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                                  THE

                          JOURNAL OF GEOLOGY


                       _JANUARY-FEBRUARY, 1893._


                   *       *       *       *       *


            ON THE PRE-CAMBRIAN ROCKS OF THE BRITISH ISLES.


During the last twenty years much has been written about the
"pre-Cambrian" rocks of the British Isles. Unfortunately when attention
began to be sedulously given to the study of these ancient formations,
the problems of metamorphism were still a hundred fold more obscure
than they have since become; the aid of the microscope had not been
seriously and systematically adopted for the investigation of the
crystalline schists, and geologists generally were still under the
belief that the broad structure of these schists could be treated like
those of the sedimentary rocks, and be determined by rapid traverses of
the ground. We have now painfully discovered that these older methods
of observation were extremely crude, and that the work performed in
accordance with them is now of little interest or value save as a
historical warning to future generations of geologists. Geological
literature has meanwhile been burdened with numerous contributions
which remain as a permanent incubus on our library shelves.

It may serve a useful purpose at the present time in possibly aiding
those who are engaged in the study of the oldest rocks of North
America, if I place before them, as briefly as possible, the main facts
which in my opinion have now been satisfactorily proved regarding the
corresponding rocks of Britain, and if I indicate at the same time some
of the more probable inferences in those cases where the facts, at
present known, do not warrant a definite conclusion.

It is obvious that in any effort to establish that a group of rocks is
older than the very base of the sedimentary fossiliferous formations,
we must somewhere find that group emerging from under the bottom of
these formations. Until lithological characters are ascertained to be
so distinctive and constant as to be comparable to fossil evidence
for purposes of stratigraphical identification, we should not assume
that detached areas of older rocks rising amid Palæozoic, Secondary or
Tertiary formations are pre-Cambrian. We should, if possible, begin
at the bottom of the Palæozoic systems and work backward, tracing
each successive system or group as these rise from under each other,
until we arrive at what appears to be the oldest traceable within
the region of observation. It is clear that in the present state of
knowledge we have no satisfactory means of identifying such successive
systems in widely separated countries. All that can be attempted in
the meantime is to ascertain the special types in each region, and to
point out their general resemblances or contrasts to those of other
regions. It is better to avoid confusion by refraining from applying
the stratigraphical names adopted for the oldest rocks of one region
to those of another geographically remote, though we may hope that
eventually it may be possible to work out the equivalence of these
local names.

In the British Isles, by much the most important region for the study
of the oldest rocks is to be found in the north-west Highlands of
Scotland. The very basement strata of the Cambrian system are there
traceable for a distance of more than 100 miles, reposing with a
strong unconformability upon all rocks of older date. They consist
of dolomitic shales with _Olenellus_, resting upon a thick group of
quartzites, full of annelid tubes. One of the most remarkable features
of these ancient strata is the persistence of their component bands
or zones which, though sometimes only a few feet thick, can be traced
throughout the whole tract of country just referred to. For the study
of the pre-Cambrian rocks this is an important point, for we can be
quite certain that even where fossil evidence locally fails, the same
basement members of the Cambrian system are persistent and lie directly
upon the pre-Cambrian series.

_Lewisian Gneiss._ Ever since the researches of Murchison and Nicol in
the north-west of Scotland, it has been known that two distinct systems
of rock underlie the quartzites to which I have just alluded. Murchison
regarded the upper of these as of Cambrian age, while he assigned the
unconformable quartzites and limestones above it to the Lower Silurian
period. But the recent discovery of the _Olenellus_ zone intercalated
conformably between the quartzites and the overlying limestones may be
regarded as proving that all the rocks which underlie the quartzites
and are separated from them by a strong unconformability must be
pre-Cambrian. It is thus established beyond any reasonable doubt that
two great pre-Cambrian systems of rock exist in the north-west of
Scotland.

These two systems differ so entirely from each other that their
respective areas can be defined with minute accuracy. The uppermost
consists chiefly of dull reddish sandstones with conglomerates, and
especially towards their base in Rosshire, some bands of dark grey
shale, the whole having a thickness of at least 8,000 or 10,000 feet,
though as both the base and the top of the series are marked by strong
unconformabilities, the whole original thickness of deposits is nowhere
seen. As these rocks are well developed around Loch Torridon, they
were named by Nicol the Torridon Sandstone--a designation which has
more recently been shortened into "Torridonian." The lower system is
mainly composed of various foliated rocks which may be embraced under
the general term "gneiss." These masses present the usual characters of
the so-called "fundamental complex", "Urgebirge," or "Archæan Series"
of other countries. The contrast between the thoroughly crystalline,
gnarled, ancient-looking gneisses below, and the overlying, nearly
horizontal Torridonian conglomerates, sandstones, and shales, which
are largely made out of their debris, is so striking that every
observer feels persuaded that in any logical system of classification
they can not be both placed in the same division of the geological
record. They are certainly both pre-Cambrian, but they must belong
to widely separated eras, and must have been produced by entirely
different processes. If it is proposed to regard the gneisses as
"Archæan," we must refuse to include the Torridonian strata in the
same section of pre-Cambrian time. But so much uncertainty exists as
to the application of this term Archæan, examples are so multiplying
wherein what was supposed to be the oldest and truly Archæan rock is
found to be intrusive in rocks that were taken to be of much younger
date, and there are such slender grounds for correlating the so-called
Archæan rocks of one country with those of another, that I prefer for
the present, at least, not to use the term at all. Let me very briefly
state some of the main characteristics of the two sharply contrasted
rock-systems of the north-west of Scotland.

The oldest gneiss of that region was originally called "Lewisian" by
Murchison, from its large development in the Island of Lewis, and I
think it would be, for the present at least, an advantage to retain
this geographical appellation. At first this "fundamental gneiss"
was thought to be a comparatively simple formation, and the general
impression probably was that it should be regarded as a metamorphic
mass, produced mainly from the alterations of very ancient stratified
rocks. Its foliation-planes were believed to be those of original
deposit which by terrestrial disturbance had been thrown into numerous
plications and corrugated puckerings. But a detailed study of this
primeval rock has revealed in it a far more complicated structure. The
supposed bedding-planes have been ascertained to have nothing to do
with sedimentary stratification, and the gneiss has been resolved into
a complex series of eruptive rocks, varying from a highly basic to an
acid type, and manifestly belonging to different times of extrusion.
With the exception of one district, to which I shall immediately refer,
no part of the whole region yet examined has revealed to the rigid
scrutiny of my colleagues of the Geological Survey, any trace of rocks
which can be regarded as probably of other than igneous origin. It is
true that our researches have been hitherto confined to the mainland
of Scotland, the large area of the Outer Hebrides, which consists of
similar gneisses, remaining to be explored. It is therefore possible
that indisputable evidence of an ancient sedimentary series through
which the gneiss was originally protruded, may yet be discovered in
the unexplored islands. But taking the gneiss as at present known in
Sutherland and Rosshire, we find it to be generally coarse in texture,
rudely foliated, and passing sometimes into massive types in which
foliation is either faintly developed or entirely absent. Much of this
gneiss is considerably more basic than the more typical rocks to which
the term gneiss was formerly restricted. It consists of plagioclase
felspar with pyroxene, hornblende, and magnetite, sometimes with blue
opalescent quartz, and sometimes with black mica. These predominant
minerals are segregated in different proportions in the different
bands, some bands consisting mainly of pyroxene or hornblende, with
little or no plagioclase, others chiefly of plagioclase, with small
quantities of the ferro-magnesian minerals and quartz, others of
plagioclase and quartz, others of magnetite. This separation of mineral
constituents can hardly be attributed to mere mechanical deformation.
It rather resembles the segregation layers which may be studied in
intrusive sills and other deep-seated masses of eruptive material, and
which are obviously due to a process of separation that went on while
the igneous magma was still in a liquid or viscous condition. At the
same time it is manifest that extensive dynamical changes have affected
the rocks since the appearance of this original banded structure.

There is further evidence that beside the original eruptive masses,
which for want of any means of discriminating their relative dates
of protrusion must in the meantime be regarded as belonging to
one eruptive period, other portions of igneous material have been
subsequently and at successive epochs, after the first mechanical
deformations, injected into the body of the original gneiss. These
consist of dykes of basalt and dolerite, followed by still more basic
peridotites and picrites, and lastly by emanations from a distinctly
acid magma in the form of granites. The oldest or doleritic dykes form
a wonderful feature in the gneiss, from their abundance, persistence
and uniformity of trend in a west-northwest direction. They have no
parallel in British Geology until we reach the crowded dykes of older
Tertiary time.

Throughout this remarkable complex of eruptive material, though its
different portions present many features that may be compared with
those of intrusive bosses and sheets belonging to later geological
periods, there is no trace of any superficial volcanic manifestation.
No tuffs or agglomerates or slaggy lavas have been detected, such
as might serve to indicate the ejection of volcanic materials to
the surface. All the phenomena of the Lewisian gneiss point to the
consolidation of successively protruded portions of eruptive material
at some depth within the crust.

Nevertheless it may yet be possible to show that these deep seated
masses have been injected into rocks of older date and of sedimentary
origin, and that they have communicated with the surface in true
volcanic eruptions. I have already alluded to one limited area where
various rocks exist, distinctly different from the prevalent types in
the Lewisian gneiss. In the area which is traversed by the long valley
of Loch Maree in western Rosshire, there occur clay-slates, fine mica
schists, graphitic schists, and saccharoid limestones. These rocks
remind us of some of the prevalent members of a series of metamorphosed
sediments. The minerals enclosed in the marbles are just such as might
be expected in the metamorphic aureole of a granite boss, piercing
limestone. But the relations of this group of rocks to the ordinary
gneiss of the region are not quite so clear as could be desired, though
they seem to point to these rocks being surrounded by and enclosed
within the gneiss.

The detailed field-work of the officers of the Geological Survey has
made known the remarkable amount of mechanical deformation which the
various rock-masses composing the Lewisian gneiss have undergone.
These rocks have been compressed, crushed, and drawn out, until what
were originally massive crystalline protrusions have been converted
into perfect schists. The dykes of dolerite have been transformed
into hornblende-schists and the granitic pegmatites have been reduced
to a kind of powder which has been rolled out so as to simulate the
flow-structure of a lava. There is evidence that most, if not all, of
this dynamical change was effected long before the deposition of the
Torridonian series, for the latter rests in nearly horizontal sheets,
with a strong unconformability upon the crushed and sheared gneiss.

_Torridon Sandstone._ This group of rocks covers only a limited area
in the north-west of Scotland, but it must once have spread over a
far more extensive region. It reaches a thickness, as I have said, of
8,000 or 10,000 feet, and consists almost wholly of dull, purplish-red
sandstones, often pebbly, and bands of conglomerate. Dark grey shales,
already alluded to as occurring towards the base of the series, are
repeated also in the highest visible portion, and have yielded tracks
of what seem to have been annelids and casts of nail-like bodies which
may have been organic. I have said that the Torridonian deposits
which were classed by Murchison as Cambrian, have been proved by the
discovery of the _Olenellus_ zone in an unconformable position above
them, to be of pre-Cambrian age. Except along the line of disturbance
to which I shall immediately refer, these strata are quite unaltered.
Indeed, in general aspect they look as young as the old red sandstones
with which Hugh Miller identified them. It is at first hard to believe
that such flat undisturbed sandstones are of higher antiquity than
the very oldest Palæozoic strata which are so generally plicated and
cleaved.

The interval of time between the deposition of the Torridon Sandstone
and of the overlying Cambrian formations must have been of enormous
duration, for the unconformability is so violent that the lowest
Cambrian strata, not only transgressively overspread all the
Torridonian horizons, but even lie here and there directly on the
old gneiss, the whole of the intervening thick mass of sandstone
having been there removed by previous denudation. At Durness, in the
north of Sutherland, about 2000 feet of Cambrian (possibly in part
Lower Silurian) strata can be traced, the lower portion consisting
of quartzites, the central and upper parts of various limestones,
sometimes abundantly fossiliferous. Nowhere else in the north of
Scotland can so thick a mass of early Palæozoic rocks be seen.
Elsewhere the limestones have been in large measure replaced by a
complex group of schistose rocks which rest upon the Cambrian strata,
and like them dip, generally at gentle angles, towards the east. It
was the opinion of Murchison, and was commonly admitted by geologists,
that these overlying schists represented a thick group of sediments,
which, originally deposited continuously after the limestones, had
been subsequently altered into their present condition by regional
metamorphism. They were variously named the "Eastern schists," the
"younger gneiss," the "gneissose and quartzose flagstones." Nicol,
who at first shared the general opinion regarding them, afterwards
maintained that they did not belong to a later formation than the
limestones, but were really only the old gneiss, brought up again from
beneath by enormous dislocations and over-thrusts. We now know from the
labors of Professor Lapworth and the officers of the Geological Survey,
that Murchison and Nicol had each seized on an essential part of the
problem, but that both of them had missed the true solution. Murchison
was in error in regarding his younger gneiss as a continuous sequence
of altered sedimentary rocks conformably resting on the Cambrian (or
to use his terminology, Lower-Silurian) formations. But he sagaciously
observed the coincidence of dip and strike between the schists and
sedimentary rocks below them and inferred that this coincidence,
traceable for many leagues, proved that the metamorphism which had
given these schists their structure must have taken place after the
deposition of the Durness limestones. Nicol, on the other hand, with
great insight recognized that there was no continuous sequence above
those limestones, but that masses of the old gneiss had been thrust
over them by gigantic faults. But he failed to see that no mere faults
would account for the coincidence between the structural lines just
referred to in the Cambrian strata, and in the overlying schists, and
that the general tectonic structures and lithological characters of the
eastern schists differed in many respects from those of the Lewisian
gneiss.

The problems in tectonic geology presented by the complicated
structures of the northwest of Scotland have been ably worked out
by the officers of the Geological Survey, to whose report in the
_Quarterly Journal of the Geological Society_ for 1888, I would
refer for full details. It has been shown that, besides stupendous
dislocations and horizontal displacements, the rocks have been cut into
innumerable slices which have been driven over each other from the
eastward, while at the same time there has been such a general shearing
of the whole region that for many hundreds of square miles the original
rock-structures have been entirely effaced, and have been replaced
by new divisional planes, which, when they approach the underlying
Cambrian strata, are roughly parallel with the bedding planes of these
strata.

In this region, therefore, we have striking proofs of a stupendous
post-Cambrian regional metamorphism. But there is still much
uncertainty regarding the geological age of the rocks which have been
affected by it. There can be no doubt that large masses of the old
gneiss, torn up from below, have been thrust bodily westward for many
miles, and are now seen with their dykes and pegmatites resting on the
Durness limestones and quartzites. It is equally certain that in other
districts huge slices of the Torridon sandstones have been similarly
treated. But where all trace of original structure has disappeared, we
have, as yet, no means of definitely determining from what formation
the present eastern schists have been produced. The ordinary gneissose
and quartzose flagstones do not appear to me to be such rocks as could
ever be manufactured by any chemical or mechanical process out of the
average type of Lewisian gneiss. I have long held the belief that
they were originally sediments, but whether they represent altered
Torridon Sandstone, or some clastic formations which may have followed
the Durness limestones, but which have been everywhere and entirely
metamorphosed, remains for future discovery. For my present purpose,
it is sufficient to observe that, in the meantime, as we can not be
sure of the origin of most of the rocks, which, between the West Coast
and the line of the Great Glen, have been subjected to a gigantic
post-Cambrian regional metamorphism, it seems safest to exclude them
from an enumeration of the pre-Cambrian rocks of Britain.

_Dalradian._ East of the line of Great Glen, which cuts the Scottish
Highlands in two, another group of crystalline schistose rocks is
largely developed. It consists mainly of what were undoubtedly
originally sedimentary deposits, though they are now found in the form
of quartzites, phyllites, graphitic schists, mica-schists, marbles,
and various other foliated masses. With them are associated numerous
eruptive rocks, both acid and basic, sometimes still massive and
easily recognizable as intrusive, sometimes more or less distinctly
foliated and passing into different gneisses, hornblende-schists,
chloritic-schists, etc. Though it is not always possible in such a
series of metamorphic rocks to be certain of any real chronological
order of succession, those of the Highland tracts have now been mapped
in detail over so wide an area, that we are probably justified in
believing that a definite sequence can be established among them.
These masses must be many thousand feet thick. Their succession and
association of materials are so unlike those of any of the known older
Palæozoic rocks of Britain, that they can hardly be the metamorphosed
equivalents of any strata which can be recognized in an unaltered
condition in these islands. Some traces of annelid casts have been
found in the quartzites, but otherwise the whole series has remained
entirely barren of organic remains.

What then is the age of this important series? I must confess that in
the meantime I can give no satisfactory answer to this question. I
have proposed, for the sake of distinction and convenient reference,
to call these rocks "Dalradian." Murchison supposed them to be a
continuation of his Durness quartzites, limestones, and "younger
gneiss." His belief may still prove to be in some measure well founded.
But at present we have no means of deciding whether the quartzites and
limestones of the Central Highlands are the more altered equivalents of
the undoubtedly Cambrian strata of the north-west. It is possible that
in the vast mass of metamorphosed rocks constituting the wide stretch
of country from the northern headlands of Aberdeen to the south-western
promontories of Argyllshire, there may be portions of the old Lewisian
gneiss, tracts of highly altered Torridon sandstone, belts of true
counterparts of the Cambrian quartzites and limestones of Durness,
and, what should not be forgotten, considerable portions of some later
sedimentary series which may have followed these limestones, but
which, by the great dislocations already referred to, have disappeared
from the north-west of Scotland. We are gradually learning more of
these rocks, as the detailed mapping of them by the Geological Survey
advances, and when the ground on either side of the Great Glen is
surveyed, it may be possible to speak with more certainty regarding
their true geological relations.

A glance at a geological map of the British Isles will show that the
metamorphic rocks of the south-western Highlands of Scotland are
prolonged into the north of Ireland, where they spread over a region
many hundred square miles in extent. They retain there the same general
character and present the same difficult problems as to their true
stratigraphical relations. Quite recently, however, a new light seems
to have arisen upon these Irish rocks. My colleagues on the Irish
Branch of the Geological Survey have detected several detached areas
of coarse gneisses, which in many respects resemble parts of the
Lewisian gneiss of north-west Scotland. In some cases these areas lie
amidst or close to "Dalradian" rocks, but with that obstinacy, which
so tries the patience of the field-geologist, they have persistently
refused to disclose their true original position with regard to these.
Some fault, thrust-plane, tract of boulder-clay or stretch of bog
is sure to intervene along the very junction-line where the desired
sections might have been looked for. There can be little doubt that
a strong unconformability exists between them. A close examination of
the ridge of old gneiss in Tyrone and Fermanagh showed me that though
the actual basement-beds of this Dalradian series could not be seen
resting on the coarse gneiss, the lithological character, and tectonic
arrangement of this series are only explicable on the supposition of a
complete discordance between it and the gneiss. As these two groups of
rock have never been found in close proximity in Scotland, and as the
determination of the true age of the Dalradian series is a question of
such great stratigraphical importance in the general mapping of the
United Kingdom, I requested Mr. A. McHenry, of the Geological Survey of
Ireland, to continue the tracing of the mutual boundaries of the old
gneiss of the Ox Mountains and the Dalradian series in County Mayo.
He informs me that he has found in that series a conglomerate full
of blocks of the old gneiss, and resting in one locality apparently
unconformably upon it. If this observation is confirmed it will finally
set at rest the relative position of the coarse massive gneiss and
some portion, at least, of the Dalradian series. Of course there is
no absolute proof that the coarse gneisses of Ireland are really the
equivalents of the Lewisian masses which they so closely resemble. But
there is a strong presumption in favor of their identity.

In England and Wales many detached areas of rock have been claimed as
pre-Cambrian, and successive formations have been classified among
them. I have already dealt in part with this question, and without
attempting here to review the voluminous literature of the subject, I
will content myself with stating briefly what seems to me to have been
established on good evidence.

There can not, I think, be now any doubt that small tracts of gneiss,
quite comparable in lithological character to portions of the Lewisian
rocks of the north-west of Scotland, rise to the surface in a few
places in England and Wales. In the heart of Anglesey, for example,
a tract of such rocks presents some striking external or scenic
resemblance to the characteristic types of ground where the oldest
gneiss forms the surface in Scotland and the west of Ireland. In the
Malvern Hills another small knob of somewhat similar material is
obviously far more ancient than the Cambrian rocks of that locality.
There may possibly be still some further exposures of similar rocks in
the south of England, as for instance in southern Cornwall. In Anglesey
a series of schists, quartzites and limestones has been included by
Mr. J. F. Blake with the coarse gneiss above referred to, and a thick
higher group of slates in what he terms the "Monian" system. These
schists, quartzites and limestones present a close resemblance to the
Dalradian series of Scotland and Ireland, and the quartzites, like
those of the Highlands, contain worm-burrows. The coarse gneiss, as
I have said, may be compared in general character with parts of the
Lewisian rocks, so that we seem to have here, as in Ireland, two groups
of schistose rocks, and both of these must be much older than the
unaltered Cambrian strata which lie above them.

Along the eastern borders of Wales, there is an interrupted ridge of
igneous rocks which were originally supposed to have broken through the
older Palæozoic formations, but which now, owing mainly to the labors
of Dr. Callaway and Professor Lapworth, are shown to be older than
the base of the Cambrian system. These rocks consist of spherulitic
and perlitic felsites, with volcanic breccias and tuffs. They are
undoubtedly older than the _Olenellus_ zone. Though the evidence is
not quite satisfactory, they may not impossibly lie at the base of
a vast mass of sedimentary rocks forming the ridge of the Longmynd.
In that case the whole of the Longmynd succession with the volcanic
group at its base must be pre-Cambrian and lie unconformably below the
_Olenellus_ zone. Dr. Callaway has proposed the name "_Uriconian_"
for this volcanic group, while the sedimentary series has been termed
"_Longmyndian_." On the supposition that the unconformability is
established, there would here be a vast mass of stratified and partly
erupted material forming a pre-Cambrian formation. Whether in that case
any portion of this English series is the equivalent of the Torridonian
rocks of Scotland remains to be determined. The northwestern part of
the Longmynd ridge is made of red sandstones and conglomerates, which
certainly resemble the Torridonian rocks of Ross and Sutherland.

At the base of the Cambrian rocks in Wales, Dr. Hicks has described a
marked volcanic series under the name of "Pebidian," which he claims as
pre-Cambrian, alleging that it is separated from the Cambrian system
by an unconformability, and a band of conglomerates. I have carefully
studied the evidence on this ground, and have come to the conclusion
that there is no unconformability at the line in question, but that the
ordinary Cambrian strata graduate downwards into the volcanic group
and can not be disjoined from it. I therefore regard the so-called
"Pebidian" as merely marking the duration of a volcanic period in early
Cambrian time.

It will thus be seen that according to my view the unmistakably
pre-Cambrian rocks of Britain consist of, first and oldest, the
Lewisian gneiss; second, the Torridonian sandstones and conglomerates.
The Uriconian and Longmyndian formations may prove to be in part or
in whole equivalents of the Torridonian. The Dalradian rocks have not
yet had their position determined. They may possibly mark a distinct
pre-Cambrian series, but it seems quite as probable that they are only
a metamorphic complex in which Archæan, Torridonian and Cambrian, or
even Lower Silurian rocks are included.

                                           =Sir Archibald Geikie=,
  Director-General of the Geological Survey of Great Britain and Ireland.




ARE THERE TRACES OF GLACIAL MAN IN THE TRENTON GRAVELS?


In a paper published in _Science_, Nov. 25. 1892, I undertook to study
the evidence relating to paleolithic man in the eastern United States
from a new point of view,--that furnished by certain recently acquired
knowledge of the contents of quarries and shops where modern aboriginal
flaked implements were made. It was shown that all rudely flaked forms
could be sufficiently accounted for without the necessity of assuming
a very rude state of culture, and that any people, paleolithic or
neolithic, would in roughing out blades--the principal product of the
flaking process--produce precisely these forms and in great numbers
as refuse. It further appeared that the finding of these objects in
sporadic cases in glacial gravels or in any formation whatsoever, could
not be considered as proving or tending to establish the existence of
a particular grade of stone-age culture for the region in which the
formation occurs, since they may as readily pertain to a neolithic
as to a paleolithic status. It was conclusively shown that no worked
stone that can with reasonable safety be called an implement has been
reported from the gravels, and that it is therefore clearly useless,
not to say unscientific, to go on enlarging upon the evidence of an
American paleolithic period and multiplying theoretic details of its
culture.

I now propose to review briefly the question of the age of our
so-called paleolithic implements, the questions of the _grade_ of
a given feature of culture and of the _age_ or chronologic place
of that culture being very properly treated separately, as they
depend for their support upon distinct classes of evidence. During
the past summer, 1892, certain important items of new evidence have
been discovered bearing upon the question of the occurrence or
non-occurrence of rudely flaked stones or of any artificial objects
whatsoever in the normal gravels of the Delaware Valley, and it
therefore becomes necessary to examine somewhat critically such of the
published evidence as seems to be seriously affected by these recent
observations.

It may be stated in beginning that no one disputes the glacial age of
the Trenton gravels. The question to be discussed is simply this,--is
the evidence satisfactory that works of art have been found in these
gravels? Nothing else need be asked or answered. I do not take up
this subject because I love controversy; disputation is really most
distasteful to me. It happens that under the Bureau of Ethnology of the
Smithsonian Institution I have been assigned to the work of making a
survey of the archeology of the Atlantic coast region in which large
areas, especially in states south of Mason and Dixon's line, remained
almost untouched by investigators, and two years have been consumed
mainly in these southern areas. But there are questions that refuse
to be confined to definite geographic limits, and evidence secured in
one section is sometimes found to bear so directly and forcibly upon
problems pertaining primarily to other sections that the student of
these problems must perforce become a free lance, and unhesitatingly
enter any province promising results of value, howsoever fully occupied
it may be by other investigators. One of the most interesting and
important questions growing out of the study of American archeology
has, as we have seen, arisen in the Delaware Valley, and the turn taken
by some of my work in the south and west is such that I cannot pass
this question by without consideration. The necessity of taking up
the subject of glacial man became more and more apparent as the years
passed on, and people continued to say to me, "You must go to Trenton;
we are not satisfied with the present status of the question there; the
evidence arrayed in favor of the theory of a paleolithic gravel man
needs critical examination."

