests in Europe now
    occupied by peat--Bog iron-ore--Preservation of animal substances in
    peat--Miring of quadrupeds--Bursting of the Solway moss--Great
    Dismal Swamp--Imbedding of organic bodies and human remains in blown
    sand--Moving sands of African deserts--De Luc on their recent
    origin--Buried temple of Ipsambul--Dried carcases in the
    sands--Towns overwhelmed by sand-floods--Imbedding of organic and
    other remains in volcanic formations on the land.


_Division of the subject._--The next subject of inquiry is the mode in
which the remains of animals and plants become fossil, or are buried in
the earth by natural causes. M. Constant Prevost has observed, that the
effects of geological causes are divisible into two great classes; those
produced during the submersion of land beneath the waters, and those
which take place after its emersion. Agreeably to this classification, I
shall consider, first, in what manner animal and vegetable remains
become included and preserved in deposits on emerged land, or that part
of the surface which is not _permanently_ covered by water, whether of
seas or lakes; secondly, the manner in which organic remains become
imbedded in subaqueous deposits.

Under the first division, I shall treat of the following topics:--1st,
the growth of peat, and the preservation of vegetable and animal remains
therein;--2dly, the burying of organic remains in blown sand;--3dly, of
the same in the ejections and alluviums of volcanoes;--4thly, in
alluviums generally, and in the ruins of landslips;--5thly, in the mud
and stalagmite of caves and fissures.


_Growth of Peat, and Preservation of Vegetable and Animal Remains
therein._

The generation of peat, when not completely under water, is confined to
moist situations, where the temperature is low, and where vegetables may
decompose without putrefying. It may consist of any of the numerous
plants which are capable of growing in such _stations_; but a species of
moss (_Sphagnum_) constitutes a considerable part of the peat found in
marshes of the north of Europe; this plant having the property of
throwing up new shoots in its upper part, while its lower extremities
are decaying.[1003] Reeds, rushes, and other aquatic plants may usually
be traced in peat; and their organization is often so entire that there
is no difficulty in discriminating the distinct species.

_Analysis of peat._--In general, says Sir H. Davy, one hundred parts of
dry peat contain from sixty to ninety-nine parts of matter destructible
by fire; and the residuum consists of earths usually of the same kind as
the substratum of clay, marl, gravel, or rock, on which they are found,
together with oxide of iron. "The peat of the chalk counties of
England," observes the same writer, "contains much gypsum: but I have
found very little in any specimens from Ireland or Scotland, and in
general these peats contain very little saline matter."[1004] From the
researches of Dr. MacCulloch, it appears that peat is intermediate
between simple vegetable matter and lignite, the conversion of peat to
lignite being gradual, and being brought about by a prolonged action of
water.[1005]

_Peat abundant in cold and humid climates._--Peat is sometimes formed on
a declivity in mountainous regions, where there is much moisture; but in
such situations it rarely, if ever, exceeds four feet in thickness. In
bogs, and in low grounds into which alluvial peat is drifted, it is
found forty feet thick, and upwards; but in such cases it generally owes
one half of its volume to the water which it contains. It has seldom, if
ever, been discovered within the tropics; and it rarely occurs in the
valleys, even in the south of France and Spain. It abounds more and
more, in proportion as we advance farther from the equator, and becomes
not only more frequent but more inflammable in northern latitudes.[1006]

The same phenomenon is repeated in the southern hemisphere. No peat is
found in Brazil, nor even in the swampy parts of the country drained by
the La Plata on the east side of South America, or in the island of
Chiloe on the west; yet when we reach the 45th degree of latitude and
examine the Chonos Archipelago or the Falkland Islands, and Tierra del
Fuego, we meet with an abundant growth of this substance. Almost all
plants contribute here by their decay to the production of peat, even
the grasses; but it is a singular fact, says Mr. Darwin, as contrasted
with what occurs in Europe, that no kind of moss enters into the
composition of the South American peat, which is formed by many plants,
but chiefly by that called by Brown _Astelia pumila_.[1007]

I learn from Dr. Forchhammer (1849) that water charged with vegetable
matter in solution does not throw down a deposit of peat in countries
where the mean temperature of the year is above 43° or 44° Fahrenheit.
Frost causes the precipitation of such peaty matter, but in warm
climates the attraction of the carbon for the oxygen of the air
mechanically mixed with the water increases with the increasing
temperature, and the dissolved vegetable matter or humic acid (which is
organic matter in a progressive state of decomposition) being converted
into carbonic acid, rises and is absorbed into the atmosphere, and thus
disappears.

_Extent of surface covered by peat._--There is a vast extent of surface
in Europe covered with peat, which, in Ireland, is said to extend over a
tenth of the whole island. One of the mosses on the Shannon is described
as being fifty miles long, by two or three broad; and the great marsh of
Montoire, near the mouth of the Loire, is mentioned, by Blavier, as
being more than fifty leagues in circumference. It is a curious and
well-ascertained fact, that many of these mosses of the north of Europe
occupy the place of forests of pine and oak, which have, many of them,
disappeared within the historical era. Such changes are brought about by
the fall of trees and the stagnation of water, caused by their trunks
and branches obstructing the free drainage of the atmospheric waters,
and giving rise to a marsh. In a warm climate, such decayed timber would
immediately be removed by insects, or by putrefaction; but, in the cold
temperature now prevailing in our latitudes, many examples are recorded
of marshes originating in this source. Thus, in Mar forest, in
Aberdeenshire, large trunks of Scotch fir, which had fallen from age and
decay, were soon immured in peat, formed partly out of their perishing
leaves and branches, and in part from the growth of other plants. We
also learn, that the overthrow of a forest by a storm, about the middle
of the seventeenth century, gave rise to a peat-moss near Lochbroom, in
Ross-shire, where, in less than half a century after the fall of the
trees, the inhabitants dug peat.[1008] Dr. Walker mentions a similar
change, when, in the year 1756, the whole wood of Drumlaurig in
Dumfries-shire was overset by the wind. Such events explain the
occurrence, both in Britain and on the Continent, of mosses where the
trees are all broken within two or three feet of the original surface,
and where their trunks all lie in the same direction.[1009]

It may however be suggested in these cases, that the soil had become
exhausted for trees, and that, on the principle of that natural rotation
which prevails in the vegetable world, one set of plants died out and
another succeeded. It is certainly a remarkable fact that in the Danish
islands, and in Jutland and Holstein, fir wood of various species,
especially Scotch fir, is found at the bottom of the peat-mosses,
although it is well ascertained that for the last five centuries no
Coniferæ have grown wild in these countries; the coniferous trees which
now flourish there having been all planted towards the close of the last
century.

Nothing is more common than the occurrence of buried trees at the bottom
of the Irish peat-mosses, as also in most of those of England, France,
and Holland; and they have been so often observed with parts of their
trunks standing erect, and with their roots fixed to the subsoil, that
no doubt can be entertained of their having generally grown on the spot.
They consist, for the most part, of the fir, the oak, and the birch:
where the subsoil is clay, the remains of oak are the most abundant;
where sand is the substratum, fir prevails. In the marsh of Curragh, in
the Isle of Man, vast trees are discovered standing firm on their
roots, though at the depth of eighteen or twenty feet below the surface.
Some naturalists have desired to refer the imbedding of timber in
peat-mosses to aqueous transportation, since rivers are well known to
float wood into lakes; but the facts above mentioned show that, in
numerous instances, such an hypothesis is inadmissible. It has,
moreover, been observed, that in Scotland, as also in many parts of the
Continent, the largest trees are found in those peat-mosses which lie in
the least elevated regions, and that the trees are proportionally
smaller in those which lie at higher levels; from which fact De Luc and
Walker have both inferred that the trees grew on the spot, for they
would naturally attain a greater size in lower and warmer levels. The
leaves, also, and fruits of each species, are continually found immersed
in the moss along with the parent trees; as, for example, the leaves and
acorns of the oak, the cones and leaves of the fir, and the nuts of the
hazel.

_Recent origin of some peat-mosses._--In Hatfield moss, in Yorkshire,
which appears clearly to have been a forest eighteen hundred years ago,
fir-trees have been found ninety feet long, and sold for masts and keels
of ships; oaks have also been discovered there above one hundred feet
long. The dimensions of an oak from this moss are given in the
Philosophical Transactions, No. 275, which must have been larger than
any tree now existing in the British dominions.

In the same moss of Hatfield, as well as in that of Kincardine, in
Scotland, and several others, Roman roads have been found covered to the
depth of eight feet by peat. All the coins, axes, arms, and other
utensils found in British and French mosses, are also Roman; so that a
considerable portion of the peat in European peat-bogs is evidently not
more ancient than the age of Julius Cæsar. Nor can any vestiges of the
ancient forests described by that general, along the line of the great
Roman way in Britain, be discovered, except in the ruined trunks of
trees in peat.

De Luc ascertained that the very sites of the aboriginal forests of
Hercinia, Semana, Ardennes, and several others, are now occupied by
mosses and fens; and a great part of these changes have, with much
probability, been attributed to the strict orders given by Severus, and
other emperors, to destroy all the wood in the conquered provinces.
Several of the British forests, however, which are now mosses, were cut
at different periods, by order of the English parliament, because they
harbored wolves or outlaws. Thus the Welsh woods were cut and burned, in
the reign of Edward I.; as were many of those in Ireland, by Henry II.,
to prevent the natives from harboring in them, and harassing his troops.

It is curious to reflect that considerable tracts have, by these
accidents, been permanently sterilized, and that, during a period when
civilization has been making great progress, large areas in Europe have,
by human agency, been rendered less capable of administering to the
wants of man. Rennie observes,[1010] with truth, that in those regions
alone which the Roman eagle never reached--in the remote circles of the
German empire, in Poland and Prussia, and still more in Norway, Sweden,
and the vast empire of Russia--can we see what Europe was before it
yielded to the power of Rome. Desolation now reigns where stately
forests of pine and oak once flourished, such as might now have supplied
all the navies of Europe with timber.

_Sources of bog iron-ore._--At the bottom of peat-mosses there is
sometimes found a cake, or "pan," as it is termed, of oxide of iron, and
the frequency of bog iron-ore is familiar to the mineralogist. The oak,
which is so often dyed black in peat, owes its color to the same metal.
From what source the iron is derived has often been a subject of
discussion, until the discoveries of Ehrenberg seem at length to have
removed the difficulty. He had observed in the marshes about Berlin a
substance of a deep ochre yellow passing into red, which covered the
bottom of the ditches, and which, where it had become dry after the
evaporation of the water, appeared exactly like oxide of iron. But under
the microscope it was found to consist of slender articulated threads or
plates, partly siliceous and partly ferruginous, of what he considered
an animalcule, _Gaillonella ferruginea_, but which most naturalists now
regard as a plant.[1011] There can be little doubt, therefore, that bog
iron-ore consists of an aggregate of millions of these organic bodies
invisible to the naked eye.[1012]

[Illustration: Fig. 101.

_Gaillonella ferruginea._

_a._ 2000 times magnified.]

_Preservation of animal substances in peat._--One interesting
circumstance attending the history of peat mosses is the high state of
preservation of animal substances buried in them for periods of many
years. In June, 1747, the body of a woman was found six feet deep, in a
peat-moor in the Isle of Axholm, in Lincolnshire. The antique sandals
on her feet afforded evidence of her having been buried there for many
ages: yet her nails, hair, and skin, are described as having shown
hardly any marks of decay. On the estate of the Earl of Moira, in
Ireland, a human body was dug up, a foot deep in gravel, covered with
eleven feet of moss; the body was completely clothed and the garments
seemed all to be made of hair. Before the use of wool was known in that
country the clothing of the inhabitants was made of hair, so that it
would appear that this body had been buried at that early period; yet it
was fresh and unimpaired.[1013] In the Philosophical Transactions we
find an example recorded of the bodies of two persons having been buried
in moist peat, in Derbyshire, in 1674, about a yard deep, which were
examined twenty-eight years and nine months afterwards; "the color of
their skin was fair and natural, their flesh soft as that of persons
newly dead."[1014]

Among other analogous facts we may mention, that in digging a pit for a
well near Dulverton, in Somersetshire, many pigs were found in various
postures, still entire. Their shape was well preserved, the skin, which
retained the hair, having assumed a dry, membranous appearance. Their
whole substance was converted into a white, friable, laminated,
inodorous, and tasteless substance; but which, when exposed to heat,
emitted an odor precisely similar to broiled bacon.[1015]

_Cause of the antiseptic property of peat._--We naturally ask whence
peat derives this antiseptic property? It has been attributed by some to
the carbonic and gallic acids which issue from decayed wood, as also to
the presence of charred wood in the lowest strata of many peat-mosses,
for charcoal is a powerful antiseptic, and capable of purifying water
already putrid. Vegetable gums and resins also may operate in the same
way.[1016]

The tannin occasionally present in peat is the produce, says Dr.
MacCulloch, of tormentilla, and some other plants; but the quantity he
thinks too small, and its occurrence too casual, to give rise to effects
of any importance. He hints that the soft parts of animal bodies,
preserved in peat-bogs, may have been converted into adipocire by the
action of water merely; an explanation which appears clearly applicable
to some of the cases above enumerated.[1017]

_Miring of quadrupeds._--The manner, however, in which peat contributes
to preserve, for indefinite periods, the harder parts of terrestrial
animals, is a subject of more immediate interest to the geologist. There
are two ways in which animals become occasionally buried in the peat of
marshy grounds; they either sink down into the semifluid mud, underlying
a turfy surface upon which they have rashly ventured, or, at other
times, as we shall see in the sequel, a bog "bursts," and animals may be
involved in the peaty alluvium.

In the extensive bogs of Newfoundland, cattle are sometimes found buried
with only their heads and necks above ground; and after having remained
for days in this situation, they have been drawn out by ropes and saved.
In Scotland, also, cattle venturing on the "quaking moss" are often
mired, or "laired," as it is termed; and in Ireland, Mr. King asserts
that the number of cattle which are lost in sloughs is quite
incredible.[1018]

_Solway moss._--The description given of the Solway moss will serve to
illustrate the general character of these boggy grounds. That moss,
observes Gilpin, is a flat area, about seven miles in circumference,
situated on the western confines of England and Scotland. Its surface is
covered with grass and rushes, presenting a dry crust and a fair
appearance; but it shakes under the least pressure, the bottom being
unsound and semifluid. The adventurous passenger, therefore, who
sometimes in dry seasons traverses this perilous waste, to save a few
miles, picks his cautious way over the rushy tussocks as they appear
before him, for here the soil is firmest. If his foot slip, or if he
venture to desert this mark of security, it is possible he may never
more be heard of.

"At the battle of Solway, in the time of Henry VIII. (1542), when the
Scotch army, commanded by Oliver Sinclair, was routed, an unfortunate
troop of horse, driven by their fears, plunged into this morass, which
instantly closed upon them. The tale was traditional, but it is now
authenticated; a man and horse, in complete armor, having been found by
peat-diggers, in the place where it was always supposed the affair had
happened. The skeleton of each was well preserved, and the different
parts of the armor easily distinguished."[1019]

The same moss, on the 16th of December, 1772, having been filled like a
great sponge with water during heavy rains, swelled to an unusual height
above the surrounding country, and then burst. The turfy covering seemed
for a time to act like the skin of a bladder retaining the fluid within,
till it forced a passage for itself, when a stream of black
half-consolidated mud began at first to creep over the plain,
resembling, in the rate of its progress, an ordinary lava-current. No
lives were lost, but the deluge totally overwhelmed some cottages, and
covered 400 acres. The highest parts of the original moss subsided to
the depth of about twenty-five feet; and the height of the moss, on the
lowest parts of the country which it invaded, was at least fifteen feet.

_Bursting of a peat-moss in Ireland._--A recent inundation in Sligo
(January, 1831), affords another example of this phenomenon. After a
sudden thaw of snow, the bog between Bloomfield and Geevah gave way; and
a black deluge, carrying with it the contents of a hundred acres of bog,
took the direction of a small stream and rolled on with the violence of
a torrent, sweeping along heath, timber, mud, and stones, and
overwhelming many meadows and arable land. On passing through some boggy
land, the flood swept out a wide and deep ravine, and part of the road
leading from Bloomfield to St. James's Well was completely carried away
from below the foundation for the breadth of 200 yards.

_Great Dismal Swamp._--I have described, in my Travels in North
America,[1020] an extensive swamp or morass, forty miles long from north
to south, and twenty-five wide, between the towns of Norfolk in
Virginia, and Weldon in North Carolina. It is called the "Great Dismal,"
and has somewhat the appearance of an inundated river-plain covered with
aquatic trees and shrubs, the soil being as black as that of a peat bog.
It is higher on all sides except one than the surrounding country,
towards which it sends forth streams of water to the north, east, and
south, receiving a supply from the west only. In its centre it rises 12
feet above the flat region which bounds it. The soil, to the depth of 15
feet, is formed of vegetable matter without any admixture, of earthy
particles, and offers an exception to a general rule before alluded to,
namely, that such peaty accumulations scarcely ever occur so far south
as lat. 36°, or in any region where the summer heat is so great as in
Virginia. In digging canals through the morass for the purpose of
obtaining timber, much of the black soil has been thrown out from time
to time, and exposed to the sun and air, in which case it soon rots away
so that nothing remains behind, showing clearly that it owes its
preservation to the shade afforded by a luxuriant vegetation and to the
constant evaporation of the spongy soil by which the air is cooled
during the hot months. The surface of the bog is carpeted with mosses,
and densely covered with ferns and reeds, above which many evergreen
shrubs and trees flourish, especially the White Cedar (_Cupressus
thyoides_), which stands firmly supported by its long tap roots in the
softest parts of the quagmire. Over the whole the deciduous cypress
(_Taxodium distichum_) is seen to tower with its spreading top, in full
leaf in the season when the sun's rays are hottest, and when, if not
intercepted by a screen of foliage, they might soon cause the fallen
leaves and dead plants of the preceding autumn to decompose, instead of
adding their contributions to the peaty mass. On the surface of the wide
morass lie innumerable trunks of large and tall trees, while thousands
of others, blown down by the winds, are buried at various depths in the
black mire below. They remind the geologist of the prostrate position of
large stems of Sigillaria and Lepidodendron, converted into coal in
ancient carboniferous rocks.

_Bones of herbivorous quadrupeds in peat._--The antlers of large and
full-grown stags are amongst the most common and conspicuous remains of
animals in peat. They are not horns which have been shed; for portions
of the skull are found attached, proving that the whole animal perished.
Bones of the ox, hog, horse, sheep, and other herbivorous animals, also
occur. M. Morren has discovered in the peat of Flanders the bones of
otters and beavers[1021]; but no remains have been met with belonging to
those extinct quadrupeds, of which the living congeners inhabit warmer
latitudes, such as the elephant, rhinoceros, hippopotamus, hyæna, and
tiger, though these are so common in superficial deposits of silt, mud,
sand, or stalactite, in various districts throughout Great Britain.
Their absence seems to imply that they had ceased to live before the
atmosphere of this part of the world acquired that cold and humid
character which favors the growth of peat.

_Remains of ships, &c., in peat mosses._--From the facts before
mentioned, that mosses occasionally burst, and descend in a fluid state
to lower levels, it will readily be seen that lakes and arms of the sea
may occasionally become the receptacles of drift peat. Of this,
accordingly, there are numerous examples; and hence the alternations of
clay and sand with different deposits of peat so frequent on some
coasts, as on those of the Baltic and German Ocean. We are informed by
Deguer, that remains of ships, nautical instruments, and oars, have been
found in many of the Dutch mosses; and Gerard, in his History of the
Valley of the Somme, mentions that in the lowest tier of that moss was
found a boat loaded with bricks, proving that these mosses were at one
period navigable lakes and arms of the sea, as were also many mosses on
the coast of Picardy, Zealand, and Friesland, from which soda and salt
are procured.[1022] The canoes, stone hatchets, and stone arrow-heads
found in peat in different parts of Great Britain, lead to similar
conclusions.


_Imbedding of human and other remains, and works of Art, in Blown Sand._

The drifting of sand may next be considered among the causes capable of
preserving organic remains and works of art on the emerged land.

_African Sands._--The sands of the African deserts have been driven by
the west winds over part of the arable land of Egypt, on the western
bank of the Nile, in those places where valleys open into the plain, or
where there are gorges through the Libyan mountains. By similar
sand-drifts the ruins of ancient cities have been buried between the
temple of Jupiter Ammon and Nubia. M. G. A. De Luc attempted to infer
the recent origin of our continents, from the fact that these moving
sands have arrived only in modern times at the fertile plains of the
Nile. The same scourge, he said, would have afflicted Egypt for ages
anterior to the times of history, had the continents risen above the
level of the sea several hundred centuries before our era.[1023] But the
author proceeded in this, as in all his other chronological
computations, on a multitude of gratuitous assumptions. He ought, in the
first place, to have demonstrated that the whole continent of Africa was
raised above the level of the sea at one period; for unless this point
was established, the region from whence the sands began to move might
have been the last addition made to Africa, and the commencement of the
sand-flood might have been long posterior to the laying dry of the
greater portion of that continent. That the different parts of Europe
were not all elevated at one time is now generally admitted. De Luc
should also have pointed out the depth of drift sand in various parts of
the great Libyan deserts, and have shown whether any valleys of large
dimensions had been filled up--how long these may have arrested the
progress of the sands, and how far the flood had upon the whole advanced
since the times of history.

We have seen that Sir J. G. Wilkinson is of opinion that, while the
sand-drift is making aggressions at certain points upon the fertile soil
of Egypt, the alluvial deposit of the Nile is advancing very generally
upon the desert; and that, upon the whole, the balance is greatly in
favor of the fertilizing mud.[1024]

No mode of interment can be conceived, more favorable to the
conservation of monuments for indefinite periods than that now so common
in the region immediately westward of the Nile. The sand which
surrounded and filled the great temple of Ipsambul, first discovered by
Burckhardt, and afterwards partially uncovered by Belzoni and Beechey,
was so fine as to resemble a fluid when put in motion. Neither the
features of the colossal figures, nor the color of the stucco with which
some were covered, nor the paintings on the walls, had received any
injury from being enveloped for ages in this dry impalpable dust.[1025]

At some future period, perhaps when the pyramids shall have perished,
the action of the sea, or an earthquake, may lay open to the day some of
these buried temples. Or we may suppose the desert to remain
undisturbed, and changes in the surrounding sea and land to modify the
climate and the direction of the prevailing winds, so that these may
then waft away the Libyan sands as gradually as they once brought them
to those regions. Thus, many a town and temple of higher antiquity than
Thebes or Memphis may reappear in their original antiquity, and a part
of the gloom which overhangs the history of the earlier nations be
dispelled.

Whole caravans are said to have been overwhelmed by the Libyan sands;
and Burckhardt informs us that "after passing the Akaba near the head of
the Red Sea, the bones of dead camels are the only guides of the pilgrim
through the wastes of sand."--"We did not see," says Captain Lyon,
speaking of a plain near the Soudah mountains, in Northern Africa, "the
least appearance of vegetation; but observed many skeletons of animals,
which had died of fatigue on the desert, and occasionally the grave of
some human being. All these bodies were so dried by the heat of the sun,
that putrefaction appears not to have taken place after death. In
recently expired animals I could not perceive the slightest offensive
smell; and in those long dead, the skin with the hair on it remained
unbroken and perfect, although so brittle as to break with a slight
blow. The sand-winds never cause these carcases to change their places;
for, in a short time, a slight mound is formed round them, and they
become stationary."[1026]

_Towns overwhelmed by sand floods._--The burying of several towns and
villages in England, France, and Jutland, by blown sand, is on record;
thus, for example, near St. Pol de Leon, in Brittany, a whole village
was completely buried beneath drift sand, so that nothing was seen but
the spire of the church.[1027] In Jutland marine shells adhering to
sea-weed are sometimes blown by the violence of the wind to the height
of 100 feet, and buried in similar hills of sand.

In Suffolk, in the year 1688, part of Downham was overwhelmed by sands
which had broken loose about 100 years before, from a warren five miles
to the south-west. This sand had, in the course of a century, travelled
five miles, and covered more than 1000 acres of land.[1028] A
considerable tract of cultivated land on the north coast of Cornwall has
been inundated by drift sand, forming hills several hundred feet above
the level of the sea, and composed of comminuted marine shells, in
which some terrestrial shells are enclosed entire. By the shifting of
these sands the ruins of ancient buildings have been discovered; and in
some cases where wells have been bored to a great depth, distinct
strata, separated by a vegetable crust, are visible. In some places, as
at New Quay, large masses have become sufficiently indurated to be used
for architectural purposes. The lapidification, which is still in
progress, appears to be due to oxide of iron held in solution by the
water which percolates the sand.[1029]


_Imbedding of Organic and other Remains in Volcanic Formations on the
Land._

I have in some degree anticipated the subject of this section in former
chapters, when speaking of the buried cities around Naples, and those on
the flanks of Etna (pp. 385. 400.). From the facts referred to, it
appeared that the preservation of human remains and works of art is
frequently due to the descent of floods caused by the copious rains
which accompany eruptions. These aqueous lavas, as they are called in
Campania, flow with great rapidity, and in 1822 surprised and
suffocated, as was stated, seven persons in the villages of St.
Sebastian and Massa, on the flanks of Vesuvius.

In the tuffs, moreover, or solidified mud, deposited by these aqueous
lavas, impressions of leaves and of trees have been observed. Some of
those, formed after the eruption of Vesuvius in 1822, are now preserved
in the museum at Naples.

Lava itself may become indirectly the means of preserving terrestrial
remains, by overflowing beds of ashes, pumice, and ejected matter, which
may have been showered down upon animals and plants, or upon human
remains. Few substances are better non-conductors of heat than volcanic
dust and scoriæ, so that a bed of such materials is rarely melted by a
superimposed lava-current. After consolidation, the lava affords secure
protection to the lighter and more removable mass below, in which the
organic relics may be enveloped. The Herculanean tuffs containing the
rolls of papyrus, of which the characters are still legible, have, as
was before remarked, been for ages covered by lava.

Another mode by which lava may tend to the conservation of imbedded
remains, at least of works of human art, is by its overflowing them when
it is not intensely heated, in which case they sometimes suffer little
or no injury.

Thus when the Etnean lava-current of 1669 covered fourteen towns and
villages, and part of the city of Catania, it did not melt down a great
number of statues and other articles in the vaults of Catania; and at
the depth of thirty-five feet in the same current, on the site of
Mompiliere, one of the buried towns, the bell of a church and some
statues were found uninjured (p. 401.).

We read of several buried cities in Central India, and among others of
Oujein (or Oojain) which about fifty years before the Christian era was
the seat of empire, of art, and of learning; but which in the time of
the Rajah Vicramaditya, was overwhelmed, according to tradition,
together with more than eighty other large towns in the provinces of
Malwa and Bagur, "by a shower of earth." The city which now bears the
name is situated a mile to the southward of the ancient town. On digging
on the spot where the latter is supposed to have stood, to the depth of
fifteen or eighteen feet, there are frequently discovered, says Mr.
Hunter, entire brick walls, pillars of stone, and pieces of wood of an
extraordinary hardness, besides utensils of various kinds, ancient
coins, and occasionally buried wheat in a state resembling
charcoal.[1030]

The soil which covers Oujein is described as "being of an ash-gray
color, with minute specks of black sand."[1031] And the "shower of
earth," said to have "fallen from heaven," has been attributed by some
travellers to volcanic agency. There are, however, no active volcanoes
in Central India, the nearest to Oujein being Denodur hill near Bhooj,
the capital of Cutch, 300 geographical miles distant, if indeed that
hill has ever poured out lava in historical times, which is doubted by
many.[1032] The latest writers on Oujein avow their suspicion that the
supposed "catastrophe" was nothing more than the political decline and
final abandonment of a great city which, like Nineveh or Babylon, and
many an ancient seat of empire in the East, after losing its importance
as a metropolis, became a heap of ruins. The rapidity with which the
sun-dried bricks, of which even the most splendid oriental palaces are
often constructed, crumble down when exposed to rain and sun, and are
converted into mounds of ordinary earth and clay, is well known.
According to Captain Dangerfield, trap tuff and columnar basalt
constitute the rocks in the environs of Oujein[1033], and the volcanic
nature of these formations, from which the materials of the bricks were
originally derived, may have led to the idea of the city having been
overwhelmed by a volcanic eruption.




CHAPTER XLVI.

BURYING OF FOSSILS IN ALLUVIAL DEPOSITS AND IN CAVES.


  Fossils in alluvium--Effects of sudden inundations--terrestrial
    animals most abundantly preserved in alluvium where earthquakes
    prevail--Marine alluvium--Buried town--Effects of Landslips--Organic
    remains in fissures and caves--Form and dimensions of caverns--their
    probable origin--Closed basins and subterranean rivers of the
    Morea--Katavothra--Formation of breccias with red cement--Human
    remains imbedded in Morea--Intermixture, in caves of South of France
    and elsewhere, of human remains and bones of extinct quadrupeds, no
    proof of former co-existence of man with those lost species.


_Fossils in alluvium._--The next subject for our consideration,
according to the division before proposed, is the embedding of organic
bodies in alluvium.

The gravel, sand, and mud in the bed of a river does not often contain
any animal or vegetable remains; for the whole mass is so continually
shifting its place, and the attrition of the various parts is so great,
that even the hardest rocks contained in it are, at length, ground down
to powder. But when sand and sediment are suddenly swept by a flood, and
then let fall upon the land, such an alluvium may envelop trees or the
remains of animals, which, in this manner, are often permanently
preserved. In the mud and sand produced by the floods in Scotland, in
1829, the dead and mutilated bodies of hares, rabbits, moles, mice,
partridges, and even the bodies of men, were found partially
buried.[1034] But in these and similar cases one flood usually effaces
the memorials left by another, and there is rarely a sufficient depth of
undisturbed transported matter, in any one spot, to preserve the organic
remains for ages from destruction.

Where earthquakes prevail, and the levels of a country are changed from
time to time, the remains of animals may more easily be inhumed and
protected from disintegration. Portions of plains, loaded with alluvial
accumulations by transient floods, may be gradually upraised; and, if
any organic remains have been imbedded in the transported materials,
they may, after such elevation, be placed beyond the reach of the
erosive power of streams. In districts where the drainage is repeatedly
deranged by subterranean movements, every fissure, every hollow caused
by the sinking in of land, becomes a depository of organic and inorganic
substances, hurried along by transient floods.

_Marine alluvium._--In May, 1787, a dreadful inundation of the sea was
caused at Coringa, Ingeram, and other places, on the coast of
Coromandel, in the East Indies, by a hurricane blowing from the N. E.,
which raised the waters so that they rolled inland to the distance of
about twenty miles from the shore, swept away many villages, drowned
more than 10,000 people, and left the country covered with marine mud,
on which the carcasses of about 100,000 head of cattle were strewed. An
old tradition of the natives of a similar flood, said to have happened
about a century before, was, till this event, regarded as fabulous by
the European settlers.[1035] The same coast of Coromandel was, so late
as May, 1832, the scene of another catastrophe of the same kind; and
when the inundation subsided, several vessels were seen grounded in the
fields of the low country about Coringa.

Many of the storms termed hurricanes have evidently been connected with
submarine earthquakes, as is shown by the atmospheric phenomena
attendant on them, and by the sounds heard in the ground and the odors
emitted. Such were the circumstances which accompanied the swell of the
sea in Jamaica, in 1780, when a great wave desolated the western coast,
and bursting upon Savanna la Mar, swept away the whole town in an
instant, so that not a vestige of man, beast, or habitation, was seen
upon the surface.[1036]

_Houses and works of art in alluvial deposits._--A very ancient
subterranean town, apparently of Hindoo origin, was discovered in India
in 1833, in digging the Doab canal. Its site is north of Saharunpore,
near the town of Behat, and seventeen feet below the present surface of
the country. More than 170 coins of silver and copper have already been
found, and many articles in metal and earthenware. The overlying deposit
consisted of about five feet of river sand, with a substratum about
twelve feet thick of red alluvial clay. In the neighborhood are several
rivers and torrents, which descend from the mountains charged with vast
quantities of mud, sand, and shingle; and within the memory of persons
now living the modern Behat has been threatened by an inundation, which,
after retreating, left the neighboring country strewed over with a
superficial covering of sand several feet thick. In sinking wells in the
environs, masses of shingle and boulders have been reached resembling
those now in the river-channels of the same district, under a deposit of
thirty feet of reddish loam. Captain Cautley, therefore, who directed
the excavations, supposes that the matter discharged by torrents has
gradually raised the whole country skirting the base of the lower hills;
and that the ancient town, having been originally built in a hollow, was
submerged by floods, and covered over with sediment seventeen feet in
thickness.[1037]

We are informed, by M. Boblaye, that in the Morea, the formation termed
céramique, consisting of pottery, tiles, and bricks, intermixed with
various works of art, enters so largely into the alluvium and vegetable
soil upon the plains of Greece, and into hard and crystalline breccias
which have been formed at the foot of declivities, that it constitutes
an important stratum which might, in the absence of zoological
characters, serve to mark our epoch in a most indestructible
manner.[1038]

_Landslips._--The landslip, by suddenly precipitating large masses of
rock and soil into a valley, overwhelms a multitude of animals, and
sometimes buries permanently whole villages, with their inhabitants and
large herds of cattle. Thus three villages, with their entire
population, were covered, when the mountain of Piz fell in 1772, in the
district of Treviso, in the state of Venice,[1039] and part of Mount
Grenier, south of Chambery, in Savoy, which fell down in the year 1248,
buried five parishes, including the town and church of St. André, the
ruins occupying an extent of about nine square miles.[1040]

The number of lives lost by the slide of the Rossberg, in Switzerland,
in 1806, was estimated at more than 800, a great number of the bodies,
as well as several villages and scattered houses, being buried deep
under mud and rock. In the same country, several hundred cottages, with
eighteen of their inhabitants and a great number of cows, goats, and
sheep, were victims to the sudden fall of a bed of stones, thirty yards
deep, which descended from the summits of the Diablerets in Vallais. In
the year 1618, a portion of Mount Conto fell, in the county of
Chiavenna, in Switzerland, and buried the town of Pleurs with all its
inhabitants, to the number of 2430.

It is unnecessary to multiply examples of similar local catastrophes,
which however numerous they may have been in mountainous parts of
Europe, within the historical period, have been, nevertheless, of rare
occurrence when compared to events of the same kind which have taken
place in regions convulsed by earthquakes. It is then that enormous
masses of rock and earth, even in comparatively low and level countries,
are detached from the sides of valleys, and cast down into the river
courses, and often so unexpectedly that they overwhelm, even in the
daytime, every living thing upon the plains.


_Preservation of Organic Remains in Fissures and Caves._

In the history of earthquakes it was shown that many hundreds of new
fissures and chasms had opened in certain regions during the last 150
years, some of which are described as being of unfathomable depth. We
also perceive that mountain masses have been violently fractured and
dislocated, during their rise above the level of the sea; and thus we
may account for the existence of many cavities in the interior of the
earth by the simple agency of earthquakes; but there are some caverns,
especially in limestone rocks, which, although usually, if not always,
connected with rents, are nevertheless of such forms, and dimensions,
alternately expanding into spacious chambers, and then contracting again
into narrow passages, that it is difficult to conceive that they can owe
their origin to the mere fracturing and displacement of solid masses.

In the limestone of Kentucky, in the basin of Green River, one of the
tributaries of the Ohio, a line of underground cavities has been traced
in one direction for a distance of ten miles, without any termination;
and one of the chambers, of which there are many, all connected by
narrow tunnels, is no less than ten acres in area and 150 feet in its
greatest height. Besides the principal series of "antres vast," there
are a great many lateral embranchments not yet explored.[1041]

The cavernous structure here alluded to is not altogether confined to
calcareous rocks; for it has lately been observed in micaceous and
argillaceous schist in the Grecian island of Thermia (Cythnos of the
ancients), one of the Cyclades. Here also spacious halls, with rounded
and irregular walls, are connected together by narrow passages or
tunnels, and there are many lateral branches which have no outlet. A
current of water has evidently at some period flowed through the whole,
and left a muddy deposit of bluish clay upon the floor; but the erosive
action of the stream cannot be supposed to have given rise to the
excavations in the first instance. M. Virlet suggests that fissures were
first caused by earthquakes, and that these fissures became the chimneys
or vents for the disengagement of gas, generated below by volcanic heat.
Gases, he observes, such as the muriatic, sulphuric, fluoric, and
others, might, if raised to a high temperature, alter and decompose the
rocks which they traverse. There are signs of the former action of such
vapors in rents of the micaceous schist of Thermia, and thermal springs
now issue from the grottoes of that island. We may suppose that
afterwards the elements of the decomposed rocks were gradually removed
in a state of solution by mineral waters; a theory which, according to
M. Virlet, is confirmed by the effect of heated gases which escape from
rents in the isthmus of Corinth, and which have greatly altered and
corroded the hard siliceous and jaspideous rocks.[1042]

When we reflect on the quantity of carbonate of lime annually poured out
by mineral waters, we are prepared to admit that large cavities must, in
the course of ages, be formed at considerable depths below the surface
in calcareous rocks.[1043] These rocks, it will be remembered, are at
once more soluble, more permeable, and more fragile, than any others, at
least all the compact varieties are very easily broken by the movements
of earthquakes, which would produce only flexures in argillaceous
strata. Fissures once formed in limestone are not liable, as in many
other formations, to become closed up by impervious clayey matter, and
hence a stream of acidulous water might for ages obtain a free and
unobstructed passage.[1044]

_Morea._--Nothing is more common in limestone districts than the
engulfment of rivers, which after holding a subterranean course for many
miles escape again by some new outlet. As they are usually charged with
fine sediment, and often with sand and pebbles where they enter, whereas
they are usually pure and limpid where they flow out again, they must
deposit much matter in empty spaces in the interior of the earth. In
addition to the materials thus introduced, stalagmite, or carbonate of
lime, drops from the roofs of caverns, and in this mixture the bones of
animals washed in by rivers are often entombed. In this manner we may
account for those bony breccias which we often find in caves, some of
which are of high antiquity while others are very recent and in daily
progress. In no district are engulfed streams more conspicuous than in
the Morea, where the phenomena attending them have been lately studied
and described in great detail by M. Boblaye and his fellow-laborers of
the French expedition to Greece.[1045] Their account is peculiarly
interesting to geologists, because it throws light on the red osseous
breccias containing the bones of extinct quadrupeds which are so common
in almost all the countries bordering the Mediterranean. It appears that
the numerous caverns of the Morea occur in a compact limestone, of the
age of the English chalk, immediately below which are arenaceous strata
referred to the period of our greensand. In the more elevated districts
of that peninsula there are many deep land-locked valleys, or basins,
closed round on all sides by mountains of fissured and cavernous
limestone. The year is divided almost as distinctly as between the
tropics into a rainy season, which lasts upwards of four months, and a
season of drought of nearly eight months' duration. When the torrents
are swollen by the rains, they rush from surrounding heights into the
inclosed basins; but, instead of giving rise to lakes, as would be the
case in most other countries, they are received into gulfs or chasms,
called by the Greeks "Katavothra," and which correspond to what are
termed "swallow-holes" in the north of England. The water of these
torrents is charged with pebbles and red ochreous earth, resembling
precisely the well-known cement of the osseous breccias of the
Mediterranean. It dissolves in acids with effervescence, and leaves a
residue of hydrated oxide of iron, granular iron, impalpable grains of
silex, and small crystals of quartz. Soil of the same description
abounds everywhere on the surface of the decomposing limestone in
Greece, that rock containing in it much siliceous and ferruginous
matter.

Many of the Katavothra being insufficient to give passage to all the
water in the rainy season, a temporary lake is formed round the mouth of
the chasm, which then becomes still farther obstructed by pebbles, sand,
and red mud, thrown down from the turbid waters. The lake being thus
raised, its waters generally escape through other openings, at higher
levels, around the borders of the plain, constituting the bottom of the
closed basin.

In some places, as at Kavaros and Tripolitza, where the principal
discharge is by a gulf in the middle of the plain, nothing can be seen
over the opening in summer, when the lake dries up, but a deposit of red
mud, cracked in all directions. But the Katavothron is more commonly
situated at the foot of the surrounding escarpment of limestone; and in
that case there is sometimes room enough to allow a person to enter, in
summer, and even to penetrate far into the interior. Within is seen a
suite of chambers, communicating with each other by narrow passages; and
M. Virlet relates, that in one instance he observed, near the entrance,
human bones imbedded in recent red mud, mingled with the remains of
plants and animals of species now inhabiting the Morea. It is not
wonderful, he says, that the bones of man should be met with in such
receptacles; for so murderous have been the late wars in Greece, that
skeletons are often seen lying exposed on the surface of the
country.[1046]

In summer, when no water is flowing into the Katavothron, its mouth,
half closed up with red mud, is masked by a vigorous vegetation, which
is cherished by the moisture of the place. It is then the favorite
hiding-place and den of foxes and jackals; so that the same cavity
serves at one season of the year for the habitation of carnivorous
beasts, and at another as the channel of an engulfed river. Near the
mouth of one chasm, M. Boblaye and his companions saw the carcass of a
horse, in part devoured, the size of which seemed to have prevented the
jackals from dragging it in: the marks of their teeth were observed on
the bones, and it was evident that the floods of the ensuing winter
would wash in whatsoever might remain of the skeleton.

It has been stated that the waters of all these torrents of the Morea
are turbid where they are engulfed; but when they come out again, often
at the distance of many leagues, they are perfectly clear and limpid,
being only charged occasionally with a slight quantity of calcareous
sand. The points of efflux are usually near the sea-shores of the Morea,
but sometimes they are submarine; and when this is the case, the sands
are seen to boil up for a considerable space, and the surface of the
sea, in calm weather, swells in large convex waves. It is curious to
reflect, that when this discharge fails in seasons of drought, the
pressure of the sea may force its salt waters into subterraneous
caverns, and carry in marine sand and shells, to be mingled with
ossiferous mud, and the remains of terrestrial animals.

In general, however, the efflux of water at these inferior openings is
surprisingly uniform. It seems, therefore, that the large caverns in the
interior must serve as reservoirs, and that the water escapes gradually
from them, in consequence of the smallness of the rents and passages by
which they communicate with the surface.

The phenomena above described are not confined to the Morea, but occur
in Greece generally, and in those parts of Italy, Spain, Asia Minor, and
Syria, where the formations of the Morea extend. The Copaic lake in
Boeotia has no outlet, except by underground channels; and hence we
can explain those traditional and historical accounts of its having
gained on the surrounding plains and overflowed towns, as such floods
must have happened whenever the outlet was partially choked up by mud,
gravel, or the subsidence of rocks, caused by earthquakes. When speaking
of the numerous fissures in the limestone of Greece, M. Boblaye reminds
us of the famous earthquake of 469 B.C., when, as we learn from Cicero,
Plutarch, Strabo, and Pliny, Sparta was laid in ruins, part of the
summit of Mount Taygetus torn off, and numerous gulfs and fissures
caused in the rocks of Laconia.

During the great earthquake of 1693, in Sicily, several thousand people
were at once entombed in the ruins of caverns in limestone, at Sortino
Vecchio; and, at the same time, a large stream, which had issued for
ages from one of the grottoes below that town, changed suddenly its
subterranean course, and came out from the mouth of a cave lower down
the valley, where no water had previously flowed. To this new point the
ancient water-mills were transferred, as I learnt when I visited the
spot in 1829.

When the courses of engulfed rivers are thus liable to change, from time
to time, by alterations in the levels of a country, and by the rending
and shattering of mountain masses, we must suppose that the dens of wild
beasts will sometimes be inundated by subterranean floods, and their
carcasses buried under heaps of alluvium. The bones, moreover, of
individuals which have died in the recesses of caves, or of animals
which have been carried in for prey, may be drifted along, and mixed up
with mud, sand, and fragments of rocks, so as to form osseous breccias.

In 1833 I had an opportunity of examining the celebrated caves of
Franconia, and among others that of Rabenstein, newly discovered. Their
general form, and the nature and arrangement of their contents, appeared
to me to agree perfectly with the notion of their having once served as
the channels of subterranean rivers. This mode of accounting for the
introduction of transported matter into the Franconian and other caves,
filled up as they often are even to their roofs with osseous breccia,
was long ago proposed by M. C. Prevost,[1047] and seems at length to be
very generally adopted. But I do not doubt that bears inhabited some of
the German caves, or that the cavern of Kirkdale, in Yorkshire, was once
the den of hyænas. The abundance of bony dung, associated with hyænas'
bones, has been pointed out by Dr. Buckland, and with reason, as
confirmatory of this opinion.

The same author observed in every cave examined by him in Germany, that
deposits of mud and sand, with or without rolled pebbles and angular
fragments of rock, were covered over with a _single_ crust of
stalagmite.[1048] In the English caves he remarked a similar absence of
_alterations_ of alluvium and stalagmite. But Dr. Schmerling has
discovered in a cavern at Chockier, about two leagues from Liège, three
distinct beds of stalagmite, and between each of them a mass of breccia,
and mud mixed with quartz pebbles, and in the three deposits the bones
of extinct quadrupeds.[1049]

This exception does not invalidate the generality of the phenomenon
pointed out by Dr. Buckland, one cause of which may perhaps be this,
that if several floods pass at different intervals of time through a
subterranean passage, the last, if it has power to drift along fragments
of rock, will also tear up any alternating stalagmitic and alluvial beds
that may have been previously formed. Another cause may be, that a
particular line of caverns will rarely be so situated, in relation to
the lowest levels of a country, as to become, at two distinct epochs,
the receptacle of engulfed rivers; and if this should happen, some of
the caves, or at least the tunnels of communication, may at the first
period be entirely choked up with transported matter, so as not to allow
the subsequent passage of water in the same direction.

As the same chasms may remain open throughout periods of indefinite
duration, the species inhabiting a country may in the meantime be
greatly changed, and thus the remains of animals belonging to very
different epochs may become mingled together in a common tomb. For this
reason it is often difficult to separate the monuments of the human
epoch from those relating to periods long antecedent, and it was not
without great care and skill that Dr. Buckland was enabled to guard
against such anachronisms in his investigations of several of the
English caves. He mentions that human skeletons were found in the cave
of Wokey Hole, near Wells, in the Mendips, dispersed through reddish mud
and clay, and some of them united by stalagmite into a firm osseous
breccia. "The spot on which they lie is within reach of the highest
floods of the adjacent river, and the mud in which they are buried is
evidently fluviatile."[1050]

In speaking of the cave of Paviland on the coast of Glamorganshire the
same author states that the entire mass through which bones were
dispersed appeared to have been disturbed by ancient diggings, so that
the remains of extinct animals had become mixed with recent bones and
shells. In the same cave was a human skeleton, and the remains of recent
testacea of eatable species, which may have been carried in by man.

In several caverns on the banks of the Meuse, near Liège, Dr. Schmerling
has found human bones in the same mud and breccia with those of the
elephant, rhinoceros, bear, and other quadrupeds of extinct species. He
has observed none of the dung of any of these animals: and from this
circumstance, and the appearance of the mud and pebbles, he concludes
that these caverns were never inhabited by wild beasts, but washed in by
a current of water. As the human skulls and bones were in fragments, and
no entire skeleton had been found, he does not believe that these caves
were places of sepulture, but that the human remains were washed in at
the same time as the bones of extinct quadrupeds, and that these lost
species of mammalia co-existed on the earth with man.

_Caverns in the south of France._--Similar associations in the south of
France, of human bones and works of art, with remains of extinct
quadrupeds, have induced other geologists to maintain that man was an
inhabitant of that part of Europe before the rhinoceros, hyæna, tiger,
and many fossil species disappeared. I may first mention the cavern of
Bize, in the department of Aude, where M. Marcel de Serres met with a
small number of human bones mixed with those of extinct animals and with
land shells. They occur in a calcareous stony mass, bound together by a
cement of stalagmite. On examining the same caverns, M. Tournal found
not only in these calcareous beds, but also in a black mud which
overlies a red osseous mud, several human teeth, together with broken
angular fragments of a rude kind of pottery, and also recent marine and
terrestrial shells. The teeth preserve their enamel; but the fangs are
so much altered as to adhere strongly when applied to the tongue. Of the
terrestrial shells thus associated with the bones and pottery, the most
common are _Cyclostoma elegans_, _Bulimus decollatus_, _Helix
nemoralis_, and _H. nitida_. Among the marine are found _Pecten
jacobæus_, _Mytilus edulis_, and _Natica mille-punctata_, all of them
eatable kinds, and which may have been brought there for food. Bones
were found in the same mass belonging to three new species of deer, the
brown bear (_Ursus arctoïdeus_), and the wild bull (_Bos urus_),
formerly a native of Germany.[1051]

In the same parts of France, M. de Christol has found in caverns in a
tertiary limestone at Pondres and Souvignargues, two leagues north of
Lunel-viel, in the department of Herault, human bones and pottery
confusedly mixed with remains of the rhinoceros, bear, hyæna, and other
terrestrial mammifers. They were imbedded in alluvial mud, of the
solidity of calcareous tufa, and containing some flint pebbles and
fragments of the limestone of the country. Beneath this mixed
accumulation, which sometimes attained a thickness of thirteen feet, is
the original floor of the cavern, about a foot thick, covered with bones
and the dung of animals (_album græcum_), in a sandy and tufaceous
cement.

The human bones in these caverns of Pondres and Souvignargues were
found, upon a careful analysis, to have parted with their animal matter
to as great a degree as those of the hyæna which accompany them, and are
equally brittle, and adhere as strongly to the tongue.

In order to compare the degree of alteration of these bones with those
known to be of high antiquity, M. Marcel de Serres and M. Ballard,
chemists of Montpelier, procured some from a Gaulish sarcophagus, in the
plain of Lunel, supposed to have been buried for fourteen or fifteen
centuries at least. In these the cellular tissue was empty, but they
were more solid than fresh bones. They did not adhere to the tongue in
the same manner as those of the caverns of Bize and Pondres, yet they
had lost at least three fourths of their original animal matter.

The superior solidity of the Gaulish bones to those in a fresh skeleton
is a fact in perfect accordance with the observations made by Dr.
Mantell on bones taken from a Saxon tumulus near Lewes.

M. Tessier has also described a cavern near Mialet, in the department
of Gard, where the remains of the bear and other animals were mingled
confusedly with human bones, coarse pottery, teeth pierced for amulets,
pointed fragments of bone, bracelets of bronze, and a Roman urn. Part of
this deposit reached to the roof of the cavity, and adhered firmly to
it. The author suggests that the exterior portion of the grotto may at
one period have been a den of bears, and that afterwards the aboriginal
inhabitants of the country took possession of it either for a dwelling
or a burial-place, and left there the coarse pottery, amulets, and
pointed pieces of bone. At a third period the Romans may have used the
cavern as a place of sepulture or concealment, and to them may have
belonged the urn and bracelets of metal. If we then suppose the course
of the neighboring river to be impeded by some temporary cause, a flood
would be occasioned, which, rushing into the open grotto, may have
washed all the remains into the interior caves and tunnels, heaping the
whole confusedly together.[1052]

In the controversy which has arisen on this subject, MM. Marcel de
Serres, De Christol, Tournal, and others, have contended, that the
phenomena of this and other caverns in the south of France prove that
the fossil rhinoceros, hyæna, bear, and several other lost species, were
once contemporaneous inhabitants of the country, together with man;
while M. Desnoyers has supported the opposite opinion. The flint
hatchets and arrow-heads, he says, and the pointed bones and coarse
pottery of many French and English caves, agree precisely in character
with those found in the tumuli, and under the dolmens (rude altars of
unhewn stone) of the primitive inhabitants of Gaul, Britain, and
Germany. The human bones, therefore, in the caves which are associated
with such fabricated objects, must belong not to antediluvian periods,
but to a people in the same stage of civilization as those who
constructed the tumuli and altars.

In the Gaulish monuments we find, together with the objects of industry
above mentioned, the bones of wild and domestic animals of species now
inhabiting Europe, particularly of deer, sheep, wild-boars, dogs,
horses, and oxen. This fact has been ascertained in Quercy, and other
provinces; and it is supposed by antiquaries that the animals in
question were placed beneath the Celtic altars in memory of sacrifices
offered to the Gaulish divinity Hesus, and in the tombs to commemorate
funeral repasts, and also from a supposition prevalent among savage
nations, which induces them to lay up provisions for the manes of the
dead in a future life. But in none of these ancient monuments have any
bones been found of the elephant, rhinoceros, hyæna, tiger, and other
quadrupeds, such as are found in caves, as might certainly have been
expected had these species continued to flourish at the time that this
part of Gaul was inhabited by man.[1053]

We are also reminded by M. Desnoyers of a passage in Florus, in which it
is related that Cæsar ordered the caves into which the Aquitanian Gauls
had retreated to be closed up.[1054] It is also on record, that so late
as the eighth century, the Aquitanians defended themselves in caverns
against King Pepin. As many of these caverns, therefore, may have served
in succession as temples and habitations, as places of sepulture,
concealment, or defence, it is easy to conceive that human bones, and
those of animals, in osseous breccias of much older date, may have been
swept away together, by inundations, and then buried in one promiscuous
heap.

It is not on the evidence of such intermixtures that we ought readily to
admit either the high antiquity of the human race, or the recent date of
certain lost species of quadrupeds.

Among the various modes in which the bones of animals become preserved,
independently of the agency of land floods and engulfed rivers, I may
mention that open fissures often serve as natural pitfalls in which
herbivorous animals perish. This may happen the more readily when they
are chased by beasts of prey, or when surprised while carelessly
browsing on the shrubs which so often overgrow and conceal the edges of
fissures.[1055]

During the excavations recently made near Behat in India, the bones of
two deer were found at the bottom of an ancient well which had been
filled up with alluvial loam. Their horns were broken to pieces, but the
jaw bones and other parts of the skeleton remained tolerably perfect.
"Their presence," says Captain Cautley, "is easily accounted for, as a
great number of these and other animals are constantly lost in galloping
over the jungles and among the high grass by falling into deserted
wells."[1056]

Above the village of Selside, near Ingleborough in Yorkshire, a chasm of
enormous but unknown depth occurs in the scar-limestone, a member of the
carboniferous series. "The chasm," says Professor Sedgwick, "is
surrounded by grassy shelving banks, and many animals, tempted towards
its brink, have fallen down and perished in it. The approach of cattle
is now prevented by a strong lofty wall; but there can be no doubt that,
during the last two or three thousand years, great masses of bony
breccia must have accumulated in the lower parts of the great fissure,
which probably descends through the whole thickness of the
scar-limestone, to the depth of perhaps five or six hundred feet."[1057]

When any of these natural pit-falls happen to communicate with lines of
subterranean caverns, the bones, earth, and breccia, may sink by their
own weight, or be washed into the vaults below.

At the north extremity of the rock of Gibraltar are perpendicular
fissures, on the ledges of which a number of hawks nestle and rear their
young in the breeding season. They throw down from their nests the bones
of small birds, mice, and other animals, on which they feed, and these
are gradually united into a breccia of angular fragments of the
decomposing limestone with a cement of red earth.

At the pass of Escrinet in France, on the northern escarpment of the
Coiron hills, near Aubenas, I have seen a breccia in the act of forming.
Small pieces of disintegrating limestone are transported, during heavy
rains, by a streamlet, to the foot of the declivity, where land shells
are very abundant. The shells and pieces of stone soon become cemented
together by stalagmite into a compact mass, and the talus thus formed is
in one place fifty feet deep, and five hundred yards wide. So firmly is
the lowest portion consolidated, that it is quarried for mill-stones.

_Recent, stalagmitic limestone of Cuba._--One of the most singular
examples of the recent growth of stalagmitic limestone in caves and
fissures is that described by Mr. R. C. Taylor, as observable on the
north-east part of the island of Cuba.[1058] The country there is
composed of a white marble, in which are numerous cavities, partially
filled with a calcareous deposit of a brick-red color. In this red
deposit are shells, or often the hollow casts of shells, chiefly
referable to eight or nine species of land snails, a few scattered bones
of quadrupeds, and, what is still more singular, marine univalve shells,
often at the height of many hundred, or even one thousand feet above the
sea. The following explanation is given of the gradual increase of this
deposit. Land snails of the genera Helix, Cyclostoma, Pupa, and
Clausilia, retire into the caves, the floors of which are strewed with
myriads of their dead and unoccupied shells, at the same time that water
infiltered through the mountain throws down carbonate of lime,
enveloping the shells, together with fragments of the white limestone
which occasionally falls from the roof. Multitudes of bats resort to the
caves; and their dung, which is of a bright red color, (probably derived
from the berries on which they feed,) imparts its red hue to the mass.
Sometimes also the Hutia, or great Indian rat of the island, dies and
leaves its bones in the caves. "At certain seasons the soldier-crabs
resort to the sea-shore, and then return from their pilgrimage, each
carrying with them, or rather dragging, the shell of some marine
univalve for many a weary mile. They may be traced even at the distance
of eight or ten miles from the shore, on the summit of mountains 1200
feet high, like the pilgrims of the olden times, each bearing his shell
to denote the character and extent of his wanderings." By this means
several species of marine testacea of the genera Trochus, Turbo,
Littorina, and Monodonta, are conveyed into inland caverns, and enter
into the composition of the newly formed rock.




CHAPTER XLVII.

IMBEDDING OF ORGANIC REMAINS IN SUBAQUEOUS DEPOSITS.


  Division of the subject--Imbedding of terrestrial animals and
    plants--Increased specific gravity of wood sunk to great depths in
    the sea--Drift-timber of the Mackenzie in Slave Lake and Polar
    Sea--Floating trees in the Mississippi--in the Gulf Stream--on the
    coast of Iceland, Spitzbergen, and Labrador--Submarine
    forests--Example on coast of Hampshire--Mineralization of
    plants--Imbedding of marine plants--of insects--of reptiles--Bones
    of birds why rare--Imbedding of terrestrial quadrupeds by river
    floods--Skeletons in recent shell marl--Imbedding of mammiferous
    remains in marine strata.


_Division of the subject._--Having treated of the imbedding of organic
remains in deposits formed upon the land, I shall next consider the
including of the same in deposits formed under water.

It will be convenient to divide this branch of our subject into three
parts; considering, first, the various modes whereby the relics of
_terrestrial_ species may be buried in subaqueous formations; secondly,
the modes whereby animals and plants inhabiting _fresh water_ may be so
entombed; thirdly, how _marine_ species may become preserved in new
strata.

The phenomena above enumerated demand a fuller share of attention than
those previously examined, since the deposits which originate upon dry
land are insignificant in thickness, superficial extent, and durability,
when contrasted with those of subaqueous origin. At the same time, the
study of the latter is beset with greater difficulties; for we are here
concerned with the results of processes much farther removed from the
sphere of ordinary observation. There is, indeed, no circumstance which
so seriously impedes the acquisition of just views in our science as an
habitual disregard of the important fact, that the reproductive effects
of the principal agents of change are confined to another element--to
that larger portion of the globe, from which by our very organization we
are almost entirely excluded.[1059]


_Imbedding of Terrestrial Plants._

When a tree falls into a river from the undermining of the banks or from
being washed in by a torrent or flood, it floats on the surface, not
because the woody portion is specifically lighter than water, but
because it is full of pores containing air. When soaked for a
considerable time, the water makes its way into these pores, and the
wood becomes _waterlogged_ and sinks. The time required for this
process varies in different woods; but several kinds may be drifted to
great distances, sometimes across the ocean, before they lose their
buoyancy.

_Wood sunk to a great depth in the sea._--If wood be sunk to vast depths
in the sea, it may be impregnated with water suddenly. Captain Scoresby
informs us, in his Account of the Arctic Regions, that on one occasion a
whale, on being harpooned, ran out all the lines in the boat, which it
then dragged under water, to the depth of several thousand feet, the men
having just time to escape to a piece of ice. When the fish returned to
the surface "to blow," it was struck a second time, and soon afterwards
killed. The moment it expired it began to sink,--an unusual
circumstance, which was found to be caused by the weight of the sunken
boat, which still remained attached to it. By means of harpoons and
ropes the fish was prevented from sinking, until it was released from
the weight by connecting a rope to the lines of the attached boat, which
was no sooner done than the fish rose again to the surface. The sunken
boat was then hauled up with great labor; for so heavy was it, that
although before the accident it would have been buoyant when full of
water, yet it now required a boat at each end to keep it from sinking.
"When it was hoisted into the ship, the paint came off the wood in large
sheets; and the planks, which were of wainscot, were as completely
soaked in every pore as if they had lain at the bottom of the sea since
the flood! A wooden apparatus that accompanied the boat in its progress
through the deep, consisting chiefly of a piece of thick deal, about
fifteen inches square, happened to fall overboard, and, though it
originally consisted of the lightest fir, sank in the water like a
stone. The boat was rendered useless; even the wood of which it was
built, on being offered to the cook for fuel, was tried and rejected as
incombustible."[1060]

Captain Scoresby found that, by sinking pieces of fir, elm, ash, &c., to
the depth of four thousand and sometimes six thousand feet, they became
impregnated with sea-water, and when drawn up again, after immersion for
an hour, would no longer float. The effect of this impregnation was to
increase the dimensions as well as the specific gravity of the wood,
every solid inch having increased one-twentieth in size and twenty-one
twenty-fifths in weight.[1061]

_Drift-wood of the Mackenzie River._--When timber is drifted down by a
river, it is often arrested by lakes; and, becoming water-logged, it may
sink and be imbedded in lacustrine strata, if any be there forming;
sometimes a portion floats on till it reaches the sea. In the course of
the Mackenzie River we have an example of vast accumulations of
vegetable matter now in progress under both these circumstances.

In Slave Lake in particular, which vies in dimensions with some of the
great fresh-water seas of Canada, the quantity of drift-timber brought
down annually is enormous. "As the trees," says Dr. Richardson, "retain
their roots, which are often loaded with earth and stones, they readily
sink, especially when water-soaked; and, accumulating in the eddies,
form shoals, which ultimately augment into islands. A thicket of small
willows covers the new-formed island as soon as it appears above water,
and their fibrous roots serve to bind the whole firmly together.
Sections of these islands are annually made by the river, assisted by
the frost; and it is interesting to study the diversity of appearances
they present, according to their different ages. The trunks of the trees
gradually decay until they are converted into a blackish brown substance
resembling peat, but which still retains more or less of the fibrous
structure of the wood; and layers of this often alternate with layers of
clay and sand, the whole being penetrated, to the depth of four or five
yards or more, by the long fibrous roots of the willows. A deposition of
this kind, with the aid of a little infiltration of bituminous matter,
would produce an excellent imitation of coal, with vegetable impressions
of the willow-roots. What appeared most remarkable was the horizontal
slaty structure that the old alluvial banks presented, or the _regular
curve_ that the strata assumed from unequal subsidence.

"It was in the rivers only that we could observe sections of these
deposits; but the same operation goes on, on a much more magnificent
scale, in the lakes. A shoal of many miles in extent is formed on the
south side of Athabasca Lake, by the drift-timber and vegetable debris
brought down by the Elk River; and the Slave Lake itself must in process
of time be filled up by matters daily conveyed into it from Slave River.
Vast quantities of drift-timber are buried under the sand at the mouth
of the river, and enormous piles of it are accumulated on the shores of
every part of the lake."[1062]

The banks of the Mackenzie display almost everywhere horizontal beds of
wood coal, alternating with bituminous clay, gravel, sand, and friable
sandstone; sections, in short, of such deposits as are now evidently
forming at the bottom of the lakes which it traverses.

Notwithstanding the vast forests intercepted by the lakes, a still
greater mass of drift-wood is found where the Mackenzie reaches the sea,
in a latitude where no wood grows at present except a few stunted
willows. At the mouths of the river the alluvial matter has formed a
barrier of islands and shoals, where we may expect a great formation of
coal at some distant period.

