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Title: Man and the Glacial Period
Author: G. Frederick Wright
Release Date: January 18, 2016 [EBook #50957]
Language: English
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[Illustration: CONTOUR AND GLACIAL MAP OF THE BRITISH ISLES]
THE INTERNATIONAL SCIENTIFIC SERIES
MAN AND
THE GLACIAL PERIOD
BY
G. FREDERICK WRIGHT
D. D., LL. D., F. G. S. A.
PROFESSOR IN OBERLIN THEOLOGICAL SEMINARY
FORMERLY ASSISTANT ON THE UNITED STATES GEOLOGICAL SURVEY
AUTHOR OF THE ICE AGE IN NORTH AMERICA.
LOGIC OF CHRISTIAN EVIDENCES, ETC.
_WITH AN APPENDIX ON TERTIARY MAN_
By PROF. HENRY W. HAYNES
FULLY ILLUSTRATED
_SECOND EDITION_
NEW YORK
D. APPLETON AND COMPANY
1895
Copyright, 1892,
By D. APPLETON AND COMPANY.
Electrotyped and Printed
at the Appleton Press, U. S. A.
TO
JUDGE C. C. BALDWIN
PRESIDENT OF THE WESTERN RESERVE HISTORICAL SOCIETY
CLEVELAND
THIS VOLUME IS DEDICATED
IN RECOGNITION OF
HIS SAGACIOUS AND UNFAILING INTEREST IN
THE INVESTIGATIONS WHICH HAVE MADE IT POSSIBLE
PREFACE TO THE SECOND EDITION.
Since, as stated in the Introduction (page 1), the plan of this volume
permitted only "a concise presentation of the facts," it was impossible
to introduce either full references to the illimitable literature of
the subject or detailed discussion of all disputed points. The facts
selected, therefore, were for the most part those upon which it was
supposed there would be pretty general agreement.
The discussion upon the subject of the continuity of the Glacial period
was, however, somewhat elaborate (see pages 106-121, 311, 324, 332),
and was presented with excessive respect for the authority of those who
maintain the opposite view; all that was claimed (page 110) being that
one might maintain the _unity_ or _continuity_ of the Glacial period
"without forfeiting his right to the respect of his fellow-geologists."
But it already appears that there was no need of this extreme modesty of
statement. On the contrary, the vigorous discussion of the subject which
has characterized the last two years reveals a decided reaction against
the theory that there has been more than one Glacial epoch in Quaternary
times; while there have been brought to light many most important if not
conclusive facts in favour of the theory supported in the volume.
In America the continuity of the Glacial period has been maintained
during the past two years with important new evidence, among others
by authorities of no less eminence and special experience in glacial
investigations than Professor Dana,[A] Mr. Warren Upham,[B] and Professor
Edward H. Williams, Jr.[C] Professor Williams's investigations on the
attenuated border of the glacial deposits in the Lehigh, the most
important upper tributary to the Delaware Valley, Pa., are of important
significance, since the area which he so carefully studied lies wholly
south of the terminal moraine of Lewis and Wright, and belongs to the
portion of the older drift which Professors Chamberlin and Salisbury
have been most positive in assigning to the first Glacial epoch, which
they have maintained was separated from the second epoch by a length of
time sufficient for the streams to erode rock gorges in the Delaware and
Lehigh Rivers from two hundred to three hundred feet in depth.[D] But
Professor Williams has found that the rock gorges of the Lehigh, and
even of its southern tributaries, had been worn down approximately to
the present depth of that of the Delaware before this earliest period of
glaciation, and that the gorges were filled with the earliest glacial
_débris_.
[Footnote A: American Journal of Science, vol. xlvi, pp. 327, 330.]
[Footnote B: American Journal of Science, vols, xlvi, pp. 114-121; xlvii,
pp. 358-365; American Geologist, vols, x, pp. 339-362, especially pp.
361, 362; xiii, pp. 114, 278; Bulletin of the Geological Society of
America, vol. v, pp. 71-86, 87-100.]
[Footnote C: Bulletin of the Geological Society of America, vol. v, pp.
13-16, 281-296; American Journal of Science, vol. xlvii, pp. 33-36.]
[Footnote D: See especially Chamberlin, in the American Journal of
Science, vol. xlv, p. 192; Salisbury, in the American Geologist, vol. xi,
p. 18.]
A similar relation of the glacial deposits of the attenuated border to
the preglacial erosion of the rock gorges of the Alleghany and upper
Ohio Rivers has been brought to light by the joint investigations of Mr.
Frank Leverett and myself in western Pennsylvania, in the vicinity of
Warren, Pa., where, in an area which was affected by only the earliest
glaciation, glacial deposits are found filling the rock channels of
old tributaries to the Alleghany to a depth of from one hundred and
seventy to two hundred and fifty feet, and carrying the preglacial
erosion at that point very closely, if not quite, down to the present
rock bottoms of all the streams. This removes from Professor Chamberlin
a most important part of the evidence of a long interglacial period to
which he had appealed; he having maintained[E] that "the higher glacial
gravels antedated those of the moraine-forming epoch by the measure of
the erosion of the channel through the old drift and the rock, whose mean
depth here is about three hundred feet, of which perhaps two hundred and
fifty feet may be said to be rock," adding that the "excavation that
intervened between the two epochs in other portions of the Alleghany,
Monongahela, and upper Ohio valleys is closely comparable with this."
[Footnote E: Bulletin 58 of the United States Geological Survey, p. 35;
American Journal of Science, vol. xlv, p. 195.]
These observations of Mr. Leverett and myself seem to demonstrate the
position maintained in the volume (page 218), namely, that the inner
precipitous rock gorges of the upper Ohio and its tributaries are mainly
_pre_glacial, rather than _inter_glacial. The only way in which Professor
Chamberlin can in any degree break the force of this discovery is by
assuming that in preglacial times the present narrow rock gorges of the
Alleghany and the Ohio were not continuous, but that (as indicated in
the present volume on page 206) the drainage of various portions of that
region was by northern outlets to the Lake Erie basin, leaving, on this
supposition, the _cols_ between two or three drainage areas to be lowered
in glacial or interglacial time.
On the theory of continuity the erosion of these _cols_ would have been
rapidly effected by the reversed drainage consequent upon the arrival
of the ice-front at the southern shore of the Lake Erie basin. During
all the time elapsing thereafter, until the ice had reached its southern
limit, the stream was also augmented by the annual partial melting of
the advancing glacier which was constantly bringing into the valley
the frozen precipitation of the far north. The distance is from thirty
to seventy miles, so that a moderately slow advance of the ice at that
stage would afford time for a great amount of erosion before sufficient
northern gravel had reached the region to begin the filling of the
gorge.[F]
[Footnote F: See an elaborate discussion of the subject in its new phases
by Chamberlin and Leverett, in the American Journal of Science, vol.
xlvii, pp. 247-283.]
Mr. Leverett also presented an important paper before the Geological
Society of America at its meeting at Madison, Wis., in August, 1893,
adducing evidence which, he thinks, goes to prove that the post-glacial
erosion in the earlier drift in the region of Rock River, Ill., was
seven or eight times as much as that in the later drift farther north;
while Mr. Oscar H. Hershey arrives at nearly the same conclusions from
a study of the buried channels in northwestern Illinois.[G] But even
if these estimates are approximately correct--which is by no means
certain--they only prove the length of the Glacial period, and not
necessarily its discontinuity.
[Footnote G: American Geologist, vol. xii, p. 314f. Other important
evidence to a similar effect is given by Mr. Leverett, in an article on
The Glacial Succession in Ohio, Journal of Geology, vol. i, pp. 129-146.]
At the same time it should be said that these investigations in western
Pennsylvania somewhat modify a portion of the discussion in the present
volume concerning the effects of the Cincinnati ice-dam. It now appears
that the full extent of the gravel terraces of glacial origin in the
Alleghany River had not before been fully appreciated, since they are
nearly continuous on the two-hundred-foot rock shelf, and are often
as much as eighty feet thick. It seems probable, therefore, that the
Alleghany and upper Ohio gorge was filled with glacial gravel to a depth
of about two hundred and fifty or three hundred feet, as far down at
least as Wheeling, W. Va. If this was the case, it would obviate the
necessity of bringing in the Cincinnati ice-dam (as set forth in pages
212-216) to account directly for all the phenomena in that region, except
as this obstruction at Cincinnati would greatly facilitate the silting up
of the gorge. The simple accumulation of glacial gravel in the Alleghany
gorge would of itself dam up the Monongahela at Pittsburg, so as to
produce the results detailed by Professor White on page 215.[H]
[Footnote H: For a full discussion of these topics, see paper by
Professor B. C. Jillson, Transactions of the Academy of Science and
Art of Pittsburg, December 8, 1893; G. F. Wright, American Journal of
Science, vol. xlvii, pp. 161-187; especially pp. 177, 178; The Popular
Science Monthly, vol. xlv, pp. 184-198.]
Of European authorities who have recently favoured the theory of the
continuity of the Quaternary Glacial period, as maintained in the volume,
it is enough to mention the names of Prestwich,[I] Hughes,[J] Kendall,[K]
Lamplugh,[L] and Wallace,[M] of England; Falsan,[N] of France; Holst,[O]
of Sweden; Credner[P] and Diener,[Q] of Germany; and Nikitin[R] and
Kropotkin,[S] of Russia.[T] Among leading authorities still favouring a
succession of Glacial epochs are: Professor James Geikie,[U] of Scotland;
Baron de Geer,[V] of Sweden; and Professor Felix Wahnschaffe,[W] of
Germany.
[Footnote I: Quarterly Journal of the Geological Society for August,
1887.]
[Footnote J: American Geologist, vol. viii, p. 241.]
[Footnote K: Transactions of the Leeds Geological Association for
February 10, 1893.]
[Footnote L: Quarterly Journal of the Geological Society, August, 1891.]
[Footnote M: Fortnightly Review, November, 1893, p. 633; reprinted in The
Popular Science Monthly, vol. xliv, p. 790.]
[Footnote N: La Période glaciaire (Félix Alcan. Paris, 1889).]
[Footnote O: American Geologist, vol. viii, p. 242.]
[Footnote P: Ibid., p. 241.]
[Footnote Q: Ibid., p. 242.]
[Footnote R: Congrès International d'Archéologie, Moscow, 1892.]
[Footnote S: Nineteenth Century, January, 1894, p. 151, note.]
[Footnote T: The volume The Glacial Geology of Great Britain and Ireland,
edited from the unpublished MSS. of the late Henry Carvill Lewis (London,
Longmans, Green & Co., 1894), adds much important evidence in favour of
the continuity of the Glacial epoch; see especially pp. 187, 460, 461,
466.]
[Footnote U: Transactions of the Royal Society of Edinburgh, vol. xxxvii,
Part I, pp. 127-150.]
[Footnote V: American Geologist, vol. viii, p. 246.]
[Footnote W: Forschungen zur deutschen Landes und Volkskunde von Dr. A.
Kirchhoff. Bd. vi, Heft i.]
When the first edition was issued, two years ago, there seemed to be
a general acceptance of all the facts detailed in it which directly
connected man with the Glacial period both in America and in Europe;
and, indeed, I had studiously limited myself to such facts as had been
so long and so fully before the public that there would seem to be no
necessity for going again into the details of evidence relating to them.
It appears, however, that this confidence was ill-founded; for the
publication of the book seems to have been the signal for a confident
challenge, by Mr. W. H. Holmes, of all the American evidence, with
intimations that the European also was very likely equally defective.[X]
In particular Mr. Holmes denies the conclusiveness of the evidence of
glacial man adduced by Dr. Abbott and others at Trenton, N. J.; Dr.
Metz, at Madisonville, Ohio; Mr. Mills, at Newcomerstown, Ohio; and Miss
Babbitt, at Little Falls, Minn.
[Footnote X: Journal of Geology, vol. i, pp. 15-37, 147-163; American
Geologist, vol. xi, pp. 219-240.]
The sum of Mr. Holmes's effort amounts, however, to little more than
the statement that, with a limited amount of time and labour, neither he
nor his assistants had been able to find any implements in undisturbed
gravel in any of these places; and the suggestion of various ways in
which he thinks it possible that the observers mentioned may have been
deceived as to the original position of the implements found. But, as
had been amply and repeatedly published,[Y] Professor J. D. Whitney,
Professor Lucien Carr, Professor N. S. Shaler, Professor F. W. Putnam,
of Harvard University, besides Dr. C. C. Abbott, all expressly and with
minute detail describe finding implements in the undisturbed gravel at
Trenton, which no one denies to be of glacial origin. In the face of
such testimony, which had been before the public and freely discussed
for several years, it is an arduous undertaking for Mr. Holmes to claim
that none of the implements have been found in place, because he and
his assistants (whose opportunities for observation had scarcely been
one twentieth part as great as those of the others) failed to find any.
To see how carefully the original observations were made, one has but
to read the reports to Professor Putnam which have from time to time
appeared in the Proceedings of the Peabody Museum and of the Boston
Society of Natural History,, and which are partially summed up in the
thirty-second chapter of Dr. Abbott's volume on Primitive Industry.
[Footnote Y: Proceedings of the Boston Society of Natural History, vol.
xxi, January 19, 1881; Report of the Peabody Museum, vol. ii, pp. 44-47;
chap, xxxii of Abbott's Primitive Industry; American Geologist, vol. xi,
pp. 180-184.]
In the case of the discovery at Newcomerstown, Mr. Holmes is peculiarly
unfortunate in his efforts to present the facts, since, in endeavouring
to represent the conditions under which the implement was found by Mr.
Mills, he has relied upon an imaginary drawing of his own, in which an
utterly impossible state of things is pictured. The claim of Mr. Holmes
in this case, as in the other, is that possibly the gravel in which the
implements were found had been disturbed. In some cases, as in Little
Falls and at Madison ville, he thinks the implements may have worked down
to a depth of several feet by the overturning of trees or by the decay
of the tap-root of trees. A sufficient answer to these suggestions is,
that Mr. Holmes is able to find no instance in which the overturning of
trees has disturbed the soil to a depth of more than three or four feet,
while some of the implements in these places had been found buried from
eight to sixteen feet. Even if, as Mr. Chamberlin suggests,[Z] fifty
generations of trees have decayed on the spot since the retreat of the
ice, it is difficult to see how that would help the matter, since the
effect could not be cumulative, and fifty upturnings of three or four
feet would not produce the results of one upturning of eight feet.