The difficulty of taking up and re-examining evidence, of which the
record only remains, is, however, very great, since in most cases
the evidence rests upon or consists of field observations, and these
cannot be recalled or repeated, and there is absolutely no means of
testing directly the value of what is recorded. One may seek either to
verify or to discredit the promulgated theories, but years of search
may fail to produce a single new item of evidence bearing decisively
upon the subject. It is possible that at one period numerous finds of
implements should be reported from certain portions of the gravels,
and that afterwards the whole remaining body of these formations
should be worked over and searched without securing a trace of art;
yet this latter evidence, being negative, need not necessarily be
considered sufficient to overturn the original positive evidence if
that happens to be of a high class. There is not the least doubt,
however, that positive evidence may be so impaired by various defects
and inconsistencies, that, unsupported by renewed and well verified
observations, it will finally yield to the negative forces; and if
the theories of a gravel man in the eastern United States, howsoever
fortified by accumulated observations, are not really properly
supported in every way, they are bound in time to fall to the ground.
All I can reasonably hope to do now is to have the evidence relating to
glacial man placed on trial, and so fully examined and cross-examined
that those who accept gravel man need not longer do so blindly without
knowing that there are two sides to the question, and those who do not
accept him may know something of the reasons for the belief that is in
them.

The evidence employed to prove the presence of a race of men in
the Delaware Valley in glacial times is confined almost wholly to
the alleged discovery of rude implements in the glacial gravels.
Practically all the evidence has been collected by Dr. C. C. Abbott,
and upon his skill as an observer, his faithfulness as a recorder,
his correctness of judgment and his integrity of character, the whole
matter stands. Many visitors, men of high repute in archeology and
geology, have visited the site, but the observations made on such
occasions appear not to have been of a nature to be of great value in
evidence, the finds being doubtful works of art or not having properly
established relationships with the gravels in place. In the discussion
of gravel man in eastern America a wide range of objects and phenomena
has been considered, but the real evidence, upon which the theory of
an ancient race and a peculiar culture must depend, is furnished by a
hundred pieces--more or less--of rudely flaked stones said to have come
from the gravels in place. And now what can be said with reference to
this series of flaked stones further than that they are reported by the
collector to have been found in the gravels at definite stated depths?
I have elsewhere shown that they are not demonstrably implements
in any case, that they are identical in every respect with the
quarry-shop rejects of the American Indian, that they do not closely
resemble any one of the well established types of European paleolithic
implements, and that they are not a sufficient index of a particular
stage of culture. I shall now present such reasons as there may be
for the belief, held by many, that they were not really found in the
undisturbed glacial gravels.

It is generally understood that the earliest reported gravel finds of
importance were made on the banks of Assanpink creek within the city
limits of Trenton, where the gravels to a thickness of twenty feet or
more were exposed in a railway cutting. Later the river bluff near the
lower end of the city, where the gravels were exposed to a depth of
from twenty-five to forty feet, yielded large numbers. These two sites,
so far as I can learn, furnished at least three-fourths of the finds in
place. Other specimens were found singly in slight natural exposures,
and in excavations for cellars, sewers, etc., at various points within
the city limits.

The river bluff was for a considerable period the favorite hunting
ground of the searchers for rudely flaked stones, and many specimens
were collected. The gravels were exposed in a steep, nearly straight
bank, several hundred yards in length, the base of which was washed by
the river. There can be no question that Dr. Abbott and others have
found shaped objects of various classes upon and in the face of this
river bluff, and the visitor to-day, although the bluff is now buried
almost completely under city refuse, will hardly fail to find some
rudely flaked form in the deeper gullies or upon the narrow river bank
or beach at the base. Dr. Abbott explicitly states[1] that he obtained
certain of these specimens from the gravel outcrops, and that they were
not in talus formations, but in undisturbed deposits. How then is it
possible to do otherwise than accept these statements as satisfactory
and final?

[1] Abbott, C. C. Primitive Industry, pp. 493-510.

[Illustration: =Fig. 1.= Sketch map of the Trenton bluff, showing the
relation of the sewer trench to the "implement" yielding slope.... a-b
section line, =Fig. 2=.]

Very recently, however, fortunate circumstances have brought the
evidence furnished by this site again within our reach, thus enabling
us to re-open the discussion under favorable conditions. What I had
for some time desired to do in this case was, what I had already done
at Piny Branch, D. C., and at Little Falls, Minn., to open a trench
into the face of the bluff, and thus secure evidence for or against
the theory of a gravel man. This measure was, however, rendered
impracticable by the occupation of the bluff margin by a city street;
but it happened last summer that the city authorities, desiring to
improve the sanitary condition of the city, decided to open a great
sewer through this very bluff to get a lower outlet to the river. A
trench twelve feet wide and some thirty feet deep, the full depth
of the exposed gravels, was carried along the bluff just inside of
its margin, opening out into the river at the point where the bluff
turns toward the north-east. It was a trenching more complete and more
satisfactory than any of which I had ever dreamed. At no point for the
entire length of the bluff did the excavation depart more than forty
feet from the line of the terrace face--from the upper margin of the
slope upon which such plentiful evidence of a supposed gravel man had
been obtained. The accompanying map and section, Figs. 1 and 2, will
indicate the location of the trench, and show the exact relations of
the natural and artificial exposures of the gravels.

[Illustration: =Fig. 2.= Sections made by the river and by the sewer,
the former yielding many "implements," the latter yielding none.]

I made several visits to the place, descended frequently into the great
cut and examined the gravels and their contents with the utmost care,
but without securing a trace of art. Recognizing the vital importance
of utilizing to the fullest extent this opportunity of testing the
art-bearing nature of the gravels at this point, I resolved to
undertake a systematic study of the subject. Summoning my assistant,
Mr. William Dinwiddie, from his field of operations in the South, I had
him spend upwards of a month at the great trench, faithfully watching
the gravels as they were exposed. Mr. Dinwiddie had worked three years
under my personal direction, and had helped open upwards of twenty
trenches through similar gravel deposits, and was therefore well
qualified for the work. Prof. W. J. McGee, Prof. R. D. Salisbury, Dr.
Stewart Culin and Dr. Abbott also visited the place one or more times
each. Relics of art were found upon the surface and in such portions of
the talus as happened to be exposed, but nothing whatever was found in
the gravels in place, and the search was closed when it became fully
apparent that the case was hopeless.

It may be claimed that the conditions under which gravels are exposed
in trenching as it progresses, are not as favorable for the collection
of enclosed relics as where exposed by natural processes of weathering.
This is true in a certain measure, as specimens may be obscured by
the damp clinging sand which forms the matrix of the gravels. This,
however, would interfere but little with the discovery of large flaked
stones, such as we were led to expect in this place, and this slight
disadvantage in detecting shaped pieces in fresh exposures is more
than over-balanced by the treachery of weathered surfaces which often
give to intrusive objects the appearance of original inclusion. The
opportunity for studying the gravels in all their phases of bedding,
composition and contents, was really excellent, and no one could watch
the constantly renewed exposures hour after hour for a month without
forming a most decided notion as to the implement bearing qualities
of the formation. Not the trace of a flaked stone, or of a flake or
artificial fragment of any kind was found, and we closed the work
with the firm conviction that the gravels exposed by this trench were
absolutely barren of art. But Dr. Abbott claims to have found numerous
implements in the bluff face a few feet away and in the same gravels.
If this is true, the conditions of glacial occupation of this site
must have been indeed remarkable. It is implied that during the whole
period occupied by the melting of the ice sheet within the drainage of
the Delaware valley the hypothetical rude race lived on a particular
line or zone afterwards exposed by the river to the depth of 30 feet,
leaving his strange "tools" there by the hundreds, while another line
or zone, not more than forty feet away at most, exposed to the same
depth by an artificial trench, was so avoided by him that it does not
furnish the least memento of his presence. One vertical slice of the
gravels twelve feet thick does not yield even a broken stone, while
another slice not probably one-half as thick, cut obliquely through
the gravels near by, has furnished subject-matter for numerous books
and substantiation for a brace of theories. That no natural line of
demarcation between the two section lines is possible, is shown by
the fact that the formations are continuous, and that the deposits
indicate a constant shifting of lines and areas of accumulation;
thus it was impossible for any race to dwell continuously upon any
spot, line or plane. This is well shown in the section, Fig. 3, which
gives the relations of the art-producing section of Dr. Abbott to the
non-art-producing section of the sewer. The gravels were laid down
entirely irrespective of subsequent cutting, natural or artificial;
yet we are expected to believe that a so-called gravel man could have
resorted for a thousand years to the space _a_, leaving his half
shaped or incipient tools at all stages of the gravel building from
base to top, failing entirely to visit a neighboring space _b_, or to
leave there a single flake to reward the most faithful search. It is
much easier to believe that one man should err than that a guileless
race should thus conspire with a heartless nature to accomplish such
extraordinary results. The easier explanation of the whole matter is
that the objects found by Dr. Abbott were not really in the gravels,
but that they are Indian shop-refuse settled into the old talus
deposits of the bluff, and that his eager eyes, blinded by a prevailing
belief in a paleolithic man for all the world alike, failed to observe
with their wonted keenness and power.

[Illustration: =Fig. 3.= _a_, Reputed "implement" producing zone of the
river front. _b_, Barren zone of sewer.]

But this case does not stand alone. The first discoveries of supposed
gravel implements are said to have been made when the Pennsylvania
Railway opened a road bed through the creek terrace on the site of the
present station. At first numerous specimens of rudely flaked stones
were reported, and the locality became widely known to archeologists,
but the implement bearing portions of the gravels--and this is a most
significant fact--were limited in extent, and the deposit was soon
completely removed, the horizontal extension containing nothing. At
present there are excellent exposures of the full thickness of the
gravels at this point, but the most diligent search is vain, the only
result of days of examination being a deep conviction that these
gravels are and always were wholly barren of art.

It thus appears that here as well as upon the river front, the works
of art were confined to local deposits, limited horizontally but not
vertically, and a strong presumption is created that the finds were
confined to redistributed gravels settled upon the terrace face in the
form of talus. Dr. Abbott states that "at that point where I gathered
the majority of specimens there is a want of stratification."[2] It
is well known that such rearranged deposits are often difficult to
distinguish from the original gravels. In trenching an implement
producing terrace at Washington--where the conditions were probably
quite similar to those at the Trenton railroad station--I passed
through eighty feet of redistributed talus gravels before encountering
the gravels in place, and so deceptively were portions of these
deposits re-set that experts in gravel phenomena were unable to decide
whether they were or were not portions of the original formation
(cretaceous). The question was finally settled by the discovery of
artificially shaped stones in and beneath the deposits.

[2] Abbott, C. C. 10th Annual Report of the Peabody Museum, p. 41.

Again, an implement bearing deposit of gravel was recently discovered
by the late Miss F. E. Babbitt at Little Falls, Minnesota, and
sufficient (a very little) digging was done to satisfy the discoverer,
and all paleolithic archeologists as well, that the objects were really
imbedded in the glacial gravels. In the summer of 1892 I visited the
place and carried a trench twenty feet horizontally into the terrace
face on the "implement bed" level before encountering the gravels in
place. The talus deposits were several feet thick, and were of such
a nature that their true character could not be determined without
careful and extensive trenching. The whole talus deposit was here
well stocked with Indian quartz quarry-shop rejects, which were as
usual of paleolithic types, and it was but natural that Miss Babbitt's
conclusions, although based as they necessarily were upon inexpert
observations, backed by such well known "types" of "implements" should
be unhesitatingly accepted by believers.

The occurrence of these telling examples of the deceptive appearance
of re-set gravels would seem to justify and emphasize the conviction
created by a critical examination of the two leading so-called
paleolithic sites at Trenton, that Dr. Abbott, notwithstanding his
asseverations to the contrary, has been deceived. Very strong support,
it seems to me, is given to this conclusion by the recently published
opinion of the late Dr. H. Carvill Lewis, a glacialist familiar
with the Trenton region, and with the work of Dr. Abbott at the
period of his paleolithic castle building. Dr. Lewis is reported to
have maintained before an open meeting of the Academy of Science in
Philadelphia "that what Dr. Abbott believed to be undisturbed layers
(of gravel) were those of an ancient talus."[3] This remark may refer
to both the main sites--the one at the railroad station and the other
at the river front--or possibly only to the former. I have also heard
it stated that that eminent scholar, Dr. Leidy, who must have had ample
opportunities of forming correct opinions upon the subject, held pretty
much the same views of Dr. Abbott's finds.

[3] Brinton, D. G., Science, Oct. 28, p. 249.

[Illustration: =Fig. 4.= A freshly formed gravel bluff.]

[Illustration: =Fig. 5.= Early stage of talus formation.]

[Illustration: =Fig. 6.= An ancient talus.]

To make the above criticism entirely clear, a few words of explanation
of talus phenomena may be added. As a river cuts its channel deeper
and deeper into deposits of gravel a section is gradually exposed, but
the gravels break down readily under atmospheric influences and the
exposed face does not retain a high angle. The upper part crumbles and
descends toward the base, there to rest against the slope or to be
carried away by the stream. A supposititious case will be convenient
for illustration. A gravel terrace twenty feet in height is encroached
upon by the river at high water and undermined, and the face breaks
down vertically, leaving an exposure as illustrated in Fig. 4. In a
very short time the upper portions become loosened and fall below,
giving a steep slope as seen in Fig. 5. The process goes on with
gradually decreasing rapidity, and if the river does not again encroach
seriously, a practically stable slope is reached, as shown in Fig.
6. Such a talus may be hundreds or even thousands of years old, but
there is rarely any means of determining its exact age. If the gravels
are homogeneous in character, the talus will simulate their normal
condition so completely that the distinction cannot be made out in
ordinary gullies or by unsystematic digging. If the gravels contain
varied strata the talus will be composite, and will be more readily
distinguished from at least portions of the material in place.

Now it is important to observe what may be the possible art contents
of such a talus as that shown in Fig. 6. It may contain all objects
of art originally included in that portion of the gravels represented
by _a_, _b_, _c_, together with all articles that happened to be upon
the surface _b_, _c_, beside such objects as may have accumulated from
dwelling or shop work upon its own surface, after the slope became
sufficiently reduced to be occupied for these purposes. A talus is
therefore liable to contain, and in the utmost confusion, relics of all
periods of occupation, supposing always that there were such periods,
from the beginning of the formation of the gravel deposits down to the
present moment. As a rule such a talus, if art-containing, will have a
large percentage of shop and quarry-shop refuse, for the reason that
the exposed gravels, and the banks and beds of rivers cutting them,
furnish, as a rule, a good deal of the raw material utilized by workers
in stone, and the shops in which the work was done are usually located
upon the slopes and outer margins of the terraces. Although there is
the possibility of very considerable age for these talus deposits,
it is unlikely that any of them date back as far as the close of the
glacial epoch or at all near it, for rivers change back and forth
constantly, undermining first one bank and then the other, so that a
very large percentage of our talus deposits have been formed well
within the historic period.

At Trenton the constantly exposed gravel banks afforded considerable
argillite in bowlders, fragments and heavy masses, as well as some
other flakable stones of inferior quality little used, and it is
inevitable that the Indian who dwelt upon the shores of the river
should have sought the workable pieces along the bluff, leaving the
refuse everywhere; and it is a necessary consequence that the terrace
margin, the bluff face, and the talus deposits, places little fitted
for habitation, should for long distances contain no trace of any
art shapes save such as pertain to manufacture. Thus are fully and
satisfactorily accounted for all the turtle backs and other rude
forms that our paleolith hunters have been so assiduously gathering.
Nothing can be more fully apparent than that no other race than the
Indian in his historic character and condition need be conjured up to
reasonably account for every phase and every article of the recovered
art. Mistaken interpretations of the nature of shop rejects, and the
common association of these objects with redistributed gravels, are
probably accountable for the many misconceptions that have arisen.
Talus deposits form exceedingly treacherous records for the would-be
chronologist. They are the reef upon which more than one paleolithic
adventurer has been wrecked.

Relics of art attributed to gravel man have been collected, so far
as I can gather from museum labels and from incidental references in
various publications, from a number of sites aside from the two already
referred to. These are scattered over the city, and the finds were made
mostly in exposures of the gravels that remained visible for a short
time only, as in street and cellar excavations and well pits. These
reported finds can never be brought within the range of re-examination,
and the searcher after unimpeachable testimony must content himself
with placing them in the doubtful column on general principles.
Urban districts are so subject to disturbance through cutting down
of hills, filling in of depressions, grading of streets, digging of
foundations, cellars, sewers, wells and graves that no man can, from a
limited exposure such as those producing the reported tools necessarily
were, speak with certainty of the undisturbed nature of the deposits
penetrated. It is doubtful if any one is justified in publishing such
observations at all without serious query. Such testimony is liable
to fall of its own inherent weakness, being absolutely valueless if
unsupported by collateral evidence of real weight. It can only be made
permanently available to science by the discovery of something unusual
or unique with which to couple it, something decidedly un-Indian in
character or type, as for example the two skulls now in the Peabody
Museum. These objects and the antler knife-handle exhibited with them
may be alluded to as the only finds so far made at Trenton, having
of themselves the least potentiality as proof and these skulls and
this knife-handle must yet be subjected to the rigid examination made
necessary by the importance of the conclusions to be based upon them.

Something may now be said concerning the art remains upon which
this discussion hinges, and upon which conclusions of the greatest
importance to anthropology are supposed to depend. Let us pass over
all that has been said with regard to their manner of occurrence and
association with the gravels and ask them simply what story they tell
of themselves. Does this story, so far as we are able clearly to read
it, speak of a great antiquity and a peculiar culture, or does it hint
rather at vital weaknesses in the position taken by the advocates of
these ideas? We shall see. The history of the utilization of rudely
flaked stones in the attempt to establish a gravel man in America
has never been written, but as read between the lines of paleolithic
literature, it runs about as follows: The theory of a very rude and
ancient people, having a unique culture and certain peculiar art
limitations, was developed in Europe many years ago in a manner well
known and often rehearsed. This people was associated with the ice age
in Europe, and this epoch, with its moraines and till and sedimented
gravels, was found to have been repeated in America. It was the most
natural thing possible that these discoveries should carry with them
the suggestion that man may have existed here as in Europe during that
epoch, and that his culture was of closely corresponding grade. These
were legitimate inferences and warranted the instituting of careful
researches, but it was a dangerous suggestion to put into the minds of
enthusiastic novices with fertile brains and ready pens. The idea was
hardly transplanted to American soil before finds began to be made. The
so-called "types" of European paleoliths suggested the lines upon which
finds here should be made, and everything in the way of flaked stones
connected directly or indirectly with the glacial gravels which had not
yet been fully credited to and absorbed by the inconvenient Indian, was
seized upon as representing the ancient time and its hypothetic people
and culture. In the early days of the investigation the various rude
forms of flaked stones, resulting from failures in manufacture, had not
been studied, and were shrouded in convenient mystery, and they thus
became the foundation of the new archeologic dynasty in America, the
dynasty of the turtle-back. Dr. Abbott states in his first work[4] that
these rude "implements" are not especially characteristic of any one
locality, but seem to be scattered uniformly over the state. Specimens
of every type, he says, are "found upon the surface, and are plowed
up every spring and autumn; but this in no way militates against the
opinion that these ruder forms are far older than the well-chipped
jasper and beautifully-polished porphyry stone-work."[5] At that stage
of the investigation it was not at all necessary that a specimen should
come from the gravels in place or from any given depth, since the
"type" was supposed to be easily recognized and was a sufficient means
of settling the question of age.

[4] Abbott, C. C. The Stone Age in N. J., Sm. Rep. 1875, p. 247.

[5] Ibid, p. 252.

Rude "implements" were called for and they were found. The only
requirements were that they should not be of well-known Indian types,
that they should be rude and have some sort of resemblance to what
were known as paleolithic implements abroad. Since most of these
so-called gravel implements of Europe are also doubtless the rejects
of manufacture resemblances were readily found. The early attempts
to utilize these rejects in support of the theory, and make them
masquerade creditably as "implements" with specialized features and
self-evident adaptation to definite ice-age uses, now appear decidedly
amusing. Gradually, however, the lines have been drawn upon this early
license, and it is to-day well understood by all careful students, that
since the rude forms are so often repeated in modern neolithic refuse,
the only reliable test of a gravel "implement" is its occurrence in
the gravels in place. That a particular "implement," said to have been
obtained from the gravels, is of "paleolithic type," does not in the
least strengthen its claims to being a _bona fide_ gravel implement;
nor does its easy assignment to a "type" give any additional value to
the collector's claim that the gravels said to contain it are implement
bearing. The very names, "rude implement," "paleolithic implement,"
etc., carry with them a certain amount of mysterious suggestion; one
thinks of unique, significant shapes and of strange, archaic uses.
At their mere mention, the great ice sheet looms up with startling
realism, and the reindeer and the mighty mammoth appear upon the
scene. The reader of our paleolithic literature is led to feel that
these antiquated objects carry volumes of history in their worn and
weather-beaten faces, but this is all the figment of fertile brains.
These objects have without exception the appearance of the most
commonplace every-day rejects of manufacture without specialization and
without hidden meaning. They tell of themselves no story whatsoever,
save that of the oft-repeated failure of the aboriginal blade maker in
his struggle with refractory stones. This will be shown with greater
clearness farther on.

But the scheme does not end with the repetition of a European state of
affairs. Our gravel archeologists have not been content to adopt that
feature of the foreign scheme which utterly destroys the paleolithic
race before a higher culture is brought upon the scene. It was
thought to improve upon the borrowed plan by allowing for a gradual
development upward from the paleolithic stage, represented exclusively
by a class of meaningless bits of flaked stone, through a period less
rude, characterized by productions so far advanced as to be assigned
to a definite use. These latter productions consist mainly of rather
large and often rude blades, sometimes plain, but generally notched or
modified at the broader end as if to be set in a handle, or attached to
a spear or arrow shaft. These were assigned to post-glacial times in
such a way as to bridge or partly bridge the great space between the
glacial epoch and the present. They were separated arbitrarily from the
body of the collections of the region, and referred to as probably the
work of an Eskimo race. This arrangement produced a pleasing symmetry
and completeness, and brought the history of man down to the beginning
of the Indian epoch, which is represented by all of those forms of art
with which the red man is historically associated.

Three principal periods are thus thought to be represented by the
finds at Trenton; and in the arrangement of the collections these
grand divisions are illustrated by three great groups of relics, which
are looked upon by the founders of the scheme as an epitome of native
American art and culture. By others this grouping is looked upon as
purely empirical, as an arbitrary separation of the normal art remains
of the historic Indian, not suggested by anything in the nature or
condition of the objects, nor in the manner of their discovery.

The "Eskimo" feature of the scheme requires a more detailed examination
than can be given it here. It may be stated, however, that the
separation of the so-called Eskimo spear points, or whatever they
may be, from the great body of associated articles of flaked stone,
appears to be a highly arbitrary proceeding. That they were extensively
made by the Indians is proved by the occurrence of refuse resulting
from their manufacture on modern shop sites, and that they were used
by the Indian, is equally apparent from their common occurrence on
modern dwelling sites. The exceptionally large size of the argellite
points is readily accounted for by the nature of the material. It was
the only stone of the region well adapted to the manufacture of long
blades or projectile points. Jasper, quartz and flint have such minute
cleavage that, save in rare cases, small implements only could be
made from them. Their peculiar manner of occurrence, described at so
much length by Dr. Abbott,[6] has been given undue consideration and
weight. The phenomena observed may all be accounted for as a result of
the vicissitudes of aboriginal life and occupation within the last few
hundred years as fully and satisfactorily as by jumping thousands of
years backward into the unknown.

[6] Abbott, C. C. Popular Science Monthly, Dec., 1889.

Whatsoever real support there may be for the "Eskimo" theory, either in
the published or the unpublished evidence, it is apparent that under
the present system of solitary and inexpert research, the scientific
world will gain little that it can utilize without distrust and danger.
Whatsoever may be the final outcome--which outcome is bound to be the
truth--it is clear that there is little in the present evidence to
warrant the separation of a "paleolithic" and an "Eskimo" period of art
from that of the Indian.

That the art remains of the Trenton region are essentially a unit,
having no natural separation into time, culture or stock groups,
is easily susceptible of demonstration. I have already presented
strong reasons for concluding that all the finds upon the Trenton
sites are from the surface or from recent deposits, and that all may
reasonably be assigned to the Indian. A find has recently been made
which furnishes full and decisive evidence upon this point. At Point
Pleasant, on the Delaware, some twenty-five miles above Trenton, there
are outcrops of argillite, and here have been discovered recently the
shop sites upon which this stone was worked. There are two features
of these shops to which the closest attention must be given. The
first is that they are manifestly modern; they are situated on the
present flood plain of the Delaware, and but a few feet above average
water level, the glacial terrace here being some forty or fifty feet
in height. These shops, therefore, represent the most modern phases
of aboriginal industry, and may have been occupied at the coming of
William Penn. The second point is that every type of flaked argillite
found in the Trenton region, associated with the gravels or otherwise,
is found on this site. It was to a certain extent a quarry site, for
the great masses of argillite brought down by the floods were here
broken up and removed from the river banks or bed. It was a shop site,
for here the articles, mainly blades, were roughed out, and it was
also a dwelling place--a village site--where all the specialized forms
of flaked stones made from the blades were prepared for use. Here are
found great numbers of the rude failures, duplicating every feature
of the mysterious "paleolith" with which our museums are stocked,
and exhibiting the same masterly quitting at just the point "where
no further shaping was possible."[7] Here we see the same boldly
manipulated "cutting edge," the "flat bottom" and "high peak," and the
same mysteriously weathered and disintegrated surfaces, so skillfully
made, by a nice balancing of accidents,[8] to tell the story of
chronologic sequence in deposition.

[7] Abbott, C. C. Smithsonian Report, 1875, p. 248.

[8] Ibid. Primitive Industry, p. 487.

Beside the failures, we have here, as on other quarry shop sites, the
evidence of more advanced work, the wide, thick, defective blades, and
many of the long, thin blades broken at or near the finishing point.
Here, too, just back of the roughing-out shops, are the dwelling sites
from which many specialized forms are obtained. The "Eskimo" type
is fully represented as well as the ordinary spear point, the arrow
point, and the perforator of our Indian. There is not a type of flaked
argillite known in the Delaware valley that may not be duplicated
here on this modern Indian site, and this has been known by local
archeologists for years. Why so little has been said about the matter
is thus explained. Dr. Abbott, in 1890, discovering this site, and
finding "typical paleolithic implements" (the ordinary ruder forms of
rejects) among the refuse, was so entirely at a loss to explain the
occurrence that he felt compelled to again "take up the examination
of the gravel deposits of the valley of the Delaware" with the hope
of "finally solving the problem."[9] The true conditions would have
been at once apparent to any one not utterly blinded by the prevailing
misconceptions.

[9] Abbott, C. C. Annual Report of the Curator of the Museum of
American Archeology, University of Pennsylvania. No. 1, p. 7.