The abundance of floating timber on the Mackenzie is owing, as Dr.
Richardson informs me, to the direction and to the length of the course
of this river, which runs from south to north, so that the sources of
the stream lie in much warmer latitudes than its mouths. In the country,
therefore, where the sources are situated, the frost breaks up at an
earlier season, while yet the waters in the lower part of its course are
ice-bound. Hence the current of water, rushing down northward, reaches a
point where the thaw has not begun, and, finding the channel of the
river blocked up with ice, it overflows the banks, sweeping through
forests of pines, and carrying away thousands of uprooted trees.

_Drift-timber on coasts of Iceland, Spitzbergen, &c._--The ancient
forests of Iceland, observes Malte-Brun, have been improvidently
exhausted; but, although the Icelander can obtain no timber from the
land, he is supplied with it abundantly by the ocean. An immense
quantity of thick trunks of pines, firs, and other trees, are thrown
upon the northern coast of the island, especially upon the North Cape
and Cape Langaness, and are then carried by the waves along these two
promontories to other parts of the coast, so as to afford sufficiency of
wood for fuel and for constructing boats. Timber is also carried to the
shores of Labrador and Greenland; and Crantz assures us that the masses
of floating wood thrown by the waves upon the island of John de Mayen
often equal the whole of that island in extent.[1063]

In a similar manner the bays of Spitzbergen are filled with drift-wood,
which accumulates also upon those parts of the coast of Siberia that are
exposed to the east, consisting of larch trees, pines, Siberian cedars,
firs, and Pernambuco and Campeachy woods. These trunks appear to have
been swept away by the great rivers of Asia and America. Some of them
are brought from the Gulf of Mexico by the Bahama stream; while others
are hurried forward by the current which, to the north of Siberia,
constantly sets in from east to west. Some of these trees have been
deprived of their bark by friction, but are in such a state of
preservation as to form excellent building timber.[1064] Parts of the
branches and almost all the roots remain fixed to the pines which have
been drifted into the North Sea, into latitudes too cold for the growth
of such timber, but the trunks are usually barked.

The leaves and lighter parts of plants are seldom carried out to sea, in
any part of the globe, except during tropical hurricanes among islands,
and during the agitations of the atmosphere which sometimes accompany
earthquakes and volcanic eruptions.

_Comparative number of living and fossilized species of plants._--It
will appear from these observations that, although the remains of
terrestrial vegetation, borne down by aqueous causes from the land, are
chiefly deposited at the bottom of lakes or at the mouths of rivers, yet
a considerable quantity is drifted about in all directions by currents,
and may become imbedded in any _marine_ formation, or may sink down,
when water-logged, to the bottom of unfathomable abysses, and there
accumulate without intermixture with other substances.

It may be asked whether we have any data for inferring that the remains
of a considerable proportion of the existing species of plants will be
permanently preserved, so as to be hereafter recognizable, supposing the
strata now in progress to be at some future period upraised? To this
inquiry it may be answered, that there are no reasons for expecting that
more than a small number of the plants now flourishing in the globe will
become fossilized; since the entire habitations of a great number of
them are remote from lakes and seas, and even where they grow near to
large bodies of water, the circumstances are quite accidental and
partial which favor the imbedding and conservation of vegetable
remains. Suppose, for example, that the species of plants inhabiting the
hydrographical basin of the Rhine, or that region, extending from the
Alps to the sea, which is watered by the Rhine and its numerous
tributaries, to be about 2500 in number, exclusive of the cryptogamic
class. This estimate is by no means exaggerated; yet if a geologist
could explore the deposits which have resulted from the sediment of the
Rhine in the Lake of Constance, and off the coast of Holland, he could
scarcely expect to obtain from the recent strata the leaves, wood, and
seeds of _fifty_ species in such a state of preservation as to enable a
botanist to determine their specific characters with certainty.

Those naturalists, therefore, who infer that the ancient flora of the
globe was, at certain periods, less varied than now, merely because they
have as yet discovered only a few hundred fossil species of a particular
epoch, while they can enumerate more than one hundred thousand living
ones, are reasoning on a false basis, and their standard of comparison
is not the same in the two cases.

_Submarine forests on coast of Hants._--We have already seen that the
submarine position of several forests, or the remains of trees standing
in a vertical position on the British shores, has been due, in some
instances, to the subsidence of land.[1065] There are some cases which
require a different explanation. My friend, Mr. Charles Harris,
discovered, in 1831, evident traces of a fir-wood beneath the mean level
of the sea, at Bournmouth, in Hampshire, the formation having been laid
open during a low spring tide. It is composed of peat and wood, and is
situated between the beach and a bar of sand about 200 yards off, and
extends fifty yards along the shore. It also lies in the direct line of
the Bournmouth Valley, from the termination of which it is separated by
200 yards of shingle and drift-sand. Down the valley flows a large
brook, traversing near its mouth a considerable tract of rough, boggy,
and heathy ground, which produces a few birch-trees, and a great
abundance of the _Myrica gale_. Seventy-six rings of annual growth were
counted in a transverse section of one of the buried fir-trees, which
was fourteen inches in diameter. Besides the stumps and roots of fir,
pieces of alder and birch are found in the peat; and it is a curious
fact, that a part of many of the trees have been converted into iron
pyrites. The peat rests on pebbly strata, precisely similar to the sand
and pebbles occurring on the adjoining heaths.

As the sea is encroaching on this shore, we may suppose that at some
former period the Bourne Valley extended farther, and that its extremity
consisted, as at present, of boggy ground, partly clothed with
fir-trees. The bog rested on that bed of pebbles which we now see below
the peat; and the sea, in its progressive encroachments, eventually laid
bare, at low water, the sandy foundations; upon which a stream of fresh
water, rushing through the sand at the fall of the tides, carried out
loose sand with it. The superstratum of vegetable matter, being matted
and bound together by the roots of trees, remained; but being
undermined, sank down below the level of the sea, and then the waves
washed sand and shingle over it. In support of this hypothesis, it may
be observed, that small streams of fresh water often pass under the
sands of the sea-beach, so that they may be crossed dry-shod; and the
water is seen, at the point where it issues, to carry out sand and even
pebbles.

_Mineralization of plants_--Although the botanist and chemist have as yet
been unable to explain fully the manner in which wood becomes petrified,
it is nevertheless ascertained that, under favorable circumstances, the
lapidifying process is now continually going on. A piece of wood was
lately procured by Mr. Stokes, from an ancient Roman aqueduct in
Westphalia, in which some portions were converted into spindle-shaped
bodies, consisting of carbonate of lime, while the rest of the wood
remained in a comparatively unchanged state.[1066] It appears that in
some cases the most perishable, in others the most durable, portions of
plants are preserved, variations which doubtless depend on the time when
the mineral matter was supplied. If introduced immediately, on the first
commencement of decomposition, then the most destructible parts are
lapidified, while the more durable do not waste away till afterwards,
when the supply has failed, and so never become petrified. The converse
of these circumstances gives rise to exactly opposite results.

Professor Göppert, of Breslau, has instituted a series of curious
experiments, in which he has succeeded in producing some very remarkable
imitations of fossil petrifactions. He placed recent ferns between soft
layers of clay, dried these in the shade, and then slowly and gradually
heated them, till they were red-hot. The result was the production of so
perfect a counterpart of fossil plants as might have deceived an
experienced geologist. According to the different degrees of heat
applied, the plants were obtained in a brown or perfectly carbonized
condition; and sometimes, but more rarely, they were in a black shining
state, adhering closely to the layer of clay. If the red heat was
sustained until all the organic matter was burnt up, only an impression
of the plant remained.

The same chemist steeped plants in a moderately strong solution of
sulphate of iron, and left them immersed in it for several days, until
they were thoroughly soaked in the liquid. They were then dried, and
kept heated until they would no longer shrink in volume, and until every
trace of organic matter had disappeared. On cooling them he found that
the oxide formed by this process had taken the form of the plants. A
variety of other experiments were made by steeping animal and vegetable
substances in siliceous, calcareous, and metallic solutions, and all
tended to prove that the mineralization of organic bodies can be carried
much farther in a short time than had been previously supposed.[1067]


_Imbedding of the Remains of Insects._

I have observed the elytra and other parts of beetles in a band of
fissile clay, separating two beds of recent shell-marl, in the Loch of
Kinnordy in Forfarshire. Amongst these, Mr. Curtis recognized _Elator
lincatus_ and _Atopa cervina_, species still living in Scotland. These,
as well as other remains which accompanied them, appear to belong to
terrestrial, not aquatic species, and must have been carried down in
muddy water during an inundation. In the lacustrine peat of the same
locality, the elytra of beetles are not uncommon; but in the deposits of
drained lakes generally, and in the silt of our estuaries, the relics of
this class of the animal kingdom are rare. In the blue clay of very
modern origin of Lewes levels, Dr. Mantell has found the Indusia, or
cases of the larvæ of Phryganea, in abundance, with minute shells
belonging to the genera Planorbis, Limnea, &c., adhering to them.[1068]

When speaking of the migrations of insects, I pointed out that an
immense number are floated into lakes and seas by rivers, or blown by
winds far from the land; but they are so buoyant that we can only
suppose them, under very peculiar circumstances, to sink to the bottom
before they are either devoured by insectivorous animals or decomposed.


_Remains of Reptiles._

As the bodies of several crocodiles were found in the mud brought down
to the sea by the river inundation which attended an earthquake in Java,
in the year 1699, we may imagine that extraordinary floods of mud may
stifle many individuals of the shoals of alligators and other reptiles
which frequent lakes and the deltas of rivers in tropical climates.
Thousands of frogs were found leaping about among the wreck, carried
into the sea by the inundations in Morayshire, in 1829;[1069] and it is
evident that whenever a sea-cliff is undermined, or land is swept by
other violent causes into the sea, land reptiles may be carried in.


_Remains of Birds._

We might have anticipated that the imbedding of the remains of birds in
new strata would be of very rare occurrence; for their powers of flight
insure them against perishing, by numerous casualties to which
quadrupeds are exposed during floods; and if they chance to be drowned,
or to die when swimming on the water, it will scarcely ever happen that
they will be submerged so as to become preserved in sedimentary
deposits. In consequence of the hollow tubular structure of their bones
and the quantity of their feathers, they are extremely light in
proportion to their volume; so that when first killed they do not sink
to the bottom like quadrupeds, but float on the surface until the
carcass either rots away or is devoured by predaceous animals. To these
causes we may ascribe the absence of any vestige of the bones of birds
in the recent marl formations of Scotland; although these lakes, until
the moment when they were artificially drained, were frequented by a
great abundance of waterfowl.


_Imbedding of Terrestrial Quadrupeds._

River inundations recur in most climates at very irregular intervals,
and expend their fury on those rich alluvial plains where herds of
herbivorous quadrupeds congregate together. These animals are often
surprised; and, being unable to stem the current, are hurried along
until they are drowned, when they sink at first immediately to the
bottom. Here their bodies are drifted along, together with sediment,
into lakes or seas, and may then be covered by a mass of mud, sand, and
pebbles, thrown down upon them. If there be no sediment superimposed,
the gases generated by putrefaction usually cause the bodies to rise
again to the surface about the ninth, or at latest the fourteenth day.
The pressure of a thin covering of mud would not be sufficient to retain
them at the bottom; for we see the putrid carcasses of dogs and cats,
even in rivers, floating with considerable weights attached to them, and
in sea-water they would be still more buoyant.

Where the body is so buried in drift sand, or mud accumulated upon it,
as never to rise again, the skeleton may be preserved entire; but if it
comes again to the surface while in the process of putrefaction, the
bones commonly fall piecemeal from the floating carcass, and may in that
case be scattered at random over the bottom of the lake, estuary, or
sea; so that a jaw may afterwards be found in one place, a rib in
another, a humerus in a third--all included, perhaps, in a matrix of
fine materials, where there may be evidence of slight transporting power
in the current, or even of none, but simply of some chemical
precipitate.

A large number of the bodies of drowned animals, if they float into the
sea or a lake, especially in hot climates, are instantly devoured by
sharks, alligators, and other carnivorous beasts, which may have power
to digest even the bones; but during extraordinary floods, when the
greatest number of land animals are destroyed, the waters are commonly
so turbid, especially at the bottom of the channel, that even aquatic
species are compelled to escape into some retreat where there is clearer
water, lest they should be stifled. For this reason, as well as the
rapidity of sedimentary deposition at such seasons, the probability of
carcasses becoming permanently imbedded is considerable.

_Flood in the Solway Firth, 1794._--One of the most memorable floods of
modern date, in our island, is that which visited part of the southern
borders of Scotland, on the 24th of January, 1794, and which spread
particular devastation over the country adjoining the Solway Firth.

We learn from the account of Captain Napier, that the heavy rains had
swollen every stream which entered the Firth of Solway; so that the
inundation not only carried away a great number of cattle and sheep, but
many of the herdsmen and shepherds, washing down their bodies into the
estuary. After the storm, when the flood subsided, an extraordinary
spectacle was seen on a large sand-bank called "the beds of Esk," where
there is a meeting of the tidal waters, and where heavy bodies are
usually left stranded after great floods. On this single bank were found
collected together the bodies of 9 black cattle, 3 horses, 1840 sheep,
45 dogs, 180 hares, besides a great number of smaller animals, and,
mingled with the rest, the corpses of two men and one woman.[1070]

_Floods in Scotland, 1829._--In those more recent floods in Scotland, in
August, 1829, whereby a fertile district on the east coast became a
scene of dreadful desolation, a vast number of animals and plants were
washed from the land, and found scattered about after the storm, around
the mouths of the principal rivers. An eye-witness thus describes the
scene which presented itself at the mouth of the Spey, in
Morayshire:--"For several miles along the beach crowds were employed in
endeavoring to save the wood and other wreck with which the
heavy-rolling tide was loaded; whilst the margin of the sea was strewed
with the carcasses of domestic animals, and with millions of dead hares
and rabbits."[1071]

_Savannahs of South America._--We are informed by Humboldt, that during
the periodical swellings of the large rivers in South America great
numbers of quadrupeds are annually drowned. Of the wild horses, for
example, which graze in immense troops in the savannahs, thousands are
said to perish when the river Apure, a tributary of the Orinoco, is
swollen, before they have time to reach the rising ground of the Llanos.
The mares, during the season of high water, may be seen, followed by
their colts, swimming about and feeding on the grass, of which the top
alone waves above the waters. In this state they are pursued by
crocodiles; and their thighs frequently bear the prints of the teeth of
these carnivorous reptiles. "Such is the pliability," observes the
celebrated traveller, "of the organization of the animals which man has
subjected to his sway, that horses, cows, and other species of European
origin, lead, for a time, an amphibious life, surrounded by crocodiles,
water-serpents, and manatees. When the rivers return again into their
beds, they roam in the savannah, which is then spread over with a fine
odoriferous grass, and enjoy, as in their native climate, the renewed
vegetation of spring."[1072]

_Floods of the Parana._--The great number of animals which are drowned
in seasons of drought in the tributaries of the Plata, was before
mentioned. Sir W. Parish states, that the Parana, flowing from the
mountains of Brazil to the estuary of the Plata, is liable to great
floods, and during one of these, in the year 1812, vast quantities of
cattle were carried away, "and when the waters began to subside, and the
islands which they had covered became again visible, the whole
atmosphere for a time was poisoned by the effluvia from the innumerable
carcasses of skunks, capybaras, tigers, and other wild beasts which had
been drowned."[1073]

_Floods of the Ganges._--We find it continually stated, by those who
describe the Ganges and Burrampooter, that these rivers carry before
them, during the flood season, not only floats of reeds and timber, but
dead bodies of men, deer, and oxen.[1074]

_In Java, 1699._--I have already referred to the effects of a flood
which attended an earthquake in Java in 1699, when the turbid waters of
the Batavian river destroyed all the fish except the carp; and when
drowned buffaloes, tigers, rhinoceroses, deer, apes, and other wild
beasts, were brought down to the sea-coast by the current, with several
crocodiles which had been stifled in the mud. (See above, p. 503.)

On the western side of the same island, in the territory of Galongoon,
in the Regencies, a more recent volcanic eruption (that of 1822, before
described) (see above, p. 431) was attended by a flood, during which the
river Tandoi bore down hundreds of carcasses of rhinoceroses and
buffaloes, and swept away more than one hundred men and women from a
multitude assembled on its banks to celebrate a festival. Whether the
bodies reached the sea, or were deposited, with drift matter, in some
large intervening alluvial plains, we are not informed.[1075]

_Sumatra._--"On the coast of Orissa," says Heynes, "I have seen tigers
and whole herds of black cattle carried along by what are called
freshes, and trees of immense size."[1076]

_In Virginia, 1771._--I might enumerate a great number of local deluges
that have swept through the fertile lands bordering on large rivers,
especially in tropical countries, but I should surpass the limits
assigned to this work. I may observe, however, that the destruction of
the islands, in rivers, is often attended with great loss of lives. Thus
when the principal river in Virginia rose, in 1771, to the height of
twenty-five feet above its ordinary level, it swept entirely away Elk
Island, on which were seven hundred head of quadrupeds,--horses, oxen,
sheep, and hogs,--and nearly one hundred houses.[1077]

The reader will gather, from what was before said respecting the
deposition of sediment by aqueous causes, that the greater number of the
remains of quadrupeds drifted away by rivers must be intercepted by
lakes before they reach the sea, or buried in freshwater formations near
the mouths of rivers. If they are carried still farther, the
probabilities are increased of their rising to the surface in a state of
putrefaction, and, in that case, of being there devoured by aquatic
beasts of prey, or of subsiding into some spots whither no sediment is
conveyed, and, consequently, where every vestige of them will, in the
course of time, disappear.

_Skeletons of animals in recent shell-marl, Scotland._--In some
instances, the skeletons of quadrupeds are met with abundantly in recent
shell-marls in Scotland, where we cannot suppose them to have been
imbedded by the action of rivers or floods. They all belong to species
which now inhabit, or are known to have been indigenous in Scotland. The
remains of several hundred skeletons have been procured within the last
century from five or six small lakes in Forfarshire, where shell-marl
has been worked. Those of the stag (_Cervus Elaphas_) are most numerous;
and if the others be arranged in the order of their relative abundance,
they will nearly follow thus--the ox, the boar, the horse, the sheep,
the dog, the hare, the fox, the wolf, and the cat. The beaver seems
extremely rare; but it has been found in the shell-marl of Loch Marlie,
in Perthshire, and in the parish of Edrom, in Berwickshire.

In the greater part of these lake-deposits there are no signs of floods;
and the expanse of water was originally so confined, that the smallest
of the above-mentioned quadrupeds could have crossed, by swimming from
one shore to the other. Deer, and such species as take readily to the
water, may often have been mired in trying to land, where the bottom was
soft and quaggy, and in their efforts to escape may have plunged deeper
into the marly bottom. Some individuals, I suspect, of different
species, have fallen in when crossing the frozen surface in winter; for
nothing can be more treacherous than the ice when covered with snow, in
consequence of the springs, which are numerous, and which, retaining
always an equal temperature, cause the ice, in certain spots, to be
extremely thin, while in every other part of the lake it is strong
enough to bear the heaviest weights.

_Mammiferous remains in marine strata._--As the bones of mammalia are
often so abundantly preserved in peat, and such lakes as have just been
described, the encroachments of a sea upon a coast may sometimes throw
down the imbedded skeletons, so that they may be carried away by tides
and currents, and entombed in submarine formations. Some of the smaller
quadrupeds, also, which burrow in the ground, as well as reptiles and
every species of plant, are liable to be cast down into the waves by
this cause, which must not be overlooked, although probably of
comparatively small importance amongst the numerous agents whereby
terrestrial organic remains are included in submarine strata.

During the great earthquake of Conception in 1835, some cattle, which
were standing on the steep sides of the island of Quiriquina, were
rolled by the shock into the sea, while on a low island at the head of
the Bay of Conception seventy animals were washed off by a great wave
and drowned.[1078]





CHAPTER XLVIII.

IMBEDDING OF THE REMAINS OF MAN AND HIS WORKS IN SUBAQUEOUS STRATA.


  Drifting of human bodies to the sea by river
    inundations--Destruction of bridges and houses--Loss of lives by
    shipwreck--How human corpses may be preserved in recent
    deposits--Number of wrecked vessels--Fossil skeletons of men--Fossil
    canoes, ships, and works of art--Chemical changes which metallic
    articles have undergone after long submergence--Imbedding of cities
    and forests in subaqueous strata by subsidence--Earthquake of Cutch
    in 1819--Buried Temples of Cashmere--Berkeley's arguments for the
    recent date of the creation of man--Concluding remarks.


I shall now proceed to inquire in what manner the mortal remains of man
and the works of his hands may be permanently preserved in subaqueous
strata. Of the many hundred million human beings which perish in the
course of every century on the land, every vestige is usually destroyed
in the course of a few thousand years; but of the smaller number that
perish in the waters, a certain proportion must be entombed under
circumstances that may enable parts of them to endure throughout entire
geological epochs.

The bodies of men, together with those of the inferior animals, are
occasionally washed down during river inundations into seas and lakes.
(See pp. 726-728.) Belzoni witnessed a flood on the Nile in September,
1818, where, although the river rose only three feet and a half above
its ordinary level, several villages, with some hundreds of men, women,
and children, were swept away.[1079] It was before mentioned that a rise
of six feet of water in the Ganges, in 1763, was attended with a much
greater loss of lives. (See above, p. 278.)

In the year 1771, when the inundations in the north of England appear to
have equalled the floods of Morayshire in 1829, a great number of houses
and their inhabitants were swept away by the rivers Tyne, Can, Wear,
Tees, and Greta; and no less than twenty-one bridges were destroyed in
the courses of these rivers. At the village of Bywell the flood tore the
dead bodies and coffins out of the churchyard, and bore them away,
together with many of the living inhabitants. During the same tempest an
immense number of cattle, horses, and sheep, were also transported to
the sea, while the whole coast was covered with the wreck of ships. Four
centuries before (in 1338), the same district had been visited by a
similar continuance of heavy rains, followed by disastrous floods, and
it is not improbable that these catastrophes may recur periodically,
though at uncertain intervals. As the population increases, and
buildings and bridges are multiplied, we must expect the loss of lives
and property to augment.[1080]

_Fossilization of human bodies in the bed of the sea._--If to the
hundreds of human bodies committed to the deep in the way of ordinary
burial we add those of individuals lost by shipwrecks, we shall find
that in the course of a single year, a great number of human remains are
consigned to the subaqueous regions. I shall hereafter advert to a
calculation by which it appears that more than five hundred _British_
vessels alone, averaging each a burthen of about 120 tons, are wrecked,
and sink to the bottom, _annually_. Of these the crews for the most part
escape, although it sometimes happens that all perish. In one great
naval action several thousand individuals sometimes share a watery
grave.

Many of these corpses are instantly devoured by predaceous fish,
sometimes before they reach the bottom; still more frequently when they
rise again to the surface, and float in a state of putrefaction. Many
decompose on the floor of the ocean, where no sediment is thrown down
upon them; but if they fall upon a reef where corals and shells are
becoming agglutinated into a solid rock, or subside where the delta of a
river is advancing, they may be preserved for an incalculable series of
ages.

Often at the distance of a few hundred feet from a coral reef, where
wrecks are not unfrequent, there are no soundings at the depth of many
hundred fathoms. Canoes, merchant vessels, and ships of war, may have
sunk and have been enveloped, in such situations, in calcareous sand and
breccia, detached by the breakers from the summit of a submarine
mountain. Should a volcanic eruption happen to cover such remains with
ashes and sand, and a current of lava be afterwards poured over them,
the ships and human skeletons might remain uninjured beneath the
superincumbent mass, like the houses and works of art in the
subterranean cities of Campania. Already many human remains may have
been thus preserved beneath formations more than a thousand feet in
thickness; for, in some volcanic archipelagoes, a period of thirty or
forty centuries might well be supposed sufficient for such an
accumulation. It was stated, that at the distance of about forty miles
from the base of the delta of the Ganges there is an elliptical space
about fifteen miles in diameter, where soundings of from 100 to 300
fathoms sometimes fail to reach the bottom. (See above, p. 279.) As
during the flood season the quantity of mud and sand poured by the great
rivers into the Bay of Bengal is so great that the sea only recovers its
transparency at the distance of sixty miles from the coast, this
depression must be gradually shoaling, especially as during the
monsoons, the sea loaded with mud and sand, is beaten back in that
direction towards the delta. Now, if a ship or human body sink to the
bottom in such a spot, it is by no means improbable that it may become
buried under a depth of a thousand feet of sediment in the same number
of years.

Even on that part of the floor of the ocean to which no accession of
drift matter is carried (a part which probably constitutes, at any given
period, by far the larger proportion of the whole submarine area), there
are circumstances accompanying a wreck which favor the conservation of
skeletons. For when the vessel fills suddenly with water, especially in
the night, many persons are drowned between decks and in their cabins,
so that their bodies are prevented from rising again to the surface. The
vessel often strikes upon an uneven bottom, and is overturned; in which
case the ballast, consisting of sand, shingle, and rock, or the cargo,
frequently composed of heavy and durable materials, may be thrown down
upon the carcasses. In the case of ships of war, cannon, shot, and other
warlike stores, may press down with their weight the timbers of the
vessel as they decay, and beneath these and the metallic substances the
bones of man may be preserved.

_Number of wrecked vessels._--When we reflect on the number of curious
monuments consigned to the bed of the ocean in the course of every naval
war from the earliest times, our conceptions are greatly raised
respecting the multiplicity of lasting memorials which man is leaving of
his labors. During our last great struggle with France, thirty-two of
our ships of the line went to the bottom in the space of twenty-two
years, besides seven 50-gun ships, eighty-six frigates, and a multitude
of smaller vessels. The navies of the other European powers, France,
Holland, Spain, and Denmark, were almost annihilated during the same
period, so that the aggregate of their losses must have many times
exceeded that of Great Britain. In every one of these ships were
batteries of cannon constructed of iron or brass, whereof a great number
had the dates and places of their manufacture inscribed upon them in
letters cast in metal. In each there were coins of copper, silver, and
often many of gold, capable of serving as valuable historical monuments;
in each were an infinite variety of instruments of the arts of war and
peace; many formed of materials, such as glass and earthenware, capable
of lasting for indefinite ages when once removed from the mechanical
action of the waves, and buried under a mass of matter which may exclude
the corroding action of sea-water. The quantity, moreover, of timber
which is conveyed from the land to the bed of the sea by the sinking of
ships of a large size is enormous, for it is computed that 2000 tons of
wood are required for the building of one 74-gun ship; and reckoning
fifty oaks of 100 years growth to the acre, it would require forty acres
of oak forest to build one of these vessels.[1081]

It would be an error to imagine that the fury of war is more conducive
than the peaceful spirit of commercial enterprise to the accumulation of
wrecked vessels in the bed of the sea. From an examination of Lloyd's
lists, from the year 1793 to the commencement of 1829, Captain W. H.
Smyth ascertained that the number of _British vessels_ alone lost during
that period amounted on an average to no less than one and a half
_daily_; an extent of loss which would hardly have been anticipated,
although we learn from Moreau's tables that the number of merchant
vessels employed at one time, in the navigation of England and Scotland,
amounts to about twenty thousand, having one with another a mean burthen
of 120 tons.[1082] My friend, Mr. J. L. Prevost, also informs me that on
inspecting Lloyd's list for the years 1829, 1830, and 1831, he finds
that no less than 1953 vessels were lost in those three years, their
average tonnage being about 150 tons, or in all nearly 300,000 tons,
being at the enormous rate of 100,000 tons annually of the merchant
vessels of one nation only. This increased loss arises, I presume, from
increasing activity in commerce.

Out of 551 ships of the royal navy lost to the country during the period
above mentioned, only 160 were taken or destroyed by the enemy, the rest
having either stranded or foundered, or having been burnt by accident; a
striking proof that the dangers of our naval warfare, however great, may
be far exceeded by the storm, the shoal, the lee-shore, and all the
other perils of the deep.[1083]

_Durable nature of many of their contents._--Millions of silver dollars
and other coins have been sometimes submerged in a single ship, and on
these, when they happen to be enveloped in a matrix capable of
protecting them from chemical changes, much information of historical
interest will remain inscribed, and endure for periods as indefinite as
have the delicate markings of zoophytes or lapidified plants in some of
the ancient secondary rocks. In almost every large ship, moreover, there
are some precious stones set in seals, and other articles of use and
ornament composed of the hardest substances in nature, on which letters
and various images are carved--engravings which they may retain when
included in subaqueous strata, as long as a crystal preserves its
natural form.

It was, therefore, a splendid boast, that the deeds of the English
chivalry at Agincourt made Henry's chronicle


                  ----as rich with praise
  As is the ooze and bottom of the deep
  With sunken wreck and sumless treasuries


for it is probable that a greater number of monuments of the skill and
industry of man will, in the course of ages, be collected together in
the bed of the ocean, than will exist at any one time on the surface of
the continents.

If our species be of as recent a date as is generally supposed, it will
be vain to seek for the remains of man and the works of his hands
imbedded in submarine strata, except in those regions where violent
earthquakes are frequent, and the alterations of relative level so
great, that the bed of the sea may have been converted into land within
the historical era. We need not despair, however, of the discovery of
such monuments, when those regions which have been peopled by man from
the earliest ages, and which are at the same time the principal theatres
of volcanic action, shall be examined by the joint skill of the
antiquary and geologist.

_Power of human remains to resist decay._--There can be no doubt that
human remains are as capable of resisting decay as are the harder parts
of the inferior animals; and I have already cited the remark of Cuvier,
that "in ancient fields of battle the bones of men have suffered as
little decomposition as those of horses which were buried in the same
grave." (See above, p. 147.) In the delta of the Ganges bones of men
have been found in digging a well at the depth of ninety feet;[1084] but
as that river frequently shifts its course and fills up its ancient
channels, we are not called upon to suppose that these bodies are of
extremely high antiquity, or that they were buried when that part of the
surrounding delta where they occur was first gained from the sea.

_Fossil skeletons of men._--Several skeletons of men, more or less
mutilated, have been found in the West Indies, on the north-west coast
of the main land of Guadaloupe, in a kind of rock which is known to be
forming daily, and which consists of minute fragments of shells and
corals, incrusted with a calcareous cement resembling travertin, by
which also the different grains are bound together. The lens shows that
some of the fragments of coral composing this stone still retain the
same red color which is seen in the reefs of living coral which surround
the island. The shells belong to species of the neighboring sea
intermixed with some terrestrial kinds which now live on the island, and
among them is the _Bulimus Gaudaloupensis_ of Férussac. The human
skeletons still retain some of their animal matter, and all their
phosphate of lime. One of them, of which the head is wanting, may now be
seen in the British Museum, and another in the Royal Cabinet at Paris.
According to M. König, the rock in which the former is inclosed is
harder under the mason's saw and chisel than statuary marble. It is
described as forming a kind of glacis, probably an indurated beach,
which slants from the steep cliffs of the island to the sea, and is
nearly all submerged at high tide.

Similar formations are in progress in the whole of the West Indian
archipelago, and they have greatly extended the plain of Cayes in St.
Domingo, where fragments of vases and other human works have been found
at a depth of twenty feet. In digging wells also near Catania, in
Sicily, tools have been discovered in a rock somewhat similar.

_Buried ships, canoes, and works of art._--When a vessel is stranded in
shallow water, it usually becomes the nucleus of a sand-bank, as has
been exemplified in several of our harbors, and this circumstance tends
greatly to its preservation. Between the years 1780 and 1790 a vessel
from Purbeck, laden with three hundred tons of stone, struck on a shoal
off the entrance of Poole harbor and foundered; the crew were saved,
but the vessel and cargo remain to this day at the bottom. Since that
period the shoal at the entrance of the harbor has so extended itself in
a westerly direction towards Peveril Point in Purbeck, that the
navigable channel is thrown a mile nearer that point.[1085] The cause is
obvious; the tidal current deposits the sediment with which it is
charged around any object which checks its velocity. Matter also drifted
along the bottom is arrested by any obstacle, and accumulates round it,
just as the African sand-winds, before described, raise a small hillock
over the carcass of every dead camel exposed on the surface of the
desert.

I before alluded to an ancient Dutch vessel, discovered in the deserted
channel of the river Rother in Sussex, of which the oak wood was much
blackened, but its texture unchanged. (See above, p. 316.) The interior
was filled with fluviatile silt, as was also the case in regard to a
vessel discovered in a former bed of the Mersey, and another disinterred
where the St. Katherine Docks are excavated in the alluvial plain of the
Thames. In like manner many ships have been found preserved entire in
modern strata, formed by the silting up of estuaries along the southern
shores of the Baltic, especially in Pomerania. Between Bromberg and
Nakel, for example, a vessel and two anchors in a very perfect state
were dug up far from the sea.[1086]

Several vessels have been lately detected half buried in the delta of
the Indus, in the numerous deserted branches of that river, far from
where the stream now flows. One of these found near Vikkar in Sinde, was
400 tons in burthen, old fashioned, and pierced for fourteen guns, and
in a region where it had been matter of dispute whether the Indus had
ever been navigable by large vessels.[1087]

At the mouth of a river in Nova Scotia, a schooner of thirty-two tons,
laden with live stock, was lying with her side to the tide, when the
bore, or tidal wave, which rises there about ten feet in perpendicular
height, rushed into the estuary, and overturned the vessel, so that it
instantly disappeared. After the tide had ebbed, the schooner was so
totally buried in the sand, that the taffrel or upper rail over the
stern was alone visible.[1088] We are informed by Leigh that, on
draining Martin Meer, a lake eighteen miles in circumference, in
Lancashire, a bed of marl was laid dry, wherein no fewer than eight
canoes were found imbedded. In figure and dimensions they were not
unlike those now used in America. In a morass about nine miles distant
from this Meer a whetstone and an axe of mixed metal were dug up.[1089]
In Ayrshire, also, three canoes were found in Loch Doon some few years
ago; and during the year 1831 four others, each hewn out of separate oak
trees. They were twenty-three feet in length, two and a half in depth,
and nearly four feet in breadth at the stern. In the mud which filled
one of them was found a war-club of oak and a stone battle-axe. A canoe
of oak was also found in 1820, in peat overlying the shell-marl of the
Loch of Kinnordy, in Forfarshire.[1090]

_Manner in which ships may be preserved in a deep sea._--It is extremely
possible that the submerged woodwork of ships which have sunk where the
sea is two or three miles deep has undergone greater chemical changes in
an equal space of time, than in the cases above mentioned; for the
experiments of Scoresby show that wood may at certain depths be
impregnated in a single hour with salt water, so that its specific
gravity is entirely altered. It may often happen that hot springs,
charged with carbonate of lime, silex, and other mineral ingredients,
may issue at great depths, in which case every pore of the vegetable
tissue may be injected with the lapidifying liquid, whether calcareous
or siliceous, before the smallest decay commences. The conversion, also,
of wood into lignite is probably more rapid under enormous pressure. But
the change of the timber into lignite or coal would not prevent the
original form of a ship from being distinguished; for as we find, in
strata of the carboniferous era, the bark of the hollow reed-like trees
converted into coal, and the central cavity filled with sandstone, so
might we trace the outline of a ship in coal; while in the indurated
mud, sandstone, or limestone, filling the interior, we might discover
instruments of human art, ballast consisting of rocks foreign to the
rest of the stratum, and other contents of the ship.

_Submerged metallic substances._--Many of the metallic substances which
fall into the waters probably lose, in the course of ages, the forms
artificially imparted to them; but under certain circumstances these may
be preserved for indefinite periods. The cannon enclosed in a calcareous
rock, drawn up from the delta of the Rhone, which is now in the museum
at Montpellier, might probably have endured as long as the calcareous
matrix; but even if the metallic matter had been removed, and had
entered into new combinations, still a mould of its original shape would
have been left, corresponding to those impressions of shells which we
see in rocks, from which all the carbonate of lime has been subtracted.
About the year 1776, says Mr. King, some fishermen, sweeping for anchors
in the Gulf stream (a part of the sea near the Downs), drew up a very
curious old swivel gun, nearly eight feet in length. The barrel, which
was about five feet long, was of brass; but the handle by which it was
traversed was about three feet in length, and the swivel and pivot on
which it turned were of iron. Around these latter were formed
incrustations of sand converted into a kind of stone, of exceedingly
strong texture and firmness; whereas round the barrel of the gun, except
where it was near adjoining to the iron, there were no such
incrustations, the greater part of it being clean, and in good
condition, just as if it had still continued in use. In the incrusting
stone, adhering to it on the outside, were a number of shells and
corallines, "just as they are often found in a fossil state." These
were all so strongly attached, that it required as much force to
separate them from the matrix "as to break a fragment off any hard
rock."[1091]

In the year 1745, continues the same writer, the Fox man-of-war was
stranded on the coast of East Lothian, and went to pieces. About
thirty-three years afterwards a violent storm laid bare a part of the
wreck, and threw up near the place several masses, "consisting of iron,
ropes, and balls," covered over with ochreous sand, concreted and
hardened into a kind of stone. The substance of the rope was very little
altered. The consolidated sand retained perfect impressions of parts of
an iron ring, "just as impressions of extraneous fossil bodies are found
in various kinds of strata."[1092]

After a storm in the year 1824, which occasioned a considerable shifting
of the sands near St. Andrew's, in Scotland, a gun-barrel of ancient
construction was found, which is conjectured to have belonged to one of
the wrecked vessels of the Spanish Armada. It is now in the museum of
the Antiquarian Society of Scotland, and is incrusted over by a thin
coating of sand, the grains of which are cemented by brown ferruginous
matter. Attached to this coating are fragments of various shells, as of
the common cardium, mya, &c.

Many other examples are recorded of iron instruments taken up from the
bed of the sea near the British coast, incased by a thick coating of
conglomerate, consisting of pebbles and sand, cemented by oxide of iron.

Dr. Davy describes a bronze helmet, of the antique Grecian form, taken
up in 1825, from a shallow part of the sea, between the citadel of Corfu
and the village of Castrades. Both the interior and exterior of the
helmet were partially incrusted with shells, and a deposit of carbonate
of lime. The surface generally, both under the incrustation, and where
freed from it, was of a variegated color, mottled with spots of green,
dirty white, and red. On minute inspection with a lens, the green and
red patches proved to consist of crystals of the red oxide and carbonate
of copper, and the dirty white chiefly of oxide of tin.

The mineralizing process, says Dr. Davy, which has produced these new
combinations, has, in general, penetrated very little into the substance
of the helmet. The incrustation and rust removed, the metal is found
bright beneath; in some places considerably corroded, in others very
slightly. It proves, on analysis, to be copper, alloyed with 18.5 per
cent. of tin. Its color is that of our common brass, and it possesses a
considerable degree of flexibility.

"It is a curious question," he adds, "how the crystals were formed in
the helmet, and on the adhering calcareous deposit. There being no
reason to suppose deposition from solution, are we not under the
necessity of inferring, that the mineralizing process depends on a small
motion and separation of the particles of the original compound? This
motion may have been due to the operation of electro-chemical powers
which may have separated the different metals of the alloy.[1093]


_Effects of the Subsidence of Land, in imbedding Cities and Forests in
subaqueous Strata._

We have hitherto considered the transportation of plants and animals
from the land by _aqueous_ agents, and their inhumation in lacustrine or
submarine deposits, and we may now inquire what tendency the subsidence
of tracts of land may have to produce analogous effects. Several
examples of the sinking down of buildings, and portions of towns near
the shore, to various depths beneath the level of the sea during
subterranean movements, were before enumerated in treating of the
changes brought about by _inorganic_ causes. The events alluded to were
comprised within a brief portion of the historical period, and confined
to a small number of the regions of active volcanoes. Yet these
authentic facts, relating merely to the last century and a half, gave
indications of considerable changes in the physical geography of the
globe, and we are not to suppose that these were the only spots
throughout the surrounding land and sea which suffered similar
depressions.

If, during the short period since South America has been colonized by
Europeans, we have proof of alterations of level at the three principal
ports on the western shores, Callao, Valparaiso, and Conception,[1094]
we cannot for a moment suspect that these cities, so distant from each
other, have been selected as the peculiar points where the desolating
power of the earthquake has expended its chief fury. On considering how
small is the area occupied by the seaports of this disturbed
region--points where alone each slight change of the relative level of
the sea and land can be recognized,--and reflecting on the proofs in our
possession of the local revolutions that have happened on the site of
each port, within the last century and a half,--our conceptions must be
greatly exalted respecting the magnitude of the alterations which the
country between the Andes and the sea may have undergone, even in the
course of the last six thousand years.

_Cutch earthquake._--The manner in which a large extent of surface may
be submerged, so that the terrestrial plants and animals may be imbedded
in subaqueous strata, cannot be better illustrated than by the
earthquake of Cutch, in 1819, before alluded to (p. 460). It is stated,
that, for some years after that earthquake, the withered tamarisks and
other shrubs protruded their tops above the waves, in parts of the
lagoon formed by subsidence, on the site of the village of Sindree and
its environs; but, after the flood of 1826, they were seen no longer.
Every geologist will at once perceive, that forests sunk by such
subterranean movements may become imbedded in subaqueous deposits, both
fluviatile and marine, and the trees may still remain erect, or
sometimes the roots and part of the trunks may continue in their
original position, while the current may have broken off, or levelled
with the ground, their upper stems and branches.

_Buildings how preserved under water._--Some of the buildings which have
at different times subsided beneath the level of the sea have been
immediately covered up to a certain extent with strata of volcanic
matter showered down upon them. Such was the case at Tomboro in Sumbawa,
in the present century, and at the site of the Temple of Serapis, in the
environs of Puzzuoli, probably about the 12th century. The entrance of a
river charged with sediment in the vicinity may still more frequently
occasion the rapid envelopment of buildings in regularly stratified
formations. But if no foreign matter be introduced, the buildings, when
once removed to a depth where the action of the waves is insensible, and
where no great current happens to flow, may last for indefinite periods,
and be as durable as the floor of the ocean itself, which may often be
composed of the very same materials. There is no reason to doubt the
tradition mentioned by the classic writers, that the submerged Grecian
towns of Bura and Helice were seen under water; and it has been already
mentioned that different eye-witnesses have observed the houses of Port
Royal, at the bottom of the sea, at intervals of 88, 101, and 143 years
after the convulsion of 1692. (p. 505.)

_Buried temples of Cashmere._--The celebrated valley of Cashmere (or
Kashmir) in India, situated at the southern foot of the Himalaya range,
is about 60 miles in length, and 20 in breadth, surrounded by mountains
which rise abruptly from the plain to the height of about 5000 feet. In
the cliffs of the river Jelam and its tributaries, which traverse this
beautiful valley, strata consisting of fine clay, sand, soft sandstone,
pebbles, and conglomerate are exposed to view. They contain freshwater
shells, of the genera Lymneus, Paludina, and Cyrena, with land shells,
all of recent species, and are precisely such deposits as would be
formed if the whole valley were now converted into a great lake, and if
the numerous rivers and torrents descending from the surrounding
mountains were allowed sufficient time to fill up the lake-basin with
fine sediment and gravel. Fragments of pottery met with at the depth of
40 and 50 feet in this lacustrine formation show that the upper part of
it at least has accumulated within the human epoch.

Dr. Thomas Thomson, who visited Cashmere in 1848, observes that several
of the lakes which still exist in the great valley, such as that near
the town of Cashmere, five miles in diameter, and some others, are
deeper than the adjoining river-channels, and may have been formed by
subsidence during the numerous earthquakes which have convulsed that
region in the course of the last 2000 years. It is also probable that
the freshwater strata seen to extend far and wide over the whole of
Cashmere originated not in one continuous sheet of water once occupying
the entire valley, but in many lakes of limited area, formed and filled
in succession. Among other proofs of such lake-basins of moderate
dimensions having once existed and having been converted into land at
different periods, Dr. Thomson mentions that the ruins of Avantipura,
not far from the modern village of that name, stand on an older
freshwater deposit at the base of the mountains, and terminate abruptly
towards the plain in a straight line, such as admits of no other
explanation than by supposing that the advance of the town in that
direction was arrested by a lake, now drained or represented only by a
marsh. In that neighborhood, as very generally throughout Cashmere, the
rivers run in channels or alluvial flats, bounded by cliffs of
lacustrine strata, horizontally stratified, and these strata form low
table-lands from 20 to 50 feet high between the different watercourses.
On a table-land of this kind near Avantipura, portions of two buried
temples are seen, which have been partially explored by Major
Cunningham, who, in 1847, discovered that in one of the buildings a
magnificent colonnade of seventy-four pillars is preserved underground.
He exposed to view three of the pillars in a cavity still open. All the
architectural decorations below the level of the soil are as perfect and
fresh-looking as when first executed. The spacious quadrangle must have
been silted up gradually at first, for some unsightly alterations, not
in accordance with the general plan and style of architecture, were
detected, evidently of subsequent date, and such as could only have been
required when the water and sediment had already gained a certain height
in the interior of the temple.

This edifice is supposed to have been erected about the year 850 of our
era, and was certainly submerged before the year 1416, when the
Mahomedan king, Sikandar, called Butshikan or the idol-breaker,
destroyed all the images of Hindoo temples in Cashmere. Ferishta the
historian particularly alludes to Sikandar having demolished every
Cashmerian temple save one, dedicated to Mahadéva, which escaped "in
consequence of its foundations being below the neighboring water." The
unharmed condition of the human-headed birds and other images in the
buried edifice near Avantipura leaves no doubt that they escaped the
fury of the iconoclast by being under water, and perhaps silted up
before the date of his conquest.[1095]

_Berkeley's arguments for the recent date of the creation of man._--I
cannot conclude this chapter without recalling to the reader's mind a
memorable passage written by Bishop Berkeley a century ago, in which he
inferred, on grounds which may be termed strictly geological, the recent
date of the creation of man. "To any one," says he, "who considers that
on digging into the earth, such quantities of shells, and in some
places, bones and horns of animals, are found sound and entire, after
having lain there in all probability some thousands of years; it should
seem probable that guns, medals, and implements in metal or stone, might
have lasted entire, buried under ground forty or fifty thousand years,
if the world had been so old. How comes it then to pass that no remains
are found, no antiquities of those numerous ages preceding the Scripture
accounts of time; that no fragments of buildings, no public monuments,
no intaglios, cameos, statues, basso-relievos, medals, inscriptions,
utensils, or artificial works of any kind, are ever discovered, which
may bear testimony to the existence of those mighty empires, those
successions of monarchs, heroes, and demi-gods, for so many thousand
years? Let us look forward and suppose ten or twenty thousand years to
come, during which time we will suppose that plagues, famine, wars, and
_earthquakes_ shall have made great havoc in the world, is it not highly
probable that at the end of such a period, pillars, vases, and statues
now in being, of granite, or porphyry, or jasper (stones of such
hardness as we know them to have lasted two thousand years above ground,
without any considerable alteration), would bear record of these and
past ages? Or that some of our current coins might then be dug up, or
old walls and the foundations of buildings show themselves, as well as
the shells and stones of _the primeval world_, which are preserved down
to our times."[1096]

That many signs of the agency of man would have lasted at least as long
as "the shells of the primeval world," had our race been so ancient, we
may feel as fully persuaded as Berkeley; and we may anticipate with
confidence that many edifices and implements of human workmanship and
the skeletons of men, and casts of the human form, will continue to
exist when a great part of the present mountains, continents, and seas
have disappeared. Assuming the future duration of the planet to be
indefinitely protracted, we can foresee no limit to the perpetuation of
some of the memorials of man, which are continually entombed in the
bowels of the earth or in the bed of the ocean, unless we carry forward
our views to a period sufficient to allow the various causes of change,
both igneous and aqueous, to remodel more than once the entire crust of
the earth. _One_ complete revolution will be inadequate to efface every
monument of our existence; for many works of art might enter again and
again into the formations of successive eras, and escape obliteration
even though the very rocks in which they had been for ages imbedded were
destroyed, just as pebbles included in the conglomerates of one epoch
often contain the organized remains of beings which flourished during a
prior era.

Yet it is no less true, as a late distinguished philosopher has
declared, "that none of the works of a mortal being can be
eternal."[1097] They are in the first place wrested from the hands of
man, and lost as far as regards their subserviency to his use, by the
instrumentality of those very causes which place them in situations
where they are enabled to endure for indefinite periods. And even when
they have been included in rocky strata, when they have been made to
enter as it were into the solid framework of the globe itself, they
must nevertheless eventually perish; for every year some portion of the
earth's crust is shattered by earthquakes, or melted by volcanic fire,
or ground to dust by the moving waters on the surface. "The river of
Lethe," as Bacon eloquently remarks, "runneth as well above ground as
below."[1098]




CHAPTER XLIX.

IMBEDDING OF AQUATIC SPECIES IN SUBAQUEOUS STRATA.


  Inhumation of fresh water plants and animals--Shell marl--Fossilized
    seed-vessels and stems of chara--Recent deposits in American
    lakes--Freshwater species drifted into seas and estuaries--Lewes
    levels--Alternations of marine and freshwater strata, how
    caused--Imbedding of marine plants and animals--Cetacea stranded on
    our shores--Littoral and estuary Testacea swept into the deep
    sea--Burrowing shells--Living Testacea found at considerable
    depths--Blending of organic remains of different ages.


Having treated of the imbedding of terrestrial plants and animals, and
of human remains, in deposits now forming beneath the waters, I come
next to consider in what manner _aquatic_ species may be entombed in
strata formed in their own element.

_Freshwater plants and animals._--The remains of species belonging to
those genera of the animal and vegetable kingdoms which are more or less
exclusively confined to fresh water are for the most part preserved in
the beds of lakes or estuaries, but they are oftentimes swept down by
rivers into the sea, and there intermingled with the exuviæ of marine
races. The phenomena attending their inhumation in lacustrine deposits
are sometimes revealed to our observation by the drainage of small
lakes, such as are those in Scotland, which have been laid dry for the
sake of obtaining shell marl for agricultural uses.

In these recent formations, as seen in Forfarshire, two or three beds of
calcareous marl are sometimes observed separated from each other by
layers of drift peat, sand, or fissile clay. The marl often consists
almost entirely of an aggregate of shells of the genera Limnea,
Planorbis, Valvata, and Cyclas, of species now existing in Scotland. A
considerable proportion of the Testacea appear to have died very young,
and few of the shells are of a size which indicates their having
attained a state of maturity. The shells are sometimes entirely
decomposed, forming a pulverulent marl; sometimes in a state of good
preservation. They are frequently intermixed with stems of Charæ and
other aquatic vegetables, the whole being matted together and
compressed, forming laminæ often as thin as paper.

_Fossilized seed-vessels and stems of Chara._--As the Chara is an
aquatic plant which occurs frequently fossil in formations of different
eras, and is often of much importance to the geologist in characterizing
entire groups of strata, I shall describe the manner in which I have
found the recent species in a petrified state. They occur in a marl-lake
in Forfarshire, inclosed in nodules, and sometimes in a continuous
stratum of a kind of travertin.

[Illustration: Fig. 102.

Seed-vessel of Chara hispida.


  _a_, Part of the stem with the seed-vessel attached. Magnified.

  _b_, Natural size of the seed vessel.

  _c_, Integument of the Gyrogonite, or petrified seed-vessel
         of _Chara hispida_, found in the Scotch marl-lakes.
         Magnified.

  _d_, Section showing the nut within the integument.

  _e_, Lower end of the integument to which the stem was attached.

  _f_, Upper end of the integument to which the stigmata were attached.

  _g_, One of the spiral valves of _c_.

]

The seed-vessel of these plants is remarkably tough and hard, and
consists of a membranous nut covered by an integument (_d_, fig. 102.)
both of which are spirally striated or ribbed. The integument is
composed of five spiral valves, of a quadrangular form (_g_). In _Chara
hispida_, which abounds in the lakes of Forfarshire, and which has
become fossil in the Bakie Loch, each of the spiral valves of the
seed-vessel turns rather more than twice round the circumference, the
whole together making between ten and eleven rings. The number of these
rings differs greatly in different species, but in the same appears to
be very constant.

The stems of Charæ occur fossil in the Scotch marl in great abundance.
In some species, as in _Chara hispida_, the plant when living contains
so much carbonate of lime in its vegetable organization, independently
of calcareous incrustation, that it effervesces strongly with acids when
dry. The stems of _Chara hispida_ are longitudinally striated, with a
tendency to be spiral. These striæ, as appears to be the case with all
Charæ, turn always like the worm of a screw from right to left, while
those of the seed-vessel wind round in a contrary direction. A cross
section of the stem exhibits a curious structure, for it is composed of
a large tube surrounded by smaller tubes (fig. 103., _b_, _c_) as is
seen in some extinct as well as recent species. In the stems of several
species, however, there is only a single tube.[1099]

[Illustration: Fig. 103.

Stem and branches of Chara hispida.


  _a_, Stem and branches of the natural size.

  _b_, Section of the stem magnified.

  _c_, Showing the central tube surrounded by two rings of smaller tubes.

]

The valves of a small animal called cypris (_C. ornata?_ Lam.) occur
completely fossilized, like the stems of Charæ, in the Scotch travertin
above mentioned. The same cypris inhabits the lakes and ponds of
England, where, together with many other species, it is not uncommon.
Although extremely minute, they are visible to the naked eye, and may be
observed in great numbers, swimming swiftly through the waters of our
stagnant pools and ditches. The antennæ, at the end of which are fine
pencils of hair, are the principal organs for swimming, and are moved
with great rapidity. The animal resides within two small valves, not
unlike those of a bivalve shell, and moults its integuments annually,
which the conchiferous mollusks do not. The cast-off shells, resembling
thin scales, and occurring in countless myriads in many ancient
freshwater marls, impart to them a divisional structure, like that so
frequently derived from plates of mica.

[Illustration: Fig. 104.


  _Cypris unifasciata_, a living species, greatly
  magnified.

  _a_, Upper part.   _b_, Side view of the same.

]

[Illustration: Fig. 105.]

_Cypris vidua_, a living species, greatly magnified.[1100]]

The recent strata of lacustrine origin above alluded to are of very
small extent, but analogous deposits on the grandest scale are forming
in the great Canadian lakes, as in Lakes Superior and Huron, where beds
of sand and clay are seen inclosing shells of existing species.[1101]
The Chara also plays the same part in the subaqueous vegetation of North
America as in Europe. I observed along the borders of several freshwater
lakes in the state of New York a luxuriant crop of this plant in clear
water of moderate depth, rendering the bottom as verdant as a grassy
meadow. Here, therefore, we may expect some of the tough seed vessels to
be preserved in mud, just as we detect them fossil in the Eocene strata
of Hampshire, or in the neighborhood of Paris, and many other countries.


_Imbedding of freshwater Species in Estuary and Marine Deposits._

_In Lewes levels._--We have sometimes an opportunity of examining the
deposits which within the historical period have silted up some of our
estuaries; and excavations made for wells and other purposes, where the
sea has been finally excluded, enable us to observe the state of the
organic remains in these tracts. The valley of the Ouze between Newhaven
and Lewes is one of several estuaries from which the sea has retired
within the last seven or eight centuries; and here, as appears from the
researches of Dr. Mantell, strata thirty feet and upwards in thickness
have accumulated. At the top, beneath the vegetable soil, is a bed of
peat about five feet thick, inclosing many trunks of trees. Next below
is a stratum of blue clay containing freshwater shells of about nine
species, such as now inhabit the district. Intermixed with these was
observed the skeleton of a deer. Lower down, the layers of blue clay
contain, with the above-mentioned freshwater shells, several marine
species well known on our coast. In the lowest beds, often at the depth
of thirty-six feet; these marine Testacea occur without the slightest
intermixture of fluviatile species, and amongst them the skull of the
narwal, or sea unicorn (_Monodon monoceros_), has been detected.
Underneath all these deposits is a bed of pipe-clay, derived from the
subjacent chalk.[1102]

If we had no historical information respecting the former existence of
an inlet of the sea in this valley and of its gradual obliteration, the
inspection of the section above described would show, as clearly as a
written chronicle, the following sequence of events. First, there was a
salt-water estuary peopled for many years by species of marine Testacea
identical with those now living, and into which some of the larger
Cetacea occasionally entered. Secondly, the inlet grew shallower, and
the water became brackish, or alternately salt and fresh, so that the
remains of freshwater and marine shells were mingled in the blue
argillaceous sediment of its bottom. Thirdly, the shoaling continued
until the river-water prevailed, so that it was no longer habitable by
marine Testacea, but fitted only for the abode of fluviatile species and
aquatic insects. Fourthly, a peaty swamp or morass was formed, where
some trees grew, or perhaps were drifted during floods, and where
terrestrial quadrupeds were mired. Finally, the soil being flooded by
the river only at distant intervals, became a verdant meadow.

_In delta of Ganges and Indus._--It was before stated, that on the
sea-coast, in the delta of the Ganges, there are eight great openings,
each of which has evidently, at some ancient period, served in its turn
as the principal channel of discharge.[1103] As the base of the delta is
200 miles in length, it must happen that, as often as the great volume
of river-water is thrown into the sea by a new mouth, the sea will at
one point be converted from salt to fresh, and at another from fresh to
salt; for, with the exception of those parts where the principal
discharge takes place, the salt water not only washes the base of the
delta, but enters far into every creek and lagoon. It is evident, then,
that repeated alternations of beds containing freshwater shells, with
others filled with marine exuviæ, may here be formed. It has also been
shown by artesian borings at Calcutta (see above, p. 267), that the
delta once extended much farther than now into the gulf, and that the
river is only recovering from the sea the ground which had been lost by
subsidence at some former period. Analogous phenomena must sometimes be
occasioned by such alternate elevation and depression as has occurred in
modern times in the delta of the Indus.[1104] But the subterranean
movements affect but a small number of the deltas formed at one period
on the globe; whereas the silting up of some of the arms of great rivers
and the opening of others, and the consequent variation of the points
where the chief volume of their waters is discharged into the sea, are
phenomena common to almost every delta.

The variety of species of Testacea contained in the recent calcareous
marl of Scotland, before mentioned, is very small, but the abundance of
individuals extremely great, a circumstance very characteristic of
freshwater formations in general, as compared to marine; for in the
latter, as is seen on sea-beaches, coral-reefs, or in the bottom of the
seas examined by dredging, wherever the individual shells are
exceedingly numerous, there rarely fails to be a vast variety of
species.


_Imbedding of the Remains of Marine Plants and Animals._

_Marine plants._--The large banks of drift sea-weed which occur on each
side of the equator in the Atlantic, Pacific, and Indian oceans, were
before alluded to.[1105] These, when they subside, may often produce
considerable beds of vegetable matter. In Holland, submarine peat is
derived from Fuci, and on parts of our own coast from _Zostera marina_.
In places where Algæ do not generate peat, they may nevertheless leave
traces of their form imprinted on argillaceous and calcareous mud, as
they are usually very tough in their texture.

Sea-weeds are often cast up in such abundance on our shores during heavy
gales, that we cannot doubt that occasionally vast numbers of them are
imbedded in littoral deposits now in progress. We learn from the
researches of Dr. Forchhammer, that besides supplying in common with
land plants the materials of coal, the Algæ must give rise to important
chemical changes in the composition of strata in which they are
imbedded. These plants always contain sulphuric acid, and sometimes in
as large a quantity as 8½ per cent., combined with potash: magnesia
also and phosphoric acid are constant ingredients. Whenever large masses
of sea-weeds putrefy in contact with ferruginous clay, sulphuret of
iron, or iron pyrites, is formed by the union of the sulphur of the
plants with the iron of the clay; while the potash, released from its
union with the clay (_i. e._ silicate of alumina), forms with it a
peculiar compound. Many of the mineral characteristics of ancient rocks,
especially the alum slates, and the pyrites which occur in clay slate,
and the fragments of anthracite in marine Silurian strata, may be
explained by the decomposition of fucoids or sea-weeds.[1106]

_Imbedding of cetacea._--It is not uncommon for the larger Cetacea,
which can float only in a considerable depth of water, to be carried
during storms or high tides into estuaries, or upon low shores, where,
upon the retiring of high water, they are stranded. Thus a narwal
(_Monodon monoceros_) was found on the beach, near Boston in
Lincolnshire, in the year 1800, the whole of its body buried in the mud.
A fisherman going to his boat saw the horn, and tried to pull it out,
when the animal began to stir itself.[1107] An individual of the common
whale (_Balæna mysticetus_), which measured seventy feet,
came ashore near Peterhead, in 1682. Many individuals of the genus
Balænoptera have met the same fate. It will be sufficient to refer to
those cast on shore near Burnt Island, and at Alloa, recorded by Sibbald
and Neill. The other individual mentioned by Sibbald, as having come
ashore at Boyne, in Banffshire, was probably a razor-back. Of the genus
Catodon (_Cachalot_), Ray mentions a large one stranded on the west
coast of Holland in 1598, and the fact is also commemorated in a Dutch
engraving of the time of much merit. Sibbald, too, records that a herd
of Cachalots, upwards of 100 in number, were found stranded at
Cairston, in Orkney. The dead bodies of the larger Cetacea are sometimes
found floating on the surface of the waters, as was the case with the
immense whale exhibited in London in 1831. And the carcase of a sea-cow
or Lamantine (_Halicora_) was, in 1785, cast ashore near Leith.

To some accident of this kind we may refer the position of the skeleton
of a whale, seventy-three feet long, which was found at Airthrey, on the
Forth, near Stirling, imbedded in clay twenty feet higher than the
surface of the highest tide of the river Forth at the present day. From
the situation of the Roman station and causeways at a small distance
from the spot, it is concluded that the whale must have been stranded
there at a period prior to the Christian era.[1108]

Other fossil remains of this class have also been found in estuaries
known to have been silted up in recent times, one example of which has
been already mentioned near Lewes, in Sussex.

[Illustration: Fig. 106.

Fossil eggs of turtles from the Island of Ascension.[1109]]

_Marine reptiles._--Some singular fossils have lately been discovered in
the Island of Ascension, in a stone said to be continually forming on
the beach, where the waves threw up small rounded fragments of shells
and corals, which, in the course of time, become firmly agglutinated
together, and constitute a stone used largely for building and making
lime. In a quarry on the N. W. side of the island, about 100 yards from
the sea, some fossil eggs of turtles have been discovered in the hard
rock thus formed. The eggs must have been nearly hatched at the time
when they perished; for the bones of the young turtle are seen in the
interior, with their shape fully developed, the interstices between the
bones being entirely filled with grains of sand, which are cemented
together, so that when the egg-shells are removed perfect casts of their
form remain in stone. In the single specimen here figured (fig. 106),
which is only five inches in its longest diameter, no less than seven
eggs are preserved.[1110]

To explain the state in which they occur fossil, it seems necessary to
suppose that after the eggs were almost hatched in the warm sand, a
great wave threw upon them so much more sand as to prevent the rays of
the sun from penetrating, so that the yolk was chilled and deprived of
vitality. The shells were, perhaps, slightly broken at the same time,
so that small grains of sand might gradually be introduced into the
interior by water as it percolated through the beach.

[Illustration: Fig. 107.

One of the eggs in fig. 106, of the natural size, showing the bones of
the foetus which had been nearly hatched.]

_Marine testacea._--The aquatic animals and plants which inhabit an
estuary are liable, like the trees and land animals which people the
alluvial plains of a great river, to be swept from time to time far into
the deep; for as a river is perpetually shifting its course, and
undermining a portion of its banks with the forests which cover them, so
the marine current alters its direction from time to time, and bears
away the banks of sand and mud against which it turns its force. These
banks may consist in great measure of shells peculiar to shallow and
sometimes brackish water, which may have been accumulating for
centuries, until at length they are carried away and spread out along
the bottom of the sea, at a depth at which they could not have lived and
multiplied. Thus littoral and estuary shells are more frequently liable
even than freshwater species, to be intermixed with the exuviæ of
pelagic tribes.

After the storm of February 4, 1831, when several vessels were wrecked
in the estuary of the Forth, the current was directed against a bed of
oysters with such force, that great heaps of them were thrown _alive_
upon the beach, and remained above high-water mark. I collected many of
these oysters, as also the common eatable whelks (_Buccina_), thrown up
with them, and observed that, although still living, their shells were
worn by the long attrition of sand which had passed over them as they
lay in their native bed, and which had evidently not resulted from the
mere action of the tempest by which they were cast ashore.