Moreover, at Trenton, where the upturning of trees and the decaying of
tap-roots would have been as likely as anywhere to bury implements,
none of those of flint or jasper (which occur upon the surface by tens
of thousands) are buried more than a foot in depth; while the argillite
implements occur as low down as fifteen or twenty feet. This limitation
of flint and jasper implements to the surface is conclusively shown not
only by Dr. Abbott's discoveries, but also by the extensive excavations
at Trenton of Mr. Ernest Volk, whose collections formed so prominent
a part of Professor Putnam's Palæolithic exhibit at the Columbian
Exposition at Chicago. In the village sites explored by Mr. Volk,
argillite was the exclusive material of the implements found in the lower
strata of gravel. Similar results are indicated by the excavations of Mr.
H. C. Mercer at Point Pleasant, Pa., about twenty miles above Trenton,
where, in the lower strata, the argillite specimens are sixty-one times
more numerous than the jasper are.
[Footnote Z: American Geologist, vol. xi, p. 188.]
To discredit the discoveries at Trenton and Newcomerstown, Mr. Holmes
relies largely upon the theory that portions of gravel from the surface
had slid down to the bottom of the terrace, carrying implements with
them, and forming a talus, which, he thinks, Mr. Mills, Dr. Abbott,
and the others have mistaken for undisturbed strata of gravel. In his
drawings Mr. Holmes has even represented the gravel at Newcomerstown
as caving down into a talus without disturbing the strata to any great
extent, and at the same time he speaks slightingly of the promise which I
had made to publish a photograph of the bank as it really was. In answer,
it is sufficient to give, first, the drawing made at the time by Mr.
Mills, to show the general situation of the gravel bank at Newcomerstown,
in which the implement figured on page 252 was found; and, secondly, an
engraving from a photograph of the bank, taken by Mr. Mills after the
discovery of the implement, but before the talus had obscured its face.
The implement was found by Mr. Mills with its point projecting from a
fresh exposure of the terrace, just after a mass, loosened by his own
efforts, had fallen away. The gravel is of such consistency that every
sign of stratification disappears when it falls down, and there could be
no occasion for a mistake even by an ordinary observer, while Mr. Mills
was a well-trained geologist and collector, making his notes upon the
spot.[AA]
[Footnote AA: The Popular Science Monthly, vol. xliii, pp. 29-39.]
[Illustration: Height of Terrace exposed, 25 feet. Palæolith was found
14-3/4 feet from surface.]
[Illustration: Terrace in Newcomerstown, showing where W. C. Mills found
the Palæolithic implement.]
I had thought at first that Mr. Holmes had made out a better case against
the late Miss Babbitt's discoveries at Little Falls (referred to on
page 254), but in the American Geologist for May, 1894, page 363, Mr.
Warren Upham, after going over the evidence, expresses it as still his
conviction that Mr. Holmes's criticism fails to shake the force of the
original evidence, so that I do not see any reason for modifying any of
the statements made in the body of the book concerning the implements
supposed to have been found in glacial deposits. Yet if I had expected
such an avalanche of criticism of the evidence as has been loosened, I
should at the time have fortified my statements by fuller references,
and should possibly have somewhat enlarged the discussion. But this
seemed then the less necessary, from the fact that Mr. McGee had, in most
emphatic manner, indorsed nearly every item of the evidence adduced by
me, and much more, in an article which appeared in The Popular Science
Monthly four years before the publication of the volume (November, 1888).
In this article he had said:
"But it is in the aqueo-glacial gravels of the Delaware River at Trenton,
which were laid down contemporaneously with the terminal moraine one
hundred miles farther northward, and which have been so thoroughly
studied by Abbott, that the most conclusive proof of the existence of
glacial man is found" (p. 23). "Excluding all doubtful cases, there
remains a fairly consistent body of testimony indicating the existence of
a widely distributed human population upon the North. American continent
during the later Ice epoch" (p. 24). "However the doubtful cases may be
neglected, the testimony is cumulative, parts of it are unimpeachable,
and the proof of the existence of glacial man seems conclusive" (p. 25).
In view of the grossly erroneous statements made by Mr. McGee concerning
the Nampa image (described on pages 298, 299), it is necessary for
me to speak somewhat more fully of this important discovery. The
details concerning the evidence were drawn out by me at length in two
communications to the Boston Society of Natural History (referred to on
page 297), which fill more than thirty pages of closely printed matter,
while two or three years before the appearance of the volume the facts
had been widely published in the New York Independent, the Scientific
American, The Nation, Scribner's Magazine, and the Atlantic Monthly,
and in Washington at a meeting of the Geological Society of America
in 1890. In the second communication to the Boston Society of Natural
History an account was given of a personal visit to the Snake River
Valley, largely for the purpose of further investigation of the evidence
brought to my notice by Mr. Charles Francis Adams, and of the conditions
under which the figurine was found. Among the most important results
of this investigation was the discovery of numerous shells under the
lava deposits, which Mr. Dall, of the United States Geological Survey,
identified for me as either post-Tertiary or late Pliocene; thus throwing
the superficial lava deposits of the region into the Quaternary period,
and removing from the evidence the antecedent improbability which would
bear so heavily against it if we were compelled to suppose that the
lava of the Snake River region was all of Tertiary or even of early
Quaternary age. Furthermore, the evidence of the occurrence of a great
_débâcle_ in the Snake River Valley during the Glacial period, incident
upon the bursting of the banks of Lake Bonneville, goes far to remove
antecedent presumptions against the occurrence of human implements in
such conditions as those existing at Nampa (see below, pp. 233-237).
Mr. McGee's misunderstanding of the evidence on one point is so gross,
that I must make special reference to it. He says[AB] that this image
"is alleged to have been pounded out of volcanic tuff by a heavy drill,
... under a thick Tertiary lava bed." The statement of facts on page
298 bears no resemblance to this representation. It is there stated
that there were but fifteen feet of lava, and that near the surface;
that below this there was nothing but alternating beds of clay and
quicksand, and that the lava is post-Tertiary. The sand-pump I should
perhaps have described more fully in the book, as I had already done in
the communication to the Boston Society of Natural History. It was a
tube eight feet long, with a valve at the bottom three and a half inches
in diameter on the inside. Through this it was the easiest thing in the
world for the object, which is only one inch and a half long, to be
brought up in the quicksand without injury.
[Footnote AB: Literary Northwest, vol. ii, p. 275.]
The baseless assertions of Mr. McGee, involving the honesty of Messrs.
Kurtz and Duffes, are even less fortunate and far more reprehensible. "It
is a fact," says Mr. McGee, "that one of the best-known geologists of the
world chanced to visit Nampa while the boring was in progress, and the
figurine and the pretty fiction were laid before him. He recognized the
figurine as a toy such as the neighbouring Indians give their children,
and laughed at the story; whereupon the owner of the object enjoined
secrecy, pleading: 'Don't give me away; I've fooled a lot of fellows
already, and I'd like to fool some more.'"[AC] This well-known geologist,
on being challenged by Professor Claypole[AD] to give "a full, exact,
and certified statement of the conversation" above referred to, proved
to be Major Powell, who responded with the following statement: "In the
fall of 1889 the writer visited Boise City, in Idaho [twenty miles from
Nampa]. While stopping at a hotel, some gentlemen called on him to show
him a figurine which they said they had found in sinking an artesian
well in the neighbourhood, at a depth, if I remember rightly, of more
than three hundred feet.... When this story was told the writer, he
simply jested with those who claimed to have found it. He had known the
Indians that live in the neighbourhood, had seen their children play with
just such figurines, and had no doubt that the little image had lately
belonged to some Indian child, and said the same. While stopping at the
hotel different persons spoke about it, and it was always passed off as
a jest; and various comments were made about it by various people, some
of them claiming that it had given them much sport, and that a good many
tenderfeet had looked at it, and believed it to be genuine; and they
seemed rather pleased that I had detected the hoax."[AE]
[Footnote AC: American Anthropologist, vol. vi, p. 94: repeated by Mr.
McGee in the Literary Northwest, vol. ii, p. 276.]
[Footnote AD: The Popular Science Monthly, vol. xlii, p. 773.]
[Footnote AE: Ibid., vol. xliii, pp. 322, 323.]
Thus it appears that Major Powell has made no such statement, at least
in public, as Mr. McGee attributes to him. It should be said, also, that
Major Powell's memory is very much at fault when he affirms that there
is a close resemblance between this figurine and some of the children's
playthings among the Pocatello Indians. On the contrary, it would have
been even more of a surprise to find it in the hands of these children
than to find it among the prehistoric deposits on the Pacific coast.
To most well-informed people it is sufficient to know that no less
high authorities than Mr. Charles Francis Adams and Mr. G. M. Gumming,
General Manager for the Union Pacific line for that district, carefully
investigated the evidence at the time of the discovery, and, knowing
the parties, were entirely satisfied with its sufficiency. It was
also subjected to careful examination by Professor F. W. Putnam, who
discerned, in a deposit of an oxide of iron on various parts of the
image, indubitable evidence that it was a relic which had lain for a long
time in some such condition as was assigned to it in the bottom of the
well--all of which is detailed in the papers referred to below, on page
297.
Finally, the discovery, both in its character and conditions, is in so
many respects analogous to those made under Table Mountain, near Sonora,
Cal. (described on pages 294-297), that the evidence of one locality adds
cumulative force to that of the other. The strata underneath the lava in
which these objects were found are all indirectly, but pretty certainly,
connected with the Glacial period.[AF] No student of glacial archæology,
therefore, can hereafter afford to disregard these facts from the Pacific
coast.
[Footnote AF: See below, p. 349.]
Oberlin, Ohio, _June 2, 1894_.
PREFACE TO THE FIRST EDITION.
The wide interest manifested in my treatise upon The Ice Age in North
America and its Bearing upon the Antiquity of Man (of which a third
edition was issued a year ago), seemed to indicate the desirability of
providing for the public a smaller volume discussing the broader question
of man's entire relation to the Glacial period in Europe as well as in
America. When the demand for such a volume became evident, I set about
preparing for the task by spending, first, a season in special study
of the lava-beds of the Pacific coast, whose relations to the Glacial
period and to man's antiquity are of such great interest; and, secondly,
a summer in Europe, to enable me to compare the facts bearing upon the
subject on both continents.
Of course, the chapters of the present volume relating to America cover
much of the same ground gone over in the previous treatise; but the
matter has been entirely rewritten and very much condensed, so as to give
due proportions to all parts of the subject. It will interest some to
know that most of the new material in this volume was first wrought over
in my second course of Lowell Institute Lectures, given in Boston during
the month of March last.
I am under great obligations to Mr. Charles Francis Adams for his aid in
prosecuting investigations upon the Pacific coast of America; and also to
Dr. H. W. Crosskey, of Birmingham, England, and to Mr. G. W. Lamplugh,
of Bridlington, as well as to Mr. C. E. De Rance and Mr. Clement Reid,
of the British Geological Survey, besides many others in England who
have facilitated my investigations; but pre-eminently to Prof. Percy F.
Kendall, of Stockport, who consented to prepare for me the portion of
Chapter VI which relates to the glacial phenomena of the British Isles. I
have no doubt of the general correctness of the views maintained by him,
and little doubt, also, that his clear and forcible presentation of the
facts will bring about what is scarcely less than a revolution in the
views generally prevalent relating to the subject of which he treats.
For the glacial facts relating to France and Switzerland I am indebted
largely to M. Falsan's valuable compendium, La Période Glaciaire.
It goes without saying, also, that I am under the deepest obligation
to the works of Prof. James Geikie upon The Great Ice Age and upon
Prehistoric Europe, and to the remarkable volume of the late Mr. James
Croll upon Climate and Time, as well as to the recent comprehensive
geological treatises of Sir Archibald Geikie and Prof. Prestwich.
Finally, I would express my gratitude for the great courtesy of Prof.
Fraipont, of Liége, in assisting me to an appreciation of the facts
relating to the late remarkable discovery of two entire skeletons of
Paleolithic man in the grotto of Spy.
Comparative completeness is also given to the volume by the appendix on
the question of man's existence during the Tertiary period, prepared by
the competent hand of Prof. Henry W. Haynes, of Boston.
I trust this brief treatise will be useful not only in _interesting_
the general public, but in giving a clear view of the present state of
progress in one department of the inquiries concerning man's antiquity.
If the conclusions reached are not as positive as could be wished, still
it is both desirable and important to see what degree of indefiniteness
rests upon the subject, in order that rash speculations may be avoided
and future investigations directed in profitable lines.
G. Frederick Wright.
Oberlin, Ohio, _May 1, 1892_.
CONTENTS.
PAGES
CHAPTER I.
Introductory 1-8
CHAPTER II.
Existing Glaciers 9-42
In Europe; in Asia; in Oceanica; in South America;
on the Antarctic Continent; in North America.
CHAPTER III.
Glacial Motion 43-50
CHAPTER IV.
Signs of Past Glaciation 51-65
CHAPTER V.
Ancient Glaciers in the Western Hemisphere 66-128
New England; New York, New Jersey, and Pennsylvania;
the Mississippi Basin; west of the Rocky Mountains.
CHAPTER VI.
Ancient Glaciers in the Eastern Hemisphere 129-192
Central and Southern Europe; the British Isles--the
Preglacial Level of the Land, the Great Glacial Centres,
the Confluent Glaciers, the East Anglian Glacier,
the so-called Great Submergence; Northern Europe;
Asia; Africa.
CHAPTER VII.
Drainage Systems in the Glacial Period 193-241
In America--Preglacial Erosion, Buried Outlets and
Channels, Ice-dams, Ancient River Terraces; in Europe.
CHAPTER VIII.
Relics of Man in the Glacial Period 242-301
In Glacial Terraces of the United States; in Glacial
Terraces of Europe; in Cave Deposits in the British
Isles; in Cave Deposits on the Continent; Extinct
Animals associated with Man; Earliest Man on the
Pacific Coast of North America.
CHAPTER IX.
The Cause of the Glacial Period 302-331
CHAPTER X.
The Date of the Glacial Period 332-364
Appendix on the Tertiary Man 365-374
Index 375-385
LIST OF ILLUSTRATIONS.