The entire simplicity of the archeologic conditions in the Delaware
valley may be further illustrated. Had William Penn paused in his
arduous traffic with the tawny Delawares, and glanced out with
far-sighted eyes from beneath the pendant branches of the great elm
at Shackamaxon, he might have beheld an uncouth savage laboriously
fabricating rude ice age tools, making the clumsy turtle-back, shaping
the mysterious paleolith, thus taking that first and most interesting
theoretical step in human art and history. Had he looked again a few
moments later he might have beheld the same tawny individual deeply
absorbed in the task of trimming a long rude spear point of "Eskimo"
type from the refractory argillite. If he had again paused when another
handful of baubles had been judiciously exchanged, he would have seen
the familiar redskin carefully finishing his arrow points and fitting
them to their shafts preparatory to a hunting and fishing cruise on the
placid Delaware. Thus in a brief space of time Penn might have gleaned
the story of the ages--the history of the turtle-back, the long spear
point and their allies--as in a single sheaf. But the opportunity was
wasted, and the heaps of flinty refuse left upon the river bank by the
workmen were the only record left of the nature of the work of that
day. Two hundred years of aboriginal misfortune and Quaker inattention
and neglect have resulted in so mixing up the simple evidence of
a day's work, that it has taken twenty-five years to collect the
scattered fragments, to sift, separate and classify them, and to assign
them to theoretic places in a scheme of culture evolution that spans
ten thousand years.

Yet is there really nothing in it all, in the theories, the
observations, the collections and the books? Do I speak too positively
in condemnation of the results of years of earnest investigation?
Perhaps so, but the voluminous testimony is so overloaded with
inaccuracies, the relics of unscientific method and misleading
hypotheses, that every item must be sharply questioned; and the
conclusions reached so far overstep the limits warranted by the
evidence, that heroic measures alone can be effectual in determining
their exact value. If, as many believe, vital errors have been
embodied in the evidence presented by the advocates of the theory,
it is impossible to state the case too strongly. Error once fully
absorbed into the literature of science has many advantages over the
tardy truth; it is strongly fortified and must be attacked and exposed
without fear or favor. Truth involved with it cannot permanently
suffer. If the twin theories of a gravel and a paleolithic man in
eastern America are to be assailed as unsound or as not properly
supported, it should be done now while the originators and upholders
are alive and alert to sustain their positions or to yield to the
advances of truth. I do not wish to wrongly characterize or to unduly
minimize the evidence brought to bear in favor of these theories. I do
intend, however, to assist the world so far as possible in securing an
exact estimate of all that has been said and done, and all that is to
be done.

In a previous article I have examined the evidence relating to
paleolithic art in the eastern United States, and have indicated
its utter inadequacy and unreliability. In this paper the testimony
relating to the occurrence of gravel art, in the locality most fully
relied upon by advocates of the theory, has been partially reviewed
and subjected to the strong light of recent observations. It is found
that the whole fabric, so imposing in books and museums, shrinks away
surprisingly as it is approached. The evidence furnished by the bluff
face and by the railway cutting, the two leading sites, is fatally
weakened by the practical demonstration of the fact that the gravels
proper are at these points barren of art remains. In endeavoring to
naturalize an immigrant hypothesis, our gravel searchers, unacquainted
with the true nature of the objects collected and discussed, and little
skilled in the observation of the phenomena by means of which all
questions of age must be determined, have undoubtedly made grievous
mistakes and have thus misled an expectant and credulous public.

The articles themselves, the so-called gravel finds, when closely
studied are found to tell their own story much more fully and
accurately than it has heretofore been read by students of archeology.
This story is that the art of the Delaware valley is to all intents and
purposes a unit, that there is nothing unique or especially primitive
or ancient and nothing un-Indian in it all. All forms are found on
demonstrably recent sites of manufacture. The rude forms assigned
by some to glacial times are all apparently "wasters" of Indian
manufacture. The large blades of "Eskimo" type are only the larger
blades, knives and spear points of the Indian, separated arbitrarily
from the body of the art-remains to subserve the ends of a theory,
certain obscure phenomena of occurrence having been found to give color
to the proceeding. To place any part of this art, rude or elaborate,
permanently in any other than the ordinary Indian category will take
stronger proofs than have yet been developed in the region itself.

The question asked in the beginning, "Are there traces of glacial man
in the Trenton gravels?" if not answered decisively in the negative,
stands little chance, considering present evidence, of being answered
in the affirmative. In view of the fact that numerous observations
of apparent value have been made in other sections, there is yet
sufficient reason for letting the query stand, and we may continue to
cherish the hope that possibly by renewed effort and improved methods
of investigation, something may yet be found in the Trenton gravels
clearly demonstrative of the fascinating belief in a great antiquity
for the human race in America.

The evidence upon which _paleolithic man_ in America depends is so
intangible that, unsupported by supposed analogies with European
conditions and phenomena, and by the suggestions of an ideal scheme
of culture progress, it would vanish in thin air; and if the theory of
a _glacial man_ can summon to its aid no better testimony than that
furnished by the examples examined in this paper, the whole scheme,
so elaborately mounted and so confidently proclaimed, is in imminent
danger of early collapse.

                                                        =W. H. Holmes.=




GEOLOGY AS A PART OF A COLLEGE CURRICULUM.


The demand for scientific studies as a part of the college curriculum
is felt by all those who have to do with the provision of higher
instruction for American youth. The reasons for this may be various,
but a fundamental reason is found in the tendency among the American
people in particular, and in this age in general, toward practicality
in all things. Applied to education this practicality asks for a
training which shall have a direct bearing upon the business of life to
be followed immediately after the training period is ended. It means
a differentiation of subjects and specialization in methods to adjust
the education to the different functions which the students taking it
are preparing for. It calls for a professional education for those
who expect to become lawyers, doctors, ministers, or teachers,--a
technical education for those who are to engage in the arts of the
mechanical or civil engineer, or of the architect. It results not only
in the establishment of colleges and universities devoted to this
kind of education, but it affects the methods of the high schools and
academies, and is felt down to primary schools, and on the other hand
the older institutions founded on a different plan are adapted to the
popular demand by the addition to the regular studies of "electives,"
chosen not always for their value or disciplinary studies, but because
of the practical applicability of the information to be derived from
them, to the business of the student.

Without discussing the relative merits of the two ideas of education,
the chief contrast between them may be found in the character of the
results sought. The knowledge of things and their uses is of chief
importance in the practical education; the knowledge of ideas and skill
in their use is the aim of the liberal education. Geology is one of the
sciences which most men will at once classify as among the practical
sciences. It deals with matters of practical importance to everybody.
Coal, iron, the metals, silver, gold, tin, lead, building stone, sand,
clay, petroleum, and natural gas, and all geological products are
essential materials of modern civilization, and a knowledge of them
and of their modes and places of occurrence is one of the requisites
of an education, either from the practical or the liberal point of
view. So too the dynamics of atmospheric and hydraulic erosion, the
agency of rivers and oceans in destruction, removal and reconstruction
of geological formations have their eminently practical bearings upon
the various arts of engineering. While the practical value of geology
is thus evident and undisputed, it is not on this account that its
importance as a part of a college course of education is urged. As
a practical study geology becomes the centre of a group of studies
requiring years for mastery. Chemistry and physics are primarily
essential to a full understanding of the most common of geological
problems. And to use geological facts and phenomena, an acquaintance
with the complex methods of engineering, civil and mechanical, which
again call for a thorough mastery of mathematics, is necessary.
Mineralogy and petrography, metallurgy and mining engineering have
each reached a stage of development entitling them to the rank of
separate sciences, but the practical training of the geologist should
include them all. When we add the biological sciences connected with
historical geology, paleontology, zoölogy and botany, with all the
laboratory and field work required for their proper study, we have a
group of affiliated branches of learning requiring four or five years
of continuous study after the student has learned how to study. It is
plain therefore that only a specialist, one who is willing to neglect
other studies, or who has previously had a liberal training, can
perfect himself on the practical side in the science of geology.

But irrespective of its practical uses, as a means of training and
supplementary to the ordinary studies of a college curriculum, geology
is one of the most useful of the sciences of observation. It is
in providing that particular training to which President Eliot has
recently called attention in the _Forum_ (Dec., 1892, Wherein Popular
Education Has Failed), that geology can be used to such advantage.
Speaking particularly of the lower education, President Eliot says
it is "the judgment and reasoning powers" that particularly require
attention. Their systematic development is to be attained in the four
directions of "observing accurately, recording correctly, comparing,
grouping and inferring justly, and expressing cogently the results of
these mental operations." (p. 421.) The attainment of these ends is
one of the purposes of liberal education, whether it be in the primary
school or in the university. And geology, or any other science, is
of value in a college course in proportion to its fitness for the
exercise and development of these functions of the student. Geology may
be taught without regard to these ends, and then it is valuable from
the practical point of view, but when we examine it in respect of its
availability as a disciplinary study we find it offering particular
attractions.

Using the distinction between theory and practice, which is as old
as Aristotle, geology in its theoretical aspect is more easily
comprehended than is the theoretical aspect of most of the modern
sciences. This arises first from the fact that the facts and phenomena
are of a simple and grand nature, making it possible for the teacher
to direct certain attention to the specific facts under consideration.
The water of the rivers, the mud by the road side, the rocks and sands
on the shore are familiar objects to all, and it is a simple matter to
call attention by ordinary language to the specific facts regarding
them, which, analyzed out, are to form the basis of exact ideas and
scientific definition and classification. Geology is the one science
among the natural sciences which may begin with the common language
of the pupil, and by means of such language alone may build up ideas
of precise phenomena in scientific terms. Physiography or physical
geography surpasses geology proper in this particular, as the admirable
work of Professor Davis is showing, and on this account it is the best
introduction to geology. But the very largeness and indefiniteness
of the facts are in the way of the use of physical geography for the
exercise of the finer and more exact functions of observation. The
disciplinary value of classics and mathematics is to a considerable
extent derived from this quality, the precision with which the words
or figures kindle like ideas. So long as the object of the training
is to teach the knowledge of ideas and how to use them, classics and
mathematics are the simplest and purest means of developing a liberal
education. The addition of sciences to the college course is not
because of the usefulness of the knowledge of things thus to be gained,
but because the language of the sciences is essential to call forth the
observation and the exercise of the accompanying mental operations.

When it comes to dealing with the ideas associated with particular
sense-observation, where form or motion can not be expressed in
simple mathematical terms, language can not communicate a new idea
or kindle it in another mind with precision. It is necessary by some
means to recall or to present the object itself to the student. In
the teaching of science this point is of great importance, and much
of the unsatisfactoriness of science-teaching is doubtless due to
failure to note it. No circumlocution of words can arouse in another
or communicate to him the idea appropriate to a sensation he has never
felt. The blind man whose eyes are opened sees men as trees walking.

In the use of science for elementary training (and the training
is elementary until the student is capable of investigating and
interpreting the facts and phenomena of a science directly) that
science is the better which deals with objects which are simple, common
and easily observed. Such is geology in some of its aspects. Every time
the student walks in the country he sees the facts discussed in the
text-book or by his teacher; and from attention to those with which he
is already familiar he can be readily led to observe and give attention
to others and to analyze those already in his mind by properly directed
questions.

In the field of geology are found the ready means for the exercise
and development of observation and thought. The learner begins
with ideas which every intelligent mind associates with the objects
described or named, and by degrees the marks of his knowledge are
increased, the relations of things are grasped, and the content of his
ideas associated with the language of his science is enlarged. In the
process of learning the science he has been building up his stock of
knowledge of facts and phenomena, but, of more importance than that,
he has learned the method of observing and of scientific thinking.
He has had training in the methods of reducing the hard facts of
nature to the laws of thought and practice, he has seen the method by
which theoretical order is made out of the interminable confusion and
complexity of natural things.

Beside this primary reason for the use of geology as a disciplinary
science-study, there is a second reason arising from the symbolic
nature of a large group of its facts. This aspect of the science is
best seen in the historical and stratigraphical parts of geology, in
which fossils are the chief data for study. The interpretation of a
fossil into a species of organism, having its definite place in the
elaborate classification of the zoölogist, or as an indicator of
the time and place and mode of formation of the strata in which it
is buried, is, to be sure, a most intricate and, at first thought
it would seem, an unattractive process. But no more so, I would
say, than the interpretation of a series of Greek characters. The
interpretation of the Greek reveals to us the richest results of human
thought and most perfect laws of human speech, and we find therefore
in the analysis required the most perfect discipline of the powers
of speech and language. The fossil too holds, ready to be revealed,
the story of the history of the world and the laws of the evolution
of the organic life of the globe, and records an inexhaustible wealth
of information regarding the laws of nature. But as an instrument of
intellectual discipline its great merit lies in its symbolic nature.
It is this symbolic character of the classical languages and of the
mathematics which fits them to be universal means of liberal training.
The symbolic nature of the fossil fits it to become the exponent of
training in the pure science of nature. The fossil is a mark which
stands for something, and thus, in the nature of things, it asks
for interpretation. As a symbol it stimulates minute and accurate
observation, and kindles close and exhaustive thought; as a symbol it
leaves us the ideas it has engendered after it is lost to memory as
an observation. Thus the value of its study does not depend upon the
retention in the memory of the facts brought before the mind, but in
the training of the mental processes required in its interpretation.
The study of this branch of geology exercises and develops all the
faculties which are specially exercised in any scientific investigation.

Another aspect in which it is an ideal means for such training comes
from the fact that it is equally valuable at every stage of progress
of the student. When first examined it means nothing to him. He knows
nothing of organism, of strata, of geological time. The fossil gains
meaning only as he is able to put meaning into it. The student must
ask questions, and as step by step he answers his questions by more
minute and wider examination, the fossil holds a fuller interpretation.
His studies lead him to investigation of the whole field of nature,
the rocks, the formation of deposits, the action of the elements, the
conditions of life, the forms of organism, their functions and habits,
the laws of growth, their adaptation to environment, the changes of
events in time, the efforts of association and struggle for life, the
principles of evolution and development--the migration and origin and
extinction of organisms on the globe. Nothing in nature is without
interest to him. Further than this the amount of good he gains is not
measured by the number of fossils he studies, but by the wideness of
his research. A handful of fossils from some one fossiliferous ledge
may be the text for a year's study, and the methods acquired in the
study may be the nucleus of a life's work. In this department of
geology the possibilities for new discoveries, new developments of
science are almost endless. As a single author thoroughly read develops
a wealth of knowledge of the laws of language and thought, so geology
may be studied by the use of a limited set of its phenomena and become
the introduction to the exhaustive study of natural science.

Another advantage attaching to geology as a science-study for the
college curriculum, arises from the fact that it may be pursued deeply
without the elaborate aid to the senses required in other sciences
for making minute record or measurement of facts or phenomena. As in
language and mathematics, it is essential to acquire a familiarity
with the grammar, the dictionary and the symbols, formulas and rules
of their usage before the finer training in the use of thought begins,
so the vocabulary and the definitions of a science must be acquired
before much use can be made of the higher discipline to be derived from
scientific study. In language study this higher training comes from
practice in making the minute analysis, in detecting the fine shades
of meaning expressed in the literature itself. So it is important in
selecting a science to be used as a disciplinary study that the facts
and laws of nature with which it is concerned should be capable of
clear and precise definition, and, moreover, that it should furnish a
field for the study of the minute and intricate relationship existing
between the different facts which are to be attained by personal
inspection of the objects themselves. In most of the sciences this
deeper exercise of scientific thought requires for its successful
pursuit artificial aids to the common senses of observation. Chemistry
must have its purified acids and reagents, test tubes, and delicate
scales for measurement of weight and volume. Mineralogy must have its
chemical analyses, or optical measurements so fine that microscopes
of highest power are essential tools for the investigation. Physics
must have the most delicate measurements of time and space and weight.
Botany, for the earlier stages of study, is fully equal to geology in
these respects, but its scope is much less general. Zoölogy requires
dissections calling for skill in manipulation, and in other respects
is ill adapted to general classes. But precision in the intellectual
processes of observation and reasoning can be cultivated in the use of
geological facts to their highest and widest perfection, with scarcely
any aids to the normal faculties of observation. A couple of hammers,
a pocket lens, a chisel and a few pointed steel tools for revealing
fossils, a tape line, compass and clinometer are the few equipments
that will enable the geologist to carry his investigations to almost
any degree of thoroughness.

What has already been said applies to the study of the pure science
of geology either in the field or in the laboratory. There is
still another use to which this, as other sciences, may be put in
disciplining the college student in directions not provided for by
literary or mathematical studies,--the study of man as an investigator.
In the pursuit of the study of geology, the first instruction must be
received in didactic form, but after the text-book and lecture stage
is passed, or while it is under way consultation of the literature
of the sciences is appropriate. In the use of scientific literature
the critical judgment is brought under training, and the varying
interpretations of well known phenomena by expert scientists suggest
the prominent part which the notions already in the mind play in
the interpretation of the external facts observed. The experienced
geologist will recall many cases of honest report of impossible facts
by men who are unable to distinguish between what they saw and the
false interpretations they made of these observations. One man will
report that a live toad jumped out of the middle of a solid piece of
coal, when it was heated in the stove; another will swear that he saw
a fossil shark's tooth taken out of a ledge of Trenton limestone.
It is evident that our memory of observation is not the revival of
the object producing the sensation, but of the idea we framed of the
sensation at the time. The study of original descriptions of objects of
nature reveals the fact that the describer uses the ideas he already
has in his mind as he does the standard foot-rule in his hand for
measuring that which he describes, and it is by the study of scientific
literature and the comparison of views of many scientists that this
highest discipline of the observational faculties is attained--the
power to determine the personal equation of error for the observer,
and thus see through his descriptions a truer representation of the
facts than the observer himself saw. Geological literature is admirably
adapted for this higher discipline, and in no field of science (I think
not in astronomy itself), has wider and more comprehensive thought been
applied than in geology. While other branches of science have been
developed and become more narrow and special in their treatment of the
facts concerned, geology still stands as the most comprehensive of all
the sciences of nature.

                                                        H. S. Williams.

  =Yale College=, November 30, 1892.




THE NATURE OF THE ENGLACIAL DRIFT OF THE MISSISSIPPI BASIN.


It is of some importance, both to the practical work of the field
and the theoretical deductions of the study, to determine the nature
and amount of the drift that was carried forward in the body of the
ancient continental glaciers, and brought out on their terminal slopes
and at length deposited at their frontal edges, and to distinguish it
from that which was pushed or dragged or rolled along at the bottom of
the ice.[10] It may be helpful to indulge in a speculative discussion
at the outset to prepare the way for the specific evidence and the
inferences to which it leads.

[10] Debris, which may be imbedded in the basal layer of the ice
during some part of its transportation, but which is brought down to
the bottom and subjected to basal action in the latter part of its
course, and ultimately becomes a part of the basal deposit, is not here
included in the englacial drift.

Whenever a prominence of rock is overridden and enveloped by a
glacier of the free-moving continental type, one of two things takes
place; either that part of the ice which passes over the summit of
the prominence flows down its lee slope, carrying whatever debris it
dislodges down to the rear base, and thence onward along the bottom
of the ice, or else the currents which pass on either side of the
prominence close in behind it before the corresponding current which
passes over the summit reaches the point of their junction, in which
case the summit current is forced to pass off more nearly horizontally
into the body of the ice, carrying with it whatsoever debris it has
dislodged from the summit of the prominence and embodied within its
base. The law of the phenomena appears to be that whenever the height
of the prominence is less than one-half the base, measured transversely
to the movement of the ice, the summit current will follow down the lee
slope; but whenever the height of the prominence is more than one-half
the transverse base, the lateral currents will close in on the lee,
and the summit current will flow off into the body of the ice. This
simple law is, however, subject to very considerable modifications from
several different sources which may be grouped under (1) differences
in the friction arising from basal contact, and (2) differences of
internal friction and mobility. The lateral currents will expose more
surface to the sides and base of the hill and the adjoining plain, and
will be more subject to conflicting currents, while, on the other hand,
being deeper currents, they will presumably be more fluent. These and
other qualifying conditions will go far to vitiate the application
of the law, but its statement may have some value as representing a
general conception of the phenomena. When the height of the prominence
becomes great relative to the total thickness of the ice, the fluency
of the summit current may be much reduced relative to that of the
central parts of the lateral currents. When the prominence reaches the
surface, blocks dislodged from it are borne away on the surface of the
glacier, and constitute superglacial drift. Blocks dislodged from near
the summit, but below the surface of the ice, are presumably carried
onward in the upper zone of the glacier; while other blocks detached
at various but sufficient heights on the side of the prominence are
doubtless borne around into the lee and carried forward in the same
vertical plane as the summit stream, so that there comes to be a
vertical zone set with boulders moving on from the lee side of the
nunatak.

Lofty ledges or plateaus, with vertical or undercut faces, furnish
similar means for the lodgment of debris within the body of the ice.

In these and doubtless in other ways it appears that there came to be
lodged directly within the body of the Pleistocene glaciers at some
considerable distances above their bases, blocks derived from rock
prominences that rose with sufficient steepness above the general
surface of the country over which the ice passed. The lodgment of
debris on the lateral borders of glaciers is neglected here because
it has little or no applicability to the phenomena of the upper
Mississippi basin. It is also doubtful whether any prominences
protruded through the ice except near the thin edge, when advancing and
retreating, and these are too inconsiderable to merit attention.

It is obvious, upon consideration, that blocks detached from summits
or from the sharp angles of out-jutting ledges or plateaus might
suffer some glacial abrasion in the process of their dislodgment and
transposition along the crest or projecting angle, but that in general
such abrasion would be small, and, in most cases, nearly or quite
absent. The debris so incorporated in the body of the ice would be,
for the most part, angular, and, as it was brought forward in the ice,
it would probably suffer very little abrasion. If it continued to move
forward in the plane in which it started, descending only so much as
the bottom wastage of the ice required, it would be brought out to
the terminal slope of the ice sheet by virtue of the melting away of
the ice above, and thence it would be carried on down the terminal
slope as superglacial debris, and dropped at the frontal edge. If this
be the true and full history, there would be no commingling of this
englacial matter with the subglacial debris. It is evident, that the
englacial matter brought forward from the crest of one prominence would
be intermingled with that brought forward from other prominences lying
in a line with it, or lying so near it that the lateral spreading of
the debris would lead to commingling. It is also clear that variations
in the direction of currents would tend to the same result, so that
englacial matter from different prominences of the same general region
might be commingled. So also englacial material, by crevassing and by
the descent of streams from the surface to the base, would be carried
down to the bottom and mingled with the subglacial debris. So also
blocks broken away from the base of the prominence which yielded the
englacial erratics might be moved forward along the bottom parallel
with the englacial material above, and lodged at any point along the
line. It is therefore to be expected that the basal deposits will
contain the same rock species as the englacial, but if there be no
process by which the basal material is carried upward the reverse will
not be the case, and there will be a clear distinction between the
englacial deposit and the subglacial deposit, in composition as well as
physical state.

Not a few glacialists, however, advocate in somewhat differing forms
and phases the doctrine that basal material is carried upward into
the body of the glacier and at length reaches the surface, and that
at the extremity of the ice this is commingled with any erratics that
may be englacial or superglacial by original derivation. This doctrine
appears to have had its origin in the endeavor to explain the very
common fact that glacial drift has been carried from lower to higher
altitudes. Erratics are often found lodged several hundred feet higher
than the outcrop from which they were derived. It has never seemed to
me, however, that this phenomenon necessarily was different in kind
from that which takes place in the bottom of every stream; at least I
have not come in contact with any instances that seemed to require a
different explanation, except those connected with kames and eskers
that require a special explanation in any case. We are so accustomed
to view streams from above, and so accustomed to study the extinct
glaciers from the bottom, that we are liable to overlook the community
of some of the simpler processes involved alike in both phenomena. The
dictum that water never runs up hill is measurably true of the surface
currents of the ice as well as water, but it altogether fails when
applied to the basal currents of either. It is probable that there is
no natural stream of any length in which, at some part of its course,
basal debris is not carried from lower to higher altitudes and lodged
there. If the bed of any stream were made dry and the debris in it
critically examined, it would be found that at numerous points the
silts or sands or gravels had been carried from the bottom of some
basin in its bed to the higher rim or bar or reef that bordered it
on the downstream side. So I conceive that, on a grander scale, the
natural result of the flow of the basal ice of a continental glacier
over the inequalities of the country was the lifting of material from
some of the lower horizons and its lodgment on the crests of ridges or
the slopes or summits of mountains that lay athwart its course.

So again, it is certain that a considerable part of the peripheral
drainage of glaciers takes place through tunnels beneath the ice.
It is reasonable to suppose that during the winter season, when the
drainage is slack, these tunnels tend to collapse in greater or less
degree, under the continued pressure of the ice and the "fattening" of
the glacier, so that in the early part of the next melting season the
contracted tunnels may be over-flooded by glacial waters. To the extent
that these tunnels become incompetent the water would become ponded
back in the crevasses and moulins by which the surface-water gains
access to them. They thus come to have something of the force of water
flowing in tubes, and may be presumed to be capable of forcing rounded
material to some considerable height, and of carrying ice-imbedded
boulders to any point reached by the stream. These tunnels probably
undulate with the bottom, and lodgment along them takes place wherever
enlargement permits.

Without, therefore, appealing to any upward cross currents within
the ice itself, it is possible to explain the transportation of the
drift from lower to higher altitudes. I have never seen phenomena of
this kind that seemed to call for any other explanation than these. I
am not prepared to say that there are no such phenomena. One of the
purposes of this article will have been accomplished, if it shall call
forth a critical statement of phenomena that require the assumption
of internal upward movements of the ice to account for them, and of
the criteria which distinguish such phenomena from those that may be
referred to upward basal movements such as are common to all streams
or to the exceptionally conditioned subglacial streams. That there are
upward internal movements in most streams is as much beyond question
as the existence of upward basal currents in rivers and glaciers, but
they are dependent chiefly upon the velocity of the current and the
irregularity of the bottom. Theoretically, as I understand, a stream
moving in a straight course on a perfectly smooth bottom would not
develop an upward cross current. Each lower layer would move slower
than that above it by reason of basal friction, but they would move
on in parallel lines. But if irregularity of bottom be introduced the
parallelism is obviously destroyed, and if the velocity be high so that
the momentum of the particles becomes great relative to their cohesion,
irregular internal movements will result, and these will often be of a
rotary nature in vertical planes bringing the basal parts of the fluid
to the surface or the reverse. For this reason rapid streams abound in
rotary currents, while slow streams do not.

Now it is quite obvious that a stream of water moving at a rate of
three or four feet per day, or even fifty or sixty feet per day, would
not develop perceptible upward currents, and certainly would not
lift the lightest silt from its bottom. I do not think there are any
theoretical grounds for believing that internal glacial currents are
developed, which flow from base to surface, carrying bottom debris to
the top.