From these facts we learn that the union of the two parts of a bivalve
shell does not prove that it has not been transported to a distance;
and when we find shells worn, and with all their prominent parts rubbed
off, they may still have been imbedded where they grew.

_Burrowing shells._--It sometimes appears extraordinary, when we observe
the violence of the breakers on our coast, and see the strength of the
current in removing cliffs, and sweeping out new channels, that many
tender and fragile shells should inhabit the sea in the immediate
vicinity of this turmoil. But a great number of the bivalve Testacea,
and many also of the turbinated univalves, burrow in sand or mud. The
Solen and the Cardium, for example, which are usually found in shallow
water near the shore, pierce through a soft bottom without injury to
their shells; and the Pholas can drill a cavity through mud of
considerable hardness. The species of these and many other tribes can
sink, when alarmed, with considerable rapidity, often to the depth of
several feet, and can also penetrate upwards again to the surface, if a
mass of matter be heaped upon them. The hurricane, therefore, may expend
its fury in vain, and may sweep away even the upper part of banks of
sand or mud, or may roll pebbles over them, and yet these Testacea may
remain below secure and uninjured.

_Shells become fossil at considerable depths._--I have already stated
that, at the depth of 950 fathoms, between Gibraltar and Ceuta, Captain
Smith found a gravelly bottom, with fragments of broken shells, carried
thither probably from the comparatively shallow parts of the neighboring
straits, through which a powerful current flows. Beds of shelly sand
might here, in the course of ages, be accumulated several thousand feet
thick. But, without the aid of the drifting power of a current, shells
may accumulate in the spot where they live and die, at great depths from
the surface, if sediment be thrown down upon them; for even in our own
colder latitudes, the depths at which living marine animals abound is
very considerable. Captain Vidal ascertained, by soundings made off Tory
Island, on the northwest coast of Ireland, that Crustacea, Star-fish,
and Testacea occurred at various depths between fifty and one hundred
fathoms; and he drew up Dentalia from the mud of Galway Bay, in 230 and
240 _fathoms_ water.

The same hydrographer discovered on the Rockhall Bank large quantities
of shells at depths varying from 45 to 190 fathoms. The shells were for
the most part pulverized, and evidently recent, as they retained their
colors. In the same region a bed of fish bones was observed extending
for two miles along the bottom of the sea in eighty and ninety fathoms
water. At the eastern extremity also of Rockhall Bank, fishbones were
met with, mingled with pieces of fresh shell, at the depth of 235
fathoms.

Analogous formations are in progress in the submarine tracts extending
from the Shetland Isles to the north of Ireland, wherever soundings can
be procured. A continuous deposit of sand and mud, replete with broken
and entire shells, Echini, &c., has been traced for upwards of twenty
miles to the eastward of the Faroe Islands, usually at the depth of from
forty to one hundred fathoms. In one part of this tract (lat. 61° 50',
long. 6° 30') fish-bones occur in extraordinary profusion, so that the
lead cannot be drawn up without some vertebræ being attached. This "bone
bed," as it was called by our surveyors, is three miles and a half in
length, and forty-five fathoms under water, and contains a few shells
intermingled with the bones.

In the British seas, the shells and other organic remains lie in soft
mud or loose sand and gravel; whereas, in the bed of the Adriatic,
Donati found them frequently inclosed in stone of recent origin. This is
precisely the difference in character which we might have expected to
exist between the British marine formations now in progress and those of
the Adriatic; for calcareous and other mineral springs abound in the
Mediterranean and lands adjoining, while they are almost entirely
wanting in our own country. I have already adverted to the eight regions
of different depths in the Ægean Sea, each characterized by a peculiar
assemblage of shells, which have been described by Professor E. Forbes,
who explored them by dredging. (See above, p. 649.)

During his survey of the west coast of Africa, Captain Sir E. Belcher
found, by frequent soundings between the twenty-third and twentieth
degrees of north latitude, that the bottom of the sea, at the depth of
from twenty to about fifty fathoms, consists of sand with a great
intermixture of shells, often entire, but sometimes finely comminuted.
Between the eleventh and ninth degrees of north latitude, on the same
coast, at soundings varying from twenty to about eighty fathoms, he
brought up abundance of corals and shells mixed with sand. These also
were in some parts entire, and in others worn and broken.

In all these cases, it is only necessary that there should be some
deposition of sedimentary matter, however minute, such as may be
supplied by rivers draining a continent, or currents preying on a line
of cliffs, in order that stratified formations, hundreds of feet in
thickness, and replete with organic remains, should result in the course
of ages.

But although some deposits may thus extend continuously for a thousand
miles or more near certain coasts, the greater part of the bed of the
ocean, remote from continents and islands, may very probably receive, at
the same time, no new accessions of drift matter, all sediment being
intercepted by intervening hollows, in which a marine current must clear
its waters as thoroughly as a turbid river in a lake. Erroneous theories
in geology may be formed not only from overlooking the great extent of
simultaneous deposits now in progress, but also from the assumption that
such formations may be universal or coextensive with the bed of the
ocean.

We frequently observe, on the sea beach, very perfect specimens of
fossil shells, quite detached from their matrix, which have been washed
out of older formations, constituting the sea-cliffs. They may be all of
extinct species, like the Eocene freshwater and marine shells strewed
over the shores of Hampshire, yet when they become mingled with the
shells of the present period, and buried in the same deposits of mud and
sand, they would appear, if upraised and examined by future geologists,
to have been all of the same age. That such intermixture and blending
of organic remains of different ages have actually taken place in former
times, is unquestionable, though the occurrence appears to be very local
and exceptional. It is, however, a class of accidents more likely than
almost any other to lead to serious anachronisms in geological
chronology.




CHAPTER L.

FORMATION OF CORAL REEFS.


  Growth of coral chiefly confined to tropical regions--Principal
    genera of coral-building zoophytes--Their rate of growth--Seldom
    flourish at greater depths than twenty fathoms--Atolls or annular
    reefs with lagoons--Maldive Isles--Origin of the circular
    form--Coral reefs not based on submerged volcanic craters--Mr.
    Darwin's theory of subsidence in explanation of atolls, encircling
    and barrier reefs--Why the windward side of atolls
    highest--Subsidence explains why all atolls are nearly on one
    level--Alternate areas of elevation and subsidence--Origin of
    openings into the lagoons--Size of atolls and barrier
    reefs--Objection to the theory of subsidence
    considered--Composition, structure, and stratified arrangement of
    rocks now forming in coral reefs--Lime, whence derived--Supposed
    increase of calcareous matter in modern epochs
    controverted--Concluding remarks.


The powers of the organic creation in modifying the form and structure
of the earth's crust, are most conspicuously displayed in the labors of
the coral animals. We may compare the operation of these zoophytes in
the ocean, to the effects produced on a smaller scale upon the land by
the plants which generate peat. In the case of the Sphagnum, the upper
part vegetates while the lower part is entering into a mineral mass, in
which the traces of organization remain when life has entirely ceased.
In corals, in like manner, the more durable materials of the generation
that has passed away serve as the foundation on which the living animals
continue to rear a similar structure.

The stony part of the lamelliform zoophyte may be likened to an internal
skeleton; for it is always more or less surrounded by a soft animal
substance capable of expanding itself; yet, when alarmed, it has the
power of contracting and drawing itself almost entirely into the cells
and hollows of the hard coral. Although oftentimes beautifully colored
in their own element, the soft parts become when taken from the sea
nothing more in appearance than a brown slime spread over the stony
nucleus.[1111]

The growth of those corals which form reefs of solid stone is entirely
confined to the warmer regions of the globe, rarely extending beyond the
tropics above two or three degrees, except under peculiar circumstances,
as in the Bermuda Islands, in lat. 32° N., where the Atlantic is warmed
by the Gulf stream. The Pacific Ocean, throughout a space comprehended
between the thirtieth parallels of latitude on each side of the equator,
is extremely productive of coral; as also are the Arabian and Persian
Gulfs. Coral is also abundant in the sea between the coast of Malabar
and the island of Madagascar. Flinders describes a reef of coral on the
east coast of New Holland as having a length of nearly 1000 miles, and
as being in one part unbroken for a distance of 350 miles. Some groups
of coral islands in the Pacific are from 1100 to 1200 miles in length,
by 300 or 400 in breadth, as the Dangerous Archipelago, for example, and
that called Radack by Kotzebue; but the islands within these spaces are
always small points, and often very thinly sown.

[Illustration: Fig. 108.

_Meandrina labyrinthica_, Lam.]

Of the numerous species of zoophytes which are engaged in the production
of coral banks, some of the most common belong to the Lamarckian genera
Astrea, Porites, Madrepora, Millepora, Caryophyllia, and Meandrina.

_Rate of the growth of Coral._--Very different opinions have been
entertained in regard to the rate at which coral reefs increase. In
Captain Beechey's late expedition to the Pacific, no positive
information could be obtained of any channel having been filled up
within a given period; and it seems established, that several reefs had
remained for more than half a century, at about the same depth from the
surface.

Ehrenberg also questions the fact of channels and harbors having been
closed up in the Red Sea by the rapid increase of coral limestone. He
supposes the notion to have arisen from the circumstance of havens
having been occasionally filled up in some places with coral sand, in
others with large quantities of ballast of coral rock thrown down from
vessels.

[Illustration: Genera of Zoophytes most common in coral reefs.

Fig. 109.

_Astrea dipsacea_, Lam.]

[Illustration: Fig. 110.

Extremity of branch of _Madrepora muricata_, Lin.]

[Illustration: Fig. 111.

_Caryophyllia fastigiata_, Lam.]

[Illustration: Fig. 112.

_Porites clavaria_, Lam.]

[Illustration: Fig. 113.

_Oculina hirtella_, Lam.]

The natives of the Bermuda Islands point out certain corals now growing
in the sea, which, according to tradition, have been living in the same
spots for centuries. It is supposed that some of them may vie in age
with the most ancient trees of Europe. Ehrenberg also observed single
corals of the genera Meandrina and Favia, having a globular form, from
six to nine feet in diameter, "which must (he says) be of immense
antiquity, probably several thousand years old, so that Pharaoh may have
looked upon these same individuals in the Red Sea."[1112] They certainly
imply, as he remarks, that the reef on which they grow has increased at
a very slow rate. After collecting more than 100 species, he found none
of them covered with parasitic zoophytes, nor any instance of a living
coral growing on another living coral. To this repulsive power which
they exert whilst living, against all others of their own class, we owe
the beautiful symmetry of some large Meandrinæ, and other species which
adorn our museums. Yet Balani and Serpulæ can attach themselves to
living corals, and holes are excavated in them by saxicavous mollusca.

At the island called Taaopoto, in the South Pacific, the anchor of a
ship, wrecked about 50 years before, was observed in seven fathoms
water, still preserving its original form, but entirely incrusted by
coral.[1113] This fact would seem to imply a slow rate of augmentation;
but to form a correct estimate of the average rate must be very
difficult, since it must vary not only according to the species of
coral, but according to the circumstances under which each species may
be placed; such, for example, as the depth from the surface, the
quantity of light, the temperature of the water, its freedom from sand
or mud, or the absence or presence of breakers, which is favorable to
the growth of some kinds and is fatal to that of others. It should also
be observed that the apparent stationary condition of some coral reefs,
which according to Beechey have remained for centuries at the same depth
under water, may be due to subsidence, the upward growth of the coral
having been just sufficient to keep pace with the sinking of the solid
foundation on which the zoophytes have built. We shall afterwards see
how far this hypothesis is borne out by other evidence in the regions of
annular reefs or atolls.

In one of the Maldive islands a coral reef, which, within a few years,
existed on an islet bearing cocoa-nut trees, was found by Lieutenant
Prentice, "_entirely covered with live coral and madrepore_." The
natives stated that the islet had been washed away by a change in the
currents, and it is clear that a coating of growing coral had been
formed in a short time.[1114] Experiments, also, of Dr. Allan, on the
east coast of Madagascar, prove the possibility of coral growing to a
thickness of three feet in about half a year,[1115] so that the rate of
increase may, under favorable circumstances, be very far from slow.

It must not be supposed that the calcareous masses termed coral reefs
are exclusively the work of zoophytes: a great variety of shells, and,
among them, some of the largest and heaviest of known species,
contribute to augment the mass. In the South Pacific, great beds of
oysters, mussels, _Pinnæ marinæ_, _Chamoe_ (or _Tridacnæ_), and other
shells, cover in profusion almost every reef; and on the beach of coral
islands are seen the shells of echini and broken fragments of
crustaceous animals. Large shoals of fish are also discernible through
the clear blue water, and their teeth and hard palates cannot fail to be
often preserved although their soft cartilaginous bones may decay.

It was the opinion of the German naturalist Forster, in 1780, after his
voyage round the world with Captain Cook, that coral animals had the
power of building up steep and almost perpendicular walls from great
depths in the sea, a notion afterwards adopted by Captain Flinders and
others; but it is now very generally believed that these zoophytes
cannot live in water of great depths.

Mr. Darwin has come to the conclusion, that those species which are most
effective in the construction of reefs, rarely flourish at a greater
depth than 20 fathoms, or 120 feet. In some lagoons, however, where the
water is but little agitated, there are, according to Kotzebue, beds of
living coral in 25 fathoms of water, or 150 feet; but these may perhaps
have begun to live in shallower water, and may have been carried
downwards by the subsidence of the reef. There are also various species
of zoophytes, and among them some which are provided with calcareous as
well as horny stems, which live in much deeper water, even in some cases
to a depth of 180 fathoms; but these do not appear to give origin to
stony reefs.

There is every variety of form in coral reefs, but the most remarkable
and numerous in the Pacific consist of circular or oval strips of dry
land, enclosing a shallow lake or lagoon of still water, in which
zoophytes and mollusca abound. These annular reefs just raise themselves
above the level of the sea, and are surrounded by a deep and often
unfathomable ocean.

In the annexed cut (fig. 114), one of these circular islands is
represented, just rising above the waves, covered with the cocoa-nut and
other trees, and inclosing within a lagoon of tranquil water.

[Illustration: Fig. 114.

View of Whitsunday Island. (Capt. Beechey.)[1116]]

The accompanying section will enable the reader to comprehend the usual
form of such islands. (Fig. 115.)

[Illustration: Fig. 115.

Section of a Coral Island.


  _a_, _a_, Habitable part of the island, consisting of a strip
              of coral, inclosing the lagoon.
  _b_, _b_, The lagoon.

]

The subjoined cut (fig. 116.) exhibits a small part of the section of a
coral island on a larger scale.

[Illustration: Fig. 116.

Section of part of a Coral Island.

_a_, _b_, Habitable part of the island.

_b_, _c_, Slope of the side of the island, plunging at an angle of
forty-five to the depth of fifteen hundred feet.

_c_, _c_, Part of the lagoon.

_d_, _d_, Knolls of coral in the lagoon, with overhanging masses of
coral resembling the capitals of columns.]

Of thirty-two of these coral islands visited by Beechey in his voyage to
the Pacific, twenty-nine had lagoons in their centres. The largest was
30 miles in diameter, and the smallest less than a mile. All were
increasing their dimensions by the active operations of the lithophytes,
which appeared to be gradually extending and bringing the immersed parts
of their structure to the surface. The scene presented by these annular
reefs is equally striking for its singularity and beauty. A strip of
land a few hundred yards wide is covered by lofty cocoa-nut trees, above
which is the blue vault of heaven. This band of verdure is bounded by a
beach of glittering white sand, the outer margin of which is encircled
with a ring of snow-white breakers, beyond which are the dark heaving
waters of the ocean. The inner beach incloses the still clear water of
the lagoon, resting in its greater part on white sand, and when
illuminated by a vertical sun, of a most vivid green.[1117] Certain
species of zoophytes abound most in the lagoon, others on the exterior
margin, where there is a great surf. "The ocean," says Mr. Darwin,
"throwing its breakers on these outer shores, appears an invincible
enemy, yet we see it resisted and even conquered by means which at first
seem most weak and inefficient. No periods of repose are granted, and
the long swell caused by the steady action of the trade wind never
ceases. The breakers exceed in violence those of our temperate regions,
and it is impossible to behold them without feeling a conviction that
rocks of granite or quartz would ultimately yield and be demolished by
such irresistible forces. Yet these low insignificant coral islets stand
and are victorious, for here another power, as antagonist to the former,
takes part in the contest. The organic forces separate the atoms of
carbonate of lime one by one from the foaming breakers, and unite them
into a symmetrical structure; myriads of architects are at work night
and day, month after month, and we see their soft and gelatinous bodies
through the agency of the vital laws conquering the great mechanical
power of the waves of an ocean, which neither the art of man, nor the
inanimate works of nature could successfully resist."[1118]

As the coral animals require to be continually immersed in salt water,
they cannot raise themselves by their own efforts, above the level of
the lowest tides. The manner in which the reefs are converted into
islands above the level of the sea is thus described by Chamisso, a
naturalist, who accompanied Kotzebue in his voyages:--"When the reef,"
says he, "is of such a height that it remains almost dry at low water
the corals leave off building. Above this line a continuous mass of
solid stone is seen composed of the shells of mollusks and echini, with
their broken-off prickles and fragments of coral, united by calcareous
sand, produced by the pulverization of shells. The heat of the sun often
penetrates the mass of stone when it is dry, so that it splits in many
places, and the force of the waves is thereby enabled to separate and
lift blocks of coral, frequently six feet long and three or four in
thickness, and throw them upon the reef, by which means the ridge
becomes at length so high that it is covered only during some seasons of
the year by the spring tides. After this the calcareous sand lies
undisturbed, and offers to the seeds of trees and plants cast upon it by
the waves a soil upon which they rapidly grow, to overshadow its
dazzling white surface. Entire trunks of trees, which are carried by the
rivers from other countries and islands, find here, at length, a
resting-place after their long wanderings: with these come some small
animals such as insects and lizards, as the first inhabitants. Even
before the trees form a wood, the sea-birds nestle here; stray
land-birds take refuge in the bushes; and, at a much later period, when
the work has been long since completed, man appears and builds his hut
on the fruitful soil."[1119]

In the above description the solid stone is stated to consist of shell
and coral, united by sand; but masses of very compact limestone are also
found even in the uppermost and newest parts of the reef, such as could
only have been produced by chemical precipitation. Professor Agassiz
also informs me that his observations on the Florida reefs (which
confirm Darwin's theory of atolls to be mentioned in the sequel) have
convinced him, that large blocks are loosened, not by shrinkage in the
sun's heat, as Chamisso imagined, but by innumerable perforations of
lithodomi and other boring testacea.

The carbonate of lime may have been principally derived from the
decomposition of corals and testacea; for when the animal matter
undergoes putrefaction, the calcareous residuum must be set free under
circumstances very favorable to precipitation, especially when there are
other calcareous substances, such as shells and corals, on which it may
be deposited. Thus organic bodies may be inclosed in a solid cement, and
become portions of rocky masses.[1120]

The width of the circular strip of dead coral forming the islands
explored by Captain Beechey, exceeded in no instance half a mile from
the usual wash of the sea to the edge of the lagoon, and, in general,
was only about three or four hundred yards.[1121] The depth of the
lagoons is various; in some, entered by Captain Beechey, it was from
twenty to thirty-eight fathoms.

The two other peculiarities which are most characteristic of the annular
reef or atoll are first, that the strip of dead coral is invariably
highest on the windward side, and secondly, that there is very generally
an opening at some point in the reef affording a narrow passage, often
of considerable depth, from the sea into the lagoon.

[Illustration: Fig. 117.]

_Maldive and Laccadive Isles._--The chain of reefs and islets called the
Maldives (see fig. 117.), situated in the Indian Ocean, to the
south-west of Malabar, forms a chain 470 geographical miles in length,
running due north and south, with an average breadth of about 50 miles.
It is composed throughout of a series of circular assemblages of islets,
all formed of coral, the larger groups being from forty to ninety miles
in their longest diameter. Captain Horsburgh, whose chart of these
islands is subjoined, states, that outside of each circle or _atoll_, as
it is termed, there are coral reefs sometimes extending to the distance
of two or three miles, beyond which there are no soundings at immense
depths. But in the centre of each atoll there is a lagoon from fifteen
to forty-nine fathoms deep. In the channels between the atolls no
soundings can usually be obtained at the depth of 150 or even 250
fathoms, but during Captain Moresby's survey, soundings were struck at
150 and 200 fathoms, the only instances as yet known of the bottom
having been reached, either in the Indian or Pacific oceans, in a space
intervening between two separate and well characterized atolls.

The singularity in the form of the atolls of this archipelago consists
in their being made up, not of one continuous circular reef but of a
ring of small coral islets sometimes more than a hundred in number, each
of which is a miniature atoll in itself; in other words, a ring-shaped
strip of coral surrounding a lagoon of salt water. To account for the
origin of these, Mr. Darwin supposes the larger annular reef to have
been broken up into a number of fragments, each of which acquired its
peculiar configurations under the influence of causes similar to those
to which the structure of the parent atoll has been due. Many of the
minor rings are no less than three, and even five miles in diameter, and
some are situated in the midst of the principal lagoon; but this happens
only in cases where the sea can enter freely through breaches in the
outer or marginal reef.

The rocks of the Maldives are composed of sandstone formed of broken
shells and corals, such as may be obtained in a loose state from the
beach, and which is seen when exposed for a few days to the air to
become hardened. The sandstone is sometimes observed to be an aggregate
of broken shells, corals, pieces of wood, and shells of the
cocoa-nut.[1122]

The Laccadive islands run in the same line with the Maldives, on the
north, as do the isles of the Chagos Archipelago, on the south; so that
these may be continuations of the same chain of submerged mountains,
crested in a similar manner by coral limestones.

_Origin of the circular form--not volcanic._--The circular and oval
shape of so many reefs, each having a lagoon in the centre, and being
surrounded on all sides by a deep ocean, naturally suggested the idea
that they were nothing more than the crests of submarine volcanic
craters overgrown by coral; and this theory I myself advocated in the
earlier editions of this work. Although I am now about to show that it
must be abandoned, it may still be instructive to point out the grounds
on which it was formerly embraced. In the first place, it had been
remarked that there were many active volcanoes in the coral region of
the Pacific, and that in some places, as in Gambier's group, rocks
composed of porous lava rise up in a lagoon bordered by a circular reef,
just as the two cones of eruption called the Kamenis have made their
appearance in the times of history within the circular gulf of
Santorin.[1123] It was also observed that, as in S. Shetland, Barren
Island, and others of volcanic origin, there is one narrow breach in the
walls of the outer cone by which ships may enter a circular gulf, so in
like manner there is often a single deep passage leading into the lagoon
of a coral island, the lagoon itself seeming to represent the hollow or
gulf just as the ring of dry coral recalls to our minds the rim of a
volcanic crater. More lately, indeed, Mr. Darwin has shown that the
numerous volcanic craters of the Galapagos Archipelago in the Pacific
have all of them their southern sides the lowest, or in many cases quite
broken down, so that if they were submerged and incrusted with coral,
they would resemble true atolls in shape.[1124]

Another argument which I adduced when formerly defending this doctrine
was derived from Ehrenberg's statement, that some banks of coral in the
Red Sea were square, while many others were ribbon-like strips, with
flat tops, and without lagoons. Since, therefore, all the genera and
many of the species of zoophytes in the Red Sea agreed with those which
elsewhere construct lagoon islands, it followed that the stone-making
zoophytes are not guided by their own instinct in the formation of
annular reefs, but that this peculiar shape and the position of such
reefs in the midst of a deep ocean must depend on the outline of the
submarine bottom, which resembles nothing else in nature but the crater
of a lofty submerged volcanic cone. The enormous size, it is true, of
some atolls, made it necessary for me to ascribe to the craters of many
submarine volcanoes a magnitude which was startling, and which had often
been appealed to as a serious objection to the volcanic theory. That so
many of them were of the same height, or just level with the water, did
not present a difficulty so long as we remained ignorant of the fact
that the reef-building species do not grow at greater depths than
twenty-five fathoms.

_May be explained by subsidence._--Mr. Darwin, after examining a variety
of coral formations in different parts of the globe, was induced to
reject the opinion that their shape represented the form of the original
bottom. Instead of admitting that the ring of dead coral rested on a
circular or oval ridge of rock, or that the lagoon corresponded to a
preexisting cavity, he advanced a new opinion, which must, at first
sight, seem paradoxical in the extreme; namely, that the lagoon is
precisely in the place once occupied by the highest part of a
mountainous island, or, in other cases, by the top of a shoal.

The following is a brief sketch of the facts and arguments in favor of
this new view:--Besides those rings of dry coral which enclose lagoons,
there are others having a similar form and structure which encircle
lofty islands. Of the latter kind is Vanikoro, (see map, fig. 39, p.
351,) celebrated on account of the shipwreck of La Peyrouse, where the
coral reef runs at the distance of two or three miles from the shore,
the channel between it and the land having a general depth of between
200 and 300 feet. This channel, therefore, is analogous to a lagoon, but
with an island standing in the middle like a picture in its frame. In
like manner in Tahiti we see a mountainous land, with everywhere round
its margin a lake or zone of smooth salt water, separated from the ocean
by an encircling reef of coral, on which a line of breakers is always
foaming. So also New Caledonia, a long narrow island east of New
Holland, in which the rocks are granitic, is surrounded by a reef which
runs for a length of 400 miles. This reef encompasses not only the
island itself, but a ridge of rocks which are prolonged in the same
direction beneath the sea. No one, therefore, will contend for a moment
that in this case the corals are based upon the rim of a volcanic
crater, in the middle of which stands a mountain or island of granite.

The great barrier reef, already mentioned as running parallel to the
north-east coast of Australia for nearly 1000 miles, is another most
remarkable example of a long strip of coral running parallel to a coast.
Its distance from the mainland varies from twenty to seventy miles, and
the depth of the great arm of the sea thus enclosed is usually between
ten and twenty fathoms, but towards one end from forty to sixty. This
great reef would extend much farther, according to Mr. Jukes, if the
growth of coral were not prevented off the shores of New Guinea by a
muddy bottom, caused by rivers charged with sediment which flow from the
southern coast of that great island.[1125]

Two classes of reefs, therefore, have now been considered; first, the
atoll, and, secondly, the encircling and barrier reef, all agreeing
perfectly in structure, and the sole difference lying in the absence in
the case of the atoll of all land, and in the others the presence of
land bounded either by an encircling or a barrier reef. But there is
still a third class of reefs, called by Mr. Darwin "fringing reefs,"
which approach much nearer the land than those of the encircling and
barrier class, and which indeed so nearly touched the coast as to leave
nothing in the intervening space resembling a lagoon. "That these reefs
are not attached quite close to the shore appears to be the result of
two causes; first, that the water immediately adjoining the beach is
rendered turbid by the surf, and therefore injurious to all zoophytes;
and, secondly, that the larger and efficient kinds only flourish on the
outer edge amidst the breakers of the open sea."[1126]

[Illustration: Fig. 118.

Supposed section of an island with an encircling reef of coral.

A, The island.

_b_, _c_, Highest points of the encircling reef between which and the
coast is seen a space occupied by still water.]

It will at once be conceded that there is so much analogy between the
form and position of the strip of coral in the atoll, and in the
encircling and barrier reef, that no explanation can be satisfactory
which does not include the whole. If we turn in the first place to the
encircling and barrier reefs, and endeavor to explain how the zoophytes
could have found a bottom on which to begin to build, we are met at once
with a great difficulty. It is a general fact, long since remarked by
Dampier, that high land and deep seas go together. In other words, steep
mountains coming down abruptly to the sea-shore are generally continued
with the same slope beneath the water. But where the reef, as at _b_ and
_c_ (fig. 118), is distant several miles from a steep coast, a line
drawn perpendicularly downwards from its outer edges _b c_ to the
fundamental rock _d e_, must descend to a depth exceeding by several
thousand feet the limits at which the efficient stone-building corals
can exist, for we have seen that they cease to grow in water which is
more than 120 feet deep. That the original root immediately beneath the
points _b c_ is actually as far from the surface as _d e_, is not merely
inferred from Dampier's rule, but confirmed by the fact, that,
immediately outside the reef, soundings are either not met with at all,
or only at enormous depths. In short, the ocean is as deep there as
might have been anticipated in the neighborhood of a bold coast; and it
is obviously the presence of the coral alone which has given rise to the
anomalous existence of shallow water on the reef and between it and the
land.

After studying in minute detail all the phenomena above described, Mr.
Darwin has offered in explanation a theory now very generally adopted.
The coral-forming polypi, he states, begin to build in water of a
moderate depth, and while they are yet at work, the bottom of the sea
subsides gradually, so that the foundation of their edifice is carried
downwards at the same time that they are raising the superstructure. If,
therefore, the rate of subsidence be not too rapid, the growing coral
will continue to build up to the surface; the mass always gaining in
height above its original base, but remaining in other respects in the
same position. Not so with the land; each inch lost is irreclaimably
gone; as it sinks, the water gains foot by foot on the shore, till in
many cases the highest peak of the original island disappears. What was
before land is then occupied by the lagoon, the position of the
encircling coral remaining unaltered, with the exception of a slight
contraction of its dimensions.

In this manner are encircling reefs and atolls produced; and in
confirmation of his views Mr. Darwin has pointed out examples which
illustrate every intermediate state, from that of lofty islands, such as
Otaheite, encircled by coral, to that of Gambier's group, where a few
peaks only of land rise out of a lagoon, and lastly, to the perfect
atoll, having a lagoon several hundred feet deep, surrounded by a reef
rising steeply from an unfathomed ocean.

[Illustration: Fig. 119.]

If we embrace these views, it is clear, that in regions of growing coral
a similar subsidence must give rise to barrier reefs along the shores of
a continent. Thus suppose A (fig. 119), to represent the north-east
portion of Australia, and _b c_ the ancient level of the sea, when the
coral reef _d_ was formed. If the land sink so that it is submerged more
and more, the sea must at length stand at the level _e f_, the reef in
the mean time having been enlarged and raised to the point _g_. The
distance between the shore _f_, and the barrier reef _g_, is now much
greater than originally between the shore _c_ and the reef _d_, and the
longer the subsidence continues the farther will the coast of the
mainland recede.

When the first edition of this work appeared in 1831, several years
before Mr. Darwin had investigated the facts on which his theory is
founded, I had come to the opinion that the land was subsiding at the
bottom of those parts of the Pacific where atolls are numerous, although
I failed to perceive that such a subsidence, if conceded, would equally
solve the enigma as to the form both of annular and barrier reefs.

I shall cite the passage referred to, as published by me in 1831:--"It
is a remarkable circumstance that there should be so vast an area in
Eastern Oceanica, studded with minute islands, without one single spot
where there is a wider extent of land than belongs to such islands as
Otaheite, Owhyhee, and a few others, which either have been or are still
the seats of active volcanoes. If an equilibrium only were maintained
between the upheaving and depressing force of earthquakes, large islands
would very soon be formed in the Pacific; for, in that case, the growth
of limestone, the flowing of lava, and the ejection of volcanic ashes,
would combine with the upheaving force to form new land.

"Suppose a shoal, 600 miles in length, to sink fifteen feet, and then to
remain unmoved for a thousand years; during that interval the growing
coral may again approach the surface. Then let the mass be re-elevated
fifteen feet, so that the original reef is restored to its former
position: in this case, the new coral formed since the first subsidence
will constitute an island 600 miles long. An analogous result would have
occurred if a lava-current fifteen feet thick had overflowed the
submerged reef. The absence, therefore, of more extensive tracts of land
in the Pacific, seems to show that the amount of subsidence by
earthquakes exceeds, in that quarter of the globe, at present, the
elevation due to the same cause."[1127]

Another proof also of subsidence derived from the structure of atolls,
was pointed out by me in the following passage in all former editions.
"The low coral islands of the Pacific," says Captain Beechey, "follow
one general rule in having their windward side higher and more perfect
than the other. At Gambia and Matilda islands this inequality is very
conspicuous, the weather side of both being wooded, and of the former
inhabited, while the other sides are from twenty to thirty feet under
water; where, however, they may be perceived to be equally _narrow_ and
well defined. It is on the leeward side also that the entrances into the
lagoons occur; and although they may sometimes be situated on a side
that runs in the direction of the wind, as at Bow Island, yet there are
none to windward." These observations of Captain Beechey accord with
those which Captain Horsburgh and other hydrographers have made in
regard to the coral islands of other seas. From this fortunate
circumstance ships can enter and sail out with ease; whereas if the
narrow inlets were to windward, vessels which once entered might not
succeed for months in making their way out again. The well-known
security of many of these harbors depends entirely on this fortunate
peculiarity in their structure.

"In what manner is this singular conformation to be accounted for? The
action of the waves is seen to be the cause of the superior elevation
of some reefs on their windward sides, where sand and large masses of
coral rock are thrown up by the breakers; but there is a variety of
cases where this cause alone is inadequate to solve the problem; for
reefs submerged at considerable depths, where the movements of the sea
cannot exert much power, have, nevertheless, the same conformation, the
leeward being much lower than the windward side.[1128]

"I am informed by Captain King, that, on examining the reefs called
Rowley Shoals, which lie off the north-west coast of Australia, where
the east and west monsoons prevail alternately, he found the open side
of one crescent-shaped reef, the Impérieuse, turned to the east, and of
another, the Mermaid, turned to the west; while a third oval reef, of
the same group, was entirely submerged. This want of conformity is
exactly what we should expect, where the winds vary periodically.

"It seems impossible to refer the phenomenon now under consideration to
any original uniformity in the configuration of submarine volcanoes, on
the summits of which we may suppose the coral reefs to grow; for
although it is very common for craters to be broken down on one side
only, we cannot imagine any cause that should breach them all in the
same direction. But the difficulty will, perhaps, be removed, if we call
in another part of the volcanic agency--subsidence by earthquakes.
Suppose the windward barrier to have been raised by the mechanical
action of the waves to the height of two or three yards above the wall
on the leeward side, and then the whole island to sink down a few
fathoms, the appearances described would then be presented by the
submerged reef. A repetition of such operations, by the alternate
elevation and depression of the same mass (an hypothesis strictly
conformable to analogy), might produce still greater inequality in the
two sides, especially as the violent efflux of the tide has probably a
strong tendency to check the accumulation of the more tender corals on
the leeward reef; while the action of the breakers contributes to raise
the windward barrier."[1129]

Previously to my adverting to the signs above enumerated of a downward
movement in the bed of the ocean, Dr. MacCulloch, Captain Beechey, and
many other writers, had shown that masses of recent coral had been laid
dry at various heights above the sea-level, both in the Red Sea, the
islands of the Pacific, and in the East and West Indies. After
describing thirty-two coral islands in the Pacific, Captain Beechey
mentioned that they were all formed of living coral except one, which,
although of coral formation, was raised about seventy or eighty feet
above the level of the sea, and was encompassed by a reef of living
coral. It is called Elizabeth or Henderson's Island, and is five miles
in length by one in breadth. It has a flat surface, and, on all sides,
except the north, is bounded by perpendicular cliffs about fifty feet
high, composed entirely of dead coral, more or less porous, honey-combed
at the surface, and hardening into a compact calcareous mass, which
possesses the fracture of secondary limestone, and has a species of
millepore interspersed through it. These cliffs are considerably
undermined by the action of the waves, and some of them appear on the
eve of precipitating their superincumbent weight into the sea. Those
which are less injured in this way present no alternate ridges or
indication of the different levels which the sea might have occupied at
different periods; but a smooth surface, as if the island, which has
probably been raised by volcanic agency, had been forced up by one great
subterraneous convulsion.[1130] At the distance of a few hundred yards
from this island, no bottom could be gained with 200 fathoms of line.

[Illustration: Fig. 120.

Elizabeth, or Henderson's Island.]

It will be seen, from the annexed sketch, communicated to me by
Lieutenant Smith, of the Blossom, that the trees came down to the beach
towards the centre of the island; a break at first sight resembling the
openings which usually lead into lagoons; but the trees stand on a steep
slope, and no hollow of an ancient lagoon was perceived.

Beechey also remarks, that the surface of Henderson's Island is flat,
and that in Queen Charlotte's Island, one of the same group, but under
water, there was no lagoon, the coral having grown up everywhere to one
level. The probable cause of this obliteration of the central basin or
lagoon will be considered in the sequel.

That the bed of the Pacific and Indian oceans, where atolls are
frequent, must have been sinking for ages, might be inferred, says Mr.
Darwin, from simply reflecting on two facts; first, that the efficient
coral-building zoophytes do not flourish in the ocean at a greater depth
than 120 feet; and, secondly, that there are spaces occupying areas of
many hundred thousand square miles, where all the islands consist of
coral, and yet none of which rise to a greater height than may be
accounted for by the action of the winds and waves on broken and
triturated coral. Were we to take for granted that the floor of the
ocean had remained stationary from the time when the coral began to
grow, we should be compelled to assume that an incredible number of
submarine mountains of vast height (for the ocean is always deep, and
often unfathomable between the different atolls) had all come to within
120 feet of the surface, and yet no one mountain had risen above water.
But no sooner do we admit the theory of subsidence, than this great,
difficulty vanishes. However varied may have been the altitude of
different islands, or the separate peaks of particular mountain-chains,
all may have been reduced to one uniform level by the gradual
submergence of the loftiest points, and the additions made to the
calcareous cappings of the less elevated summits as they subsided to
great depths.

_Openings into the lagoons._--In the general description of atolls and
encircling reefs, it was mentioned that there is almost always a deep
narrow passage opening into the lagoon, or into the still water between
the reef and the shore, which is kept open by the efflux of the sea as
the tide goes down.

The origin of this channel must, according to the theory of subsidence
before explained, be traced back to causes which were in action during
the existence of the encircling reef, and when an island or mountain-top
rose within it, for such a reef precedes the atoll in the order of
formation. Now in those islands in the Pacific, which are large enough
to feed small rivers, there is generally an opening or channel in the
surrounding coral reef at the point where the stream of fresh water
enters the sea. The depth of these channels rarely exceeds twenty-five
feet; and they may be attributed, says Captain Beechey, to the aversion
of the lithophytes to fresh water, and to the probable absence of the
mineral matter of which they construct their habitations.[1131]

Mr. Darwin, however, has shown, that mud at the bottom of river-courses
is far more influential than the freshness of the water in preventing
the growth of the polypi, for the walls which inclose the openings are
perpendicular, and do not slant off gradually, as would be the case, if
the nature of the element presented the only obstacle to the increase of
the coral-building animals.

When a breach has thus been made in the reef, it will be prevented from
closing up by the efflux of the sea at low tides; for it is sufficient
that a reef should rise a few feet above low-water mark to cause the
waters to collect in the lagoon at high tide, and when the sea falls, to
rush out at one or more points where the reef happens to be lowest or
weakest. This event is strictly analogous to that witnessed in our
estuaries, where a body of salt water accumulated during the flow issues
with great velocity at the ebb of the tide, and scours out or keeps open
a deep passage through the bar, which is almost always formed at the
mouth of a river. At first there are probably many openings, but the
growth of the coral tends to obstruct all those which do not serve as
the principal channels of discharge; so that their number is gradually
reduced to a few, and often finally to one. The fact observed
universally, that the principal opening fronts a considerable valley in
the encircled island, between the shores of which and the outer reef
there is often deep water, scarcely leaves any doubt as to the real
origin of the channel in all those countless atolls where the nucleus of
land has vanished.

_Size of atolls and barrier reefs._--In regard to the dimensions of
atolls, it was stated that some of the smallest observed by Beechey in
the Pacific were only a mile in diameter. If their external slope under
water equals upon an average an angle of 45°, then would such an atoll
at the depth of half a mile, or 2640 feet, have a diameter of two miles.
Hence it would appear that there must be a tendency in every atoll to
grow smaller, except in those cases where oscillations of level enlarge
the base on which the coral grows by throwing down a talus of detrital
matter all round the original cone of limestone.

Bow Island is described by Captain Beechey as seventy miles in
circumference, and thirty in its greatest diameter, but we have seen
that some of the Maldives are much larger.

As the shore of an island or continent which is subsiding will recede
from a coral reef at a slow or rapid rate according as the surface of
the land has a steep or gentle slope, we cannot measure the thickness of
the coral by its distance from the coast; yet, as a general rule, those
reefs which are farthest from the land imply the greatest amount of
subsidence. We learn from Flinders, that the barrier reef of
north-eastern Australia is in some places seventy miles from the
mainland, and it should seem that a calcareous formation is there in
progress 1000 miles long from north to south, with a breadth varying
from twenty to seventy miles. It may not, indeed, be continuous over
this vast area, for doubtless innumerable islands have been submerged
one after another between the reef and mainland, like some which still
remain, as, for example, Murray's Islands, lat. 9° 54' S. We are also
told that some parts of the gulf inclosed within a barrier are 400 feet
deep, so that the efficient rock-building corals cannot be growing
there, and in other parts of it islands appear encircled by reefs.

It will follow as one of the consequences of the theory already
explained that, provided the bottom of the sea does not sink too fast to
allow the zoophytes to build upwards at the same pace, the thickness of
coral will be great in proportion to the rapidity of subsidence, so that
if one area sinks two feet while another sinks one, the mass of coral in
the first area will be double that in the second. But the downward
movement must in general have been very slow and uniform, or where
intermittent, must have consisted of a great number of depressions, each
of slight amount, otherwise the bottom of the sea would have been
carried down faster than the corals could build upwards, and the island
or continent would be permanently submerged, having reached a depth of
120 or 150 feet, at which the effective reef-constructing zoophytes
cease to live. If, then, the subsidence required to account for all the
existing atolls must have amounted to three or four thousand feet, or
even sometimes more, we are brought to the conclusion that there has
been a _slow_ and _gradual_ sinking to this enormous extent. Such an
inference is perfectly in harmony with views which the grand scale of
denudation, everywhere observable in the older rocks, has led geologists
to adopt in reference to upward movements. They must also have been
gradual and continuous throughout indefinite ages to allow the waves and
currents of the ocean to operate with adequate power.

The map constructed by Mr. Darwin to display at one view the
geographical position of all the coral reefs throughout the globe is of
the highest geological interest (see above, p. 351.), leading to
splendid generalizations, when we have once embraced the theory that all
atolls and barrier reefs indicate recent subsidence, while the presence
of fringing reefs proves the land to be stationary or rising. These two
classes of coral formations are depicted by different colors; and one of
the striking facts brought to light by the same classification of coral
formations is the absence of active volcanoes in the areas of
subsidence, and their frequent presence in the areas of elevation. The
only supposed exception to this remarkable coincidence at the time when
Mr. Darwin wrote, in 1842, was the volcano of Torres Strait, at the
northern point of Australia, placed on the borders of an area of
subsidence; but it has been since proved that this volcano has no
existence.

We see, therefore, an evident connection, first, between the bursting
forth every now and then of volcanic matter through rents and fissures,
and the expansion or forcing outwards of the earth's crust, and,
secondly, between a dormant and less energetic development of
subterranean heat, and an amount of subsidence sufficiently great to
cause mountains to disappear over the broad face of the ocean, leaving
only small and scattered lagoon islands, or groups of atolls, to
indicate the spots where those mountains once stood.

On a review of the differently-colored reefs on the map alluded to, it
will be seen that there are large spaces in which upheaval, and others
in which depression prevails, and these are placed alternately, while
there are a few smaller areas where movements of oscillation occur. Thus
if we commence with the western shores of South America, between the
summit of the Andes and the Pacific (a region of earthquakes and active
volcanoes), we find signs of recent elevation, not attested indeed by
coral formations, which are wanting there, but by upraised banks of
marine shells. Then proceeding westward, we traverse a deep ocean
without islands, until we come to a band of _atolls_ and encircled
islands, including the Dangerous and Society archipelagoes, and
constituting an area of subsidence more than 4000 miles long and 600
broad. Still farther, in the same direction, we reach the chain of
islands to which the New Hebrides, Salomon, and New Ireland belong,
where fringing reefs and masses of elevated coral indicate another area
of upheaval. Again, to the westward of the New Hebrides we meet with the
encircling reef of New Caledonia and the great Australian barrier,
implying a second area of subsidence.

The only objection deserving attention which has hitherto been advanced
against the theory of atolls, as before explained (p. 759.), is that
proposed by Mr. Maclaren.[1132] "On the outside," he observes, "of coral
reefs very highly inclined, no bottom is sometimes found with a line of
2000 or 3000 feet, and this is by no means a rare case. It follows that
the reef ought to have this thickness; and Mr. Darwin's diagrams show
that he understood it so. Now, if such masses of coral exist under the
sea, they ought somewhere to be found on _terra firma_; for there is
evidence that all the lands yet visited by geologists, have been at one
time submerged. But neither in the great volcanic chain, extending from
Sumatra to Japan, nor in the West Indies, nor in any other region yet
explored, has a bed or formation of coral even 500 feet thick been
discovered, so far as we know."

When considering this objection, it is evident that the first question
we have to deal with is, whether geologists have not already discovered
calcareous masses of the required thickness and structure, or precisely
such as the upheaval of atolls might be expected to expose to view? We
are called upon, in short, to make up our minds both as to the internal
composition of the rocks that must result from the growth of corals,
whether in lagoon islands or barrier reefs, and the external shape which
the reefs would retain when upraised gradually to a vast height,--a task
by no means so easy as some may imagine. If the reader has pictured to
himself large masses of entire corals, piled one upon another, for a
thickness of several thousand feet, he unquestionably mistakes
altogether the nature of the accumulations now in progress. In the first
place, the strata at present forming very extensively over the bottom of
the ocean, within such barrier reefs as those of Australia and New
Caledonia, are known to consist chiefly of horizontal layers of
calcareous sediment, while here and there an intermixture must occur of
the detritus of granitic and other rocks brought down by rivers from the
adjoining lands, or washed from sea-cliffs by the waves and currents.
Secondly, in regard to atolls, the stone-making polypifers grow most
luxuriantly on the outer edge of the island, to a thickness of a few
feet only. Beyond this margin broken pieces of coral and calcareous sand
are strewed by the breakers over a steep seaward slope, and as the
subsidence continues the next coating of live coral does not grow
vertically over the first layer, but on a narrow annular space within
it, the reef, as was before stated (p. 761), constantly contracting its
dimensions as it sinks. Thirdly, within the lagoon the accumulation of
calcareous matter is chiefly sedimentary, a kind of chalky mud derived
from the decay of the softer corallines, with a mixture of calcareous
sand swept by the winds and waves from the surrounding circular reef.
Here and there, but only in partial clumps, are found living corals,
which grow in the middle of the lagoon, and mixed with fine mud and
sand, a great variety of shells, and fragments of testacea and
echinoderms.

We owe to Lieutenant Nelson the discovery that in the Bermudas the
calcareous mud resulting from the decomposition of the softer corallines
is absolutely undistinguishable when dried from the ordinary white chalk
of Europe,[1133] and this mud is carried to great distances by currents,
and spread far and wide over the floor of the ocean. We also have
opportunities of seeing in upraised atolls, such as Elizabeth Island,
Tonga, and Hapai, which rise above the level of the sea to heights
varying from ten to eighty feet, that the rocks of which they consist do
not differ in structure or in the state of preservation of their
included zoophytes and shells from some of the oldest limestones known
to the geologist. Captain Beechey remarks that the dead coral in
Elizabeth Island is more or less porous and honeycombed at the surface,
and hardening into a compact rock which has the fracture of _secondary
limestone_.[1134]

The island of Pulo Nias, off Sumatra (see Map, fig. 39. p. 351), which
is about 3000 feet high, is described by Dr. Jack as being overspread by
coral and large shells of the _Chama (Tridacna) gigas_, which rest on
quartzose and arenaceous rocks, at various levels from the sea-coast to
the summit of the highest hills.

The cliffs of the island of Timor in the Indian Ocean are composed, says
Mr. Jukes, of a raised coral reef abounding in _Astræa_, _Meandrina_,
and _Porites_, with shells of _Strombus_, _Conus_, _Nerita_, _Arca_,
_Pecten_, _Venus_, and _Lucina_. On a ledge about 150 feet above the
sea, a Tridacna (or large clam shell), two feet across, was found bedded
in the rock with closed valves, just as they are often seen in barrier
reefs. This formation in the islands of Sandlewood, Sumbawa, Madura, and
Java, where it is exposed in sea cliffs, was found to be from 200 to 300
feet thick, and is believed to ascend to much greater heights in the
interior. It has usually the form of a "chalk-like" rock, white when
broken, but in the weathered surface turning nearly black.[1135]

It appears, therefore, premature to assert that there are no recent
coral formations uplifted to great heights, for we are only beginning to
be acquainted with the geological structure of the rocks of equatorial
regions. Some of the upraised islands, such as Elizabeth and Queen
Charlotte, in the Pacific, although placed in regions of atolls, are
described by Captain Beechey and others as flat-topped, and exhibiting
no traces of lagoons. In explanation of the fact, we may presume that
after they had been sinking for ages, the descending movement was
relaxed; and while it was in the course of being converted into an
ascending one, the ground remained for a long season almost stationary,
in which case the corals within the lagoon would build up to the
surface, and reach the level already attained by those on the margin of
the reef. In this manner the lagoon would be effaced, and the island
acquire a flat summit.

It may, however, be thought strange that many examples have not been
noticed of fringing reefs uplifted above the level of the sea. Mr.
Darwin, indeed, cites one instance where the reef preserved, on dry land
in the Mauritius, its peculiar moat-like structure; but they ought, he
says, to be of rare occurrence, for in the case of atolls or of barrier
or fringing reefs, the characteristic outline must usually be destroyed
by denudation as soon as a reef begins to rise; since it is immediately
exposed to the action of the breakers, and the large and conspicuous
corals on the outer rim of the atoll or barrier are the first to be
destroyed and to fall to the bottom of vertical and undermined cliffs.
After slow and continued upheaval a wreck alone can remain of the
original reef. If, therefore, says Mr. Darwin, "at some period as far in
futurity as the secondary rocks are in the past, the bed of the Pacific
with its atolls and barrier reefs should be converted into a continent,
we may conceive that scarcely any or none of the existing reefs would be
preserved, but only widely spread strata of calcareous matter derived
from their wear and tear."[1136]

When it is urged in support of the objection before stated (p. 767),
that the theory of atolls by subsidence implies the accumulation of
calcareous formations 2000 or 3000 feet thick, it must be conceded that
this estimate of the minimum density of the deposits is by no means
exaggerated. On the contrary, when we consider that the space over which
atolls are scattered in Polynesia and the Indian oceans may be compared
to the whole continent of Asia, we cannot but infer from analogy that
the differences in level in so vast an area have amounted, antecedently
to subsidence, to 5000 or even a greater number of feet. Whatever was
the difference in height between the loftiest and lowest of the original
mountains or mountainous islands on which the different atolls are
based, that difference must represent the thickness of coral which has
now reduced all of them to one level. Flinders, therefore, by no means
exaggerated the volume of the limestone, which he conceived to have been
the work of coral animals; he was merely mistaken as to the manner in
which they were enabled to build reefs in an unfathomed ocean.

But is it reasonable to expect, after the waste caused by denudation,
that calcareous masses, gradually upheaved in an open sea, should retain
such vast thicknesses? Or may not the limestones of the cretaceous and
oolitic epochs, which attain in the Alps and Pyrenees a density of 3000
or 4000 feet, and are in great part made up of coralline and shelly
matter, present us with a true geological counterpart of the recent
coral reefs of equatorial seas?

Before we attach serious importance to arguments founded on negative
evidence, and opposed to a theory which so admirably explains a great
variety of complicated phenomena, we ought to remember that the upheaval
to the height of 4000 feet of atolls in which the coralline limestone
would be 4000 feet thick, implies, first, a slow subsidence of 4000
feet, and, secondly, an elevation of the same amount. Even if the
reverse or ascending movement began the instant the downward one ceased,
we must allow a great lapse of ages for the accomplishment of the whole
operation. We must also assume that at the commencement of the period in
question, the equatorial regions were as fitted as now for the support
of reef-building zoophytes. This postulate would demand the continuance
of a complicated variety of conditions throughout a much longer period
than they are usually persistent in one place.

To show the difficulty of speculating on the permanence of the
geographical and climatal circumstances requisite for the growth of
reef-building corals, we have only to state the fact that there are no
reefs in the Atlantic, off the west coast of Africa, nor among the
islands of the Gulf of Guinea, nor in St. Helena, Ascension, the Cape
Verdes, or St. Paul's. With the exception of Bermuda, there is not a
single coral reef in the central expanse of the Atlantic, although in
some parts the waves, as at Ascension, are charged to excess with
calcareous matter. This capricious distribution of coral reefs is
probably owing to the absence of fit stations for the reef-building
polypifers, other organic beings in those regions obtaining in the great
struggle for existence a mastery over them. Their absence, in whatever
manner it be accounted for, should put us on our guard against expecting
upraised reefs at all former geological epochs, similar to those now in
progress.

_Lime, whence derived._--Dr. Maculloch, in his system of Geology, vol.
i. p. 219, expressed himself in favor of the theory of some of the
earlier geologists, that all limestones have originated in organized
substances. If we examine, he says, the quantity of limestone in the
primary strata, it will be found to bear a much smaller proportion to
the siliceous and argillaceous rocks than in the secondary; and this may
have some connexion with the rarity of testaceous animals in the ancient
ocean. He farther infers, that in consequence of the operations of
animals, "the quantity of calcareous earth deposited in the form of mud
or stone is always increasing; and that as the secondary series far
exceeds the primary in this respect, so a third series may hereafter
arise from the depths of the sea, which may exceed the last in the
proportion of its calcareous strata."

If these propositions went no farther than to suggest that every
particle of lime that now enters into the crust of the globe, may
possibly in its turn have been subservient to the purposes of life, by
entering into the composition of organized bodies, I should not deem the
speculation improbable; but, when it is hinted that lime may be an
animal product combined by the powers of vitality from some simple
elements, I can discover no sufficient grounds for such an hypothesis,
and many facts militate against it.

If a large pond be made in almost any soil, and filled with rain water,
it may usually become tenanted by testacea; for carbonate of lime is
almost universally diffused in small quantities. But if no calcareous
matter be supplied by waters flowing from the surrounding high grounds,
or by springs, no tufa or shell-marl are formed. The thin shells of one
generation of mollusks decompose, so that their elements afford
nutriment to the succeeding races; and it is only where a stream enters
a lake, which may introduce a fresh supply of calcareous matter, or
where the lake is fed by springs, that shells accumulate and form marl.

All the lakes in Forfarshire which have produced deposits of shell-marl
have been the sites of springs, which still evolve much carbonic acid,
and a small quantity of carbonate of lime. But there is no marl in Loch
Fithie, near Forfar, where there are _no springs_, although that lake is
surrounded by these calcareous deposits, and although, in every other
respect, the site is favorable to the accumulation of aquatic testacea.

We find those Charæ which secrete the largest quantity of calcareous
matter in their stems to abound near springs impregnated with carbonate
of lime. We know that, if the common hen be deprived altogether of
calcareous nutriment, the shells of her eggs will become of too slight a
consistency to protect the contents; and some birds eat chalk greedily
during the breeding season.

If, on the other hand, we turn to the phenomena of inorganic nature, we
observe that, in volcanic countries, there is an enormous evolution of
carbonic acid, either free, in a gaseous form, or mixed with water; and
the springs of such districts are usually impregnated with carbonate of
lime in great abundance. No one who has travelled in Tuscany, through
the region of extinct volcanos and its confines, or who has seen the map
constructed by Targioni (1827), to show the principal sites of mineral
springs, can doubt, for a moment, that if this territory was submerged
beneath the sea, it might supply materials for the most extensive coral
reefs. The importance of these springs is not to be estimated by the
magnitude of the rocks which they have thrown down on the slanting sides
of hills, although of these alone large cities might be built, nor by a
coating of travertin that covers the soil in some districts for miles in
length. The greater part of the calcareous matter passes down in a state
of solution to the sea, and in all countries the rivers which flow from
chalk and other marly and calcareous rocks carry down vast quantities of
lime into the ocean. Lime is also one of the component parts of augite
and other volcanic and hypogene minerals, and when these decompose is
set free, and may then find its way in a state of solution to the sea.

The lime, therefore, contained generally in sea water, and secreted so
plentifully by the testacea and corals of the Pacific, may have been
derived either from springs rising up in the bed of the ocean, or from
rivers fed by calcareous springs, or impregnated with lime derived from
disintegrated rocks, both volcanic and hypogene. If this be admitted,
the greater proportion of limestone in the more modern formations as
compared to the most ancient, will be explained, for springs in general
hold no argillaceous, and but a small quantity of siliceous matter in
solution, but they are continually subtracting calcareous matter from
the inferior rocks. The constant transfer, therefore, of carbonate of
lime from the lower or older portions of the earth's crust to the
surface, must cause at all periods and throughout an indefinite
succession of geological epochs, a preponderance of calcareous matter in
the newer as contrasted with the older formations.


THE END.

CONCLUDING REMARKS.


In the concluding chapters of the first book, I examined in detail a
great variety of arguments which have been adduced to prove the
distinctness of the state of the earth's crust at remote and recent
epochs. Among other supposed proofs of this distinctness, the dearth of
calcareous matter, in the ancient rocks above adverted to, might have
been considered. But it would have been endless to enumerate all the
objections urged against those geologists who represent the course of
nature at the earliest periods as resembling in all essential
circumstances the state of things now established. We have seen that, in
opposition to this doctrine, a strong desire has been manifested to
discover in the ancient rocks the signs of an epoch when the planet was
uninhabited, and when its surface was in a chaotic condition and
uninhabitable. The opposite opinion, indeed, that the oldest of the
rocks now visible may be the last monuments of an antecedent era in
which living beings may already have peopled the land and water, has
been declared to be equivalent to the assumption that there never was a
beginning to the present order of things.

With equal justice might an astronomer be accused of asserting that the
works of creation extended throughout _infinite_ space, because he
refuses to take for granted that the remotest stars now seen in the
heavens are on the utmost verge of the material universe. Every
improvement of the telescope has brought thousands of new worlds into
view; and it would, therefore, be rash and unphilosophical to imagine
that we already survey the whole extent of the vast scheme, or that it
will ever be brought within the sphere of human observation.

But no argument can be drawn from such premises in favor of the infinity
of the space that has been filled with worlds; and if the material
universe has any limits, it then follows, that it must occupy a minute
and infinitesimal point in infinite space.

So if, in tracing back the earth's history, we arrive at the monuments
of events which may have happened millions of ages before our times, and
if we still find no decided evidence of a commencement, yet the
arguments from analogy in support of the probability of a beginning
remain unshaken; and if the past duration of the earth be finite, then
the aggregate of geological epochs, however numerous, must constitute a
mere moment of the past, a mere infinitesimal portion of eternity.

It has been argued, that, as the different states of the earth's
surface, and the different species by which it has been inhabited have
all had their origin, and many of them their termination, so the entire
series may have commenced at a certain period. It has also been urged,
that, as we admit the creation of man to have occurred at a
comparatively modern epoch--as we concede the astonishing fact of the
first introduction of a moral and intellectual being--so also we may
conceive the first creation of the planet itself.

I am far from denying the weight of this reasoning from analogy; but,
although it may strengthen our conviction, that the present system of
change has not gone on from eternity, it cannot warrant us in presuming
that we shall be permitted to behold the signs of the earth's origin, or
the evidences of the first introduction into it of organic beings. We
aspire in vain to assign limits to the works of creation in _space_,
whether we examine the starry heavens, or that world of minute
animalcules which is revealed to us by the microscope. We are prepared,
therefore, to find that in time also the confines of the universe lie
beyond the reach of mortal ken. But in whatever direction we pursue our
researches, whether in _time_ or space, we discover everywhere the clear
proofs of a Creative Intelligence, and of His foresight, wisdom, and
power.

As geologists, we learn that it is not only the present condition of the
globe which has been suited to the accommodation of myriads of living
creatures, but that many former states also have been adapted to the
organization and habits of prior races of beings. The disposition of the
seas, continents, and islands, and the climates, have varied; the
species likewise have been changed; and yet they have all been so
modelled, on types analogous to those of existing plants and animals, as
to indicate, throughout, a perfect harmony of design and unity of
purpose. To assume that the evidence of the beginning or end of so vast
a scheme lies within the reach of our philosophical inquiries, or even
of our speculations, appears to be inconsistent with a just estimate of
the relations which subsist between the finite powers of man and the
attributes of an Infinite and Eternal Being.


FOOTNOTES:


   [1] Essays on the Philosophy of the Hindoos.

   [2] Institutes of Hindoo Law, or the Ordinances of Menù, from the
       Sanscrit, translated by Sir William Jones, 1796.

   [3] Menù, Inst. c. i. 66, and 67.

   [4] Herodot. Euterpe, 12.

   [5] A Persian MS. copy of the historian Ferishta, in the library
       of the East India Company, relating to the rise and progress of
       the Mahomedan empire in India, was procured by Colonel Briggs from
       the library of Tippoo Sultan in 1799; which has been referred to
       at some length by Dr. Buckland. (Geol. Trans. 2d Series, vol. ii.
       part iii. p. 389.)

   [6] See Davis on "The Chinese," published by the Soc. for the
       Diffus. of Use. Know. vol. i. pp. 137, 147.

   [7] Humboldt et Bonpland, Voy. Relat. Hist. vol. i. p. 30.

   [8] Prichard's Egypt. Mythol. p. 177.

   [9] Plut. de Defectu Oraculorum, cap. 12. Censorinus de Die
       Natali. See also Prichard's Egypt. Mythol. p. 182.

   [10] Prichard's Egypt. Mythol. p. 182.

   [11] Prichard's Egypt. Mythol. p. 193.

   [12] Plato's Timæus.

   [13] Ovid's Metamor. lib. 15.

   [14] Eluvie mons est deductus in æquor, v. 267. The meaning of
        this last verse is somewhat obscure; but, taken with the context,
        may be supposed to allude to the abrading power of floods,
        torrents, and rivers.

   [15] The impregnation from new mineral springs, caused by
        earthquakes in volcanic countries, is perhaps here alluded to.

   [16] That is probably an allusion to the escape of inflammable
        gas, like that in the district of Baku, west of the Caspian; at
        Pietramala, in the Tuscan Apennines; and several other places.

   [17] Many of those described seem fanciful fictions, like the
        virtue still so commonly attributed to mineral waters.

   [18] Raspe, in a learned and judicious essay (De Novis Insulis,
        cap. 19), has made it appear extremely probable that all the
        traditions of certain islands in the Mediterranean having at some
        former time frequently shifted their positions, and at length
        become stationary, originated in the great change produced in
        their form by earthquakes and submarine eruptions, of which there
        have been modern examples in the new islands raised in the time
        of history. When the series of convulsions ended, the island was
        said to become fixed.

   [19] It is not inconsistent with the Hindoo mythology to suppose
        that Pythagoras might have found in the East not only the system
        of universal and violent catastrophes and periods of repose in
        endless succession, but also that of periodical revolutions,
        effected by the continued agency of ordinary causes. For Brahma,
        Vishnu, and Siva, the first, second, and third persons of the
        Hindoo triad, severally represented the Creative, the Preserving,
        and the Destroying powers of the Deity. The coexistence of these
        three attributes, all in simultaneous operation, might well
        accord with the notion of perpetual but partial alterations
        finally bringing about a complete change. But the fiction
        expressed in the verses before quoted from Menù of eternal
        vicissitudes in the vigils and slumbers of Brahma seems
        accommodated to the system of great general catastrophes followed
        by new creations and periods of repose.

   [20] Meteor. lib. i. cap. 12.

   [21] De Die Nat.

   [22] Lib. ii. cap. 14, 15, and 16.

   [23] Lib. ii. cap. 14, 15, and 16.

   [24] Omne ex integro animal generabitur, dabiturque terris homo
        inscius scelerum.--Quæst. Nat. iii. c. 29.