FIG. PAGE
1. Zermatt Glacier 2
2. Formation of veined structure 3
3, 4. Formation of marginal fissures and veins 4
5. Fissures and seracs 4
6. Section across glacial valley, showing old lateral moraines 5
7. Mont Blanc glacier region 10
8. Svartisen Glacier 13
9. Floating berg 18
10. Iceberg in the Antarctic Ocean 20
11. Map of southeastern Alaska 22
12. Map of Glacier Bay, Alaska 25
13. Front of Muir Glacier 26
14. Map of glaciers in the St. Elias Alps 31
15. Map of Greenland 33
16. Diagram showing the character of glacial motion 43
17. Line of most rapid glacial motion 45
18. Diagram showing retardation of the bottom of a glacier 46
19. Bed-rock scored with glacial marks 52
20. Scratched stone from the till of Boston 54
21. Typical section of till in Seattle, Wash. 55
22. Ideal section showing how the till overlies the stratified
rocks 56
23. Vessel Rock, a glacial boulder 56
24. Map of Rhône Glacier 58
25. Conglomerate boulder found in Boone County, Ky. 63
26. Mohegan Rock 72
27. Drumlins in Goffstown, N. H. 73
28. Map of drumlins in the vicinity of Boston 75
29. Section of kame 77
30. Map of kames in Andover, Mass. 78
31. Longitudinal kames near Hingham, Mass. 79
32. Map showing the kames of Maine and southeastern New Hampshire 81
33. Western face of the Kettle Moraine near Eagle, Wis. 99
34. Section of the east-and-west glacial furrows on Kelly's
Island 103
35. Same as the preceding 105
36. Section of till near Germantown, Ohio 108
37. Moraines of Grape Creek, Col. 123
38. Map of North America in the Ice period 127
39. Quartzite boulder on Mont Lachat 128
40. Map showing glaciated areas in North America and Europe 130
41. Maps showing lines of _débris_ extending from the Alps into
the plains of the Po 134
42. Section of the Cefn Cave 148
43. Map showing moraine between Speeton and Flamborough 156
44. Diagram-section near Cromer 166
45. Section through the westerly chalk bluff at Trimingham,
Norfolk 162
46. Section across Wales 172
47. Section of cliff at Flamborough Head 176
48. Enlarged section of the shelly sand and surrounding clay
at _B_ in preceding figure 177
49. Map showing the glaciated area of Europe 184
50. Map showing old channel and mouth of the Hudson 195
51. New York Harbor in preglacial times 197
52. Section across the valley of the Cuyahoga River 200
53. Map of Mississippi River from Fort Snelling to Minneapolis 209
54. Map showing the effect of the glacial dam at Cincinnati 213
55. Map of Lake Erie-Ontario 219
56. Map of Cuyahoga Lake 221
57. Section of the lake ridges near Sandusky, Ohio 223
58. Map showing stages of recession of the ice in Minnesota 225
59. Glacial terrace on Raccoon Creek, in Ohio 227
60. Ideal section across a river-bed in drift region 229
61. Map of Lakes Bonneville and Lahontan 234
62. Parallel roads of Glen Roy 239
63. Map showing glacial terraces on the Delaware and
Schuylkill Rivers 243
64. Palæolith found by Abbott in New Jersey 244
65. Section across the Delaware River at Trenton, N. J. 245
66. Section of the Trenton gravel 246
67. Face view of argillite implement found by Dr. C. C. Abbott
in 1876. 247
68. Argillite implement found by Dr. C. C. Abbott, March, 1879 248
69. Chipped pebble of black chert found by Dr. C. L. Metz,
October, 1885 249
70. Map showing glaciated area in Ohio 250
71. Palæoliths from Newcomerstown and Amiens (face view) 252
72. Edge view of the preceding 253
73. Section across the Mississippi Valley at Little Falls, Minn. 254
74. Quartz implement found by Miss F. E. Babbitt, 1878, at Little
Falls, Minn 255
75. Argillite implement found by H. T. Cresson, 1887 259
76. General view of Baltimore and Ohio Railroad cut,
Claymont, Del. 260
77. Section across valley of the Somme 262
78. Mouth of Kent's Hole 268
79. Engis skull (reduced) 274
80. Comparison of forms of skulls 276
81. Skull of the Man of Spy 277
82. Tooth of Machairodus neogæus 281
83. Perfect tooth of an Elephas 281
84. Skull of Hyena spelæa 282
85. Celebrated skeleton of mammoth in St. Petersburg Museum 283
86. Molar tooth of mammoth 284
87. Tooth of Mastodon Americanus 284
88. Skeleton of Mastodon Americanus 286
89. Skeleton of Rhinoceros tichorhinus 287
90. Skull of cave-bear 287
91. Skeleton of the Irish elk 288
92. Musk-sheep 289
93. Reindeer 290
94. Section across Table Mountain, Tuolumne County, Cal. 294
95. Calaveras skull 295
96. Three views of Nampa image, drawn to scale 298
97. Map showing Pocatello, Nampa, and the valley of Snake River 299
98. Section across the channel of the Stanislaus River 300
99. Diagram showing effect of precession 308
100. Map showing course of currents in the Atlantic Ocean 314
101. Map showing how the land clusters about the north pole 319
102. Diagram showing oscillations of land-surface and ice-surface
during the Glacial epoch 323
103. Diagram of eccentricity and precession 333
104. Map of the Niagara River below the Falls 334
105. Section of strata along the Niagara Gorge 336
106. Map showing the recession of the Horseshoe Falls since 1842 338
107. Section of kettle-hole near Pomp's Pond, Andover, Mass. 345
108. Flint-flakes collected by Abbé Bourgeois 368
MAPS.
TO FACE PAGE
Contour and glacial map of the British Isles _Frontispiece._
Map showing the glacial geology of the United States 66
Map of glacial movements in France and Switzerland 132
MAN AND THE GLACIAL PERIOD.
CHAPTER I.
INTRODUCTORY.
That glaciers now exist in the Alps, in the Scandinavian range, in
Iceland, in the Himalayas, in New Zealand, in Patagonia, and in the
mountains of Washington, British Columbia, and southeastern Alaska, and
that a vast ice-sheet envelops Greenland and the Antarctic Continent,
are statements which can be verified by any one who will take the
trouble to visit those regions. That, at a comparatively recent date,
these glaciers extended far beyond their present limits, and that others
existed upon the highlands of Scotland and British America, and at one
time covered a large part of the British Isles, the whole of British
America, and a considerable area in the northern part of the United
States, are inferences drawn from phenomena which are open to every one's
observations. That man was in existence and occupied both Europe and
America during this great expansion of the northern glaciers is proved
by evidence which is now beyond dispute. It is the object of the present
volume to make a concise presentation of the facts which have been
rapidly accumulating during the past few years relating to the Glacial
period and to its connection with human history.
Before speaking of the number and present extent of existing glaciers,
it will be profitable, however, to devote a little attention to the
definition of terms.
[Illustration: Fig. 1.--Zermatt Glacier (Agassiz).]
A _glacier_ is a mass of ice so situated and of such size as to have
motion in itself. The conditions determining the character and rate
of this motion will come up for statement and discussion later. It is
sufficient here to say that ice has a capacity of movement similar to
that possessed by such plastic substances as cold molasses, wax, tar, or
cooling lava.
The limit of a glacier's _motion_ is determined by the forces which fix
the point at which its final melting takes place. This will therefore
depend upon both the warmth of the weather and upon the amount of ice.
If the ice is abundant, it will move farther into the region of warm
temperature than it will if it is limited in supply.
Upon ascending a glacier far enough, one reaches a comparatively
motionless part corresponding to the lake out of which a river often
flows. Technically this is called the _névé_.
_Glacial ice_ is formed from snow where the annual fall is in excess
of the melting power of the sun at that point. Through the influence
of pressure, such as a boy applies to a snow-ball (but which in the
_névé_-field arises from the weight of the accumulating mass), the lower
strata of the _névé_ are gradually transformed into ice. This process, is
also assisted by the moisture which percolates through the snowy mass,
and which is furnished both by the melting of the surface snow and by
occasional rains.
The division between the _névé_ and the glacier proper is not always
easily determined. The beginnings of the glacial movement--that is, of
the movement of the ice-stream flowing out of the _névé_-field--are
somewhat like the beginnings of the movement of the water from a great
lake into its outlet. The _névé_ is the reservoir from which the glacier
gets both its supply of ice and the impulse which gives it its first
movement. There can not be a glacier without a _névé_-field, as there can
not be a river without a drainage basin. But there may be a _névé_-field
without a glacier--that is, a basin may be partially filled with snow
which never melts completely away, while the equilibrium of forces is
such that the ice barely reaches to the outlet from which the tongue-like
projection (to which the name glacier would be applied) fails to emerge
only because of the lack of material.
[Illustration: Fig. 2.--Illustrates the formation of veined structure by
pressure at the junction of two branches.]
A glacier is characterised by both _veins_ and _fissures_. The veins
give it a banded or stratified appearance, blue alternating with
lighter-coloured portions of ice. As these bands are not arranged with
any apparent uniformity in the glacier, their explanation has given
rise to much discussion. Sometimes the veins are horizontal, sometimes
vertical, and at other times at an angle with the line of motion. On
close investigation, however, it is found that the veins are always
at right angles to the line of greatest pressure. This leads to the
conclusion that pressure is the cause of the banded structure. The
blue strata in the ice are those from which the particles of air have
been expelled by pressure; the lighter portions are those in which the
particles are less thoroughly compacted. Snow is but pulverized ice, and
differs in colour from the compact mass for the same reason that almost
all rocks and minerals change their colour when ground into a powder.
[Illustration: Figs. 3, 4.--Illustrate the formation of marginal fissures
and veins.]
[Illustration: Fig. 5.--_c_, _c_, show fissures and seracs where the
glacier moves down the steeper portion of its incline; _s_, _s_, show the
vertical structure produced by pressure on the gentler slopes.]
The _fissures_, which, when of large size, are called _crevasses_, are
formed in those portions of a glacier where, from some cause, the ice
is subjected to slight tension. This occurs especially where, through
irregularities in the bottom, the slope of the descent is increased. The
ice, then, instead of moving in a continuous stream at the top, cracks
open along the line of tension, and wedge-shaped fissures are formed
extending from the top down to a greater or less distance, according to
the degree of tension. Usually, however, the ice remains continuous in
the lower strata, and when the slope is diminished the pressure reunites
the faces of the fissure, and the surface becomes again comparatively
smooth. Where there are extensive areas of tension, the surface of the
ice sometimes becomes exceedingly broken, presenting a tangled mass of
towers, domes, and pinnacles of ice called _seracs_.
[Illustration: Fig. 6.--Section across Glacial Valley, showing old
Lateral Moraines.]
Like running water, moving ice is a powerful agent in _transporting_
rocks and earthy _débris_ of all grades of fineness; but, owing to the
different consistencies of ice and water, there are great differences in
the mode and result of transportation by them. While water can hold in
suspension only the very finest material, ice can bear upon its surface
rocks of the greatest magnitude, and can roll or shove along under it
boulders and pebbles which would be Unaffected except by torrential
currents of water. We find, therefore, a great amount of earthy material
of all sizes upon the top of a glacier, which has reached it very much as
_débris_ reaches the bed of a river, namely, by falling down upon it from
overhanging cliffs, or by land-slides of greater or less extent. Such
material coming into a river would either disappear beneath its surface,
or would form a line of _débris_ along the banks; in both cases awaiting
the gradual erosion and transportation which running water is able to
effect. But, in case of a glacier, the material rests upon the surface of
the ice, and at once begins to partake of its motion, while successive
accessions of material keep up the supply at any one point, so as to form
a train of boulders and other _débris_, extending below the point as far
as the glacial motion continues.
Such a line of _débris_ is called a _moraine_. When it forms along the
edge of the ice, it is called a _lateral_ moraine. It is easy to see
that, where glaciers come out from two valleys which are tributary to
a larger valley, their inner sides must coalesce below the separating
promontory, and the two lateral moraines will become united and will
move onward in the middle of the surface of the glacier. Such lines of
_débris_ are called _medial_ moraines. These are characteristic of all
extensive glaciers formed by the union of tributaries. There is no limit
to the number of medial moraines, except in the number of tributaries.
A medial moraine, when of sufficient thickness, protects the ice
underneath it from melting; so that the moraine will often appear to
be much larger than it really is: what seems to be a ridge of earthy
material being in reality a long ridge of ice, thinly covered with earthy
_débris_, sliding down the slanting sides as the ice slowly wastes away
Large blocks of stone in the same manner protect the ice from melting
underneath, and are found standing on pedestals of ice, often several
feet in height. An interesting feature of these blocks is that, when the
pedestal fails, the block uniformly falls towards the sun, since that is
the side on which the melting has proceeded most rapidly.
If the meteorological forces are so balanced that the foot of a glacier
remains at the same place for any great length of time, there must be a
great accumulation of earthy _débris_ at the stationary point, since the
motion of the ice is constantly bearing its lines of lateral and medial
moraine downwards to be deposited, year by year, at the melting line
along the front.
Such accumulations are called _terminal_ moraines, and the process of
their formation may be seen at the foot of almost any large glacier. The
pile of material thus confusedly heaped up in front of some of the larger
glaciers of the world is enormous.
The melting away of the lower part of a glacier gives rise also to
several other characteristic phenomena. Where the foot of a glacier
chances to be on comparatively level land, the terminal moraine often
covers a great extent of ice, and protects it from melting for an
indefinite period of time. When the ice finally melts away and removes
the support from the overlying morainic _débris_, this settles down in
a very irregular manner, leaving enclosed depressions to which there
is no natural outlet. These depressions, from their resemblance to a
familiar domestic utensil, are technically known as _kettle-holes_. The
terminal moraines of ancient glaciers may often be traced by the relative
abundance of these kettle-holes.
The streams of water arising both from the rainfall and from the melting
of the ice also produce a peculiar effect about the foot of an extensive
glacier. Sometimes these streams cut long, open channels near the end
of the glacier, and sweep into it vast quantities of morainic material,
which is pushed along by the torrential current, and, after being
abraded, rolled, and sorted, is deposited in a delta about its mouth, or
left stranded in long lines between the ice-walls which have determined
its course. At other times the stream has disappeared far back in the
glacier, and plunged into a crevasse (technically called a _moulin_),
whence it flows onwards as a subglacial stream. But in this case the
deposits might closely resemble those of the previous description. In
both cases, when the ice has finally melted away, peculiar ridge-like
deposits of sorted material remain, to mark the temporary line of
drainage. These exist abundantly in most regions which have been covered
with glacial ice, and are referred to in Scotland as _kames_, in Ireland
as _eskers_, and in Sweden as _osars_. In this volume we shall call them
_kames_, and the deltas spread out in front of them will be referred to
as _kame-plains_.