One of the most remarkable expressions of the drift phenomena of the
Upper Mississippi region consists of belts of boulders stretching
for great distances over the face of the country, and disposing
themselves in great loops after the fashion of the terminal moraines
of the region with which they are intimately connected. Besides this,
there are numerous patches of boulders of more or less irregular form
and uncertain relations. The whole of these have not been studied
in detail, but a sufficient portion of them have received careful
examination to justify the drawing of certain conclusions from them.
Those which have been most studied lie in Ohio, Indiana, Illinois,
Michigan, Wisconsin, Iowa and Dakota. Those of the first three States
have been most carefully traced and their constitution is such as to
give them the greatest discriminative value. To these our discussion
will be limited chiefly.[11]

[11] Parts of these tracts were long since described by Bradley of
the Illinois Survey. (Geol. Surv. Ill., Vol. IV. p. 227). Collet of
the Indiana Survey (An. Rep. 1875, p. 404) and Orton and Hussey of
the Ohio Survey (Geol. Surv. Ohio, Vol. III., pp. 412, 414 and 475).
The relationship of these tracts to morainic lines and to each other
I worked out some years since (Third An. Rep. U. S. G. S. pp. 331,
332, 334) but I owe many details and some important additions to my
associate, Mr. Leverett.

Emerging from the dunes at a point north of the Iroquois river in
Jasper county, northwestern Indiana, a well characterized belt of
surface boulders stretches westward to the State line, just beyond
which it curves about to the south and then to the east, and re-enters
Indiana a little south of the northwest corner of Benton county. It
soon turns abruptly to the south and reaches the Wabash river near the
centre of Warren county. The immediate valley of the Wabash is thickly
strewn with boulders from the point where the belt reaches it to the
vicinity of West Point on the western line of Tippecanoe county. The
uplands, however, do not give any clear indication of the continuity
of the belt, and the connection is not altogether certain. There is an
inner well-marked belt that branches away from this in the central part
of Benton county and runs southeasterly into the northwestern quarter
of Tippecanoe county, beyond which only scattered boulders occur, which
leaves its precise connections also in doubt. But starting from West
Point, which is less than a dozen miles from the point where the two
belts cease to be traceable with certainty, a well-defined belt, one
or two miles wide, runs southeasterly across the southwestern corner
of Tippecanoe county and the northeastern quarter of Montgomery county
to the vicinity of Darlington, beyond which its connection is again
obscure, although boulders occur frequently between this point and the
northwestern corner of Brown county, where boulders are very abundant.
So also, patches of exceptionally abundant boulders occur in the west
central part of Clinton county. These may be entitled to be regarded
as a connecting link between the train which enters northwestern
Tippecanoe county and that of northwestern Boone county, as scattered
boulders of the surface type, but of not very exceptionally frequent
occurrence, lie between them. However this may be, a belt of much
more than usually frequent surface boulders stretches southeasterly
to the vicinity of Indianapolis, and probably connects with a very
well-marked belt lying near the south line of the southeast quarter
of Marion county and in the northeastern part of Johnson county.
There is also a well-defined tract in southeastern Hendricks county,
running east and west, without evident connection with the foregoing
tracts, though it may be the equivalent of the Darlington belt. There
is also a somewhat unusual aggregation in the form of irregular belts
in southeastern Johnson county, in the vicinity of Nineveh, and in
southern Shelby county. The belt south of Indianapolis is probably to
be correlated by scattered boulders only slightly more abundant than
those of the adjacent region, but of the surface type, stretching
northeasterly to near the center of the west half of Henry county,
where a well-marked belt again sets in. From this point the tract runs
northeasterly nearly to the north limit of the county, where it turns
easterly and runs in the vicinity of the line between Randolph and
Wayne counties to near the Ohio line, where it curves to the southeast
entering Ohio near the northwest corner of Preble county. In its
southeasterly course across that county it is phenomenally developed as
has been well shown by the descriptions of Professor Orton. Soon after
entering Montgomery county it curves about to a northeasterly course,
and crossing the great Miami river, a few miles above Dayton, holds
its northeast course across the southeastern part of Miami county,
the northwestern part of Champaign county, and thence on to about the
center of Logan county, where it curves about and runs in a direction a
little east of south to near the southeast corner of Champaign county,
beyond which it ceases to be a specially notable phenomenon.

In the region between the Wabash and Kankakee rivers, in northern
Indiana, there are numerous tracts of irregular form over which surface
boulders in phenomenal abundance are scattered. These are particularly
noticeable in southern Jasper county; in the vicinity of Wolcott, Monon
and Chalmers in White county; near Star City in Pulaski county; in
the southeastern corner of Stark county, and very generally along the
great interlobate moraines, lying parallel with the Eel river, and
some others of the Saginaw glacial lobe. These are so associated with
the inter-tangled morainic phenomena of that region as not to admit of
convenient and brief description in their genetic relationships.

The well-defined tracts have a most significant distribution. The first
part described is associated with the terminal moraine that marked
the margin of a lobe of ice that moved westward along the axis of the
Iroquois basin to a point a few miles beyond the Indiana-Illinois line.
The portion that runs southward to the Wabash is associated with the
moraine that follows the same course, and runs at right angles over the
older moraines of the Lake Michigan lobe. The tract in Tippecanoe and
Montgomery counties, that in south Marion county, and that in Henry and
Randolph counties, in the eastern part of the state, are associated
with the terminal moraines that form a broad loop with the West White
river basin lying in its axis. In western Ohio the belt is intimately
associated with a moraine that bordered the Miami lobe of the ice
sheet, and the south-trending portion in eastern Logan and Champaign
counties lies on the western margin of the Scioto lobe.

The relationship of these tracts to terminal moraines is very clear and
specific. They constitute marginal phenomena of the ancient ice sheet.
Their distribution completely excludes their reference to floating ice,
for they not only undulate over the surface utterly negligent of any
horizontal distribution, but they are disposed in loops in crossing the
basins of the region, and the convexities of these loops are turned
down stream. These basins for the most part open out in southerly or
westerly directions which makes it improbable that ice-bearing bodies
of water occupied them. But if this were not fatal, certainly the
fact that the convexities of the boulder belts are turned down stream
and cross the centers of the basins is precisely contrary to the
distribution they must have assumed if they were due to floating ice
in bodies of water occupying the basins. I hold it, therefore, to be
beyond rational question that these tracts were deposited as we find
them by the margins of the glacial lobes that invaded the region.

If these boulder belts were of the same nature as the average boulders
of the till-sheets beneath them, then the simple fact of unusual
aggregation might be plausibly referred to the accidents of gathering
and deposition. But they are very clearly distinguished from the
average boulders of the till by several characteristics.

1. They are superficial. Sometimes they rest completely on the surface,
sometimes they are very slightly imbedded, sometimes half buried,
sometimes they protrude but a slight portion, and sometimes they are
entirely concealed, but lie immediately at the surface. In all cases
the aggregation is distinctly superficial. Where they are buried, the
burying material is usually of different texture and composition from
the subjacent till, and appears to be distinct in origin from it. The
superficiality of the tract is very obvious almost everywhere, and is
especially so in regions where the subjacent till is of the pebble-clay
rather than boulder-clay order, for the comparative absence of boulders
below emphasizes the contrast. Throughout most of the region the
subjacent till is not of a very bouldery type, so that the distinction
is generally a marked one.

2. The boulders of the belts are almost without exception derivatives
from the crystalline terranes of Canada. Those of the great tract
especially under consideration were derived from the typical Huronian
rocks of the region north of Lake Huron, and from granitic and
gneissoid rocks referable to the Laurentian series of the same region.
These last, however, cannot be sharply distinguished from the granitic
rocks derived from other parts of the Laurentian terrane. The Huronian
rocks are very easily identified because of the peculiarities of some
of the species. Among these the one most conspicuously characterized
is a quartz-and-jasper conglomerate. The matrix is usually a whitish
quartzite. This is studded with pebbles of typical red jasper and of
duller rocks of jasperoid nature, which grade thence into typical
quartzite pebbles. With these are mingled crystalline pebbles of other
varieties. Another peculiar erratic comes from the "slate conglomerate"
of Logan. It consists of a slaty matrix through which are scattered
rather distantly pebbles of granitic, quartzitic and other crystalline
rocks. This is one of the forms of the "basal conglomerate" of Irving.
Other varieties of this "basal conglomerate" are present. In addition
to these very peculiar rocks, a quartzite of a very light greenish
semi-translucent hue has a wide distribution along the tract. It is
readily distinguishable from the numerous other quartzites of the drift
of the interior. Some years since, on returning from my first field
examination of a portion of this belt, I sent a typical series of chips
from the characteristic erratics to Professor Irving, who had recently
returned from the study of the original Huronian region. He returned a
suite of chippings that matched them perfectly throughout, all of which
were taken _in situ_ in the region north of Lake Huron.

Among the boulders of the belt are occasionally found specimens of
impure limestone or of limy sandstone that might perhaps be referred
doubtfully to some member of the paleozoic series; but on the other
hand, might with equal or greater probability perhaps be referred to
the similar rocks of the Huronian series. These are quite rare, never
forming, so far as my observations go, as much as one per cent. of
the series. In the several definite enumerations made to determine
the percentage of the doubtful specimens, the result never exceeded
a fraction of one per cent. In the most extensive enumeration the
result was about one-half of one per cent. Aside from these doubtful
specimens there are practically no boulders in the belts that can be
referred to any of the paleozoic rocks that intervene in the 500 miles
between the parent series north of Lake Huron and the tract over which
the boulders are now strewn. Occasionally there may be seen erratics
from the paleozoic series at or near the surface, but they are not
usually so disposed on the surface as to appear to be true members of
the superficial boulder tract. There is, therefore, the amplest ground
for the assertion that these boulder tracts are of distant derivation,
and that they are essentially uncommingled with derivatives from the
intermediate region.

3. The boulders of this series are much more angular than those of
the typical till sheets. Some of them, indeed, are rounded, but the
rounding is generally of the type which boulders derived by surface
degradation and exfoliation present. They rarely have the forms that
are distinctively glacial. Quite a large percentage are notably
angular, and have neither suffered glacial rounding nor spherical
exfoliation. Some few are glacially worn and scratched, but the
percentage of these is small.

The tracts therefore present these four salient characteristics: (1)
the boulders are derived from distant crystalline terranes (400 to 500
miles) and are essentially uncommingled with rock from the intervening
paleozoic terranes; (2) they are essentially superficial, and the
associated earthy material has a texture differing from that of the
subglacial tills; (3) they are notably angular and free from glacial
abrasion, except in minor degree; (4) the tracts are so associated with
terminal moraines and so related to the topography of the region, that
there is no rational ground for doubt that the boulders were borne to
their present places by the glaciers that produced the correlative
moraines.

In contrast to these superficial boulder formations, the till sheets
below are made up of a very large percentage of glacial clay whose
constitution shows that it was produced in part by the grinding down
of the paleozoic series. In this are imbedded boulders and pebbles
that were derived from the paleozoic series as indicated by their
petrological character, and, in many instances, demonstrated by
contained fossils. While a small part of the boulders contained in the
till are angular or but slightly worn, the larger part are blunted,
bruised, scratched and polished by typical glacial action. This obvious
grinding of the boulders, taken in connection with the clay product
resulting from the grinding, affords a clear demonstration that the
deposit was produced at the base of the ice by its pushing, dragging,
rolling action.

The two formations, therefore, stand in sharp contrast; the one
indicating the passive transporting action of the ice in bearing from
their distant homes north of the lakes the crystalline boulders and
dropping them quietly on the surface, the other indicating the active
dynamic function of the ice in rubbing, bruising and scoring the
material at its base. The one seems to me a clear instance of englacial
and superglacial transportation; the other an equally clear example of
subglacial push, drag and kneading.

Now if it were the habit of an ice-sheet of this kind to carry material
from its bottom to the surface by internal movement, it would seem
that the distance of 400 to 500 miles which intervened between the
source of the crystallines and the place of their deposit would have
furnished ample opportunity for its exercise, and that there would
have been commingled with the englacial and superglacial material many
derivatives from the intermediate region, and these derivatives should
have borne the characteristic markings received by them while at the
base of the ice. The very conspicuous absence of such commingling,
and the absence or phenomenal rarity of anything that even looks like
such a commingling, appears to me to testify in quite unmistakable
terms to the distinctness of the methods of transportation. In view
of the great territory over which this particular belt is spread,
and the greater territory which is embraced in the other tracts not
here specially considered, there is left little ground for doubt
that this distinctness of englacial from basal transportation was
a prevailing fact and not an exceptional one. This is supported
by concurrent evidence derived from the territory west of Lake
Michigan. This territory unfortunately does not bear erratics that
have equally distinct characteristics, but, so far as my observation
goes, the phenomena are alike throughout. I am therefore brought to
the conclusion that, in the interior at least, there was no habitual
lifting of boulders from the base of the ice sheets to the surface,
nor any habitual commingling of basal with englacial and superglacial
material, except, of course, as it took place by virtue of the falling
of the latter through crevasses to the base, and by mechanical
intermixture of the two at the edge of the ice.

The amount of englacial till under this view is little more than that
which was lodged in the body of the ice in its passage over the knobs
and ridges of the hilly and semi-mountainous regions of the north. To
this is perhaps to be added occasional derivatives from the more abrupt
prominences of the paleozoic region and the superficial dust blown upon
the ice from the surrounding land, which was probably the chief source
of the silty material intermingled with the superficial boulders. The
total amount is thus quite small, though important in its significance.

The eskers and kames of the region are made up of derivatives from
the basal material as shown by (1) the local origin of the material
in large part, (2) the mechanical origin of the sands and silts, (3)
the not infrequent glacial markings of the pebbles and boulders, and
(4) the disturbed stratification of the beds.[12] If I am correct
in respect to the kind and amount of the englacial and superglacial
material, it is obvious that eskers and kames, such as are found in the
interior, could not be derived from englacial or superglacial sources.
The term englacial as here used does not include such materials as
may be lodged in the basal stratum of the ice and brought down to the
actual bottom by basal melting.

[12] See "Hillocks of Angular Gravel and Disturbed Stratification," Am.
Jour. Sci. Vol. XXVII., May 1884, pp. 378-390.

The conclusions drawn from the phenomena of the plains of the interior
are not necessarily applicable to more hilly or mountainous regions.

                                                    =T. C. Chamberlin.=




=_Studies for Students._=


DISTINCT GLACIAL EPOCHS, AND THE CRITERIA FOR THEIR RECOGNITION.[13]

[13] Read before the American Geological Society at Ottawa, Dec., 1892.


I. =Introduction.=

It has long been evident that writers on glacial geology are not at
one concerning some of the important questions which underlie the
interpretation of the history of the glacial period. Certain recent
publications have served to emphasize the differences between them.
There are two questions, at least, concerning which there must be
agreement, or at any rate a common understanding, before existing
differences can be eliminated or justly evaluated. When the answers
to these questions have been agreed upon, or when the positions of
the contending parties are clearly understood, it may be found that
some of the apparent antagonisms have no better basis than differences
in definition. Stated interrogatively, the two questions referred to
are these: 1. What constitutes a glacial epoch as distinct from other
glacial epochs? and 2. What are the criteria for the recognition of
distinct glacial epochs, if such there were?


II. =The Idea of a Glacial Epoch.=

It is conceivable that, after the development and extension of a
continental ice-sheet, it might be wholly wasted away. The maximum
extension of such an ice-sheet would mark the culmination of a glacial
epoch. If subsequently another ice-sheet of considerable dimensions
were accumulated, its development and extension would constitute a
second glacial epoch. These successive ice-sheets might be so related
to each other in time, in position, and in the sequence of geological
events, as to be regarded as separate epochs of the same glacial
period.[14] On the other hand they might be so widely separated from
each other in time, in position, and in the sequence of geological
events, as to make their reference to separate glacial periods more
appropriate. In any case their separation would be sufficiently marked
to necessitate their reference to separate ice epochs. So far we
believe there would be no disagreement.

[14] The terms period and epoch are here used in the sense in which
they have been used most commonly in the literature of glacial geology
in the United States.

If, instead of entirely disappearing, the first ice-sheet suffered
great reduction of volume and area, and if this reduction were followed
by a second great expansion of the ice, might the time of such
expansion be regarded as a second glacial epoch of the common glacial
period? To this question, too, as thus stated, we apprehend there would
be but one answer, and that affirmative.

It seems certain that the edge of the continental ice-sheet was subject
to more or less extensive oscillations, as are the ends of glaciers
and the edges of ice-sheets to-day. How much of an oscillation is
necessary, and under what attendant conditions must it take place, in
order that the recession of the ice-edge shall mark an interglacial and
its re-advance a distinct glacial epoch? When the question takes this
specific form, and when inquiry is made concerning the quantitative
value of the different elements entering into the problem, we reach
the battled ground. It is the battled ground, partly because it is
the ground of misunderstanding. It is the ground of misunderstanding,
partly because glacialists are not agreed as to the meaning of certain
terms in common use by them.

Four elements seem to enter into the idea of an ice epoch as distinct
from other ice epochs. These are (1) the distance to which the ice
retreated between successive advances; (2) the duration of the retreat,
or the time which elapsed between successive ice extensions; (3) the
temperature of the region freed from ice during the time between maxima
of advance; and (4) the intervention between successive advances, of
changes interrupting the continuity of geological processes.

(1.) It would be arbitrary to name any definite distance to which
the ice must recede in order to constitute its re-advance a distinct
ice epoch. It would be not so much a question of miles as a question
of proportions. Considering this point alone, we presume it would
be agreed that an ice-sheet should have suffered the loss of a very
considerable proportion of its mass, and that it should have dwindled
to proportions very much less than those subsequently attained, before
its re-advance could properly be called a separate glacial epoch. To be
specific, if the North American ice-sheet, after its maximum extension,
retreated so far as to free the whole of the United States from ice,
we should be inclined to regard a re-advance as marking a distinct
ice epoch of the same glacial period, if in such re-advance the ice
reached an extension comparable with that of the earlier ice-sheet.
Especially should we be inclined to refer the second ice advance to a
second glacial epoch, if it, as well as the preceding retreat, were
accompanied by favoring phases of some or all the other three elements
entering into the notion of a glacial epoch. In this statement we
do not overlook the fact that a northerly region--as Labrador or
Greenland--might be continuously covered with ice throughout the time
of the two glaciations of the more southerly regions. But this is not
regarded as a sufficient reason for discarding the notion of duality.
Greenland has very likely been experiencing continuous glaciation since
a time antedating that of our first glacial deposits. The renewal
to-day of glaciation comparable in extent to that of the glacial period
would certainly be regarded as a distinct glacial epoch, if not a
distinct glacial period, even though Greenland's glaciation may not
have been interrupted. Scandinavia and Switzerland have probably not
been freed from ice since the glacial period. Their snow and ice fields
are probably the direct descendants of the ice fields of the glacial
period. An expansion of the existing bodies of ice in these countries
to their former dimensions, would constitute a new glacial epoch, if
not a new glacial period. Analogous subdivisions in pre-Pleistocene
formations have been frequently recognized.

(2) The application of the time element is hardly susceptible of
quantitative statement. We are inclined to think that it would be
generally agreed that, with a given amount of recession of the ice, its
re-advance would be more properly regarded as a distinct glacial epoch
if the interval which had elapsed since the first advance were long.
Whether a longer time between the separate advances might reduce the
amount of recession necessary in order to constitute the second advance
a second epoch, we are not prepared to assert; but we are inclined to
think it might.

(3) The third element is perhaps somewhat more tangible than the
second. If, during the retreat of the ice, the climate of a region
which was twice glaciated became as temperate as that of the present
day in the same locality, we should be inclined to regard the preceding
and succeeding glaciations as distinct ice epochs, especially if the
intervening recession were great and its duration long.

Unfortunately for simplicity and ease of determination, there are
difficulties in determining with precision how far the ice retreated
between successive maxima of advance, how long the interval during
which it remained in retreat, and the extent to which the climate was
ameliorated, as compared with that which went before and that which
followed.

(4) If changes of any sort which interrupt the continuity of geological
processes intervened between successive maxima of advance of the ice,
the separation of the later advance from the earlier, as a distinct
ice epoch, would be favored. How great the intervening changes should
be in order to constitute the re-advance a distinct ice epoch, is a
point concerning which there might be difference of opinion. But it is
altogether possible that such changes might intervene as alone to give
sufficient basis for the separation. Orographic movements, resulting
either in continental changes of altitude or attitude are among the
events which might come in to separate one ice epoch from another.
Changes of this sort have often furnished the basis for the major
and minor divisions of time in other parts of geological history, so
that there can be no question as to their adequacy, if they were of
sufficient magnitude. We hold that the intervention of orographic or
other important geologic changes might reduce to a minimum the amount
of recession, the duration of the recession, and the warmth of the
intervening climate necessary to constitute the separate ice advances
separate ice epochs. The absence of great orographic or other changes
in glaciated regions between successive advances of the ice would be
no proof that such advances should not be regarded as separate epochs.
Divisions of equal importance have often been made without evidence of
such changes.

From the foregoing discussion, brief as it is, it will be seen that
within certain narrow limits the definition of a glacial epoch, as
distinct from other glacial epochs, must be more or less arbitrary.
It is less important that an arbitrary definition should be accepted,
than that the same meaning should be attached to technical terms in
common use among geologists. In the interest of harmony and of a common
understanding, and without the violation of any truth of science, we
believe it would be well if the conception of a glacial epoch, as
framed by those who are our leaders in position and in fact, were made
the basis for our usage of the term.


III. =The Criteria of Distinct Glacial Epochs.=

If there have been differences of opinion concerning the nature of ice
epochs, as distinct from each other and from ice periods, there has
been a failure to adequately apprehend the nature, the extent, and the
meaning of the real criteria on which the final recognition of separate
ice epochs, if such there were, must be based.

Such criteria are several in number. They are of unequal value. In some
instances a single one of them might be quite sufficient to establish
the fact of two ice epochs. In other cases, single criteria which might
not be in themselves demonstrative, have great corroborative weight,
when found in association with others. In all cases, much discretion
must be used in the interpretation of these criteria. They may be
enumerated under several specific heads.

(1) _Forest Beds._ Beds of vegetal deposits or old soils are frequently
found between layers of glacial drift. This is one of the criteria
most commonly cited, because it is of common occurrence and easy of
recognition. The advocates of the unity of the glacial period maintain
that such beds of organic matter might become interbedded with morainic
debris during minor oscillations of the ice's edge. The phenomena of
existing glaciers make it evident that forest beds or soils might
be enclosed by the deposits of an oscillating ice edge. By repeated
oscillations of the ice's edge during the general retreat of the ice,
such vegetal beds might become interstratified with glacial drift more
or less frequently over all the area once covered by the ice, and from
which it has now disappeared. The mere presence of vegetable material
between beds of drift is therefore no proof of distinct ice epochs.
This does not destroy the value of the vegetal beds as a criterion for
the recognition of distinct ice epochs, but it makes caution necessary
in its application. It does not follow that, since _some_ inter-drift
forest-beds do not prove interglacial epochs, _none_ do. The question
is not how forest-beds might originate, but how existing forest-beds
did originate.

Where the plant-remains found in the relations indicated are so well
preserved as to make identification of the species possible, we have
a means of determining, with some degree of accuracy, the climatic
conditions which must have obtained at the place where the plants grew
during the time of their life. If these interbedded plant-remains are
of such a character as to indicate a temperate climate, we can not
suppose that they grew at the immediate edge of the ice, and therefore
that they were buried beneath its oscillating margin. To be specific,
if the inter-drift plant remains in any given locality of the area
once covered by ice are such as to indicate a climate _as warm as the
present in the same locality_, the ice must have receded so far to the
northward that its re-advance might, in our judgment, appropriately be
regarded as a separate ice epoch.

It has been suggested in opposition that temperate conditions may
obtain even up to the edge of the ice, and that interbedded vegetal
remains indicating temperate climate do not prove any considerable
recession of the ice. The phenomena about existing glaciers have been
appealed to in support of this demurrer. But the objection is not well
taken. The climatic conditions which obtain about the borders of small,
local glaciers, are not a safe guide as to climatic conditions which
obtained about the margin of a continental ice-sheet, any more than the
climatic conditions which obtain about a small inland lake are a safe
criterion as to the climatic conditions about a sea-coast. The general
principles of climatology, as well as specific facts concerning plant
distribution, seem to us to indicate that the climate about the border
of a continental ice-sheet must have been arctic.

It is evident that the greater the distance north of the overlying
drift remains of temperate plants are found, the more conclusive
becomes the evidence. Plant remains indicating temperate climate at
the very margin of the drift sheet which overlies them, would be less
conclusive than similar evidences one hundred miles to the northward.
It might be difficult to prove in any given instance that the ice which
deposited the drift overlying plant remains advanced one hundred miles,
or any other specific distance, south of any particular underlying
forest bed. If the forest bed were continuous for the whole distance,
the case would be clear. It would also be conclusive if the continuity
of the drift overlying a forest bed at any point with that of a
remote point to the south, could be demonstrated. In spite of these
difficulties in its application, the vegetal beds constitute a valuable
criterion in making the discriminations under consideration, when they
are properly applied. Under proper circumstances the criterion may be
conclusive when taken alone, and it may have corroborative significance
when not itself conclusive.

The absence of forest beds and of all traces of vegetal deposits
whatsoever between beds of drift, is no proof of the absence of
recurrent ice epochs, since the second advance of the ice might have
destroyed all trace of the preëxistent soil and its vegetal life. It
is always possible, too, that such beds exist, even if they have not
been discovered. It would have been anticipated that they would not be
abundant, or wide spread. The absence of forest beds is therefore at
best no more than negative evidence.

(2) _Remains of Land Animals._ Bones of mammalia or remains of other
land animals, occurring in relations similar to those in which forest
beds occur, may have a like significance. Their value as a criterion of
separate glacial epochs is subject to essentially the same limitations
as forest beds.

(3) _Inorganic Products formed during a time of Ice Recession._
The recession of the ice after a maximum of advance would leave
a land surface more or less affected with marshes and ponds. In
such situations, bog iron ore might accumulate, if conditions were
favorable. Such ore beds, buried by the drift of a later ice advance,
would have a significance comparable to that of forest beds, except
that they would give less definite information as to climate, and would
be correspondingly less trustworthy. Should such ore beds be found in
such relations as to prove that the underlying and overlying bodies
of drift were deposited by ice sheets which extended great distances
further south, their significance would be enhanced. From the thickness
of the ore beds some inference might be drawn as to the length of time
concerned in their accumulation. But because of the variable rate
at which bog ore may accumulate, such inference should be used with
caution.

Concretions of iron oxide might be formed in the marshes or in
ill-drained drift areas where accumulations of greater extent were
not made. A subsequent incursion of the ice might incorporate these
nodules with its drift, wearing and striating them as other stones,
and depositing them as constituent parts of the later drift. Such
iron nodules in the later drift would mean a recession and re-advance
of the ice with some considerable interval between, although not
necessarily an interval sufficiently warm or long to be regarded as
an interglacial epoch.[15] Calcareous concretions, like those of the
loess, would possess a like significance, in like relations. While in
themselves these inorganic products of a time of ice recession might
fail to be conclusive of separate ice epochs, they might have much
corroborative significance when associated with other phenomena. An
inter-till iron ore bed, associated with a forest bed which indicated a
warm climate, would be most significant.