   [25] This author was Regius Professor of Syriac and Arabic at
        Paris, where, in 1685, he published a Latin translation of many
        Arabian MSS. on different departments of philosophy. This work
        has always been considered of high authority.

   [26] Gerbanitæ docebant singulos triginta sex mille annos
        quadringentos, viginti quinque bina ex singulis animalium
        speciebus produci, marem scilicet ac feminam ex quibus animalia
        propagantur, huncque inferiorem incolunt orbem. Absoluta autem
        coelestium orbium circulatione, quæ illo annorum conficitur
        spatio, iterum alia producuntur animalium genera et species,
        quemadmodum et plantarum aliarumque rerum, et primus destruitur
        ordo, sicque in infinitum producitur.--Histor. Orient Suppl. per
        Abrahamum Ecchellensem, Syrum Maronitam, cap. 7. et 8. ad calcem
        Chronici Orientali. Parisiis, e Typ. Regia. 1685, fol.

        I have given the punctuation as in the Paris edition, there being
        no comma after quinque; but, at the suggestion of M. de Schlegel,
        I have referred the number twenty-five to the period of years,
        and not to the number of pairs of each species created at one
        time, as I had done in the two first editions. Fortis inferred
        that twenty-five new _species_ only were created at a time; a
        construction which the passage will not admit. Mém. sur l'Hist.
        Nat. de l'Italie, vol. i. p. 202.

   [27] "Quod enim hoc attollitur aut subsidit, et vel inundat
        quædam loca, vel ab iis recedit, ejus rei causa non est, quod
        alia aliis sola humiliora sint aut altiora; sed quod idem solum
        modò attollitur modò deprimitur, simulque etiam modò attollitur
        modò deprimitur, mare: itaque vel exundat vel in suum redit
        locum."

        Posteà, p. 88. "Restat, ut causam adscribamus solo, sive quod
        mari subest sive quod inundatur; potiùs tamen ei quod mari
        subest. Hoc enim multò est mobilius, et quod ob humiditatem
        celeriùs multari possit."--Strabo, Geog. Edit. Almelov. Amst.
        1707, lib. 1.

   [28] _Volcanic eruptions_, eruptiones flatuum, in the Latin
        translations, and in the original Greek, αναφυσηματα,
        gaseous eruptions? or _inflations_ of land?--Ibid. p. 93.

   [29] Strabo, lib. vi. p. 396.

   [30] Book iv.

   [31] L. vi. ch. xiii.

   [32] Mod. Univ. Hist. vol. ii. chap. iv. section iii.

   [33] Montes quandóque fiunt ex causa essentiali, quandóque ex
        causa accidentali. Ex essentiali causa, ut ex vehementi motu
        terræ elevatur terra, et fit mons. Accidentali, &c.--De
        Congelatione Lapidum, ed. Gedani, 1682.

   [34] Von Hoff, Geschichte der Veränderungen der Erdoberfläche,
        vol. i. p. 406, who cites Delisle, bey Hismann Welt- und
        Völkergeschichte. Alte Geschichte 1ᵗᵉʳ theil, s. 234.--The
        Arabian persecutions for heretical dogmas in theology were often
        very sanguinary. In the same ages wherein learning was most in
        esteem, the Mahometans were divided into two sects, one of whom
        maintained that the Koran was increate, and had subsisted in the
        very essence of God from all eternity; and the other, the
        Motazalites, who, admitting that the Koran was instituted by God,
        conceived it to have been first made when revealed to the Prophet
        at Mecca, and accused their opponents of believing in two eternal
        beings. The opinions of each of these sects were taken up by
        different caliphs in succession, and the followers of each
        sometimes submitted to be beheaded, or flogged till at the point
        of death, rather than renounce their creed.--Mod. Univ. Hist.
        vol. ii. ch. iv.

   [35] Koran, chap. xli.

   [36] Sale's Koran, chap. xi. see note.

   [37] Ibid.

   [38] Kossa, appointed master to the Caliph Al Mamûd, was author
        of a book entitled "The history of the Patriarchs and Prophets,
        _from the Creation of the World_."--Mod. Univ. Hist. vol. ii. ch.
        iv.

   [39] Translated by MM. Chezy and De Sacy, and cited by M. Elie de
        Beaumont, Ann. des Sci. Nat. 1832.

   [40] See Venturi's extracts from Da Vinci's MMS. now in Library
        of Institute of France. They are not mentioned by Brocchi, and my
        attention was first called to them by Mr. Hallam. L. da Vinci
        died A. D. 1519.

   [41] Museum Calceol.--See Brocchi's Discourse on the Progress of
        the Study of Fossil Conchology in Italy, where some of the
        following notices on Italian writers will be found more at large.

   [42] In Sicily, in particular, the title-deeds of many valuable
        grants of land to the monasteries are headed by such preambles,
        composed by the testators about the period when the good King
        Roger was expelling the Saracens from that island.

   [43] De Fossilib. pp. 109, 176.

   [44] Aristotle, On Animals, chaps. 1, 15.

   [45] Brocchi, Con. Fos. Subap. Disc, sui Progressi. vol. i. p.
        57.

   [46] De Metallicis.

   [47] Dies Caniculares.

   [48] Storia Naturale.

   [49] Osserv. sugli Animali aquat. e terrest. 1626.

   [50] Sex itaque distinctas Etruriæ facies agnoscimus, dum bis
        fluida, bis plana, et sicca, bis aspera fuerit, &c.

   [51] Scilla quotes the remark of Cicero on the story that a stone
        in Chios had been cleft open, and presented the head of Paniscus
        in relief:--"I believe," said the orator, "that the figure bore
        some resemblance to Paniscus, but not such that you would have
        deemed it sculptured by Scopas; for chance never perfectly
        imitates the truth."

   [52] De Testaceis fossilibus Mus. Septaliani.

   [53] The opinions of Boyle, alluded to by Quirini, were published
        a few years before, in a short article entitled "On the Bottom of
        the Sea." From observations collected from the divers of the
        pearl fishery, Boyle inferred that, when the waves were six or
        seven feet high above the surface of the water, there were no
        signs of agitation at the depth of fifteen fathoms; and that even
        during heavy gales of wind, the motion of the water was
        exceedingly diminished at the depth of twelve or fifteen feet. He
        had also learnt from some of his informants, that there were
        currents running in opposite directions at different
        depths.--Boyle's Works, vol. iii. p. 110. London, 1744.

   [54] See Conybeare and Phillips, "Outlines of the Geology of
        England and Wales," p. 12.

   [55] Unde jam duplex origo intelligitur primorum corporum, una,
        cum ab ignis fusione refrigescerent, altera, cum reconcrescerent
        ex solutione aquarum.

   [56] Redeunte mox simili causâ strata subinde alia aliis
        imponerentur, et facies teneri adhuc orbis sæpius novata est.
        Donec quiescentibus causis, atque æquilibratis, consistentior
        emergeret rerum status.--For an able analysis of the views of
        Leibnitz, in his Protogoea, see Mr. Conybeare's Report to the
        Brit. Assoc. on the Progress of Geological Science, 1832.

   [57] Between the year 1688 and his death, in 1703, he read
        several memoirs to the Royal Society, and delivered lectures on
        various subjects, relating to fossil remains and the effects of
        earthquakes.

   [58] Posth. Works, Lecture, Feb. 29, 1688.

   [59] Posth. Works, p. 327.

   [60] Posth. Works, Lecture, Feb. 15, 1688. Hooke explained with
        considerable clearness the different modes wherein organic
        substances may become lapidified; and, among other illustrations,
        he mentions some silicified palm-wood brought from Africa, on
        which M. de la Hire had read a memoir to the Royal Academy of
        France (June, 1692), wherein he had pointed out, not only the
        tubes running the length of the trunk, but the roots at one
        extremity. De la Hire, says Hooke, also treated of certain trees
        found petrified in the "river that passes by Bakan, in the
        kingdom of _Ava_, and which has for the space of ten leagues the
        virtue of petrifying wood." It is an interesting fact that the
        silicified wood of the Irawadi should have attracted attention
        more than one hundred years ago. Remarkable discoveries have been
        made there in later times of fossil animals and vegetables, by
        Mr. Crawfurd and Dr. Wallich.--See Geol. Trans. vol. ii. part
        iii. p. 377, second series. De la Hire cites Father Duchatz, in
        the second volume of "Observations made in the Indies by the
        Jesuits."

   [61] Posth. Works, Lecture, May 29, 1689.

   [62] Posth. Works, p. 312.

   [63] Posth. Works, p. 410.

   [64] Ray's Physico-theological Discourses were of somewhat later
        date than Hooke's great work on earthquakes. He speaks of Hooke
        as one "whom for his learning and deep insight into the mysteries
        of nature he deservedly honored."--_On the Deluge_, chap. iv.

   [65] Essay towards a Natural History of the Earth, 1695. Preface.

   [66] Ibid.

   [67] Consequences of the Deluge, p. 165.

   [68] First published in Latin between the years 1680 and 1690.

   [69] An Examination of Dr. Burnet's Theory, &c., 2d ed. 1734.

   [70] Ramazzini even asserted, that the ideas of Burnet were
        mainly borrowed from a dialogue of one Patrizio; but Brocchi,
        after reading that dialogue, assures us that there was scarcely
        any other correspondence between these systems, except that both
        were equally whimsical.

   [71] Dei Corpi Marini, Lettere critiche, &c. 1721.

   [72] Brocchi, p. 28.

   [73] Ibid. p. 33.

   [74] Ibid.

   [75] Sui Crostacei ed altri Corpi Marini che si trovano sui
        Monti.

   [76] Moro does not cite the works of Hooke and Ray; and although
        so many of his views were in accordance with theirs, he was
        probably ignorant of their writings, for they had not been
        translated. As he always refers to the Latin edition of Burnet,
        and a French translation of Woodward, we may presume that he did
        not read English.

   [77] Saggio fisico intorno alla Storia del Mare, part i. p. 24.

   [78] "Abbomino al sommo qualsivoglia sistema, che sia di pianta
        fabbricato in aria; massime quando è tale, che non possa
        sostenersi senza un miracolo," &c.--De' Crostacei e di altre
        Produz. del Mare, &c. 1749.

   [79] "Senza violenze, senza finzioni, senza supposti, senza
        miracoli." De' Crostacei e di altre Produz. del Mare, &c. 1749.

   [80] Sui Testacei della Sicilia.

   [81] Hist. Nat. tom. v. éd. de l'Imp. Royale, Paris, 1769.

   [82] Essai d'une Hist. Nat. des Couches de la Terre, 1759.

   [83] John Gesner published at Leyden, in Latin.

   [84] Part ii. chap. 9.

   [85] Giornale del Criselini, 1759.

   [86] See a sketch of the History of English Geology, by Dr.
        Fitton, in Edinb. Rev. Feb. 1818, re-edited Lond. and Edinb.
        Phil. Mag. vols. i. and ii. 1832-3. Some of Michell's
        observations anticipate in so remarkable a manner the theories
        established forty years afterwards, that his writings would
        probably have formed an era in the science, if his researches had
        been uninterrupted. He held, however, his professorship only
        eight years, when his career was suddenly cut short by preferment
        to a benefice. From that time he appears to have been engaged in
        his clerical duties, and to have entirely discontinued his
        scientific pursuits, exemplifying the working of a system still
        in force at Oxford and Cambridge, where the chairs of
        mathematics, natural philosophy, chemistry, botany, astronomy,
        geology, mineralogy, and others, being frequently filled by
        clergymen, the reward of success disqualifies them, if they
        conscientiously discharge their new duties, from farther
        advancing the cause of science, and that, too, at the moment when
        their labors would naturally bear the richest fruits.

   [87] Sui Corpi Marini del Feltrino, 1761.

   [88] De Novis e Mari Natis Insulis. Raspe was also the editor of
        the "Philosophical Works of Leibnitz. Amst. et Leipzig, 1765;"
        also author of "Tassie's Gems," and "Baron Munchausen's Travels."

   [89] Acta Academiæ Electoralis Maguntinæ, vol. ii. Erfurt.

   [90] This account of Fuchsel is derived from an excellent
        analysis of his memoirs by M. Keferstein. Journ. de Géologie,
        tom. ii. Oct. 1830.

   [91] Saggio orittografico, &c. 1780, and other Works.

   [92] Lett. sui Pesci Fossili di Bolca. Milan, 1793.

   [93] This argument of Testa has been strengthened of late years
        by the discovery that dealers in shells had long been in the
        habit of selling Mediterranean species as shells of more southern
        and distant latitudes, for the sake of enhancing their price. It
        appears, moreover, from several hundred experiments made by that
        distinguished hydrographer, Capt. Smith, on the water within
        eight fathoms of the surface, that the temperature of the
        Mediterranean is on an average 3½° of Fahrenheit higher than
        the western part of the Atlantic ocean; an important fact, which
        in some degree may help to explain why many species are common to
        tropical latitudes and to the Mediterranean.

   [94] Inquiry into the Original State and Formation of the Earth,
        1778.

   [95] Observ. on the Formation of Mountains. Act Petrop. ann.
        1778, part i.

   [96] Nov. comm. Petr. XVII. Cuvier, Eloge de Pallas.

   [97] Cuvier, Eloge de Werner.

   [98] I am indebted for this information partly to Messrs.
        Sedgwick and Murchison, who have investigated the country, and
        partly to Dr. Charles Hartmann, the translator of this work into
        German.

   [99] Cuvier, Eloge de Desmarest.

  [100] Journ. de Phys. vol. xiii. p. 115; and Mém. de l'Inst.,
        Sciences Mathémat. et. Phys. vol. vi. p. 219.

  [101] Journ. de Phys. tom. xxxv. p. 191.

  [102] Ib. tom. xxxvii. part ii. p. 200.

  [103] Cuvier, Eloge de Desmarest.

  [104] Ed. Phil. Trans. 1788.

  [105] Playfair's Works, vol. iv. p. 75.

  [106] "Before me things create were none, save things
         Eternal."--Dante's _Inferno_, canto iii. Cary's Translation.

  [107] Playfair's Works, vol. iv. p. 55.

  [108] In allusion to the theories of Burnet, Woodward, and
        other physico-theological writers, he declared that they were
        as fond of changes of scene on the face of the globe, as were
        the populace at a play. "Every one of them destroys and
        renovates the earth after his own fashion, as Descartes framed
        it: for philosophers put themselves without ceremony in the
        place of God, and think to create a universe with a
        word."--Dissertation envoyée a l'Academie de Boulogne, sur les
        Changemens arrivés dans notre Globe. Unfortunately, this and
        similar ridicule directed against the cosmogonists was too well
        deserved.

  [109] See the chapter on "Des Pierres figurés."

  [110] In that essay he lays it down, "that all naturalists are
        now agreed that deposits of shells in the midst of the
        continents are monuments of the continued occupation of these
        districts by the ocean." In another place also, when speaking
        of the fossil shells of Touraine, he admits their true origin.

  [111] As an instance of his desire to throw doubt
        indiscriminately on all geological data, we may recall the
        passage where he says, that "the bones of a reindeer and
        hippopotamus discovered near Etempes did not prove, as some
        would have it, that Lapland and the Nile were once on a tour
        from Paris to Orleans, but merely that a lover of curiosities
        once preserved them in his cabinet."

  [112] "Some drill and bore The solid earth, and from the strata there
        Extract a register, by which we learn That he who made it, and
        revealed its date To Moses, was mistaken in its age." The Task,
        book iii. "The Garden."

  [113] P. 577.

  [114] P. 59.

  [115] Introd. p. 2.

  [116] London, 1809.

  [117] In a most able article, by Mr. Drinkwater, on the "Life
        of Galileo," published in the "Library of Useful Knowledge," it
        is stated that both Galileo's work, and the book of Copernicus,
        "Nisi corrigatur" (for, with the omission of certain passages,
        it was sanctioned), were still to be seen on the forbidden list
        of the Index at Rome, in 1828. I was, however, assured in the
        same year, by Professor Scarpellini, at Rome, that Pius VII., a
        pontiff distinguished for his love of science, had procured a
        repeal of the edicts against Galileo and the Copernican system.
        He had assembled the Congregation; and the late Cardinal
        Toriozzi, assessor of the Sacred Office, proposed that they
        should wipe off this scandal from the church." The repeal was
        carried, with the dissentient voice of one Dominican only. Long
        before that time the Newtonian theory had been taught in the
        Sapienza, and all Catholic universities in Europe (with the
        exception, I am told, of Salamanca); but it was always required
        of professors, in deference to the decrees of the church, to
        use the term _hypothesis_, instead of theory. They now speak of
        the Copernican _theory_.

  [118] Elementary Treatise on Geology. London, 1809. Translated
        by De la Fite.

  [119] See Dr. Fitton's Memoir, before cited, p. 57.

  [120] Whewell, British Critic, No. xvii. p. 187, 1831.

  [121] Discours sur les Révol. &c.

  [122] Niebuhr's Hist. of Rome, vol. i. p. 5. Hare and
        Thirlwall's translation.

  [123] Gibbon, Decline and Fall, chap. xxxiii.

  [124] Id. Ibid.

  [125] In the earlier editions of this work, a fourth book was
        added on Geology Proper, or Systematic Geology, containing an
        account of the former changes of the animate and inanimate
        creation, brought to light by an examination of the crust of
        the earth. This I afterwards (in 1838) expanded into a separate
        publication called the Elements of Manual Geology, of which a
        fourth edition appeared December, 1851.

  [126] See two articles by the Rev. Dr. Fleming, in the
        Edinburgh New Phil. Journ. No. xii. p. 277, April, 1829; and
        No. xv. p. 65, Jan. 1830.

  [127] Book iii. chaps. 46, 47, &c.

  [128] Macacus pliocenus, Owen, Brit. Foss. Mam. Intr. p. 37,
        found with the extinct elephant, &c. in the modern freshwater
        beds at Grays Thurrock (Essex), in the valley of the Thames.

  [129] Geol. Proceedings, No. xxxvi. June, 1834.

  [130] Phil. Mag., Sept. 1829, and Jan. 1830.

  [131] Fleming, Ed. New Phil. Journ., No. xii. p. 282, 1829. The
        zebra, however, inhabits chiefly the extra-tropical parts of
        Africa.

  [132] Humboldt, Fragmens de Géologie, &c., tome ii. p. 388.
        Ehrenberg, Ann. des Sci. Nat., tome xxi. p. 387.

  [133] Ehrenberg, ibid. p. 390.

  [134] Journ. of Asiat. Soc., vol. i. p. 240.

  [135] Rafinesque, Atlantic Journ., p. 18.

  [136] Darwin's Journal of Travels in South America, &c., 1832
        to 1836, in Voyage of H. M. S. Beagle, p. 159.

  [137] Ehrenberg, ibid.

  [138] The speculations which follow, on the ancient physical
        geography of Siberia, and its former fitness as a residence for
        the mammoth, were first given in their present form in my 4th
        edition, June, 1835. Recently Sir R. Murchison and his
        companions in their great work on the Geology of Russia, 1845
        (vol. i. p. 497), have, in citing this chapter, declared that
        their investigations have led them to similar conclusions.
        Professor Owen, in his excellent History of British Fossil
        Mammalia, 1844, p. 261, _et seq._, observes that the teeth of
        the mammoth differ from those of the living Asiatic or African
        elephant in having a larger proportion of dense enamel, which
        may have enabled it to subsist on the coarser ligneous tissues
        of trees and shrubs. In short, he is of opinion, that the
        structure of its teeth, as well as the nature of its epidermis
        and coverings, may have made it "a meet companion for the
        reindeer."

  [139] Pallas, Reise in Russ. Reiche, pp. 409, 410.

  [140] Nov. Com. Petrop. vol. xvii. p. 584.

  [141] Nov. Com. Petrop. vol. xvii. p. 591.

  [142] Quart. Journ. Geol. Soc. Lond. vol. iv. p. 10, Memoirs.

  [143] Journal du Nord, St. Petersburg, 1807.

  [144] Fleming, Ed. New Phil. Journ., No. xii. p. 285.

        Bishop Heber informs us (Narr. of a Journey through the Upper
        Provinces of India, vol. ii. p. 166-219), that in the lower
        range of the Himalaya mountains, in the northeastern borders of
        the Delhi territory, between lat. 29° and 30°, he saw an Indian
        elephant of a small size, covered with shaggy hair. But this
        variety must be exceedingly rare; for Mr. Royle (late
        superintendent of the East India Company's Botanic Garden at
        Saharunpore) has assured me, that being in India when Heber's
        Journal appeared, and having never seen or heard of such
        elephants, he made the strictest inquiries respecting the fact,
        and was never able to obtain any evidence in corroboration. Mr.
        Royle resided at Saharunpore, lat. 30° N., upon _the extreme
        northern limits_ of the range of the elephant. Mr. Everest also
        declares that he has been equally unsuccessful in finding any
        one aware of the existence of such a variety or breed of the
        animal, though one solitary individual was mentioned to him as
        having been seen at Delhi, with a good deal of long hair upon
        it. The greatest elevation, says Mr. E., at which the wild
        elephant is found in the mountains to the north of Bengal, is
        at a place called Nahun, about 4000 feet above the level of the
        sea, and in the 31st degree of N. lat., where the mean yearly
        temperature may be about 64° Fahrenheit, and the difference
        between winter and summer very great, equal to about 36° F.,
        the month of January averaging 45°, and June, the hottest
        month, 81° F. (Everest on climate of Foss. Eleph., Journ. of
        Asiat. Soc., No. 25, p. 21.)

  [145] See Dr. Buckland's description of these bones, Appen. to
        Beechy's Voy.

  [146] Darwin, Journal of Travels in S. America, &c., 1832-36,
        in voyage of H. M. S. Beagle, p. 98. 2d Ed. London, 1845, p.
        86.

  [147] Darwin, Journal of Travels in S. America, &c., p. 99, 2d
        Ed. p. 85.

  [148] Burchell, cited by Darwin, ibid. p. 101. 2d Ed. p. 87.

  [149] Since the above passage was first printed in a former
        edition, June, 1835, it has been shown by the observations of
        Sir R. Murchison, M. de Verneuil, and Count Keyserling, and
        more recently by M. Middendorf (see above, p. 81), that the
        Lowland of Siberia has actually been extended, since the
        existing species of shells inhabited the northern seas.

  [150] Humboldt, Fragmens Asiatiques, tom. ii. p. 393.

  [151] Reboul. Geol. de la Période Quaternaire, who cites
        Observ. sur la Sibérie, Bibl. Univ., Juillet, 1832.

  [152] Conjectured to be the wild stock of Bos grunniens.

  [153] Recollections of a Journey through Tartary, Thibet, and
        China (ch. xv. p. 234), by M. Huc. Longman, 1852.

  [154] For an account of the more modern changes of the tertiary
        fauna and flora of the British Isles and adjoining countries,
        and particularly those facts which relate to the "glacial
        epoch," see an admirable essay by Prof. E. Forbes. Memoirs of
        Geol. Survey of Great Brit. vol. i. p. 336. London, 1846. To
        this important memoir I shall have frequent occasion to refer
        in the sequel.

  [155] See a paper by Charles J. F. Bunbury, Esq., Journ. of
        Geol. Soc., London, No. 6, p. 88. 1846.

  [156] The Calamites were formerly regarded by Adolphe
        Brongniart as belonging to the tribe of Equisetaceæ; but he is
        now inclined to refer them to the class of gymnogens, or
        gymnospermous exogens, which includes the Coniferæ and Cycadeæ.
        Lepidodendron appears to have been either a gigantic form of
        the lycopodium tribe, or, as Dr. Lindley thinks, intermediate
        between the lycopodia and the fir tribe. The Sigillariæ were
        formerly supposed by Ad. Brongniart, to be arborescent ferns;
        but the discovery of their internal structure, and of their
        leaves, has since proved that they have no real affinity to
        ferns. According to the view now taken of their structure,
        their nearest allies in the recent world are the genera Cycas
        and Zamia; while Corda, on the other hand, maintains that they
        were closely related to the succulent euphorbias. Stigmaria is
        now generally admitted to have been merely the root of
        sigillaria. The scalariform vessels of these two genera are not
        conclusive in proving them to have a real affinity with ferns,
        as Mr. Brown has discovered the same structure of vessels in
        Myzodendron, a genus allied to the mistletoe; and Corda has
        lately shown that in two species of Stigmaria, hardly
        distinguishable by external characters, the vessels of the one
        are scalariform, and of the other dotted.

  [157] Mr. Lindley endeavored formerly (1834) to show, in the
        "Fossil Flora," that Trigonocarpum Noeggerathii, a fruit found
        in the coal measures, has the true structure of a palm-fruit;
        but Ad. Brongniart has since inclined to regard it as
        cycadeous; nor is the French botanist satisfied that some
        specimens of supposed palm wood from the coal-mines of Radnitz
        in Bohemia, described by Corda, really belong to palms. On the
        other hand, Corda has proved Flabellaria borassifolia of
        Sternberg to be an exogenous plant, and Brongniart contends
        that it was allied to the Cycadeæ. See Tableau des Genres de
        Végétaux Fossiles. Paris, 1849.

  [158] Prodrome d'une Hist. des Végét. Foss. p. 179. See also a
        late paper, Quart. Journ. of Geol. Soc. London, 1846, in which
        coal-plants of Alabama, lat. 33° N., collected by the author,
        are identified by Mr. Bunbury with British fossil species,
        showing the great southern extension of this flora.

  [159] König, Journ. of Sci., vol. xv. p. 20. Mr. König informs
        me that he no longer believes any of these fossils to be tree
        ferns, as he at first stated, but that they agree generically
        with plants in our English coal-beds. The Melville Island
        specimens, now in the British Museum, are very obscure
        impressions.

  [160] Fossil Flora of Great Britain, by John Lindley and
        William Hutton, Esqrs., No. IV.

  [161] Fossil Flora of Great Britain, by John Lindley and
        William Hutton, Esqrs. No. IV.

  [162] Fossil Flora, No. X.

  [163] This has been proved by Mr. Lindley's experiments, ibid.
        No. XVII.

  [164] I have treated of this subject in my Manual of Geology,
        and still more fully in my Travels in N. America, vol. ii. p.
        178. For a full account of the facts at present known, and the
        theories entertained by the most eminent geologists and
        botanists on this subject, see Mr. Horner's Anniversary Address
        to the Geological Society of London, February, 1846. Consult
        also Sir H. de la Beche, on the formation of rocks in South
        Wales, Memoirs of Geol. Survey of Great Britain, 1846, p. 1 to
        296.

  [165] The theory proposed in this and the following chapters,
        to account for former fluctuations of climate at successive
        geological periods, agrees in every essential particular, and
        has indeed been reprinted almost verbatim from that published
        by me twenty years ago in the first edition of my Principles,
        1830. It was referred to by Sir John F. W. Herschel in his
        Discourse on Natural Philosophy, published in 1830. In
        preceding works the gradual diminution of the earth's central
        heat was almost the only cause assigned for the acknowledged
        diminution of the superficial temperature of our planet.

  [166] We are indebted to Baron Alex. von Humboldt for having
        first collected together the scattered data on which he founded
        an approximation to a true theory of the distribution of heat
        over the globe. Many of these data were derived from the
        author's own observations, and many from the works of M. Pierre
        Prevost, of Genera, on the radiation of heat, and from other
        writers.--See Humboldt on Isothermal Lines, Mémoires d'Arcueil,
        tom. iii. translated in the Edin. Phil. Journ. vol. iii. July,
        1820.

        The map of Isothermal Lines, recently published by Humboldt and
        Dove (1848), supplies a large body of well-established data for
        such investigations, of which Mr. Hopkins has most ably availed
        himself in an essay "On the Causes which may have produced
        Changes in the earth's Superficial Temperature."--Q. Journ.
        Geol. Soc. 1852, p. 56.

  [167] Sir J. Richardson's Appendix to Sir G. Bach's Journal,
        1843-1845, p. 478.

  [168] Malte-Brun, Phys. Geol. book xvii.

  [169] On Isothermal Lines, &c.

  [170] Rennell on Currents, p. 96. London, 1832.

  [171] Ibid. p. 153.

  [172] Ibid. p. 25.

  [173] Scoresby's Arctic Regions, vol. i. p. 208.--Dr. Latta's
        Observations on the Glaciers of Spitzbergen, &c. Edin. New
        Phil. Journ. vol. iii. p. 97.

  [174] Rennell on Currents, p. 95.

  [175] Humboldt on Isothermal Lines.

  [176] Journ. of Travels in S. America, &c. p. 272.

  [177] Darwin's travels in S. America, p. 271.

  [178] Mr. Hopkins raises the question whether, in South
        Georgia, the descent of glaciers to the margin of the sea might
        not have been mistaken by Capt. Cook for the descent of the
        snow-line to the sea level. Quart. Journ. Geol. Soc. p. 85,
        1852. The great navigator is generally very accurate, and there
        seem to be no observations of more recent date either to
        confirm or invalidate his statements.

  [179] After all these modern discoveries, the area still
        unexplored, within the antarctic circle, is more than double
        the area of Europe. The surface of the latter contains about
        2,793,000 square geographical miles. The unexplored antarctic
        region, as calculated for me by Mr. Gardner, in 1840, equalled
        about 7,620,000 square miles.

  [180] On icebergs in low latitudes, by Capt. Horsburgh, by whom
        the sketch was made. Phil. Trans. 1830.

  [181] Scoresby's Arctic Regions, vol. i. p. 234.

  [182] This follows, observes Herschel, from a very simple
        theorem, which may be thus stated:--"The amount of heat
        received by the earth from the sun, while describing any part
        of its orbit, is proportional to the angle described round the
        sun's centre." So that if the orbit be divided into two
        portions by a line drawn _in any direction_ through the sun's
        centre, the heat received in describing the two unequal
        segments of the eclipse so produced will be equal. Geol. Trans.
        vol. iii. part. ii. p. 298; second series.

  [183] On Isothermal Lines.

  [184] A full consideration of the effect of changes in physical
        geography on the distribution and extinction of species is
        given in book iii.

  [185] For calculations founded on astronomical data, see
        Young's Nat. Phil., Lect. xlvii.; Mrs. Somerville's Connex. of
        Phys. Sci., sect. 14, p. 110. Laplace, endeavoring to estimate
        the probable depth of the sea from some of the phenomena of the
        tides, says of the ocean generally, "que sa profondeur moyenne
        est du même ordre que la hauteur moyenne des continens et des
        isles au-dessus de son niveau, hauteur qui ne surpasse pas
        mille mètres (3280 ft.)" Mec. Céleste, tom. xi. et Syst. du
        Monde, p. 254. The expression "du même ordre" admits in
        mathematical language of considerable latitude of
        signification, and does not mean that the depth of the water
        below the level of the sea corresponds exactly to the height of
        the land above it.

        It appeared from the observations of Sir James Ross,
        communicated to me in 1849, by himself, and his fellow voyager,
        Dr. Joseph Hooker, that in latitude 15° 3' S., longitude 23°
        14' W. (the island of Trinidad, the nearest land, being 486
        miles distant, and bearing S. 47 W.), they sounded with a
        weight of 76 lbs., and 4600 fathoms of line, which ran out to
        the very end, without finding bottom. Here therefore in
        mid-ocean the depth exceeded 27,600 feet. One of the shallowest
        soundings ever obtained in the open sea during the same survey,
        struck bottom with 2677 fathoms, or 16,062 feet, latitude 33°
        21' S., longitude 9° 4' E. The surveyors arrived at the
        conclusion, that at a moderate distance from the shore, the
        depth of the great ocean always exceeds 4000 feet.

        During the American survey in 1849, a much greater depth, or
        5700 fathoms (34,200 feet), was sounded in the Atlantic by
        Lieut. Walsh, without reaching the bottom, in lat. 31° 59' N.,
        long. 58° 43' W., or between the Bermudas and the Azores. But
        the deepest soundings yet published were taken Oct. 30th 1852,
        by Capt. Henry M. Denham, R. N., who reached bottom at 7706
        fathoms (46,236 feet), lat. 36° 49' S., long. 37° 6' W., the
        nearest land being at the mouth of the River Plate. A weight of
        9 lbs. was attached to the line, which was one-tenth of an inch
        in diameter; the day was calm, and the line took 9 hours 24
        minutes to run out. When the bottom was struck the line was
        raised 50 fathoms, and then allowed to run out again. It struck
        at the same point as before, verifying the observations.
        Nevertheless some experienced surveyors have remarked that the
        experiment would have been more satisfactory had the weight
        been greater. The highest summits of the Himalaya are about
        28,000 feet; the Pacific, according to this sounding, is
        probably at some points twice as deep as the Himalaya are high.

  [186] Mr. Hopkins, reasoning on data furnished by Dove's
        Isothermal maps, has arrived at the very interesting
        conclusion, that both on Snowdon and the lower mountains of the
        West of Ireland the snow-line would descend to within 1000 feet
        of the sea level, and glaciers reach the sea, if we could
        simply assume the three following geographical changes:--

        1st, The diversion of the Gulf stream from its present
        northerly course; 2dly, the depression of the existing land of
        Northern and Western Europe, to the amount of no more than 500
        feet; and 3dly, a cold current from the North sweeping over the
        submerged area. Quart. Journ. Geol. Soc. 1852, p. 85.

  [187] Daniell's Meteorological Essays, p. 103.

  [188] Observed by J. Crawfurd, Esq.

  [189] In speaking of the circulation of air and water in this
        chapter, no allusion is made to the trade winds, or to
        irregularities in the direction of currents, caused by the
        rotary motion of the earth. These causes prevent the movements
        from being direct from north to south, or from south to north,
        but they do not affect the theory of a constant circulation.

  [190] See Scoreby's Arctic Regions, vol. i. p. 378.

  [191] Ibid. p. 320.

  [192] This is shown by projecting a map on the horizon of
        London, that is to say, by supposing the eye of the observer to
        be placed above that city, and to see from thence one half of
        the globe. For it so happens that from that point, and no
        other, we should behold the greatest possible quantity of land;
        and if we are then transferred to the opposite or antipodal
        point, we should see the greatest possible quantity of water.
        (See figs. 3 and 4.) A singular fact, first pointed out by Mr.
        James Gardner, namely, that only one twenty-seventh part of the
        dry land has any land opposite to it, is intimately connected
        with this excess of land in one of the two hemispheres above
        alluded to. Thus, in fig. 3, the land shaded black in part of
        China answers to that portion of the extremity of South America
        and Tierra del Fuego which is opposite or antipodal to it,
        whilst the dark spots in the northern and central parts of
        South America represent Borneo, Sumatra, and other antipodal
        islands in the Eastern Archipelago. See Gardner, Geol. Soc.
        Proceedings, 1833, vol. i. p. 488.

  [193] Humboldt on Isothermal Lines

  [194] Humboldt, Tableaux de la Nature, tom. i. p. 112.

  [195] Ad. Brongniart, Consid. Générales sur la Nat. de la
        Végét. &c. Ann. des Sciences Nat., Nov. 1828.

  [196] Sir J. Richardson, Proceedings of Geol. Soc. No. 7, p.
        68, March, 1828.

  [197] Ad. Brongniart, Consid. Générales sur la Nat. de la
        Végét. &c., Ann. des Sci. Nat., Nov. 1828.

  [198] See a Memoir on the Alps, by Professor Sedgwick and Sir
        Rod. Murchison, Trans. of Geol. Soc. second ser. vol. iii.
        accompanied by a map.

  [199] See Proceedings of Geol. Soc. vol. ii. p. 334.

  [200] It may be observed, that the facts and inferences
        exhibited in this map bear not merely on the theory of climate
        above proposed, but serve also to illustrate the views
        explained in the third book respecting the migration of animals
        and plants and the gradual extinction of species.

  [201] See Sir R. Murchison's Paper on the Alps, Quart. Journ.
        Geol. Soc. vol. v. and my Anniversary Address for 1850, ibid.
        vol. vi.

  [202] Allgemeine Literatur Zeitung, No. cxxxix. July, 1833.

  [203] In this estimate, the space within the antarctic circle
        is not taken into account: if included, it would probably add
        to the excess of dry land; for the late discoveries of Capt.
        Sir James Ross, who penetrated to lat. 78° 10' S., confirm the
        conjecture of Captain Cook that the accumulation of antarctic
        ice implies the presence of a certain quantity of terra firma.
        The number of square miles on the surface of the globe are
        148,522,000, the part occupied by the sea being 110,849,000,
        and that by land, 37,673,000; so that the land is very nearly
        to the sea as 1 part in 4. I am informed by Mr. Gardner that,
        according to a rough approximation, the land between the 30° N.
        lat. and the pole occupies a space _about equal to that of the
        sea_, and the land between the 30° S. lat. and the antarctic
        circle about one-sixteenth of that zone.

  [204] See papers by Mr. Smith of Jordanhill, F. G. S., and the
        author, Proceedings Geol. Soc. No. 63, 1839, also that of Prof.
        E. Forbes, before cited, p. 86, note.

  [205] The theorem is thus stated:--"The eccentricity of the
        orbit varying, the total quantity of heat received by the earth
        from the sun in one revolution is inversely proportional to the
        minor axis of the orbit. The major axis is invariable, and
        therefore, of course, the absolute length of the year: hence it
        follows that the mean annual average of heat will also be in
        the same inverse ratio of the minor axis."--Geol. Trans. second
        series, vol. iii. p. 295.

  [206] Ann. du Bur. des Long. 1834.

  [207] Poisson, Théorie Mathémat. de la Chaleur, Comptes Rendus
        de l'Acad. des Sci., Jan. 30, 1837.

  [208] Quart. Journ. Geol. Soc. 1852, p. 62.

  [209] Proceedings Roy. Astronom. Soc. No. iii. Jan. 1840.

  [210] See a Memoir on the Temperature of the Terrestrial Globe,
        and the Planetary Spaces, Ann. de Chimie et Phys. tom. xxvii.
        p. 136. Oct. 1824.

  [211] Sir H. Davy, Consolations in Travel: Dialogue III. "The
        Unknown."

  [212] Quart. Journ. Geol. Soc. 1852.

  [213] Buckland's Bridgewater Treatise, p. 409.

  [214] Owen's Report on "British Fossil Reptiles, to Brit. Soc."
        1841, p. 200.

  [215] Quart. Journ. Geol. Soc. No. 6, p. 96.

  [216] See Hitchcock's Report on Geol. of Massachusetts, and
        Lyell's Travels in North America, chap. 12.

  [217] See Manual of Geol. by the Author, index _Microlestes_.

  [218] This figure (No. 8) is from a drawing by Professor C.
        Prevost, published Ann. des Sci. Nat. Avril, 1825. The fossil
        is a lower jaw, adhering by its inner side to the slab of
        oolite, in which it is sunk. The form of the condyle, or
        posterior process of the jaw, is convex, agreeing with the
        mammiferous type, and is distinctly seen, an impression of it
        being left on the stone, although in this specimen the bone is
        wanting. The anterior part of the jaw has been partially broken
        away, so that the double fangs of the molar teeth are seen
        fixed in their sockets, the form of the fangs being
        characteristic of the mammalia. Ten molars are preserved, and
        the place of an eleventh is believed to be apparent. The enamel
        of some of the teeth is well preserved.

  [219] A colored figure of this small and elegant quadruped is
        given in the Trans. Zool. Soc. vol. ii. pl. 28. It is
        insectivorous, and was taken in a hollow tree, in a country
        abounding in ant-hills, ninety miles to the southeast of the
        mouth of Swan River in Australia.--It is the first living
        marsupial species known to have nine molar teeth in the lower
        jaw, and some of the teeth are widely separated from others,
        one of the peculiarities in the thylacotherium of Stonesfield,
        which at first induced M. Blainville to refer that creature to
        the class of reptiles.

  [220] This figure (No. 10) was taken from the original,
        formerly in Mr. Broderip's collection, and now in the British
        Museum. It consists of the right half of a lower jaw, of which
        the inner side is seen. The jaw contains seven molar teeth, one
        canine, and three incisors; but the end of the jaw is
        fractured, and traces of the alveolus of a fourth incisor are
        seen. With this addition, the number of teeth would agree
        exactly with those of a lower jaw of a didelphis. The fossil is
        well preserved in a slab of oolitic structure containing shells
        of trigoniæ and other marine remains. Two or three other
        similar jaws, besides those above represented, have been
        procured from the quarries of Stonesfield.--See Broderip, Zool.
        Journ. vol. ii. p. 408. Owen, Proceedings Geol. Soc., November,
        1838.

  [221] Darwin's Journal, chap. 19. Lyell's Manual of Geol. chap.
        21, p. 279.

  [222] Taylor's Annals of Nat. Hist. Nov. 1839.

  [223] See notice by the Author, and Professor Owen, Taylor's
        Annals of Nat. Hist. Nov. 1839.

  [224] See Principles of Geology, 1st ed. 1830, vol. i p. 152.

  [225] The first quadrumanous fossils discovered in India were
        observed in 1836 in the Sewalik Hills, a lower range of the
        Himalayan Mountains, by Lieutenants Baker and Durond, by whom
        their osteological characters were determined (Journ. of Asiat.
        Soc. of Bengal, vol. v. p. 739), and in the year following, other
        fossils of the same class were brought to light and described by
        Capt. Cantley and Dr. Falconer. These were imbedded, like the
        former, in tertiary strata of conglomerate, sand, marl, and clay,
        in the Sub-Himalayan Mountains. (Ibid. vol. v. p. 379. Nov. 1836;
        and vol. vi. p. 354. May, 1837.)

        The Brazilian quadrumane was found, with a great many other
        extinct species of animals, by a Danish naturalist, Dr. Lund,
        between the rivers Francisco and Velhas, in 1837.

        The gibbon of the South of France was found by M. Lartet in the
        beginning of 1837, and determined by M. de Blainville. It
        occurred near Auch, in the department of Gers, about forty miles
        west of Toulouse, in freshwater marl, limestone, and sand. They
        were accompanied by the remains of the mastodon, dinotherium,
        palæotherium, rhinoceros, gigantic sloth, and other extinct
        quadrupeds. (Bulletin de la Soc. Geol. de France, tom. viii. p.
        92.)

        The British quadrumane was discovered in 1839, by Messrs. William
        Colchester and Searles Wood, at Kyson, near Woodbridge, in
        Suffolk, and was referred by Professor Owen to the genus Macacus.
        (Mag. of Nat. Hist. Sept. 1839. Taylor, Annals of Nat. Hist. No.
        xxiii. Nov. 1839.)

  [226] Owen's Introduction to British Fossil Mammals, p. 46.

  [227] Proceedings of Acad. Nat. Sci. Philad. Dec. 9, 1851.

  [228] See ch. 48.

  [229] Ibid.

  [230] Ibid.

  [231] Phys. Hist. of Mankind, vol. ii. p. 594.

  [232] Virgil, Eclog. iv. For an account of these doctrines, see
        Dugald Stewart's Elements of the Philosophy of the Human Mind,
        vol. ii. chap. ii. sect. 4, and Prichard's Egypt. Mythol. p. 177.

  [233] See ch. 41.

  [234] See ch. 35.

  [235] See ch. 37, 38, 39, 41.

  [236] See also Manual of Geology, ch. 11, 12.

  [237] It has been suspected ever since the middle of the last
        century, that the Caspian was lower than the ocean, it being
        known that in Astrakhan the mercury in the barometer generally
        stands above thirty inches. In 1811, MM. Engelhardt and Parrot
        attempted to determine the exact amount of difference by a series
        of levellings and barometrical measurements across the isthmus at
        two different places near the foot of Mount Caucasus. The result
        of their operations led them to the opinion that the Caspian was
        more than 300 feet below the Black Sea. But the correctness of
        the observations having afterwards been called in question, M.
        Parrot revisited the ground in 1829 and 1830, and inferred from
        new levellings, that the mouth of the Don was between three and
        four feet lower than that of the Wolga; in other words, that the
        sea of Azof, which communicates with the Black Sea, was actually
        lower than the Caspian! Other statements, no less contradictory,
        having been made by other observers, the Russian government at
        length directed the Academy of St. Petersburg to send an
        expedition, in 1836, to decide the point by a trigonometrical
        survey, from which it appeared that the Caspian is 101 Russian,
        or 108 English, feet lower than the Black Sea. (For authorities,
        see Journ. Roy. Geograph. Soc. vol. viii. p. 135). Sir R.
        Murchison, however, concludes, in 1845, from the best Russian
        authorities, that the depression of the Caspian is only 83 feet 6
        inches.

        The measurements of Major Anthony Symonds, since confirmed by
        French authorities, make the Dead Sea to be 1200 feet below the
        Mediterranean.

  [238] See Lyell's Travels in N. America, ch. 2 and 25.

  [239] See Manual of Geology, chap. 29 to 33, inclusive.

  [240] See ch. 26, _infrà._

  [241] See ch. 27, _infrà._

  [242] Ann. des Sci. Nat., Septembre, Novembre, et Décembre, 1829.
        Revue Française, No. 15, May, 1830. Bulletin de la Société Géol.
        de France, p. 864, May, 1847. The latest edition of M. de
        Beaumont's theory will be found in the 12th vol. of the
        Dictionnaire Universel d'Hist. Nat. 1852, art. "Systèmes des
        Montagues;" also the same printed separately.

  [243] Système de Mont. p. 762.

  [244] Ibid. pp. 761 and 773.

  [245] Phil. Mag. and Annals, No. 58. New Series, p. 242.

  [246] Système de Montagnes, 1852, p. 429.

  [247] Phil. Mag. and Annals, No. 58. New series, p. 243.

  [248] Système de Montagnes, 1852, p. 429.

  [249] For page, see Index, "Hopkins."

  [250] Art. Système de Montagnes, p. 775.

  [251] M. E de Beaumont in his later inquiries (Comptes rendus,
        Sept. 1850, and Systèmes des Montagnes) has come to the
        conclusion, that the principal mountain ranges, if prolonged,
        would intersect each other at certain angles, so as to produce a
        regular geometric arrangement, which he calls "a pentagonal
        network." This theory has been ably discussed and controverted by
        Mr. Hopkins, in his Anniversary Address as President of the Geol.
        Soc., Feb. 1853.

  [252] Darwin's Geology of South America, p. 248. London, 1846.

  [253] Système de Montagnes, p. 748.

  [254] See Lyell's Manual of Elementary Geology, ch. 5.

  [255] See the Author's Anniversary Address, Quart. Journ. Geol.
        Soc. 1850, vol. vi. p. 46, from which some of the above passages
        are extracted.

  [256] See Lyell's Manual of Elementary Geology.

  [257] Reports to Brit. Assoc. 1842, 1843, and Introd. to Brit.
        Foss. Mamm. p. 31. The conchological evidence respecting the
        British Miocene, Pliocene, and Pleistocene fossils, examined by
        Mr. Forbes, in the paper before cited, p. 88, note, bear out some
        of the most important conclusions of M. Deshayes, quoted by me in
        the first edition of the Principles, 1831, and the recent
        observations of Philippi in regard to the passage of species from
        one formation to another. I refer to these authorities more
        especially because this doctrine of a gradual transition has been
        opposed by some living naturalists of high distinction, among
        whom I may mention M.A. d'Orbigny and M. Agassiz. I have long
        been convinced that we must abandon many of the identifications
        formerly made of Eocene with recent shells; but some errors of
        this kind do not affect the general reasoning on the subject. See
        a discussion on this question, Quarterly Journ. of Geog. Soc.,
        No. 5, p. 47 Feb. 1846.

  [258] Darwin's Journal, p. 163. 2d. ed. p. 139.

  [259] Journ. Roy. Geograph. Soc. vol. iii. p. 142.

  [260] Book iii. ch. 50.

  [261] Darwin's S. America, pp. 136, 139.

  [262] Miller, Phil. Trans. 1851, p. 155.

  [263] Phil. Trans. 1850, p. 354.

  [264] Hooker's Himalayan Journal, ined.

  [265] Ibid.

  [266] See Manual of Geology, Index, _Rain-prints_.

  [267] See Lyell on recent and fossil rains. Quart. Journ. Geol.
        Soc. 1851, vol. vii. p. 239.

  [268] Lyell's Second Visit to the United States, 1846, vol. ii.
        p. 25.

  [269] Encyc. Brit. art. _Rivers_.

  [270] Sir T. D. Lauder's Account of the Great Floods in
        Morayshire, August, 1829.

  [271] Quarterly Jour. of Sci. &c. No. xii. New Series, p. 331.

  [272] Culley, Proceed. Geol. Soc. 1829.

  [273] Silliman's Journal, vol. xv. No. 2, p. 216. Jan. 1829.

  [274] Silliman's Journal, vol. xxxiv. p. 115.

  [275] See Lyell's Second Visit to the U. S. vol. i. p. 69.

  [276] This block was measured by Capt. B. Hall, R. N.

  [277] Inundation of the Val de Bagnes, in 1818, Ed. Phil. Journ.,
        vol. i. p. 187, from memoir of M. Escher.

  [278] Lib. viii. Epist. 17.

  [279] When at Tivoli, in 1829, I received this account from
        eye-witnesses of the event.

  [280] Illustr. of Hutt. Theory, § 3, p. 147.

  [281] Quadro Istorico dell' Etna, 1824.

  [282] The reader will find in my Travels in North America, vol.
        i. ch. 2, a colored geological map and section of the Niagara
        district, also a bird's-eye view of the Falls and adjacent
        country, colored geologically, of which the first idea was
        suggested by the excellent original sketch given by Mr. Bakewell.
        I have referred more fully to these and to Mr. Hall's Report on
        the Geology of New York, as well as to the earlier writings of
        Hennepin and Kalm in the same work, and have speculated on the
        origin of the escarpment over which the Falls may have been
        originally precipitated. Vol. i. p. 32, and vol. ii. p. 93.

  [283] Consid. sur les Blocs Errat. 1829.

  [284] Capt. Bayfield, Geol. Soc. Proceedings, vol. ii. p. 223.

  [285] M. Arago, Annuaire, &c. 1833; and Rev. J. Farquharson,
       Phil. Trans. 1835, p. 329.

  [286] Journ. of Roy. Geograph. Soc. vol. vi. p. 416.

  [287] See Système Glaciaire, by Agassiz, Guyot, and Desor, pp.
        436, 437, 445. Mr. Agassiz, at p. 462, states that he published
        in the Deutsche Vierteljahrschrift for 1841, this result as to
        the central motion being greater than that of the sides, and
        was, therefore, the first to correct his own previous mistake.

  [288] J. Forbes. 8th Letter on Glaciers, Aug. 1844.

  [289] See Mr. Hopkins on Motion of Glaciers, Cambridge Phil.
        Trans. 1844, and Phil. Mag. 1845. Some of the late concessions
        of this author as to a certain plasticity in the mass, appear
        to me to make the difference between him and Professor Forbes
        little more than one of degree. (For the latest summary of
        Prof. Forbes' views, see Phil. Trans. 1846, pt. 2.)

  [290] This experiment is cited by Mr. Forbes, Phil. Trans.
        1846, p. 206; and I have conversed with Mr. Christie on the
        subject.

  [291] Etudes sur les Glaciers, 1840.

  [292] See Manual of Geol. ch. xi.

  [293] Agassiz, Jam. Ed. New Phil. Journ. No. 54, p. 388.

  [294] Charpentier, Ann. des Mines, tom. viii.; see also Papers
        by MM. Venetz and Agassiz.

  [295] Voyage in 1822, p. 233.

  [296] Travels in Norway.

  [297] Darwin's Journal, p. 283.

  [298] Journ. of Roy. Geograph. Soc. vol. ix. p. 526.

  [299] Journ. of Roy. Geograph. Soc. vol. ix. p. 529.

  [300] Ibid. vol. viii. p. 221.

  [301] In my Travels in N. America, pp. 19, 23, &c., and Second
        Visit to the U. S., vol. i. ch. 2, also in my Manual of
        Geology, a more full account of the action of floating ice and
        coast-ice, and its bearing on geology, will be found.

  [302] Jam. Ed. New Phil. Journ. No. xlviii. p. 439.

  [303] Bulletin de la Soc. Géol. de France, 1847, tom. iv. pp.
        1182, 1183.

  [304] Consult J. Prestwich, Water-bearing Strata around
        London. 1851. (Van Voorst)

  [305] Sabine, Journ. of Sci. No. xxxiii. p. 72. 1824.

  [306] Héricart de Thury, "Puits Forés," p. 49.

  [307] Prestwich, p. 69.

  [308] Bull. de la Soc. Géol. de France, tom. iii. p. 194.

  [309] Boué Résumé des Prog. de la Géol. en 1832, p. 184.

  [310] Seventh Rep. Brit. Ass. 1837, p. 66.

  [311] H. de Thury, p. 295.

  [312] Bull. de la Soc. Géol de France, tom. i. p. 93.

  [313] Bull. de la Soc. Géol. de France, tom. ii. p. 248.

  [314] See Glossary, "Tufa," "Travertin."

  [315] Dr. Grosse on the Baths of San Filippo, Ed. Phil. Journ.
        vol. ii p. 292.

  [316] Consolations in Travel, pp. 123-125.

  [317] Ibid. p. 127.

  [318] C. Prevost, Essai sur la Constitution Physique du Bassin
        de Vienne, p. 10.

  [319] Travels across the Andes, p. 240.

  [320] Annalen der Chem. 1847.

  [321] Daubeny on Volcanoes, p. 222.

  [322] Dr. Webster on the Hot Springs of Furnas, Ed. Phil.
        Journ. vol. vi. p. 306.

  [323] See a cut of the Icelandic geyser, chap. 32.

  [324] M. Robert, Bullétin de la Soc. Géol. de France, tom.
        vii. p. 11.

  [325] Barrow's Iceland, p. 209.

  [326] See Lyell's Manual of Elementary Geology; and Dr.
        Turner, Jam. Ed. New Phil. Journ. No. xxx. p. 246.

  [327] L. Horner, Geol. Trans, vol. ii. p. 94.

  [328] Ann. de l'Auvergne, tome i. p. 234.

  [329] Ann. Scient. de l'Auvergne, tome ii. June, 1829.

  [330] Edinb. New Phil. Journ. Oct. 1839.

  [331] See Lyell's Travels in N. America, vol. i p. 150.

  [332] Symes, Embassy to Ava, vol. ii. Geol. Trans. second
        series, vol. ii. part iii. p. 388.

  [333] Dr. Nugent, Geol. Trans. vol. i. p. 69.

  [334] Ibid. p. 67.

  [335] De la Beche, Ed. Phil. Journ. vol. ii. p. 107. Jan.
        1820.

  [336] De la Beche, MS.

  [337] De la Beche, MS.

  [338] Trans. of Lit. and Hist. Soc. of Quebec, vol. i. p. 5,
        1829.

  [339] Prony, see Cuvier, Disc. Prelim, p. 146.

  [340] See De Beaumont, Géologie Pratique, vol. i. p. 323,
        1844.

  [341] Prony, cited by Cuvier, Discours Prélimin.

  [342] Brocchi, Conch. Foss. Subap. vol. i. p. 118.

  [343] Archiac, Histoire des Progrés de la Géol. 1848, vol. ii.
        p. 232.

  [344] Brocchi, Conch. Foss. Subap. vol. i. p. 39.

  [345] Ibid. vol. ii. p. 94.

  [346] Mém. d'Astruc, cited by Von Hoff, vol. i. p. 288.

  [347] Lib. ii. c. v.

  [348] Bouche, Chorographie et Hist. de Provence, vol. i. p.
        23, cited by Von Hoft, vol. i. p. 290.

  [349] Hist. Phys. de la Mer.

  [350] Karamania, or a brief Description of the Coast of Asia
        Minor, &c. London, 1817.

  [351] Geog. Syst. of Herod, vol. ii. p. 107.

  [352] Euterpe, XI.

  [353] Journ. of Roy. Geograph. Soc. vol. ix. p. 432.

  [354] Quart. Journ. Geol. Soc. vol. v.; Memoirs, p. 20; and
        Lassaigue, Journ. Pharm. t. v. p. 468.

  [355] Quart. Journ. Geol. Soc. 1848, vol. iv. p. 342.

  [356] Flint's Geography, vol. i. p. 142. Lyell's Second Visit
        to the United States, vol. ii chaps. 28 to 34.

  [357] Geograph. Descrip. of Louisiana, by W. Darby,
        Philadelphia, 1816, p. 102.

  [358] Flint's Geography, vol. i. p. 152.

  [359] Travels in North America, vol. iii. p. 361.

  [360] Travels in North America, vol. iii. p. 362.

  [361] "The boats are fitted," says Captain Hall, "with what is
        called a snag-chamber;--a partition formed of stout planks,
        which is calked, and made so effectually water-tight that the
        foremost end of the vessel is cut off as entirely from the
        rest of the hold as if it belonged to another boat. If the
        steam-vessel happen to run against a snag, and that a hole is
        made in her bow, under the surface, this chamber merely fills
        with water."--Travels in North America, vol. iii. p. 363.

  [362] Darby's Louisiana, p. 33.

  [363] Featherstonhaugh, Geol. Report, Washington, 1835, p. 84.

  [364] Trees submerged in an upright position have been
        observed in other parts of N. America. Thus Captains Clark and
        Lewis found, about the year 1807, a forest of pines standing
        erect under water in the body of the Columbia river, which
        they supposed, from the appearance of the trees, to have been
        submerged only about twenty years. (Travels, &c. vol. ii. p.
        241.) More lately (1835), the Rev. Mr. Parker observed on the
        same river (lat. 45° N., long. 121° W.) trees standing in
        their natural position in spots where the water was more than
        twenty feet deep. The tops of the trees had disappeared; but
        between high and low water-mark the trunks were only partially
        decayed; and the roots were seen through the clear water,
        spreading as they had grown in their native forest. (Tour
        beyond the Rocky Mountains, p. 132.) Some have inferred from
        these facts that a tract of land, more than twenty miles in
        length, must have subsided vertically; but Capt. Fremont, Dec.
        1845 (Rep. of Explor. Exped. p. 195), satisfied himself that
        the submerged forests have been formed by immense land-slides
        from the mountains, which here closely shut in the river.

  [365] For an account of the "sunk country," shaken by the
        earthquake of 1811-12, see Lyell's Second Visit to the United
        States, ch. 33.

  [366] Darby's Louisiana, p. 103.

  [367] The calculations here given were communicated to the
        British Association, in a lecture which I delivered at
        Southampton in September, 1846. (See Athenæum Journal, Sept.
        26, 1846, and Report of British Association, 1846, p. 117.)
        Dr. Riddell has since repeated his experiments on the quantity
        of sediment in the river at New Orleans without any material
        variation in the results.

        Mr. Forshey, in a memoir on the Physics of the Mississippi,
        published in 1850, adopts Dr. Riddell's estimate for the
        quantity of mud, but takes 447,199 cubic feet per second as
        the average discharge of water for the year at Carrolton, nine
        miles above New Orleans, a result deduced from thirty years of
        observations. This being one-tenth more than I had assumed,
        would add a tenth to the sediment, and would diminish by
        one-eleventh the number of years required to accomplish the
        task above alluded to. "The cubic contents of sedimentary
        matter," says Forshey, "are equal to 4,083,333,333, and this
        sediment would annually cover twelve miles square one foot
        deep."

  [368] The Mississippi is continually shifting its course in
        the great alluvial plain, cutting frequently to the depth of
        100, and even sometimes to the depth of 250 feet. As the old
        channels become afterwards filled up, or in a great degree
        obliterated, this excavation alone must have given a
        considerable depth to the basin, which receives the alluvial
        deposit, and subsidences like those accompanying the
        earthquake of New Madrid in 1811-12 may have given still more
        depth.

  [369] Account of the Ganges and Burrampooter rivers, by Major
        Rennell, Phil. Trans. 1781.

  [370] Trans. of the Asiatic Society, vol. vii. p. 14.

  [371] Cuvier referred the true crocodiles of the Ganges to a
        single species, _C. biporcatus_. But I learn from Dr. Falconer
        that there are three well-marked species, _C. biporcatus_, _C.
        palustris_, and _C. bombifrons_. _C. bombifrons_ occurs in the
        northern branches of the Ganges, 1000 miles from Calcutta; _C.
        biporcatus_ appears to be confined to the estuary; and _C.
        palustris_, to range from the estuary to the central parts of
        Bengal. The garial is found along with _C. bombifrons_ in the
        north, and descends to the region of _C. biporcatus_ in the
        estuary.

  [372] See below, ch. 22 and 29.

  [373] Second Visit to the United States, vol. ii. p. 145.

  [374] Asiatic Researches, vol. xvii. p. 466.

  [375] Lyell's Second Visit to the United States, vol. ii.
        chap. 34.

  [376] See Manual of Geology by the Author.

  [377] See p. 13.

  [378] Geog. of Herod, vol ii. p. 331.

  [379] Ibid. p. 328.

  [380] Romme, Vents et Courans, vol. ii. p. 2. Rev. F. Fallows,
        Quart. Journ. of Science, March, 1829.

  [381] The heights of these tides were given me by the late
        Captain Hewett, R. N.

  [382] On the authority of Admiral Sir F. Beaufort, R. N.

  [383] Consult the map of Currents by Capt. F. Beechy, R. N.,
        Admiralty Manual, 1849, London.

  [384] Rennell on Currents, p. 58.

  [385] Rennell on the Channel current.

  [386] An. du Bureau des Long. 1836.

  [387] Second Parliamentary Report on Steam Communication with
        India, July, 1851.

  [388] Phil. Trans. 1830, p. 59.

  [389] See Capt. B. Hall, On Theory of Trade Winds, Fragments
        of Voy. second series, vol. i., and Appendix to Daniell's
        Meteorology.

  [390] Treatise on Astronomy, chap. 3.

  [391] Descrip. of Shetland Islands, p. 527, Edin. 1822, to
        which work I am indebted for the following representations of
        rocks in the Shetland Isles.

  [392] Dr. Hibbert, from MSS. of Rev. George Low, of Fetlar.

  [393] Hibbert, p. 528.

  [394] Hibbert, p. 519.

  [395] Account of Erection of Bell Rock Lighthouse, p. 163.

  [396] Ed. Phil. Journ. vol. iii. p. 54, 1820.

  [397] Quart. Journ. of Sci. &c., No. xiii. _N. S._ March,
        1830.

  [398] Buist, Quart. Journ. of Agricult., No. xlv. p. 34, June,
        1839.

  [399] Phillips's Geology of Yorkshire, p. 61.

  [400] Rivers, Mountains, and Sea-coast of Yorkshire p. 122,
        1853, London.

  [401] Arctic Zoology, vol. i. p. 10, Introduction.

  [402] Phillips's Geol. of York. p. 60.

  [403] Arct. Zool. vol. i. p. 13, Introd.

  [404] Taylor's Geology of East Norfolk, p. 32.

  [405] Ibid.

  [406] De Beaumont, Géologie Pratique, p. 218.

  [407] Taylor's Geology of East Norfolk, p. 10.

  [408] From Mr. R. C. Taylor's Mem., see Phil. Mag., Oct. 1827, p.
        297.

  [409] Consequences of the Deluge, Phys. Theol. Discourses.

  [410] History of British Birds, vol. ii. p. 220 ed. 1821.

  [411] Tidal Harbor Commissioners' First Report, 1845, p. 176.

  [412] On authority of Dr. Mitchell, F. G. S.

  [413] On the authority of W. Gunnell, Esq., and W. Richardson,
        Esq., F. G. S.

  [414] Vol. ii. New Ser. 1809, p. 801.

  [415] Geog. of Herod. vol. ii. p. 326.

  [416] Dodsley's Ann. Regist. 1772.

  [417] See J. B. Redman on Changes of S. E. Coast of England,
        Proceed. Instit. Civil Engin. vol. ii. 1851, 1852.

  [418] Stevenson, Ed. Phil Journ. No. v. p. 45, and Dr. Fitton,
        Geol. Trans. 2d series, vol. iv. plate 9.

  [419] On the authority of Mr. J. Meryon, of Rye.

  [420] Redman, ibid, see p. 315.

  [421] Edin. Journ. of Sci. No. xix. p. 56.

  [422] Redman as cited, p. 315.

  [423] Webster, Geol. Trans. vol. ii. p. 192, 1st series.