With this preliminary description of glacial phenomena, we will proceed
to give, first, a brief enumeration and description of the ice-fields
which are still existing in the world; second, the evidences of the
former existence of far more extensive ice-fields; and, third, the
relation of the Glacial period to some of the vicissitudes which have
attended the life of man in the world.
The geological period of which we shall treat is variously designated by
different writers. By some it is simply called the "post-Tertiary," or
"Quaternary"; by others the term "post-Pliocene" is used, to indicate
more sharply its distinction from the latter portion of the Tertiary
period; by others this nicety of distinction is expressed by the term
"Pleistocene." But, since the whole epoch was peculiarly characterised
by the presence of glaciers, which have not even yet wholly disappeared,
we may properly refer to it altogether under the descriptive name of
"Glacial" period.
CHAPTER II.
EXISTING GLACIERS.
_In Europe._--Our specific account of existing glaciers naturally begins
with those of the Alps, where Hugi, Charpentier, Agassiz, Forbes, and
Guyot, before the middle of this century, first brought clearly to light
the reality and nature of glacial motion.
According to Professor Heim, of Zürich, the total area covered by the
glaciers and ice-fields of the Alps is upwards of three thousand square
kilometres (about eleven hundred square miles). The Swiss Alps alone
contain nearly two-thirds of this area. Professor Heim enumerates 1,155
distinct glaciers in the region. Of these, 144 are in France, 78 in
Italy, 471 in Switzerland, and 462 in Austria.
Desor describes fourteen principal glacial districts in the Alps, the
westernmost of which is that of Mont Pelvoux, in Dauphiny, and the
easternmost that in the vicinity of the Gross Glockner, in Carinthia. The
most important of the Alpine systems are those which are grouped around
Mont Blanc, Monte Rosa, and the Finsteraarhorn, the two former peaks
being upwards of fifteen thousand feet in height, and the latter upwards
of fourteen thousand. The area covered by glaciers and snow-fields
in the Bernese Oberland, of which Finsteraarhorn is the culminating
point, is about three hundred and fifty square kilometres (a hundred
square miles), and contains the Aletsch Glacier, which is the longest
in Europe, extending twenty-one kilometres (about fourteen miles) from
the _névé_-field to its foot. The Mer de Glace, which descends from Mont
Blanc to the valley of Chamounix, has a length of about eight miles
below the _névé_-field. In all, there are estimated to be twenty-four
glaciers in the Alps which are upwards of four miles long, and six which
are upwards of eight miles in length. The principal of these are the Mer
de Glace, of Chamounix, on Mont Blanc; the Gorner Glacier, near Zermatt,
on Monte Rosa; the lower glacier of the Aar, in the Bernese Oberland;
and the Aletsch Glacier and Glacier of the Rhône, in Vallais; and the
Pasterzen, in Carinthia.
[Illustration: Fig. 7.--Mount Blanc Glacier Region: _m_, Mer de Glace;
_g_, Du Géant; _l_, Leschaux; _t_, Taléfre; _B_, Bionassay; _b_, Bosson.]
These glaciers adjust themselves to the width of the valleys down which
they flow, in some places being a mile or more in width, and at others
contracting into much narrower compass. The greatest depth which Agassiz
was able directly to measure in the Aar Glacier was two hundred and
sixty metres (five hundred and twenty-eight feet), but at another point
the depth was estimated by him to be four hundred and sixty metres (or
fifteen hundred and eighty-four feet).
The glaciers of the Alps are mostly confined to the northern side and
to the higher portions of the mountain-chain, none of them descending
below the level of four thousand feet, and all of them varying slightly
in extent, from year to year, according as there are changes in the
temperature and in the amount of snow-fall.
The Pyrenees, also, still maintain a glacial system, but it is of
insignificant importance. This is partly because the altitude is much
less than that of the Alps, the culminating point being scarcely more
than eleven thousand feet in height. Doubtless, also, it is partly due to
the narrowness of the range, which does not provide gathering-places for
the snow sufficiently extensive to produce large glaciers. The snow-fall
also is less upon the Pyrenees than upon the Alps. As a consequence of
all these conditions, the glaciers of the Pyrenees are scarcely more
than stationary _névé_-fields lingering upon the north side of the range.
The largest of these is near Bagnères de Luchon, and sends down a short,
river-like glacier.
In Scandinavia the height of the mountains is also much less than that of
the Alps, but the moister climate and the more northern latitude favours
the growth of glaciers at a much lower level North of the sixty-second
degree of latitude, the plateaus over five thousand feet above the sea
pretty generally are gathering-places for glaciers. From the Justedal a
snow-field, covering five hundred and eighty square miles, in latitude
62°, twenty-four glaciers push outwards towards the German Sea, the
largest of which is five miles long and three-quarters of a mile wide.
The Fondalen snow-field, between latitudes 66° and 67°, covers an
area about equal to that of the Justedal; but, on account of its more
northern position, its glaciers descend through the valleys quite to the
ocean-level. The Folgofon snow-field is still farther south, but, though
occupying an area of only one hundred square miles, it sends down as many
as three glaciers to the sea-level. The total area of the Scandinavian
snow-fields is about five thousand square miles.
In Sweden Dr. Svenonius estimates that there are, between latitudes 67°
and 68-1/2°, twenty distinct groups of glaciers, covering an area of four
hundred square kilometres (one hundred and forty-four square miles), and
he numbers upwards of one hundred distinct glaciers of small size.
As is to be expected, the large islands in the Polar Sea north of Europe
and Asia are, to a great extent, covered with _névé_-fields, and numerous
glaciers push out from them to the sea in all directions, discharging
their surplus ice as bergs, which float away and cumber the waters with
their presence in many distant places.
[Illustration: Fig. 8.--The Svartisen Glacier on the west coast of
Norway, just within the Arctic circle, at the head of a fiord ten miles
from the ocean. The foot of the Glacier is one mile wide, and a quarter
of a mile back from the water. Terminal moraine in front. (Photographed
by Dr. L. C. Warner.)]
The island of Spitzbergen, in latitude 76° to 81°, is favourably situated
for the production of glaciers, by reason both of its high northern
latitude, and of its relation to the Gulf Stream, which conveys around
to it an excessive amount of moisture, thus ensuring an exceptionally
large snow-fall over the island. The mountainous character of the island
also favours the concentration of the ice-movement into glaciers of vast
size and power. Still, even here, much of the land is free from snow and
ice in summer. But upon the northern portion of the island there is an
extensive table-land, upwards of two thousand feet above the sea, over
which the ice-field is continuous. Four great glaciers here descend to
tide-water in Magdalena Bay. The largest of these presents at the front a
wall of ice seven thousand feet across and three hundred feet high; but,
as the depth of the water is not great, few icebergs of large size break
off and float away from it.
Nova Zembla, though not in quite so high latitude, has a lower mean
temperature upon the coasts than Spitzbergen. Owing to the absence of
high lands and mountains, however, it is not covered with perpetual snow,
much less with glacial ice, but its level portions are "carpeted with
grasses and flowers," and sustain extensive forests of stunted trees.
Franz-Josef Land, to the north of Nova Zembla, both contains high
mountains and supports glaciers of great size. Mr. Payer conducted a
sledge party into this land in 1874, and reported that a precipitous wall
of glacial ice, "of more than a hundred feet in height, formed the usual
edge of the coast." But the motion of the ice is very slow, and the ice
coarse-grained in structure, and it bears a small amount only of morainic
material. So low is here the line of perpetual snow, that the smaller
islands "are covered with caps of ice, so that a cross-section would
exhibit a regular flat segment of ice." It is interesting to note, also,
that "many ice-streams, descending from the high _névé_ plateau, spread
themselves out over the mountain-slopes," and are not, as in the Alps,
confined to definite valleys.
Iceland seems to have been properly named, since a single one of the
snow-fields--that of Vatnajoküll, with an extreme elevation of only six
thousand feet--is estimated by Helland to cover one hundred and fifty
Norwegian square miles (about seven thousand English square miles), while
five other ice-fields (the Langjoküll, the Hofsjoküll, the Myrdalsjoküll,
the Drangajoküll, and the Glamujoküll) have a combined area of ninety-two
Norwegian or about four thousand five hundred English square miles. The
glaciers are supposed by Whitney to have been rapidly advancing for some
time past.
_In Asia._--Notwithstanding its lofty mountains and its great extent
of territory lying in high latitudes, glaciers are for two reasons
relatively infrequent: 1. The land in the more northern latitudes is low.
2. The dryness of the atmosphere in the interior of the continent is such
that it unduly limits the snow-fall. Long before they reach the central
plateau of Asia, the currents of air which sweep over the continent from
the Indian Ocean have parted with their burdens of moisture, having left
them in a snowy mantle upon the southern flanks of the Himalayas. As a
result, we have the extensive deserts of the interior, where, on account
of the clear atmosphere, there is not snow enough to resist continuously
the intense activity of the unobstructed rays of the sun.
In spite of their high latitude and considerable elevation above the
sea-level, glaciers are absent from the Ural Mountains, for the range is
too narrow to afford _névé_-fields of sufficient size to produce glaciers
of large extent.
The Caucasus Mountains present more favourable conditions, and for a
distance of one hundred and twenty miles near their central portion
have an average height of 12,000 feet, with individual peaks rising to
a height of 16,000 feet or more; but, owing to their low latitude, the
line of perpetual snow scarcely reaches down to the 11,000-foot level. So
great are the snow-fields, however, above this height that many glaciers
push their way down through the narrow mountain-gorges as far as the
6,000-foot level.
The Himalaya Mountains present many favourable conditions for the
development of glaciers of large size. The range is of great extent and
height, thus affording ample gathering-places for the snows, while the
relation of the mountains to the moisture-laden winds from the Indian
Ocean is such that they enjoy the first harvest of the clouds where
the interior of Asia gets only the gleanings. As is to be expected,
therefore, all the great rivers which course through the plains of
Hindustan have their rise in large glaciers far up towards the summits of
the northern mountains. The Indus and the Ganges are both glacial streams
in their origin, as are their larger tributary branches--the Basha, the
Shigar, and the Sutlej. Many of the glaciers in the higher levels of
the Himalaya Mountains where these streams rise have a length of from
twenty-five to forty miles, and some of them are as much as a mile and
a half in width and extend for a long distance, with an inclination as
small as one degree and a half or one hundred and thirty-eight feet to a
mile.
In the Mustagh range of the western Himalayas there are two adjoining
glaciers whose united length is sixty-five miles, and another not far
away which is twenty-one miles long and from one to two miles wide in its
upper portion. Its lower portion terminates at an altitude of 16,000 feet
above tide, where it is three miles wide and two hundred and fifty feet
thick.
_Oceanica._---Passing eastward to the islands of the Pacific Ocean, New
Zealand is the only one capable of supporting glaciers. Their existence
on this island seems the more remarkable because of its low latitude
(42° to 45°); but a grand range of mountains rises abruptly from the
water on the western coast of the southern island, culminating in Mount
Cook, 13,000 feet above the sea, and extending for a distance of about
one hundred miles. The extent and height of this chain, coupled with
the moisture of the winds, which sweep without obstruction over so
many leagues of the tropical Pacific, are specially favourable to the
production of ice-fields of great extent. Consequently we find glaciers
in abundance, some of which are not inferior in extent to the larger ones
of the Alps. The Tasman Glacier, described by Haas, is ten miles long
and nearly two miles broad at its termination, "the lower portion for a
distance of three miles being covered with morainic _detritus_." The
Mueller Glacier is about seven miles long and one mile broad in its lower
portion.
_South America._--In America, existing glaciers are chiefly confined to
three principal centres, namely, to the Andes, south of the equator; to
the Cordilleras, north of central California; and to Greenland.
In South America, however, the high mountains of Ecuador sustain a few
glaciers above the twelve-thousand-foot level. The largest of these are
upon the eastern slope of the mountains, giving rise to some of the
branches of the Amazon--indeed, on the flanks of Cotopaxi, Chimborazo,
and Illinissa there are some glaciers in close proximity to the equator
which are fairly comparable in size to those of the Alps.
In Chili, at about latitude 35°, glaciers begin to appear at lower
levels, descending beyond the six-thousand-foot line, while south of this
both the increasing moisture of the winds and the decreasing average
temperature favour the increase of ice-fields and glaciers. Consequently,
as Darwin long ago observed, the line of perpetual snow here descends to
an increasingly lower level, and glaciers extend down farther and farther
towards the sea, until, in Tierra del Fuego, at about latitude 45°, they
begin to discharge their frozen contents directly into the tidal inlets.
Darwin's party surveyed a glacier entering the Gulf of Penas in latitude
46° 50', which was fifteen miles long, and, in one part, seven broad. At
Eyre's Sound, also, in about latitude 48°, they found immense glaciers
coming clown to the sea and discharging icebergs of great size, one of
which, as they encountered it floating outwards, was estimated to be "_at
least_ one hundred and sixty-eight feet in total height."
In Tierra del Fuego, where the mountains are only from three thousand
to four thousand feet in height and in latitude less than 55°, Darwin
reports that "every valley is filled with streams of ice descending to
the sea-coast," and that the inlets penetrated by his party presented
miniature likenesses of the polar sea.
[Illustration: Fig. 9.--Floating berg, showing the proportions above and
under the water. About seven feet under water to one above.]
_Antarctic Continent._--Of the so-called Antarctic Continent little is
known; but icebergs of great size are frequently encountered up to 58°
south latitude, in the direction of Cape Horn, and as far as latitude
33° in the direction of Cape of Good Hope. Nearly all that is known
about this continent was discovered by Sir J. C. Ross during the period
extending from 1839 to 1843, when, between the parallels of 70° and 78°
south latitude, he encountered in his explorations a precipitous mountain
coast, rising from seven thousand to ten thousand feet above tide.
Through the valleys intervening between the mountain-ranges huge glaciers
descended, and "projected in many places several miles into the sea and
terminated in lofty, perpendicular cliffs. In a few places the rocks
broke through their icy covering, by which alone we could be assured that
land formed the nucleus of this, to appearance, enormous iceberg."[AG]
[Footnote AG: Quoted by Whitney in Climatic Changes, p. 314.]