[15] This point concerning iron nodules was suggested to the writer by
Mr. W. J. McGee.

The absence of knowledge of ore beds between sheets of till, and the
absence from an upper bed of till of concretions of iron and lime
carbonate formed during a recession of the ice, would be no proof that
interglacial epochs did not occur. These products were probably formed
in relatively few localities. They stood good chance of destruction at
the hands of the returning ice, and they may exist, where they have not
been discovered, or where their significance has not been understood.
Their absence is at best no more than negative evidence.

(4) _Beds of Marine and Lacustrine Origin._ If between beds of glacial
drift there be found beds of lacustrine or of marine origin, such beds
would indicate a recession of the ice during their time of deposition.
Their position would be a minimum measure of ice recession. If such
lacustrine beds contain organic remains, they will bear testimony
concerning the climatic conditions which existed where they occur,
at the time of their deposition. If the fossils in such beds denote
a temperate climate, or a climate as mild as that of the present day
in the same region, the ice must have receded so far to the northward
as, in our judgment, to constitute its re-advance a distinct ice
epoch. This line of argument may be even stronger than that drawn
from remains of terrestrial life, since the ice would probably affect
the temperature of the sea to greater distances than that of the
land, and affect it to a greater degree within a given distance. The
argument becomes stronger the further north the inter-drift marine and
lacustrine deposits occur, since the ice must always have receded to
a position still further north. If marine or lacustrine beds lying far
north of the later ice limit contain proof of temperate climate, the
argument becomes conclusive.

The absence of marine and lacustrine deposits between beds of drift,
would be no proof that interglacial epochs did not occur. Lacustrine
beds could be made only where there were lakes, and lakes would be the
exception rather than the rule. Marine beds in similar positions would
rarely be known, except where a definite succession of changes of level
has taken place. Both classes of deposits, if once formed, would be
subject to destruction by the over-riding ice of a later epoch, if such
there were. Neither would be likely to be preserved at all points where
formed, and both may exist at many points where their existence is
not known. The absence of these beds is at best no more than negative
evidence.

(5) _Beds of Subaërial Gravel, Sand and Silt._ Layers of stratified
drift between layers of ground moraine are of common occurrence in many
regions. Under ordinary conditions their existence is not regarded as
evidence that the underlying and overlying tills are to be referred
to separate ice epochs. But it is conceivable that beds of stratified
drift may, under the proper circumstances and relations, be strong
evidence of separate ice epochs. The last stages of ice work in the
glacial period were accompanied, in many regions, by the deposition
upon adjacent land surfaces, of extensive bodies of gravel and sand,
washed on beyond the ice by waters issuing from it. Except in valleys
through which strong currents coursed, such deposits were apparently
not carried far beyond the edge of the ice. But as the edge of the ice
withdrew to the northward, sand plains may have extended themselves
in the same direction, by additions to their ice-ward faces. It is
conceivable that the process of subaërial plain building at the edge
of a receding phase of ice, might be carried so far under favorable
circumstances, as to result in the construction of plains of great
extent. In this event, a subsequent ice-advance might overspread
such plains in such wise as to bury, without destroying them, though
such a course of events would certainly be exceptional. In order to
constitute the interstratified gravel and sand evidence of separate
ice-epochs, its continuity for great distances between beds of till,
and in the direction of ice movement, would need to be demonstrated.
In themselves, these beds, under the conditions indicated, would
simply be a minimum measure of the amount of ice recession between
the deposition of the underlying and overlying bodies of till. It is
hardly likely, though possible, that the continuity of interbedded
gravel and sand could be proved for a sufficient distance north of the
southern limit of the less extensive bed of ground moraine, to alone
constitute evidence of a recession of ice great enough to make it
necessary to refer its re-advance to a new epoch. Beds of silt in like
relations, deposited by waters beyond the edge of the ice, would have
a like significance so far as the question here under consideration
is concerned. Such beds of stratified drift might sometimes have
corroborative value when their testimony, taken by itself, is
inconclusive. If, for example, their surfaces are marked by forest
beds, and especially by forest beds whose plants denote a warm climate,
the association becomes most significant.

In view of what has been said, it is evident that the absence of beds
of subaërially stratified silt, sand, and gravel, between beds of till
can not be brought in evidence against separate ice epochs. It would
rarely be true that topographic and hydro-*graphic conditions would
make possible the construction of plains of sufficient extent to serve
as criteria for the purpose here indicated, and few of those formed
would escape such a degree of destruction as to leave them demonstrably
continuous. There is also the further possibility that such beds exist,
even though their continuity be not known. To prove the continuity of
a buried bed of stratified and incoherent drift, even if it existed,
would be a most difficult task.

(6) _Differential Weathering._ If, after covering a given region, the
ice retreated, the drift which it left in the area which it previously
covered would be subject to oxidation, leaching and disintegration.
The depth to which this oxidation, leaching and disintegration would
extend, would be dependent upon the length of time during which the
drift was exposed, and upon the climate which affected the region
during its exposure. The longer the exposure and the warmer the
climate, the deeper would the weathering extend. If, subsequently,
the ice extended over the same region, it might, in some places,
override and bury the old surface without destroying it. The earlier
oxidized and leached drift would thus come to be buried by the newer,
unoxidized, unleached drift. If, therefore, beneath the newer drift
of any given locality there be found a lower drift, the surface of
which is oxidized and leached to a considerable depth, the evidence
is strong that the lower drift was exposed for a long period of time
before the upper drift was deposited upon it. Within certain limits a
similar result might be brought about, it is true, if the ice, after
having reached a certain maximum stage of advance, were to retreat for
a short distance only and there remain for a very long period of time.
A subsequent minor advance might bury the oxidized surface of the drift
beyond the position of the long ice-halt. Under these conditions, the
climate which would have obtained in the area of the drift exposed
during the minor retreat would have been cold, and oxidation, leaching,
and disintegration would have proceeded slowly. If they reached
considerable depths, the time involved must have been very long. If
this surface of oxidized and leached and disintegrated drift were found
to reach far to the northward beneath the layer of newer and upper
drift, it would indicate a great recession of the ice. We maintain that
if it were found sufficiently far north of the margin of the overlying
drift, and if its depth were sufficiently great, extending well down
below any possible accumulation of superglacial till, it might be a
positive criterion of so great a recession of the ice, protracted
through so great an interval of time, as to constitute its new advance
a separate ice epoch.

There is much reason to believe that the soil developed under the
influence of a warm climate differs in some respects from one developed
from similar material under other conditions. The well-known fact that
red and reddish soils are especially characteristic of low latitudes
and warm climates is significant. If therefore a soil developed on
the surface of one sheet of drift and buried by another, be found
to possess, in addition to unmistakable marks of long exposure, the
peculiar marks which seem to be characteristic of soils developed under
high temperatures, the argument gains in strength.

This argument from oxidation and weathering has another application.
If in a later advance, following a protracted recession, the ice-sheet
failed to reach the limit of its earlier advance, there would remain
an area of drift deposited by the first ice-sheet, outside the drift
deposited by the later. Now if the time interval between these two
advances was great, and especially if during this interval the climate
was mild, the oxidation and weathering of the older drift surface would
be markedly different in degree from that of the newer. If, under
these circumstances, the surface of the older sheet were found to be
weathered and oxidized and reddened up to the border of the newer
drift sheet, and if here there were found to be a sudden change in
the character of the surface of the drift so far as depth and degree
of oxidization and weathering is concerned, we should have strong
evidence that the one sheet of drift was much older than the other.
The statement sometimes urged that the drift which was deposited near
the edge of the greatest ice advance would be largely made up of the
residual materials which occupied the surface invaded by the ice,
would not meet the case. For if it be granted that this statement is
qualitatively good, we should find the greatest degree of weathering
and oxidation at the extreme margin of the drift, and it should be
found to be less and less on receding from this margin. There would in
this case be no sudden transition from a deeply weathered and oxidized
surface, to one which is fresh and unoxidized, along a definite line.
We maintain that if the whole of the drift deposits are referable to
one epoch, there should be no sudden transition in the surface of the
drift from that which is deeply weathered to that which is not, the
one surface being separated from the other by a definite and readily
traceable line.

It has been urged against the criterion of differential weathering
that superglacial material is or may be thoroughly oxidized before
its deposition, and that a layer of oxidized drift between layers of
till may be no more than superglacial debris deposited during a minor
recession of the ice.[16] We believe that this attempt to eliminate
the value of this criterion rests partly on an exaggerated idea
concerning the amount of superglacial material, but more especially
on a failure to apprehend the real meaning of the argument for the
validity of the criterion, and upon a failure to note the limitations
imposed upon it by its advocates. It is not affirmed that a layer of
oxidized drift between beds of unoxidized drift is _per se_ proof of
two glacial epochs; but it is affirmed that if such layer of weathered
drift can be shown to extend far below any possible superglacial till,
into the subglacial till below, in such wise as to indicate that it
is the result of subaërial exposure in a warm climate subsequent to
its deposition and prior to the deposition of the overlying till,
it constitutes the best possible evidence of an interglacial epoch,
especially when accompanied by the corroborative testimony of other
criteria. It is further affirmed that if the second sheet of drift
failed to reach the limit of the first, and if the drift which was
deposited by the first and never covered by the second ice-sheet, is
more thoroughly and more deeply weathered than that deposited by the
second, and especially if the two types of drift surface meet along
a definite and readily traceable line, the argument becomes, in our
judgment, irrefragable. In its application, this criterion would be
infallible only in the hands of one who could distinguish between
superglacial and superglacially oxidized material on the one hand, and
material subaërially weathered after its deposition, on the other.

[16] This point was urged at the reading of the paper at Ottawa, by
Prof. C. H. Hitchcock, Mr. Upham, and others.

In circumstances and relations where the weathering of the drift is
not in itself conclusive, it might still have corroborative value in
association with other lines of evidence.

The absence of an oxidized and disintegrated zone of drift below a
superficial layer which is not oxidized, would be no proof that there
were not distinct ice epochs, since the ice of any later epoch, if such
there were, might have planed off the surface of the drift left by its
predecessor to the depth of the weathering. The preservation of such
surfaces after a second ice invasion must be regarded as the exception
rather than as the rule. There is always the possibility, too, that
an oxidized and weathered zone marking the surface of an older drift
sheet exists, where excavations have not opened full sections of drift
to view. The absence of weathered zones of drift beneath the surface,
or the absence of knowledge of their existence, is therefore at best
no more than negative evidence. The absence of greater weathering of
the drift outside the limit of the drift supposed to belong to a later
epoch, would be positive evidence against the reference of the two
sheets of drift concerned to different epochs.

A specific part of the above line of evidence may be separately
mentioned. One phase of weathering is the disintegration of boulders,
and this is a point which can be readily applied even by those who are
not geologists. If the boulders of one region are much more commonly
disintegrated than those of another, and if the two regions are
separated from each other by a well-marked boundary line, the inference
lies close at hand that the boulders in the one case have been much
longer exposed to disintegrating agencies than in the other. It is
no answer to this argument to say that the materials lying at the
very front of the drift deposits contain boulders which were derived
from the disintegrated rock over which the ice has passed, and that
they were therefore in a less firm state at the outset. In many cases
these boulders have come from great distances, and coming from great
distances they must have come in a firm and solid state, else they
could not have suffered such extensive transportation, except indeed
their position was superglacial throughout their whole journey. This
argument has equal force when applied to the area covered by the two
sheets of drift where two exist. If within the region of drift under
investigation we find a surface layer of greater or less depth,
the boulders of which are hard and fresh, and if beneath this we
find another layer of drift, the stony material of which is largely
disintegrated, at least in its upper parts, we have good evidence
that the surface bearing the disintegrated boulders was exposed for
a considerable length of time before the deposition of the overlying
drift, which carries fresh boulders. Since the disintegration of
boulders is only one phase of weathering, the limitations of this
argument are identical with those already noted in connection with the
general argument from differential weathering.

(7) _Differential Subaërial Erosion._ If the drift deposited by one
ice-sheet were to be exposed for a considerable interval of time, and
if the ice in its subsequent advance failed to reach the limit of
its first invasion, the two areas should show different amounts of
subaërial erosion, since the one has been exposed to the action of air
and water much longer than the other. The line which marks the limit
of the later ice invasion should be the line of more or less sudden
transition from an area without, where stream erosion has been greater,
to an area within, where stream erosion has been less.

The point here made can not be met by the suggestion that the greater
erosion of the outer area was effected by the water issuing from the
ice which had retreated to the position now marked by the border of the
area of the lesser erosion. So far as we know, such waters would be
depositing, not eroding. Furthermore, much of the erosion of the outer
area would have such relation to drainage lines that waters issuing
from the ice could never have reached the localities where it is shown.

If the outer and older drift be found to have suffered ten times as
much stream erosion as the inner and newer, it is fair to assume that
it has been exposed something like ten times as long, if the conditions
for erosion are equally favorable in the two regions. The argument has
especial weight if it can be found that beneath the newer drift the
surface of the older is such as to indicate that it was deeply eroded
before the newer was placed upon it. The argument is stronger the
farther from the margin of the newer drift such erosion on the surface
of the underlying older drift can be proved to have taken place. In
other words, if, in addition to the greater surface erosion of the
older drift sheet as now exposed outside the limit of the newer drift,
we find a notable unconformity between the newer and the older drift,
and especially if this unconformity lie far enough north of the margin
of the newer drift, the argument becomes conclusive.

When differential erosion and drift unconformities are not in
themselves conclusive, they may have great corroborative value in
conjunction with differential weathering, forest beds, or other
indications of separate ice epochs.

The absence of observable unconformity between sheets of drift would
be no proof that there were not distinct and widely separated ice
epochs, since the later ice invasion might have so far modified the
surface which it transgressed, as to destroy all patent evidences
of unconformity. It would have been anticipated that distinct
unconformities in the drift would be rare, even if there were distinct
ice epochs, for the same reason that weathered zones and forest beds
would be rare. But if the drift which lies outside a line supposed to
mark the limit of a sheet of drift belonging to a later ice epoch, be
not more eroded than that which lies within such line, the absence of
greater erosion in the outer drift is positive evidence against the
reference of the drift of the two areas to distinct ice epochs, if
conditions for erosion in the two areas are equally favorable.

(8) _Valleys Excavated Between Successive Depositions of Drift._ A
closely related, but not identical, point may be found in the extent of
the valley excavations which can be proved to have taken place between
the deposition of the earlier and later drift. We do not refer to
valleys excavated in the drift especially, but to those excavated in
other formations as well. If it can be shown, for example, that after
the deposition of an earlier drift sheet, and before the deposition
of a later, valleys were excavated which extended not merely into the
drift itself, but far beneath the drift into the underlying rock,
these valleys would be conclusive evidence of a long interval between
the deposition of the two bodies of drift. The argument is of especial
force when such excavations in the rock beneath the drift can be shown
to have taken place at great distances within the margin of the newer
drift. For valleys in such situations imply that the ice had receded at
least as far to the north as they lie, during the interval between the
two drift depositions, and may be so situated as to show that the ice
had wholly left the drainage basin where they occur.

The absence of evidences of deep valley excavations in any given region
during a supposed interglacial epoch, is no proof that such interval
did not exist. The conditions may not have been everywhere favorable
for erosion within the limits of any narrowly circumscribed area, and
the absence of interglacial valleys would be only negative evidence
against an interglacial epoch. The absence of such evidence everywhere
would bear against the existence of an interglacial epoch of much
duration in such wise as to be more than negative evidence.

(9) _Different Directions of Movement._ If, after its maximum advance,
the ice suffered merely a minor recession and then remained stationary,
or nearly so, for a time, the general direction of its movement in a
subsequent advance would probably be essentially the same as in the
earlier. But if, after its maximum advance, the ice receded to a great
distance, and especially if it entirely disappeared, a subsequent
ice-sheet might have a very different direction of movement, since
its center of accumulation and dispersion might be very different.
It is conceivable that this center might shift during the history of
a single ice-sheet. In this case there should be a gradual change in
the direction of ice movement, not an abrupt one. If, therefore, there
be found one sheet of drift made by an ice movement in one direction,
overlaid by another sheet of drift deposited by ice moving in a very
different direction, with an abrupt transition between them, such
drift sheets would be presumptive evidence of distinct ice epochs. An
exception would need to be made in the case of drift sheets along the
margins of confluent or proximate ice lobes. In such cases, if the
one lobe temporarily secured the advantage of the other, drift beds
formed by movements from opposite directions might be found in vertical
succession, without being evidence of separate ice epochs.

It is no part of the purpose of this essay to point out the
difficulties which might arise in the application of this criterion
of diverse directions of ice movements. It is possible that gradual
changes in the direction of movement might leave records which would
seem to indicate abrupt changes instead. This possibility makes care
necessary in the application of the criterion, but does not destroy its
value. When not itself conclusive, this criterion may be so associated
with differential weathering, differential erosion, forest beds, etc.,
that their combined testimony makes but one conclusion possible.

The absence of evidence of radically diverse directions of movement
during the time of deposition of the various sheets of drift, would
be no proof that there were not distinct epochs. In the first place,
the movements of different epochs might be harmonious--a condition of
things more probable than any other if the more common views of the
causes of glaciation be correct. In the second place, if the movements
were diverse, the deposits might still be so similar that their
differentiation, when the one is buried, might not be easily made. In
the third place, the later ice might have so far incorporated the older
drift material with that which belonged more properly to it, as to have
destroyed all definition between them.

(10) _The Superposition of Beds of Till of Different Physical
Constitution._ After the retreat of an ice-sheet, the surface of the
country thus discovered would be largely mantled with drift. This drift
would serve to protect the underlying rock from disintegration. But
where there was little or no drift, the rock surface would be subject
to all the disrupting agencies which affect surface rocks. The same
would be true of all rock surfaces bared by subaërial erosion after the
disappearance of the ice. Under these conditions, if a second sheet
of ice invaded the region in question after it had been long exposed,
it would find a surface prepared to yield large bowlders. The result
would be the deposition of a new sheet of drift containing bowlders
much larger than those which would have been proper to an ice-sheet
overspreading a surface but recently abandoned. If, therefore, in
the upper of two layers of subglacial till, bowlders of great size
predominate, as compared with those of a lower homologous layer, they
may be indicative of a great interval of time between the deposition
of the upper and lower beds of drift. If the home of these bowlders
be far north of the limit of the lesser sheet of drift, the distance,
as well as the duration, of the ice retreat must have been great, and
the reference of the two beds of till to distinct ice epochs would be
favored. The case might be so strong as to make no other interpretation
possible. Where in itself inconclusive, this criterion would have
corroborative significance. In its application, the discrimination of
subglacial and superglacial till would be imperative.

The absence of physical dissimilarity between superposed layers of
subglacial till would not be proof of the absence of separate glacial
epochs. The phenomena constituting the criterion could hardly be
expected to be of common occurrence. They would never be obtrusive, and
may easily have escaped attention where they exist.[17]

[17] The 10th criterion, in the order here named, was suggested by Mr.
McGee in the discussion which followed the reading of the paper at
Ottawa.

(11) _Varying Altitudes and Attitudes of the Land._ Another line of
argument has to do with the altitude and attitude of the land during
the deposition of various members of the drift complex. If during
the deposition of one part of the drift that part of the continent
covered by the outer part of the ice was low, the drainage from it
would be sluggish. If the deposits of this drainage persist to the
present time, we may find in their character evidence of the nature
of the drainage, and therefore of the attitude of the land. If at a
later time of drift deposition the glacial drainage in the same region
was more vigorous, the deposits made by the glacial streams would be
correspondingly coarser. In these deposits, if they persist to the
present day, we should find conclusive evidence of the swiftness of the
streams. If it can be shown that during the deposition of one sheet of
drift drainage was sluggish, and that during the deposition of a later
body of drift the drainage was vigorous, these facts are evidence of an
interval between the two times of drift deposition, sufficiently long
to accomplish the corresponding changes in elevation or attitude. Since
such changes of altitude and attitude are generally believed to have
been accomplished slowly, the interval must be believed to have been of
considerable duration.

It is true that continental altitudes and attitudes might change during
a single epoch of glaciation. If the change thus brought about resulted
in increased slope, the more sluggish drainage of the earlier part
of the epoch would be gradually transformed into the more vigorous
drainage of the later part. In this case, if the evidence of both the
earlier sluggish drainage and of the later vigorous drainage remain,
there should also remain the evidence of the intermediate stages. If
the deposits representing the intermediate condition of drainage do not
exist, while those representing both extremes do, there would be the
best of reason for believing that the intermediate phases of drainage
did not exist during a glacial epoch, but during an interglacial
epoch, when streams were not handling glacial debris, and when they
were eroding rather than depositing. The deposits of the slow and of
the swift drainage might occur in such relations as to prove, beyond
peradventure, that intermediate stages of _glacial_ drainage never
existed.

If the sluggish drainage accompanied the maximum ice invasion, while
the vigorous accompanied a lesser, the evidence of the swift streams
might be found far north of the southern limit of the earlier drift.
The farther north of the outer border of the older drift the gravel
representing the vigorous drainage of the later and minor ice-sheet
occurs, the further the ice must have retreated before the change from
the one type of drainage to the other was effected. On the other
hand, the farther north of the limit of the later ice advance the
sluggish drainage accompanying the earlier ice-sheet may be traced,
the farther must the ice have receded before the changes resulting in
vigorous drainage occurred. Under certain relations, the retreat of the
ice might be shown to have been great enough, before the orographic
movements which altered the nature of the drainage, to constitute
in our judgment, a re-advance a distinct ice epoch. If for example
throughout the course of a long river whose basin was largely covered
with ice, there be evidence that sluggish drainage obtained during the
maximum ice advance, and during all stages of the ice retreat until the
basin was free from ice, and if there be evidence of a vigorous glacial
drainage in the same valley at a later time, with no gradations between
the two types, we have proof positive of at least a great recession,
and of a considerable elevation of the land after the ice had receded
beyond the limits of the drainage basin and before it again reached
it in its re-advance. We hold that these phases of glacial drainage
deposits may be so related to each other, to the valleys in which
they occur, and to more or less distinct bodies of glacier drift, as
to prove so great a recession of ice between the diverse phases of
drainage deposition, as to constitute the second advance a distinct ice
epoch.

The absence of evidence that the land stood at different elevations
during different parts of the period of drift deposition, does not
in any way militate against the theory of recurrent and distinct ice
epochs. A constant attitude of the land is the thing to be assumed,
until positive evidence to the contrary is adduced.

(12) _Vigor and Sluggishness of Ice Action._ If it can be shown that
during one epoch of glaciation, we will say the epoch of maximum ice
extension, the ice action was relatively sluggish, while during a later
and minor advance its action was vigorous, the difference of action
might be regarded as presumptive evidence of distinct ice epochs.
Evidence of the two phases of ice action here referred to are difficult
of definition, but they have been independently noted by more than
one glacialist. It is true that a forward oscillation of the ice edge
might be more forceful than an earlier forward movement which might
have reached a greater extension. In itself, therefore, this line of
evidence can not be regarded as possessing great value.

It has been indicated that under certain circumstances, and in certain
relations, some of the foregoing criteria, taken singly, may be
conclusive of glaciations so distinct from each other, as to make their
reference to separate epochs proper. But where the facts and relations
which constitute one of the criteria are found, the facts and relations
constituting one or more of the others are likely to be found as
well. Where two of the foregoing criteria are found to be coexistent,
their joint force is greater than that of either one. If neither one
be absolutely conclusive, the two may still be, since the one may
exactly meet the deficiency of the other. If three or more concurrent
lines of evidence exist in any locality, the case is still further
strengthened. We maintain that several of the foregoing criteria may be
so related to each other and to the formations concerned, as not only
to make the recognition of separate ice epochs proper, but to make the
failure of such recognition altogether unscientific. Even when a single
line of evidence, or when double, or triple, or quadruple lines of
evidence are not absolutely conclusive in ruling out every conceivable
technical escape from the conclusion that there were separate ice
epochs, their cumulative and corroborative force may still be such as
to carry conviction scarcely less positive than that which mathematical
demonstration would afford. In the nature of the case not all of these
various lines of evidence could be expected to be found in any one
locality, or perhaps in any one limited geographic area, but where one
occurs, some or all of the others are liable to be found under favoring
circumstance. The number of criteria, and the great extent of area
where they may hope for application, afford great possibilities.

From the foregoing discussion, it will be readily seen that the nature
of the criteria and the limitations imposed upon their application by
the difficulty of proving stratigraphic continuity in such a formation
as the drift, necessitate the greatest care in their use, and reduce
the value of hasty and inexpert conclusions to a minimum.


IV. =Areas Where the Criteria find Readiest Application.=

The foregoing criteria find their readiest application in regions where
a later sheet of drift, suspected of belonging to a later ice epoch,
failed to reach the border of an earlier sheet of drift, suspected of
belonging to an earlier ice epoch. The 1st, 2d, 3d, 4th, 5th and 10th
as enumerated above, find their application wholly within the area
affected by the drift of the separate epochs, if such there were. While
within this general area they may be looked for at any point, they
are likely to be of rare occurrence, except along a somewhat narrow
belt, say 50 to 100 miles, adjacent to the border of the lesser ice
advance. The conditions for their occurrence and detection are greatly
favored if the lesser drift sheet be the later. The 6th, 7th, 9th and
12th criteria might hope for application within the same belt, but
especially along a narrow zone on either side of the margin of the
later drift sheet. It is along this zone that the types of surface are
thrown into sharpest contrast, both as to material and topography. The
8th and 11th criteria have still wider limits of application, both
within and without the border of the lesser ice advance.