  [424] Mantell, Geology of Sussex, p. 293.

  [425] See Palmer on Shingle Beaches, Phil. Trans. 1834, p. 568.

  [426] Groins are formed of piles and wooden planks, or of fagots
        staked down and are used either to break the force of the waves,
        or to retain the beach.

  [427] Redman as cited, p. 315.

  [428] Rob. A. C. Austen on the Valley of the English Channel,
        Quart. Journ. G. S. vol. vi. p. 72.

  [429] See Palmer on Motion of Shingle Beaches, Phil. Trans. 1834,
        p. 568; and Col. Sir W. Reid, Papers of Royal Engineers, 1838,
        vol ii. p. 128.

  [430] De la Beche, Geolog. Manual, p. 82.

  [431] According to the measurement of Carpenter of Lyme.

  [432] Rev. W. D. Conybeare, letter dated Axminster, Dec. 31,
        1839.

  [433] London, J. Murray, 1840.

  [434] Boase, Trans. Royal Geol. Soc. of Cornwall, vol. ii. p.
        129.

  [435] Boase, ibid. vol. ii. p. 135.

  [436] De la Beche's Report on the Geology of Devon, &c. chap.
        xiii.

  [437] Geol. Trans. 1st series, vol. iii. p. 383.

  [438] Boase, vol. ii. p. 130.

  [439] Stevenson, Jameson's Ed. New Phil. Journ. No. 8, p. 386.

  [440] Camden, who cites Gyraldus; also Ray, "On the Deluge,"
        Phys. Theol. p. 228.

  [441] Meyrick's Cardigan.

  [442] Von Hoff, Geschichte, &c. vol. i. p. 49.

  [443] E. de Beaumont, Géologie Pratique, vol. i. p. 316, and
        ibid. p. 260.

  [444] Belpaire, Mém. de l'Acad. Roy. de Bruxelles, tom. x. 1837.
        Dumont, Bulletin of the same Soc. tom. v. p. 643.

  [445] Von Hoff, vol. i. p. 364.

  [446] Quart. Journ. Geol. Soc. vol. iv. p. 32; Memoirs.

  [447] See examples in Von Hoff; vol. i. p. 73, who cites
        Pisansky.

  [448] Book vii. Cimbri.

  [449] Lib. iii. cap 3.

  [450] New Monthly Mag. vol. vi. p. 69.

  [451] Von Hoff, vol. i. p. 96.

  [452] Phil. Trans. 1833, p. 204.

  [453] See Lyell's Travels in North America, in 1842, vol. ii. p.
        166. London, 1845.

  [454] Rennell, Phil. Trans. 1781.

  [455] MS. of Capt. Bayfield, R. N.

  [456] Silliman's Journ. vol. xxxiv. p. 349.

  [457] Phil. Trans. 1829, part i. p. 29.

  [458] Phil. Trans. 1724.

  [459] Bull. de la Soc. Géol de France,--Résumé, p. 72, 1832.

  [460] Clarke's Travels in Europe, Asia, and Africa, vol. iii. pp.
        340 and 363, 4th edition.

  [461] Nouvelle Chronique de la Ville de Bayonne, pp. 113, 139:
        1827.

  [462] Stevenson on bed of German Ocean, Ed. Phil. Journ. No. v.
        p. 44: 1820.

  [463] Stevenson, ibid. p. 47: 1820.

  [464] Robt. A. C. Austen, Quart. Journ. Geol. Soc. vol. vi. p.
        76.

  [465] Experiments to determine the Figure of the Earth, &c. p.
        445.

  [466] Lochead on Nat. Hist. of Guiana, Edin. Trans. vol. iv.

  [467] On the authority of Mr. Faraday.

  [468] On the authority of Mr. R. Phillips.

  [469] See Von Buch's Description of Canary Islands (Paris, ed.
        1836) for a valuable sketch of the principal volcanoes of the
        globe.

  [470] Darwin, Geol. Trans. 2d series, vol. v. p. 612.

  [471] Ibid. p. 606.

  [472] Bull. de la Soc. Géol. tom. vi. p. 55.

  [473] Bull. de la Soc. Géol. de France, tom. vi. p. 56.

  [474] Caldeleugh, Phil. Trans. 1836, p. 27.

  [475] Comptes Rendus, 1849, vol. xxix. p. 531.

  [476] See map of volcanic lines in Von Buch's work on the
        Canaries.

  [477] Von Buch, ibid. p. 409.

  [478] Darwin, Structure and Distrib. of Coral reefs, &c., London,
        1842. In the subjoined map, fig. 39, I have copied with
        permission a small part of the valuable map accompanying this
        work.

  [479] Von Buch, Descrip. des Iles Canar. p. 450, who cites Erman
        and others.

  [480] Paper read at meeting of Brit. Assoc. Southampton, Sept.
        1846.

  [481] Macclelland, Report on Coal and Min. Resources of India.
        Calcutta, 1838.

  [482] Geology of the American Exploring Expedition. See also
        Lyell's Manual, "Sandwich I. Volcanoes"--Index.

  [483] Strabo, ed Fal., p. 900.

  [484] Researches in Asia Minor, vol. ii. p. 39.

  [485] Virlet, Bulletin de la Soc. Géol. de France, tom. iii. p.
        109.

  [486] Daubeny on Mount Vultur, Ashmolean Memoirs. Oxford, 1835.

  [487] Book v. ch. xlvi.--See letter of M. Virlet, Bulletin de la
        Soc. Géol. de France, tom. ii. p. 341.

  [488] See ch. 32, _Cause of Volcanic Eruptions_.

  [489] Verneur, Journal des Voyages, tom. iv. p. 111. Von Hoff,
        vol. ii. p. 275.

  [490] Lib. v.

  [491] Nat. Hist. lib. iii. c. 6.

  [492] See Poulett Scrope, Geol. Trans. 2d series, vol. ii. pl.
        34.

  [493] De Rerum Nat. vi. 740.--Forbes, on Bay of Naples, Edin.
        Journ. of Sci. No iii. new series, p. 87. Jan. 1830.

  [494] Humboldt, Voy. p. 317.

  [495] Von Buch, Ueber einen vulcanischen Ausbruch auf der Insel
        Lanzerote.

  [496] Haustæ aut obrutæ urbes.--Hist. lib. i.

  [497] Hist. Rom. lib. lxvi.

  [498] The earliest authority, says Mr. Forbes, given for this
        fact, appears to be Capaccio, quoted in the Terra Tremante of
        Bonito.--Edin. Journ. of Sci. &c. No. i. new series, p. 127.
        July, 1829.

  [499] Geol. Trans. second series, vol. ii. p. 346.

  [500] Lib. vi. de Bello Neap. in Grævii Thesaur.

  [501] Prodig. libel. c. cxiv.

  [502] This representation of the Phlegræan Fields is reduced
        from part of Plate xxxi. of Sir William Hamilton's great work
        "Campi Phlegræi." The faithfulness of his colored delineations
        of the scenery of that country cannot be too highly praised.

  [503] Campi Phlegræi, p. 70.

  [504] Campi Phlegræi, p. 77.

  [505] P. 347. Paris, 1836.

  [506] "Magnus terræ tractus, qui inter radices montis, quem
        Barbarum incolæ appellant, et mare juxta Avernum jacet, sese
        erigere videbatur, et montis subitò nascentis figuram imitari.
        Eo ipso die horâ noctis II., iste terræ cumulus, aperto veluti
        ore, magno cum fremitu, magnos ignes evomuit; pumicesque, et
        lapides, cineresque."--Porzio, Opera Omnis, Medica, Phil., et
        Mathemat., in unum collecta, 1736, cited by Dufrénoy, Mém.
        pour servir à une Description Géologique de la France, tom.
        iv. p. 274.

  [507] See Neues Jahr Buch for 1846, and a translation in the
        Quarterly Journ. of the Geol. Soc. for 1847, vol iii. p. 20,
        Memoirs.

  [508] Mem. Roy. Acad. Nap. 1849.

  [509] "Verum quod omnem superat admirationem, mons circum eam
        voraginem ex pummicibus et cincere plusquàm mille passuum
        altitudine unà nocte congestus aspicitur."

  [510] Mém. de la Soc. Géol. de France, tom. ii. p. 91.

  [511] Dufrénoy, Mem. pour servir, &c. p. 277.

  [512] Darwin's Volcanic Islands, 106, note.

  [513] Geology of the American Exploring Expedition, in
        1838-1842, p. 354.

  [514] Ibid. p. 328.

  [515] See chap. 29.

  [516] Hamilton (writing in 1770) says, "the new mountain
        produces as yet but a very slender vegetation."--Campi
        Phlegræi, p. 69. This remark was no longer applicable when I
        saw it, in 1828.

  [517] Hamilton's Campi Phlegræi, folio, vol. i. p. 62; and
        Brieslak, Campanie, tome i. p. 186.

  [518] Account of the Eruption of Vesuvius in October, 1822, by
        G. P. Scrope, Esq., Journ. of Sci. &c. vol. xv. p. 175.

  [519] Mr. Forbes, Account of Mount Vesuvius, Edin. Journ. of
        Sci. No. xviii. p. 195. Oct. 1828.

  [520] Ibid. p. 194.

  [521] Monticelli and Covelli, Storia di Fenon. del Vesuv. en
        1821-23.

  [522] Campi Phlegræi.

  [523] Otter's Life of Dr. Clarke.

  [524] Phil. Trans. 1846, p. 154.

  [525] Ibid. p. 148.

  [526] Ibid. p. 241.

  [527] Bulletin de la Soc. Géol. de France, tom. vii. p. 43;
        and Illustrations of Vesuvius and Etna, p. 3.

  [528] Geognost. Beobachtungen, &c., p. 182. Berlin, 1839.

  [529] Von Buch, Descrip. Phys. des Iles Canaries, p. 342.
        Paris, 1836.

  [530] Vues Illust. de Phénom. Géol. Observ. sur le Vésuve et
        l'Etna. Berlin, 1837.

  [531] Ibid. p. 2.

  [532] 2d edit. 1848, p. 216.

  [533] So called from travellers leaving their horses and mules
        there when they prepare to ascend the cone on foot.

  [534] Dufrénoy, Mém. pour servir à une Descrip. Gèol. de la
        France, tom. iv. p. 294.

  [535] Descrip. Phys. des Iles Canaries, p. 344.

  [536] See Daubeny's Volcanoes, p. 400.

  [537] Geol. of American Explor. Exped. p. 359, note. Mr. Dana
        informed me (Sept. 1852), that an angle of 60° instead of 30°,
        was given by mistake in his work.

  [538] Ibid. p. 354.

  [539] Geol. Trans. 2d series, vol. ii. p. 341.

  [540] See a paper by the Author on "Craters of Denudation,"
        Quart. Journ. Geol. Soc. 1850.

  [541] Dufrénoy, Mém. pour servir, &c. tom. iv. p. 285.

  [542] Journal of Science, vol. xv. p. 177.

  [543] Voy. dans la Campanie, tome i. p. 201.

  [544] Mr. Forbes, Edin. Journ. of Sci. No. xviii. Oct. 1828.

  [545] Daubeny on Volcanoes, p. 169.

  [546] Scrope, Geol. Trans. second series, vol. ii. p. 346.

  [547] Monticelli and Covelli, Prodrom. della Mineral. Vesuv.

  [548] The great eruption, in 1822, caused a covering only a
        few inches thick on Pompeii. Several feet are mentioned by
        Prof. J. D. Forbes.--Ed. Journ. of Science, No. xix. p. 181,
        Jan. 1829. But he must have measured in spots where it had
        drifted. The dust and ashes were five feet thick at the top of
        the crater, and decreased gradually to ten inches at Torre del
        Annunziata. The size and weight of the ejected fragments
        diminished very regularly in the same continuous stratum, as
        the distance from the centre of projection was greater.

  [549] Forbes, Ed. Journ. of Sci. No. xix. p. 130, Jan. 1829.

  [550] Scrope, Geol. Trans. second series, vol. ii. p. 346.

  [551] Napoli, 1816.

  [552] Not a few of the organic bodies, called by Ehrenberg
        "infusoria," such as Galionella and Bacillaria, have been
        recently claimed by many botanists as belonging to the
        vegetable kingdom, and are referred to the classes called
        Diatomaceæ and Desmidiæ.

  [553] See Ehrenberg, Proceedings (Berichte) of the Royal Acad.
        of Sci. Berlin, 1844, 1845, and an excellent abstract of his
        papers by Mr. Ansted in the Quart. Journ. of the Geol. Soc.
        London, No. 7, Aug. 1846. In regard to marine infusoria found
        in volcanic tuff; it is well known that on the shores of the
        island of Cephalonia in the Mediterranean (Proceedings, Geol.
        Soc. vol. ii. p. 220), there is a cavity in the rock, into
        which the sea has been flowing for ages, and many others
        doubtless exist in the leaky bottom of the ocean. The marine
        current has been rushing in for many years, and as the
        infusoria inhabiting the waters of the Mediterranean are
        exceedingly abundant, a vast store of their cases may
        accumulate in submarine caverns (the water, perhaps, being
        converted into steam, and so escaping upwards), and they may
        then be cast up again to furnish the materials of volcanic
        tuff, should an eruption occur like that which produced Graham
        Island, off the coast of Sicily, in 1831.

  [554] Hamilton, Observ. on Mount Vesuvius, p. 94. London,
        1774.

  [555] Swinburne and Lalande. Paderni, Phil. Trans. 1758, vol.
        i. p. 619.

  [556] Prof. J. D. Forbes, Edin. Journ. of Sci. No. xix. p.
        130, Jan. 1829.

  [557] In one of the manuscripts which was in the hands of the
        interpreters when I visited the museum in 1828, the author
        indulges in the speculation that all the Homeric personages
        were allegorical--that Agamemnon was the ether, Achilles the
        sun, Helen the earth, Paris the air, Hector the moon, &c.

  [558] Sir H. Davy, Consolations in Travel, p. 66.

  [559] Forsyth's Italy, vol. ii.

  [560] In 1815, Captain Smyth ascertained, trigonometrically,
        that the height of Etna was 10,874 feet. The Catanians,
        disappointed that their mountain had lost nearly 2000 feet of
        the height assigned to it by Recupero, refused to acquiesce in
        the decision. Afterwards, in 1824, Sir J. Herschel, not being
        aware of Captain Smyth's conclusions, determined by careful
        barometrical measurement that the height was 10,872½ feet.
        This singular agreement of results so differently obtained was
        spoken of by Herschel as "a happy accident;" but Dr. Wollaston
        remarked that "it was one of those accidents which would not
        have happened to two fools."

  [561] Book iii. at the end.

  [562] The hill which I have here introduced was called by my
        guide Vampolara, but the name given in the text is the nearest
        to this which I find in Gemmellaro's Catalogue of Minor Cones.

  [563] Mém. pour servir, &c. tom. iv. p. 116.

  [564] See Prof. J. D. Forbes, Phil. Trans. 1846, p. 155, on
        Velocity of Lava.

  [565] Ferrara, Descriz. dell' Etna, p. 108.

  [566] Ferrara, Descriz. dell' Etna. Palermo, 1818.

  [567] This view is taken from a sketch made by Mr. James
        Bridges, corrected after comparison with several sketches of
        my own.

  [568] Scrope on Volcanoes, p. 153.

  [569] This drawing is part of a panoramic sketch which I made
        from the summit of the cone, December 1, 1828, when every part
        of Etna was free from clouds except the Val del Bove. The
        small cone, and the crater nearest the foreground, were among
        those formed during the eruptions of 1810 and 1811.

  [570] Scrope on Volcanoes, p. 102.

  [571] Ferara, Descriz. dell' Etna, p. 116.

  [572] Mr. Nasmyth, the inventor of the steam-hammer, has
        lately illustrated, by a very striking experiment, the
        non-conductibility of a thin layer of dry sand and clay. Into
        a caldron of iron one-fourth of an inch thick, lined with sand
        and clay five-eighths of an inch thick, he poured eight tons
        of melted iron at a white heat. After the fused metal had been
        twenty minutes in the caldron the palm of the hand could be
        applied to the outside without inconvenience, and after forty
        minutes there was not heat enough to singe writing-paper. This
        fact may help us to explain how strata in contact with dikes,
        or beds of fused matter, have sometimes escaped without
        perceptible alteration by heat.

  [573] Journ. of Roy. Geograph. Soc. vol. i. p. 64.

  [574] Hoffman, Geognost. Beobachtungen, p. 701. Berlin, 1839.

  [575] Mém. pour servir, &c., tom. iv. Paris, 1838.

  [576] Geognost. Beobachtungen, &c. Berlin, 1839.

  [577] De Beaumont, Mém. pour servir, &c. tom. iv. pp. 187,
        188.

  [578] Mém. pour servir, tom. iv. p. 149.

  [579] P. 62, _supra_.

  [580] See p. 366.

  [581] On the Longevity of Trees, Bibliot. Univ., May, 1831.

  [582] Sedgwick, Anniv. Address to Geol. Soc. p. 35. Feb. 1831.

  [583] Von Hoff, vol. ii. p. 393.

  [584] The first narrative of the eruption was drawn up by
        Stephenson, then Chief Justice in Iceland, appointed
        Commissioner by the King of Denmark for estimating the damage
        done to the country, that relief might be afforded to the
        sufferers. Henderson was enabled to correct some of the
        measurements given by Stephenson, of the depth, width, and
        length of the lava currents, by reference to the MS. of Mr.
        Paulson, who visited the tract in 1794, and examined the lava
        with attention. (Journal of a Residence in Iceland, &c. p.
        229.) Some of the principal facts are also corroborated by Sir
        William Hooker, in his "Tour in Iceland," vol. ii. p. 128.

  [585] Henderson's Journal, &c. p. 228.

  [586] Jameson's Phil. Journ. vol. xxvi. p. 291.

  [587] Tableau des Terrains qui composent l'Ecorce du Globe, p.
        52. Paris, 1829.

  [588] Daubeny on Volcanoes, p. 337.

  [589] See Scrope on Volcanoes, p. 267.

  [590] Leonhard and Bronn's Neues Jahrbuch, 1835, p. 36.

  [591] Van der Boon Mesch, de Incendiis Montium Javæ, &c. Lugd.
        Bat. 1826; and Official Report of the President, Baron Van der
        Capellen; also, Von Buch, Iles Canar. p. 424.

  [592] Journ. de Géol. tome i.

  [593] In a former edition, I selected the name of Sciacca out
        of seven which had been proposed; but the Royal and
        Geographical Societies have now adopted Graham Island; a name
        given by Capt. Senhouse, R. N., the first who succeeded in
        landing on it. The seven rival names are Nerita, Ferdinanda,
        Hotham, Graham, Corrao, Sciacca, Julia. As the isle was
        visible for only about three months, this is an instance of a
        wanton multiplication of synonyms which has scarcely ever been
        outdone even in the annals of zoology and botany.

  [594] Phil. Trans. 1832, p. 255.

  [595] Journ. of Roy. Geograph. Soc. 1830-31.

  [596] Phil. Trans. part. ii. 1832, reduced from drawings by
        Capt. Wodehouse, R. N.

  [597] In the annexed sketch (fig. 60), drawn by M. Joinville,
        who accompanied M. C. Prevost, the beds seem to slope towards
        the centre of the crater; but I am informed by M. Prevost that
        these lines were not intended by the artist to represent the
        dip of the beds.

  [598] See Memoir by M. C. Prevost, Ann. des Sci. Nat. tom.
        xxiv.

  [599] Geol. of Fife and the Lothians, p. 41. Edin. 1839.

  [600] Phil. Trans. 1832, p. 243.

  [601] Ibid. p. 249.

  [602] Darwin's Volcanic Islands, p. 92.

  [603] Ibid. p. 6.

  [604] This account was principally derived by Von Buch from
        the MS. of Don Andrea Lorenzo Curbeto, curate of Yaira, the
        point where the eruption began.--Ueber einen vulcanischen
        Ausbruch auf der Insel Lanzerote.

  [605] Férussac, Bulletin des Sci. Nat. tome v. p. 45: 1825.

  [606] Comptes Rendus Acad. Sci. Paris, Juin, 1846.

  [607] Virlet, Bull. de la Soc. Géol. de France, tom. iii. p.
        103.

  [608] Phil. Trans. No. 332.

  [609] E. Forbes, Brit. Association, Report for 1843.

  [610] See a paper read to the Geographical Society in 1849.

  [611] Bull. de la Soc. Géol. de France, tome iii.

  [612] Virlet, Bull. de la Soc. Géol. de France, tome iii. p.
        103.

  [613] Poggendorf's Annalen, 1836, p. 183.

  [614] See Admiralty Chart, with views and sections, 1842.

  [615] For height of cone and references, see Buist, Volcanoes
        of India, Trans. Bombay Geol. Soc. vol. x. p. 143.

  [616] Humboldt's Cosmos.

  [617] Daubeny, Volcanoes, p. 267.

  [618] See Buist, Volcanoes of India, Trans. Bombay Geol. Soc.
        vol. x. p. 154, and Captain Robertson, Journ. of Roy. Asiat.
        Soc. 1850.

  [619] See Glossary.

  [620] Bunsen, Volcanic Rocks of Iceland.

  [621] Bulletin de la Soc. Géol. de France, tom. ii. p. 206.

  [622] Since the publication of the first edition of this work,
        numerous accounts of recent earthquakes have been published;
        but as they do not illustrate any new principle, I cannot
        insert them, as they would enlarge too much the size of my
        work. The late Von Hoff published from time to time, in
        Poggendorf's Annalen, lists of earthquakes which happened
        between 1821 and 1836; and, by consulting these, the reader
        will perceive that every month is signalized by one or many
        convulsions in some part of the globe. See also Mallet's
        Dynamics of Earthquakes, Trans. Roy. Irish Acad. 1846; and
        "Earthquakes," Admiralty Manual, 1849; also Hopkins' Report,
        Brit. Assoc. 1847-8.

  [623] Darwin, Geol. Proceedings, vol. ii. p. 658.

  [624] Dumoulin, Comptes Rendus de l'Acad. des Sci. Oct. 1838,
        p. 706.

  [625] Phil. Trans. 1836, p. 21.

  [626] Phil. Trans. 1826.

  [627] Darwin's Journ. of Travels in South America, Voyage of
        Beagle, p. 372.

  [628] Biblioth. Univ. Oct. 1828, p. 157.

  [629] Phil. Mag. July 1828, p. 37.

  [630] Geol. Trans. vol. i. 2d ser., and Journ. of Sci. 1824,
        vol. xvii. p. 40.

  [631] Geol. Trans, vol. i. 2d ser. p. 415.

  [632] Journ. of Sci. vol. xvii. p. 42.

  [633] Reise um die Erde; and see Dr. Meyen's letter cited
        Foreign Quart. Rev. No. 33, p. 13, 1836.

  [634] Geol. Soc. Proceedings, No. xl. p. 179, Feb. 1835.

  [635] Proceed. Geol. Soc. vol. ii. p. 447.

  [636] Geol. Trans. vol. i. 2d ser. p. 415.

  [637] Journal of Science, vol. xvii. pp. 40, 45.

  [638] See Asiatic Journal, vol. i.

  [639] Macmurdo Ed. Phil. Journ. iv. 106.

  [640] I was indebted to my friend the late Sir Alexander
        Burnes for the accompanying sketch (fig. 72) of the fort of
        Sindree, as it appeared eleven years before the earthquake.

  [641] This Memoir is now in the Library of the Royal Asiatic
        Society of London.

  [642] Several particulars not given in the earlier edition
        were afterwards obtained by me from personal communication
        with Sir A. Burnes in London.

  [643] Capt. Burnes' Account.

  [644] Capt. Macmurdo's Memoir, Ed. Phil. Journ. vol. iv. p.
        106.

  [645] Quart. Geol. Journ. vol. ii. p. 103.

  [646] MS. of J. Crawfurd, Esq.

  [647] Raffles' Java, vol. i. p. 28.

  [648] Raffles' Hist, of Java, vol. i. p. 25. Ed. Phil Journ.
        vol. iii. p. 389.

  [649] Life and Services of Sir Stamford Raffles, p. 241.
        London, 1830.

  [650] Humboldt's Pers. Nar. vol. iv. p. 12; and Ed. Phil.
        Journ. vol. i. p. 272: 1819.

  [651] Cramer's Navigator, p. 243. Pittsburgh, 1821.

  [652] Long's Exped. to the Rocky Mountains, vol. iii. p. 184.

  [653] Silliman's Journ. Jan. 1829.

  [654] See Lyell's Second Visit to the United States, ch.
        xxxiii.

  [655] Bemerkungen auf einer Reise um die Welt. bd. ii. s. 209.

  [656] Neue Allgem. Geogr. Ephemer. bd. iii. s. 348.

  [657] Cavanilles, Journ. de Phys. tome xlix. p. 230. Gilbert's
        Annalen, bd. vi. Humboldt's Voy. p. 317.

  [658] Humboldt's Voy., Relat. Hist., part. i. p. 309.

  [659] Macgregor's Travels in America.

  [660] Humboldt's Voy., Relat. Hist., part. ii. p. 632.

  [661] Ferrara, Camp. fl., p. 51.

  [662] Batav. Trans, vol. viii. p. 141.

  [663] Istoria de'Tremuoti della Calabria del 1783.

  [664] Descriz de'Tremuoti Accad. nelle Calabria nel 1783.
        Napoli, 1784.

  [665] Istoria de' Fenomeni del Tremoto, &c., nell' An. 1783,
        posta in luce dalla Real. Accad., &c. di Nap. Napoli, 1783,
        fol.

  [666] Dissertation on the Calabrian Earthquake, &c.,
        translated in Pinkerton's Voyages and Travels, vol. v.

  [667] Proceed. Roy. Irish Acad. 1846, p. 26.

  [668] Journal of a Naturalist, p. 376, and ii. ib. 308.

  [669] Proceedings Roy. Irish Acad. 1846, pp. 14-16.

  [670] See Mr. Mallet's attempt to controvert this view, p. 32
        ibid.

  [671] Phil. Trans. vol. lxxiii. p. 180.

  [672] Pinkerton's Voyages and Travels, vol. v. as cited above,
        p. 455, note.

  [673] Dolomieu, ibid.

  [674] Sir H. Davy's Consolations in Travel, p. 246.

  [675] Dr. Horsfield, Batav. Trans. vol. viii. p. 26. Dr. H.
        informs me that he has seen this truncated mountain; and,
        though he did not ascend it, he has conversed with those who
        have examined it. Raffles' account (History of Java, vol. i.)
        is derived from Horsfield.

  [676] Essai sur l'Hist. Nat. de l'Isle de St. Domingue. Paris,
        1776.

  [677] Hist. de l'Acad. des Sciences. 1752, Paris.

  [678] M'Clelland's Report on Min. Resources of India: 1838,
        Calcutta. For other particulars, see Phil. Trans. vol. liii.

  [679] Journ. Asiat. Soc. Bengal, vol. x. pp. 351, 433.

  [680] Hist, and Philos. of Earthquakes, p. 317.

  [681] Cosmos, vol. i.

  [682] Rev. C. Davy's Letters, vol. ii. Letter ii. p. 12, who
        was at Lisbon at the time, and ascertained that the boats and
        vessels said to have been swallowed were missing.

  [683] On the Formation of the Earth, p. 55.

  [684] Geol. Soc. Proceedings, No. 60, p. 36. 1838.

  [685] Michell on Earthquakes, Phil. Trans. vol. li. p. 566.
        1760.

  [686] Michell, Phil. Trans. vol. li. p. 614.

  [687] Quarterly Review, No. lxxxvi. p. 459.

  [688] Darwin's Travels in South America, &c., 1832 to 1836.
        Voyage of H. M. S. Beagle, vol. iii. p. 377.

  [689] Ann. de Ch. et de Ph., tom. xxii. p. 428.

  [690] Mallet, Proceed. Roy. Irish Acad. 1846.

  [691] See Father Acosta's work; and Sir Woodbine Parish, Geol
        Soc. Proceedings, vol. ii. p. 215.

  [692] Molina, Hist. of Chili, vol. ii.

  [693] Captain Belcher has shown me these shells, and the
        collection has been examined by Mr. Broderip.

  [694] Ulloa's Voyage to South America, vol. ii. book viii. ch.
        vi.

  [695] Ibid. vol. ii. book vii. ch. vii.

  [696] Ulloa's Voyage, vol. ii. p. 82.

  [697] Wafer, cited by Sir W. Parish, Geol. Soc. Proceedings,
        vol. ii. p. 215.

  [698] Hist. of America, decad. iii. book xi. ch. i.

  [699] Darwin's Journal, p. 451.

  [700] Ibid. p. 413.

  [701] Misspelt "Sales" in Hooke's Account.

  [702] Hooke's Posthumous Works, p. 437. 1705.

  [703] Phil. Trans. 1700.

  [704] Humboldt, Atl. Pit. p. 106.

  [705] Phil. Trans. 1693-4.

  [706] Phil. Trans. 1693.

  [707] Manual of Geol. p. 133, second edition.

  [708] Vol. i. p. 235, 8vo ed. 3 vols. 1801.

  [709] Letter to the Author, May, 1838.

  [710] Phil. Trans. 1694.

  [711] This view of the temple (substituted for one by A. de
        Jorio, given in the earlier editions) has been reduced from
        part of a beautiful colored drawing taken in 1836, with the
        aid of the camera lucida, by Mr. l'Anson to illustrate a paper
        by Mr. Babbage on the temple, read March, 1834, and published
        in the Quart. Journ. of the Geol. Soc. of London, vol. iii.
        1847.

  [712] Mr. Babbage examined this spot in company with Sir
        Edmund Head in June, 1828, and has shown me numerous specimens
        of the shells collected there, and in the Temple of Serapis.

  [713] This view is taken from Sir W. Hamilton, Campi Phlegræi,
        plate 26.

  [714] This spot here indicated on the summit of the cliff is
        that from which Hamilton's view, plate 26, Campi Phlegræi
        (reduced in fig. 88, p. 509) is taken, and on which, he says,
        Cicero's villa, called the Academia, anciently stood.

  [715] On the authority of Captain W. H. Smyth, R. N.

  [716] Dissertazione sulla Sagra Archittetura degli Antichi.

  [717] This appears from the measurement of Captain Basil Hall,
        R. N., Proceedings of Geol. Soc., No. 38, p. 114; see also
        Patchwork, by the same author, vol. iii. p. 158. The fact of
        the three standing columns having been each formed out of a
        single stone was first pointed out to me by Mr. James Hall,
        and is important, as helping to explain why they were not
        shaken down.

  [718] _Modiola lithophaga_, Lam. _Mytilus lithophagus_, Linn.

  [719] _Serpula contortuplicata_, Linn., and _Vermilia
        triquetra_, Lam. These species, as well as the _Lithodomus_,
        are now inhabitants of the neighboring sea.

  [720] Brieslak, Voy. dans la Campanie, tom. ii. p. 167.

  [721] Ed. Journ. of Science, new series, No. II. p. 281.

  [722] Sul Tempio di Serap. ch. viii.

  [723] Tavola Metrica Chronologica, &c. Napoli, 1838. Mr.
        Smith, of Jordan Hill, writing in 1847, estimated the rate of
        subsidence, at that period, at _one inch_ annually. Quart.
        Journ. Geol. Soc. vol. iii. p. 237.

  [724] Voy. dans la Campanie, tome ii. p. 162.

  [725] Mr. Forbes, Physical Notices of the Bay of Naples. Ed.
        Journ. of Sci., No. II., new series, p. 280. October, 1829.
        When I visited Puzzuoli, and arrived at the above conclusions,
        I knew nothing of Mr. Forbes's observations, which I first saw
        on my return to England the year following.

  [726] Quart. Journ. Geol. Soc. 1847, vol. iii. p. 203.

  [727] Nuove Ricerche sul Temp. di Serap.

  [728] The Swedish measure scarcely differs from ours; the foot
        being divided into twelve inches, and being less than ours by
        three-eighths of an inch only.

  [729] For a full account of the Celsian controversy, we may
        refer our readers to Von Hoff, Geschichte, &c. vol. i. p. 439.

  [730] Piteo, Luleo, and Obo are spelt, in many English maps,
        Pitea, Lulea, Åbo; the _a_ is not sounded in the Swedish
        diphthong _ao_ or _å_.

  [731] Sect. 393.

  [732] Sect. 398.

  [733] Transl. of his Travels, p. 387.

  [734] In the earlier editions I expressed many doubts as to
        the validity of the proofs of a gradual rise of land in
        Sweden. A detailed statement of the observations which I made
        in 1834, and which led me to change my opinion, will be found
        in the Philosophical Transactions for 1835, part i.

  [735] See Professor Johnston's Paper, Ed. New Phil. Journ. No.
        29, July 1833; and my remarks, Phil. Trans. 1835, p. 12.

  [736] See p. 522; also chap. 15, _supra_.

  [737] See a paper by the Author, Phil. Trans. 1835, part i.

  [738] See my paper before referred to, Phil. Trans. 1885, part
        i. p. 8, 9. Attempts have been since made to explain away the
        position of this hut, by conjecturing that a more recent
        trench had been previously dug here, which had become filled
        up in time by sand drifted by the wind. The engineers who
        superintended the works in 1819, and with whom I conversed,
        had considered every hypothesis of the kind, but could not so
        explain the facts.

  [739] Quart. Journ. of Geol. Soc. No. 4, p. 534. M. Bravais'
        observations were verified in 1849 by Mr. R. Chambers in his
        "Tracings of N. of Europe," p. 208.

  [740] See Proceedings of Geol. Soc. No. 42, p. 208. I also
        conversed with Dr. Pingel on the subject at Copenhagen in
        1834.

  [741] Keilhau, Bulletin de la Soc. Géol de France, tom. vii.
        p. 18.

  [742] Illust. of Hutt. Theory, § 435-443.

  [743] Herschel's Astronomy, chap. iii.

  [744] See Hennessy, On Changes in Earth's Figure, &c. Journ.
        Geol. Soc. Dublin, 1849; and Proc. Roy. Irish Acad. vol. iv.
        p. 337.

  [745] Young's Lectures, and Mrs. Somerville's Connection of
        the Physical Sciences, p. 90.

  [746] Phil. Trans. 1839, and Researches in Physical Geology,
        1st, 2d, and 3d series, London, 1839-1842; also on Phenomena
        and Theory of Volcanoes, Report Brit. Assoc. 1847.

  [747] Ed. Journ. of Sci. April, 1832.

  [748] Cordier, Mém. de l'Instit. tom. vii.

  [749] Pog. Ann. tom. xv. p. 159.

  [750] See M. Cordier's Memoir on the Temperature of the
        Interior of the Earth, read to the Academy of Sciences, 4th
        June, 1827.--Edin. New Phil. Journal, No. viii. p. 273.

  [751] Cordier, Mém. de l'Instit. tom. vii.

  [752] Phil. Mag. and Ann. Feb. 1830.

  [753] The heat was measured in Wedgwood's pyrometer by the
        contraction of pure clay, which is reduced in volume when
        heated, first by the loss of its water of combination, and
        afterwards, on the application of more intense heat, by
        incipient vitrification. The expansion of platina is the test
        employed by Mr. Daniell in his pyrometer, and this has been
        found to yield uniform and constant results, such as are in
        perfect harmony with conclusions drawn from various other
        independent sources. The instrument for which the author
        received the Rumford Medal from the Royal Society, in 1833, is
        described in the Phil. Trans. 1830, part ii., and 1831, part
        ii.

  [754] The above remarks are reprinted verbatim from my third
        edition, May, 1834. A memoir was afterwards communicated by M.
        Poisson to the Academy of Sciences, January, 1837, on the
        solid parts of the globe, containing an epitome of a work
        entitled "Théorie Mathématique de la Chaleur," published in
        1835. In this memoir he controverts the doctrine of the high
        temperature of a central fluid on similar grounds to those
        above stated. He imagines, that if the globe ever passed from
        a liquid to a solid state by radiation of heat, the central
        nucleus must have begun to cool and consolidate first.

  [755] Consolations in Travel, p. 271.

  [756] Phil. Trans. 1830, p. 399.

  [757] Biblioth. Univers. 1833, Electricité.

  [758] Phil. Trans. 1832, p. 176; also pp. 172, 173, &c.

  [759] Hist. Mundi, lib. ii. c. 107.

  [760] Reduced, by permission, from a figure in plate 40 of Sir
        H. De la Beche's Geological Sections and Views.

  [761] Phil. Trans. 1828, p. 250.

  [762] Geology of American Exploring Expedition, p. 369.

  [763] Davy, Phil. Trans. 1828, p. 244.

  [764] Ann. de Chim. et de Phys. tom. iii. p. 181.

  [765] Phil. Trans. 1832, p. 240.

  [766] Ann. de Chim. et de Phys. tom. xxii.

  [767] Quart. Journ. of Sci. 1823, p. 132, note by editor.

  [768] Phenom. Géol. &c. p. 3.

  [769] Phil. Trans. 1828.

  [770] See Daubeny, Encyc. Metrop. part 40.

  [771] Jam. Ed. New Phil. Journ. No. li. p. 31.

  [772] See Daubeny's Reply to Bischoff, Jam. Ed. New Phil.
        Journ. No. lii. p. 291; and note in No. liii. p. 158.

  [773] Poggend. Ann. 1851 translated, Sci. Mem. 1852.

  [774] Proceed. Americ. Assoc. 1849.

  [775] Reduced from a sketch given by Sir W. J. Hooker, in his
        Tour in Iceland, vol. i. p. 149.

  [776] Journal of a Residence in Iceland, p. 74.

  [777] Mackenzie's Iceland.

  [778] MS. read to Geol. Soc. of London, Feb. 29, 1832.

  [779] From Sir George Mackenzie's Iceland.

  [780] See Mr. Horner's Anniversary Address, Quart. Journ.
        Geol. Soc. 1847, liii.

  [781] Liebig's Annalen der Chimie und Pharmacie, translated in
        "Reports and Memoirs" of Cavendish Soc. London, 1848.

  [782] On the Cause and Phenomena of Earthquakes, Phil. Trans.
        vol. li. sec. 58, 1760.

  [783] Trans. of Assoc. of American Geol. 1840-1842, p. 520.

  [784] Mallet, p. 39.

  [785] Scrope on Volcanoes, pp. 58-60.

  [786] Archiac, Hist, des Progrés de la Géol, 1847, vol. i. pp.
        605-610.

  [787] Silliman's American Journ. vol. xxii. p. 136. The
        application of these results to the theory of earthquakes was
        first suggested to me by Mr. Babbage.

  [788] Bulletin de la Soc. Géol. 2d series, vol. iv. p. 1312.

  [789] See p. 468.

  [790] Phil. Zool. tom. i. p. 84.

  [791] Phil. Zool. tom. i. p. 62.

  [792] Ibid.

  [793] Phil. Zool. tom. i. p. 227.

  [794] Ibid. p. 232.

  [795] Phil. Zool. tom. i. p. 234.

  [796] Phil. Zool. p. 64.

  [797] Animaux sans Vert. tom. i. p. 56, Introduction.

  [798] Lamarck's Phil. Zool. tom. i. p. 356.

  [799] Ibid. p. 357.

  [800] Genus omne est naturale, in primordio tale creatum, &c.
        Phil. Bot. § 159. See also ibid. § 162.

  [801] Cuvier, Dîscours Prélimin. p. 128.

  [802] Phil. Zool. tom. i. p. 266.

  [803] Dureau de la Malle, An. des Sci. Nat. tom. xxi. p. 53.
        Sept. 1830.

  [804] Disc. Prél. p. 139. sixth edition.

  [805] Ibid.

  [806] Güldenstädt, cited by Pritchard, Phys. Hist. of Mankind,
        vol. i. p. 96.

  [807] History of British Quadrupeds, p. 200. 1837.

  [808] Ann. du Muséum d'Hist. Nat. tom. i. p. 234. 1802. The
        reporters were MM. Cuvier, Lacépède, and Lamarck.

  [809] I by no means wish to express an opinion that seeds
        cannot retain their vitality after an entombment of 3,000
        years; but one of my botanical friends who entertained a
        philosophical doubt on this subject, being desirous of
        ascertaining the truth of three or four alleged instances of
        the germination of "mummy wheat," discovered, on communicating
        with several Egyptian travellers, that they had procured the
        grains in question, not directly from the catacombs, but from
        the Arabs, who are always ready to supply strangers with an
        article now very frequently in demand. The presence of an
        occasional grain of Indian corn or maize in several of the
        parcels of grain shown to my friend as coming from the
        catacombs confirmed his scepticism.

  [810] Phil. Zool., tom. i. p. 227.

  [811] L'Origine et la Patrie des Céréales, &c., Annales des
        Sciences Natur., tom. ix. p. 61.

  [812] Smith's Introduction to Botany, p. 138, edit. 1807.

  [813] See Mr. Knight's Observations, Hort Trans., vol. ii. p.
        160.

  [814] Hort. Trans. vol. iv. p. 19.

  [815] Loudon's Mag. of Nat. Hist., Sept. 1830, vol. iii. p.
        408.

  [816] Hort. Trans. vol. iii. p. 173.

  [817] M. Roulin, Ann. des Sci. Nat. tom. xvi. p. 16. 1829.

  [818] Mem. du Mus. d'Hist. Nat.--Jameson, Ed. New Phil. Journ.
        Nos. 6, 7, 8.

  [819] In the New Forest, near Ringwood, Hants, by Mr. Toomer,
        keeper of Broomy Lodge. I have conversed with witnesses of the
        fact.

  [820] Mém. du Mus. d'Hist. Nat.

  [821] Dureau de la Malle. Ann. des Sci. Nat., tom. xxi. p. 58.

  [822] Darwin's Journ. in Voyage of H.M.S. Beagle, p. 475.

  [823] Fauna Boreali-Americana, p. 273.

  [824] Mr. Corse on the Habits, &c. of the Elephant, Phil.
        Trans., 1799.

  [825] Linn. Trans. vol. xiii. p. 244.

  [826] Pers. Narr. of Travels to the Equinoctial Regions of the
        New Continent in the years 1779-1804.

  [827] Phil. Trans. 1787. Additional Remarks, Phil. Trans.
        1789. See also Essays by the late Dr. Samuel G. Morton, on
        Prolific Hybrids, &c.; and on Hybridity as a Test of
        Species.--American Journ. of Science, vol. iii. 1847.

  [828] Prichard, vol. i. p. 217.

  [829] Ibid. p. 97.

  [830] See Barton on the Geography of Plants, p. 67.

  [831] Georg. lib. iii. 273.

  [832] Hon. and Rev. W. Herbert, Hort. Trans., vol. iv. p. 41.

  [833] Ibid.

  [834] Essai Elémentaire, &c., 3me partie.

  [835] Intr. to Entom. vol. ii. p. 504. ed. 1817.

  [836] Prichard's Phys. Hist. of Mankind, vol. i. p. 159.

  [837] Ch. White on the Regular Gradation in Man, &c. 1799.

  [838] R. G. Latham, The Nat. Hist. of the Varieties of Man,
        8vo. London, 1850.

  [839] Lawrence, Lectures on Phys. Zool. and Nat. Hist. of Man,
        p. 190. Ed. 1823.

  [840] E. R. A. Serres, Anatomie comparée du Cerveau,
        illustrated by numerous plates, tome i. 1824.

  [841] Barton's Lectures on the Geography of Plants, p. 2.
        1827.

  [842] Pers. Nar., vol. v. p. 180.

  [843] Ibid.

  [844] Essai Elémentaire de Géographie Botanique. Extrait du
        18me vol. du Dict. des Sci. Nat.

  [845] Prichard, vol. i. p. 36. Brown, Appendix to Flinders.

  [846] Foster, Observations, &c.

  [847] Humboldt, Pers. Nar., vol. i. p. 270 of the translation.
        Prichard, Phys. Hist. of Mankind, vol. i. p. 37.

  [848] Voyage of the Beagle, 2d edition, 1845, p. 377.

  [849] See a farther subdivision, by which twenty-seven
        provinces are made, by M. Alph. De Candolle, son of De
        Candolle. Monogr. des Campanulées. Paris, 1830.

  [850] De Candolle, Essai Elémen. de Géog. Botan., p. 45.

  [851] I am indebted for the above sketch of distinct regions
        of algæ to my friend Dr. Joseph Hooker, who refers the
        botanical student to the labors of Dr. Harvey, of Trinity
        College, Dublin.

  [852] Annuaire du Bureau des Longitudes.

  [853] Linn., Tour in Lapland, vol. ii. p. 282.

  [854] Fries, cited by Lindley, Introd. to Nat. Syst. of
        Botany.

  [855] System of Physiological Botany, vol. ii. p. 405.

  [856] Brown, Append. to Tuckey, No. v. p. 481.

  [857] Phil. Trans. 1696.

  [858] System of Physiological Botany, vol. ii. p. 403.

  [859] Greville, Introduction to Algæ Britannicæ, p. 12.

  [860] Linnæus, Amoen. Acad., vol. ii. p. 409.

  [861] Amoen. Acad., vol. iv. Essay 75. § 8.

  [862] Ibid., vol. vi. § 22.

  [863] Smith's Introd. to Phys. and Syst. Botany, p. 304. 1807.

  [864] This information was communicated to me by Professor
        Henslow, of Cambridge.

  [865] Book iii. ch. iv.

  [866] De Candolle, Essai Elémen. &c., p. 50.

  [867] Quarterly Review, vol. xxx. p. 8.

  [868] Essay on the Habitable Earth, Amoen. Acad., vol. ii. p.
        409.

  [869] Principles of Botany, p. 389.

  [870] Ibid.

  [871] Buffon, vol. v.--On the Virginian Opossum.

  [872] Prichard's Phys. Hist. of Mankind, vol. i. p. 54.

  [873] In the above enumeration of the leading zoological
        provinces of land quadrupeds I have been most kindly assisted
        by Mr. Waterhouse of the British Museum, author of a most able
        and comprehensive work on the "Natural History of the
        Mammalia," now in the course of publication. London,
        Bailliere, 1846.

  [874] Pennant's Hist. of Quadrupeds, cited by Prichard, Phys.
        Hist. of Mankind, vol. i. p. 66.

  [875] Natural History of the Mammalia, vol. i., on the
        Marsupials. London, Bailliere, 1846.

  [876] Description of the Equatorial Regions.

  [877] Prichard, Phys. Hist., of Mankind, vol. i. p. 75.

  [878] Buffon, vol. v. p. 204.

  [879] Sir T. D. Lauder, Bart., on the Floods in Morayshire,
        Aug. 1829, p. 302, second edition.

  [880] Expedition from Pittsburg to the Rocky Mountains, vol.
        ii. p. 153.

  [881] Richardson's Fauna Boreali-Americana, p. 16.

  [882] Phil. Trans., vol. ii. p. 872.

  [883] Wood's Zoography, vol. i. p. 11.

  [884] On the authority of Mr. Campbell. Library of Entert.
        Know., Menageries. vol. i. p. 152.

  [885] Cuvier's Animal Kingdom by Griffiths, vol. ii. p. 109.
        Library of Entertaining Knowledge, Menageries, vol. i. p. 366.

  [886] Horsfield, Zoological Researches in Java, No. ii., from
        which the figure is taken.

  [887] Append. to Parry's Second Voyage, years 1819-20.

  [888] Account of the Arctic Regions, vol. i. p. 518.

  [889] Turton in a note to Goldsmith's Nat. Hist., vol. iii. p.
        43.

  [890] Supplement to Parry's First Voyage of Discovery, p. 189.

  [891] Goldman's American Nat. Hist., vol. i. p. 22.

  [892] Dr. Richardson, Brit. Assoc. Report, vol. v. p. 161.

  [893] System of Geography, vol. v. p. 157.

  [894] Spix and Martius, Reise, &c., vol. iii. pp. 1011. 1013.

  [895] Sir W. Parish's Buenos Ayres, p. 187., and Robertson's
        Letters on Paraguay, p. 220.

  [896] United Service Journal, No. xxiv. p. 697.

  [897] Krantz, vol. i. p. 129., cited by Goldsmith, Nat. Hist.,
        vol. iii. p. 260.

  [898] Darwin's Journal, &c., p. 461.

  [899] Prichard, vol. i. p. 47.

  [900] Bewick's Birds, vol. ii. p. 294., who cites Latham.

  [901] Pisa, 1827 (not sold).

  [902] Bachman, Silliman's Amer. Journ., No. 61, p. 92.

  [903] Voyage aux Régions Equinoxiales, tome vii. p. 429.

  [904] Fleming, Phil. Zool., vol. ii. p. 43.

  [905] Silliman's Amer. Journ., No. 61. p. 83.

  [906] Richardson, Brit. Assoc. Rep., vol. v. p. 202.

  [907] Brit. Animals, p. 149., who cites Sibbald.

  [908] Zool. Journ. vol iii. p. 406. Dec. 1827.

  [909] Sur les Habitations des Animaux Marins.--Ann. du Mus.,
        tome. xv., cited by Prichard, Phys. Hist. of Mankind, vol. i.
        p. 51.

  [910] Brit. Assoc. Reports, vol. v. p. 203.

  [911] Report to the Brit. Assoc., 1845, p. 192.

  [912] Richardson, ibid. p. 190.

  [913] Sir J. Richardson, ibid. p. 190.

  [914] Phil. Trans. 1747, p. 395.

  [915] Amoen. Acad., Essay 75.

  [916] Report to the Brit Assoc. 1843, p. 130.

  [917] Quart. Journ., Geol. Soc., 1846, vol. ii. p. 268.

  [918] Four individuals of a large species of land shell
        (_Bulimus_), from Valparaiso, were brought to England by
        Lieutenant Graves, who accompanied Captain King in his
        expedition to the Straits of Magellan. They had been packed up
        in a box, and enveloped in cotton: two for a space of
        thirteen, one for seventeen, and a fourth for upwards of
        twenty months: but, on being exposed by Mr. Broderip to the
        warmth of a fire in London, and provided with tepid water and
        leaves, they revived, and lived for several months in Mr.
        Loddiges' palm-house, till accidentally drowned.

  [919] Camb. Phil. Trans., vol. iv. 1831.

  [920] Edin. New Phil. Journ., April 1844.

  [921] Phil. Trans. 1835, p. 303.

  [922] The specimen is preserved in the Museum of the Zool.
        Soc. of London.

  [923] This specimen is in the collection of my friend Mr.
        Broderip, who observes, that this crab, which was apparently
        in perfect health, could not have cast her shell for six
        years, whereas some naturalists have stated that the species
        moults annually, without limiting the moulting period to the
        early stages of the growth of the animal.

  [924] Quart. Journ. Geol. Soc., vol. iv. p. 336.

  [925] Voy. aux Terres Australes, tom. i. p. 492.

  [926] Géographie Générale des Insectes et des Arachnides. Mém.
        du Mus. d'Hist. Nat., tom. iii.

  [927] Kirby and Spence, vol. iv. p. 487; and other authors.

  [928] Kirby and Spence, vol. iv. p. 497.

  [929] Washington Irving's Tour in the Prairies, ch. ix.

  [930] Malte-Brun, vol. v. p. 379.

  [931] Kirby and Spence, vol. ii. p. 9. 1817.

  [932] Kirby and Spence, vol. ii. p. 12. 1817.

  [933] I am indebted to Lieutenant Graves, R.N., for this
        information.

  [934] I state this fact on the authority of my friend, Mr.
        John Curtis.

  [935] Brand's Select Dissert. from the Amoen. Acad., vol. i.
        p. 118.

  [936] Ibid.

  [937] Sir H. Davy, Consolations in Travel, p. 74.

  [938] W. von Humboldt, "On the Kawi Language," &c. cited in
        Cosmos. Introduction.

  [939] Egypten's Stelle, &c. Egypt restored to her Place in
        Universal History, by C. C. J. Bunsen. 1845.

  [940] For Grecian and Asiatic deluges, see above, p. 356.;
        Cimbrian, p. 331., Chinese, p. 7. Peruvian, p. 502.; Chilian
        or Araucanian deluge, p. 500.

  [941] See p. 615.

  [942] Malte-Brun's Geography, vol. iii. p. 419.

  [943] Chamisso states that the water which they brought up was
        cooler, and _in their opinion_, less salt. It is difficult to
        conceive its being fresher near the bottom, except where
        submarine springs may happen to rise.

  [944] Kotzebue's Voyage, 1815-1818. Quarterly Review, vol.
        xxvi. p. 361.

  [945] Narrative of a Voyage to the Pacific, &c., in the years
        1825, 1826, 1827, 1828, p. 170.

  [946] Gloger, Abänd. der Vögel, p. 103.; Pallas, Zoog.
        Rosso-Asiat., tom. ii. p. 197.

  [947] Syst. of Geog., vol. viii. p. 169.

  [948] De terrâ habitabili incremento; also Prichard, Phys.
        Hist, of Mankind, vol. i. p. 17., where the hypotheses of
        different naturalists are enumerated.

  [949] Necker, Phytozool. Philosoph. p. 21.; Brocchi, Conch.
        Foss. Subap., tome i. p. 229.

  [950] Amoen. Acad. vol. vi. p. 17. § 12.

  [951] Ibid. vol. vii. p. 409.

  [952] Amoen. Acad., vol. vi. p. 17. § 11, 12.

  [953] Kirby and Spence, vol. i. p. 178.

  [954] Amoen. Acad., vol. vi. p. 26. § 14.

  [955] Kirby and Spence, vol. iv. p. 218.

  [956] Kirby and Spence, vol. i. p. 250.

  [957] Wilcke, Amoen. Acad. c. ii.

  [958] Kirby and Spence, vol. i. p. 174.

  [959] Trans. Linn. Soc., vol. vi.

  [960] Lib. Ent. Know., Insect Trans., p. 203. See Haworth,
        Lep.

  [961] Reaumur, ii. 337.

  [962] Lib. Ent. Know., Insect Trans., p. 212.

  [963] Kirby and Spence, vol. i. p. 183. Castle, Phil. Trans.,
        xxx. 346.

  [964] Travels in Africa, p. 257. Kirby and Spence, vol. i. p.
        215.

  [965] Journal of a Residence in Iceland, p. 276.

  [966] Tour in Iceland, vol. i. p. 64, 2nd edit.

  [967] Travels in Brazil, vol. i. p. 260.

  [968] Ed. Phil. Journ., No. xxii p. 287. Oct. 1824.

  [969] Ray. Syn. Quad., p. 214.

  [970] Fleming, Ed. Phil. Journ., No. xxii. p. 295.

  [971] Fleming, ibid., p. 292.

  [972] Vol. iii. London, 1821.

  [973] Land Birds, vol. i. p. 316. ed. 1821.

  [974] Some have complained that inscriptions on tomb-stones
        convey no general information, except that individuals were
        born and died, accidents which must happen alike to all men.
        But the death of a _species_ is so remarkable an event in
        natural history that it deserves commemoration, and it is with
        no small interest that we learn, from the archives of the
        University of Oxford, the exact day and year when the remains
        of the last specimen of the dodo, which had been permitted to
        rot in the Ashmolean Museum, were cast away. The relics, we
        are told, were "a musæo subducta, annuente vice-cancellario
        aliisque curatoribus, ad ea lustranda convocatis, die Januarii
        8vo, A.D. 1755." Zool. Journ. No. 12. p. 559. 1828.

  [975] Penny Cyclopædia, "Dodo." 1837.

  [976] Messrs. Strickland and Melville on "the Dodo and its
        Kindred." London, 1848.

  [977] Pers. Nar. vol. iv.

  [978] Quarterly Review, vol. xxi. p. 335.

  [979] Ibid.

  [980] Ulloa's Voyage. Wood's Zoog. vol. i. p. 9.

  [981] Buffon, vol. v. p. 100. Ulloa's Voyage, vol. ii. p. 220.

  [982] Travels in Iceland in 1810, p. 342.

  [983] Maclaren, art. America, Encyc. Brit.

  [984] See a note on this subject, chap. x. p. 157.

  [985] See above, p. 317.

  [986] Darwin's Journal, p. 156., 2d ed. p. 133. Sir W. Parish,
        Buenos Ayres, &c. p. 371. and 151.

  [987] See above, chap. vii. p. 112.

  [988] See above, chaps. vi. vii. and viii.

  [989] Journ. of Nat. Hist. &c. 2d edit., 1845, p. 175; also
        Lyell's 2d Visit to the United States, vol. i. p. 351.

  [990] This and the preceding chapter, on the causes of
        extinction of species and their present geographical
        distribution, are reprinted almost verbatim from the original
        edition of the second volume of "The Principles," published in
        January, 1832. It was I believe the first attempt to point out
        how former changes in the geography and local climate of many
        parts of the globe must be taken into account when we endeavor
        to explain the actual provinces of plants and animals, the
        changes alluded to having been proved by geological evidence
        to be subsequent to the creation of a great proportion of the
        species now living, and these having been, according to the
        view which I advocated, introduced in succession, and not all
        at one geological epoch. In my third volume, published in May,
        1833, I announced my conviction that the greater part of the
        existing Fauna and Flora of Sicily were older than the
        mountains, plains, and rivers, which the same species of
        animals and plants now inhabit. (Prin. of Geol., vol. iii. ch.
        ix.; repeated in Elements of Geol., 2d edit., vol. i. p. 297.)
        This line of reasoning has since been ably followed up and
        elucidated by Professor E. Forbes in an excellent paper
        (published in 1846) already alluded to. (See page 86.)

  [991] Essai Elémentaire, &c. p. 46.

  [992] Geog. des Plantes. Diet. des Sci.

  [993] See Catalogue of Brit. Insects, by John Curtis, Esq.

  [994] See some good remarks on the Formation of Soils,
        Bakewell's Geology, chap. xviii.

  [995] See Professor Sedgwick's Anniversary Address to the
        Geological Society, Feb. 1831, p. 24.

  [996] Treatise on Rivers and Torrents, p. 5. Garston's
        translation.

  [997] De la Beche, Geol. Man., p. 184., 1st ed.

  [998] Phil. Trans., vol. ii. p. 294.

  [999] Maclaren, art. America, Encyc. Britannica.

 [1000] Maclaren, art. America, Encyc. Britannica, where the
        position of the American forests, in accordance with this
        theory, is laid down in a map.

 [1001] Annuaire du Bureau des Long. 1834.

 [1002] Since this was written I have seen in New Brunswick
        (1852) a lake formed by beavers who had thrown a dam,
        consisting of stakes, stones, and mud, across the course of a
        small streamlet, between Dorchester and the Portage south of
        the Peticodiac river. The beavers have since been extirpated
        by man, but the lake remains, and musk rats have taken
        possession of the shallow parts of the lake to build their
        habitations in them.

 [1003] For a catalogue of plants which form peat, see Rev. Dr.
        Rennie's Essays on Peat, p. 171; and Dr. MacCulloch's Western
        Isles, vol. i. p. 129.

 [1004] Irish Bog Reports, p. 209.

 [1005] System of Geology, vol. ii. p. 353.

 [1006] Rev. Dr. Rennie on Peat, p. 260.

 [1007] Darwin's Journal, p. 349.; 2d ed. p. 287.

 [1008] Rennie's Essays on Peat, p. 65.

 [1009] Ibid. p. 30.

 [1010] Essays on Peat, &c., p. 74.

 [1011] See above, p. 388, note.

 [1012] Ehrenberg, Taylor's Scientific Mem. vol. i. part iii.
        p. 402.

 [1013] Dr. Rennie, on Peat, p. 521; where several other
        instances are referred to.

 [1014] Phil. Trans., vol. xxxviii. 1734.

 [1015] Dr. Rennie, on Peat, &c., p. 521.

 [1016] Syst. of Geol. vol. ii. pp. 340-346.

 [1017] Ibid. p. 531.

 [1018] Phil. Trans. vol. xv. p. 949.

 [1019] Gilpin, Observ. on Picturesque Beauty, &c., 1772.

 [1020] Travels, &c., in 1841, 1842, vol. i. p. 143.

 [1021] Bulletin de la Soc. Géol. de France, tom. ii. p. 26.

 [1022] Dr. Rennie, Essays on Peat Moss, p. 205.

 [1023] M. G. A. De Luc, Mercure de France, Sept. 1809.

 [1024] See p. 262.

 [1025] Stratton, Ed. Phil. Journ., No. v. p. 62.

 [1026] Travels in North Africa in the Years 1818, 1819, and
        1820, p. 83.

 [1027] Mém. de l'Acad. des Sci. de Paris, 1772. See also the
        case of the buried church of Eccles, above, p. 306.

 [1028] Phil. Trans., vol. ii. p. 722.

 [1029] Boase on Submersion of Part of the Mount's Bay, &c.,
        Trans. Roy. Geol. Soc. of Cornwall, vol. ii. p. 140.

 [1030] Narrative of Journey from Agra to Oujein, Asiatic
        Researches, vol. vi. p. 36.

 [1031] Asiatic Journal, vol. ix. p. 35.

 [1032] See above, p. 460.

 [1033] Sir J. Malcolm's Central India. Appendix, No. 2. p.
        324.

 [1034] Sir T. D. Lauder, Bart., on Floods in Morayshire, Aug.
        1839, p. 177.

 [1035] Dodsley's Ann. Regist., 1788.

 [1036] Edwards, Hist. of West Indies, vol. i. p. 235, ed.
        1801.

 [1037] Journ. of Asiat. Soc., Nos. xxv. and xxix., 1834.

 [1038] Ann. des Sci. Nat. tom. xxii. p. 117, Feb. 1831.

 [1039] Malte-Brun's Geog., vol. i. p. 435.

 [1040] Bakewell, Travels in the Tarentaise, vol. i. p. 201.

 [1041] Nahum Ward, Trans. of Antiq. Soc. of Massachusetts.
        Holmes's United States, p. 438.

 [1042] Bull. de la Soc. Géol. de France, tom. ii. p. 329.

 [1043] See above, p. 240.

 [1044] See remarks by M. Boblaye, Ann. des Mines, 3me série,
        tom. iv.

 [1045] Ann. des Mines, 3me série, tom. iv., 1833.

 [1046] Bull. de la Soc. Géol. de France, tom. iii. p. 223.

 [1047] Mém. de la Soc. d'Hist, Nat. de Paris, tom. iv.

 [1048] Reliquiæ Diluvianæ, p. 108.

 [1049] Journ. de Géol., tom. i. p. 286. July, 1830.

 [1050] Reliquiæ Diluvianæ, p. 165.

 [1051] M. Marcel de Serres, Géognosie des Terrains Tertiaires,
        p. 64. Introduction.

 [1052] Bull. de la Soc. Géol. de France, tom. ii. pp. 56-63.

 [1053] Desnoyers, Bull. de la Soc. Géol. de France, tom. ii.
        p. 252.

 [1054] Hist. Rom. Epit., lib. iii. c. 10.

 [1055] Buckland, Reliquiæ Diluvianæ, p. 25.

 [1056] See above, pp. 730, 731.

 [1057] On the Lake Mountains of North of England, Geol. Soc.
        Jan. 5, 1831.

 [1058] Notes on Geol. of Cuba, 1836, Phil. Mag., July, 1837.

 [1059] See above, p. 67.

 [1060] Account of the Arctic Regions, vol. ii. p. 193.

 [1061] Ibid. p. 202.

 [1062] Dr. Richardson's Geognost Obs. on Capt. Franklin's
        Polar Expedition.

 [1063] Malte-Brun, Geog., vol. v. part 1. p. 112.--Brantz,
        Hist. of Greenland, tom. 1. pp. 53, 54.

 [1064] Olafsen, Voyage to Iceland, tom. i.--Malte-Brun's
        Geog., vol. v. part i. p. 112.

 [1065] See above, pp. 303 and 323.

 [1066] Geol. Trans., second series, vol. v. p. 212.

 [1067] Göppert, Poggendorff's Annalen der Physik und Chemie,
        vol. xxxviii. part iv., Leipsic, 1836. See also Lyell's Manual
        of Geol., p. 40.

 [1068] Trans. Geol. Soc., vol. iii. part i. p. 201, second
        series.