Again, speaking of the region in the vicinity of the lofty volcanoes
Terror and Erebus, between ten thousand and twelve thousand feet high,
the same navigator says:
"We perceived a low, white line extending from its extreme eastern
point, as far as the eye could discern, to the eastward. It presented
an extraordinary appearance, gradually increasing in height as we got
nearer to it, and proving at length to be a perpendicular cliff of ice,
between one hundred and fifty and two hundred feet above the level of
the sea, perfectly flat and level at the top, and without any fissures
or promontories on its even, seaward face. What was beyond it we could
not imagine; for, being much higher than our mast-head, we could not
see anything except the summit of a lofty range of mountains extending
to the southward as far as the seventy-ninth degree of latitude. These
mountains, being the southernmost land hitherto discovered, I felt
great satisfaction in naming after Sir Edward Parry.... Whether Parry
Mountains again take an easterly trending and form the base to which this
extraordinary mass of ice is attached, must be left for future navigators
to determine. If there be land to the southward it must be very remote,
or of much less elevation than any other part of the coast we have seen,
or it would have appeared above the barrier."
This ice-cliff or barrier was followed by Captain Ross as far as 198°
west longitude, and found to preserve very much the same character during
the whole of that distance. On the lithographic view of this great
ice-sheet given in Ross's work it is described as "part of the South
Polar Barrier, one hundred and eighty feet above the sea-level, one
thousand feet thick, and four hundred and fifty miles in length."
A similar vertical wall of ice was seen by D'Urville, off the coast of
Adelie Land. He thus describes it: "Its appearance was astonishing. We
perceived a cliff having a uniform elevation of from one hundred to one
hundred and fifty feet, forming a long line extending off to the west....
Thus for more than twelve hours we had followed this wall of ice, and
found its sides everywhere perfectly vertical and its summit horizontal.
Not the smallest irregularity, not the most inconsiderable elevation,
broke its uniformity for the twenty leagues of distance which we followed
it during the day, although we passed it occasionally at a distance of
only two or three miles, so that we could make out with ease its smallest
irregularities. Some large pieces of ice were lying along the side of
this frozen coast; but, on the whole, there was open sea in the offing."
[AH]
[Footnote AH: Whitney's Climatic Changes, pp. 315, 316.]
[Illustration: Fig. 10.--Iceberg in the Antarctic Ocean.]
_North America._--In North America living glaciers begin to appear in
the Sierra Nevada Mountains, in the vicinity of the Yosemite Park, in
central California. Here the conditions necessary for the production
of glaciers are favourable, namely, a high altitude, snow-fields of
considerable extent, and unobstructed exposure to the moisture-laden
currents of air from the Pacific Ocean. Sixteen glaciers of small size
have been noted among the summits to the east of the Yosemite; but none
of them descend much below the eleven-thousand-foot line, and none of
them are over a mile in length. Indeed, they are so small, and their
motion is so slight, that it is a question whether or not they are to be
classed with true glaciers.
Owing to the comparatively low elevation of the Sierra Nevada north of
Tuolumne County, California, no other living glaciers are found until
reaching Mount Shasta, in the extreme northern part of the State. This
is a volcanic peak, rising fourteen thousand five hundred feet above the
sea, and having no peaks within forty miles of it as high as ten thousand
feet; yet so abundant is the snow-fall that as many as five glaciers are
found upon its northern side, some of them being as much as three miles
long and extending as low down as the eight-thousand-foot level. Upon the
southern side glaciers are so completely absent that Professor Whitney
ascended the mountain and remained in perfect ignorance of its glacial
system. In 1870 Mr. Clarence King first discovered and described them on
the northern side.
North of California glaciers characterise the Cascade Range in increasing
numbers all the way to the Alaskan Peninsula. They are to be found upon
Diamond Peak, the Three Sisters, Mount Jefferson, and Mount Hood, in
Oregon, and appear in still larger proportions upon the flanks of Mount
Rainier (or Tacoma) and Mount Baker, in the State of Washington. The
glacier at the head of the White River Valley is upon the north side of
Rainier, and is the largest one upon that mountain, reaching down to
within five thousand feet of the sea-level, and being ten miles or more
in length. All the streams which descend the valleys upon this mountain
are charged with the milky-coloured water which betrays their glacial
origin.
[Illustration: Fig. 11.--Map of Southeastern Alaska. The arrow-points
mark glaciers.]
In British Columbia, Glacier Station, upon the Canadian Pacific Railroad,
in the Selkirk Mountains, is within half a mile of the handsome
Illicilliwaet Glacier, while others of larger size are found at no great
distance. The interior farther north is unexplored to so great an extent
that little can be definitely said concerning its glacial phenomena. The
coast of British Columbia is penetrated by numerous fiords, each of which
receives the drainage of a decaying glacier; but none are in sight of the
tourist-steamers which thread their way through the intricate network of
channels characterising this coast, until the Alaskan boundary is crossed
and the mouth of the Stickeen River is passed.
A few miles up from the mouth of the Stickeen, however, glaciers of
large size come down to the vicinity of the river, both from the north
and from the south, and the attention of tourists is always attracted
by the abundant glacial sediment borne into the tide-water by the river
itself and discolouring the surface for a long distance beyond the
outlet. Northward from this point the tourist is rarely out of sight of
ice-fields. The Auk and Patterson Glaciers are the first to come into
view, but they do not descend to the water-level. On nearing Holcomb
Bay, however, small icebergs begin to appear, heralding the first of the
glaciers which descend beyond the water's edge. Taku Inlet, a little
farther north, presents glaciers of great size coming down to the
sea-level, while the whole length of Lynn Canal, from Juneau to Chilkat,
a distance of eighty miles, is dotted on both sides by conspicuous
glaciers and ice-fields.
The Davidson Glacier, near the head of the canal, is one of the most
interesting for purposes of study. It comes down from an unknown
distance in the western interior, bearing two marked medial moraines upon
its surface. On nearing tide-level, the valley through which it flows is
about three-quarters of a mile in width; but, after emerging from the
confinement of the valley, the ice spreads out over a fan-shaped area
until the width of its front is nearly three miles. The supply of ice
not being sufficient to push the front of the glacier into deep water,
equilibrium between the forces of heat and cold is established near the
water's edge. Here, as from year to year the ice melts and deposits its
burdens of earthy _débris_, it has piled up a terminal moraine which
rises from two hundred to three hundred feet in height, and is now
covered with evergreen trees of considerable size. From Chilkat, at the
head of Lynn Canal, to the sources of the Yukon River, the distance is
only thirty-five miles, but the intervening mountain-chain is several
thousand feet in height and bears numerous glaciers upon its seaward side.
About forty miles west of Lynn Canal, and separated from it by a range
of mountains of moderate height, is Glacier Bay, at the head of one of
whose inlets is the Muir Glacier, which forms the chief attraction for
the great number of tourists that now visit the coast of southeastern
Alaska during the summer season. This glacier meets tide-water in
latitude 58° 50', and longitude 136° 40' west of Greenwich. It received
its name from Mr. John Muir, who, in company with Rev. Mr. Young, made
a tour of the bay and discovered the glacier in 1879. It was soon found
that the bay could be safely navigated by vessels of large size, and from
that time on tourists in increasing number have been attracted to the
region. Commodious steamers now regularly run close up to the ice-front,
and lie-to for several hours, so that the passengers may witness the
"calving" of icebergs, and may climb upon the sides of the icy stream
and look into its deep crevasses and out upon its corrugated and broken
surface.
[Illustration: Fig. 12.--Map of Glacier Bay. Alaska, and its
surroundings. Arrow-points indicate glaciated area.]
The first persons who found it in their way to pay more than a tourist's
visit to this interesting object were Rev. J. L. Patton, Mr. Prentiss
Baldwin, and myself, who spent the entire month of August, 1886, encamped
at the foot of the glacier, conducting such observations upon it as
weather and equipment permitted. From that time till the summer of 1890
no one else stopped off from the tourist steamers to bestow any special
study upon it. But during this latter season Mr. Muir returned to the
scene of his discovered wonder, and spent some weeks in exploring the
interior of the great ice-field. During the same season, also, Professors
H. F. Reid and H. Cushing, with a well-equipped party of young men,
spent two months or more in the same field, conducting observations and
experiments, of various kinds, relating to the extent, the motion, and
the general behaviour of the vast mass of moving ice.
[Illustration: Fig. 13.--Shows central part of the front of Muir Glacier
one half mile distant. Near the lower left hand corner the ice is seen
one mile distant resting for about one half mile on gravel which it had
overrun. The ice is now retreating in the channel. (From photograph.)]
The main body of the Muir Glacier occupies a vast amphitheatre, with
diameters ranging from thirty to forty miles, and covers an area of about
one thousand square miles. From one of the low mountains near its mouth I
could count twenty-six tributary glaciers which came together and became
confluent in the main stream of ice. Nine medial moraines marked the
continued course of as many main branches, which becoming united formed
the grand trunk of the glacier. Numerous rocky eminences also projected
above the surface of the ice, like islands in the sea, corresponding to
what are called "_nunataks_" in Greenland. The force of the ice against
the upper side of these rocky prominences is such as to push it in great
masses above the surrounding level, after the analogy of waves which
dash themselves into foam against similar obstructions. In front of the
_nunataks_ there is uniformly a depression, like the eddies which appear
in the current below obstacles in running water.
Over some portions of the surface of the glacier there is a miniature
river system, consisting of a main stream, with numerous tributaries,
but all flowing in channels of deep blue ice. Before reaching the front
of the glacier, however, each one of these plunges down into a crevasse,
or _moulin_, to swell the larger current, which may be heard rushing
along in an impetuous course hundreds of feet beneath, and far out of
sight. The portion of the glacier in which there is the most rapid
motion is characterised by innumerable crags and domes and pinnacles of
ice, projecting above the general level, whose bases are separated by
fissures, extending in many cases more than a hundred feet below the
general level. These irregularities result from the combined effect
of the differential motion (as illustrated in the diagram on page 4),
and the influence of sunshine and warm air in irregularly melting the
unprotected masses. The description given in our introductory chapter of
medial moraines and ice-pillars is amply illustrated everywhere upon the
surface of the Muir Glacier. I measured one block of stone which was
twenty feet square and about the same height, standing on a pedestal of
ice three or four feet high.
The mountains forming the periphery of this amphitheatre rise to a height
of several thousand feet; Mount Fairweather, upon the northwest, from
whose flanks probably a portion of the ice comes, being, in fact, more
than fifteen thousand feet high. The mouth of the amphitheatre is three
miles wide, in a line extending from shoulder to shoulder of the low
mountains which guard it. The actual water-front where the ice meets
tide-water is one mile and a half.[AI] Here the depth of the inlet is so
great that the front of the ice breaks off in icebergs of large size,
which float away to be dissolved at their leisure. At the water's edge
the ice presents a perpendicular front of from two hundred and fifty to
four hundred feet in height, and the depth of the water in the middle of
the inlet immediately in front of the ice is upwards of seven hundred
feet; thus giving a total height to the precipitous front of a thousand
feet.
[Footnote AI: These are the measurements of Professor Reid. In my former
volume I have given the dimensions as somewhat smaller.]
The formation of icebergs can here be studied to admirable advantage.
During the month in which we encamped in the vicinity the process
was going on continuously. There was scarcely an interval of fifteen
minutes during the whole time in which the air was not rent with the
significant boom connected with the "calving" of a berg. Sometimes this
was occasioned by the separation of a comparatively small mass of ice
from near the top of the precipitous wall, which would fall into the
water below with a loud splash. At other times I have seen a column of
ice from top to bottom of the precipice split off and fall over into the
water, giving rise to great waves, which would lash the shore with foam
two miles below.
This manner of the production of icebergs differs from that which has
been ordinarily represented in the text-books, but it conforms to the law
of glacial motion, which we will describe a little later, namely, that
the upper strata of ice move faster than the lower. Hence the tendency
is constantly to push the upper strata forwards, so as to produce
a perpendicular or even projecting front, after the analogy of the
formation of breakers on the shelving shore of a large body of water.
Evidently, however, these masses of ice which break off from above the
water do not reach the whole distance to the bottom of the glacier below
the water; so that a projecting foot of ice remains extending to an
indefinite distance underneath the surface. But at occasional intervals,
as the superincumbent masses of ice above the surface fall off and
relieve the strata below of their weight, these submerged masses suddenly
rise, often shooting up considerably higher than they ultimately remain
when coming to rest. The bergs formed by this latter process often bear
much earthy material upon them, which is carried away with the floating
ice, to be deposited finally wherever the melting chances to take place.
Numerous opportunities are furnished about the front and foot of
this vast glacier to observe the manner of the formation of _kames_,
kettle-holes, and various other irregular forms into which glacial
_débris_ is accustomed to accumulate. Over portions of the decaying
foot of the glacier, which was deeply covered with morainic _débris_,
the supporting ice is being gradually removed through the influence of
subglacial streams or of abandoned tunnels, which permit the air to exert
its melting power underneath. In some places where old _moulins_ had
existed, the supporting ice is melting away, so that the superincumbent
mass of sand, gravel, and boulders is slowly sliding into a common
centre, like grain in a hopper. This must produce a conical hill, to
remain, after the ice has all melted away, a mute witness of the
impressive and complicated forces which have been so long in operation
for its production.
In other places I have witnessed the formation of a long ridge of gravel
by the gradual falling in of the roof of a tunnel which had been occupied
by a subglacial stream, and over which there was deposited a great amount
of morainic material. As the roof gave way, this was constantly falling
to the bottom, where, being exempt from further erosive agencies, it must
remain as a gravel ridge or kame.
In other places, still, there were vast masses of ice covering many
acres, and buried beneath a great depth of morainic material which had
been swept down upon it while joined to the main glacier. In the retreat
of the ice, however, these masses had become isolated, and the sand,
gravel, and boulders were sliding down the wasting sides and forming long
ridges of _débris_ along the bottom, which, upon the final melting of
the ice, will be left as a complicated network of ridges and knolls of
gravel, enclosing an equally complicated nest of kettle-holes.
Beyond Cross Sound the Pacific coast is bounded for several hundred
miles by the magnificent semicircle of mountains known as the St. Elias
Alps, with Mount Crillon at the south, having an elevation of nearly
sixteen thousand feet, and St. Elias in the centre, rising to a greater
height. Everywhere along this coast, as far as the Alaskan Peninsula,
vast glaciers come down from the mountain-sides, and in many cases their
precipitous fronts form the shore-line for many miles at a time. Icy
Bay, just to the south of Mount St, Elias, is fitly named, on account of
the extent of the glaciers emptying into it and the number of icebergs
cumbering its waters.