                                                 =Rollin D. Salisbury.=




                            =_Editorials._=


It is the chief function of the national, state and provincial
geological surveys to bring forth the great concrete facts relative
to the structure and resources of their several fields. Within their
special domains they also do an important work in the correlation
of structures and formations, in the systematic aggregation of the
facts, in the organizing of results, and in the development of the
fundamental principles of geological science. To some extent they are
permitted to do this beyond their own fields, but in the main the
boundaries of these fields are the limits of their coördinations. They
therefore leave a great function to be performed by some other agency
in the coördination of interstate, international, and intercontinental
factors. They are also restrained by their relationships to a somewhat
too narrowly utilitarian public from devoting much direct attention
to the solution of the deeper and broader problems that constitute
the soul of science, though their contributions bear upon these in
the most radical and important way. In the primary work of systematic
observation, and the development of the immediate conclusions that
spring therefrom, these surveys surpass all other agencies in the
value of their contributions to the growth of the science, but in
the secondary and ulterior work of correlation, in the synthetic
aggregation and organization of results, and in the analytical and
philosophical treatment of the whole, they need to be supplemented
by agencies whose facilities and limitations lie in other lines,
agencies whose relations and dependencies are complementary in nature.
This secondary and ulterior work, in some degree, has been done by
individual master students of systematic and philosophical geology, but
to a very great extent it has not been done at all. It is a function
which properly falls to universities, if the universities can only rise
to meet it; for it is the function of universities, in the larger
modern view, not only to rehearse science, nor merely even to educate
young geologists, important as that is, but to develop science for
science's own sake, and for its own inherent and permanent utilities
as distinguished from its immediate applicabilities. To fulfill this
function they must not only realize and appreciate it, but they must
be equipped for field and experimental work, as well as library and
laboratory study. Ideal correlations and academic systematizing are as
apt to be hindrances as helps to the progress of science. While a few
of the great universities of this country and Europe have made notable
advances in these directions, the universities are, on the whole, far
behind the great surveys in the performance of the work which properly
falls to them. This is due not so much to a lack of appreciation of the
function as to the lack of facilities.

With the development of this higher function of the universities there
goes a coördinate function for a university journal of geology, a
journal whose special efforts shall be devoted to promoting the growth
of systematic, philosophical, and fundamental geology, and to the
education of professional geologists. No part of the wide domain can
wisely be neglected by any journal, but there seems to be an open field
for a periodical which specially invites the discussion of systematic
and fundamental themes, and of international and intercontinental
relations, and which in particular seeks to promote the study of
geographic and continental evolution, orographic movements, volcanic
coördinations and consanguinities, biological developments and
migrations, climatic changes, and similar questions of wide and
fundamental interest. This field is not likely to be successfully
cultivated except by a systematic endeavor, pursued through a period of
years, to bring together the latest and best summations of the results
attained in the several national fields in a common medium, where they
can be compared and discussed, and where tentative correlations will
suggest themselves, out of which, in turn, working hypotheses will
naturally spring, leading on to such direct investigations as the
nature of each question invites. It would be presumptuous to assume
that the =Journal of Geology= can cultivate with more than very partial
success this field, but it especially invites contributions of this
class.

Another phase of geology which is thought to stand in much need of
active cultivation is found in the clear and sharp analysis of its
processes, the exhaustive classification of its phenomena, especially
on genetic bases, the development of criteria of discrimination, the
more complete evolution and formulation of its principles and the
development of its working methods. The recent opening of new fields
of research and the rapid progress of several new and important
departments of the science give peculiar emphasis to this need. The
rising generation of geologists, the hope of the science, should be
schooled in these latest and most critical aspects of the science. A
department of the =Journal=, entitled "Studies for Students," has been
opened for the special cultivation of this field and for its adaptation
to advanced students and progressive teachers of geology. Mere
elementary presentations of processes and principles are not desired,
but searching and critical expositions are solicited suited to the
needs of young geologists who seek the highest professional equipment,
and to progressive teachers who desire the fullest practicable command
of the newest developments of the subject. These contributions may not
be without their value to those who have already borne a considerable
part of the heat and burden of life's professional day.

It is our desire to open the pages of the =Journal= as broadly as a
due regard for merit will permit, and to free it as much as possible
from local and institutional aspects. It will have the very important
advantage of being published under the auspices and guarantee of the
University of Chicago, and will be free from the usual financial
embarrassments attending the publication of a scientific magazine. This
necessarily imposes upon the local editors the immediate responsibility
for its editorship. Beyond this, it is hoped that its institutional
relationship will disappear entirely in an earnest effort to promote
the widest interests of the science. As an earnest of this wider
effort several eminent geologists, representing some of the leading
universities of this country, and some of the great geological
organizations of Europe, have kindly consented to act as associate
editors.

                                                               T. C. C.

[Illustration]

Upon invitation of the World's Congress Auxiliary of the World's
Columbian Exposition committees were appointed by the several sections
of the American Association for the Advancement of Science at its
Rochester meeting to coöperate with it in completing the organization
of scientific congresses to be held at Chicago in connection with the
forthcoming World's Fair. The committee appointed by the geological
and geographical section consisted of Thomas C. Chamberlin, John C.
Branner, Grove K. Gilbert, W. J. McGee, Rollin D. Salisbury, Eugene A.
Smith, Charles D. Walcott, J. F. Whiteaves, Geo. H. Williams, H. S.
Williams and N. H. Winchell.

It has been arranged that this committee should undertake the work
of preparing the scientific program for the Geological Congress. The
committee have prepared a provisional schedule of topics, which they
have submitted to the Advisory Council for revision. It has seemed
to the committee that all contributions should be such as to have an
international interest. Preferably, they should be subjects that can
only be treated most advantageously in such a congress, especially
those that involve the bringing together of data from different lands
for comparison. The committee suggest the organization of the subjects
under the following general classes:

=First.= Such as shall show the present state of geological progress.
It is believed that this can best be done by an exhibition of
geological maps which shall show the latest and best results of
official and other surveys. As such maps will be prepared, it is hoped,
for the World's Fair, duplicates can be made at a slight expense for
the use of the Congress. It is hoped that each country that has made
any notable progress in mapping its geological formations will furnish
for the Congress at least a general geological map, if not also special
or analytical maps.

=Second.= Such subjects as bear upon continental growth and
intercontinental relations. It is proposed to make this a leading
line of discussion during the Congress, in the belief that there is
no subject more appropriate, and that there is none which better
represents the present efforts of geologists or commands a more
general interest. It is hoped that analytical maps will be prepared
by the geologists of the several countries representing the stages of
growth of these regions in each of the great eras from the Archean
to the Pleistocene, and that such analytical maps may constitute a
leading feature of the several presentations. Among the subjects upon
which contributions are specially invited are the following: The
correlation of continental and intercontinental orographic movements
and geographic accretions by sedimentation; The coördination of periods
of vulcanism in the different countries; The coördination of climatic
states and changes; The correlation of faunal and floral variations
and migrations. It is hoped that one session may be devoted to such
coördination papers bearing upon each of the great subdivisions: viz.,
Archean, Paleozoic, Mesozoic, Cenozoic, and Pleistocene.

=Third.= Papers on Paleontological and Archeological Geology of
international scope.

=Fourth.= Contributions to Physical, Structural and Petrological
Geology having international or general bearings.

=Fifth.= Contributions to Economic Geology having general bearings.

=Sixth.= Miscellaneous papers of especial and general interest.

The foregoing groups are intended to embrace and coördinate the list of
special themes announced in the circular issued by the local committee
some months since, except such as may be best suited to popular
presentation, for which special provision is to be made.

It will be determined later, when the number and nature of the papers
are ascertained, whether all will be arranged so as to form a
continuous program, or whether sub-sections will be formed and two or
more sessions held simultaneously.

It is the desire of the World's Congress Auxiliary that a few addresses
of a popular nature shall be given, with a view to stimulating an
interest in the development of the science on the part of the public.

                                                               T. C. C.

[Illustration]

Extra copies of the articles appearing under the head of Studies for
Students will be printed and kept on sale for the use of teachers and
advanced classes. The prices will be fixed as low as practicable, and a
standing list published in the advertising columns of the =Journal=.




                             =_Reviews._=


  _On the Glacial Succession in Europe._ By Prof. =James Geikie=.
       Transactions of the Royal Society of Edinburgh, Vol. XXXVII.,
       Part I. (No. 9), 1892, pp. 127-149 (with a map).

In this timely essay Prof. Geikie reaches the following conclusions:

1. The record of the first glacial epoch is found in the Weyborn Crag
of Britain, and the ground moraine beneath the "Lower Diluvium" of the
continent. During this epoch, the direction of the ice movement in
southern Sweden was from the south-east to the northwest. This first
glacial epoch of which direct evidence is adduced was followed by an
interglacial interval, during which the forest-bed of Cromer, the
breccia of Hötting, the lignites of Leffe and Pianico, and certain beds
in central France were deposited. During this interglacial epoch, the
climate is believed to have been very mild.

2. There followed a second epoch of glaciation, when the ice sheet of
Britain became confluent with that of the continent. This was the epoch
during which the ice sheet reached its southernmost extension. Its
depositions are found in the lower boulder clays of Britain, the lower
diluvium of Scandinavia and north Germany (in part), the lower glacial
deposits of south Germany and central Russia, the ground moraines and
high level gravel terraces of Alpine lands, and the terminal moraines
of the outer zone. During this second glacial epoch, Alpine glaciers
are believed to have attained their greatest development. This epoch
of extreme glaciation was followed by an interglacial interval, during
which Britain is believed to have been joined to the continent. During
this interval, the climate became temperate. In Russia (near Moscow)
there seems to be evidence that it was milder and more humid than that
of the same region at the present day. Toward the close of the mild
epoch, submergence seems to have been accompanied by an increasing
degree of cold, which finally ended in another glacial epoch.

3. The subsidence which marked the close of the second interglacial
interval, marked likewise the inauguration of the third glacial
epoch. Its work is represented in Britain by the upper boulder clay,
in Scandinavia and Germany by the lower diluvium (in part), in central
Russia by the upper glacial series, in Alpine lands by ground moraines
and gravel terraces. The ice sheets of Scandinavia and Britain were
again confluent, but did not extend quite so far south as during the
second glacial epoch. This third glacial epoch is believed to have
been followed by another interglacial interval, during which fresh
water alluvia, lignite and peat accumulations were made. These are
represented by the interglacial beds of north Germany, and by some
of the so-called post-glacial alluvia of Britain. There were also
marine deposits on the coasts of Britain and on the borders of the
Baltic. During this interglacial interval, Britain is believed to
have been continental. The climate was temperate, but in the course
of time became more severe. This increasing severity seems to have
been accompanied by submergence, which amounted to something like 100
ft. below the present sea-level on the coasts of Scotland. The Baltic
provinces of Germany were also invaded by the waters of the North Sea.

4. There followed a fourth period of glaciation, during which the major
part of the Scottish Highland was covered by an ice sheet. Local ice
sheets existed in the southern uplands of Scotland and in mountain
districts in other parts of Britain, and the great valley glaciers
sometimes coalesced on the low lands. Icebergs floated out at the
mouths of some of the highland sea-lochs. In some places, terminal
moraines were deposited upon marine beds which were then in process of
formation. These beds are now 100 ft. above the sea level. At this time
Scandinavia was covered by a great ice sheet, which yielded icebergs
to the sea along the whole west coast of Norway. The ground moraines
and terminal moraines of the mountain regions of Britain represent the
deposits of this ice epoch. The upper diluvium of Scandinavia, Finland,
and north Germany represent the work of the contemporaneous, but not
confluent, ice sheet of the continent. In the Alps, terminal moraines
in the large longitudinal valleys were made at the same time.

This fourth glacial epoch was followed by a fourth interglacial
interval, during which fresh water alluvial deposits were made, and
also the "lower buried forest and peat" of Britain and northwestern
Europe. At this time, Scotland seems to have stood 45 to 50 feet lower
than now, and Carse clays and raised beaches represent the work of the
sea. During this interglacial interval, Britain is believed to have
become again continental, while the climate became so far ameliorated
as to allow the growth of great forests. Subsequently the insulation
of Britain was effected, and this was followed by a climate which was
probably colder than the present.

5. The severity of the climate which marked the close of the fourth
interglacial interval was such as to bring about local glaciation in
some of the mountain valleys of Britain. Here and there the glaciers
projected their moraines so far down the mountains that they rest on
what is now the 45 to 50 feet beach. In the Alps, this fifth epoch of
glaciation is represented by the so-called post-glacial moraines in
the upper valleys. This is believed to have been the last appearance
of glaciers in Britain. The dissolution of these glaciers was again
followed by an emergence of the island, and by more genial climatic
conditions.

In support of his conclusions, Prof. Geikie cites some striking facts
which are not so widely known as they should be. For example, Swedish
geologists have found evidences that there was an ice sheet antedating
that which deposited the "lower diluvium," and that during this earlier
glaciation the direction of ice movement in southern Sweden was from
the south-east to the north-west. The ground moraine deposited by this
ice sheet is overlain by the "lower diluvium" which was produced by
an ice movement from the north north-east to the south south-west, or
nearly at right angles to the first. Again, near Moscow, there exist
interglacial beds whose plant remains indicate a climate milder and
more humid than that of the present time. These interglacial beds, it
will be observed, occur in the region of the "lower diluvium" quite
beyond the margin of the ice which produced the "upper diluvium" of
Germany and Scandinavia. During this interglacial interval, Prof.
Geikie maintains that no part of Russia could have been covered with
ice. If, then, within the limits of the area covered by the "lower
diluvium," and not by the "upper," distinct beds of glacial drift
are separated by such beds as those cited, there can be no question
but that such separation marks two distinct glacial epochs. If there
was an earlier glaciation when the movement of the ice in Sweden was
at right angles to that during which the lower part of the "lower
diluvium" was produced, this also would seem to be good evidence of
three ice epochs prior to the "upper diluvium." The epoch of the "upper
diluvium" would then constitute the fourth glacial epoch, and this is
the interpretation of Prof. Geikie.

Outside the area of the European continental ice sheet, facts are
adduced in striking confirmation of the multiple ice epoch theory.
These facts are found in Switzerland, where evidences of multiple
glaciation have been recognized, and in the Pyrenees where evidences
of three separate ice epochs have been found. In France, evidences
of an interglacial interval have been found in the region of the Puy
de Dôme of such duration as to allow the excavation of valleys to a
depth of 900 feet. The length of time which would be required for such
stupendous erosion must certainly be regarded as sufficient to allow
the preceding and succeeding glaciations to be considered as belonging
to two distinct epochs.

Another point of great significance and interest which Prof. Geikie's
essay brings out, is the correlation in Britain between epochs of
glaciation and epochs of subsidence on the one hand, and between
interglacial intervals and epochs of elevation on the other. If Prof.
Geikie's interpretation be well founded, and so far as we are able to
judge from the facts presented this is the case, his conclusions would
seem to be fatal to the hypothesis that glacial climate was produced by
northern elevation.

The map which Prof. Geikie gives, showing the limit of ice advance
during the fourth glacial epoch, seems to us open to criticism. On the
ground of personal observation, the writer believes that the ice sheet
of the glacial epoch here represented did not extend notably, if at
all, beyond the Baltic Ridge.[18]

[18] See _American Journal of Science_, May, 1887. In a recent letter,
Prof. Geikie indicates that he is convinced, from subsequent personal
observation, that his map is erroneous so far as the limit of the ice
of this epoch is concerned. The mapping given was based on the opinion
of others.

Prof. Geikie is an advocate of Dr. Croll's astronomical theory of
glacial climate, and thinks that even five is not the full number of
glacial epochs belonging to the Pleistocene period. He believes there
may have been a series of glacial epochs increasing in severity to a
maximum represented by what is now designated as the second glacial
epoch. This maximum was followed by a series of epochs of diminishing
severity, represented by what he designates the third, fourth and fifth
epochs. The essay is a timely contribution to glacial geology.

                                                 =Rollin D. Salisbury.=




          =_Analytical Abstracts of Current Literature._=[19]

[19] Abstracts in this number are prepared by Henry B. Kummel, Chas. E.
Peet, J. A. Bownocker.


  _The Sub-Glacial Origin of Certain Eskers._ By =William Morris
       Davis=, Harvard University. (Proceedings of the Boston Society
       of Natural History, Vol. XXV., May 18, 1892).

A critical discussion of the conditions under which it is conceived
certain eskers and sand plateaus (plains) were formed. The Auburndale
district, ten miles east of Boston, presents three classes of modified
drift deposits;--sand plateaus, eskers, and kames. These deposits are
well exposed.

The sand plateaus have the characteristics of delta deposits of
glacial streams,--even surfaces, well-bedded sands and gravels, the
beds sloping outward from the "head" at an angle of 12° to 20°, and in
close agreement with the slope of the plateau front, a lobate margin,
deposits distinctly coarser at the head than near the front, and a
series of nearly horizontal roughly cross-bedded gravels overlying the
sloping beds.

The eskers are essentially of the same material as that of the plateau,
often so poorly stratified as to render differentiation of the beds
difficult. The interstices between the pebbles are often unfilled,
although there is abundance of fine material in adjoining layers.
This "open work" is taken to indicate rapid deposition, and seems to
preclude the supposition that the gravels have settled down from a
superglacial position, or been traversed by currents of any volume.
In several instances the eskers can be followed to direct union with
sand plateaus. Towards its lower end the esker frequently "gives out
branches" and "the adjacent lowland surface becomes more or less
encumbered with sand mounds or kames," indicating a decayed margin of
the ice.

Prof. Davis' conclusions are:

"1. The eskers and sand plateaus of Auburndale and Newtonville were
formed by running water just inside and outside of the ice margin in
the closing stage of the last glacial epoch.

"2. The ice-sheet was a stagnant, decaying mass at the time of their
formation, as is shown by the ragged outline of its margin.

"3. Eskers and sand plateaus are genetically connected; the term,
feeding-esker, is fully warranted by the relation of the two in
position, structure, and composition.

"4. The sand plateaus were made rapidly; this is proved by the absence
of disordered beds at their heads, where space would have been opened
by the backward melting of the ice had the forward growth of the
plateau been slow. The eskers were also made rapidly, as is shown by
their 'open-work gravels.'

"5. The diversion of the feeding streams to other outlets left the
plateaus and the eskers without further energetic action as the ice
melted away from them.

"6. The present form and structure of the eskers are more accordant
with the supposition of a subglacial origin than of a superglacial
origin; but it is not intended to imply that other eskers of more
irregular form and different structure could not have been deposited in
superglacial channels."

                                                               H. B. K.

                   *       *       *       *       *


  _Studies in Structural Geology._ By =Bailey Willis=, U. S. Geol.
       Surv. (Transactions of the American Institute of Mining
       Engineers, June, 1892).

The paper aims "to present some of the results of observation of the
geologists of the Appalachian division during the past three years
on the subject of structural geology in the Appalachian province."
The structural features are all of one type but of different phases,
comprised in four great districts. 1) the district of close folding,
2) a district whose chief structural characteristic is cleavage, 3) a
district of open folding, 4) a district of faulting and folding. The
answer to the questions, Why did the strata bend in the district of
open folding, and why did they break in the district of faulting, is
that the thrust affected them according to their rigidity under their
respective conditions of superincumbent load. "We know that load up
to a certain point restrains fracture in material under thrust." In
the district of open folding the Devonian limestone is the most rigid
of the strata and "the one which would most effectively transmit the
compressing thrust and would control the resulting structure." In the
district of open folding this limestone was prevented from breaking
and faulting by a load of superincumbent strata exerting a pressure of
10,000 to 23,000 pounds per square inch, while in the faulted district
a load of 5,000 to 10,000 pounds per square inch permitted the strata
to break and fault.

The answer to the question, Why did the compression affect this
zone, is given. "It becomes apparent on study of sections that where
compression raised a great arch there previously existed a bend from
a nearly horizontal to a descending position in the principal stratum
transmitting the thrust. Greater anticlines and synclines originated in
upward and downward convexity of initial dips, due to unequal deposits
of sediments which depress underlying strata in proportion to their
weight. Such folds may be called original." The Pottsville, Mahanoy,
Shamokin and Wyoming coal basins of Pennsylvania belong to this class.

Experiments have recently been carried on in the office of the United
States Geological Survey reproducing the different forms of folding.
The experiments differed from other experiments in that 1) the
materials used to simulate the stratified rocks varied in consistency
from brittle to plastic, according to the depth at which deformation is
supposed to take place; 2) the compression was exerted under a movable
load representing the weight of superincumbent strata; 3) the strata
rested on a yielding base to simulate the condition of support of any
arc of the earth's crust. The following are the conclusions from the
experiments:

1. "When a thrust tangentially affects a stratified mass, it is
transmitted in the direction of the strata, and by each stratum
according to its inflexibility. At any bend the force is resolved into
components, one radial, the other tangential to the dip beyond the
bend; the radial component, if directed downward, tends to depress the
stratum and displace its support.

2. "A thrust so resolved can only raise an anticline or arch which is
strong enough to sustain the load lifted by its development; such an
arch may be called competent; and since strength is a function of the
proportions of a structure, it follows that, for a given stratum, the
size of a competent anticline will vary inversely as the load; or for a
given load the size will vary as the thickness of the effective stratum.

3. "The superincumbent load borne by a competent anticline is
transferred to the supports of the arch at the points of inflection of
the limbs.

4. "When a competent arch is raised by thrust from one side, the load
transferred may so depress the resulting syncline further from the
force that an initial dip will be produced in otherwise undisturbed
strata; this dip will rise to a bend from which a new anticline may be
developed. This anticline is a result of the first, and may be called
'subsequent' in distinction to original folds. Since subsequent folds
are simply competent structures, their size will be determined by
conditions of thickness and load, and for like conditions they should
be equal; and they must, in consequence of conditions of development,
be parallel to the original fold and to each other. An example of an
original fold with its subsequent anticlines is the Nittany arch and
the group of parallel anticlines which lie southeast of it, extending
northeast from the Broad Top basin."

                                                               C. E. P.

                   *       *       *       *       *


  _The Catskill Delta in the Post-Glacial Hudson Estuary._ By =William
       Morris Davis=. (From the Proceedings of the Boston Society of
       Natural History, Vol. XXV., 1891).

The post-Tertiary trenches of the Hudson and its tributaries are in the
main filled with clay beds, which, covered by a thin deposit of sand,
rise in terraces 130, 150, or even 180 feet above tide-water. These
clays are the result of a late glacial or post-glacial submergence of
the valley, but their upper surface does not indicate the amount of
their submergence, as they are bottom deposits. Delta deposits made by
the tributary streams, where they entered the Hudson estuary, would
indicate the amount of submergence.

Such deposits are found on the Catskill a mile north of Cairo, and
eroded remnants are traceable for three or four miles down stream.
The surface is characterized by great numbers of water-worn stones
up to fifteen or eighteen inches in diameter. The lobate margin,
where present, is poorly defined. These deposits range from 290 feet
(aneroid) above tide, up river, to 270 feet further down. One-tenth of
a cubic mile of material seems to have been washed into the Catskill
trench at the point of this delta between the time of the ice departure
and the elevation of the land. Subsequent terracing has removed half
that amount.

The course of the Catskill at Leeds, where it crosses a ledge of hard
Corniferous limestone is probably of post-glacial superimposed origin,
but the preglacial valley cannot be definitely fixed.

                                                               H. B. K.

                   *       *       *       *       *


  _Geological Survey of Alabama.--Bulletin 4._ By =C. Willard Hayes=.
       (Report of the Geology of Northeastern Alabama and Adjacent
       Portions of Georgia and Tennessee).

This report covers an area of 5950 miles, two-thirds in Alabama.
Topographically it falls into three divisions: 1) the Cumberland
and other plateaus of the northwest; 2) in the center, anticlinal
valleys--Browns and Wills, with the synclinal mountains--Sand and
Lookout; 3) the monoclinal mountains, the "flatwoods" (Coosa shales)
and the chert hills (Knox limestone) of the southeast. The drainage of
the first is radial from the center of the plateau to the Tennessee;
that of the second, once consequent upon the folded structure, is now
adjusted to the strike of the soft beds.

The formations are Cambrian, Silurian, Devonian and Carboniferous.
Total thickness is from 13,000 to 18,000 feet in the east, but
decreases westward. Hard sandstones of the Carboniferous form the
cappings of the plateaus and synclinal mountains. In the anticlinal
and monoclinal valleys the Silurian and Cambrian appear. The rocks
pass from the nearly horizontal beds of the plateau region, by narrow
unsymmetrical anticlines with steeper dip on the northwest side, and
by broad shallow synclines, to the complicated folds of the southeast.
The axes of these latter folds dip more or less abruptly northward and
southward, causing the ridges to assume zigzag courses. Synclines are
often crossed by anticlines.

Thrust faults exist, some of great magnitude, and traceable for 200
to 300 miles. By the "Rome thrust fault" the Cambrian shales have
been shoved four to five miles over upon the Carboniferous shales.
Most of the overthrust strata have been worn away, but tongues of
Cambrian shale still remain to all appearances lying conformably upon
the Carboniferous strata. Transverse thrust faults terminate Gaylor's
ridge, Dirt Seller Mountain, and Lookout Mountain on the south.

                                                               H. B. K.

                   *       *       *       *       *


  _The Correlation of Moraines with Raised Beaches of Lake Erie._
       By =Frank Leverett=, U. S. Geol. Surv. (Wisconsin Academy of
       Science. Vol. VIII., 1891).

References have been made in Geological literature to the beaches of
the eastern portion of the Lake Erie basin, but up to the time of
Mr. Leverett's work none of the beaches had been completely traced.
Mr. Gilbert had discovered that several of the raised beaches do not
completely encircle Lake Erie, and supposed that their eastern termini
represent the successive positions of the front of the continental
glacier during its retreat northeastward across the Lake Erie basin.
Mr. Leverett verifies this theory by demonstrating that certain
moraines are the correlatives of the beaches. They are as follows:

I. The Van Wert or upper beach and its correlative moraine, the
Blanchard ridge. II. The Leipsic or second beach and its correlative
moraines. III. The Belmore, or third beach and its correlative moraine.

I. The Van Wert beach extends eastward from the former southwestward
outlet of Lake Erie near Fort Wayne, Indiana, to Findlay, Ohio, where
it joins the Blanchard moraine. Through Indiana and Ohio its altitude
is quite uniformly 210 feet above Lake Erie.

While the Van Wert beach was forming, the ice front was the
northeastern shore of the lake as far east as Findlay, Ohio, its
position being marked by the Blanchard moraine. East of Findlay, where
the Van Wert beach joins it, the moraine is of the normal type. But
west of Findlay, it presents peculiarities of topography and structure,
resulting from the presence of lake water beneath the ice margin.
The water was shallow and incapable of buoying up the ice-sheet,
and producing icebergs. The motion of the water under the ice-sheet
produced a variable structure. This is the only instance of a moraine
demonstrably formed in lake water.

II. The Leipsic, or second beach, was formed after the ice had
retreated from its position marked by the Blanchard moraine. Its
altitude is 195 to 200 feet above Lake Erie. It has its terminus near
Cleveland, where it connects with the western end of a moraine.

III. The Belmore beach and its correlative moraine. Between the Leipsic
beach and the present shore of Lake Erie are several beaches. One of
these, the Belmore beach, terminates near Cleveland, while the others
extend into southwestern New York, and probably connect with moraines,
though this connection has not been traced. The general altitude of
the Belmore beach in Ohio is 160 to 170 feet above Lake Erie. Unlike
the Van Wert and Leipsic beaches, it does not directly connect with a
moraine at its eastern end, but a gap of ten miles intervenes. Terraces
at Cleveland, Mr. Leverett thinks, make a connection between the
eastern end of the beach and the western end of the moraine at Euclid,
Ohio.