 [1069] Sir T. D. Lauder's Account, 2d. ed., p. 312.

 [1070] Treatise on Practical Store Farming, p. 25.

 [1071] Sir T. D. Lauder's Floods in Morayshire, 1829; and
        above, p. 196.

 [1072] Humboldt's Pers. Nar., vol. iv. p. 394.

 [1073] Buenos Ayres and La Plata, p. 187.

 [1074] Malte-Brun's Geog., vol. iii. p. 22.

 [1075] This account I had from Mr. Baumhauer, Director-General
        of Finances in Java.

 [1076] Tracts on India, p. 397.

 [1077] Scots Mag., vol. xxxiii.

 [1078] Darwin's Journal, p. 372. 2d ed., 1845, p. 304.

 [1079] Narrative of Discovery in Egypt, &c., London, 1820.

 [1080] Scots Mag., vol. xxxiii., 1771.

 [1081] Quart. Journ. of Agricult., No. ix p. 433.

 [1082] Cæsar Moreau's Tables of the Navigation of Great
        Britain.

 [1083] I give these results on the authority of Captain W. H.
        Smyth, R. N.

 [1084] Von Hoff, vol. i. p. 379.

 [1085] This account I received from the Honorable and Rev.
        Charles Harris.

 [1086] Von Hoff, vol. i. p. 368.

 [1087] Lieut. Carless, Geograph. Journ., vol. viii. p. 338.

 [1088] Silliman's Geol. Lectures, p. 78, who cites Penn.

 [1089] Leigh's Lancashire, p. 17, A. D. 1700.

 [1090] Geol. Trans., second series, vol. ii. p. 87.

 [1091] Phil. Trans., 1799.

 [1092] Phil. Trans., vol. lxix., 1779.

 [1093] Phil. Trans., 1826, part. ii. p. 55.

 [1094] See above, pp. 453. 457. 499. 501.

 [1095] Thomson's Western Himalaya and Thibet, p. 292. London,
        1852. Cunningham, vol. xvii. Journ. Asiat. Soc. Bengal, pp.
        241, 277.

 [1096] Alciphron, or the Minute Philosopher, vol. ii. pp. 84,
        85, 1732.

 [1097] Davy, Consolations in Travel, p. 276.

 [1098] Essay on the Vicissitude of Things.

 [1099] On Freshwater Marl, &c. By C. Lyell. Geol. Trans., vol.
        ii., second series, p. 73.

 [1100] See Desmarest's Crustacea, pl. 55.

 [1101] Dr. Bigsby, Journ. of Science, &c. No. xxxvii. pp. 262,
        263.

 [1102] Mantell, Geol. of Sussex, p. 285; also Catalogue of
        Org. Rem., Geol. Trans., vol. iii. part i p. 201., 2nd series.

 [1103] Page 276.

 [1104] Page 460.

 [1105] Page 599.

 [1106] Forchhammer, Report British Assoc. 1844.

 [1107] Fleming's Brit. Animals, p. 37; in which work other
        cases are enumerated.

 [1108] Quart. Journ. of Lit. Sci., &c., No. xv., p. 172. Oct.
        1819.

 [1109] This specimen has been presented by Mr. Lonsdale to the
        Geological Society of London.

 [1110] The most conspicuous of the bones represented within
        the shell in fig. 107, appear to be the clavicle and coracoid
        bone. They are hollow; and for this reason resemble, at first
        sight, the bones of birds rather than of reptiles; for the
        latter have no medullary cavity. Prof. Owen, of the College of
        Surgeons, in order to elucidate this point, dissected for me a
        very young turtle, and found that the exterior portion only of
        the bones was ossified, the interior being still filled with
        cartilage. This cartilage soon dried up and shrank to a mere
        thread upon the evaporation of the spirits of wine in which
        the specimen had been preserved, so that in a short time the
        bones became as empty as those of birds.

 [1111] Ehrenberg, Nat. und Bild. der Coralleninseln. &c.,
        Berlin, 1834.

 [1112] See Ehrenberg's work above cited, p. 751.

 [1113] Stutchbury, West of England Journal, No. i. p. 49.

 [1114] Darwin's Coral Reefs, p. 77.

 [1115] Ibid. 78.

 [1116] Voyage to the Pacific, &c. in 1825-28.

 [1117] Darwin's Journal, &c., p. 540, and new edit., of 1845,
        p. 453.

 [1118] Darwin's Journal, &c., pp. 547, 548., and 2d edit., of
        1845, p. 460.

 [1119] Kotzebue's Voy., 1815-18, vol. iii. pp. 331-333.

 [1120] Stutchbury, West of Eng. Journ., No. i. p. 50.

 [1121] Captain Beechey, part i. p. 188.

 [1122] Captain Moresby on the Maldives, Journ. Roy. Geograph.
        Soc., vol. V. part ii. p. 400.

 [1123] See above, p. 442.

 [1124] Darwin, Volcanic Islands, p. 113.

 [1125] Quart. Journ. Geol. Soc. 4. XCIII.

 [1126] Darwin's Journal, p. 557. 2d edit. chap. 20, and Coral
        Islands, chapters 1, 2, 3.

 [1127] See Principles of Geology, 1st edit., vol. ii. p. 296.

 [1128] Voyage to the Pacific, &c., p. 189.

 [1129] See Principles of Geology, 1st ed., 1832, vol. ii. p.
        293.

 [1130] Beechey's Voyage to the Pacific, &c., p. 46.

 [1131] Voyage to the Pacific, &c., p. 194.

 [1132] Scotsman, Nov. 1842, and Jameson's Edin. Journ. of
        Science, 1843.

 [1133] Trans. Geol. Soc., London, 2d series, vol. v.

 [1134] Beechey's Voyage, vol. i. p. 45.

 [1135] Paper read to Brit. Assoc., Southampton, 1846.

 [1136] Letter to Mr. Maclaren, Scotsman, 1843.




  GLOSSARY

  OF GEOLOGICAL AND OTHER SCIENTIFIC TERMS USED IN THIS
  WORK.


  ACEPHALOUS. The Acephala are that division of molluscous animals
    which, like the oyster and scallop, are without heads. The class
    Acephala of Cuvier comprehends many genera of animals with bivalve
    shells, and a few which are devoid of shells. _Etym._, α, _a_,
    without, and κεφαλη, _cephale_, the head.

  ACIDULOUS. Slightly acid.

  ACROGENS. One of five classes into which all plants may be divided;
    it includes such flowerless ones as grow from the top only, and
    whose stems consequently do not increase materially in bulk, as
    Mosses, Ferns, Lycopodiums, Equisetums, &c. The trunk of a tree fern
    is a good example. They are also called Acrobrya. _Etym._, ακρον,
    _acron_, the top, and γενεσις, _genesis_, increase.

  ADIPOCIRE. A substance apparently intermediate between fat and wax,
    into which dead animal matter is converted when buried in the earth,
    and in a certain stage of decomposition. _Etym._, _adeps_, fat, and
    _cera_, wax.

  ALBITE. See "Felspar."

  ALEMBIO. An apparatus for distilling.

  ALGÆ. An order or division of the cryptogamic class of plants. The
    whole of the sea-weeds are comprehended under this division, and the
    application of the term in this work is to marine plants. _Etym._,
    _alga_, sea-weed.

  ALLUVIAL. The adjective of alluvium, which see.

  ALLUVION. Synonymous with alluvium, which see.

  ALLUVIUM. Earth, sand, gravel, stones, and other transported matter
    which has been washed away and thrown down by rivers, floods, or
    other causes upon land not _permanently_ submerged beneath the
    waters of lakes or seas. _Etym._, _alluo_, to wash upon, or
    _alluvio_, an inundation.

  ALUM-STONE, ALUMEN, ALUMINOUS. Alum is the base of pure clay, and
    strata of clay are often met with containing much iron pyrites. When
    the latter substance decomposes, sulphuric acid is produced, which
    unites with the aluminous earth of the clay to form sulphate of
    alumine, or common alum. Where manufactories are established for
    obtaining the alum, the indurated beds of clay employed are called
    Alum-stone.

  AMMONITE. An extinct and very numerous genus of the order of
    molluscous animals called Cephalopoda, allied to the modern genus
    Nautilus, which inhabited a chambered shell, curved like a coiled
    snake. Species of it are found in all geological periods of the
    secondary strata; but they have not been seen in the tertiary beds.
    They are named from their resemblance to the horns on the statues of
    Jupiter Ammon.

  AMORPHOUS. Bodies devoid of regular form. _Etym._, α, _a_, without,
    and μορφη, _morphe_, form.

  AMYGDALOID. One of the forms of the Trap-rocks, in which agates and
    simple minerals appear to be scattered like almonds in a cake.
    _Etym._, αμυγδαλα, _amygdala_, an almond.

  ANALCIME. A simple mineral of the Zeolite family, also called
    Cubizite, of frequent occurrence in the Trap-rocks.

  ANALOGUE. A body that resembles or corresponds with another body. A
    recent shell of the same species as a fossil shell is the analogue
    of the latter.

  ANGOIOSPERMS. A term applied to all flowering plants in which the
    ovules are inclosed in an ovary, and the seeds in a pericarp or
    covering, as in all flowering plants except those mentioned under
    gymnosperms and gymnogens, which see. _Etym._, αγγος, _angos_,
    a vessel, and περμα, a seed.

  ANOPLOTHERIUM. A fossil extinct quadruped belonging to the order
    Pachydermata, resembling a pig. It has received its name because the
    animal must have been singularly wanting in means of defence, from
    the form of its teeth and the absence of claws, hoofs, and horns.
    _Etym._, ανοπλος, _anoplos_, unarmed, and θηριον, _therion_, a wild
    beast.

  ANTAGONIST POWER. Two powers in nature, the action of the one
    counteracting that of the other, by which a kind of equilibrium or
    balance is maintained, and the destructive effect prevented that
    would be produced by one operating without a check.

  ANTENNÆ. The articulated horns with which the heads of insects are
    invariably furnished.

  ANTHRACITE. A shining substance like black-lead; a species of
    mineral charcoal. _Etym._, ανθραξ, _anthrax_, coal.

  ANTHRACOTHERIUM. A name given to an extinct quadruped, supposed to
    belong to the Pachydermata, the bones of which were first found in
    lignite and coal of the tertiary strata. _Etym._, ανθραξ,
    _anthrax_, coal, and θηριον, _therion_, wild beast.

  ANTHROPOMORPHOUS. Having a form resembling the human. _Etym._,
    ανθρωπος, _anthropos_, a man, and μορφη, _morphe_, form.

  ANTISEPTIC. Substances which prevent corruption in animal and
    vegetable matter, as common salt does, are said to be antiseptic.
    _Etym._, αντι, _anti_, against, and σηπω, _sepo_, to putrefy.

  ARENACEOUS. Sandy. _Etym._, _arena_, sand.

  ARGILLACEOUS. Clayey, composed of clay. _Etym._, _argilla_, clay.

  ARRAGONITE. A simple mineral, a variety of carbonate of lime, so
    called from having been first found in Aragon in Spain.

  ATOLLS. Coral islands of an annular form, or consisting of a
    circular strip or ring of coral surrounding a central lagoon.

  AUGITE. A simple mineral of a dark green, or black color, which
    forms a constituent part of many varieties of volcanic rocks. Name
    applied by Pliny to a particular mineral, from the Greek αυγη,
    _auge_, lustre.

  AVALANCHES. Masses of snow which, being detached from great heights
    in the Alps, acquire enormous bulk by fresh accumulations as they
    descend; and when they fall into the valleys below often cause great
    destruction. They are also called _lavanges_ and _lavanches_ in the
    dialects of Switzerland.


  BASALT. One of the most common varieties of the Trap-rocks. It is a
    dark green or black stone, composed of augite and felspar, very
    compact in texture, and of considerable hardness, often found in
    regular pillars of three or more sides called basaltic columns.
    Remarkable examples of this kind are seen at the Giant's Causeway,
    in Ireland, and at Fingal's Cave, in Staffa, one of the Hebrides.
    The term is used by Pliny, and is said to come from _basal_, an
    Æthiopian word signifying iron. The rock often contains much iron.

 "BASIN" of Paris, "BASIN" of London. Deposits lying in a hollow or
    trough, formed of older rocks; sometimes used in geology almost
    synonymously with "formations," to express the deposits lying in a
    certain cavity or depression in older rocks.

  BELEMNITE. An extinct genus of the order of molluscous animals
    called Cephalopoda, having a long, straight, and chambered conical
    shell. _Etym._, βελεμνον, _belemnon_, a dart.

  BITUMEN. Mineral pitch, of which the tar-like substance which is
    often seen to ooze out of the Newcastle coal when on the fire, and
    which makes it cake, is a good example. _Etym._, _bitumen_, pitch.

  BITUMINOUS SHALE. An argillaceous shale, much impregnated with
    bitumen, which is very common in the Coal Measures.

  BLENDE. A metallic ore, a compound of the metal zinc with sulphur.
    It is often found in brown shining crystals; hence its name among
    the German miners, from the word _blenden_, to dazzle.

  BLUFFS. High banks presenting a precipitous front to the sea or a
    river. A term used in the United States of North America.

  BOTRYOIDAL. Resembling a bunch of Grapes. _Etym._, βοτρυς,
    _botrys_, a bunch of grapes, and ειδος, _eidos_, form.

  BOULDERS. A provincial term for large rounded blocks of stone lying
    on the surface of the ground, or sometimes imbedded in loose soil,
    different in composition from the rocks in their vicinity, and which
    have been therefore transported from a distance.

  BRECCIA. A rock composed of angular fragments connected together by
    lime or other mineral substance. An Italian term.

  CALC SINTER. A German name for the deposits from springs holding
    carbonate of lime in solution--petrifying springs. _Etym._, _kalk_,
    lime, and _sintern_, to drop.

  CALCAIRE GROSSIER. An extensive stratum, or rather series of strata,
    found in the Paris Basin, belonging to the Eocene tertiary period.
    _Etym._, _calcaire_, limestone, and _grossier_, coarse.

  CALCAREOUS ROCK. Limestone. _Etym._, _calx_, lime.

  CALCAREOUS SPAR. Crystallized carbonate of lime.

  CARBON. An undecomposed inflammable substance, one of the simple
    elementary bodies. Charcoal is almost entirely composed of it.
    _Etym._, _carbo_, coal.

  CARBONATE OF LIME. Lime combines with great avidity with carbonic
    acid, a gaseous acid only obtained fluid when united with
    water,--and all combinations of it with other substances are called
    _Carbonates_. All limestones are carbonates of lime, and quicklime
    is obtained by driving off the carbonic acid by heat.

  CARBONATED SPRINGS. Springs of water, containing carbonic acid gas.
    They are very common, especially in volcanic countries; and
    sometimes contain so much gas, that if a little sugar be thrown into
    the water it effervesces like soda-water.

  CARBONIC ACID GAS. A natural gas which often issues from the ground,
    especially in volcanic countries. _Etym._, _carbo_, coal; because
    the gas is obtained by the slow burning of charcoal.

  CARBONIFEROUS. A term usually applied, in a technical sense, to an
    ancient group of secondary strata; but any bed containing coal may
    be said to be carboniferous. _Etym._, _carbo_, coal, and _fero_, to
    bear.

  CATACLYSM. A deluge. _Etym._, κατακλυζω, _catacluzo_, to deluge.

  CEPHALOPODA. A class of molluscous animals, having their organs of
    motion arranged round their head. _Etym._, κεφαλη, _cephale_,
    head, and ποδα, _poda_, feet.

  CETACEA. An order of vertebrated mammiferous animals inhabiting the
    sea. The whale, dolphin, and narwal are examples. _Etym._, _cete_,
    whale.

  CHALCEDONY. A siliceous simple mineral, uncrystallized. Agates are
    partly composed of chalcedony.

  CHALK. A white earthy limestone, the uppermost of the secondary
    series of strata.

  CHERT. A siliceous mineral, nearly allied to chalcedony and flint,
    but less homogeneous and simple in texture. A gradual passage from
    chert to limestone is not uncommon.

  CHLORITIC SAND. Sand colored green by an admixture of the simple
    mineral chlorite. _Etym._, χλωρυς, _chlorus_, green.

  CLEAVAGE. Certain rocks, usually called Slate-rocks, may be cleaved
    into an indefinite number of thin laminæ which are parallel to each
    other, but which are generally not parallel to the planes of the
    true strata or layers of deposition. The planes of cleavage,
    therefore, are distinguishable from those of stratification.

  CLINKSTONE, called also phonolite, a felspathic rock of the trap
    family, usually fissile. It is sonorous when struck with a hammer,
    whence its name.

  COAL FORMATION. This term is generally understood to mean the same
    as the Coal Measures, or Carboniferous group.

  COLEOPTERA. An order of insects (Beetles) which have four wings, the
    upper pair being crustaceous and forming a shield. _Etym._, coleos,
    _coleos_, a sheath, and πτερον, _pteron_, a wing.

  CONFORMABLE. When the planes of one set of strata are generally
    parallel to those of another set which are in contact, they are said
    to be conformable. Thus the set _a_, _b_, Fig. 98, rest conformably
    on the inferior set _c_, _d_; but _c_, _d_ rest unconformably on E.

    [Illustration: Fig. 98.]

  CONGENERS. Species which belong to the same genus.

  CONGLOMERATE, or PUDDINGSTONE. Rounded water-worn fragments of rock
    or pebbles, cemented together by another mineral substance, which
    may be of a siliceous, calcareous, or argillaceous nature. _Etym._,
    _con_, together, _glomero_, to heap.

  CONIFERÆ. An order of plants, all of which have disks in their wood
    fibres, by which they are recognized in a fossil state. Their ovules
    are naked (see GYMNOGENS). Most of the northern kinds bear the seeds
    in cones; but the yew does not, nor do a host of tropical and south
    temperate species. _Etym._, _conus_, a cone, and _fero_, to bear.

  COSMOGONY, COSMOLOGY. Words synonymous in meaning, applied to
    speculations respecting the first origin or mode of creation of the
    earth. _Etym._, κοσμος, _kosmos_, the world, and γονη, _gonee_,
    generation, or λογος, _logos_, discourse.

  CRAG. A provincial name in Norfolk and Suffolk for certain tertiary
    deposits usually composed of sand with shells, belonging to the
    Older Pliocene period.

  CRATER. The circular cavity at the summit of a volcano, from which
    the volcanic matter is ejected. _Etym._, _crater_, a great cup or
    bowl.

  CRETACEOUS. Belonging to chalk. _Etym._, _creta_, chalk.

  CROP OUT. A miner's or mineral surveyor's term, to express the
    rising up or exposure at the surface of a stratum or series of
    strata.

  CRUST OF THE EARTH. See "Earth's crust."

  CRUSTACEOUS. Animals having a shelly coating or crust which they
    cast periodically. Crabs, shrimps, and lobsters are examples.

  CRYPTOGAMIC. Asexual, flowerless, or Acotyledonous plants; a term
    applied to half the vegetable kingdom in contradistinction to
    Phænogamic, sexual, or flowering plants. It includes Fungi,
    Sea-weeds, Lichens, Mosses, Ferns, &c., which have no obvious
    flowers, and no cotyledons (seed-lobes) to their spores or seeds.
    _Etym._, κρυπτος, _cruptos_, concealed, and γαμος, _gamos_,
    marriage.

  CRYSTALS. Simple minerals are frequently found in regular forms,
    with facets like the drops of cut glass of chandeliers. Quartz being
    often met with in rocks in such forms, and beautifully transparent
    like ice, was called _rock-crystal_, κρυσταλλος, crystallos, being
    Greek for ice. Hence the regular _forms_ of other minerals are
    called crystals, whether they be clear or opake.

  CRYSTALLIZED. A mineral which is found in regular forms or crystals
    is said to be crystallized.

  CRYSTALLINE. The internal texture which regular crystals exhibit
    when broken, or a confused assemblage of ill-defined crystals.
    Loaf-sugar and statuary-marble have a _crystalline_ texture.
    Sugar-candy and calcareous spar are crystallized.

  CUPRIFEROUS. Copper-bearing. _Etym._, _cuprum_, copper, and _fero_,
    to bear.

  CYCADEÆ. A small and very anomalous order of flowering plants,
    chiefly found in Mexico, the East Indian Islands, South Africa, and
    Australia. They are Gymnogens as to ovules, and neither Exogens nor
    Endogens in the wood of their short, simple, or branched trunks, and
    they have dicotyledonous seeds. The leaves are pinnated (like those
    of cocoa-nut palms), and when young are rolled inwards as in Ferns.
    The wood fibres are curiously perforated, and marked, by which they
    are recognized in a fossil state as well as by the trunk and
    foliage, and the cones, which contain the male flowers. The term is
    derived from κυκας, _cycas_, a name applied by the ancient Greek
    naturalist Threophrastus to a palm.

  CYPERACEÆ. A tribe of plants answering to the English sedges; they
    are distinguished from grasses by their stems being solid, and
    generally triangular, instead of being hollow and round. Together
    with _Gramineæ_, they constitute what writers on botanical geography
    often call _glumaceæ_.


  DEBACLE. A great rush of waters, which, breaking down all opposing
    barriers, carries forward the broken fragments of rocks, and spreads
    them in its course. _Etym._, _débacler_, French, to unbar, to break
    up as a river does at the cessation of a long-continued frost.

  DELTA. When a great river, before it enters the sea, divides into
    separate streams, they often diverge and form two sides of a
    triangle, the sea being the base. The land included by the three
    lines, and which is invariably alluvial, was first called, in the
    case of the Nile a delta, from its resemblance to the letter of the
    Greek alphabet which goes by that name Δ. Geologists apply the term
    to alluvial land formed by a river at its mouth, without reference
    to its precise shape.

  DENUDATION. The carrying away by the action of running water of a
    portion of the solid materials of the land, by which inferior rocks
    are laid bare. _Etym._, _denudo_, to lay bare.

  DEOXIDIZED, DEOXIDATED. Deprived of oxygen. Disunited from oxygen.

  DESICCATION. The art of drying up. _Etym._, _desicco_, to dry up.

  DETRITUS. Matter worn or rubbed off from rocks. _Etym._, _de_, from,
    and _tero_, to rub.

  DICOTYLEDONOUS. A grand division of the vegetable kingdom, founded
    on the plant having two _cotyledons_, or seed-lobes. _Etym._,
    δις, _dis_, double, and κοτυληδον, _cotyledon_.

  DIKES. When a mass of the unstratified or igneous rocks, such as
    granite, trap, and lava, appears as if injected into a rent in the
    stratified rocks, cutting across the strata, it forms a dike. They
    are sometimes seen running along the ground, and projecting, like a
    wall, from the softer strata on both sides of them having wasted
    away; whence they were first called in the north of England and in
    Scotland _dikes_, a provincial name for wall. It is not easy to draw
    the line between dikes and veins. The former are generally of larger
    dimensions, and have their sides parallel for considerable
    distances; while veins have generally many ramifications, and these
    often thin away into slender threads.

  DILUVIUM. Those accumulations of gravel and loose materials, which,
    by some geologists, are said to have been produced by the action of
    a diluvian wave or deluge sweeping over the surface of the earth.
    _Etym._, _diluvium_, deluge.

  DIP. When a stratum does not lie horizontally, but is inclined, it
    is said to dip towards some point of the compass, and the angle it
    makes with the horizon is called the angle of dip or inclination.

  DIPTERA. An order of insects, comprising those which have only two
    wings. _Etym._, δις, _dis_, double, and πτερον, _pteron_, wing.

  DOLERITE. One of the varieties of the Trap-rocks, composed of augite
    and felspar.

  DOLOMITE. A crystalline limestone, containing magnesia as a
    constituent part. Named after the French geologist Dolomieu.

  DUNES. Low hills of blown sand that skirt the shores of Holland,
    England, Spain, and other countries.


  EARTH'S CRUST. Such superficial parts of our planet as are
    accessible to human observation.

  EOPYROSIS. A Greek term for a destruction by fire.

  ELYTRA. The wing-sheaths, or upper crustaceous membranes, which form
    the superior wings in the tribe of beetles. They cover the body, and
    protect the true membranous wing. _Etym._, ελυτρον, _elytron_, a
    sheath.

  ENDOGENS. A class of flowering plants, whose stems present no
    distinction of wood, pith, and bark. The wood is disposed in
    bundles, placed nearer the axis than those of the previous year, as
    in palm trunks. This class answers to the Monocotyledones of
    Jussieu. _Etym._, ενδον, _endon_, within, and γενεσις, _genesis_,
    increase.

  ENTOMOSTRACA. Cuvier's second section of Crustacea; so called from
    their relationship to insects. _Etym._, εντομα, _entoma_,
    insects.

  EOCENE. A name given to the lowest division of the tertiary strata,
    containing an extremely small percentage of living species amongst
    its fossil shells, which indicate the first commencement or dawn of
    the existing state of the animate creation. _Etym._, ηως, _eos_,
    aurora or the dawn, and καινος, _kainos_, recent.

  ESCARPMENT. The abrupt face of a ridge of high land. _Etym._,
    _escarper_, French, to cut steep.

  ESTUARIES. Inlets of the land, which are entered both by rivers and
    the tides of the sea. Thus we have the estuaries of the Thames,
    Severn, Tay, &c. _Etym._, _æstus_, the tide.

  EXOGENS. A class of flowering plants whose stems have bark, wood,
    and pith. The bark is increased by layers deposited within the
    previously formed layers and the wood of layers or rings placed
    outside of those of the previous year. This class answers to the
    Dicotyledones of Jussieu, and includes all common English trees
    except pines, &c. (See GYMNOGENS.) _Etym._, εξο, _exo_, outside,
    γενεσις, _genesis_, increase.

  EXPERIMENTUM CRUCIS. A decisive experiment, so called, because, like
    a cross or direction-post, it directs men to true knowledge; or, as
    some explain it, because it is a kind of torture whereby the nature
    of the thing is extorted, as it were, by violence.

  EXUVIÆ. Properly speaking, the transient parts of certain animals
    which they put off or lay down to assume new ones, as serpents and
    caterpillars shift their skins; but in geology it refers not only to
    the cast-off coverings of animals, but to fossil shells and other
    remains which animals have left in the strata of the earth. _Etym._,
    _exuere_, to put off or divest.


  FALUNS. A French provincial name for some tertiary strata abounding
    in shells in Touraine, which resemble in lithological characters the
    "Crag" of Norfolk and Suffolk.

  FAULT, in the language of miners, is the sudden interruption of the
    continuity of strata in the same plane, accompanied by a crack or
    fissure, varying in width from a mere line to several feet, which is
    generally filled with broken stone, clay, &c.

    [Illustration: Fig. 99.]

    The strata, _a_, _b_, _c_, &c., must at one time have been
    continuous; but a fracture having taken place at the fault F, either
    by the upheaving of the portion A, or the sinking of the portion B,
    the strata were so displaced that the bed _a_ in B is many feet
    lower than the same bed _a_ in the portion A.

  FAUNA. The various kinds of animals peculiar to a country constitute
    its FAUNA, as the various kinds of plants constitute its FLORA. The
    term is derived from the FAUNI, or rural deities, in Roman
    Mythology.

  FELSPAR. A simple mineral, which, next to quartz, constitutes the
    chief material of rocks. The white angular portions in granite are
    felspar. This mineral always contains some alkali in its
    composition. In _common felspar_ the alkali is potash; in another
    variety, called Albite or Cleavlandite, it is soda. Glassy felspar
    is a term applied when the crystals have a considerable degree of
    transparency. _Compact_ felspar is a name of more vague
    signification. The substance so called appears to contain both
    potash and soda.

  FELSPATHIC. Of or belonging to felspar.

  FERRUGINOUS. Any thing containing iron. _Etym._, _ferrum_, iron.

  FISSILE, easily cleft, dividing readily into an indefinite number of
    parallel laminæ, like slates.

  FLOETZ ROCKS. A German term applied to the secondary strata by the
    geologists of that country, because these rocks were supposed to
    occur most frequently in flat horizontal beds. _Etym._, _flotz_, a
    layer or stratum.

  FLORA. The various kinds of trees and plants found in any country
    constitute the FLORA of that country in the language of botanists.

  FLUVIATILE. Belonging to a river. _Etym._, _fluvius_, a river.

  FORAMINIFERA. A name given by D'Orbigny to a family of microscopic
    shells. Their different chambers are united by a small perforation
    or _foramen_. Recent observation has shown that some at least are
    not Cephalopoda, as D'Orbigny supposed.

  FORMATION. A group, whether of alluvial deposits, sedimentary
    strata, or igneous rocks, referred to a common origin or period.

  FOSSIL. All minerals were once called fossils, but geologists now
    use the word only to express the remains of animals and plants found
    buried in the earth. _Etym._, _fossilis_, any thing that may be dug
    out of the earth.

  FOSSILIFEROUS. Containing organic remains.


  GALENA. A metallic ore, a compound of lead and sulphur. It has often
    the appearance of highly polished lead. _Etym._, γαλεω, _galeo_,
    to shine.

  GARNET. A simple mineral, generally of a deep red color,
    crystallized; most commonly met with in mica slate, but also in
    granite and other igneous rocks.

  GASTEROPODS. A division of the Testacea, in which, as in the limpet,
    the foot is attached to the body. _Etym._, γαστηρ, _gaster_, belly,
    and ποδα, _poda_, feet.

  GAULT. A provincial name in the east of England for a series of beds
    of clay and marl, the geological position of which is between the
    Upper and Lower Greensand.

  GAVIAL. A kind of crocodile found in India.

  GEM, or GEMMULE, from the Latin _gemma_, a bud. The term, applied to
    zoophytes, means a young animal not confined within an envelope or
    egg.

  GEOLOGY, GEOGNOSY. Both mean the same thing; but with an unnecessary
    degree of refinement in terms, it has been proposed to call our
    description of the structure of the earth _geognosy_ (_Etym._,
    γεα, _gea_, earth, and γινωσcω, _ginosco_, to know), and our
    theoretical speculations as to its formation _geology_ (_Etym._,
    γεα, and λογος, _logos_, a discourse).

  GLACIER. Vast accumulations of ice and hardened snow in the Alps and
    other lofty mountains. _Etym._, _glace_, French for ice.

  GLACIS. A term borrowed from the language of fortification, where it
    means an easy insensible slope or declivity, less steep than a
    _talus_, which see.

  GNEISS. A stratified primary rock, composed of the same materials as
    granite, but having usually a larger proportion of mica and a
    laminated texture. The word is a German miner's term.

  GRAMINEÆ. The order of plants to which grasses belong. _Etym._,
    _gramen_, grass.

  GRANITE. An unstratified or igneous rock, generally found inferior
    to or associated with the oldest of the stratified rocks, and
    sometimes penetrating them in the form of dikes and veins. It is
    usually composed of three simple minerals, felspar, quartz, and
    mica, and derives its name from having a coarse _granular_
    structure; _granum_, Latin for grain. Waterloo bridge, and the
    paving-stones in the carriage-way of the London streets, afford good
    examples of the most common varieties of granite.

  GREENSAND. Beds of sand, sandstone, limestone, belonging to the
    Cretaceous Period. The name is given to these beds because they
    often, but not always, contain an abundance of green earth or
    chlorite scattered through the substance of the sandstone,
    limestone, &c.

  GREENSTONE. A variety of trap, composed of hornblende and felspar.

  GREYWACKÉ. _Grauwacke_, a German name, generally adopted by
    geologists for some of the most ancient fossiliferous strata. The
    rock is very often of a gray color; hence the name, _grau_, being
  German for gray, and _wacke_, being a provincial miner's term.

  GRIT. A provincial name for a coarse-grained sandstone.

  GYMNOSPERMOUS. _Etym._, γυμνος, _gymnos_, naked, and σπερμα,
    _sperma_, a seed. (See GYMNOGENS.)

  GYMNOGENS. A class of flowering plants, in which the ovules are not
    inclosed in an ovary. They are also called _gymnosperms_, the seeds
    in like manner not being inclosed in a pericarp. It includes all
    _Coniferæ_, as pine, fir, juniper, cypress, yew, cedar, &c., and
    _Cycadeæ_. All are Dicotyledonous (a few have many cotyledons), and
    all Exogenous, except _Cycas_, the growth of which is anomalous. The
    term is applied in contradistinction to _Angiosperms_, which see.
    _Etym._, γυμνος, naked, and γενεσις, increase.

  GYPSUM. A mineral composed of lime and sulphuric acid, hence called
    also _sulphate_ of _lime_. Plaster and stucco are obtained by
    exposing gypsum to a strong heat. It is found so abundantly near
    Paris, that plaster of Paris is a common term in this country for
    the white powder of which casts are made. The term is used by Pliny
    for a stone used for the same purposes by the ancients. The
    derivation is unknown.

  GYPSEOUS, of or belonging to gypsum.

  GYROGONITES. Bodies found in freshwater deposits, originally
    supposed to be microscopic shells, but subsequently discovered to be
    seed-vessels of freshwater plants of the genus _Chara_. See above
    p. 742. _Etym._, γυρος, _gyros_, curved, and γονος, _gonos_, seed,
    on account of their external structure.

  HEMIPTERA. An order of insects, so called from a peculiarity in
    their wings, the superior being coriaceous at the base and
    membranous at the apex, ἡμισυ, _hemisu_, half, and πτερον,
    _pteron_, wing.

  HORNBLENDE. A simple mineral of a dark green or black color, which
    enters largely into the composition of several varieties of the
    Trap-Rocks.

  HORNSTONE. A siliceous mineral substance, sometimes approaching
    nearly to flint, or common quartz. It has a conchoidal fracture, and
    is infusible, which distinguishes it from compact felspar.

  HUMERUS. The bone of the upper arm.

  HYDROPHYTES. Plants which grow in water. _Etym._, ὑδωρ, _hydor_,
    water, and φυτον, _phyton_, plant.

  HYPOGENE ROCKS. Those rocks which are _nether-formed_, or which have
    not assumed their present form and structure at the surface, such as
    granite, gneiss, &c. The term, which includes both the plutonic and
    metamorphic rocks, is substituted for _primary_, because some
    members of both these classes, such as granite and gneiss, are
    posterior to many secondary or fossiliferous rocks. _Etym._, ὑπο,
    _hypo_, under, and γινομαι, _ginomai_, to be formed or produced.


  ICEBERG. Great masses of ice, often the size of hills, which float
    in the polar and adjacent seas. _Etym._, ice, and _berg_, German for
    hill.

  ICHTHYOSAURUS. A gigantic fossil marine reptile, allied in part of
    its structure to a fish. _Etym._, ιχθυς, _ichthus_, a fish, and
    σαυρα, _saura_, a lizard.

  IGNEOUS ROCKS. All rocks, such as lava, trap, and granite, known or
    supposed to have been melted by volcanic heat.

  INCANDESCENT. White hot--having a more intense degree of heat than
    red heat.

  INDUCTION. A consequence, inference, or general principle drawn from
    a number of particular facts or phenomena. The inductive philosophy,
    says Mr. Whewell, has been rightly described as a science which
    ascends from particular facts to general principles, and then
    descends again from these general principles to particular
    applications.

  INFUSORY ANIMALCULES. Minute living creatures found in many
    _infusions_; and the term _infusori_ has been given to all such
    animalcules, whether found in infusions or in stagnant water,
    vinegar, &c.

  INSPISSATED. Thickened. _Etym._, _spissus_, thick.

  INVERTEBRATED ANIMALS. Animals which are not furnished with a
    back-bone. For a further explanation, see "Vertebrated Animals."

  ISOTHERMAL. Such zones or divisions of the land, ocean, or
    atmosphere, which have an equal degree of mean annual warmth, are
    said to be isothermal, from ισος, _isos_, equal, and θερμη,
    _therme_, heat.


  IOINTS. Fissures or lines of parting in rocks, often at right angles
    to the planes of stratification. The partings which divide columnar
    basalt into prisms are joints.

  IURA LIMESTONE. The limestones belonging to the Oolite Group
    constitute the chief part of the mountains of Jura between France
    and Switzerland; and hence the geologists of the Continent have
    given the name to the group.


  KEUPER. A German name for a member of the Upper New Red Sandstone.

  KIMMERIDGE CLAY. A thick bed of clay, constituting a member of the
    Oolite Group. So called because it is found well developed at
    Kimmeridge, in the Isle of Purbeck, Dorsetshire.


  LACUSTRINE. Belonging to a lake. _Etym._, _lacus_, a lake.

  LAMANTINE. A living species of the herbivorous Cetacea or whale
    tribe which inhabits the mouth of rivers on the coasts of Africa and
    South America: the sea-cow.

  LAMELLIFEROUS. Having a structure consisting of thin plates or
    leaves like paper. _Etym._, _lamella_, the diminutive of _lamina_,
    plate, and _fero_, to bear.

  LAMINÆ. Latin for plates; used in geology for the smaller layers of
    which a stratum is frequently composed.

  LANDSLIP. A portion of land that has slid down in consequence of
    disturbance by an earthquake, or from being undermined by water
    washing away the lower beds which supported it.

  LAPIDIFICATION. Lapidifying process. Conversion into stone. _Etym._,
    _lapis_, stone, and _fio_, to make.

  LAPILLI. Small volcanic cinders. _Lapillus_, a little stone.

  LAVA. The stone which flows in a melted state from a volcano.

  LEPIDODENDRON, a genus of fossil plants of the Coal Measures,
    intermediate in character between the Lycopodiums and coniferous
    plants.

  LEUCITE. A simple mineral found in volcanic rocks, crystallized, and
    of a white color. _Etym._, λευcος, _leucos_, white.

  LIAS. A provincial name for an argillaceous limestone, characterized
    together with its associated beds by peculiar fossils, and forming a
    particular group of strata, interposed between the Oolite and the
    New Red Sandstone.

  LIGNIPERDOUS. A term applied to insects which destroy wood. _Etym._,
    _lignum_, wood, and _perdo_, to destroy.

  LIGNITE. Wood converted into a kind of coal. _Etym._, _lignum_,
    wood.

  LITHODOMI. Molluscous animals which form holes in the solid rocks in
    which they lodge themselves. The holes are not perforated
    mechanically, but the rock appears to be dissolved. _Etym._, λιθος,
    _lithos_, stone, and δεμο, _demo_, to build.

  LITHOGENOUS POLYPS. Animals which form coral.

  LITHOGRAPHIC STONE. A slaty compact limestone, of a yellowish color
    and fine grain, used in lithography, which is the art of drawing
    upon and printing from stone _Etym._, λιθος, _lithos_, stone, and
    γραφο, _grapho_, to write.

  LITHOIDAL. Having a stony structure.

  LITHOLOGICAL. A term expressing the stony structure or character of
    a mineral mass. We speak of the lithological character of a stratum
    as distinguished from its zoological character. _Etym._, λιθος,
    _lithos_, stone, and λογος, _logos_, discourse.

  LITHOPHAGI. Molluscous animals which form holes in solid stones. See
    "Lithodomi." _Etym._, λιθος, _lithos_, stone, and φαγειν,
    _phagein_, to eat.

  LITHOPHITES. The animals which form Stone-coral.

  LITTORAL. Belonging to the shore. _Etym._, _littus_, the shore.

  LOAM. A mixture of sand and clay.

  LOPHIODON. A genus of extinct quadrupeds, allied to the tapir, named
    from eminences on the teeth.

  LYCOPODIACEÆ. Plants of an inferior degree of organization to
    Coniferæ, some of which they very much resemble in foliage, but all
    recent species are infinitely smaller. Many of the fossil species
    are as gigantic as recent Coniferæ. Their mode of reproduction is
    analogous to that of ferns. In English they are called club-mosses,
    generally found in mountainous heaths in the north of England.

  LYDIAN STONE. Flinty slate; a kind of quartz or flint, allied to
    Hornstone, but of a grayish black color.


  MACIGNO. In Italy this term has been applied to a siliceous
    sandstone sometimes containing calcareous grains, mica, &c.

  MADREPORE. A genus of corals, but generally applied to all the
    corals distinguished by superficial star-shaped cavities. There are
    several fossil species.

  MAGNESIAN LIMESTONE. An extensive series of beds, the geological
    position of which is immediately above the Coal Measures; so called,
    because the limestone, the principal member of the series, contains
    much of the earth magnesia as a constituent part.

  MAMMIFEROUS. Mammifers. Animals which give suck to their young. To
    this class all the warm-blooded quadrupeds, and the Cetacea, or
    whales, belong. _Etym._, _mamma_, a breast, _fero_, to bear.

  MAMMILLARY. A surface which is studded over with rounded
    projections. _Etym._, _mammilla_, a little breast or pap.

  MAMMOTH. An extinct species of the elephant (_E. primigenius_), of
    which the fossil bones are frequently met with in various countries.
    The name is of Tartar origin, and is used in Siberia for animals
    that burrow under ground.

  MANATI. One of the Cetacea, the sea-cow, or lamantine (_Trichechus
    manatus_, Lin.)

  MARL. A mixture of clay and lime; usually soft, but sometimes hard,
    in which case it is called indurated marl.

  MARSUPIAL ANIMALS. A tribe of quadrupeds having a sack or pouch
    under the belly, in which they carry their young. The kangaroo is a
    well-known example. _Etym._, _marsupium_, a purse.

  MASTODON. A genus of fossil extinct quadrupeds allied to the
    elephants; so called from the form of the hind teeth or grinders,
    which have their surface covered with conical mammillary crests.
    _Etym._, μαστος, _mastos_, pap, and οδων, _odon_, tooth.

  MATRIX. If a simple mineral or shell, in place of being detached, be
    still fixed in a portion of rock, it is said to be in its matrix.
    _Matrix_, womb.

  MECHANICAL ORIGIN, ROCKS OF. Rocks composed of sand, pebbles, or
    fragments, are so called to distinguish them from those of a uniform
    crystalline texture, which are of chemical origin.

  MEDUSÆ. A genus of marine radiated animals, without shells; so
    called, because their organs of motion spread out like the snaky
    hair of the fabulous Medusa.

  MEGALOSAURUS. A fossil gigantic amphibious animal of the saurian or
    lizard and crocodile tribe. _Etym._, μεγαλη, _megale_,
    great, and σαυρα, _saura_, lizard.

  MEGATHERIUM. A fossil extinct quadruped, resembling a gigantic
    sloth. _Etym._, μεγα, _mega_, great, and θηριον, _therion_,
    wild beast.

  MELASTOMA. A genus of MELASTOMACEA, an order of exotic plants of the
    evergreen tree and shrubby kinds. _Etym._, μελας, _melas_, black,
    and στομα, _stoma_, mouth; because the fruit of one of these
    species stains the lips.

  MESOTYPE. A simple mineral, white, and needle-shaped, one of the
    Zeolite family, frequently met with in the Trap-rocks.

  METAMORPHIC ROCKS. A stratified division of hypogene rocks, highly
    crystalline, such as gneiss and mica-schist, and so named because
    they have been _altered_ by plutonic action. _Etym._, μετα,
    _meta_, trans, and μορφη, _morphe_, form.

  MICA. A simple mineral, having a shining silvery surface, and
    capable of being split into very thin elastic leaves or scales. It
    is often called _talc_ in common life; but mineralogists apply the
    term talc to a different mineral. The brilliant scales in granite
    are mica. _Etym._, _mico_, to shine.

  MICA-SLATE, MICA-SCHIST, MICACEOUS SCHISTUS. One of the metamorphic
    or crystalline stratified rocks of the hypogene class, which is
    characterized by being composed of a large proportion of mica united
    with quartz.

  MIOCENE. A division of tertiary strata intervening between the
    Eocene and Pliocene formations; so called, because a minority of its
    fossil shells are referable to living species. _Etym._, μειων,
    _meion_, less, and καινος, _kainos_, recent.

  MOLASSE. A provincial name for a soft green sandstone, associated
    with marl and conglomerates, belonging to the Miocene Tertiary
    Period, extensively developed in the lower country of Switzerland.
    _Etym._, French, _molle_, soft.

  MOLLUSCA, MOLLUSCOUS ANIMALS. Animals, such as shell-fish, which,
    being devoid of bones, have soft bodies. _Etym._, _mollis_, soft.

  MONAD. The smallest of visible animalcules, spoken of by Buffon and
    his followers as constituting the elementary molecules of organic
    beings.

  MONITOR. An animal of the saurian or lizard tribe, species of which
    are found in both the fossil and recent state.

  MONOCOTYLEDONOUS. A grand division of the vegetable kingdom
    (including palms, grasses, Lilaceæ, &c.), founded on the plant
    having only one _cotyledon_, or seed-lobe. _Etym._, μονος,
    _monos_, single.

  MORAINE, a Swiss term for the débris of rocks brought into valleys
    by glaciers. See p. 228.

  MOSCHUS. A quadruped resembling the chamois or mountain goat, from
    which the perfume musk is obtained.

  MOUNTAIN LIMESTONE, OR CARBONIFEROUS LIMESTONE. A series of
    limestone strata of marine origin, usually forming the lowest member
    of the Coal Measures.

  MOYA. A term applied in South America to mud poured out from
    volcanoes during eruptions.

  MULTILOCULAR. Many-chambered; a term applied to those shells which,
    like the nautilus, ammonite, and others, are divided into many
    compartments. _Etym._, _multus_, many, and _loculus_, a partition.

  MURIATE OF SODA. The scientific name for common culinary salt,
    because it is composed of muriatic acid and the alkali soda.

  MUSACEÆ. A family of tropical monocotyledonous plants, including the
    banana and plantains.

  MUSCHELKALK. A limestone, belonging to the Upper New Red Sandstone
    group. Its position is between the Magnesian Limestone and the Lias.
    This formation has not yet been found in England, and the German
    name is adopted by English geologists. The word means shell
    limestone. _Etym._, _muschel_, shell, and _kalkstein_, limestone.


  NAPHTHA. A very thin, volatile, inflammable, and fluid mineral
    substance, of which there are springs in many countries,
    particularly in volcanic districts.

  NENUPHAR. A yellow water-lily. P. 618.

  NEW RED SANDSTONE. A formation so named, because it consists chiefly
    of sandy and argillaceous strata, the predominant color of which is
    brick-red, but containing portions which are of a greenish-gray.
    These occur often in spots and stripes, so that the series has
    sometimes been called the variegated sandstone. This formation is
    divided into the Upper New Red in which the Muschelkalk is included,
    and the Lower New Red, of which the Magnesian Limestone is a member.

  NODULE. A rounded irregular-shaped lump or mass. _Etym._, diminutive
    of _nodus_, knot.

  NORMAL GROUPS. Groups of certain rocks taken as a rule or standard.
    _Etym._, _norma_, rule or pattern.

  NUCLEUS. A solid central piece, around which other matter is
    collected. The word is Latin for kernel.

  NUMMULITES. An extinct genus of the order of molluscous animals,
    called Cephalopoda, of a thin lenticular shape, internally divided
    into small chambers. _Etym._, _nummus_, Latin for money, and λιθος,
    _lithos_, stone, from its resemblance to a coin.


  OBSIDIAN. A volcanic product, or species of lava, very like common
    green bottle glass, which is almost black in large masses, but
    semi-transparent in thin fragments. Pumice-stone is obsidian in a
    frothy state; produced, most probably, by water that was contained
    in or had access to the melted stone, and converted into steam.
    There are very often portions in masses of solid obsidian, which are
    partially converted into pumice.

  OCHRE. A yellow powder, a combination of some earth with oxide of
    iron.

  OGYGIAN DELUGE. A great inundation mentioned in fabulous history,
    supposed to have taken place in the reign of Ogyges in Attica, whose
    death is fixed in Blair's Chronological Tables in the year 1764
    before Christ. See p. 341.

  OLD RED SANDSTONE. A formation immediately below the Carboniferous
    Group. The term Devonian has been recently proposed for strata of
    this age, because in Devonshire they are largely developed, and
    contain many organic remains.

  OLIGOCLASE. A mineral of the felspar family.

  OLIVINE. An olive-colored, semi-transparent, simple mineral, very
    often occurring in the form of grains and of crystals in basalt and
    lava.

  OOLITE, OOLITIC. A limestone; so named because it is composed of
    rounded particles like the roe or eggs of a fish. The name is also
    applied to a large group of strata, characterized by peculiar
    fossils, in which limestone of this texture occurs. _Etym._, ωον,
    _oon_, egg, and λιθος, _lithos_, stone.

  OPALIZED WOOD. Wood petrified by siliceous earth, and acquiring a
    structure similar to the simple mineral called opal.

  OPHIDIOUS REPTILES. Vertebrated animals, such as snakes and
    serpents. _Etym._, οφις, _ophis_, a serpent.

  ORGANIC REMAINS. The remains of animals and plants (_organized_
    bodies) found in a fossil state.

  ORTHOCERATA OR OHTHOCERÆ. An extinct genus of the order of
    molluscous animals, called Cephalopoda, that inhabited a
    long-chambered conical shell, like a straight horn. _Etym._, ορθος,
    orthos], _orthos_, straight, and κερας, _ceras_, horn.

  OSSEOUS BRECCIA. The cemented mass of fragments of bones of extinct
    animals found in caverns and fissures. _Osseous_ is a Latin
    adjective, signifying bony.

  OSTEOLOGY. That division of anatomy which treats of the bones; from
    οστεον, _osteon_, bone, and λογος, _logos_, a discourse.

  OUTLIERS. When a portion of a stratum occurs at some distance,
    detached from the general mass of the formation to which it belongs,
    some practical mineral surveyors call it an _outlier_, and the term
    is adopted in geological language.

  OVATE. The shape of an egg. _Etym._, _ovum_, egg.

  OVIPOSITING. The laying of eggs.

  OXIDE. The combination of a metal with oxygen; rust is oxide of
    iron.

  OXYGEN. One of the constituent parts of the air of the atmosphere;
    that part which supports life. For a farther explanation of the
    word, consult elementary works on chemistry.


  PACHYDERMATA. An order of quadrupeds, including the elephant,
    rhinoceros, horse, pig, &c., distinguished by having thick skins.
    _Etym._, παχυς, _pachus_, thick, and δερμα, _derma_, skin,
    or hide.

  PACHYDERMATOUS. Belonging to Pachydermata.

  PALÆOTHERIUM, PALEOTHERE. A fossil extinct quadruped, belonging to
    the order Pachydermata, resembling a pig, or tapir, but of great
    size. _Etym._, παλαιος, _palaios_, ancient, and θηριον,
    _therion_, wild beast.

  PALEONTOLOGY. The science which treats of fossil remains, both
    animal and vegetable. _Etym._, παλαιος, _palaios_, ancient,
    οντα, _onta_, beings, and λογος, _logos_, a discourse.

  PELAGIAN, PELAGIC. Belonging to the _deep_ sea. _Etym._, _pelagus_,
    sea.

  PEPERINO. An Italian name for a particular kind of volcanic rock,
    formed like tuff, by the cementing together of volcanic sand,
    cinders, or scoriæ, &c.

  PETROLEUM. A liquid mineral pitch, so called because it is seen to
    ooze like oil out of the rock. _Etym._, _petra_, rock, and _oleum_,
    oil.

  PHÆNOGAMOUS or PHANEROGAMIC PLANTS. A name given by Linnæus to those
    plants in which the reproductive organs are apparent. _Etym._,
    φανερος, _phaneros_, evident, or φαινω, _phaino_, to show, and
    γαμος, _gamos_, marriage.

  PHLEGRÆAN FIELDS. Campi Phlegræi, or "the Burnt Fields." The country
    around Naples, so named by the Greeks, from the traces of igneous
    action everywhere visible.

  PHONOLITE. See "Clinkstone."

  PHRYGANEA. A genus of four-winged insects, the larvæ of which,
    called caddis-worms, are used by anglers as a bait.

  PHYSICS. The department of science which treats of the properties of
    natural bodies, laws of motion, &c.; sometimes called natural
    philosophy and mechanical philosophy. _Etym._, φυσις, _physis_,
    nature.

  PHYTOLOGY, PHYTOLOGICAL. The department of science which relates to
    plants--synonymous with, botany and botanical. _Etym._, φυτον,
    _phyton_, plant, and λογος, _logos_, discourse.

  PHYTOPHAGOUS. Plant-eating. _Etym._, φυτον, _phyton_, plant, and
    φαγειν, _phagein_, to eat.

  PISOLITE. A stone possessing a structure like an agglutination of
    peas. _Etym._, πισον, _pison_, pea, and λιθος, _lithos_, stone.

  PISTIA. P. 618. The plant mentioned by Malte-Brun is probably the
    _Pistia Stratiotes_, a floating plant, related to English duckweed,
    but very much larger.

  PIT COAL. Ordinary coal; called so, because it is obtained by
    sinking pits in the ground.

  PITCHSTONE. A rock of a uniform texture, belonging to the
    unstratified and volcanic classes, which has an unctuous appearance
    like indurated pitch.

  PLASTIC CLAY. One of the beds of the Eocene Tertiary Period; so
    called, because it is used for making pottery. The formation to
    which this name is applied is a series of beds chiefly sands, with
    which the clay is associated. _Etym._, πλασσω, _plasso_, to
    form or fashion.

  PLESIOSAURUS. A fossil extinct amphibious animal, resembling the
    saurian, or lizard and crocodile tribe. _Etym._, πλησιον,
    _plesion_, near to, and σαυρα, _saura_, a lizard.

  PLIOCENE, OLDER and NEWER. Two divisions of the Tertiary Period
    which are the most modern, and of which the largest part of the
    fossil shells are of recent species. _Etym._, πλειων, _pleion_,
    more, and καινος, _kainos_, recent.

  PLUTONIC ACTION. The influence of volcanic heat and other
    subterranean causes under pressure.

  PLUTONIC ROCKS. Granite, porphyry, and other igneous rocks supposed
    to have consolidated from a melted state at a great depth from the
    surface.

  POLIPARIA. CORALS. A numerous class of invertehrated animals,
    belonging to the great division called Radiata.

  PORPHYRY. An unstratified or igneous rock. The term is as old as the
    time of Pliny, and was applied to a red rock with small, angular,
    white bodies diffused through it, which are crystallized felspar,
    brought from Egypt. The term is hence applied to every species of
    unstratifled rock in which detached crystals or felspar or some
    other mineral are diffused through a base of other mineral
    composition. _Etym._, πορφυρα, _porphyra_, purple.

  PORTLAND LIMESTONE, PORTLAND BEDS. A series of limestone strata,
    belonging to the upper part of the Oolite Group, found chiefly in
    England in the Island of Portland on the coast of Dorsetshire. The
    great supply of the building-stone used in London is from these
    quarries.

  POZZUOLANA. Volcanic ashes, largely used as mortar for buildings,
    similar in nature to what is called in this country Roman cement. It
    gets its name from Puzzuoli, a town in the Bay of Naples, from which
    it is shipped in large quantities to all parts of the Mediterranean.

  PRECIPITATE. Substances which, having been dissolved in a fluid, are
    separated from it by combining chemically and forming a solid, which
    falls to the bottom of the fluid. This process is the opposite to
    that of chemical solution.

  PRODUCTA. An extinct genus of fossil bivalve shells occurring only
    in the older secondary rocks. It is closely allied to the living
    genus Terebratula.

  PTERODACTYL. A flying reptile: species of this genus have been found
    in the Oolite and Muschelkalk. Some of the finger-joints are
    lengthened, so as to serve as the expansors of a membranous wing.
    Hence the name _wing-fingered_. _Etym._, πτερον, _pteron_, a wing,
    and δακτυλος, _dactylos_, a finger.

  PUBESCENCE. The soft hairy down on insects. _Etym._, _pubesco_, the
    first growth of the beard.

  PUDDINGSTONE. See "Conglomerate."

  PUMICE. A light spongy lava, chiefly felspathic, of a white color,
    produced by gases or watery vapor getting access to the particular
    kind of glassy lava called obsidian, when in a state of fusion; it
    may be called the froth of melted volcanic glass. The word comes
    from the Latin name of the stone, _pumex_.

  PURBECK LIMESTONE, PURBECK BEDS. Limestone strata, belonging to the
    Wealden Group, which intervenes between the Greensand and the
    Oolite.

  PYRITES. (Iron.) A compound of sulphur and iron, found usually in
    yellow shining-crystals like brass, and in almost every rock,
    stratified and uustratifled. The shining metallic bodies so often
    seen in common roofing slate are a familiar example of the mineral.
    The word is Greek, and comes from πυρ, _pyr_, fire; because
    tinder particular circumstances, the stone produces spontaneous
    heat, and even inflammation.

  PYROMETER. An instrument for measuring intense degrees of heat.


  QUADRUMANA. The order of mammiferous animals to which apes belong.
    _Etym._, _quadrus_, a derivative of the Latin word for the number
    four, and _manus_, hand, the four feet of those animals being in
    some degree usable as hands.

  QUA-QUA-VERSAL DIP. The dip of beds to all points of the compass
    around a centre, as in the case of beds of lava round the crater of
    a volcano. _Etym._, _quâ-quâ-versum_, on every side.

  QUARTZ. A German provincial term, universally adopted in scientific
    language for a simple mineral composed of pure silex, or earth of
    flints: rock-crystal is an example.

  QUARTZITE or QUARTZ ROCK. An aggregate of grains of quartz,
    sometimes passing into compact quartz.


  RED MARL. A term often applied to the New Red Sandstone.

  RETICULATE. A structure of cross lines, like a net, is said to be
    reticulated, from _rete_, a net.

  ROCK SALT. Common culinary salt, or muriate of soda, found in vast
    solid masses or beds, in different formations, extensively in the
    New Red Sandstone formation, as in Cheshire; and it is then called
    _rock_-salt.

  RUBBLE. A term applied by quarry-men to the upper fragmentary and
    decomposed portion of a mass of stone.

  RUMINANTIA. Animals which ruminate or chew the cud, such as the ox,
    deer, &c. _Etym._, the Latin verb _rumino_, meaning the same thing.


  SACCHAROID, SACCHARINE. When a stone has a texture resembling that
    of loaf-sugar. _Etym._, σακχαρ, _sacchar_, sugar, and ειδος,
    _eidos_, form.

    [Illustration: Fig. 100.]

  SALIENT ANGLE. In a zigzag line _a a_ are the salient angles, _b b_
    the re-entering angles. _Etym._, _salire_, to leap or bound forward.

  SALT SPRINGS. Springs of water containing a large quantity of common
    salt. They are very abundant in Cheshire and Worcestershire, and
    culinary salt is obtained from them by mere evaporation.

  SANDSTONE. Any stone which is composed of an agglutination of grains
    of sand, whether calcareous, siliceous, or of any other mineral
    nature.

  SAURIAN. Any animal belonging to the lizard tribe. _Etym._, σαυρα,
    _saura_, a lizard.

  SAXICAVOUS. Hollowing out stone.

  SCHIST is often used as synonymous with slate; but it may be very
    useful to distinguish between a schistose and a slaty structure. The
    hypogene or primary _schists_, as they are termed, such as gneiss,
    mica-schist, and others, cannot be split into an indefinite number
    of parallel laminæ like rocks which have a true slaty cleavage. The
    uneven schistose layers of mica-schist and gneiss are probably
    layers of deposition, which have assumed a crystalline texture. See
    "Cleavage." _Etym._, _schistus_, adj. Latin, that which may be
    split.

  SCHISTOSE ROCKS. See "Schist."

  SCORIÆ. Volcanic cinders. The word is Latin for cinders.

  SEAMS. Thin layers which separate two strata of greater magnitude.

  SECONDARY STRATA. An extensive series of the stratified rocks which
    compose the crust of the globe, with certain characters in common,
    which distinguish them from another series below them called
    _primary_, and from a third series above them called _tertiary_.

  SECULAR REFRIGERATION. The periodical cooling and consolidation of
    the globe from a supposed original state of fluidity from heat.
    _Sæculum_, age or period.

  SEDIMENTARY ROCKS are those which have been formed by their
    materials having been thrown down from a state of suspension or
    solution in water.

  SELENITE. Crystallized gypsum, or sulphate of lime--a simple
    mineral.

  SEPTARIA. Flattened balls of stone, generally a kind of iron-stone,
    which, on being split, are seen to be separated in their interior
    into irregular masses. _Etym._, _septa_, inclosures.

  SERPENTINE. A rock usually containing much magnesian earth, for the
    most part unstratified, but sometimes appearing to be an altered or
    metamorphic stratified rock. Its name is derived from frequently
    presenting contrasts of color, like the skin of some serpents.

  SHALE. A provincial term, adopted by geologists, to express an
    indurated slaty clay. _Etym._, German _schalen_, to peel, to split.

  SHELL MARL. A deposit of clay, peat, and other substances mixed with
    shells, which collects at the bottom of lakes.

  SHINGLE. The loose and completely water-worn gravel on the
    sea-shore.

  SILEX. The name of one of the pure earths, being the Latin word for
    _flint_, which is wholly composed of that earth. French geologists
    have applied it as a generic name for all minerals composed
    entirely of that earth, of which there are many of different
    external forms.

  SILICA. One of the pure earths. _Etym._, _silex_, flint, because
    found in that mineral.

  SILICATE. A chemical compound of silica and another substance, such
    as silicate of iron. Consult elementary works on chemistry.

  SILICEOUS. Of or belonging to the earth of flint. _Etym._, _silex_,
    which see. A siliceous rock is one mainly composed of silex.

  SILICIFIED. Any substance that is petrified or mineralized by
    _siliceous_ earth.

  SILT. The more comminuted sand, clay, and earth, which is
    transported by running water. It is often accumulated by currents in
    banks. Thus the mouth of a river is silted up when its entrance into
    the sea is impeded by such accumulation of loose materials.

  SIMPLE MINERAL. Individual mineral substances, as distinguished from
    rocks, which last are usually an aggregation of simple minerals.
    They are not simple in regard to their nature; for when subjected to
    chemical analysis, they are found to consist of a variety of
    different substances. Pyrites is a simple mineral in the sense we
    use the term, but it is a chemical compound of sulphur and iron.

  SINTER, CALCAREOUS OR SILICEOUS. A German name for a rock
    precipitated from mineral waters. _Etym._, _sintern_, to drop.

  SLATE. See "Cleavage" and "Schist."

  SOLFATARA. A volcanic vent from which sulphur, sulphureous, watery,
    and acid vapors and gases are emitted.

  SPORULES. The reproductory corpuscula (minute bodies) of cryptogamic
    plants. _Etym._, σπορα, _spora_, a seed.

  STALACTITE. When water holding lime in solution deposits it as it
    drops from the roof of a cavern, long rods of stone hang down like
    icicles, and these are called _stalactites_. _Etym._, σταλαζω,
    _stalazo_, to drop.

  STALAGMITE. When water holding lime in solution drops on the floor
    of a cavern, the water evaporating leaves a crust composed of layers
    of limestone: such a crust is called _stalagmite_, from σταλαγμα,
    _stalagma_, a drop, in opposition to _stalactite_, which see.

  STATICAL FIGURE. The figure which results from the equilibrium of
    forces. From στατος, _statos_, stable, or standing still.

  STERNUM. The breast-bone, or the flat bone occupying the front of
    the chest.

  STILBITE. A crystallized simple mineral, usually white, one of the
    Zeolite family, frequently included in the mass of the Trap-rocks.

  STRATIFIED. Rocks arranged in the form of _strata_, which see.

  STRATIFICATION. An arrangement of rocks in _strata_, which see.

  STRATA, STRATUM. The term stratum, derived from the Latin verb
    _struo_, to strew or lay out, means a bed or mass of matter spread
    out over a certain surface by the action of water, or in some cases
    by wind. The deposition of successive layers of sand and gravel in
    the bed of a river, or in a canal, affords a perfect illustration
    both of the form and origin of stratification. A large portion of
    the masses constituting the earth's crust are thus stratified, the
    successive strata of a given rock preserving a general parallelism
    to each other; but the planes of stratification not being perfectly
    parallel throughout a great extent like the planes of _cleavage_,
    which see.

  STRIKE. The direction or line of bearing of strata, which is always
    at right angles to their prevailing dip.

  STUFAS. Jets of steam issuing from fissures in volcanic regions at a
    temperature often above the boiling point.