In the summer of 1890 a party, under the lead of Mr. I. C. Russell, of
the United States Geological Survey, made an unsuccessful attempt to
scale the heights of Mount St. Elias; but the information brought back
by them concerning the glaciers of the region amply repaid them for their
toil and expense, and consoled them for the failure of their immediate
object.
[Illustration: Fig. 14.--By the courtesy of the National Geographical
Society.]
Leaving Yakutat Bay, and following the route indicated upon the
accompanying map, they travelled on glacial ice almost the entire
distance to the foot of Mount St. Elias. The numerous glaciers coming
down from the summit of the mountain-ridge become confluent nearer the
shore, and spread out over an area of about a thousand square miles. This
is fitly named the Malaspina Glacier, after the Spanish explorer who
discovered it in 1792.
It is not necessary to add further particulars concerning the results
of this expedition, since they are so similar to those already detailed
in connection with the Muir Glacier. A feature, however, of special
interest, pertains to the glacial lakes which are held in place by the
glacial ice at an elevation of thousands of feet above the sea. One of
considerable size is indicated upon the map just south of what was called
Blossom Island, which, however, is not an island, but simply a _nunatak_,
the ice here surrounding a considerable area of fertile land, which is
covered with dense forests and beautified by a brilliant assemblage of
flowering plants. In other places considerable vegetation was found upon
the surface of moraines, which were probably still in motion with the
underlying ice.
_Greenland._--The continental proportions of Greenland, and the extent
to which its area is covered by glacial ice, make it by far the most
important accessible field for glacial observations. The total area of
Greenland can not be less than five hundred thousand square miles--equal
in extent to the portion of the United States east of the Mississippi
and north of the Ohio. It is now pretty evident that the whole of this
area, except a narrow border about the southern end, is covered by one
continuous sheet of moving ice, pressing outward on every side towards
the open water of the surrounding seas.
For a long time it was the belief of many that a large region in the
interior of Greenland was free from ice, and was perhaps inhabited.
It was in part to solve this problem that Baron Nordenskiöld set out
upon his expedition of 1883. Ascending the ice-sheet from Disco Bay, in
latitude 69°, he proceeded eastward for eighteen days across a continuous
ice-field. Rivers were flowing in channels upon the surface like those
cut on land in horizontal strata of shale or sandstone, only that the
pure deep blue of the ice-walls was, by comparison, infinitely more
beautiful. These rivers were not, however, perfectly continuous. After
flowing for a distance in channels on the surface, they, one and all,
plunged with deafening roar into some yawning crevasse, to find their way
to the sea through subglacial channels. Numerous lakes with shores of ice
were also encountered.
[Illustration: Fig. 15.--Map of Greenland. The arrow-points mark the
margin of the ice-field.]
"On bending down the ear to the ice," says this explorer, "we could hear
on every side a peculiar subterranean hum, proceeding from rivers flowing
within the ice; and occasionally a loud, single report, like that of a
cannon, gave notice of the formation of a new glacier-cleft.... In the
afternoon we saw at some distance from us a well-defined pillar of mist,
which, when we approached it, appeared to rise from a bottomless abyss,
into which a mighty glacier-river fell. The vast, roaring water-mass had
bored for itself a vertical hole, probably down to the rock, certainly
more than two thousand feet beneath, on which the glacier rested."[AJ]
[Footnote AJ: Geological Magazine, vol. ix, pp. 393, 399.]
At the end of the eighteen days Nordenskiöld found himself about a
hundred and fifty miles from his starting-point, and about five thousand
feet above the sea. Here the party rested, and sent two Eskimos forward
on _skidor_--a kind of long wooden skate, with which they could move
rapidly over the ice, notwithstanding the numerous small, circular holes
which everywhere pitted the surface. These Eskimos were gone fifty-seven
hours, having slept only four hours of the period. It is estimated that
they made about a hundred and fifty miles, and attained an altitude of
six thousand feet. The ice is reported as rising in distinct terraces,
and as seemingly boundless beyond. If this is the case, two hundred miles
from Disco Bay, there would seem little hope of finding in Greenland
an interior freed from ice. So we may pretty confidently speak of that
continental body of land as still enveloped in an ice-sheet. Up to about
latitude 75°, however, the continent is fringed by a border of islands,
over which there is no continuous covering of ice. In south Greenland
the continuous ice-sheet is reached about thirty miles back from the
shore.
A summary of the results of Greenland exploration was given by Dr. Kink
in 1886, from which it appears that since 1876 one thousand miles of
the coast-line have been carefully explored by entering every fiord and
attempting to reach the inland ice. According to this authority--
We are now able to demonstrate that a movement of ice from the central
regions of Greenland to the coast continually goes on, and must be
supposed to act upon the ground over which it is pushed so as to detach
and transport fragments of it for such a distance.... The plainest idea
of the ice-formation here in question is given by comparing it with an
inundation.... Only the marginal parts show irregularity; towards the
interior the surface grows more and more level and passes into a plain
very slightly rising in the same direction. It has been proved that,
ascending its extreme verge, where it has spread like a lava-stream over
the lower ground in front of it, the irregularities are chiefly met with
up to a height of 2,000 feet, but the distance from the margin in which
the height is reached varies much. While under 68-1/2° north latitude it
took twenty-four miles before this elevation was attained, in 72-1/2° the
same height was arrived at in half the distance....
A general movement of the whole mass from the central regions towards the
sea is still continued, but it concentrates its force to comparatively
few points in the most extraordinary degree. These points are represented
by the ice-fiords, through which the annual surplus ice is carried off
in the shape of bergs.... In Danish Greenland are found five of the
first, four of the second, and eight of the third (or least productive)
class, besides a number of inlets which only receive insignificant
fragments. Direct measurements of the velocity have now been applied on
three first-rate and one second-rate fiords, all situated between 69°
and 71° north latitude. The measurements have been repeated during the
coldest and the warmest season, and connected with surveying and other
investigations of the inlets and their environs. It is now proved that
the glacier branches which produce the bergs proceed incessantly at a
rate of thirty to fifty feet per diem, this movement being not at all
influenced by the seasons. . . .
In the ice-fiord of Jakobshavn, which spreads its enormous bergs over
Disco Bay and probably far into the Atlantic, the productive part of the
glacier is 4,500 metres (about 2-1/2 miles) broad. The movement along its
middle line, which is quicker than on the sides nearer the shores, can
be rated at fifty feet per diem. The bulk of ice here annually forced
into the sea would, if taken on the shore, make a mountain two miles
long, two miles broad, and 1,000 feet high. The ice-fiord of Torsukatak
receives four or five branches of the glacier; the most productive of
them is about 9,000 metres broad (five miles), and moves between sixteen
and thirty-two feet per diem. The large Karajak Glacier, about 7,000
metres (four miles) broad, proceeds at a rate of from twenty-two to
thirty-eight feet per diem. Finally, a glacier branch dipping into the
fiord of Jtivdliarsuk, 5,800 metres broad (three miles), moved between
twenty-four and forty-six feet per diem.[AK]
[Footnote AK: See Transactions of the Edinburgh Geological Society for
February 18, 1886, vol. v, part ii, pp. 286-293.]
The principal part of our information concerning the glaciers of
Greenland north of Melville Bay was obtained by Drs. Kane and Hayes,
in 1853 and 1854, while conducting an expedition in search of Sir
John Franklin and his unfortunate crew. Dr. Hayes conducted another
expedition to the same desolate region in 1860, while other explorers
have to some extent supplemented their observations. The largest glacier
which they saw enters the sea between latitude 79° and 80°, where it
presents a precipitous discharging front more than sixty miles in width
and hundreds of feet in perpendicular height.
Dr. Kane gives his first impressions of this grand glacier in the
following vivid description:
"I will not attempt to do better by florid description. Men only
rhapsodize about Niagara and the ocean. My notes speak simply of the
'long, ever-shining line of cliff diminished to a well-pointed wedge in
the perspective'; and, again, of 'the face of glistening ice, sweeping
in a long curve from the low interior, the facets in front intensely
illuminated by the sun.' But this line of cliff rose in a solid,
glassy wall three hundred feet above the water-level, with an unknown,
unfathomable depth below it; and its curved face, sixty miles in length
from Cape Agassiz to Cape Forbes, vanished into unknown space at not more
than a single day's railroad-travel from the pole. The interior, with
which it communicated and from which it issued, was an unsurveyed _mer de
glace_--an ice-ocean to the eye, of boundless dimensions.
"It was in full sight--the mighty crystal bridge which connects the two
continents of America and Greenland. I say continents, for Greenland,
however insulated it may ultimately prove to be, is in mass strictly
continental. Its least possible axis, measured from Cape Farewell to the
line of this glacier, in the neighbourhood of the eightieth parallel,
gives a length of more than 1,200 miles, not materially less than that of
Australia from its northern to its southern cape.
"Imagine, now, the centre of such a continent, occupied through nearly
its whole extent by a deep, unbroken sea of ice that gathers perennial
increase from the water-shed of vast snow-covered mountains and all the
precipitations of its atmosphere upon its own surface. Imagine this,
moving onwards like a great glacial river, seeking outlets at every fiord
and valley, rolling icy cataracts into the Atlantic and Greenland seas;
and, having at last reached the northern limit of the land that has borne
it up, pouring out a mighty frozen torrent into unknown arctic space!
"It is thus, and only thus, that we must form a just conception of a
phenomenon like this great glacier. I had looked in my own mind for such
an appearance, should I ever be fortunate enough to reach the northern
coast of Greenland; but, now that it was before me, I could hardly
realize it. I had recognized, in my quiet library at home, the beautiful
analogies which Forbes and Studer have developed between the glacier and
the river. But I could not comprehend at first this complete substitution
of ice for water.
"It was slowly that the conviction dawned on me that I was looking upon
the counterpart of the great river-system of Arctic Asia and America. Yet
here were no water-feeders from the south. Every particle of moisture had
its origin within the polar circle and had been converted into ice. There
were no vast alluvions, no forest or animal traces borne down by liquid
torrents. Here was a plastic, moving, semi-solid mass, obliterating life,
swallowing rocks and islands, and ploughing its way with irresistible
march through the crust of an investing sea."[AL]
[Footnote AL: Arctic Explorations in the Years 1853, 1854, and 1855, vol.
i, pp. 225-228.]
Much less is known concerning the eastern coast of Greenland than
about the western coast. For a long time it was supposed that there
might be a considerable population in the lower latitudes along the
eastern side. But that is now proved to be a mistake. The whole coast
is very inhospitable and difficult of approach. From latitude 65° to
latitude 69° little or nothing is known of it. In 1822-'23 Scoresby,
Cleavering, and Sabine hastily explored the coast from latitude 69° to
76°, and reported numerous glaciers descending to the sea-level through
extensive fiords, from which immense icebergs float out and render
navigation dangerous. In 1869 and 1870 the second North-German Expedition
partly explored the coast between latitude 73° and 77°. Mr. Payer, an
experienced Alpine explorer, who accompanied the expedition, reports the
country as much broken, and the glaciers as "subordinated in position to
the higher peaks, and having their moraines, both lateral and terminal,
like those of the Alpine ranges, and on a still grander scale." Petermann
Peak, in latitude 73°, is reported as 13,000 feet high. Captain Koldewey,
chief of the expedition, found extensive plateaus on the mainland, in
latitude 75°, to be "entirely clear of snow, although only sparsely
covered with vegetation." The mountains in this vicinity, also, rising to
a height of more than 2,000 feet, were free from snow in the summer. Some
of the fiords in this vicinity penetrate the continent through several
degrees of longitude.
An interesting episode of this expedition was the experience of the crew
of the ship Hansa, which was caught in the ice and destroyed. The crew,
however, escaped by encamping on the ice-floe which had crushed the ship.
From this, as it slowly floated towards the south through several degrees
of latitude, they had opportunity to make many important observations
upon the continent itself. As viewed from this unique position the coast
had the appearance everywhere of being precipitous, with mountains of
considerable height rising in the background, from which numerous small
glaciers descended to the sea-level.
In 1888 Dr. F. Nansen, with Lieutenant Sverdrup and four others, was
left by a whaler on the ice-pack bordering the east of Greenland about
latitude 65°, and in sight of the coast. For twelve days the party was
on the ice-pack floating south, and so actually reached the coast only
about latitude 64°. From this point they attempted to cross the inland
ice in a northwesterly direction towards Christianshaab. They soon
reached a height of 7,000 feet, and were compelled by severe northerly
storms to diverge from their course, taking a direction more to the west.
The greatest height attained was 9,500 feet, and the party arrived on the
western coast at Ameralik Fiord, a little south of Godhaab, about the
same latitude at which they entered.
It thus appears that subsequent investigations have confirmed in a
remarkable manner the sagacious conclusions made by the eminent Scotch
geologist and glacialist Robert Brown in 1875, soon after his own
expedition to the country. "I look upon Greenland and its interior
ice-field," he writes, "in the light of a broad-lipped, shallow vessel,
but with chinks in the lips here and there, and the glacier like viscous
matter in it. As more is poured in, the viscous matter will run over the
edges, naturally taking the line of the chinks as its line of outflow.
The broad lips of the vessel are the outlying islands or 'outskirts';
the viscous matter in the vessel the inland ice, the additional matter
continually being poured in in the form of the enormous snow covering,
which, winter after winter, for seven or eight months in the year, falls
almost continuously on it; the chinks are the fiords or valleys down
which the glaciers, representing the outflowing viscous matter, empty the
surplus of the vessel--in other words, the ice floats out in glaciers,
overflows the land in fact, down the valleys and fiords of Greenland
by force of the superincumbent weight of snow, just as does the grain
on the floor of a barn (as admirably described by Mr. Jamieson) when
another sackful is emptied on the top of the mound already on the floor.
'The floor is flat, and therefore does not conduct the grain in any
direction; the outward motion is due to the pressure of the particles
of grain on one another; and, given a floor of infinite extension and a
pile of sufficient amount, the mass would move outward to any distance,
and with a very slight pitch or slope it would slide forward along the
incline.' To this let me add that if the floor on the margin of the heap
of grain was undulating the stream of grain would take the course of
such undulations. The want, therefore, of much slope in a country and
the absence of any great mountain-range are of very little moment to the
movement of land-ice, _provided we have snow enough_" On another page Dr.
Brown had well said that "the country seems only a circlet of islands
separated from one another by deep fiords or straits, and bound together
on the landward side by the great ice covering which overlies the whole
interior.... No doubt under this ice there lies land, just as it lies
under the sea; but nowadays none can be seen, and as an insulating medium
it might as well be water."