                                                               C. E. P.

                   *       *       *       *       *


  _The Climate of Europe During the Glacial Epoch._ By =Clement Reid=.
       (Natural Science. Vol. I, No. 6, 1892).

_Temperature of the Sea._--The temperature of the English Channel was
similar to that where the isotherm of 32° F. is now situated. The
winter temperature can scarcely have been 20° colder than at present.
The Mediterranean was perhaps 5° colder than now.

_Temperature of the Land (air)._--It does not appear that the climate
of the lowlands of southern Europe can have been 20° lower than the
present mean; 10° or perhaps less appear to have been the refrigeration
in the Mediterranean region. The temperature at the southern margin of
the ice-sheet was about 20° colder than at present. The temperature
increased rapidly towards the south. Recent observations seem to show
that throughout central Europe there was a period of _dry_ cold,
causing the country to resemble the arid regions of central Asia.

                                                               J. A. B.

                   *       *       *       *       *


  _On the Glacial Period and the Earth-Movement Hypothesis._ By
       =James Geikie=, Edinburgh, Scotland. (Read before the Victoria
       Institute, London).

Geologists generally admit that there have been at least two glacial
epochs, separated by one well-marked interglacial period. The closing
stage of the Pleistocene period was one of cold conditions in
northwestern Europe, accompanied by land depressions. After this came a
genial climate with a union of the British islands among themselves and
also with the continent. This was followed by a cold, humid condition.

Upham maintains that the whole of North America north of the Gulf of
Mexico stood at least three thousand feet higher at the beginning of
the glacial epoch than at present. Fiords were formed before glacial
times and so can not be cited as evidence of high land during the
glacial period. An elevation of land in the northern part of North
America and Europe could not produce glaciation in their southern
parts. The deflection of the Gulf Stream by the sinking of the Panama,
Professor Geikie argues, could not produce the conditions which
prevailed during the glacial epoch. The Earth-Movement hypothesis, he
believes, accounts neither for the widespread phenomena of the ice-age,
nor for the remarkable interglacial climates. Some maintain that the
warm interglacial period was produced by the rise of the Panama land,
the sinking of the lands to the north, and the turning of the Gulf
Stream from the Pacific into the Atlantic. Why then, asks Professor
Geikie, do we not have such a climate now?

                                                               J. A. B.




                         =_Acknowledgments._=


The following papers have been donated to the library of the Geological
Department of the University of Chicago, mainly by their authors:

=Abbe, Cleveland.=

  --On the Production of Rain. 8 pp. 1892.

=Ami, Henry M.=, M.A., F.G.S.

  --On Canadian Extinct Vertebrates. 4 pp.--Ottawa Naturalist.

  --On the Geology of Quebec and Environs. 26 pp., 1 pl.--Bull. Geol.
       Soc. Am., vol. 2, pp. 477-502.

  --On the Geology of Quebec City, Canada. 4 pp.--Canadian Record Sci.,
       April, 1891.

  --Additional Notes on Ganiograptus Thureani, McCoy, from the Levis
       Formation Canada. 2 pp.--Canad. Record Sci., Oct. 1889.

  --Reviews of Reports and Papers on Canadian Geology and Paleontology.
       8 pp.--Ottawa Naturalist, Oct.-Dec. 1892.

  --Notes and Descriptions of some new or hitherto unrecorded species
       of Fossils from the Cambro-Silurian (Ordovician) Rocks of the
       Province of Quebec. 15 pp.--Canadian Record of Sci., April, 1892.

  --Review of Catalogue of the Fossil Cephalopoda of the British
       Museum, Part 8, Nautiloidea. By Arthur H. Foord, F.G.S. 3
       pp.--Canadian Record of Sci., Sept. 1891.

  --On the Sequence of Strata forming the Quebec Group of Logan and
       Billings, with Remarks on the Fossil Remains found therein. 4
       pp.--Ottawa Naturalist, June, 1892.

=Andeæ, A. and A. Osann.=

  --Beiträge zur Geologie des Blattes Heidelberg. 39 pp., III., 2
       pl.--Aus den Mittheilungen der Grossh. Badischen Geologischen
       Landesanstalt, II Bd. VII-XI.

=Baltzer, A.=

  --Beiträge zur Geognosie der Schweizer-Alpen über die Frage,
       ob der Granit-Gneiss der nördlichen Gränzregion der
       Finsteraarhorn-Centralmass eruptiv sei oder nicht, und über
       damit zusammenhängende Probleme. 41 pp., 2 pl.--Neues Jahrbuch
       für Mineralogie, 1878.

  --Beiträge zur Geognosie der Schweizer-Alpen. Ueber die Marmorlager
       am Nordrand des Finsteraarhorn-massivs. 20 pp., 2 pl.--Aus dem
       Neuen Jahrbuch für Mineralogie, 1877.

  --Ueber den Hautschild eines Rochen aus der marinen Molasse. 4 pp., 1
       pl.--Aus den Mittheilungen der Naturforschenden Gesellschaft in
       Bern.

  --Ueber den natürlichen Verkohlungsprozess. 23 pp.--Aus der
       Vierteljahrs-schrift der zürcherischen naturforschenden
       Gesellschaft.

  --Randerscheinungen der centralgranitischen Zone in Aarmassiv. 18
       pp., 1 pl.--Aus dem Neuen Jahrbuch, 1885. II Band.

  --Beiträge zur Geognosie der Schweizer-Alpen. Ein Beitrag zur
       Kenntniss der Glarnerschlinge. 20 pp., 1 pl.--Aus dem Neuen
       Jahrbuch für Mineralogie, Geol. und Pal. 1876.

  --Geologische Skizze des Wetterhorns in Berner Oberland. 14 pp., 2
       pl., Zeit. der Deut. geolog. Gesell, 1878.

  --Geognostich-chemische Mittheilungen über die neuesten Eruptionen
       auf Vulcano und die Producte derselben. 29 pp., 3 pl.--Zeit. d.
       Deut. Geolog. Gesell, 1875.

  --Ueber Bergstürze in den Alpen. 50 pp., 1 pl.--Aus dem Jahrbuch des
       S.A.C. (X. Jahrgang) Zürich, 1875.

=Baker, Frank C.=

  --Notes on a Collection of Shells from the Mauritius; with a
       consideration of the Genus Magilus of Montfort. 22 pp., 1
       pl.--Proc. Rochest. Acad. Sci., Vol. 2, 1892.

  --Catalogue and Synonomy of the Recent Species of the Family of
       Muricidæ, First Paper. 20 pp.--Proc. Rochest. Acad. Sci., Vol.
       I, 1891.

  --Description of New Species of Muricidæ with Remarks on the Apices
       of Certain Forms. 9 pp., 1 pl.--Proc. Rochest. Acad. Sci., Vol.
       I, 1891.

=Barrois, Charles.=

  --Sur la présence de fossiles dans le terrain azoique. 4 pp.--Comptes
       Rendus des Séances de L'Académie des Sciences, Aug. 8, 1892.

=Beecher, C.E., Ph.D.=

  --The Development of some Silurian Brachiopods. 8 pl., 96 pp.--N. Yr
       State Mus., Vol. I, No. I, Oct. 1892.

  --Brachiospongidæ, a Memoir on a Group of Silurian Sponges. 28 pp., 6
       pl. Memoirs of the Peabody Mus., Vol. II, Part I, 1889.

  --Insecta by Alpheus Hyatt and J. M. Arms.--Am. Jour. Sci., March,
       1891.

  --New Types of Carboniferous Cockroaches from the Carboniferous
       Deposits of the United States; (2) New Carboniferous Myriapoda
       from Ill.; (3) Illustrations of the Carboniferous Arachnida
       of N. A., of the orders Anthracomarti and Pedipalpi; (4) The
       Insects of the Triassic Beds at Fairplay, Col., Samuel H.
       Scudder. 2 pp.--Am. Jour. Sci., Jan., 1891.

  --Some Abnormal and Pathologic Forms of Fresh Water Shells from the
       Vicinity of Albany, N. Y. 2 pp., 2 pl.--36th Rep. N. Y. State
       Mus. of Nat. Hist.

  --The Development of a Paleozoic Poriferous Coral. Symmetrical Cell
       Development in the Favositidæ. 12 pp., 7 pl.--Trans. Conn. Acad.
       Sci., Vol. 8, 1891.

  --On Leptænisca, a New Genus of Brachiopod from the L. Helderberg
       Group. N. A. Species of Strophalosia. 8 pp., 1 pl.--Am. Jour.
       Sci., Sept., 1890.

  --Ceratiocaridæ from the Chemung and Waverly Groups at Warren, Penn.
       22 pp., 2 pl.--Rep. of Prop., PPP, 2d Geol. Surv. Penn., 1884.

  --A Spiral Bivalve from the Waverly Group of Penn. 4 pp., 1
       pl.--39th An. Rep. N. Y. State Mus., 1886.

  --On the Lingual Dentition and Systematic Position of Pyrgula. 8 pp.,
       1 pl. Jour. N. Y. Mic. Soc., Jan., 1890.

  --On the Occurrence of U. Silurian Strata near Penobscot Bay, Maine.
       6 pp., Ill.--Am. Jour. Sci., May, 1892.

  --Koninckina and Related Genera. 9 pp., 1 pl.--Am. Jour. Sci., Sept.,
       1890.

  --Development of the Brachiopoda, Part I, Introduction. 14 pp., 1
       pl.--Am. Jour. Sci., Apr., 1892.

  --Development of the Brachiopoda. Part II, Classification of the
       Stages of Growth and Decline. 22 pp., 1 pl.--Am. Jour. Sci.,
       Aug., 1892.

=Beachler, Chas. S.=

  --Keokuk Group of the Miss. Valley. 8 pp.--Am. Geol., Aug., 1892. 3
       copies.

  --The Rocks at St. Paul, Indiana and Vicinity. 2 pp.--Am. Geol.,
       Mch., 1891. 3 copies.

=Bigelow, Frank H.=

  --Notes on a new Method for the Discussion of Magnetic Observations.
       40 pp., 2 pl.--Bull. Weather Bureau, 1892.

=Boehm, Georg.=

  --Ueber den Fussmuskeleindruck bei Pachyerisma. 2 pp.--Berichte der
       Naturforschenden Gesellschaft in Freiburg i. B., 1892. VI. 3.

  --Megalodon, Pachyerisma und Diceras. 24 pp. 9 wood cuts.--Aus den
       Berichten der Naturforschenden Gesellschaft VI. 2. zu Freiburg
       i. B., 1891.

  --Lithiotis Problematica. 16 pp., 3 pl.--Naturforschenden Gesell. in
       Freiburg, Band II. Heft 3.

  --Ueber das Alter der Kalke des col dei Schiosi. 4 pp.--Der Deut.
       Geolog. Gesell, 1887.

  --Ein Beitrag zur Kenntniss der Kreide in den Venetianer Alpen. 16
       pp., 4 pl. 3 cuts.--Aus den Berichten der Naturforschenden
       Gesellschaft zu Freiburg i. B. Band VI. Heft 4.

  --Die Bivalven der Schichten des Diceras Muensteri (Diceraskalk) von
       Kelhein. 8 pp.--Zeit. Deut. Geol. Gesell. 1881.

  --Ueber die Fauna der Schichten mit Durga im Departement der Sarthe.
       12 pp., 1 pl. 2 wood cuts.--Zeit. der Deut. geol. Gesell. Bd.
       XL., 1888.

  --Die Facies der grauen Kalke von Venetien im Departement der Sarthe.
       6 pp.--Aus der Zeit. der Deut. geol. Gesell, 1887.

  --Südalpine Kreideablagerungen. 6 pp.--Aus der Zeit. d. Deut. geol.
       Gesell, Bd., 33, 2 Heft.

  --Ueber eine Anomalie im Kelche von Millericrinus mespiliformis. 5
       pp., Ill. Zeit. der Deut. Geol. Gesell., Bd. 43, Heft 3.

=Bowerman, A.=

  --The Chinook Winds and other Climatic Conditions of the Northwest. 6
       pp.--Hist. and Sci. Soc'y of Manitoba, Apr. 22, 1886.

=Blanford, W. T.=, LL.D., F.R.S.

  --On Additional Evidence of the Occurrence of Glacial Conditions
       in the Paleozoic Era, and in the Geological Age of the Beds
       Containing Plants of the Mesozoic Type in India and Australia.

=Brigham, Albert P.=

  --A Chapter in Glacial History with Illustrative Notes from Central
       New York.--Trans. Oneida Hist. Society, 1889-91.

  --The Geology of Oneida County. 18 pp.--Trans. Oneida Hist. Society,
       1887-88.

  --Rivers and the Evolution of Geographic Forms. 21 pp., Ill.--Am.
       Geog. Soc'y, Mch., 1892.

=Chamberlin, T. C.=

  --Hillocks of Angular Gravel and Disturbed Stratification. 12 pp.,
       Ill.--Am. Jour. Sci., May, 1884.

=Carter, Prof.= O. C. S.

  --Ores, Minerals and Geology of Montgomery County, Pennsylvania, with
       map.--Hist. of Mont. Co.

  --Artesian Wells in the Lowest Trias at Norristown. 7 pp.--Proc. Am.
       Phil. Soc., May 1, 1891.

=Carpenter, Commander A.=, R. N.

  --Soundings Recently Taken off Barren Island Narcondam, Pl.--Records
       Geol. Sur. Ind., Vol. XX, Part 1, 1887.

=Clarke, F. W.=

  --The Meteoric Collection in the U. S. Nat. Mus. A Catalogue of
       Meteorites Represented. Nov. 1, 1886. 13 pp. Ill., 1 pl.

  --Some Nickel Ores from Oregon, Ill. 7 pp.--Am. Jour. Sci., June,
       1888.

  --Tschemak's Theory of the Chlorite group and its Alternative. 10
       pp.--Am. Jour. Sci., March, 1892.

  --On Nephrite and Jadeite. 15 pp. 1 pl. Proc. U. S. Nat. Mus. XI,
       1888.

  --Studies in the Mica Group. 6 pp.--Am. Jour. Sci., Aug., 1889.

  --A New occurrence of Gyrolite. 2 pp.--Am. Jour. Sci., Aug., 1887.

  --Experiments upon the Constitution of the Natural Silicates. 25
       pp.--Am. Jour. Sci., Oct., Nov., Dec., 1890.

  --Mica. 6 pp.--Min. Resources of the U. S., 1883-4.

  --Note on the Constitution of Ptilolite and Mordenite.--Am. Jour.
       Sci., Aug., 1892.

  --On Some Phosphides of Iridium and Platinum on Cadmium Iodide.
       Some Sp. Gr. Determinations. Researches on the Tartrates of
       Antimony.--Am. Chem. Jour. Vol. V., No. 4.

  --The Fractional Analysis of Silicates. 7 pp.--Jour. Am. Chem. Soc.,
       Vol. XII, No. 10.

  --A Theory of the Mica Group. 10 pp.--Am. Jour. Sci., Nov. 1889.

=Clarke F. W. (and J. S. Diller.)=

  --Topaz from Stoneham, Maine. 7 pp.--Am. Jour. Sci., May, 1888.

  --Turquois from New Mexico. 7 pp.--Am. Jour. Sci., Sept., 1886.

=Clarke F. W. (and Charles Catlett.)=

  --A Platiniferous Nickel Ore from Canada. 3 pp.--Am. Jour. Sci.,
       May, 1889.

=Clarke F. W. (and E. A. Schneider.)=

  --On the Constitution of Certain Micas, Vermiculites and Chlorites.
       10 pp.--Am. Jour. Sci., Sept., 1891.

=Cohen, E.=

  --Ueber einige eigenthümliche Melaphyr-Mandelsteine aus Süd-Afrika.
       15 pp. Map, 1 pl.--Aus dem Neuen Jahrb. Min., 1875. Mandelsteine
       Aus Den Maluti-Bergen, Süd-Africa, 1 p. Ibid., 1880, Bd. I.

  --Ueber Laven von Hawaii und einigen anderen Inseln des Grossen
       Oceans nebst einigen Bemerkungen ueber glasige Gesteine im
       allgemeinen. 30 pp.--Aus dem Neuen Jahrb. Min. Geol. und Pal.
       1880, Bd. II.

  --Goldführende Conglomerate in Süd-Afrika. 3 pp.--Mit. des naturw.
       Vereins für Neu-Vorpommern und Ruegen, 1887.

  --Ueber die Trennung von Thonerde, Eisenoxyd und Titansäure. 2
       pp.--Aus Neuem Jahrb. für Min. 1884.

  --Chemische Untersuchung des Meteoreisens von S. Juliao de Moreira,
       Portugal, sowie einiger anderen hexaëdrischen Eisen. 12 pp.--Aus
       dem Neuen Jahrbuch für Mineralogie, 1889, Bd. I.

  --Zusammenstellung petrographischer Untersuchungsmethoden nebst
       Angabe der Literatur. 36 pp.--Aus den Mit. aus dem naturw.
       Verein für Neu-Vorpommern und Ruegen in Greifswald.

  --Ueber die Entstehung des Seifengoldes. 20 pp.--Mit. des naturw.
       Vereins für Neu-Vorpommern und Ruegen, 1887.

  --Geonostisch-petrographische Skizzen aus Süd-Afrika. 48 pp. 1
       pl.--Aus dem Neuen Jahrbuch, Min. 1874.

  --Ueber einige Vogesengesteine. 6 pp.--Aus dem Neuen Jahrb. Min.
       Geol. und Pal., 1883, Bd. I.

  --Andalusitführende Granite. 3 pp.--Aus dem Neuen Jahrb. Min. 1887,
       Bd. II.

  --Nekrolog von Jonas Gustaf Oscar Linnarsson. 2 pp.--Aus dem Neuen
       Jahrb. Min. 1882. Bd. I.

  --Versammlung des Oberrhein, geologischen Vereins zu Duerkheim,
       bayr. Rheinpfalz, am 13, 14 und 15 April, 1882. Ueber einen
       Aventurinquartz aus Ostindien.

  --Berichtigung bezüglich des "Olivin-Diallag-Gesteins" von
       Schriesheim im Odenwald. 2 pp.--Aus dem Neuen Jahrb. Min. 1885,
       Bd. I.

  --Ueber Pleochroitische Höfe in Biotit. 5 pp.--Aus den Neuen Jahrb.
       Min. 1888, Bd. I.

  --Kersantit von Laveline. 2 pp.--Aus den Neuen Jahrb. Min. 1879.

  --Das Labradoritführende Gestein der Küste von Labrador. 3 pp.--Aus
       den Neuen Jahrb. Min. 1885, Bd. I.

  --Ueber eine verbesserte Methode der Isolirung von
       Gesteinsgemengtheilen vermittelst Flussäure. 3 pp.--Mit. des
       naturw. Vereines für Neu-Vorpommern und Ruegen, 1888.

  --Die Gold production Transvaal in Jahre 1889.

  --Ueber eine Pseudomorphose nach Markasit aus der Kreide von Arcona
       auf Ruegen. 4 pp.--Aus den Sitzungsberichten des naturw. Vereins
       für Neu-Vorpommern und Ruegen, 1886.

  --Das Obere Weilerthal und das Zunächst Angrenzende Gebirge.
       150 pp.--Abhandlungen zur Geologischen Speciakarte von
       Elsass--Lothringen.

  --Ueber den Granat der süd-afrikanischen Diamantfelder und ueber den
       Chromgehalt der Pyrope. 4 pp.--Aus der Mit. des naturw. Vereins
       für Neu-Vorpommern und Ruegen, 1888.

  --Ueber Speckstein, Pseudophit und dichten Muscovit aus Süd-Afrika. 6
       pp.--Aus dem Neuen Jahrb. Min. 1887, Bd. I.

  --Titaneisen von den Diamantfeldern in Süd-Afrika. 2 pp.--Aus dem
       Neuen Jahrb. Min. 1877.

  --Ueber den Meteoriten von Zsadany, Temesvar Comitat, Banat. 10
       pp.--Aus den Verhandlungen des Naturhist-Med. Vereins zu
       Heidelberg. II Bd., 2 Heft.

=Cohen E.= und =W. Deecke=.

  --Ueber Geschiebe aus Neu-Vorpommern und Ruegen. 84 pp.--Aus den
       Mitt. des naturwiss. Vereines für Neu-Vorpommern und Ruegen,
       1881.

  --Sind die Stoerungen in der Lagerung der Kreide an de Ostküste von
       Jasmund (Ruegen) durch Faltungen zu erklären? 10 pp. 3 pl.--Aus
       den Mit. des naturwiss. Vereins für Neu-Vorpommern und Ruegen,
       1889.

  --Ueber das Krystalline Grundgebirge der Inseln Bornholm.

=Cohen E.= und =E. Weinschenk=.

  --Meteoreisen-Studien. 32 pp.--Annalen des K. K. Naturhistorischen
       Hofmuseums. Bd. VI. Heft 2, 1891.

=Cross, Whitman.=

  --The Post-Laramie Beds of Middle Park, Colo. 27 pp.--Proc. Colo.
       Sci. Soc., Oct. 3, 1892.

  --Post-Laramie Deposits of Colorado. 22 pp.--Am. Jour. Sci., July,
       1892.

  (and L. G. Eakins).

  --A New Occurrence of Ptilolite.--Am. Jour. Sci., Aug., 1892.

=Crosskey, H. W.=

  --On a section of Glacial drift recently explored in Icknield Street,
       Birmingham. 8 pp., 3 pl.--Proc. Birm. Phil. Soc. Vol. III, p.
       209.

  --Notes on some of the Glacial Phenomena of the Vosges Mountain, with
       an account of the Glacier of Kertoff. 12 pp.--Jan. 9, 1879.

  --Recent Researches into the Post-Tertiary Geology of Scotland. 12
       pp.--Phil. Soc., Glasgow, Dec. 7, 1868.

  --On the Tellino Calcarea Bed at Chappel Hall, near Airdrie.

  --Some additions to the Fauna of the Bridlington (post-Tertiary) Bed.
       6 pp.--Proc. Birmingham Phil. Soc. Vol. II, part II, June 9,
       1891.

  --Report of the Committee of the B. A. A. S. appointed for the
       purpose of recording the position, height above sea-level,
       character, etc. of Erratic blocks of Eng. Wales and Ire.--Brit.
       Assoc. 1873, 1878, 1882, 1883, 1884, 1885, 1886, 1887, 1888,
       1891.

  (and =David Robertson=).

  --The Post-tertiary Fossiliferous Beds of Scotland. 16 pp., 1
       pl.--Trans. Geol. Soc. Glasgow, Vol. IV, Part III, page 241. 8
       pp., Vol. V., Part I, page 29.

=Davis W. M.=

  --The Convex Profile of Bad Land Divides.--Sci., Oct. 28, 1892.

  --The Deflective Effect of the Earth's Rotation. 8 pp.--Am. Met.
       Jour., April, 1885.

  --The Subglacial Origin of Certain Eskers. 23 pp.--Proc. Boston Soc'y
       of Nat. Hist. Vol. XXI, May, 1892.

  --Outline of a Course in Elementary Descriptive and Physical
       Geography for Grades IV. and V. in the Cambridge Grammar School,
       1892-3. 4 pp.

  --Outline of Elementary Meteorology. A synopsis of course "Geology I"
       at Harvard College, 1892-3.

=Dawson, Geo.= M.D., D. Sc., F.G.S.

  --Recent observations in the Glaciation of Br. Columbia and Adjacent
       Regions. 4 pp., 1 pl.--Geol. Mag., Aug., 1888.

=Dawson, Sir Wm. J.=

  --The Geological History of Plants. 2 pp.--Botanical Gazette, Vol.
       XIII., No. 6.

=Deeche, W.=

  --Der Monte Vulture in der Basilicata (Unteritalien) 78 pp. 1 Map., 1
       pl.--Aus dem Neuen Jahrb. Min. Geol. und Pal. Beilageband VII.

=Dewey, Frederic P.=

  --A Preliminary Catalogue of the Systematic Collection in Economic
       Geology and Metallurgy in the U. S. National Museum. 256
       pp.--Bull. U. S. Nat. Mus. No. 42.

  --Plan to Illustrate Resources of the U. S. and their Utilizations,
       at the World's Industrial and Cotton Centennial Exposition
       of 1884-85 at New Orleans. 8 pp. Proc. U. S. Nat. Mus. 1884,
       Appendix.

  --Photographing the Interior of a Coal Mine. 8 pp., 4 pl.--Am. Inst.
       Min. Eng., July, 1887.

  --Some Canadian Iron Ores. 12 pp.--Trans. Am. Inst. Min. Eng., Vol.
       XII. 1884.

  --Report of the Department of Metallurgy in the U. S. National
       Museum. 4 pp.--Report to the Nat. Mus., 1888-89.

  --The Department of Metallurgy and Economic Geology in the U. S. Nat.
       Mus. 26 pp.--Am. Inst. Min. Eng., Sept., 1890.

  --Hampe's Method of Determination Cu_{2}O in Metallic Copper. 6
       pp.--Proc. U. S. Nat. Mus., 1888.

  --Porosity of Specific Gravity of Coke. 16 pp.--Trans. Am. Inst. Min.
       Eng., June, 1888.

  --The Lewis and Bartlett Bag-Process of collecting Lead Fumes at the
       Lone Elm Works, Joplin, Mo. 32 pp., Ill.--Am. Inst. Min. Eng.,
       Feb., 1890.

  --Note on the Nickel-Ore of Russell Springs, Logan Co., Kan.--Am.
       Inst. Min. Eng.

  --Note on the Falling Cliff Zinc Mine. 2 pp.--Am. Inst. Min. Eng.,
       May, 1891.

  --The Heroult Process of Smelting Aluminum Alloys. 8 pp.--Am. Inst.
       Min. Engin., Feb., 1890.

  --Pig Iron of Unusual Strength. 18 pp.--Am. Inst. Min. Eng., Oct.,
       1888.

=Diller, J. S.=

  --Geology of the Taylorville Region of California. 25 pp.,
       Ill.--Bull. Geol. Soc. Am., Vol. 3. pp. 369-394.

  --Peridotite of Elliott County, Kentucky. 32 pp., Ill.--Bull. U. S.
       G. S., No. 38.

  --Notes on the Geology of Northern Cal. 224 pp.--Bull. U. S. G. S.,
       No. 33.

  --Fulgurite from Mt. Thielson, Oregon. 7 pp., Ill.--Am. Jour. Sci.,
       Oct., 1884.

  --Notes on the Peridotite of Elliot County, Ky. 5 pp.--Am. Jour.
       Sci., Aug., 1886.

  --A Late Volcanic Eruption in Northern Cal. and its Peculiar Lava.
       33 pp., XVII pl., 4 cuts.--Bull. U. S. G. S., 79, 1891.

=Emmons, S. F.=

  --Abstract of a Report upon the Geology and Mining Industry of
       Leadville, Colorado. 90 pp., with maps.--Ann. Rep. U. S. G. S.,
       1880-81.