  SUBAPENNINES. Low hills which skirt or lie at the foot of the great
    chain of the Apennines in Italy. The term. Subapennine is applied
    geologically to a series of strata of the Older Pliocene Period.

  SYENITE. A kind of granite; so called, because it was brought from
    Syene in Egypt.


  TALUS. When fragments are broken off by the action of the weather
    from the face of a steep rock, as they accumulate at its foot, they
    form a sloping heap, called a talus. The term is borrowed from the
    language of fortification, where _talus_ means the outside of a wall
    of which the thickness is diminished by degrees, as it rises in
    height, to make it the firmer.

  TARSI. The feet in insects, which are articulated, and formed of
    five or a less number of joints.

  TERTIARY STRATA. A series of sedimentary rocks, with characters
    which distinguish them from two other great series of strata--the
    secondary and primary--which lie _beneath_ them.

  TESTACEA. Molluscous animals, having a shelly covering. _Etym._,
    _testa_, a shell, such as snails, whelks, oysters, &c.

  THALLOGENS. A class of flowerless plants including all those that
    have no defined axis, stem, or leaves; as Lichens, Seaweeds, and
    Fungi. _Etym._, θαλλος, _thallos_, a branch, and γενεσις,
    _genesis_, increase.

  THERMAL. Hot. _Etym._, θερμος, _thermos_, hot.

  THERMO-ELECTRICITY. Electricity developed by heat.

  THIN OUT. When a stratum, in the course of its prolongation in any
    direction, becomes gradually less in thickness, the two surfaces
    approach nearer and nearer; and when at last they meet, the stratum
    is said to thin out or disappear.

  TRACHYTE. A variety of lava essentially composed of glassy felspar,
    and frequently having detached crystals of felspar in the base or
    body of the stone, giving it the structure of porphyry. It sometimes
    contains hornblende and augite; and when these last predominate, the
    trachyte passes into the varieties of trap, called Greenstone,
    Basalt, Dolorite, &c. The term is derived from τραχυς, _trachus_,
    rough, because the rock has a peculiar rough feel.

  TRAP and TRAPPEAN ROCKS. Volcanic rocks composed of felspar, augite,
    and hornblende. The various proportions and state of aggregation of
    these simple minerals, and differences in external forms, give rise
    to varieties, which have received distinct appellations, such as
    Basalt, Amygdaloid, Dolorite, Greenstone, and others. The term is
    derived from _trappa_, a Swedish word for stair, because the rocks
    of this class sometimes occur in large tabular masses, rising one
    above another like steps.

  TRAVERTIN. A white concretionary limestone, usually hard and
    semi-crystalline, deposited from the water of springs holding lime
    in solution.--_Etym._ This stone was called by the ancients Lapis
    Tiburtinus, the stone being formed in great quantity by the river
    Anio, at Tibur, near Rome. Some suppose travertin to be an
    abbreviation of trasterverino from transtiburtinus.

  TRIPOLI. The name of a powder used for polishing metals and stones,
    first imported from Tripoli, which, as well as a certain kind of
    siliceous stone of the same name, has been lately found to be
    composed of the flinty cases of Infusoria.

  TROPHI, of Insects. Organs which form the mouth, consisting of an
    upper and under lip, and comprising the parts called mandibles,
    maxillæ, and palpi.

  TUFA, CALCAREOUS. A porous rock deposited by calcareous waters on
    their exposure to the air, and usually containing portions of plants
    and other organic substances incrusted with carbonate of lime. The
    more solid form of the same deposit is called "travertin," into
    which it passes.

  TUFA, VOLCANIC. See "Tuff."

  TUFACEOUS. A rock with the texture of tuff, or tufa, which see.

  TUFF, or TUFA VOLCANIC. An Italian name for a variety of volcanic
    rock of an earthy texture, seldom very compact, and composed of an
    agglutination of fragments of scoriæ and loose materials ejected
    from a volcano.

  TURBINATED. Shells which have a spiral or screw-form structure.
    _Etym._, _turbinatus_, made like a top.

  TURRILITE. An extinct genus of chambered shells, allied to the
    Ammonites, having the siphuncle near the dorsal margin.


  UNCONFORMABLE. See "Conformable."

  UNOXIDIZED, UNOXIDATED. Not combined with oxygen.


  VEINS, MINERAL. Cracks in rocks filled up by substances different
    from the rock, which may either be earthy or metallic. Veins are
    sometimes many yards wide; and they ramify or branch off into
    innumerable smaller parts, often as slender as threads, like the
    veins in an animal, hence their name.

  VERTEBRATED ANIMALS. A great division of the animal kingdom,
    including all those which are furnished with a back-bone, as the
    mammalia, birds, reptiles, and fishes. The separate joints of the
    back-bone are called _vertebræ_, from the Latin verb _verto_, to
    turn.

  VESICLE. A small, circular, inclosed space, like a little bladder.
    _Etym._, diminutive of _vesica_, Latin for a bladder.

  VITRIFICATION. The conversion of a body into glass by heat.

  VOLCANIC BOMBS. Volcanoes throw out sometimes detached masses of
    melted lava, which, as they fall, assume rounded forms (like
    bomb-shells), and are often elongated into a pear-shape.

  VOLCANIC FOCI. The subterranean centres of action in volcanoes,
    where the heat is supposed to be in the highest degree of energy.

  WACKE. A rock nearly allied to basalt, of which it may be regarded
    as a soft and earthy variety.

  WARP. The deposit of muddy waters, artificially introduced into low
    lands. See p. 326.


  ZEOLITE. A family of simple minerals, including stilbite, mesotype,
    analcime, and some others, usually found in the trap or volcanic
    rocks. Some of the most common varieties swell or boil up when
    exposed to the blow-pipe, and hence the name of ζεο, _zeô_,
    to boil, and λιθος, _lithos_, stone.

  ZOOPHITES. Corals, sponges, and other aquatic animals allied to
    them; so called because, while they are the habitation of animals,
    they are fixed to the ground, and have the form of plants. _Etym._,
    ζωον, _zoon_, animal, and φυτον, _phyton_, plant.




  INDEX.



  A.

  Abich, M., on eruption of Vesuvius in 1834, 378, 380, 550.

  Abo, 522, 523.

  Acosta cited, 499, 502.

  Adams, Mr., on fossil elephant, 80.

  Adanson on age of the baobab tree, 422.

  Addison on Burnet's theory, 32.

  Adige, embankment of the, 255.
  ----, delta of the, 257.

  Adour, R., new passage formed by, 338.

  Adria, formerly a seaport, 256.

  Adriatic, deposits in, 36, 88, 71, 257, 774.

  Ægean Sea, Prof. E. Forbes dredging in, 649.

  Africa, fossil shells of, mentioned by ancients, 15.
  ----, indigenous quadrupeds of, 82.
  ----, heat radiated by, 94.
  ----, currents on coast of, 292, 342.
  ----, drift sands of deserts, 726.
  ----, devastations of locusts in, 674.
  ----, strata forming off tropical coast of, 774.
  ----, desert of its area, 694.

  Agassiz, M., on fish of coal formation, 136.
  ----, on abrupt transition from one fossil fauna to another, 184.
  ----, on motion, &c., of glaciers, 224, 226.

  Agricola on fossil remains, 21.

  Airthrey, fossil whale found at, 771.

  Alabama, coal plants, 88.

  Alaska, volcanoes in, 352.

  Aldborough, incursions of sea at, 311.

  Alderney, race of, 293.

  Aleutian Isles, eruptions, &c., in, 352, 468.

  Alexandria, temple of Serapis at, 512.

  Algæ, known provinces of, 617.

  Allan, Dr., on coral in Madagascar, 778.

  Alloa, whale cast ashore at, 771.

  Alluvium, imbedding of organic remains in, 780.
  ----, volcanic, 386.
  ----, stalagmite, alternating with, in caves, 736.

  Alps, Saussure on the, 45.
  ----, tertiary rocks of the, 119.
  ----, greatly raised during tertiary epoch, 124.
  ----, signs of lateral pressure in the, 171.

  Altered rocks, 177.

  Amazon, R., land formed by its deposits, 342.
  ----, animals floated down on drift-wood by, 640.

  America, its coast undermined, 331.
  ----, recent strata in lakes of, 254, 768.
  ----, specific distinctness of animals of, 612, 629.
  ----, domesticated animals run wild in, 585, 685.
  ----, N., continuous beds of coal in, 115.
  ----, N., deposit "New red" like English, 158.
  ----, N. and S., mammiferous fauna of, 633.

  Ammonia in lavas, 550.

  Amonoosuck, flood in valley of, 209.

  Ampère, M., on electric currents in the earth, 543.

  Amphitherium, in oolite of Stonesfleld, 138.

  Andes, changes of level in, 762.
  ----, height of perpetual snow on, 112.
  ----, volcanoes of, 346.
  ----, sudden upheaval of, 170.
  ----, signs of lateral pressure in, 171.

  Andesite, rock described, 347.

  Angiospermous plants wanting in older rocks, 133.

  Animals, extinction of, 700.
  ----, quantity of food required by large, 82.
  ----, Lamarck on production of new organs in, 568.
  ----, imported into America have ran wild, 585, 685.
  ----, aptitude of some kinds to domestication, 593, 598.
  ----, hereditary instincts of, 593.
  ----, domestic qualities of, 592, 595.
  ----, their acquired habits rarely transmissible, 595, 600.
  ----, changes in brain of foetus in, 609.
  ----, plants diffused by, 623.
  ----, their geographical distribution, 76, 77.
  ----, migrations of, 685.
  ----, causes which determine the stations of, 669, 676.
  ----, influence of man on their distribution, 682.
  ----, fossil, in peat caves, &c., 722, 725, 730, 732, 749, 752.

  Anio, R., flood of the, 212.
  ----, travertin formed by, 244.

  Anoplotherium, fossil of Isle of Wight, 142.

  Antarctic circle, area still unexplored, 99.

  Antwerp, sunk region near, 327.

  Apennines, their relative age, 119, 124.

  Aphides, account of a shower of, 656.
  ----, their multiplication, 673.

  Aqueous causes, supposed former intensity of, 153.
  ----, their action described, 198.

  Aqueous lavas, description of, 374, 385, 728.

  Arabian Gulf filling with coral, 776.

  Arabian writers, 17.

  Arago, M., on influence of forests on climate, 715.
  ----, on solar radiation, 127.
  ----, on level of Mediterranean and Red Sea, 294.
  ----, on formation of ground ice, 221.

  Araucanian tradition of a flood, 499.

  Araucaria, fir in coal, 88.

  Arbroath, houses, &c., swept away by sea at, 302.

  Archiac, M., 257.

  Arctic fauna extended farther south than now, 125.

  Arduino, memoirs of, 41.
  ----, on submarine volcanoes, 41, 71.

  Areas of elevation and subsidence proved by coral islands, 792.

  Aristarchus, 212.

  Aristotle, opinions of, 12.
  ----, on spontaneous generation, 22.
  ----, on deluge of Deucalion, 356.

  Arkansas, R., 264.
  ----, floods of, 270.

  Arso, volcanic eruption of, in Ischia, 365.

  Artesian well at Paris, temperature of water, 234.
  ----, well, at Fort William, near Calcutta, 280.
  ----, well in delta of Po, 257.

  Artesian wells near London, 234.
  ----, wells, phenomena brought to light by, 233, 538.

  Arve, sediment transported by the, 258.
  ----, section of débris deposited by, 289.

  Ascension, Island of, bounded by lofty shores, 622.
  ----, fossil eggs of turtle from, 771.

  Ashes, volcanic, transported to great distances, 106, 349, 464.

  Asia, subject to earthquakes, 9.
  ----, coast of, changed, 18.
  ----, causes of extreme cold of part of, 94.
  ----, Minor, gain of land on coast of, 260.
  ----, Western, great cavity in, 692.

  Ass, wild, 638, 686.

  Astruc, on Delta of Rhone, 258.

  Atchafalaya, R., 264.
  ----, drift-wood in, 267.

  Atlantic, mean depth of, 104.
  ----, its relative level, 294.
  ----, rise of the tide in, 295.
  ----, absence of coral reefs in, 796.

  Atlantis, submersion of, 9.

  Atolls described, 782, 786.
  ----, theory of, Mr. Maclaren's objections to, 792.

  Atrio del Cavallo, 381.

  Aubenas, fissures filled with breccia near, 741.

  Austen, Mr. R. A. C., on shores of English Channel, 319.
  ----, on new strata formed in, 341.

  Australia, animals of, 139, 143, 684.
  ----, coral reefs of, 776, 784.
  ----, land quadrupeds of, 633.

  Auvergne, salt springs in, 248.
  ----, carbonic acid gas disengaged in, 248.
  ----, state of in tertiary period, 122.
  ----, fossils in volcanic ashes of, 349.
  ----, volcanic rocks of, 48.
  ----, tertiary red marl and sandstone of, 158.

  Ava, fossils of, 28.

  Avantipura, in Cashmere, 763.

  Avernus lake, 368.

  Avicenna on cause of mountains, 17.

  Axmouth, great landslip near, 321.

  Azores, icebergs drifted to, 99.
  ----, volcanic line from, to central Asia, 354.
  ----, siliceous springs of, 246.


  B.

  Babbage, Mr., on the coast near Puzzuoli, 507.
  ----, on Temple of Serapis, 517.
  ----, on expansion of rocks by heat, 562.

  Bachman, Mr., on birds, 643, 644.

  Bacon, Lord, cited, 765.

  Baden, gypseous springs of, 245.

  Baffin's Bay, icebergs in, 96.

  Bagnes, valley of, bursting of a lake in the, 210.

  Baiæ, changes on coast of the bay of, 507.
  ----, ground plan of the coast of, 507.
  ----, sections in bay of, 508, 510.

  Baker, on Caspian, mud volcanoes at, 448.

  Baker, Lieut., on fossil quadrumana, 144.

  Bakewell, Mr., on formation of soils, 709.
  ----, on fall of Mount Grenier, 782.

  Bakewell, Mr. jun., on Falls of Niagara, 217.

  Bakie loch, charæ fossil in, 767.

  Baku, inflammable gas of, 11, 355.

  Balaruc, thermal waters of, 259.

  Baldassari, on Sienese fossils, 39.

  Balize, mouth of Mississippi, 263, 272.

  Baltic Sea, lowering of level of, 520.
  ----, drifting of rocks by ice in, 219, 231.
  ----, currents on its shores, 330.

  Banks of Mississippi higher than alluvial plain, 266.

  Baobab tree, its size, probable age, &c., 422.

  Barbadoes, rain diminished by felling of forests in, 713.

  Barren Island described, 447.

  Barrow, Mr., on a bank formed in sea by locusts, 675.

  Barrow, Mr. jun., on the Geysers of Iceland, 247.

  Barton, Mr., on geography of plants, 612.

  Basalt, opinions of the early writers on, 48, 71.

  Batavia, effects of earthquake at, 502.

  Baton Rouge, in Louisiana, 265.

  Bay of Bengal, its depth, recent deposits in, &c., 279.

  Bayfield, Capt., on geology of Lake Superior, 254.
  ----, on drifting of rock by ice, 221, 230.
  ----, on bursting of a peninsula by Lake Erie, 333.
  ----, on earthquakes in Canada, 470.

  Beaches, raised, 184.

  Beachey Head, 317.

  Bears, once numerous in Wales, 683.
  ----, black, migrations of, 637.
  ----, drifted on ice, 679.

  Beaufort, Sir F., on gain of land in Asia Minor, 260.
  ----, on rise of tides, 291.

  Beaumont, M. Elie de, geological map of France, 122.
  ----, on pentagonal network of mountain chains, 170.
  ----, his theory of contemporaneous origin of parallel
          mountain chains considered, 163.
  ----, on structure and origin of Etna, 400, 416.
  ----, on sand-dunes, 307.
  ----, on inroads of sea in Holland, 327.

  Beaver once inhabited Scotland and Wales, 683.
  ----, fossil in Perthshire, 752.
  ----, lake formed by, in New Brunswick, 716.

  Beche, Sir H. de la. See De la Beche.

  Bee, migrations of the, 655.

  Beechey, Capt., upheaval of Bay of Conception, 500.
  ----, on drifting of canoes, 662.
  ----, on temple of Ipsambul, 727.
  ----, on coral islands, 780, 782, 787.
  ----, on changes of level in Pacific, 788.
  ----, on dead coral in Elizabeth Island, 794.

  Beila, in India, mud volcanoes, 449.

  Belcher, Sir E., on upheaval of Conception, 500.
  ----, on strata forming off coast of Africa, 774.

  Bell, Mr., on the Dog, 585.

  Bell rock, stones thrown up by storms on, 302.

  Belzoni, on temple of Ipsambul, 726.
  ----, on a flood of the Nile, 753.

  Benin, currents in Bay of, 292.

  Bérard, M., on depth and temperature of Mediterranean, 296, 336.

  Berkeley, on recent origin of man, 764.

  Bermudas, only coral reef far out in Atlantic, 796.
  ----, coral reefs of the, 776, 778.

  Bewick cited, 310, 643, 683.

  Bhooj, in Cutch, destroyed by earthquake, 459.
  ----, volcanic eruption at, 460, 729.

  Bies Bosch formed, 328.

  Bigsby, Dr., on North American lakes, 768.

  Birds, diffusion of plants by, 624.
  ----, geographical distribution of, 642, 663.
  ----, fossils in secondary rocks, 137.
  ----, tameness of, in uninhabited Islands, 597.
  ----, rate of flight of, 644.
  ----, migrations of, 643.
  ----, recent extermination of some species of, 683.
  ----, bones of, in Gibraltar breccia, 741.
  ----, rarity of their remains in new strata, 748.
  ----, rare in deposits of all ages, 137.

  Bischoff, Professor, on volcanoes, 551.
  ----, on carbonic acid in extinct craters on Rhine, 248.

  Biscoe, Capt., discoveries in south Polar Seas, 99.

  Bison, fossil, in Yorkshire, 76.

  Bisons, in Mississippi valley, 636.

  Bistineau lake, 269.

  Bitumen, oozing from bottom of sea, near Trinidad, 250.

  Bituminous springs, 250.

  Black Sea, salt by evaporation in, 335.
  ----, _See_ Euxine.

  Blue mountains in Jamaica, 505.

  Bluffs of Mississippi described, 264.

  Boa constrictor, migration of, 646.

  Boase, Mr., on inroads of sea in Cornwall, 323.
  ----, on drift-sand in Cornwall, 728.

  Boblaye, M., on ceramique, in Morea, 731.
  ----, on engulfed rivers and caves in Morea, 734.
  ----, on earthquakes in Greece, 736.

  Bog iron-ore, whence derived, 722.

  Bogota, earthquake of, 457.

  Bonpland, on plants common to Old and New World, 614.

  Bore, a tidal wave frequent in Bristol Channel and Ganges, 332.

  Bory de St. Vincent, M., on isle of Santorin, 445.

  Bosphorus, 334.
  ----, traditions of deluges on shores of the, 356.

  Botanical evidence bearing on theory of progressive development, 133.
  ----, geography, 613.
  ----, provinces, their number, 616, 666, 668.

  Bothnia, Gulf, gradual elevation of coast of, 520.

  Bourbon, island, volcanic, 546.

  Bournmouth, submarine forest at, 746.

  Boussingault. M., on volcanoes in Andes, 348.
  ----, on gases evolved by volcanoes, 549.

  Bowen, Lieut., on drifting of rocks by ice, 220, 230.

  Boyle, on bottom of the sea, 26.

  Bracini, on Vesuvius before 1631, 374.

  Brahmapootra, delta of, 275, 278.

  Brahmins, their doctrines, 4.

  Brander, on fossils of Hampshire, 46.

  Brandt, Professor, cited, 80.
  ----, on Wilui rhinoceros, 80.

  Bravais, M., on upraised sea-coast in Finmark, 530.

  Breccias, in Val del Bove, 411.
  ----, in caves now forming in the Morea, 734.

  Brenta, delta of the, 256.

  Brieslak, on temple of Serapis, 517.
  ----, on Vesuvius, 381, 384.

  Briggs, Mr., his discovery of water in African desert, 235.

  Brighton, waste of cliffs of, 317.

  Brine springs, 247.

  Bristol Channel, currents in, 293.

  Brittany, village, buried under blown sand, 727.
  ----, marine tertiary strata of, 122.
  ----, waste of coast of, 324.

  Brocchi, on fossil conchology, 20.
  ----, on Burnet's theory, 34.
  ----, on delta of Po, 257.
  ----, on extinction of species, 668.
  ----, on the Subapennines, 118.

  Broderip, Mr., on opossum of Stonesfield, 139.
  ----, on shells from Conception Bay, 500.
  ----, on bulimi revived, 650.
  ----, on moulting of crabs, 653.
  ----, on naturalization of a foreign landshell, 664.
  ----, on the Dodo, 684.

  Brongniart, M. Adolphe, 87.
  ----, on fossil plants of coal, 88, 117, 133.
  ----, on plants in islands, 112.

  Brongniart, M. Alex., on modern lava streams, 427.
  ----, on elevated beaches in Sweden, 527.

  Brown, Mr. R., on structure of vessels in myzodendron, 88.
  ----, on plants common to Africa, Guiana, and

  Brazil, 621.
  ----, on wheat in Egyptian tombs, 587.

  Buch. _See_ Von Buch.

  Buckland, Rev. Dr., on landslip near Axmouth, 321.
  ----, on fossil elephants, &c., in India, 7.
  ----, on fossils from Eschscholtz's Bay, 82.
  ----, on fossils in caves and fissures, 739, 740.
  ----, on Val del Bove, 402.

  Buffon, his theory of the earth, 39.
  ----, reproved by the Sorbonne, 39.
  ----, on geographical distribution of animals, 590, 612, 629.
  ----, on extinction of species, 701.

  Buist, Mr., on submarine forests in the estuary of Tay, 303.
  ----, on mud volcanoes in India, 448.

  Bunbury, Mr., on coal plants of Alabama, 88.
  ----, on ferns in carboniferous era, 87.

  Bunsen, Chevalier, on Ancient Egypt, 659.

  Bunsen, Professor, on Geysers of Iceland, 558.
  ----, on mineral springs in Iceland, 246.
  ----, on mud volcanoes of Iceland, 447.
  ----, on solfataras of Iceland, 551.

  Bunter Sandstein, fossils of, 193.

  Bura, submerged Grecian town, 15, 762.

  Buried cones on Etna, section of, 397.
  ----, temples of Cashmere, 762.

  Burnes, Sir A., on Cutch, earthquake of, 461, 464.

  Burnet, his theory of the earth, 31.

  Burntisland, whale cast ashore near, 771.

  Burrampooter, R., delta of the, 275. _See_ Brahmapootra.
  ----, bodies of men, deer, &c. floated off by, 751.

  Bustards recently extirpated in England, 688.


  C.

  Calabria, geological description of, 474.
  ----, earthquake of 1783 in, 471.
  ----, tertiary strata of, 74.

  Calanna, lava of Etna turned from its course by hill of, 409, 410.
  ----, valley of, 402, 404.

  Calcareous springs, 239.

  Calcutta, artesian well at, 280.

  Caldcleugh, Mr., on earthquake in Chili, 1835, 453.
  ----, on eruption of Coseguina, 349.

  California, volcanoes in, 349.

  Callao town destroyed by sea, 502.
  ----, changes caused by earthquakes at, 501, 761.

  Camels, carcasses of, imbedded in drift sand, 727.

  Campagna di Roma, calcareous deposits of, 242.

  Campania, aqueous lavas in, 728.

  Camper, on facial angle, 608.

  Canada, earthquakes frequent in, 470.
  ----, climate of, 582.
  ----, probably colder in newest tertiary period, 125.

  Canary Islands, eruptions in, 436.

  Cannon in calcareous rock, 759.
  ----, account of one taken up near the Downs, 726.

  Canoes drifted to great distances, 661.
  ----, fossil, 759.

  Cape May, encroachment of sea at, 332.
  ----, of Good Hope, icebergs seen off, 100.

  Capocci, M., on temple of Serapis, 518.

  Caraccas, earthquakes in, 465, 470.

  Carang Assam volcano, 465.

  Carbonated springs, 248.

  Carbonic acid, supposed atmosphere of, 248.
  ----, gas, its effects on rocks, 249.

  Carboniferous series, 115, 137.
  ----, era, predominance of ferns in, 87.
  ----, era, climate in, 87.
  ----, flora, knowledge of, recently acquired, 126.
  ----, period, vast duration of, 249.
  ----, _See_ Coal.

  Cardiganshire, tradition of loss of land in, 324.

  Cardium, locomotive powers when young, 652.

  Caribbean Sea, tides in, 342.

  Carpenter, Dr., observations on Mississippi R., 272.
  ----, on encroachment of sea at Lyme Regis, 321.

  Carrara marble, 177.

  Cashmere, temples buried in freshwater strata, 762.

  Caspian, Pallas on former extent of, 45.
  ----, evaporation of the, 260.
  ----, its level, 156, 692.

  Catalonia, devastation of torrents in, 713.

  Catania, in part overwhelmed by lava, 400, 728.
  ----, destroyed by earthquakes, 503.
  ----, tools discovered in digging a well at, 753.

  Catastrophes, theories respecting, 7.

  Catcott, on deluges in different countries, 42.

  Cattegat, devastations caused by current in the, 331.

  Cautley, Capt., on buried Hindoo town, 731.
  ----, on fossil quadrumana, 144.
  ----, on bones in ancient wells, 740.

  Caves, organic remains in, 732.
  ----, alternations of, and stalagmite in, 736.
  ----, on Etna, 401.

  Celestial Mountains, 77, 355.

  Celsius, on diminution of Baltic, 33, 521.

  Central America, volcanoes of, 349.
  ----, Asia, volcanic line from, to the Azores, 354.
  ----, France, lavas excavated in, 213.
  ----, France, comparison between the lavas of Iceland and, 426, 427.

  Centres, specific doctrine of, 630.

  Centrifugal force, 534, 544.

  Cephalonia, earthquakes in, 474.
  ----, infusoria in submarine caverns in, 389.

  Cesalpino, on organic remains, 22.

  Cetacea, geographical range of, 635.
  ----, migrations of the, 642.
  ----, imbedding of, in recent strata, 770.
  ----, fossil, absence of in secondary rocks, 145.
  ----, fossil in New Jersey chalk, 145.
  ----, rarity of in secondary rocks, 145.

  Chagos coral isles, 783.

  Chaluzet, calcareous spring at, 239.
  ----, volcanic cone of, 248.

  Chambers, Robert, cited, 530.

  Chamisso, M., on coral islands, 781.

  Chamouni, glaciers of, 223.

  Chara, growing in lakes of N. America, 768.

  Charæ, fossilized, 767.

  Charlevoix, chart of coast of Gulf of Mexico, 272.

  Charpentier, M., on glaciers, 223, 227.

  Cheirotherium, in old red sandstone and coal, 136.

  Chemical theory of volcanoes, 542, 546.

  Chepstow, rise of the tides at, 291.

  Cheshire, brine springs of, 247.
  ----, waste of coast of, 324.

  Chesil bank, 320.

  Chesilton, overwhelmed by sea, 320.

  Chili, earthquakes in, 65, 347, 357, 453, 457.
  ----, numerous volcanoes in, 346.
  ----, coast of, upheaved, 170, 172, 347, 455, 457.

  Chiloe, 349.

  Chimborazo, height of, 102.

  China, climate of, 95.
  ----, earthquakes in, 355.

  Chinese deluge, 7.

  Chines, or narrow ravines, described, 319.

  Chittagong, earthquakes at, 476.

  Chockier, cave at, 736.

  Chonos archipelago, rise of land in, 453.

  Christchurch Head promontory, 319.

  Christie, Mr., on plasticity of ice, 226.

  Christol, M. de, on fossils in caves, 738, 739.

  Chronology of Hebrew Scriptures, 659.
  ----, of Dr. Hales, 659.

  Cimbrian deluge, 331.

  Cisterna on Etna, how formed, 414.

  Cities engulfed, 173.

  Civita Vecchia, springs at, 243.

  Clarke, Dr., on lava in motion, 377.

  Cleavage, or slaty structure, 176.

  Clermont, calcareous springs at, 239.

  Climate of Europe, Raspe on former, 43.
  ----, changes of 75, 86.
  ----, change of, in northern hemisphere, 73, 123.
  ----, on causes of vicissitudes in, 92.
  ----, astronomical causes of fluctuations in, 126.
  ----, its influence on distribution of plants, 613.
  ----, effect of changes in, on range of species, 696.
  ----, influence of vegetation on, 713.

  Climates, insular and excessive, 94.

  Coal, modern, at mouths of Mackenzie, 743.
  ----, ancient beds, formed of plants, 90.
  ----, ancient, formed in deltas, 116.
  ----, fields, American, 115.
  ----, formed by plants which grow on the spot, 115.
  ----, period, warmth, moisture, &c. of climate, 126.
  ----, formation, fossil plants of the, 88, 115, 133.
  ----, climate indicated by, 91.
  ----, reptilian fossils in, 136.
  ----, _See_ Carboniferous.

  Colchester, Mr. W., on fossil quadrumana, 144.

  Colebrooke, Mr. H. T., on age of Vedas, 4.
  ----, on crocodiles of the Ganges, 277.
  ----, Major R. H., on the Ganges, 277.

  Colle, travertin of, 240.

  Colombia, earthquakes in, 456.

  Colonna, on organic remains, 23.

  Columbia, R., submerged forest in, 270.

  Conception, earthquakes at, 453, 456, 499, 761.

  Conglomerates, now formed by rivers, &c., 289.
  ----, volcanic, 411, 438.

  Coniferæ of coal, 133.
  ----, Araucarian, in coal, 88.

  Consolidation of strata, 175.

  Conybeare, Rev. W. D., on Lister, 26.
  ----, on landslip near Axmouth, 321, 322.

  Cook, Captain, on drifting of canoes far, 661.
  ----, on highland near the South Pole, 98, 99.

  Copaic lake, 735.

  Copernican theory, edicts against, repealed at Rome, 56.

  Copiapo, earthquakes at, 347.
  ----, raised banks of shells at, 458.

  Coral islands, 775, 776, 793.
  ----, origin of their circular form, 783.
  ----, linear direction of, 782.
  ----, rate of growth, 776.
  ----, downward movement slow and uniform, 791.
  ----, absence of, in Atlantic, &c., 796.

  Coralline crag fossils, 142.

  Corda, on palm wood in Bohemian coal, 88.
  ----, cited, 133.

  Cordier, M., on rate of increase of heat in mines, 538, 539.
  ----, his theory on central heat and fluidity, 540.
  ----, on tides in the internal melted ocean, 541.

  Cordilleras shaken by earthquakes, 457, 466.
  ----, parallel ridges successively upheaved, 170.

  Corinth, decomposition of rocks in, 733.

  Cornwall, waste of cliffs of, 323.
  ----, land inundated by drift-sand in, 727.
  ----, temperature of mines in, 538.

  Coromandel, inundations of sea on coast of, 730.

  Coseguina volcano, great eruption of, 347.

  Cosmogony distinct from geology, 3.
  ----, of the Hindoos, 4.
  ----, Egyptian, 8.
  ----, of the Koran, 18.

  Cosmopolite shells, 650.

  Coste, Capt., on elevation caused by earthquakes, 453.

  Cotopaxi, 348, 560.

  Covelli, M., on hot spring in Ischia, 456.
  ----, on Vesuvian minerals, 385.

  Cowper, the poet, on age of earth, 55.

  Crag strata, fossils of the, 142.

  Craters of elevation, theory of, 371, 380, 415.

  Crawfurd, Mr., his discovery of fossils in Ava, 28.
  ----, on eruption in Sumbawa, 106, 464, 465.
  ----, on drifting of canoes, 662.

  Creation, supposed centres or foci of, 667.
  ----, epoch of, difference of opinion on, 660.

  Cremona, lakes filled up near, 255.

  Crocodiles imbedded by a river inundation in Java, 503, 748.

  Cromer, waste of cliffs of, 306.

  Cropthorn, fossils found at, 76.

  Cruickshanks, Mr. A., on Chilian earthquake, 457.

  Cuba, fossils in caves of, 741.

  Culver, cliff, 318.

  Cumana, earthquake of, 470.

  Cunningham, Major, on buried temples of Cashmere, 764.

  Cupressus thyoides, 725.

  Currents from equatorial regions, 96.
  ----, from the pole to the equator, 107.
  ----, causes and velocity of, 293.
  ----, polar and tropical, direction of, 295.
  ----, destroying and transporting power of, 297, 340.
  ----, in estuaries, their power, 337.
  ----, in the Straits of Gibraltar, 333.

  Currents, reproductive effects of, 337.
  ----, on the British shores, 339.
  ----, convey species from Antarctic to Arctic Ocean, 622.

  Curtis, Mr., on ravages caused by aphides, 674.
  ----, on power of the Tipulæ to cross the sea, 657.
  ----, on number of British insects, 705.
  ----, on fossil insects, 748.

  Curves of the Mississippi, 265.

  Cutch, changes caused by earthquake of 1819 in, 469, 761.

  Cuvier on durability of bones of men, 147, 757.
  ----, on crocodiles of Ganges, 277.
  ----, on variability in species, 583, 584.
  ----, on fish not crossing the Atlantic, 647.
  ----, on identity of Egyptian mummies with living species, 586.
  ----, on number of fishes, 705.

  Cuvier, M. F., on aptitude of some animals to domestication, 593.
  ----, on influence of domestication, 595.

  Cypris, fossil and living, 768.


  D.

  Dana, Mr., on Sandwich Islands, 354, 372, 383, 548.
  ----, on fragments of recent coral thrown up by Polynesian
          volcanoes, 372.
  ----, on Mount Loa, volcano, 552.
  ----, on "volcanoes no safety-valves," 552.

  Dangerfield, Capt F., on buried cities In India, 729.
  ----, on Onjein, 729.

  Daniell, Professor, on the trade winds, 106.
  ----, on melting point of iron, 539.

  Dante cited, 52, 256.

  Dantzic, waste of land near, 331.

  Darby, on lakes formed by Red River, 269.
  ----, on delta of Mississippi, 272.

  Darwin, Mr. C., on distribution of animals and plants, 77, 98, 141.
  ----, on vegetation required for support of large quadrupeds, 82.
  ----, Mr. C., on drifting of rocks by ice, 228.
  ----, on earthquakes, 347, 458, 456, 476, 753.
  ----, on earthquake waves, 497.
  ----, on rise of land, 458, 502.
  ----, on oolitic travertin, 439.
  ----, on great droughts in S. America, 696.
  ----, on peat of S. America, 719.
  ----, on coral islands, 779, 780, 782, 785, 789.
  ----, geology of S. America, 170.
  ----, on recent shells in Chili, 190.
  ----, on shingle on coast of S. America, 342.
  ----, map of coral reefs, 352, 791, 794.
  ----, on crateriform hills of Galapagos, 372.
  ----, infusoria brought home by, 388.
  ----, on new islands forming in Atlantic, 436.
  ----, on nat. hist. of Galapagos, 141, 597, 615, 616, 642.
  ----, on extinction of animals, 700.

  Daubeny, Dr., on springs, 237.
  ----, on Mount Vultur, 356.
  ----, on Vesuvius, 380.
  ----, on decomposition of trachyte, 385.
  ----, on flowing of lava under water, 383.
  ----, on volcanoes, 548, 549, 550, 551.

  D'Aubuisson cited, 58, 411.

  Davis, Mr., on Chinese deluge, 7.

  Davy, Sir H., on lake of the Solfatara, 243.
  ----, on formation of travertin, 243.
  ----, on theory of progressive development, 131.
  ----, on eruption of Vesuvius, 378.
  ----, on chemical agency of electricity, 542.
  ----, his theory of unoxidated metallic nucleus, 546.
  ----, on agency of air and water in volcanoes, 548, 550.
  ----, his analysis of peat, 718.

  Davy, Dr., on Graham Island, 436, 549.
  ----, on helmet taken from sea near Corfu, 760.

  De Beaumont. _See_ Beaumont, De.

  Debey, Dr., of Aix, on cretaceous dicotyledons, 133.

  De Candolle, on hybrid plants, 605.
  ----, on distribution of plants, 613, 616.
  ----, on agency of man in dispersion of plants, 625.
  ----, on stations of plants, 670.
  ----, on barriers separating botanical provinces, 703.
  ----, on number of land plants, 705.
  ----, on longevity of trees, 422.

  Dechen, Von, map of Germany, &c., 123.

  Dee, R., bridge over, swept away by floods, 208.

  Deer, their powers of swimming, 636.
  ----, diminished number in Great Britain, 683.
  ----, remains of, in marl lakes, 752.

  De la Beche, Sir H., on rocks in S. Wales, 91.
  ----, on delta of Rhone in Lake of Geneva, 253.
  ----, on storm of Nov., 1824, 321.
  ----, on submarine forests, 323.
  ----, on earthquake of Jamaica, 1692, 504.
  ----, on action of rain in the tropics, 713.

  De la Hire, on fossil wood from Ava, 1692, 28.

  Delhi territory, elephants in, 81.

  Delta of the Adige and Brenta, 256.
  ----, of the Brahmapootra or Burrampooter, 275.
  ----, of the Ganges, 275 to 284.
  ----, of the Mississippi, 263 to 275.
  ----, of the Mississippi, antiquity of. 271.
  ----, of the Nile, 261.
  ----, of the Po, 256.
  ----, of Rhone, in Lake of Geneva, 252.
  ----, of Rhone, in Mediterranean, 258.

  Deltas, chronological computations of age of, 253, 285.
  ----, of Lake Superior, 253.
  ----, grouping of strata in, 286.

  De Luc, his treatise on Geology, 56.
  ----, on conversion of forests into peat mosses, 721.

  De Luc, M. G. A., his natural chronometers, 726.

  Deluge, ancient theories on, 18, 23, 25, 31, 42, 155.
  ----, fossil shells referred to the, 20.

  Deluges, local, how caused, 7, 269.
  ----, traditions of different, 7, 11, 42, 331, 356, 500, 501.

  Demaillet, speculative views of, 572.

  Denudation can only keep pace with deposition, 154.
  ----, effects of, 708.

  Deposition of sediment, shifting of the area of, 188.
  ----, and denudation parts of the same process, 154.

  Deshayes, M., on fossils of tertiary, 184.

  Desmarest, his definition of geology, 3.
  ----, on Auvergne, 49.

  Desnoyers, M., on human remains in caves, 739.

  Desor, M., on glacier motion, 224.

  Deucalion's deluge, 12.

  Deville, M., on contraction of granite, 173.
  ----, on trachytes, 440.

  Devonian strata formed in deep seas, 117.

  Diatomaceæ, 388.

  Dikes, composition and position of, 379.
  ----, how caused, 379.

  Diluvial waves, no signs of on Etna, 423.
  ----, theory of earlier geologists, 25.

  Diodorus Siculus cited, 357.

  Dion Cassius cited, 364.

  Dodo, recent extinction of the, 684.

  Dog, varieties of the, 570, 584.
  ----, hybrids between wolf and, 601.
  ----, acquired instincts hereditary in, 593.
  ----, has run wild in America, 686.

  Doggerbank, 340.

  Dollart, formation of estuary of the, 329.

  Dolomieu on Val di Noto, Vicentin, and Tyrol, 49.
  ----, on lavas of Etna, 49.
  ----, on decomposition of granite, 249.
  ----, on earthquake of 1783 in Calabria, 473, 475, 478, 480.

  Domestication, aptitude of some animals for, 593, 599.
  ----, influence of, 595.

  Don, river, rocks transported by, 208.

  Donati on bed of Adriatic, 38, 71, 774.

  Donny, Mr., cited, 557.

  D'Orbigny, M. A., on abrupt transition from one fossil
    fauna to another, 184.

  Dorsetshire, landslip in, 321.
  ----, waste of cliffs of, 319.

  Dove, Mr., map of isothermal lines, 93.

  Dover, waste of chalk cliffs of, 314.
  ----, depth of sea near, 315.
  ----, formation of Straits of, 315.
  ----, strata at foot of cliffs of, 314.

  Downham buried by blown sand, 727.

  Dranse, R., 210.

  Drift, northern, fossil marine shells in, 186.

  Drift-sand, fossils in, 727.

  Drift-wood of Mississippi, 268.
  ----, abundant in North Sea, 744.

  Drontheim, 529.

  Droughts in S. America, animals destroyed by, 696.

  Druids, their doctrines, 16.

  Dufresnoy, M., geological map of France, 122.
  ----, on formation of Monte Nuovo, 371, 372.
  ----, on tuffs of Somma, 382.
  ----, on lavas of Vesuvius, 384.

  Dujardin, M., on shells, &c., brought up by artesian well at Tours, 236.

  Dumont, M., cited, 120, 328.

  Dumoulin, M.. on earthquakes in Chili, 453.

  Dunes, hills of blown sand, 305, 307.

  Dunwich destroyed by the sea, 310.

  Durand, Lieut., on fossil quadrumana, 144.

  Dureau de la Malle, M., cited, 584, 593.

  Durham, waste of coast of, 303.

  D'Urville, Capt, on temperature of Mediterranean, 296.


  E.

  Earth, antiquity of the, 21.
  ----, on changes in its axis, 80.
  ----, proportion of land and sea on surface, 125.
  ----, spheroidal form of the, 534.
  ----, mean density of the, 535.
  ----, attempt to calculate thickness of its crust, 536.

  Earth, electric currents in the, 543.
  ----, sections of the (_see_ figs. 70, 71), 539.
  ----, effects produced by powers of vitality on surface, 708.

  Earthquakes, chronologically described, 458, _et seq._
  ----, energy of, probably uniform, 58.
  ----, earth's surface continually remodelled by, 102.
  ----, recurrence of, at stated periods, accidental, 345.
  ----, felt at sea, 358.
  ----, land elevated by, 458, 455, 457, 462.
  ----, all countries liable to slight shocks of, 358.
  ----, phenomena attending, 452.
  ----, in Cutch, 1819 (_see_ Map), 460.
  ----, in Calabria, 1783, 471.
  ----, difficulty of measuring the effects of, 477.
  ----, chasms formed by, 479.
  ----, excavation of valleys aided by, 488.
  ----, renovating effects of, 565.
  ----, cause of the wave-like motion of, 475, 558.
  ----, cause of great waves and retreat of sea during, 496, 498.
  ----, ravages caused by sea during, 499, 501, 730.
  ----, connection between state of atmosphere and, 561.
  ----, people entombed in caverns during, 736.
  ----, causes of volcanoes and, 533.
  ----, recurrence of, in certain zones of country, 172.
  ----, of Lisbon, area over which it extended, 496.
  ----, more frequent in winter, 561.

  Eccles, old church of, buried under blown sand, 306.

  Edmonstone Island, 279.

  Eels, migration of, 647.

  Egypt nearly exempt from earthquakes, 9, 358.

  Egypt, towns buried under drift-sand in, 726.
  ----, date of civilization of, according to Bunsen, 636.

  Egyptian cosmogony, 8.
  ----, mummies identical with living species, 585.

  Ehrenberg, on Bengal tiger in Siberia, 77.
  ----, on origin of bog-iron ore, 722.
  ----, on corals of Red Sea, 777.
  ----, on ashes enveloping Pompeii, 388.
  ----, on infusoria in volcanic tuff, 389.

  Electricity, a source of volcanic heat, 542.
  ----, whence derived, 543.

  Elephant, fossil, in ice, 45, 80.
  ----, covered with hair in Delhi, 81.
  ----, sagacity of, not attributable to intercourse with man, 598.
  ----, their powers of swimming, 636.

  Elevation of land, how caused, 29, 448, 444, 453, 455, 457.
  ----, proofs of, slow and gradual, 170, 184, 518, 563.

  Elevation and subsidence, proportion of, 564.
  ----, alternate areas of, in Pacific, 790.

  Elevation crater theory, 371, 380, 420.

  Elevation, valleys of, 420.

  Elizabeth or Henderson's Island, upraised atoll of, 788, 794.

  Elsa, travertin formed by the, 239.

  Embankment, system of, in Italy, 255.

  Emu in Australia will become exterminated, 684.

  Englehardt on the Caspian Sea, 157.

  England, waste of cliffs on coast of, 303.
  ----, slight earthquakes felt in, 358.
  ----, height of tides on coast of, 291, 308.
  ----, tertiary strata of, 76.

  Eocene period, fossils of the, 142, 144, 183.

  Epomeo, Mount, in Ischia, 362.

  Equatorial current, 95.

  Equinoxes, precession of the, 100, 537.

  Erebus, Mount, the active volcano of, 99.

  Erie, Lake, peninsula cut through by, 333.
  ----, waste of cliffs in, 333.

  Erman, M., on eruptions in Kamschatka, 353.

  Erratic blocks, 122, 154, 220.
  ----, icebergs charged with, 86.

  Erratic blocks, submarine, laid dry by upheaval, 229.

  Eruptions, volcanic, number of per year, 450.
  ----, cause of, 533.

  Erzgebirge, mica slate of the, 48.

  Escher, M., on flood in valley of Bagnes, 211.

  Eschscholtz Bay, fossils of, 82.

  Essex, tertiary strata of, 76.
  ----, inroads of sea on coast of, 311.

  Estuaries, how formed, 327, 337.
  ----, imbedding of freshwater species in, 768.

  Etna, description of and its eruptions, 396 to 424.
  ----, towns overflowed by lava of, 400, 728.
  ----, subterranean caverns on, 401.
  ----, a glacier under lava on, 412.
  ----, marine formations at its base, 401.
  ----, antiquity of cone of, 422.

  Euganean Hills, lavas of, 359.

  Euphrates, delta of advancing rapidly, 284.

  Euxine burst its barrier, according to Strabo, 14.
  ----, gradually filling up, 14.
  ----, _See_ Black Sea.

  Evaporation, water carried off by, 260, 294, 334.
  ----, currents caused by, 294.

  Everest, Rev. E., on climate of fossil elephant, 81.
  ----, on sediment of Ganges, 282.

  Excavation of valleys, 488.

  Expansion of rocks by heat, 560.

  Extinction of species, 697, 701.
  ----, of animals, 700, 702.


  F.

  Fabio Colonna, 23.

  Facial angle, 608.

  Fair Island, action of the sea on, 301.

  Falconer, Dr., on fossil quadrumana, 144.
  ----, on crocodiles of Ganges, 277.

  Falconer, Dr., on peat near Calcutta, 280.

  Falconi on elevation of coast of Baiæ, 367.

  Falkland Islands, quadrupeds of, 141, 635.

  Falloppio on fossils, 21.

  Falls of Niagara, 214.
  ----, of St. Mary, 254.

  Faluns of Touraine, 142.

  Faraday, Mr., on water of the Geysers, 246.
  ----, on slow deposition of sulphate of baryta, 343.
  ----, on electric currents In the earth, 543.
  ----, on metallic reduction by voltaic agency, 548.
  ----, on liquefaction of gases, 560.

  Faroe Islands, deposits forming near the, 774.

  Farquharson, Rev. J., on floods in Scotland, 208.
  ----, on formation of ground ice, 222.

  Faujas, on Velay and Vivarais, 1779, 49.

  Faults, 162.

  Fauna formerly as diversified as now, 160.
  ----, arctic, described by Sir J. Richardson, 634.

  Felspar, decomposition of, 247.

  Ferrara on lavas of Etna, 283.
  ----, on floods on Etna, 412.
  ----, on earthquake in Sicily, 471.

  Ferruginous springs, 247.

  Fez, earthquakes in, 358.

  Fife, trap rocks of, 160.
  ----, coast of, submarine forests on, 303.
  ----, encroachments of sea on, 203.

  Findhorn town swept away by sea, 302.

  Fish, their distribution, and migrations, 646.
  ----, fossil, 745.
  ----, fossil of coal formation, 136.

  Fissures, sulphur, &c., ejected by, 470.
  ----, caused by Calabrian earthquake, 479, 480, 481.
  ----, caused by earthquake near New Madrid, 468.
  ----, preservation of organic remains in, 732.

  Fitton, Dr., on history of English geology, 51.

  Fitzroy, Capt., on earthquake in Chili, 1835, 453, 455.

  Flamborough Head, waste of, 303.

  Fleming, Dr., on uniformity in climate, 74.
  ----, on fossil elephant, 76.
  ----, on submarine forests, 303.
  ----, on rapid flight of birds, 646.
  ----, on turtles taken on coast of England, 645.
  ----, on changes in the animal kingdom caused by man, 683.
  ----, on stranding of cetacea, 771.

  Flinders on coral reefs, 776, 791.

  Flint on course of Mississippi, &c., 264, 265.
  ----, on earthquakes in Mississippi valley, 466.

  Floods, by bursting of lakes, 269.
  ----, in North America, 209.
  ----, in valley of Bagnes, 210.
  ----, in Scotland, 207, 750.
  ----, traditions of, 499, 501.
  ----, causes which may give rise to, 156.
  ----, at Tivoli, 211.
  ----, caused by melting of snow by lava, 348, 411.
  ----, _See_ Deluge.

  Flysch, of the Alps, eocene, 124.

  Folkstone, subsidence of land at, 316.

  Fontenelle, his eulogy on Palissy, 23.

  Foot-marks, fossil, in North America, 136.

  Forbes, Prof. E., on glacial epoch, 86.
  ----, on fossils of tertiary, 184.
  ----, on new island in Gulf of Santorin, 443.
  ----, on regions of depth in Ægean Sea, 649.
  ----, on migration of mollusca, 651.
  ----, cited, 703.

  Forbes, Prof. J. D., on glacier motion, 224.
  ----, on rate of flowing of lava, 378, 400.
  ----, on temple of Serapis, 515, 517.

  Forchhammer, Dr., on boulders drifted by ice, 231.
  ----, on peat, 719.

  Forests, influence of, 712, 713, 715.
  ----, sites of, now covered by peat, 720.
  ----, destroyed by insects, 717.
  ----, submarine, 303, 323, 746.

  Forests, submerged. In Colombia R. by landslides, 215.

  Forfarshire, waste of coast of, 302.
  ----, marl lakes of, 766, 796.

  Forshey, Mr., on Mississippi, 264, 271.

  Forster, Mr., on coral reefs, 778.

  Forsyth on climate of Italy, 395.

  Fortis cited, 42.
  ----, views of Arduino confirmed by, 48.
  ----, and Testa on fossil fish, 44.

  Fort William, near Calcutta, artesian well, 280.

  Fossiliferous formations, breaks in the series, 180.

  Fossilization of organic remains on emerged land, 718, 775.
  ----, in peat mosses, 722.
  ----, In caves and fissures, 732.
  ----, in alluvium and landslips, 730.
  ----, in volcanic formations on land, 349, 728.
  ----, in subaqueous deposits, 742, 753.
  ----, in marl lakes, 752.

  Fossils, early speculations concerning their nature, 19, 24 to 27.
  ----, distinctness of secondary and tertiary, 119.
  ----, mammiferous of tertiary eras, 137, 140.
  ----, why distinct in successive groups, 190.
  ----, _See_ Organic Remains.

  Fossil trees, upright position of some, 91.

  Fourier, Baron, on temperature of spaces surrounding our atmosphere,
    108.
  ----, on central heat, 127.
  ----, on radiation of heat, 127.

  Fox, Mr., on heat in mines, 538.
  ----, on electric currents in the earth, 543.

  France, waste of coast of, 324.
  ----, caves of, 737.

  Franconia, caves of, 736.

  Franklin, on a whirlwind in Maryland, 619.

  Fremont, Capt., on submerged forests in Columbia, 270.

  Freshwater plants and animals fossilized, 766, 768.
  ----, strata in Cashmere, 762.

  Freyberg, school at, 46, 52.

  Fries, on dispersion of cryptogamic plants, 620.

  Fringing reef, nature and origin of, 785.
  ----, upraised, 794.

  Fuchsel, opinions of, 1762, 43.

  Funchal. rise of sea at, during earthquake, 496.

  Fundy, Bay of, wave called the "bore" in, 332.


  G.

  _Gaillonella ferruginea_, 722.

  Galapagos, peculiar character of the fauna of 139, 635, 643.
  ----, island, tameness of birds in, 597.
  ----, Archipelago, craters form hills in, 372.

  Galongoon, great eruption of, 353, 430.

  Gambier coral island, 783, 787.

  Ganges, delta of, and Brahmapootra, 275 to 284.
  ----, antiquity of delta of, 281.
  ----, quantity of sediment in waters of, 278.
  ----, islands formed by the, 276.
  ----, bones of men found in delta of. 757.
  ----, artesian borings in delta of, 268.

  Gardner, Mr., on unexplored Antarctic land, 99.

  Gases, liquefaction of, 560.
  ----, evolved by volcanoes, 549.

  Gefle, upraised shelly deposits near, 526, 528.

  Gemmellaro on Etna, 408.
  ----, on ice under lava, 412.

  Generation, spontaneous, theory of, 22.

  Generelli. on state of geology in Europe in middle of eighteenth
    century, 35, 53.

  Geneva, lake of, delta of Rhone in, 252.

  Geognosy of Werner, 46.

  Geographical distribution of plants, 613.
  ----, of animals, 629.
  ----, of birds, 642.
  ----, of reptiles, 644.
  ----, of fishes, 646.
  ----, of testacea. 649.
  ----, of zoophytes, 653.

  Geographical distribution of insects, 654.
  ----, of man, 659.

  Geography, proofs of former changes in physical, 114,121.
  ----, effect of changes in, on species, 690.

  Geological society of London, 59.
  ----, theories, causes of error in, 61.

  Geology defined, 1.
  ----, distinct from cosmogony, 3.
  ----, causes of its retardation, 24, 55, 61.
  ----, state of, before eighteenth century, 86.
  ----, modern progress of, 58.

  Georgia, Island of, snow to level of sea in, 99, 108.
  ----, U. S., new ravines formed in, 205.

  Gerbanites, an Arabian sect, their doctrines, 14.

  German Ocean, filling up, 340.

  Gesner, John, on organic remains, 41.

  Geysers of Iceland, 533, 553.
  ----, cause of their intermittent action, 555.

  Gibraltar, birds' bones in breccia at, 740.
  ----, Straits of, 383.

  Gironde, tides in its estuary, 338.

  Glacial epoch, 75.

  Glacier under lava, on Etna, 412.
  ----, moraines of, 223.
  ----, view of, 223.

  Glaciers, formation of, 222 to 227.
  ----, motion of, 228.
  ----, of Spitzbergen, 96.
  ----, transportation of rocks by, 155.

  Glen Tilt, granite veins of, 51.

  Gloucestershire, gain of land in, 324.

  Gmelin on distribution of fish, 648.

  Goats, multiplication of, in South America, 686.

  Goeppert, Prof., 87.
  ----, on fossilization of plants, 747.

  Golden age, doctrine whence derived, 9.

  Goodwin Sands, 814.

  Gothenburg, rise of land near, 526.

  Graab, Capt., on subsidence of Greenland, 530.

  Graham, Mrs., on earthquake of Chili in 1822, 459.

  Graham Island, newly formed in 1831, 432.
  ----, supposed section of, 435.

  Granite of the Hartz, Werner on, 47.
  ----, disintegration of, 221, 346.
  ----, formed at different periods, 177.
  ----, veins observed by Hutton in Glen Tilt, 51.

  Grant, Capt., on Chilian earthquake, 462.

  Graves, Capt., on diffusion of insects by winds, 656.
  ----, survey of Santorin by, 441.

  Gray, Mr., on _Mytilus polymorphus_, 658.

  Great Dismal Swamp, Virginia, 724.

  Grecian Archipelago, new isles of the, 43.
  ----, volcanoes of the, 355, 442, 450.

  Greece, earthquakes in, 355.
  ----, traditions of deluges in, 356.

  Greeks, geology of, 13.

  Greenland, why colder than Lapland, 94.
  ----, gradual subsidence of, 530, 562.
  ----, timber drifted to shores of, 745.

  Grevllle, Dr., on drift sea-weed, 623.

  Groins described, 818.

  Grooves in rocks formed by glaciers, 155, 227, 228.

  Grotto del Cane, 248.

  Ground ice, 221.
  ----, transporting rocks in Baltic, 231.

  Guadalonpe, human skeletons of 757.

  Guatemala, active volcanoes in, 349.

  Gulana, partly formed by sediment of Amazon, 342.

  Guilding, Rev. L., on migration of Boa Constrictor, 646.

  Guinea current, 296.

  Guinea, New, mammalia of, 682.

  Gulf stream, 96, 292, 294. 621.
  ----, stream aids migration of fish, 648.

  Guyot, M., on glacier motion, 224.

  Gyrogonite described, 766.


  H.

  Habitations of plants described, 614.

  Hales, Dr., on epoch of the creation, 659.

  Hall, Sir J., his experiments on rocks, 51.
  ----, Captain B., on flood in valley of Bagnes, 211.
  ----, on the trade-winds, 295.
  ----, on temple of Serapis, 512.
  ----, Mr., State Geologist of New York, 216, 218.
  ----, Mr. J., on temple of Serapis, 512.

  Hamilton, Mr. W. J., on volcanoes near Smyrna, 355.
  ----, Sir W., on Herculaneum, 389.
  ----, on earthquake in Calabria, 473, 483, 485.
  ----, Sir W., on formation of Monte Nuovo, 367.
  ----, on eruption of Vesuvius in 1779, 377.

  Hamilton, Sir C., on submerged houses in Port Royal, 504.

  Hampshire, Brander on fossils of, 44.
  ----, submarine forest on coast of, 746.

  Harcourt, Rev. W. V. V., on bones of mammoth, &c.,
    in Yorkshire, 76.

  Harris, Hon. C., on sunk vessel near Poole, 758.
  ----, on submarine forest, Hampshire, 746.

  Hartmann, Dr., on fossils of Hartz, 48.

  Hartz mountains, 48.

  Harwich, waste of cliffs at, 811.

  Hatfleld moss, trees found in, 721.

  Head, Sir Edmund, on temple of Serapis, 512.

  Heat, laws which govern the diffusion of, 93.

  Heat, whether gradual decline of, in globe, 129.
  ----, expansion of rocks by, 561.

  Heber, Bishop, on animals of Himalaya, 81.

  Hecla, columnar basalt of, 48.
  ----, eruptions of, 424.

  Helena, St, bounded by lofty shores, 622.

  Heligoland, inroads of sea on, 329.

  Helix, range of species of, 650.

  Henderson on eruption of Skaptar Jokul, 1783, 425.

  Henderson's Island described, 788.

  Henslow, Rev. Prof., on the cowslip, 590.
  ----, on diffusion of plants, 624.

  Herbert, Hon. Mr., on varieties and hybrids in plants, 590, 605.

  Herculaneum, 385, 389.

  Herne Bay, waste of cliffs in, 312.

  Herodotus cited, 8, 261.

  Herschel, Sir J. F. W, on varying heat received
  by the two hemispheres, 100.
  ----, on astronomical causes of changes in climate, 126.
  ----, on variable splendor of stars, 128.
  ----, on the trade-winds, 297.
  ----, on height of Etna, 396.
  ----, on form of the earth, 534.
  ----, on Geysers of Iceland, 555.
  ----, on the effects of heat on seeds, 621.
  ----, on the author's theory of climate, 92.

  Herschel, Sir W., on the elementary matter of the earth, 533.

  Hewett, Capt, on rise of tides, 291.
  ----, on currents, 293.
  ----, on banks in North Sea, 808, 840.

  Hibbert, Dr., on the Shetland Islands, 299, 300.

  Hilaire, M. Geof. St., on animal kingdom, 567.

  Himalaya mountains, animals inhabiting the, 81.
  ----, height of perpetual snow on, 112.

  Hindoo cosmogony, 4.
  ----, town buried, 731.

  Hindostan, earthquakes in, 494.

  Hippopotamus indicates warmth of river, 75.

  Hitchcock, Report on Geol. of Massachusetts, 137.

  Hoff, Von, on level of Caspian, 18.
  ----, on encroachments of sea, 331, 332.
  ----, on earthquakes, 359.
  ----, on human remains in delta of Ganges, 757.
  ----, on a buried vessel, 758.

  Hoffmann, M., on lavas of Vesuvius, 379.
  ----, on Etna, 415, 416.

  Holland, gradual sinking of coast, 327.
  ----, inroads of sea in, 328.
  ----, submarine peat in, 770.

  Hooke on duration of species, 27, 28.
  ----, on earthquakes, 27, 29, 503.

  Hooker, Dr. J., on Icebergs in antarctic seas, 229.
  ----, on tropical plants, 614.
  ----, floras of islands in Southern Ocean, 615.
  ----, on flora of Galapagos Islands, 616.
  ----, on wide range of certain plants, 618, 621, 623.
  ----, on delta of Ganges, 280.
  ----, on rain in India, 200.

  Hocker, Sir W., on eruption of Skaptar Jokul, 425.
  ----, his view of the crater of the great Geyser, 554.
  ----, on drifting of a fox on ice, 680.

  Hopkins, Mr., on glacier motion, 224, 225.
  ----, on thickness of earth's crust, 536.

  Hopkins, Mr., on astronomical causes of change of climate, 128.
  ----, on changes of climate, 93.
  ----, on earthquakes, 453.
  ----, on M. E. de Beaumont's theory of mountain chains, 170.

  Hordwell, loss of land at, 318.

  Horner, Mr., on brine springs, 247.
  ----, on submarine forest in Somersetshire, 323.
  ----, dissertation on coal, 91.

  Horsburgh, Capt, on icebergs in low latitudes, 99.

  Horsburgh on coral islands, 782, 787.

  Horses drowned in rivers in South America, 750.

  Horsfield, Dr., on earthquakes in Java, 471, 494.
  ----, on distribution of _Mydaus meliceps_ in Java, 639.

  Hubbard, Prof., cited, 210.

  Huc, on Yaks frozen in ice in Thibet, 85.

  Human race geologically modern, 660.

  Human remains in peat mosses, 722.
  ----, in caves, 735, 736, 739.
  ----, their durability, 147, 757.
  ----, in delta of Ganges, 757.
  ----, in calcareous rock at Guadaloupe, 757.
  ----, in breccias in the Morea, 735.

  Humber, warp of the, 288.
  ----, encroachment of sea in its estuary, 304.

  Humboldt on laws regulating diffusion of heat, 93.
  ----, on preservation of animals in frozen mud, 85.
  ----, on distribution of land and sea, 109.
  ----, on transportation of sediment by currents, 342.
  ----, his definition of volcanic action, 345.
  ----, on mud eruptions in the Andes, 348.
  ----, on volcanic eruptions in Tartary, 355.
  ----, on eruption of Jorullo, 428.
  ----, on earthquakes, 466, 470.
  ----, on distribution of species, 613, 614.
  ----, on migrations of animals, 644, 656, 685.
  ----, cited, 8, 77, 84.
  ----, on earthquake in New Madrid, 466.
  ----, on earthquake of Lisbon, 495.
  ----, on mud volcanoes, 448.

  Humboldt, W. von, on dawn of oriental civilization, 659.

  Humming-birds, distribution, &c., 97, 643.

  Hunter, John, on mule animals, 601.

  Huron, Lake, recent strata of, 768.

  Hurricanes connected with earthquakes, 731.
  ----, plants drifted to sea by, 745.

  Hurst Castle shingle bank, 318.

  Hutchinson, John, his "Moses's Principia," 33.

  Hutton, distinguished geology from cosmogony, 3.
  ----, on igneous rocks and granite, 51.
  ----, represented oldest rock as derivatives, 52.

  Huttonian theory, 51, 57.

  Hybrid races, Lamarck on, 572.
  ----, animals, 600.
  ----, plants, 602.

  Hydrogen, deoxidating power of, 547.
  ----, flame of; seen in eruption of Vesuvius, 378.
  ----, why not found in a separate form among volcanic gases, 548.

  Hydrophytes, distribution of, 617, 623.

  Hydrostatic pressure of ascending lava, 416, 553.

  Hypogene rocks, 178.

  Hyracotherium, Eocene mammifer, 142.

  Hythe, encroachments of sea at, 316.


  I.