In his recently published volumes descriptive of the journey across
the Greenland ice-sheet, alluded to on page 39, Dr. Nansen sums up his
inferences in very much the same way: "The ice-sheet rises comparatively
abruptly from the sea on both sides, but more especially on the east
coast, while its central portion is tolerably flat. On the whole, the
gradient decreases the farther one gets into the interior, and the mass
thus presents the form of a shield with a surface corrugated by gentle,
almost imperceptible, undulations lying more or less north and south,
and with its highest point not placed symmetrically, but very decidedly
nearer the east coast than the west."
From this rapid glance at the existing glaciers of the world we see that
a great ice age is not altogether a strange thing in the world. The lands
about the south pole and Greenland are each continental in dimensions,
and present at the present time accumulations of land-ice so extensive,
so deep, and so alive with motion as to prepare our minds for almost
anything that may be suggested concerning the glaciated condition of
other portions of the earth's surface. The _vera causa_ is sufficient
to accomplish anything of which glacialists have ever dreamed. It only
remains to enquire what the facts really are and over how great an extent
of territory the actual results of glacial action may be found. But we
will first direct more particular attention to some of the facts and
theories concerning glacial motion.
CHAPTER III.
GLACIAL MOTION.
That glacial ice actually moves after the analogy of a semi-fluid has
been abundantly demonstrated by observation. In the year 1827 Professor
Hugi, of Soleure, built a hut far up upon the Aar Glacier in Switzerland,
in order to determine the rate of its motion. After three years he found
that it had moved 330 feet; after nine years, 2,354 feet; and after
fourteen years Louis Agassiz found that its motion had been 4,712 feet.
In 1841 Agassiz began a more accurate series of observation upon the same
glacier. Boring holes in the ice, he set across it a row of stakes which,
on visiting in 1842, he found to be no longer in a straight line. All had
moved downwards with varying velocity, those near the centre having moved
farther than the others. The displacements of the stakes were in order,
from side to side, as follows: 160 feet, 225 feet, 269 feet, 245 feet,
210 feet, and 125 feet. Agassiz followed up his observations for six
years, and in 1847 published the results in his celebrated work System
Glacière.
[Illustration: Fig. 16.]
But in August, 1841, the distinguished Swiss investigator had invited
Professor J. D. Forbes, of Edinburgh, to interest himself in solving the
problem of glacial motion. In response to this request, Professor Forbes
spent three weeks with Agassiz upon the Aar Glacier. Stimulated by the
interest of this visit, Forbes returned to Switzerland in 1842 and began
a series of independent investigations upon the Mer de Glace. After a
week's observations with accurate instruments, Forbes wrote to Professor
Jameson, editor of the Edinburgh New Philosophical Journal, that he had
already made it certain that "the central part of the glacier moves
faster than the edges in a very considerable proportion, quite contrary
to the opinion generally maintained." This letter was dated July 4, 1842,
but was not published until the October following, Agassiz's results, so
far as then determined, were, however, published in Comptes Rendus of
the 29th of August, 1842, two months before the publication of Forbes's
letter. But Agassiz's letter was dated twenty-seven days later than that
of Forbes. It becomes certain, therefore, that both Agassiz and Forbes,
independently and about the same time, discovered the fact that the
central portion of a glacier moves more rapidly than the sides.
In 1857 Professor Tyndall began his systematic and fruitful observations
upon the Mer de Glace and other Alpine glaciers. Professor Forbes had
already demonstrated that, with an accurate instrument of observation,
the motion of a line of stakes might be observed after the lapse
of a single clay, or even of a few hours. As a result of Tyndall's
observations, it was found that the most rapid daily motion in the Mer de
Glace in 1857 was about thirty-seven inches. This amount of motion was
near the lower end of the glacier On ascending the glacier, the rate was
found in general to be diminished; but the diminution was not uniform
throughout the whole distance, being affected both by the size and by the
contour of the valley. The motion in the tributary glaciers was also much
less than that of the main glacier.
This diminution of movement in the tributary glaciers was somewhat
proportionate to their increase in width. For example, the combined
width of the three tributaries uniting to form the Mer de Glace is 2,597
yards; but a short distance below the junction of these tributaries the
total width of the Mer de Glace itself is only 893 yards, or one-third
that of the tributaries combined. Yet, though the depth of the ice is
probably here much greater than in the tributaries, the rapidity of
movement is between two and three times as great as that of any one of
the branches.[AM]
[Footnote AM: See Tyndall's Forms of Water, pp. 78-82.]
From Tyndall's observations it appears also that the line of most rapid
motion is not exactly in the middle of the channel, but is pushed by its
own momentum from one side to the other of the middle, so as always to be
nearer the concave side; in this respect conforming, as far as its nature
will permit, to the motion of water in a tortuous channel.
[Illustration: Fig. 17.]
It is easy to account for this differential motion upon the surface
of a glacier, since it is clear that the friction of the sides of the
channel must retard the motion of ice as it does that of water. It is
clear also that the friction of the bottom must retard the motion of ice
even more than it is known to do in the case of water. In the formation
of breakers, when the waves roll in upon a shallowing beach, every one
is familiar with the effect of the bottom upon the moving mass. Here
friction retards the lower strata of water, and the upper strata slide
over the lower, and, where the water is of sufficient depth and the
motion is sufficiently great, the crest breaks down in foam before the
ever-advancing tide. A similar phenomenon occurs when dams give way and
reservoirs suddenly pour their contents into the restricted channels
below. At such times the advancing water rolls onwards like the surf with
a perpendicular front, varying in height according to the extent of the
flood.
Seasoning from these phenomena connected with moving water, it was
naturally suggested to Professor Tyndall that an analogous movement must
take place in a glacier. Choosing, therefore, a favourable place for
observation on the Mer de Glace where the ice emerged from a gorge, he
found a perpendicular side about one hundred and fifty feet in height
from bottom to top. In this face he drove stakes in a perpendicular line
from top to bottom. Upon subsequently observing them, Tyndall found, as
he expected, that there was a differential motion among them as in the
stakes upon the surface. The retarding effect of friction upon the bottom
was evident. The stake near the top moved forwards about three times as
fast as the one which was only four feet from the bottom.
[Illustration: Fig. 18.]
The most rapid motion (thirty-seven inches per day) observed by Professor
Tyndall upon the Alpine glaciers occurred in midsummer. In winter
the rate was only about one-half as great; but in the year 1875 the
Norwegian geologist, Helland, reported a movement of twenty metres (about
sixty-five feet) per day in the Jakobshavn Glacier which enters Disco
Bay, Greenland, about latitude 70°. For some time there was a disposition
on the part of many scientific men to doubt the correctness of Holland's
calculations. Subsequent observations have shown, however, that from the
comparatively insignificant glaciers of the Alps they were not justified
in drawing inferences with respect to the motion of the vastly larger
masses which come down to the sea through the fiords of Greenland.
The Jakobshavn Glacier was about two and a half miles in width and its
depth very likely more than a thousand feet, making a cross-section of
more than 1,400,000 square yards, whereas the cross-section of the Mer
de Glace at Montanvert is estimated to be but 190,000 square yards or
only about one-seventh the above estimate for the Greenland glacier. As
the friction of the sides would be no greater upon a large stream than
upon a small one, while upon the bottom it would be only in proportion
to the area, it is evident that we cannot tell beforehand how rapidly
an increase in the volume of the ice might augment the velocity of the
glacier.
At any rate, all reasonable grounds for distrusting the accuracy of
Helland's estimates seem to have been removed by later investigations.
According to my own observations in the summer of 1886 upon the Muir
Glacier, Alaska, the central portions, a mile back from the front of
that vast ice-current, were moving from sixty-five to seventy feet per
day. These observations were taken with a sextant upon pinnacles of ice
recognizable from a baseline established upon the shore. It is fair
to add, however, that during the summer of 1890 Professor H. F. Reid
attempted to measure the motion of the same glacier by methods promising
greater accuracy than could be obtained by mine. He endeavoured to plant,
after the method of Tyndall, a line of stakes across the ice-current. But
with his utmost efforts, working inwards from both sides, he was unable
to accomplish his purpose, and so left unmeasured a quarter of a mile
or more of the most rapidly-moving portion of the glacier. His results,
therefore, of ten feet per day in the most rapidly-moving portion
observed cannot discredit my own observations on a portion of the stream
inaccessible by his method. A quarter of a mile in width near the centre
of so vast a glacier gives ample opportunity for a much greater rate of
motion than that observed by Professor Reid. Especially may this be true
in view of Tyndall's suggestion that the contour of the bottom over which
the ice flows may greatly affect the rate in certain places. A sudden
deepening of the channel may affect the motion of ice in a glacier as
much as it does that of water in a river.
Other observations also amply sustain the conclusions of Helland. As
already stated, the Danish surveying party under Steenstrup, after
several years' work upon the southwestern coast of Greenland, have
ascertained that the numerous glaciers coming down to the sea in that
region and furnishing the icebergs incessantly floating down Baffin's
Bay, move at a rate of from thirty to fifty feet per day, while
Lieutenants Ryder and Bloch, of the Danish Navy, who spent the year 1887
in exploring the coast in the vicinity of Upernavik, about latitude 73°,
found that the great glacier entering the fiord east of the village had a
velocity of ninety-nine feet per day during the month of August.[AN]
[Footnote AN: Nature, December 29, 1887.]
It is easier to establish the fact of glacial motion than to explain how
the motion takes place, for ice seems to be as brittle as glass. This,
however, is true of it only when compelled suddenly to change its form.
When subjected to slow and long-continued pressure it gradually yet
readily yields, and takes on new forms. From this capacity of ice, it has
come to be regarded by some as a really viscous substance, like tar or
cooling lava, and upon that theory Professor Forbes endeavours to explain
all glacial movement.
The theory, however, seems to be contradicted by familiar facts; for
the iceman, after sawing a shallow groove across a piece of ice, can
then split it as easily as he would a piece of sandstone or wood. On the
glaciers themselves, likewise, the existence of innumerable crevasses
would seem to contradict the plastic theory of glacier motion; for,
wherever the slope of the glacier's bed increases, crevasses are formed
by the increased strain to which the ice is subjected. Crevasses are also
formed in rapidly-moving glaciers by the slight strain occasioned by the
more rapid motion of the middle portion. Still, in the words of Tyndall,
"it is undoubted that the glacier moves like a viscous body. The centre
flows past the sides, the top flows over the bottom, and the motion
through a curved valley corresponds to fluid motion."[AO]
[Footnote AO: Forms of Water, p. 163.]
To explain this combination of the seemingly contradictory qualities of
brittleness and viscosity in ice, physicists have directed attention
to the remarkable transformations which take place in water at the
freezing-point. Faraday discovered in 1850 that "when two pieces of
thawing ice are placed together they freeze together at the point of
contact.[AP]
[Footnote AP: Ibid., p. 164.]
"Place a number of fragments of ice in a basin of water and cause them
to touch each other; they freeze together where they touch. You can form
a chain of such fragments; and then, by taking hold of one end of the
chain, you can draw the whole series after it. Chains of icebergs are
sometimes formed in this way in the arctic seas."[AQ]
[Footnote AQ: Ibid., pp. 164, 165.]
This is really what takes place when a hard snow-ball is made by pressure
in the hand. So, by subjecting fragments of ice to pressure it is first
crumbled to powder, and then, as the particles are pressed together in
close contact, it resumes the nature of ice again, though in a different
form, taking now the shape of the mould in which it has been pressed.
Thus it is supposed that, when the temperature of ice is near the
melting-point, the pressure of the superincumbent mass may produce at
certain points insensible disintegration, while, upon the removal of
the pressure by change of position, regulation instantly takes place,
and thus the phenomena which simulate plasticity are produced. As the
freezing-point of water is, within a narrow range, determined by the
amount of pressure to which it is subjected, it is not difficult to see
how these changes may occur. Pressure slightly lowers the freezing-point,
and so would liquefy the portions of ice subjected to greatest pressure,
wherever that might be in the mass of the glacier, and thus permit
a momentary movement of the particles, until they should recongeal
in adjusting themselves to spaces of less pressure.[AR] This is the
theory by which Professor James Thompson would account for the apparent
plasticity of glacial ice.
[Footnote AR: Forms of Water, p. 168.]
CHAPTER IV.
SIGNS OF PAST GLACIATION.
The facts from which we draw the inference that vast areas of the earth's
surface which are now free from glaciers were, at a comparatively
recent time, covered with them, are fourfold, and are everywhere
open to inspection. These facts are: 1. Scratches upon the rocks. 2.
Extensive unstratified deposits of clay and sand intermingled with
scratched stones and loose fragments of rock. 3. Transported boulders
left in such positions and of such size as to preclude the sufficiency
of water-carriage to account for them. 4. Extensive gravel terraces
bordering the valleys which emerge from the glaciated areas. We will
consider these in their order:
1. The scratches upon the rocks.
Almost anywhere in the region designated as having been covered with
ice during the Glacial period, the surface of the rocks when freshly
uncovered will be found to be peculiarly marked by grooves and scratches
more or less fine, and such as could not be produced by the action of
water. But, when we consider the nature of a glacier, these marks seem
to be just what would be produced by the pushing or dragging along of
boulders, pebbles, gravel, and particles of sand underneath a moving mass
of ice.
Running water does indeed move gravel, pebbles, and boulders along with
the current, but these objects are not held by it in a firm grasp, such
as is required to make a groove or scratch in the rock. If, also, there
are inequalities in the compactness or hardness of the rock, the natural
action of running water is to hollow out the soft parts, and leave the
harder parts projecting. But, in the phenomena which we are attributing
to glacial action, there has been a movement which has steadily planed
down the surface of the underlying rock; polishing it, indeed, but also
grooving it and scratching it in a manner which could be accomplished
only by firmly held graving-tools.
[Illustration: Fig. 19.--Bed-rock scored with glacial marks, near
Amherst, Ohio. (From a photograph by Chamberlin.)]
This polishing and scratching can indeed be produced by various
agencies; as, for example, by the forces which fracture the earth's
crust, and shove one portion past another, producing what is called a
_slicken-side_. Or, again, avalanches or land-slides might be competent
to produce the results over limited and peculiarly situated areas.