  --Orographic Movements in the Rocky Mountains. 22 pp.--Bull. Geol.
       Soc'y Am., Vol. I., pp 245-86.

  --Notes on the Geology of Butte, Montana. 14 pp.--Trans. Am. Inst.
       Min. Eng., July, 1887.

  --The Genesis of Certain Ore Deposits. 22 pp.--Trans. Am. Inst. Min.
       Eng., March, 1886.

  --Structural Relations of Ore Deposits. 36 pp.--Am. Inst. Min. Eng.,
       Feb., 1888.

  --Notes on the Gold Deposits of Montgomery County, Maryland. 22
       pp.--Am. Inst. Min. Eng., Feb., 1890.

  --On Glaciers in the Rocky Mountains. 16 pp.--Proc. Col. Sci. Soc'y,
       1887.

  --Preliminary Notes on Aspen, Col. 26 pp.--Proc. Col. Sci. Soc'y,
       1887.

  --Fluor-Spar Deposits of Southern Ill. 24 pp, map.--Am. Inst. Min.
       Eng., Baltimore Meeting, Feb., 1892.

  --The Mining Work of the U. S. Geol. Survey. 13 pp.--Trans. Am. Inst.
       Min. Eng., Washington Meeting, Feb., 1892.

  --On the Origin of Fissure Veins. 20 pp.--Proc. Col. Sci. Soc'y, 1887.

=Emmons, S. F.= (and =G. E. Becker=).

  --Geological Sketches of the Precious Metal Deposits of the Western
       United States, with notes on Lead Smelting at Leadville. 296
       pp.--Tenth Census U. S., Vol. XIII "Statistics and Technology of
       the Precious Metals."

=Emerson, George H.=

  --Observations on Crystals and Precipitations in Blowpipe Beads. 18
       pp., Ill.--Proc. Am. Acad. of Arts and Sci., March, 1865.

=Fisher, Rev. O.=

  --Mr. Mallet's Theory of Volcanic Energy Tested. 18 pp.--Phil. Mag.,
       Oct., 1875.

  --Review of Captain Dutton's Critical Observations on Theories of the
       Earth's Physical Evolution. 8 pp.--Geol. Mag., Aug., 1876.

  --On the Possibility of Changes in the Latitude of places on the
       Earth's Surface. Being an appeal to Physicists. 7 pp.--Geol.
       Mag., July, 1878.

  --On Theories to Account for Glacial Submergence. 8 pp.--Phil. Mag.,
       Oct., 1892.

  --On Dynamo Metamorphism. 2 pp.--Geol. Mag., July, 1890.

  --On the Warp, its Age and Probable Connection with the last
       Geological Events. 12 pp., Ill.--Quart. Jour. Geol. Soc'y, Nov.,
       1866.

  --On Implement-bearing Loams in Suffolk. 5 pp.--Proc. Cambridge Phil.
       Soc'y, Vol. III, Pt. VII.

  --On the Brocklesham Beds of the Isle of Wight Basin. 30 pp.--Proc.
       Geol. Soc'y, May, 1862.

  --On a Mammaliferous Deposit at Barrington, near Cambridge. 11 pp.,
       Ill.--Quart. Journ. Geol. Soc'y, Nov., 1879.

  --On the Denudation of Soft Strata. 4 pp.--Quart. Journ. Geol. Soc'y,
       Feb., 1861.

  --On the Occurrence of Elephas Meridonalis at Dervlish, Dorset. 8
       pp., Ill.--Quart. Journ. Geol. Soc'y, Nov., 1888.

  --Glacial Action and Raised Sea-Beds. 4 pp., Ill.--Geol. Mag., April,
       1873.

  --On the Origin of the Estuary of the Fleet in Dorsetshire.

  --On the Brick-pit at Lexden, near Colchester (with notes on the
       Coleoptera, by T. U. Wollaston). 9 pp., Ill.--Quart. Journ.
       Geol. Soc'y of London, 1863.

  --On Faulting, Jointing and Cleavage. 72 pp., Ill.--Geol. Mag., May,
       1884.

  --Remarks upon Mr. Mallet's Strictures on the Mathematical Test
       applied to his Theory of Volcanic Energy, by Mr. O. Fisher. 6
       pp.--Phil. Mag., Feb., 1876.

  --On the Phosphatic Nodules of the Cretaceous Rock of Cambridgeshire.
       14 pp., 1 pl.--Quart. Journ. Geol. Soc'y, Feb., 1873.

  --On Faults. Reply to Professor Blake's Criticisms. 3 pp.--Geol.
       Mag., Sept., 1884.

  --"Uniformity" and "Vulcanicity." 3 pp.--Geol. Mag., March, 1875.

  --The Cause of Slaty Cleavage. 4 pp.--Geol. Mag., April, 1885.

  --On the Thermal Conditions and on the Stratification of the
       Antarctic Ice. 13 pp.--Phil. Mag., June, 1879.

  --On Cleavage and Distortion. 11 pp.--Geol. Mag., Sep., 1884.

  --On the Ages of the "Trail" and "Warp." 7 pp.--Geol. Mag., May, 1867.

  --Review of Dutton's Grand Cañon, Colorado. 4 pp.--Geol. Mag., July,
       1883.

  --On the Theory of the Erosion of Lake Basins by Glaciers. 2
       pp.--Geol. Mag., June, 1876.

  --Oblique and Orthogonal Sections of a Folded Plane. 4 pp.,
       Ill.--Geol. Mag., Jan., 1891.

  --On the Cromer Cliffs. 4 pp., Ill.--Geol. Mag., April, 1880.

  --On Some Natural Pits on the Heaths of Dorsetshire. 2 pp.--Quart.
       Journ. Geol. Soc'y, London, 1858.

  --On Cirques and Toluses. 4 pp.--Geol. Mag., Jan., 1872.

  --On a Worked Flint from the Buck-Earth of Crayford, Kent. 2
       pp.--Geol. Mag., June, 1872.

=Frazer, Dr. Persifor.=

  --General Notes on the New Orleans Industrial and Cotton Exhibition.
       20 pp.--Journal Franklin Institution, June, 1885.

  --The Eozoic and Lower Paleozoic in South Wales and their Comparison
       with their Appalachian Analogues. 18 pp.--Am. Inst. Min. Engin.,
       Feb., 1883.

  --Geological and Mineral Studies in Nuevo Leon and Coahuilla, Mexico.
       36 pp., =III=, and maps.--Am. Inst. Min. Engin., Feb., 1884.

  --Trap Dykes in the Archaean Rocks of Southeastern Pennsylvania. 4
       pp.--Am. Phil. Soc., Oct. 17, 1884.

  --Classification of Coals. 22 pp.--Trans. Am. Inst. Min. Engin., Vol.
       VI, 1879.

  --Descriptive Table of Elements. 2 pp.--1891.

  --The late International Geological Congress at Berlin. 4 pp.--Am.
       Phil. Soc'y, Nov. 20, 1885.

  --Report of the American Committee of the International Congress of
       Geologists. 5 pp.--Proc. A. A. A. S., Vol. XXXV, August, 1886.

  --General Notes on the Geology of York County, Penn. 20 pp.--Colored
       maps.

  --On the Physical and Chemical Characteristics of a Trap occurring at
       Williamson's Point, Penn. 8 pp., 1 colored plate. Read before
       Am. Phil. Soc'y, Dec. 20, 1878.

  --An Hypothesis of the Structure of the Copper Belt of the South
       Mountain. 4 pp., Ill.--Trans. Am. Inst. Min. Engin., June, 1883.
       Read at the Roanoke, Va., Meeting.

  --A Broader Field for the U. S. Geological Survey. 4 pp.--Journ.
       Franklin Instit., Sept., 1888.

  --The Peach Bottom Slates of the Lower Susquehanna, with sections of
       the Right and Left Banks. 5 pp., 3 pl.--Am. Inst. Min. Eng.,
       Oct., 1883.

  --Reply to a paper entitled "Notes on the Geology of Chester Valley
       and Vicinity." 8 pp.--Journ. Franklin Inst., April, 1884.

  --Mr. Theodore D. Rand's Criticism of Vol. C_{4} Geology of Chester
       County, Penn. 6 pp.--Journ. Franklin Inst., Oct., 1883.

  --Archaean Characters of the Rocks of the Nucleal Ranges of the
       Antilles. 1 p.--Brit. Assn., 1888.

  --Notes on Fresh-Water Wells of the Atlantic Beach. 4 pp.--Journ.
       Franklin Inst., Sept., 1890.

  --The Position of the American New Red Sandstone. 8 pp.--Trans. Am.
       Inst. Min. Engin., Vol. V.

  --On the Traps of the Mesozoic Sandstone in York and Adams Counties,
       Penn. 13 pp., 4 pl.--Am. Phil. Soc'y, April 16, 1875.

  --The Whopper Lode, Gunnison County, Colo. 10 pp.--Am. Inst. Min.
       Engin., Aug., 1880.

  --Some Copper Deposits of Carroll County, Md. 8 pp., 1 pl.--Am. Inst.
       Min. Engin., Aug., 1880.

  --A Convenient Device to be Applied to the Hand Compass. 1 p.--Am.
       Phil. Soc'y, Dec. 5, 1884.

  --The Approaches to a Theory of the Causes of Magnetic Declination.
       16 pp.--Am. Phil. Soc'y, Apr. 6, 1877.

  --On Improvement in the Construction of the Hypsometric Aneroid.--Am.
       Phil. Soc'y, March 2, 1883.

  --An Exfoliation of Rocks near Gettysburg. 2 pp.--Am. Phil. Soc'y,
       Dec. 4, 1874.

  --Note on the New Geological Map of Europe. 6 pp.--Trans. Am. Inst.
       Min. Engin.

  --Some Supposed Fossils from the Susquehanna River, just South of the
       Pennsylvania-Maryland Line. 3 pp., 1 pl.--Proc. Am. Phil. Soc'y
       XVIII, Sept. 18, 1879.

  --Missing Ores of Iron. 12 pp., Ill.--Trans. Am. Inst. Min. Engin.,
       Vol. VI, 1879.

  --The Peach Bottom Slates of Southeastern York and Southern Lancaster
       Counties, Penn. 5 pp., 1. pl.--Trans. Am. Inst. Mining Engin.,
       1883.

  --A Speculation on Protoplasm. 7 pp.--Am Nat., July, 1876.

  --A Mirror for Illuminating Opaque Objects for the Projecting
       Microscope. 2 pp.--Am. Phil. Soc'y, Feb. 20, 1880.

  --The Progress of Chemical Theory; Its Helps and Hindrances. 37
       pp.--Journ. Franklin Instit., Apr., May and June, 1891.

  --Mineral Formulæ. 6 pp.--Proc. Acad. Nat. Sci., Phila., July 7, 1874.

  --Notes from the Literature on the Geology of Egypt, and Examination
       of the Syenitic Granite of the Obelisk which Lieut. Comd'r
       Gorringe, U. S. N., brought to New York. 27 pp., 4 pl.--Trans.
       Am. Inst. Mining Engin., 1883.

  --Report of Committee on the International Congress of Geologists. 3
       pp.--Proc. A. A. A. S., Vol. XXXIX, 1890.

  --On Certain Trap Rocks from Brazil. 3 pp.--Proc. Acad. Sci., Phila.,
       1876.

  --An Unjust Attack. 8 pp.--Am. Geol., Jan., 1889.

  --The Philadelphia Meeting of the International Congress of
       Geologists. 10 pp., Am. Geol., June, 1890.

  --Report of the Berlin International Geological Congress. 13 pp.--Am.
       Jour. Sci., XXX, December, 1885.

  --Mesozoic Sandstone of the Atlantic Slope. 9 pp.--Am. Nat., May,
       1879.

  --Archæan-Paleozoic Contact near Philadelphia, Penn. 6 pp., 1
       pl.--Proc. A. A. A. S., Vol. XXXIII, Sept., 1884.

  --Report of the Sub-Committee of the Berlin Congress of Geologists on
       the Archæan. 80 pp.

  --Crystallization. 11 pp., Ill.--Journal Franklin Inst., Aug., 1885.

  --Origin of the Lower Silurian Limonites of York and Adams Counties,
       6 pp.--Am. Phil. Soc'y, March 19, 1875.

  --The Northern Serpentine Belt in Chester County, Pa. 8 pp.--Trans.
       Am. Inst. Min. Engin., 1883.

  --The Persistence of Plant and Animal Life under Changing Conditions
       of Environment. 13 pp.--Am. Nat., June, 1890.

  --International Congress of Geologists, 1886. 109 pp., 1 pl.

  --International Congress of Geologists, Reports of the Sub-Committee
       appointed by the American Committee. 239 pp., 1888.

  --Other Short Articles.

=Frisbie, Dr. J. F.=

  --Glacial Moraines. 16 pp.

  --Mountain Building and Mountain Sculpture. 13 pp.

  --The Franconia Flume, the Causes that led to its Formation. 8 pp.

  --Planet Building. 11 pp., 1 pl.

  --   "      "      17 pp., 2 pl.

=Geikie, Sir Archibald=, LL.D., D.Sc, F.R.S.E., P.G.S.

  --Address to the Geological Section of the British Association. 23 pp.

  --Address by Sir Archibald Geikie, President of British Association
       for the Advancement of Science. 1892. 24 pp.

  --Progress of the Geological Survey in Scotland. 10 pp.--Proc. Royal
       Soc'y, Edinburgh, Vol. II, Session 1864-5.

  --On the Tertiary Volcanic Rocks of the British Islands. 4 pp.--Proc.
       Royal Soc'y, Edinburgh, 1866-67.

  --The History of Volcanic Action during the Tertiary Period in the
       British Islands (Abstract). 5 pp.--Proc. Royal Soc'y, Edin.,
       1888.

  --Address delivered at the 36th Anniversary Meeting of the Edinburgh
       Geological Society. Also Notes for a Comparison of the Volcanic
       Geology of Central Scotland with that of Auvergne and the Eifel.
       16 pp.--Trans. of the Edinburgh Geological Society, 1869-70,
       Vol. II, Part I.

  --On Modern Denudation. 38 pp.--Trans. Geol. Soc'y of Glasgow, Vol.
       III, p. 153.

  --On Denudation now in Progress. 6 pp.--Geol. Mag., Vol. I, No. 6,
       June, 1868.

  --Earth Sculpture and the Huttonian School of Geology. The Inaugural
       Address Delivered at the 40th Anniversary Meeting of the
       Edinburgh Geological Society, Nov. 6, 1873.

  --Recent Researches into the Origin and Age of the Highlands of
       Scotland and the West of Ireland. 19 pp.

  --Royal Institute of Great Britain, 1889.

  --The Cañons of the Far West.--Ibid., April 6, 1883. 4 pp.

  --Rock-Weathering, as illustrated in Edinburgh Churchyards. 15 pp., 1
       pl.--Proc. Royal Soc'y, Edinburgh, Vol. X., April 19, 1880.

  --The Ancient Glaciers of the Rocky Mountains. 7 pp.--Am. Nat. Jan.
       1881.

  --The Ice Age in Britain.--Science Lectures for the People. 17 pp.

  --The Old Man of Hoy. 6 pp., 1 pl.--Report Brit. Assoc., 1871.

  --On the Old Red Sandstone of the South of Scotland. 12 pp., 1
       pl.--Quarterly Journal Geol. Soc'y, Aug. 1860.

  --On the Geology of Strath, Skye, (with descriptions of some Fossils
       from Skye, by T. Wright, M.D., F.R.S.E.) 36 pp., 1 pl.

  --The History of Volcanic Action in the Area of the British Isles.
       119 pp.--Quarterly Journal of the Geological Society of London,
       Vol. XLVIII, 1892.

  --On the Supposed Pre-Cambrian Rocks of St. David's. 66 pp., 3
       pl.--Quarterly Journal of the Geological Society, Aug. 1883.

  --On the Tertiary Volcanic Rocks of the British Islands. 31 pp., 1 pl.

  --The Geological Origin of the Present Scenery of Scotland. 21 pp.
       Ill.--The Journal of Travel and Natural History.

  --On the Age of the Altered Limestone of Strath, Skye.--13 pp.
       Ill.--Quart. Journal Geol. Soc'y, 1888.

  --Address of the President of the Geological Society of London, Feb.
       20, 1891. 126 pp.

  --The Origin of Coral Reefs. 13 pp. Ill.--Proc. Royal Physical Soc'y.
       Vol. VIII, p.; 1884.

  --The "Pitchstone" of Eskdale, a retrospect and comparison of
       Geological Methods. Ibid, Vol V, 1880.

=Genth, F. A.=

  --Ueber Nordamerikanische Tellur-und Wismuth-Mineralien. 14
       pp.--Journal für Praktische Chemie, 1874.

  --Ueber Lansfordit, Nesquehonit und Pseudomorphosen von Nesquehonit
       nach Lansfordit. (F. A. Genth und S. L. Penfield). 18 pp., 1
       pl.--Zeit. für Krystallographie, 1890.

  --Contributions to Mineralogy. 18 pp., 1 pl. Read before Am. Phil.
       Soc'y, Oct. 2, 1885.

  --do. 21 pp. Read before Am. Phil. Soc'y, March 18, 1887.

  --Investigation of Iron Ores and Limestones from Blair and Huntingdon
       counties, Pa. 26 pp.--Read before the Am. Phil. Soc'y, Feb. 6,
       1874.

  --Contributions to Mineralogy. 6 pp.--Am. Jour. Sci., Sept. 1889; 4
       pp. Jan., 1890.

  --do. with Crystallographic notes by S. L. Penfield. 9 pp.--Am. Jour.
       Sci., Sept., 1890; 10 pp. May, 1891: 6 pp. March, 1892.

  --On American Tellurium and Bismuth Minerals. 9 pp.--Am. Phil. Soc'y,
       Aug. 21, 1874.

  --On Herderite. 7 pp. Read before Am. Phil. Soc'y, Oct. 17, 1884.

  --On Lansfordite, Nesquehonite, a New Mineral and Pseudomorphs of
       Nesquehonite after Lansfordite. 17 pp., 1 pl.--Am. Jour. Sci.,
       Feb., 1890.

  --The Minerals of North Carolina.--Bulletin 74, U. S. G. S. 120 pp.

  --The Minerals and Mineral Localities of North Carolina. 122
       pp.--Geol. of North Carolina, Vol. II, 1881.

  --First Annual Report of Dr. F. A. Genth, Chemist of the Pennsylvania
       Board of Agriculture. 32 pp., 1878.

  --Second Preliminary Report on the Mineralogy of Pennsylvania, with
       Analyses of Mineral Spring Waters. 38 pp.

  --Ueber einige Tellur-und Vanad-Mineralien. 13 pp.--Zeit. für
       Krystallographie, etc., 1877.

  --On the Equivalent of Cerium by the late Dr. Charles Wolf. 10
       pp.--Am. Jour. Sci., May, 1868.

  --Contributions to Mineralogy, No. 54; (with Crystallographic Notes
       by S. L. Penfield). 9 pp.--Am. Jour. Sci., Nov., 1892.

  --On Penfieldite, a new species. 1 pp.--Am. Jour. Sci., Sept., 1892.

  --Mineralogische Mittheilungen, by F. A. Genth (with Crystallographic
       Notes by S. L. Penfield). 10 pp. Ill.--"Zeit. für Krystallog."
       XVIII, 6, (1891).

  --Examination of the North Carolina Uranium Minerals. 7 pp.--Am.
       Chem. Jour. Vol. I, Nos. 2 and 3.

  --On some American Vanadium Minerals. 6 pp.--Am. Jour. Sci., July,
       1876.

  --On an undescribed Meteoric Iron from East Tennessee. 4 pp., 2
       pl.--Proc. Acad. Nat. Sci. Phila., Dec. 28, 1886.

  --Lansfordit, ein neues Mineral, 2 pp.

  --On the Vanadates and Iodyrite, from Lake Valley, Sierra Co., New
       Mexico. 13 pp. Read before Am. Phil. Soc'y Apr. 17, 1885.

  --Contributions to Mineralogy.--Am. Jour. Sci., Sept. 1859; March,
       1862, May, 1868.

  --Meteorology. 6 pp.

  --Meteorology. 4 pp.--Am. Jour. Sci., Nov., 1861.

  --Re-examination of the Tetradymite from Field's Gold Mine, Georgia.

  --On Pyrophyllite from Schuylkill Co., Penn. Read before Am. Phil.
       Soc'y, July 18, 1878.

  --Mineralogische Mittheilungen. 31 pp., 2 pl.--Zeit. für
       Krystallographie, 1885.

  --Jarosite from Utah. 1 p.--Am. Jour. Sci., Jan., 1890.

  --On Two Minerals from Delaware Co., Pa. 3 pp.--Proc. Acad. Sci. of
       Phila., 1889.

  --Contributions from the Laboratory of the University of Pennsylvania.

=Gilbert, G. K.=

  --The Colorado Plateau Region considered as a Field for Geological
       Study. 27 pp.--Am. Jour. Sci., July and August, 1876.

  --The Strength of the Earth's Crust. 5 pp.--Bull. Geol. Soc. Am. Vol.
       I, 1889.

  --The History of the Niagara River. 24 pp., 8 pl.--Sixth An. Rept. of
       Com. of State Reservation at Niagara, 1889.

  --The Work of the International Congress of Geologists. 22 pp.--Am.
       Jour. Sci., Dec, 1887.

  --The Sufficiency of Terrestrial Rotation for the Deflection of
       Streams. 6 pp.--Nat. Acad. Sci., 1884.

=Gordon, C. H.=

  --Observations on the Keokuk Species of Agaricocrinus. 7 pp., 1
       pl.--Am. Geol., May, 1890.

  --On the Brecciated Character of the St. Louis Limestone. 9 pp., 2
       pl.--Am. Nat., April, 1890.

  --Proceedings of the Iowa Academy of Sciences for 1887, 1889, 1889.
       101 pp.

  --Quaternary Geology of Keokuk, Iowa, with Notes on the Underlying
       Rock Structure. 8 pp., 2 pl.

=Grant, Uly. S.=

  --Notes on the Molluscan Fauna of Minnesota. 4 pp.--16th An. Rept.
       Geol. and Nat. Hist. Survey, Minn. (1887).

  --Account of a Deserted Gorge of the Mississippi near Minnehaha
       Falls. 6 pp., 1 pl.

  --Conchological Notes. 12 pp.--14th An. Rept. Geol. and Nat. Hist.
       Survey, Minn.

  --The Stratigraphical Position of the Ogishke Conglomerate of
       Northeastern Minnesota. 8 pp.--Am. Geol. Vol. X, July, 1892.

  --Report of Geological Observations made in Northeastern Minnesota
       during the Summer of 1888. 67 pp.--Geol. and Nat. Hist. Survey
       of Minn.; part IV. 17th An. Rept.

=Hall, C. W.=

  --Notes on a Geological Excursion into Central Wisconsin. 18 pp., 1
       pl.

=Hallock, William.=

  --Chemical Action between Solids. 4 pp.--Am. Jour. Sci., May, 1889.

  --The Flow of Solids or the Behavior of Solids under High Pressure. 8
       pp.--Bull. U. S. G. S., No. 55.

  --Ueber die Lichtgeschwindigkeit in verschiedenen Quartzflächen. 3
       pp.--Annalen der Physik und Chemie, 1881. Bd. XII.

  --Preliminary Report of Observations at the Deep Well at Wheeling, W.
       Va.--Proc. A. A. A. S., 1891, vol. XL.

=Harden, John Hy.=, M. E.

  --Rock Salt Deposit of Huron and Bruce Counties, Ontario, Canada. 6
       pp.--Proc. Engineer's Club. Phila., Vol. I, No. 3.

  --The Construction of Maps in Relief. 23 pp., Ill., 1 pl.--Trans. Am.
       Inst. Min. Eng., 1887.

=Harpe, Phil. de la.=

  --Description des Nummulites appartenant à la Zone supérieure des
       Falaises de Biarritz. 20 pp., 1 pl.--Bulletin de la Société de
       Borda, 1879.

  --Une Échelle des Nummulites ou Tableau de la distribution
       stratigraphique des Espèces de Nummulites. 5
       pp.--"Verhandlungen" de la Soc. Helv. des Sc. Nat., session de
       St. Gall, 1879.

  --Note sur les Nummulites des Alpes occidentales. 6 pp.--Extrait des
       actes de la Soc. Helv. des Sc. Nat., 1877.

  --Note sur les Nummulites des environs de Nice et de Menton. 22 pp.,
       1 pl.--Bulletin de la Société Geologique de France, Octobre,
       1877.

  --Ossements appartenant à L'Anthracotherium Magnum recueillis dans
       les Lignites des environs de Lausanne. 14 pp.--Bulletin de la
       Soc. vaud. des Sc. Nat., 1854.

  --Note sur la Géologie des environs de Louèche-les-Bains. 32 pp., 1
       pl.--Bulletin de la Soc. vaud. des Sc. Nat., 1877.

  --Étude sur les Nummulites du Comté de Nice suivie d'une Échelle des
       Nummulites ou Tableau de la distribution stratigraphique des
       Espèces de ce genre. 44 pp., 1 pl.--Bulletin de la Soc. vaud.
       des Sc. Nat.

  --Nummulites des Alpes Francaises. 26 pp.--Bulletin de la Soc. vaud.
       Sc. Nat. XVI, 82.

  --Description des Nummulites des Falaises de Biarritz. 16 pp., 1
       pl.--Extrait du Bulletin de la Société de Borda, 1881.

  --Description des Nummulites appartenant à la Zone inférieure des
       Falaises de Biarritz des environs de la Villa Bruce jusqu'à
       Handia. 44 pp.--Bulletin de la Société de Borda, 1881.

  --Description des Nummulites appartenant à la Zone moyenne des
       Falaises de Biarritz. 8 pp., Ill.--Bulletin de la Société de
       Borda, 1880.

=Hayes, C. Willard.=

  --The Overthrust Faults of the Southern Appalachians. 14 pp., 2
       pl.--Bulletin Geol. Soc. Am., Vol. II, pp. 141-154.

  --Report on the Geology of Northeastern Alabama and Adjacent Portions
       of Georgia and Tennessee. 84 pp., 1 pl., 1 map.--Bulletin No. 4,
       Geol. Surv. of Alabama.

  --An Expedition through the Yukon District. 46 pp., 3 maps.--Nat.
       Geog. Mag.

=Heyes, J. F.=, M.A.

  --Aspects of Imperial Federation. 8 pp.

  --Scientific Aspects of Imperial Unity.--European Mail.

  --The Recognition of Geography. 7 pp.


(_Further acknowledgments of pamphlets and of specimens will be made in
the next issue._)


       *       *       *       *       *


Transcriber Note


Illustrations were moved so as to not split paragraphs. Minor errors
were corrected.