  _Ianthina fragilis_, its range, &c., 650.

  Ice, animals imbedded in, 83.

  Ice of rivers, transporting power of, 219.
  ----, drift, influence of, on temperature, 95.
  ----, predominance of, in antarctic circle, 98.
  ----, formation of field, 107.
  ----, transportation of rocks by, 155, 219, 521.

  Icebergs, formation of, 96, 97.
  ----, distance to which they float, 100, 227.
  ----, limits of glaciers and, 228.
  ----, plants and animals transported by, 622, 639.
  ----, action of, when stranded, 228.
  ----, rocks transported by. _See_ Ice.
  ----, floating in Northern hemisphere, 86.
  ----, not all formed by glaciers, 228.

  Iceland, icebergs stranded on, 97.
  ----, geysers of, 246, 553, 555.

  Iceland, volcanic eruptions in, 424.
  ----, comparison between the lavas of Central France and, 426.
  ----, new island near, 425.
  ----, polar bear drifted to, 679.

  Igneous action. _See_ Volcanic.

  Igneous causes. _See_ Book II.
  ----, the antagonist power to action of running water, 198, 563, 711.

  Ilford, tertiary strata at, 76.

  Imbedding of organic remains. _See_ Fossilization.

  India, buried cities in, 729, 731.
  ----, terrestrial mammalia of, 632.

  Indo-pacific province of mollusca, 649.

  Indus, delta of. recent changes in, 459, 769.
  ----, buried ships in, 758.

  Infusoria in bog iron-ore, 722.
  ----, in volcanic rocks in Mexico, Peru, &c., 388.

  Infusorial tuff, Pompeii, 388.

  Inland cliffs, no proof of sudden elevation, 531.
  ----, seas, deltas of, 255.

  Insects, geographical distribution of, 654.
  ----, certain types of, distinguish particular countries, 655.
  ----, their agency in preserving an equilibrium of species, 671.
  ----, fossil, 748.

  Instincts, migratory, occasional development of, in animals, 642.
  ----, hereditary, 593, 596.
  ----, modified by domestication, 595.

  Insular climates, description of, 94.

  Inverness-shire, inroads of sea on coast of, 302.

  Irawadi, R., silicified wood of, noticed in 1692, 28.

  Ireland, raised beaches on coast of, 122.
  ----, reptiles of, 645.
  ----, peat of, and fossils in, 719, 720, 724.
  ----, deposits in progress off coast of, 774.

  Iron, melting point of, 539.
  ----, in wood, peat, &c., 722.
  ----, instruments taken up from sea, 760.

  Ischia, hot springs of, 247, 456.
  ----, eruptions and earthquakes in, 360, 365, 456.

  Islands, vegetation of small, 112, 615, 667.
  ----, animals in, 635.
  ----, formed by the Ganges, 276.
  ----, migrations of plants aided by, 622.
  ----, new volcanic, 43, 425, 432, 468.
  ----, coral, 775.
  ----, of driftwood, 640.

  Isle of Purbeck, vertical chalk in, 318.

  Isle of Wight, mammiferous fossils of, 142.
  ----, waste of its shores, 317.

  Isothermal lines, Humboldt on, 95.

  Italian geologists, their priority, 19, 23.
  ----, of the 18th century, 33.

  Italy, tertiary strata of, 64, 74.


  J.

  Jack, Dr., on island of Pulo Nias, 794.

  Jamaica, earthquakes in, 350, 504, 517.
  ----, subsidence in, 504, 517.
  ----, rain diminished in, by felling of forests, 713.
  ----, a town swept away by sea in, 731.

  Java, volcanoes and earthquakes in, 354, 464, 498, 502.
  ----, valley of poison in, 353.
  ----, subsidence of volcano of Papandayang in, 493.
  ----, river-floods in, 503, 748, 751.

  Jones, Sir W., on Institutes of Hindoo law, 5.

  Jorullo, eruption of, 349, 428.

  Juan Fernandez, 357, 453, 499, 686.

  Jukes, Mr., on cliffs in Island of Timor, 794.
  ----, on volcanic islands near Java, 354.
  ----, on coral reef, 784.

  Jura, Saussure on the, 45.

  Jutland, inroads of sea in, 330.


  K.

  Kamtschatka, volcanoes in, 353.
  ----, new island near, 468.

  Kangaroo, extirpation of; to Australia, 684.

  Kashmir. _See_ Cashmere.

  Katavothrons of Greece, breccias formed in, 734.

  Kazwini on changes in position of land and sea, 19.

  Keilhan, Prof., of Christiana, on changes of level in Norway, 529, 531.

  Keith on dispersion of plants, 620.

  Kent, loss of land on coast of, 312.

  Kentucky, caves in limestone, 733.

  Keyserling, Count, on lowland of Siberia, 84.

  Kincardineshire, village in, washed away by sea, 302.

  King, Captain P., on humming birds in Tierra del Fuego, 97, 643.
  ----, on currents in Straits of Magellan, 293.
  ----, on coral reefs, 788.

  King, Mr., on cattle lost in bogs in Ireland, 723.
  ----, on submerged cannon, 759.

  Kinnordy, Loch of, insects in marl in, 748.
  ----, canoe in peat of, 759.

  Kirby, Rev. Mr., on insects, 606, 655, 673, 674.

  Kirwan, his geological Essays, 56.
  ----, on connection of geology and religion, 56.

  Knight, Mr., on varieties of fruit trees, 589.

  König, Mr., on Guadaloupe human skeleton, 757.
  ----, on fossils from Melville Island, 88.

  Koran, cosmogony of the, 17.

  Kotzebue on drifted canoe, 662.

  Kunker, concretionary limestone of Ganges, 280.

  Kurile Isles, active volcanoes in, 353.


  L.

  Labrador, drift-timber of, 745.
  ----, rocks drifted by ice on coast of, 230.

  Laccadive Islands, 782.

  Lagoons, or salt lakes, in delta of Rhone, 259.
  ----, of coral islands, 780.

  Lagullas current, 95.

  Lagunes on coast of Adriatic, 256.

  Lake Erie. _See_ Erie, Lake.
  ----, of Geneva. _See_ Geneva, Lake of.
  ----, Maeler, 524, 528.
  ----, Superior. _See_ Superior, Lake.

  Lakes, filling up of 252.
  ----, formation of; in basin of Mississippi, 466, 269.
  ----, formed by earthquakes, 466, 481, 505.
  ----, crescent-shaped, in plain of Mississippi, 266.
  ----, Canadian, strata forming in, 768.

  Lamarck, his definition of species, 567.
  ----, on transmutation of species, 567, 587, 696, 699.
  ----, on conversion of orang into man, 575.
  ----, on numbers of polyps, 706.

  Lancashire, fossil canoes in, 759.

  Lancerote, eruptions in, 436, 439.

  Land, quantity of, in northern and southern hemispheres, 102, 109, 110.
  ----, upraised at successive periods, 118, 119.
  ----, proofs of existence of, at all periods, 188.
  ----, proportion of sea and, 124.
  ----, elevation of, how caused, 171, 453, 457, 459, 562.

  Landslips, 319, 321, 485, 505.
  ----, imbedding of organic remains by, 732.

  Languedoc, deposits on coast of, 260.

  Laplace on change in the earth's axis, 32.
  ----, on mean depth of Atlantic and Pacific, 104.
  ----, on no contraction of globe, 129.
  ----, on mean density of the earth, 536.

  Lapland, why milder than Greenland, 94.
  ----, migrations of animals in, 637.

  Lateral pressure caused by landslips, 322.
  ----, pressure in Andes and Alps, 171.

  Latham, Dr. R. G., on Natural History of Man, 609.

  Lauder, Sir T. D., on floods in Scotland, 208, 686, 730, 748.

  Lava excavated by rivers, 213.
  ----, effects of decomposition on, 385.
  ----, flowing of, under water, 383.
  ----, hydrostatic pressure of ascending, 552.
  ----, of Iceland and Central France, 426, 427.
  ----, comparative volume of ancient and modern, 161, 427.
  ----, pretended distinction between ancient and modern, 438.
  ----, mineral composition of, 449, 551.
  ----, rate of flowing, 378, 400.

  Lazzaro Moro, _See_ Moro.

  Lehman, treatise of, 1759, 40.

  Leibnitz, theory of, 26.

  Leidy, Dr., on Priscodelphinus, 145.

  Lemings, migrations of, 637.

  Lena, R., fossil bones on banks of, 78, 80.

  Leonardo da Vinci, 19.

  Lewes, human bones in tumulus near, 739.
  ----, estuary recently filled up near, 748, 768.

  Liege, caves near, 737.

  Light, influence of, on plants, 89.

  Lightning, effect of, in Shetland Islands, 299.

  Lignite, conversion of wood into, 759.

  Lima destroyed by earthquake, 501.
  ----, elevated recent marine strata at, 502.

  Lime, whence derived, 796.

  Lincolnshire, inroads of sea on coast of, 304.

  Lindley, Dr., on fossil plants of Melville Islands, 88.
  ----, on number of plants, 705.
  ----, on dispersion of plants, 620.
  ----, on fossil plants of coal, 88, 133.
  ----, cited, 133.

  Linnæus on filling up of Gulf of Bothnia, 521.
  ----, on subsidence of Scania, 530.
  ----, on constancy of species, 568.
  ----, on real existence of genera, 578.
  ----, on diffusion of plants, 624, 626.
  ----, on introduction of species, 665.
  ----, cited, 671.

  Lionnesse tradition in Cornwall, 324.

  Lippi on Herculaneum and Pompeii, 387.

  Lipsius, 12.

  Lisbon, earthquakes at, 358, 495.

  Lister, first proposed geological maps, 26.
  ----, on fossil shells, 26.

  Lloyd, Mr., on levels of Atlantic and Pacific, 294.

  Loa, Mount, volcano of Sandwich Isles, 552.

  Locusts, devastations of, 674.
  ----, bank formed in sea by, 675.

  Loess of the Rhine, 185.
  ----, of the Mississippi valley, 265.

  Loire, tertiary strata of the, 142.

  London, artesian wells near, 234.

  London basin, tertiary deposits of, 121.
  ----, clay, its fossils, 142, 144.

  Lowestoff Ness described, 309.
  ----, cliffs undermined near, 309.

  Lowland of Siberia, 78, 80, 83, 85.

  Luckipour, on the Ganges, 276, 277.
  ----, new islands formed near, 276.

  Luckput, subsidence near, 460.

  Lund, Dr., on fossil quadrumana, 144.

  Lybian sands, caravans overwhelmed by, 727.

  Lyme Regis, waste of cliffs at, 321.

  Lym-Fiord, breaches made by the sea in, 330.


  M.

  MacClelland, Dr., on earthquakes In Chittagong, 494.
  ----, on volcanic line In Bay of Bengal, 354.

  MacCulloch, Dr., on gradation from peat to coal, 719.
  ----, on origin of limestones, 796.

  Macacus pliocenus of Owen, fossil in valley of Thames, 144.
  ----, Suffolk Eocene species, 144.

  Macaluba, in Sicily, mud volcanoes, 447.

  Mackenzie, Sir G., his section of geyser, 556.
  ----, on reindeer in Iceland, 686.

  Mackenzie River, driftwood of, 90, 743.
  ----, floods of, 84.

  Maclaren, Mr. C., on Graham Island, 435.
  ----, on quantity of useful soil in America, 687.
  ----, on position of American forests, 714.
  ----, remarks, theory of atolls, 792.

  Macmurdo, Captain, on earthquake of Cutch, 460.

  Madagascar, extent of coral near, 776.
  ----, assemblage of quadrupeds in, 632.

  Madrid, New, great earthquake at, 466.
  ----, sunk country near it, 270.

  Maeler, lake, 524, 528.

  Magellan, Straits of, tides in, 291, 293.

  Magnesia deposited by springs, 283.

  Magnesian limestone and travertin compared, 240.

  Magnetism, terrestrial, phenomena of, 543.
  ----, solar, 129.

  Mahomet, his cosmogony, 18.

  Malabar, coral near, 776.

  Maldive Islands, coral reefs of, 778, 782.

  Mallet, Captain, on petroleum of Trinidad, 250.

  Mallet, Mr., on the dynamics of earthquakes, 453, 475.
  ----, on whirling motion during earthquakes, 476.
  ----, cited, 560.
  ----, on transit of the earth-wave, 483.
  ----, on theory of waves, 498.

  Mammalia, different regions of indigenous, 629.
  ----, fossil, of successive tertiary periods. 138, 139.
  ----, imbedding of, in subaqueous strata, 749, 753.

  Mammifer, fossil of trias, 137.

  Mammoth, Siberian, 75.
  ----, bones of, in Yorkshire, 76.

  Man, recent origin of, 147, 182, 687, 764.
  ----, why able to live in all climates, 609.
  ----, diffusion of, 657.
  ----, changes caused by, 150, 182, 630, 663, 681, 713.
  ----, durability of the bones of, 147, 757.
  ----, remains of, in osseous breccias of Morea, 735.
  ----, his remains and works fossil, 753.

  Manetho, 63.

  Mantell, Dr., on bones from Saxon tumulus, 788.
  ----, on Lewes levels, 748, 768.

  Map of Siberia, 79.
  ----, of World, showing present unequal distribution of land and sea,
          110.
  ----, showing position of land and sea, which might produce extremes
          of heat and cold, 111.
  ----, of Europe, showing extent of land covered by sea since
          commencement of tertiary period (Pl. I.), 121.

  Map of coast from Nieuport to mouth of Elbe, 326.
  ----, of volcanoes from Philippine Islands to Bengal, 351.
  ----, of volcanic district of Naples, 361.
  ----, of Gulf of Santorin, 442.
  ----, of Chili, 454, 455.
  ----, of Cutch, 460.
  ----, of Calabria, 472.
  ----, of Sweden, 522.

  Maracaybo, Lake, 466.

  Marine deposits, imbedding of land quadrupeds in, 749, 752.
  ----, of human remains and works of art in, 756.
  ----, of freshwater species in, 768.
  ----, plants and animals imbedded in, 770.

  Marine vegetation. 617, 622.

  Marl lakes of Scotland, animals and plants fossilized in, 752, 766.

  Marsili, on arrangement of shells in Adriatic, 36, 38, 40.
  ----, on deposits of coasts of Languedoc, 260.

  Marsupial animals, distribution of, 633.
  ----, fossil, 138.

  Martigny destroyed by floods, 211.

  Martius, on drifting of animals by the Amazon, 641.
  ----, on Brazil, 682.

  Maryland, whirlwind in, 619.

  Mattani on fossils of Volterra, 34.

  Mattioli on organic remains, 21.

  Mauritius, reef uplifted above level of sea, 794.

  Mediterranean, microscopic testacea of, 44.
  ----, deposition of salt in the, 334.
  ----, new island in, 432.
  ----, its temperature, depth, level, &c., 45, 294, 334, 510.
  ----, same level as Red Sea, 294.

  Megna, R., arm of Brahmapootra, 279.

  Melville Island, fossils of, 90.
  ----, migrations of animals into, 640.

  Melville, Dr., on dodo, 684.

  Memphis, in delta of Nile, 261.

  Mendip Hills, caves of, 737.

  Menu's Institutes, 4, 5.

  Mercati on organic remains, 22.

  Mersey, vessel in bed of, 758.

  Messina, tide in Straits of, 290.
  ----, earthquakes at, 477, 488, 490.

  Metallic nucleus, theory of an unoxidated, 545.

  Metallic substances changed by submersion, 759.

  Metamorphic rocks, how formed, 177.
  ----, of the Alps, 178.
  ----, why those visible to us must be very ancient, 178.

  Mexico, Gulf of, tides in, 295.
  ----, currents in, 96, 292.
  ----, volcanoes of, 349, 546.

  Meyen, Dr., on earthquake in Chili, 1822, 458.

  Michell on phenomena of earthquakes, 41.
  ----, on the geology of Yorkshire, 42.
  ----, on earthquake at Lisbon, 358, 497.
  ----, on retreat of the sea during earthquakes, 498.
  ----, on wave-like motion of earthquakes, 558.
  ----, on earthquakes cited, 499.

  Microlestes, triassic mammifer, 138, 145.

  Middendorf, Mr., on Siberian mammoth, 81.

  Migrations of plants, 618.
  ----, of animals, 635, 636.
  ----, of cetacea, 642.
  ----, of birds, 642.
  ----, of fish, 646.
  ----, of zoophytes, 653.
  ----, of insects, 655.

  Migratory powers indispensable to animals, 689.

  Milford Haven, rise of tides at, 291.

  Millennium, 20, 32.

  Mineral waters, their connection with volcanoes, 237.
  ----, ingredients most common in. _See_ Springs, 237.

  Mineralization of plants, 747.

  Mines, heat in, augments with the depth, 538.

  Miocene strata of Suffolk, fossils of, 142.
  ----, proportion of living species in fossil shells of the, 183.

  Mississippi, its course, delta, &c., 268, 275.
  ----, drift-wood of the, 261.
  ----, earthquakes in valley of, 270, 350.
  ----, antiquity of delta of, 272.
  ----, earthquake region of, 467.
  ----, banks higher than swamps, 266.

  Missouri, R., 264.

  Mitchell, Dr., on waste of cliffs, 311.

  Moel Tryfane, recent marine shells on, 122.

  Mollusca. _See_ Testacea.
  ----, provinces of, 649.

  Molluscous animals, longevity of species of, 76.

  Moluccas, eruptions in the, 504.

  Monkeys, fossil, 144.

  Monte Barbaro, description of, 373.
  ----, Bolca, fossil fish of, 44.
  ----, Nuovo, formation of, 369, 518.
  ----, Somma, structure of, 382.

  Monti Rossi on Etna described, 397, 399, 422.

  Montlosier, on Auvergne, 49.

  Moraines of glaciers, 223, 226, 228.

  Morayshire, town in, destroyed by sea, 302.
  ----, effect of floods in, 208, 730.

  Morea, Céramiqne of, 731.
  ----, osseous breccias now forming in the, 734.
  ----, human remains imbedded in, 735.

  Moriot, on subsidence in Adriatic, 257.

  Moro, Lazzaro, his geological views, 34.
  ----, on primary rocks, 52.

  Morocco, earthquakes at, 358.

  Morton, Dr. S. G., on hybrids and species, 601.

  Mountain chains, on the elevation of, 65.
  ----, theory of sudden rise of, 163.

  Moya of the Andes described, 348, 470.

  Mud eruptions in Quito, 1797, 348.
  ----, volcanoes, 447.

  Mules sometimes prolific, 601.

  Murchison, Sir R., on the Hartz mountains, 48.
  ----, on tertiary deposits of the Alps, 119.
  ----, on geography of Siberia, 78, 84, 124.
  ----, map of Russia, 123.
  ----, on depression of Caspian, 157.
  ----, on travertin of Tivoli, 245.
  ----, on tertiary deposits of Alps, 124.

  Muschelkalk, 193.

  _Mydaus meliceps_, 639.

  _Myrmecobius, fasciatus_, 138.

  _Mytilus polymorphus_, 652.


  N.

  Nantucket, banks of, 293.

  Naples, volcanic district round, 361.
  ----, recent tertiary strata near, 74.

  Narwal stranded near Boston, 771.
  ----, fossil near Lewes, 769.

  Nasmyth, Mr., on non-conductibility of dry sand and clay, 418.

  Needles of Isle of Wight, 318.

  Negro physiognomy traced back 3000 years, 660.

  Neill on whales stranded, 771.

  Nelson, Lieut, on coral reefs, 798.

  Neptune, temple of, under water, 516.

  Neptunists and Vulcanists, rival factions of, 50, 55.

  Nerbuddah, river, 705.

  Newbold, Lieut., on mud of Nile, 262.

  Newfoundland cattle mired in bogs of, 723.

  Newhaven, its cliffs undermined, 317.

  New Holland, plants of, 112, 614.
  ----, animals of, 630.
  ----, coral reefs of, 776, 791.

  New Kameni, formation of, 443.

  New Madrid, U. S., earthquakes at, 350, 466.

  New Zealand, animals in, 635.
  ----, tree ferns in, 89.

  Niagara, Falls of, 214.
  ----, their recession, 217, 218.
  ----, height of, 216.

  Niccolini, M., on Temple of Serapis, 518.

  Nicolosi destroyed by earthquake, 399.

  Nile, R., delta of the, 261.
  ----, cities buried under blown sand near the, 726.
  ----, swept away by flood of, 753.

  Nilson, M., on subsidence of Scania, 530.
  ----, on migrations of eels, 648.

  Nitrogen in springs, 710.

  Nomenclature of geology, remarks on, 158.

  Norfolk, waste of cliffs of, 305.
  ----, gain of land on coast of, 308.

  North Cape, drift-wood on, 745.

  Northumberland, land destroyed by sea in, 303.

  Norway free from earthquakes, 531.
  ----, rise of land in, 192, 527, 529.

  Norwich once situated on an arm of the sea, 307.

  Norwich Crag, fossils of, 142.

  Nova Scotia, rise of tides in, 332.

  Nummulitic limestone, 124.

  Nymphs, temple of, under water, 516.

  Nyoe, a new island formed in 1783, 425, 432.


  O.

  Obi, E., fossils on shores of, 81.

  Ocean, permanency of its level, 518.

  Odoardi on tertiary strata of Italy, 42.

  Oersted, discoveries of, 543.

  Ogygian deluge, 349, 356.

  Ohio, junction of, with Mississippi, 264.

  Oldham, Mr., on raised sea beaches in Ireland, 122.

  Old red sandstone formation, fossils of, 135, 193.

  Old red sandstone, reptile in, 135.

  Olivi on fossil remains, 22.

  Omar, an Arabian writer, 17.

  Ontario, Lake, distance from Niagara, 216.

  Oolite, fossils of the, 137.

  Oolitic structure, recent, in Lancerote, &c., 439.

  Orang-outang, change of, to man, 575.

  Orbigny, M. A. de, on Pampean mud, 170.

  Organic remains, controversy as to real nature of, 19.
  ----, imbedding of. _See_ Fossillzation.
  ----, importance of the study of, 60.
  ----, abrupt transition from those of the secondary to those
          of the tertiary rocks, 120.
  ----, _See_ also Fossils.

  Oriental philosophers, 10.

  Oriental cosmogony, 7.

  Orkney Islands, waste of, 301.

  Orleans, New, ground sinking, 268.
  ----, trunks of trees in soil of delta, 268.

  Osseous breccias, 735, 736, 741.

  Otaheite, coral reefs of, 784, 786.

  Oujein, buried Indian city, 729.

  Ouse, R., has filled up an arm of the Sea, 744.

  Ovid cited, 10, 345.

  Owen, Prof., on bones of turtles, 772.
  ----, on the dog and wolf, 584.
  ----, on tertiary mammalia, 142, 144.
  ----, quoted, 184.
  ----, teeth of mammoth, 78.
  ----, on British fossil mammalia and birds, 137.

  Owhyhee, 787.

  Oysters, &c., thrown ashore alive by storm, 773.
  ----, migrations of, 652.


  P.

  Pacific Ocean, depth of, 104.
  ----, its height above the Atlantic, 294.
  ----, subsidence greater than elevation in, 787.
  ----, coral and volcanic islands of, 354, 776, 780, 787.

  Palæotherium of Isle of Wight, 142.

  Palestine shaken by earthquakes, 355.

  Palissy on organic remains, 23.

  Pallas on mountains of Siberia, 45.
  ----, on Caspian Sea, 45.
  ----, on fossil bones of Siberia, 45, 78, 80.
  ----, cited, 333.

  Palmer, Mr., on shingle beaches, 313, 320.

  Palms, rare in carboniferous group, 88.

  Pampas, gradual rise of, 170.

  Panama, tides in Bay of, 295.

  Papandayang, eruption of, 493.
  ----, its cone truncated, 493.

  Papyrus rolls in Herculaneum, 392.

  Paradise, Burnet on seat of, 32.

  Parana, R., animals drifted down on rafts by, 641.
  ----, animals drowned in, 696.

  Paris basin, formations of the, 121.
  ----, fossils of the, 142.

  Parish, Sir W., on inroads of sea during earthquakes, 499, 502.
  ----, on drifting of animals on floating rafts, 641.
  ----, on great droughts in S. America, 696.
  ----, on floods of Parana R., 751.

  Parma, tertiary strata near, 74.

  Paroxysmal energy of ancient causes controverted, 174.

  Parrot, on Caspian Sea, 157.

  Parrots near Cape Horn, 97.

  Parry, Captain, highest northern latitude reached by, 98.
  ----, on migration of polar bear, 640.
  ----, on animals of Melville Island, 640.

  Patagonia, tides on coast of, 291.

  Paviland cave, 737.

  Peat in delta of Ganges, 280.
  ----, on preservation of fossils in, 711, 718, 722.
  ----, distribution of, 719.
  ----, bogs, bursting of, 724.
  ----, submarine, 725.

  Peat of Great Dismal Swamp, Virginia, 724.

  Pembrokeshire, loss of land in, 324.

  Penco destroyed by earthquake, 499.
  ----, elevation near, 500.

  Pennant on waste of Yorkshire coast, 304.
  ----, on migration of animals, 77, 631, 637.

  Pentagonal network of mountain chains, M. E. de Beaumont on, 170.

  Penzance, loss of land near, 323.

  Permian rocks, reptiles in, 136.

  Péron on distribution of species, 647.

  Perrey, M. Alexis, on frequency of earthquakes in winter, 561.

  Persian Gulf, coral in, 776.

  Peru, volcanoes in, 347.
  ----, earthquakes in, 347, 501.

  Peruvian tradition of a great flood, 8, 502.

  Peterhead, whale stranded near, 771.

  _Phascolotherium Bucklandi_, 139.

  Philippi, Dr. A., on fossil tertiary shells of Sicily, 183.

  Phillips, Mr. J., on waste of Yorkshire coast, 304.

  Phlegræan fields, volcanoes of, 373.

  Physical Geography. _See_ Geography.

  Pietra Mala, inflammable gas of, 11.

  Pigs, instincts of, 595.
  ----, swim to great distances, 635.
  ----, fossil, 723.

  Pilla, M., on Monte Somma, 382.

  Pindar cited, 398.

  Pingel, Dr., on subsidence of Greenland, 530.

  Pisolitic limestone of France, 120.

  Pitch lake of Trinidad, 250.

  Plants, carboniferous, wide geographical range, 160.
  ----, varieties in, produced by horticulture, 588.
  ----, extent of variation in, 589.
  ----, their geographical distribution, 97, 112, 613.
  ----, dispersion of, 618.
  ----, stations of, 614, 669.
  ----, equilibrium among, kept up by insects, 672.
  ----, number of terrestrial, 705.
  ----, imbedding of, in subaqueous deposits, 742, 765, 770.
  ----, on number which are now becoming fossil, 745.
  ----, mineralization of, 747.

  Plants, fossil, of the coal strata, 87, 115, 133.

  Plastic clay fossils, 142.

  Plastic force, fossil shell ascribed to, 20.

  Playfair on Huttonian theory, 53, 57.
  ----, on instability of the earth's surface, 212.
  ----, on gradual rise of Sweden, 523.
  ----, on form of the earth, 534.

  Plieninger, Professor, on triassic mammifer, 137.

  Pliny the Elder, 16.
  ----, on delta of Rhone, 258.
  ----, on Islands at the mouth of the Texel, 329..
  ----, killed by eruption of Vesuvius, A. D. 79, 364.

  Pliny the Younger, on Vesuvius, 364.

  Pliocene strata, fossils of, 143.

  Plot on organic remains, 26.

  Pluche, theory of, 1732, 83.

  Plutonic rocks, how formed, 161.
  ----, action, changes produced by, 176, 178.

  Po, R., 207.
  ----, frequently shifts to course, 255.
  ----, embankment of the, 256.
  ----, delta of the, 256, 284.
  ----, subsidence in delta of, 257.

  Poisson, M., on astronomical causes of changes in climate, 127.

  Polyps. _See_ Zoophytes.

  Pomerania, fossil ships in, 758.

  Pompeii, how destroyed, 365, 385, 387.
  ----, section of the mass enveloping, 386.
  ----, objects preserved in, 390.
  ----, infusorial beds covering it, 388.

  Pont Gibaud, gneiss decomposed at, 248.
  ----, calcareous springs near, 239.

  Poole Bay cut into by sea, 319.

  Popayan, volcanoes and earthquakes in, 349.

  Portland, fossil ammonites of, 28.
  ----, its peninsula wasting. 319.

  Port Royal, subsidence of, 504, 517, 691, 762.

  Porto Praya, Azores, calcareous stratum, 436.

  Portugal, earthquakes in, 358.

  Porzio on formation of Monte Nuovo, 369, 371.

  Post-tertiary formations, 184.

  Precession of the equinoxes, 100, 537.

  Prentice, Lieut, on coral reef in Maldives, 778.

  Pressure, effects of, 171.

  Prestwich, Mr., on artesian wells, 234.

  Prevost Const., on Stonefield fossil mammalia, 138.
  ----, Const., on gypseous springs, 245.
  ----, on rents formed by upheaval, 371.
  ----, on new island in Mediterranean, 433.
  ----, on geological causes, 718.
  ----, on osseous breccias of caves, 736.

  Prevost, Pierre, on radiation of heat, 93.

  Prevost, Mr. J. L., on number of wrecked vessels, 756.

  Primary fossiliferous rocks, fossils of, 114.

  Priscodelphinus, cetacean, of chalk, 145.

  Pritchard, Dr., on Egyptian cosmogony, 8.
  ----, on recent origin of man, 147.
  ----, on hybrid races, 602.
  ----, on facial angle, 608.
  ----, on distribution of animals, 629, 631.

  Procida, island of, ancient writers on, 360.

  Progressive development, theory of, 130-153.
  ----, in animals, Lamarck's theory of, 567.

  Provinces, geographical, of Testacea, 649.

  Provinces, zoological and land quadrupeds, 631.

  Pterodactyles, 137.

  Pulo Nias, upraised coral in, 794.

  Purbeck, its peninsula wasting, 319.

  Pursh on plants of United States, 614.

  Puzzuoli, Temple of Serapis near, 507.
  ----, inland cliffs near, 508, 510.
  ----, date of re-elevation of coast of, 515, 518.
  ----, encroachment of sea near, 515.
  ----, coast near, now subsiding, 516.

  Pyrenees, their relative age, height, &c., 120, 166.

  Pythagoras, system of, 10.
  ----, on Etna, 345.


  Q.

  Quadrumana, fossil, 144.

  Quadrupeds, domestic, multiply in America, 584, 685.
  ----, regions of indigenous, 630, 636.
  ----, imbedding of terrestrial, 749.

  Quaggas, migrations of, 638.

  Quebec, climate of, 95.
  ----, earthquakes in, 470.

  Queenstown, Canada, table land terminates at, 216.

  Quintero elevated by earthquake of 1822, 457.

  Quiriui, theory of, 25.

  Quito, earthquakes and volcanoes in, 346, 348, 469.


  R.

  Rabenstein cave, 736.

  Race of Alderney, its velocity, 293.

  "Races," tidal currents so called, 341.

  Raffles, Sir S., cited, 465, 599.

  Rafts, drift-timber in Mississippi, &c., 267.

  Rain, action of, 713.
  ----, diminished by felling of forests, 713.
  ----, fall of, in basin of Ganges, 278.
  ----, Huttonian theory of, 199.
  ----, fall of, varying with latitude, 199.
  ----, fall of, in Eastern Bengal, 200.

  Rain-prints, recent, on mud in Nova Scotia, 202.

  Raised beaches, 184.

  Ramree, volcanic island, 354.

  Raspe on islands shifting their position (note), 11.
  ----, his theory, 1763, 42, 43, 48.

  Rats, migrations of, 637.
  ----, introduced by man into America, 663, 686.

  Rawlinson, Col., on delta of Tigris, 285.

  Ray, his physico-theology, &c., 30, 31.
  ----, cited, 645, 683.

  Reaumur on insects, 674.

  Reculver cliff; action of sea on, 312.

  Rocupero on flowing of lava, 401.

  Red Crag, fossils of, 142.

  Redman, J. B., on changes of English coast, 315, 316, 319.

  Red marl, supposed universality of, 158.

  Red River, new lakes formed by, 269.
  ----, drift-wood in, 267.
  ----, and Mississippi, their junction recent, 264, 284.

  Red Sea, level of, and of Mediterranean, 294.
  ----, coral reefs of, 777, 784.

  Reefs, coral, outline destroyed by denudation, 795.

  Refrigeration, Leibnitz's theory of, 26.
  ----, causes which might produce the extreme of, 106.

  Reid, Col., on motion of shingle beaches, 320.

  Rein-deer, geographical range of, 637.
  ----, migrations of, 640.
  ----, imported into Iceland, 686.

  Rennel, Major, on delta of Ganges, 275.
  ----, on delta of Nile, 261.
  ----, on currents, 95, 97, 291, 292, 293.
  ----, on the tide-wave called "the Bore," 333.

  Rennel, Mr., on delta of Ganges, 275.

  Rennie, Rev. Dr., on peat, and fossils in peat, 718, 719, 720, 722.

  Reptiles, their geographical distribution, 645.
  ----, their powers of diffusion, 645.
  ----, in carboniferous epoch, 136.
  ----, in Ireland, 645.
  ----, imbedded in subaqueous strata, 748, 771.
  ----, fossil, in old red sandstone, 135.
  ----, in coal, 136.

  Rhine, R., description, of its course, 325.
  ----, its delta, 326.
  ----, tuff made of siliceous cases of infusoria, 388.

  Rhinoceros, fossil, food of, 80.

  Rhone, delta of, in Mediterranean, 258.
  ----, delta of, in Lake of Geneva, 189, 252, 286.
  ----, deposits at its confluence with the Arve, 288.

  Rhone, a cannon in calcareous rock in its delta, 759.

  Richardson, Sir J., on rocks near Mackenzie River, 115.
  ----, on sheep of Rocky Mountains, 598.
  ----, on distribution of animals, 640, 645.
  ----, on drift timber, in Slave Lake, 743.
  ----, on arctic fauna, 634.
  ----, on diffusion of fish, 647.
  ----, on isothermal lines, 94.

  Richardson, Mr. W., on Herne Bay, 312.

  Riddell, Dr., on sediment of Mississippi, 273.

  Rive, M. de la, on terrestrial magnetism, 543.

  River-ice, carrying power of, 219.

  Rivers, difference in the sediment of, 189, 258.
  ----, sinuosities of, 205.
  ----, submarine, in Thessaly, &c., 357.
  ----, when confluent, do not occupy bed of proportionally larger
          surface, 207.

  Robert, M., on geysers of Iceland, 246.

  Robertson, Capt., on mud volcanoes, 449.

  Rockhall bank, recent deposits on, 778.

  Rocks, specific gravity of, 206.
  ----, difference in texture of older and newer, 175.
  ----, altered by subterranean gases, 248.
  ----, origin of the primary, 176.
  ----, persistency of mineral character in, 157.
  ----, older, why most solid and disturbed, 162.
  ----, action of frost on, 221, 231.
  ----, transportation of, by ice, 155, 219.
  ----, grooved by glacial action, 155, 227, 229.

  Rogers, Prof., on Appalachian chain, 559.

  Roman roads under water in Bay of Baiæ, 517.

  Romney Marsh, gained from sea, 316.

  Rose, M. G., on hornblende and augite, 449.

  Ross, Sir J., on cold of antarctic regions, 99.
  ----, obtained soundings at depth of 27,600 feet, 104.
  ----, confirms Cook as to antarctic ice, 125.
  ----, on icebergs, 98, 229.

  Rossberg, slide of the, 732.

  Rotation of the earth, currents caused by, 296.
  ----, of crops, 670, 720.

  Rother, River, vessel found in its old bed, 316, 758.

  Royle, Mr., 81.

  Runn of Cutch described, 463.

  Rye formerly destroyed by sea, 316.


  S.

  Saarbuck, reptiles in coal strata at, 136.

  Sabine, Capt., on well at Chiswick, 234.
  ----, on waters of Amazon discoloring the sea, 342.

  Sabine, Col., on solar magnetic period, 129, 544.

  Sabrina, island of, 432.

  Saco, R., flood on, 209.

  Sahrunpore, buried town near, 731.

  St. Andrew's, loss of land at, 303.
  ----, gun-barrel, fossil, near, 760.

  St. Domingo, hot springs caused by earthquake in, 494.
  ----, fossil human skeleton in, 758.

  St. Helena, tides at, 291.

  St. Jago, earthquake at, 457.

  St. Katherine's Docks, a fossil vessel found in, 758.

  St. Lawrence, Gulf of, earthquakes in, 470.
  ----, rocks drifted by ice in the, 220.

  St. Maura, earthquakes in, 474.

  St. Michael, siliceous springs of, 246.

  St. Michael's Mount, 323.

  St. Paul, volcanic island, 446.

  St. Vincent's, volcanoes of, 466.
  ----, counter-currents in the air proved by eruption in, 106.
  ----, boa constrictor conveyed on drift-wood to, 646.

  Salt, on its deposition in the Mediterranean, 334.

  Salt springs 18, 247.

  Saltholm, island of, 520.

  Samothracian deluge, 356.

  Sand bars along western coast of Adriatic, 257.
  ----, drift, estuaries blocked up by, 307.

  Sand, imbedding of towns, &c. in, 726.
  ----, cones of thrown up during earthquake, 483.

  Sandown Bay, excavated by sea, 318.

  Sandwich Islands volcanoes, 354, 372, 383, 429, 548, 552.

  Sandwich Land, perpetual snow to level of sea-beach in, 99.

  San Filippo, travertin of, 241.

  San Lio, on Etna, fissures in plain of, 399.

  Santa Maria, island of, raised 10 feet, 455.

  Santorin, geological structure of, 445.
  ----, chart and section of, 442.
  ----, new islands in Gulf of, 441.

  Saracens, learning of the, 17.

  Saussure on the Alps and Jura, 45.
  ----, on glaciers in Alps, 223.

  Savanna la Mar, swept away by sea, 731.

  _Saxicava rugosa_, cosmopolite shell, 650.

  Scandinavia called an island by the ancients, 520.
  ----, gradual rise of, 520, 563.
  ----, _See_ Sweden.

  Scania, gradual subsidence of, 530.

  Scacchi, Sig., on temple of Serapis, 516.
  ----, on origin of Monte Nuovo, 371.

  Scheuchzer, his theory, 1708, 33.

  Schmerling, Dr., on fossils in caves, 737.

  Schwabe, M., on spots in the sun, 129, 544.

  Sciacca, island of. _See_ Graham Island.

  Scilla on organic remains, 1670, 24.

  Scilla, rock of, 488.

  Scoresby, Capt, on the Gulf stream, 96.
  ----, on formation of field ice, 108.
  ----, on weight of rocks transported by icebergs, 227.
  ----, cited, 640, 743.

  Scotland, floods in, 207, 750.
  ----, colder climate indicated by newest tertiary strata of, 125.
  ----, waste of islands and coast of, 298.
  ----, slight earthquakes felt in, 358.
  ----, peat-mosses of, 720, 723.
  ----, marl lakes of, 752, 766, 770.

  Scrope, Mr. G. P., on eruption of Vesuvius in 1822, 375.
  ----, on columnar basalts of Vesuvius, 385.
  ----, on pisolitic globules at Pompeii, 387.
  ----, on eruptions of Etna, 408, 410.
  ----, on cause of convexity of plain of Malpais, 429.
  ----, on connection between state of atmosphere and earthquakes, 561.

  Sea does not change its level, but land, 15.
  ----, its influence on climate, 97.
  ----, area covered by, 124.
  ----, its encroachments on coasts, 298, 302, 324.
  ----, its rise and retreat during earthquakes, 407.

  Sea-beaches, raised, in Ireland, 122.
  ----, progressive motion of, 316.

  Seals, migration of, 642.

  Sea-weed, banks formed by drift, 622, 770.

  Secondary rocks, fossils of the, 86.
  ----, origin of the, 117.

  Sedgwick, Professor, on the Hartz mountains, 48.
  ----, on tertiary deposits of the Alps, 119.
  ----, on the antagonist power of vegetation, 711.
  ----, on organic remains in fissures, 740.
  ----, on diluvial waves, 423.

  Sediment of the Mississippi, 272.
  ----, laws governing deposition o£ 188, 842.
  ----, in river water, 270.
  ----, of Ganges compared to lavas of Etna, 283.
  ----, rate of subsidence of some kinds of, 342.
  ----, area over which it may be transported by currents, 343.

  Sedimentary deposition, causes which occasion a shifting of the areas
    of, 189.

  Seeds, vitality of, 587.
  ----, of Leguminosæ adapted for water-carriage, 622.

  Serapis, temple of, 507.
  ----, ground-plan of environs of, 507.
  ----, date of its re-elevation, 512.
  ----, now again subsiding, 516.
  ----, worship of, in Italy, 512.

  Serres, E. R. A., on changes in brain of foetus, 609.

  Serres, E. Marcel de, on fossil human remains, 738.

  Severn, tides in estuary of, 291.
  ----, gain of land in its estuary, 324.

  Shakspeare's cliff, waste of, 314.

  "Shambles," a shoal off Portland Bill, 32.

  Sharpe, Mr. D., on earthquake of Lisbon, 496.

  Sheep, multiplication of, in South America, 686.

  Shell marl, fossils in, 752, 766, 769.

  Shells, fossil of older strata buried in newer or recent beds, 775.
    _See_ Testacea.

  Sheppey, waste of cliffs, 312.

  Shetland Islands, action of the sea on, 298.
  ----, rock masses drifted by sea in, 298.
  ----, effect of lightning on rocks in, 299.
  ----, formation in progress near, 774.

  Shingle beaches, 318, 320.

  Ships, number of British, wrecked annually, 754, 755.
  ----, fossil, 316, 725, 758.

  Siberia, rhinoceros entire in frozen soil of, 45, 82.
  ----, map of, 79.
  ----, the Bengal tiger found in, 78.
  ----, lowland of, 78, 83, 85.
  ----, drift timber on coast of, 745.

  Siberian lowlands, climate of, 83.
  ----, mammoths, 80.

  Sicily, earthquakes in, 357, 470, 477, 479, 503, 736.
  ----, geological structure of, 74, 167, 183.
  ----, mud volcanoes of, 447.

  Sienna, fossil shells of, 39, 74.

  Sigillariæ, structure of, 88.

  Silex, deposited by springs, 246.

  Silliman, Professor, cited, 759.

  Silurian rocks, wide range of the fossils, 160.
  ----, fauna, no land or freshwater plants in, 134.
  ----, horizontal, 187.
  ----, altered, 177.
  ----, strata formed in deep seas, 117.

  Simeto, R., lava excavated by, 213.

  Sindree, changes caused by earthquakes of 1819, near, 461, 464, 761.
  ----, view of the fort of, before the earthquake (_see_ Pl. xi.),
          461.
  ----, its appearance in 1838, 463.

  Skaptâr Jokul, eruption of, 425.

  Slave Lake, drift timber in, 743.

  Sleswick, waste of coast of, 330, 694.

  Sligo, bursting of a peat-moss in, 724.

  Sloane, Sir H., on earthquake in Jamaica, 505.
  ----, on dispersion of plants, 621.

  Smith, William, agreement of his system with Werner's, 48.
  ----, his "Tabular View of the British Strata," 1790, 58.
  ----, his map of England, 58.
  ----, priority of his arrangement, 58.

  Smith, Mr., of Jordan Hill, on the colder climate of newest tertiary
    period, 126.
  ----, on temple of Serapis, 516.

  Smyrna, volcanic country round, 355.

  Smyth, Capt. W. H., on the Mediterranean, 45, 259, 296, 511.
  ----, on height Of Etna, 396.
  ----, on Straits of Gibraltar, 333, 336.
  ----, on depth of sea from which Graham Island rose, 432.
  ----, on floating islands of drift-wood, 641.
  ----, on drifting of birds by the wind, 645.
  ----, on diffusion of insects, 657.
  ----, on average number of British ships lost, from 1793 to 1829,
            755.
  ----, found shells at great depths between Gibraltar and Ceuta, 773.

  Snow, height of perpetual, in the Andes, 112.
  ----, in Himalaya mountains, 112.
  ----, lowest limits of perpetual, at equator, 222.
  ----, lowest limits of perpetual, at Swiss Alps, 222.

  Sodertelje, buried hut in canal of, 524, 528.

  Soil, its influence on plants, 590.

  Soils, on formation of, 709.
  ----, influence of plants on, 670.

  Soldani, on microscopic shells of Mediterranean, 44.
  ----, on the Paris basin, 44.

  Solent, its channel widening, 318.

  Solfatara, lake of, 243.
  ----, volcano, 358, 363, 367, 385.

  Solitaire, recently extinct bird, 684.

  Solway Moss, 723.

  Solway Firth, animals washed by river floods into, 760.

  Somersetshire, land gained in, 324.
  ----, submarine forest on coast of, 323.

  Somerville, Mrs., on depth of ocean, 104.

  Somma, escarpment of, 381.
  ----, dikes of, 382.
  ----, supposed section of Vesuvius and, 381.

  Sorbonne, College of the, 39.

  Sorting power of water, 287.

  South Carolina, earthquake in, 466.

  South Downs, waste of plastic clay on, 317.

  Spain, earthquakes in, 358.

  Spallanzani on effects of heat on seeds, 621.
  ----, on flight of birds, 644.

  Species, definition of the term, 567.
  ----, Linnæus on constancy of, 568.
  ----, Lamarck's theory of transmutation of, 567, 580, 699.
  ----, reality of, in nature, 583, 591, 592, 611.
  ----, geographical distribution of, 612.
  ----, theories respecting their origin, 666, 703.
  ----, Brocchi on extinction of, 668.
  ----, reciprocal influence of aquatic and terrestrial, 676.
  ----, their successive creation and extinction, 678, 689, 707.
  ----, effect of changes in geography, climate, &c., on their
          distribution, 105, 690, 697.
  ----, superior longevity of molluscous, 76.

  Specific centres, doctrine of, 630.

  Spence, Mr., on insects, cited, 606, 655, 673.

  Spitzbergen, glaciers of, 96.

  Spix, M., on animals drifted by Amazon, 641.
  ----, on Brazil, 682.

  Spontaneous generation, theory of, 22.

  Springs, origin of, 232.
  ----, the theory of, illustrated by bored wells, 233.
  ----, most abundant in volcanic regions, 237.
  ----, affected by earthquake, 237, 453, 456, 483, 494.
  ----, transporting power of, 238.
  ----, calcareous, 239.
  ----, sulphureous and gypseous, 245.
  ----, siliceous, 246.
  ----, ferruginous, 249.
  ----, brine, 247.
  ----, carbonated, 248.
  ----, petroleum, 250.

  Squirrels, migrations of, 637.

  Stabiæ, buried city of, 394.

  Stalagmite alternating with alluvium in caves, 737.

  Stars, variable splendor of, 128.

  Statical figure of the earth, 534, 544.

  Stations of plants, description of, 614.
  ----, of animals, 677.

  Stelluti on organic remains, 23.

  Steno, opinions of, 23.

  Stephenson on eruption in Iceland, 425.

  Stephenson, Mr. R., on level of Red Sea and Mediterranean, 294.

  Stevenson, Mr., on drift stones on Bell-Rock, 302.
  ----, on the German Ocean, 315, 340.
  ----, on waste of cliffs, 324.

  Stockholm, rise of land near, 526, 527.

  Stokes, Mr., on mineralization of plants, 747.

  Stonesfleld, fossils of, 138, 145.

  Storm of November, 1824, effect of, 317, 318, 320.

  Strabo cited, 14, 260, 355, 361.
  ----, geology of, 14.

  Strachey, Capt, R., on delta of Ganges, 283.

  Straits of Dover, formation of, 315.
  ----, their depth, 315.

  Straits of Gibraltar, currents in, &c., 333, 335.

  Strata, laws governing deposition of, 188.
  ----, slow deposition of, proved by fossils, 154.
  ----, on consolidation of, 175.

  Stratifications in deltas, causes of, 287.
  ----, of debris deposited by currents, 288.
  ----, unconformable, inferences derived from, 187.

  Strabo, hypothesis of, 14.

  Strickland, Mr., on tertiary strata, Cropthorn, 76.
  ----, on dodo, 684.

  Stromboli, its appearance during Calabrlan earthquakes, 488.
  ----, constancy in eruption, 546, 561.

  Stufas, jets of steam in volcanic regions, 237, 546.

  Stutchbury, Mr., on coral islands, 778, 782.

  Subapennine strata, 74.
  ----, early Italian geologists on, 42, 71.

  Submarine forests, 303, 323, 746.
  ----, peat, 724, 770.
  ----, rivers, 357.
  ----, volcanoes, 431, 454.
  ----, eruptions in mid Atlantic, 436.

  Subsidence of land, 460, 465, 470, 477, 495, 503, 504, 507, 691, 761,
    762.
  ----, great areas of, 170, 790.
  ----, greater than elevation, 563, 787.
  ----, simultaneous in Miocene epoch, 192.
  ----, of land, delta of Mississippi, 271.
  ----, of coral islands, slow and uniform, 791.

  Subterranean movements, uniformity of, 186.
  ----, movements near New Madrid, 1811-12, 270.

  Suffolk, cliffs undermined, 309.
  ----, tertiary strata of, 142.

  Sulphuric acid, lake of, in Java, 353.

  Sulphureous springs, 245.

  Sumatra, volcanoes in, 354.
  ----, animals destroyed by river floods in, 751.

  Sumbawa, subsidence in island of, 1815, 464, 762.
  ----, ashes, transported to great distances by eruptions of, 106.

  Sun, variations in spots of, 129.

  Sunda, Isles of, volcanic region of, 350.

  Sunderbunds, part of delta of Ganges, 276.

  "Sunk country," west of New Madrid in U. S., 467.

  Superior, Lake, deltas of, 254.
  ----, recent deposits in, 254, 768.
  ----, its depth, extent, &c., 254.
  ----, bursting of, would cause a flood, 156.

  Sussex, waste of its coast, 317.

  Sutlej, R., fossils near, 6.

  Swanage Bay, excavated by sea, 318.

  Sweden, gradual rise of, 520, 563.
  ----, gradual subsidence of south of, 530.
  ----, earthquakes in, 531.
  ----, land rising, 192.
  ----, _See_ also Scandinavia.

  Switzerland, towns destroyed by landslips in, 732.

  Syria, earthquakes in, 355, 453.


  T.

  Tacitus cited, 364.

  Tagliamento, R., delta of the, 258.

  Targioni, on geology of Tuscany, 40.

  Tartary, volcanoes in, 355.

  Taxodium distichum in Great Dismal Swamp, 725.

  Tay, estuary of, encroachment of sea in, 302.
  ----, submarine forests in, 303.

  Taylor, Mr. R. C., on waste of cliff's, 306.
  ----, on gain of land on coast of Norfolk, 308.
  ----, on caves in isle of Cuba, 741.

  Tchihatchoff, M., map of Italy, 123.

  Teissier, M., on human bones in caves, &c., 739.

  Temperature, great changes in, 92.
  ----, difference of, in places in same latitudes, 95.
  ----, warmer in tertiary periods, 75.
  ----, oscillation of, 125.
  ----, _See_ Climate.

  Temples, buried, in Egypt, 726.
  ----, under water in Bay of Baiæ, 518.
  ----, buried in Cashmere, 762.

  Teneriffe, volcanic eruptions in, 439.

  Terra del Fuego, fauna of, 141.

  Terranuova, subsidence near, 470.
  ----, fault in the tower of, 478.
  ----, landslips near, 485.

  Tertiary formations, general remarks on, 141, 182, 183.
  ----, geographical changes implied by, 118.
  ----, glacial in Scotland, 126.
  ----, origin of successive periods, 182.
  ----, circumstances under which these and the secondary formations
          may have originated, 117, 118.
  ----, fossils of the newest, 183.
  ----, fossil mammals of successive, 142.
  ----, formations of England, 76, 142.
  ----, of the Paris basin, 142.
  ----, deposits, climate of warmer, 86.

  Testacea, their geographical distribution, 649.
  ----, fossil, importance of, 183.
  ----, marine, imbedding of, 768.
  ----, freshwater, 770.
  ----, burrowing, 773.
  ----, longevity of species of, 76.
  ----, number of recent, in different tertiary periods, 142, 183.

  Texel, waste of islands near the, 328.

  Thames, valley of, tertiary strata in, 76.
  ----, gain and loss of land in its estuary, 312.
  ----, tide in its estuary, 338.
  ----, buried vessels in alluvial plain of the, 758.

  Thanet, Isle of, loss of land in, 313.

  Thermo-electricity, 543.

  Thibet, yak or wild ox of, in ice, 85.

  Thomson, Dr. T., on Western Himalaya and Thibet, 763.
  ----, on buried temples in Cashmere, 763.

  Thrace subject to earthquakes, 355.

  Thury, M. Hericart de, on artesian wells, 234, 236.

  _Thylacotherium Prevostii_, 138.

  Tiber, growth of its delta, 243.

  Tide wave of the Atlantic, 308.

  Tides, height to which they rise, 279, 290.
  ----, effect of winds on the, 295.
  ----, effects of, on wells near London, 233.
  ----, their destroying and transporting power, 291.
  ----, their reproductive effects, 337.
  ----, and currents, drifting remains of animals by, 753.

  Tiedemann on changes in brain of foetus, 609.

  Tiger of Bengal found in Siberia, 77.

  Tigris and Euphrates, their union a modern event, 284.

  Tigris, river, delta of, advancing, 284.

  Tilesius on Siberian mammoth, 81.

  Time, prepossessions in regard to the duration of past, 62.

  Tivoli, flood at, 211.
  ----, travertin of, 244.

  Tomboro, volcano, eruption of, 465.
  ----, town of, submerged, 465.

  Torre del Greco overflowed by lava, 394.
  ----, columnar lavas of, 384.

  Torrents, action of, in widening valleys, 204.

  Torres' Strait, volcano of, 792.

  Totten, Col., on expansion of rocks by heat, 562.

  Tournal, M., on French caves, 738, 739.

  Towns destroyed by landslips, 732.

  Trade-winds, 106, 295.

  Traditions of losses of land, 324, 327.
  ----, of floods, 500, 501.

  Transition texture, 176.
  ----, formations, 177.

  Trap rocks of many different ages, 160.

  Travertin of the Elsa, 239.
  ----, of San Vignone, 240.
  ----, of San Filippo, 241.
  ----, spheroidal structure of, 242.
  ----, compared to English magnesian limestone, 243.
  ----, of Tivoli, 244.

  Travertin politic, recent, in Lancerote, 439.

  Tree-ferns, distribution of, 88.

  Tree-ferns, extend more south than north of equator, 86.

  Trees, longevity of, 422.

  Trias, fossil mammifer of, 137.

  Trimmer, Mr., on recent marine shells in Wales, 122.

  Trinidad, subsidence in, 250.
  ----, pitch lake of, 250.

  Tripergola, 370, 371, 395.

  Tripolitza, plain of, breccias in, 734.

  Trollhattan, 527.

  Truncation of volcanic cones, 352, 493.

  Tufa. _See_ Travertin.

  Tuff, infusorial, 388.

  Turner, Dr., on decomposition of felspar, 247.

  Turtles, migrations of, 645.
  ----, eggs of, fossil, 771.

  Turton cited, 646.

  Tuscany, geology of, 23, 40.
  ----, calcareous springs of, 239.

  Tyrol, Dolomieu on the, 49.


  U.

  Uddevalla, upraised deposits at, 184, 527.

  Uliah Bund, formation of the, 462.

  Ulloa cited, 501, 502, 685.

  Unconformable strata, inferences derived from, 187.

  Uniformity of laws of nature, 71, 149, 373.
  ----, of system of past changes in animate and inanimate world, 181.

  Universal formations, theory of, 49, 154.

  Universal ocean, theory of, 26, 34.
  ----, disproved by organic remains, 191.

  Upsala, strata near, 528.


  V.

  Val d'Arno, Upper, effect of destruction of forests in, 712.

  Val del Bove on Etna described, 403.
  ----, form, composition, and origin of dikes in, 406.
  ----, lavas and breccias of the, 411.
  ----, origin of the, 413.
  ----, floods in, 411.

  Val di Calanna, 405, 407, 410.

  Val di Noto, Dolomieu on the, 49.

  Valdivia, earthquake at, 453.

  Valenciennes, M., on fish not crossing the Atlantic, 647.

  Valley, newly formed in Georgia, U. S., 205.

  Valleys, Targioni on origin of, 40.
  ----, excavation of, in Central France, 213.
  ----, of elevation, section of, 420.
  ----, on Etna, account of, 404.
  ----, the excavation of, assisted by earthquakes, 484.

  Vallisneri on the origin of springs, 33.
  ----, on marine deposits of Italy, 34.
  ----, cited, 34, 35, 52.

  Valparaiso, changes caused by earthquakes at, 457, 517, 761.

  Van Dieman's Land, climate of, 97.

  Vedas, sacred hymns of, 4.

  Vegetable soil, why it does not increase, 709.
  ----, how formed, 710.

  Vegetation, luxuriant, not required to support
  large animals, 82.
  ----, centres of, 703.
  ----, its conservative influence, 710, 711.
  ----, its influence on climate, 713.

  Veins, mineral, on their formation, 484.
  ----, of lava. _See_ Dikes.

  Verneuil, M. de, on lowland of Siberia, 84.

  Verona, fossils of, 20, 22, 34.
  ----, Arduino on mountains of, 41.

  Verstegan, on separation of England from France, 315, 642.

  Vertebrated animals in oldest strata, 135.

  Vessels, fossil. _See_ Ships.

  Vesta, temple of, 212.

  Vesuvius, excavation of tuff on, 213.
  ----, history of, 263, 374.
  ----, eruptions of, 364, 374.
  ----, dikes of, 379.
  ----, lava of, 384.
  ----, structure and origin of the cone of, 383.
  ----, and Somma, probable section of, 381.
  ----, volcanic alluvium on, 728.

  Vicentin, Dolomieu on the, 49.
  ----, submarine lavas of the, 71.

  Victoria land, skirted by ice, 99.

  Vidal, Capt., on Rockhall bank, 773.

  Villages buried by landslips, 732.

  Virlet, M., on Samothracian deluge, 356.
  ----, on volcanoes of Greece, 355.
  ----, on Santorin, 443, 445, 446.
  ----, on corrosion of rocks by gases, 733.
  ----, on human bones imbedded in Morea, 735.

  Vivarais, basalts of the, 48.

  Volcanic action, defined, 345.
  ----, power adequate to effect lateral pressure, 172.
  ----, lines, 169, 352.
  ----, craters in Galapagos with southern side lowest, 783.
  ----, action, uniformity of, 162, 711.
  ----, cones, truncation of, 352, 493.
  ----, their perfect state no proof of relative age, 712.
  ----, conglomerates, 438.
  ----, dikes. _See_ Dikes.
  ----, eruptions, causes of, 542.
  ----, average number of, per annum, 450.
  ----, formations, fossils in, 349, 728.
  ----, products, mineral composition of, 449.
  ----, regions, their geographical boundaries, 346.
  ----, map showing extent of, 351.
  ----, rocks, subterranean, 178, 450.
  ----, of all geological periods, 160.

  Volcanoes, safety-valves according to Strabo, 15.
  ----, remarks on their position, 346, 355.
  ----, and earthquakes, effects of same causes, 345.
  ----, agency of water in, 545.
  ----, mode of computing the age of, 420.
  ----, sometimes inactive for centuries, 346, 421.
  ----, of Sandwich Islands, 354, 372, 548, 383, 429.
  ----, chemical theory of, 546.
  ----, mud, 447.
  ----, "no safety-valves," Dana on, 553.

  Voltaire on systems of geology, 54.

  Volterra, Mattani, on fossils of, 34.

  Von Baer, Prof., on frozen soil of Siberia, 84.
  ----, on ice-drifted rocks, 231.

  Von Buch on rise of land in Sweden, 523, 526.
  ----, on volcanic lines, 352.
  ----, on volcanoes of Greece, 355.
  ----, on formation of Monte Nuovo, 369.
  ----, on Vesuvius and Somma, 367, 380, 382, 384.
  ----, on eruption in Lancerote, 436.
  ----, on glaciers, 228.
  ----, on new islands, 468.
  ----, on volcanic regions, 346.

  Von Hoff. _See_ Hoff.

  Vulcanists and Neptunists, factions of, 50, 55.

  Vultur, Mount, 356.

  Vultures, range of, 643.


  W.

  Wallerius, theory of, 45.

  Wallich, Dr., on Ava fossils, 28.
  ----, on wood in peat near Calcutta, 280.

  Warping, land gained by, 288, 339.

  Water, action of running, 204.
  ----, its power on freezing, 204.
  ----, excavating power of, 204.
  ----, transporting power of, 204.
  ----, sorting power of, 286.
  ----, agency of, in volcanoes, 548.

  Waterhouse, Mr., of British Museum, on provinces of indigenous land
    quadrupeds, 631.

  Wealden strata, fossils of, 117, 137, 140.

  Webster, Dr., of Nova Scotia, on rain-prints, 202.

  Wells, artesian, 233.

  Wener, Lake, strata near, 527.

  Werner, Professor of Mineralogy at Freyberg, 1775, 46.
  ----, his lecture, 47.
  ----, on granite of the Hartz, 47.
  ----, principal merit of his system, 48.
  ----, technical terms of, 58.
  ----, on transition rocks, 176.

  West Indian land quadrupeds, 634.

  West Indies, earthquakes in, 29, 350, 505.
  ----, active volcanoes in, 350.

  Whales stranded, 771.

  Whewell, Rev. Dr., on modern progress of geology, 59.
  ----, on the tides, 332.

  Whirlwinds, violent, during eruption in Sumbawa, 465.

  Whirlwind, dispersion of seeds by, 619.

  Whiston, his theory of the earth, 32.

  White Mountains, landslips in the, 209.

  Whitehurst, theory of, 1778, 45.
  ----, on subsidence at Lisbon, 495.

  Wildenow on diffusion of plants by man, 626.
  ----, on centres of vegetable creation, 703.

  Wilkinson, Sir J. G., on deposits of Nile, 262.
  ----, on sand drift in Egypt, 726.

  Wilson, Prof., on cosmogony of Vedas, 4.

  Winds, trade, 106, 295.
  ----, currents caused by the, 293.
  ----, sand drifted by the, 307, 726.

  Wolf, and dog, distinct species, 585.
  ----, hybrids between the, 601.
  ----, drifted to sea on ice, 640.
  ----, extirpated in Great Britain, 683.

  Wollaston, Dr., on water of Mediterranean, 334.

  Wood, Mr. S., on fossil quadrumana, 144.

  Wood impregnated with salt water when sunk to great depths, 743.
  ----, drift, 90, 268, 640, 743.
  ----, converted into lignite, 759.

  Woodward, theory of, 31, 84, 54, 66.

  Wrecks, number of, annually, 754, 755.


  X.

  Xanthus, the Lydian, his theory, 14.


  Y.

  Yak, wild ox of Thibet, frozen in ice, 85.

  Yakutzt, frozen soil of, 84.

  Yaou, flood of, 7.

  Yarmouth, estuary silted up at, 307.
  ----, rise of the tide at, 291, 307.

  Yenesei, R., fossils on banks of, 79.

  Yorkshire, bones of mammoth in, 76.
  ----, waste of its coasts, 303.

  Young, Dr., on effects of compression at earth's centre, 536.


  Z.

  Zante, earthquakes in island of, 474.

  Zealand, New, number of ferns, 116.
  ----, resemblance of plants with ancient carboniferous flora, 116.
  ----, length and breadth of, 116.

  Zeuglodon, eocene cetacea, 145.

  Zoological provinces how formed, 666.
  ----, why not more blended together, 668.

  Zoophytes, their geographical distribution, 651.
  ----, their powers of diffusion, 654.
  ----, abundance of, 706.
  ----, which form coral reefs, 776.

  Zuyder Zee, formation, 328.
  ----, great mosses on the site of, 327.

       *       *       *       *       *

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