Icebergs, also, and shore ice which is moved backwards and forwards
by the waves, would produce a certain amount of such grooving and
scratching. But the phenomena to which we refer are so extensive, and
occur in such a variety of situations, that the movement of glacial ice
is alone sufficient to afford a satisfactory explanation. Moreover, in
Alaska, Greenland, Norway, and Switzerland, and wherever else there are
living glaciers, it is possible to follow up these grooved and striated
surfaces till they disappear underneath the existing glaciers which are
now producing the phenomena. Thus by its tracks we can, as it were,
follow this monster to its lair with as great certainty as we could any
animal with whose footprints we had become familiar.
2. The till, or boulder-clay.
A second sign of the former existence of glaciers over any area consists
of an unstratified deposit of earthy material, of greater or less depth,
in which scratched pebbles and fragments of rock occur without any
definite arrangement.
Moving water is a most perfect sieve. During floods, a river shoves
along over its bed gravel and pebbles of considerable size, whereas in
time of low-water the current may be so gentle as to transport nothing
but fine sand, and the clay will be carried still farther onwards, to
settle in the still water and form a delta about the river's mouth. The
transporting capacity of running water is in direct ratio to the sixth
power of its velocity. Other things being equal, if the velocity be
doubled, the size of the grains of sand or gravel which it transports
is increased sixty-four fold.[AS] So frequent are the changes in the
velocity of running water, that the stratification of its deposits is
almost necessary and universal. If large fragments of rocks or boulders
are found embedded in stratified clay, it is pretty surely a sign that
they have been carried to their position by floating ice. A small
mountain stream with great velocity may move a good-sized boulder, while
the Amazon, with its mighty but slow-moving current, would pass by it
forever without stirring it from its position. But the vast area which
is marked in our map as having been covered with ice during the Glacial
period is characterised by deep and extensive deposits of loose material
devoid of stratification, and composed of soil and rock gathered in
considerable part from other localities, and mixed in an indiscriminate
mass with material which has originated in the disintegration of the
underlying local strata.
[Footnote AS: Le Conte's Geology, p. 19.]
[Illustration: Fig. 20.--Scratched stone from the till of Boston.
Natural size about one foot and a half long by ten inches wide. (From
photograph.)]
[Illustration: Fig. 21.--Typical section of till in Seattle. Washington
State, about two hundred feet above Puget Sound. This is on the height
between the sound and Lake Washington.]
[Illustration: Fig. 22.--Ideal section, showing how the till overlies the
stratified rocks.]
[Illustration: Fig. 23.--Vessel Rock, a glacial boulder in Gilsum. N. H.
(C. H. Hitchcock.)]
3. Transported boulders.
Where there is a current of water deep enough to float large masses of
ice, there is scarcely any limit to the size of boulders which may be
transported upon them, or to the distance to which the boulders may be
carried and dropped upon the bottom. The icebergs which break off from
the glaciers of Greenland may bear their burdens of rock far down into
the Atlantic, depositing them finally amidst the calcareous ooze and
the fine sediment from the Gulf Stream which is slowly covering the
area between Northern America and Europe. Northern streams like the St.
Lawrence, which are deeply frozen over with ice in the winter, and are
heavily flooded as the ice breaks up in the spring, afford opportunity
for much transportation of boulders in the direction of their current.
In attributing the transportation of a boulder to glacial ice, it is
necessary, therefore, to examine the contour of the country, so as to
eliminate from the problem the possibility of the effects having been
produced by floating ice.
Another source of error against which one has to be on his guard arises
from the close resemblance of boulders resulting from disintegration
to those which have been transported by ice from distant places. Owing
to the fact that large masses of rocks, especially those which are
crystalline, are seldom homogeneous in their structure, it results that,
under the slow action of disintegrating and erosive agencies, the softer
parts often are completely removed before the harder nodules are sensibly
affected, and these may remain as a collection of boulders dotting the
surface. Such boulders are frequent in the granitic regions of North
Carolina and vicinity, where there has been no glacial transportation.
Several localities in Pennsylvania, also, south of the line of glacial
action as delineated by Professor Lewis and myself, had previously
been supposed to contain transported boulders of large size, but on
examination they proved in all cases to be resting upon undisturbed
strata of the parent rock, and were evidently the harder portions of
the rock left in loco by the processes of erosion spoken of. In New
England, also, it is possible that some boulders heretofore attributed to
ice-action may be simply the results of these processes of disintegration
and erosion. Whether they are or not can usually be determined by their
likeness or unlikeness to the rocks on which they rest; but oftentimes,
where a particular variety of rock is exposed over a broad area, it
is difficult to tell whether a boulder has suffered any extensive
transportation or not.
One of the most interesting and satisfactory demonstrations of the
distribution of boulders by glacial ice was furnished by Guyot in
Switzerland in 1845. His observations and argument will be most readily
understood by reference to the accompanying map, taken from Lyell's clear
description.[AT] The Jura Mountains are separated from the Alps by a
valley, about eighty miles in width, which constitutes the main habitable
portion of Switzerland, and they rise upwards of two thousand feet above
it. But large Alpine boulders are found as high as two thousand feet
above the Lake Neufchâtel upon the flanks of the Jura Mountains beyond
Chasseron (at the point marked G on the map), and the whole valley is
dotted with Alpine boulders. Upon comparing these with the native rocks
in the Alps, Guyot in many cases was able to determine the exact centres
from which they were distributed, and the distribution is such as to
demonstrate that glacial ice was the medium of distribution.
[Footnote AT: Antiquity of Man, p. 299.]
[Illustration: Fig. 24.--Map showing the outline and course of flow of
the great Rhône Glacier (after Lyell).]
For example, the dotted lines upon the map indicate the motion of the
transporting medium. On ascending the valley of the Rhône to A, the
diminutive representative of the ancient glacier is still found in
existence, and is at work transporting boulders and moraines according
to the law of ice-movement. Following down the valley from A, boulders
from the head of the Rhône Valley are found distributed as far as B at
Martigny, where the valley turns at right angles towards the north. It
is evident that floating ice in a stream of water would by its momentum
be carried to the left bank, so that if icebergs were the medium of
transportation we should expect to find the boulders from the right-hand
side of the Rhône Valley distributed towards the left end of the great
valley of Switzerland--that is, in the direction of Geneva. But, instead,
the boulders derived from C, D, and E, on the Bernese Oberland side,
instead of crossing the valley at B, continue to keep on the right-hand
side and are distributed over the main valley in the direction of the
river Aar.
As is to be expected also, the direct northward motion of the ice from
B is stronger than the lateral movement to the right and left after it
emerges from the mouth of the Rhône Valley, at F, and consequently it has
pushed forwards in a straight line, so as to raise the Alpine boulders
to a greater height upon the Jura Mountains at G than anywhere else, the
upper limit of boulders at G being 1,500 feet higher than the limits at I
or K on the left and right, points distant about one hundred miles from
each other. All the boulders to the right of the line from B to G have
been derived from the right side of the Rhône, while all the boulders to
the left of that line have been derived from its left side.
A boulder of talcose granite containing 61,000 French cubic feet,
measuring about forty feet in one direction, came, according to
Charpentier, from the point _n_, near the head of the Rhône Valley, and
must have travelled one hundred and fifty miles to reach its present
position.
It scarcely needs to be added that the grooves and scratches upon the
rocks over the floor of this great valley of Switzerland indicate a
direction of the ice-movement corresponding to that implied in the
distribution of boulders. Thus, at K upon the map referred to, Lyell
reports that the abundant grooves and striæ upon the polished marble all
trend down the valley of the Aar.[AU]
[Footnote AU: Antiquity of Man, p. 305.]
Similar facts concerning the transportation of boulders have been
observed at Trogen, in Appenzel, where boulders derived from Trons,
one hundred miles distant, are found to keep upon the left bank of the
Rhine, however much the valley may wind about; and in some places, as at
Mayenfeld, it turns almost at right angles, as did the Rhône at Martigny.
Upon reaching the lower country at Lake Constance, these granite blocks
from the left side of the valley deploy out upon the same side and do not
cross over, as they would inevitably have done had they been borne along
by currents of water.
In America Ave do not have quite so easy a field as is presented
in Switzerland for the discovery of crucial instances showing that
boulders have been transported by glacial ice rather than by floating
ice, for in Switzerland the glaciated area is comparatively small and
the diminutive remnants of former glaciers are still in existence,
furnishing a comprehensive object-lesson of great interest and convincing
power. Still, it is not difficult to find decisive instances of glacial
transportation even in the broad fields of America which now retain no
living remnants of the great continental ice-sheet.
As every one who resides in or who visits New England knows, boulders are
scattered freely over all parts of that region, but for a long time the
theory suggested to account for their distribution was that of floating
ice during a period of submergence. One of the most convincing evidences
that the boulders were distributed by glacial ice rather than by icebergs
is found in Professor C. H. Hitchcock's discovery of boulders on the
summit of Mount Washington (over 6,000 feet above the sea), which he
was able to identify as derived from the ledges of light grey Bethlehem
gneiss, whose nearest outcrop is in Jefferson, several miles to the
northwest, and 3,000 or 4,000 feet lower than Mount Washington. However
difficult it may be to explain the movement of these boulders by glacial
ice, it is not impossible to do so, but the attempt to account for their
transportation by floating ice is utterly preposterous. No iceberg could
pick up boulders so far beneath the surface of the water, and even if it
could advance thus far in its work it could not by any possibility land
them afterwards upon the summit of Mount Washington.
Among the most impressive instances of boulders evidently transported
by glacial ice, rather than by icebergs, were some which came to my
notice when, in company with the late Professor H. Carvill Lewis, I was
tracing the glacial boundary across the State of Pennsylvania. We had
reached the elevated plateau (two thousand feet above the sea) which
extends westwards and southwards from the peak of Pocono Mountain, in
Monroe County. This plateau consists of level strata of sandstone, the
southern part of which is characterised by a thin sandy soil, such as is
naturally formed by the disintegration of the underlying rock, and there
is no foreign material to be found in it. But, on going northwards to
the boundary of Tobyhanna township, we at once struck a large line of
accumulations, stretching from east to west, and rising to a height of
seventy or eighty feet. This was chiefly an accumulation of transported
boulders, resembling in its structure the terminal moraines which are
found at the front of glaciers in the Alps and in Alaska, and indeed
wherever active glaciers still remain. But here we were upon the summit
of the mountain, where there are no higher levels to the north of
us, down which the ice could flow. Besides, among these boulders we
readily recognised many of granite, which must have come either from
the Adirondack Mountains, two hundred miles to the north, or from the
Canadian highlands, still farther away.
Limiting our observations simply to the boulders, we should indeed have
been at liberty to suppose that they had been transported across the
valley of the Mohawk or of the Great Lakes by floating ice during a
period of submergence. But we were forbidden to resort to this hypothesis
by the abrupt marginal line, running east and west, upon Pocono plateau,
along which these northern boulders ceased. South of this evident
terminal moraine there was no barrier, and there were no northern
boulders. On the theory of submergence, there was no reason for the
boundary-line so clearly manifested. Ice which had floated so far would
have floated farther.
Still further, on going a few miles east of the Pocono plateau, one
descends into a parallel valley, lying between Pocono Mountain and Blue
Mountain, and one thousand feet below their level. But our marginal
southern boundary of transported granite rocks did not extend much
farther south in the valley than it did on the plateau, except where we
could trace the action of a running stream, evidently corresponding to
the subglacial rivers which pour forth from the front of every extensive
glacier. In these facts, therefore, we had a crucial test of the glacial
hypothesis, and, in view of them, could maintain, against all objectors,
the theory of the distant glacial transportation of boulders, even over
vast areas of the North American continent.
Since that experience, I have traced this limit of southern boulders for
thousands of miles across the continent, according to the delineation
which may be seen in the map in a later chapter. If necessary, I could
indicate hundreds of places where the proof of glacial transportation
is almost as clear as that on the Pocono plateau in Pennsylvania. One
of the most interesting of these is on the hills in Kentucky, about
twelve miles south of the Ohio River, at Cincinnati, where I discovered
boulders of a conglomerate containing many pebbles of red jasper, which
can be identified as from a limited formation cropping out in Canada,
to the north of Lake Huron, six hundred or seven hundred miles distant.
That this was transported by glacial ice, and not by floating ice, is
evident from the fact that here, too, there was no barrier to the south,
requiring deposits to cease at that point, and from the further fact
that boulders of this material are found in increasing frequency all
the way from Kentucky to the parent ledges in Canada. With reference to
these boulders, as with reference to those found on the summit of Mount
Washington, we can reason, also, that any northerly subsidence permitting
a body of water to occupy the space between Kentucky and Lake Superior,
and deep enough to facilitate the movement across it of floating ice,
would render it impossible for the ice to have loaded itself with them.
[Illustration: Fig. 25.--Conglomerate boulder found in Boone County,
Kentucky. (See text.)]
The same line of reasoning is conclusive respecting the innumerable
boulders which cover the northern portion of Ohio, where I have my
residence. The whole State of Ohio, and indeed almost the entire
Mississippi basin between the Appalachian and the Rocky Mountains, is
completely covered, and to a great depth, with stratified rocks which
have been but slightly disturbed in the elevation of the continent; yet,
down to an irregular border-line running east and west, granitic boulders
everywhere occur in great numbers. In the locality spoken of in northern
Ohio the elevation of the country is from two hundred to five hundred
feet above the level of Lake Erie. The nearest outcrops of granitic rock
occur about four hundred miles to the north, in Canada. After the meeting
of the American Association for the Advancement of Science in Toronto
in the summer of 1889, I had the privilege of joining a company of
geologists in an excursion, conducted by members of the Canadian Survey,
to visit the region beyond Lake Nipissing, north of Lake Huron, where
the ancient Laurentian and Huronian rocks are most typically developed.
I took advantage of the trip to collect specimens of a great variety of
the granites and gneisses and metamorphic schists and trap-rock of the
region. On bringing them home I turned them over to the professor of
geology, who at once set his class at work to see if they could match my
fragments from Canada with corresponding fragments from the boulders of
the vicinity. To the great gratification, both of the pupils and myself,
they were able to do so in almost every case; and so they might have
done in any county or township to the south until reaching the limit of
glacier action which I had previously mapped. Here, at Oberlin, on the
north side of the water-shed, it is possible to imagine that we are on
the southern border of an ancient lake upon whose bosom floating ice
had brought these objects from their distant home in Canada. But this
theory would not apply to the portion of the State which is south of the
water-shed and which slopes rapidly towards the Gulf of Mexico. Yet the
distribution of boulders is practically uniform over the glaciated area
on both sides of the water-shed, constituting thus an indisputable proof
of the glacial theory.
4th. As the significance of the gravel terraces which mark the lines of
outward drainage from the glaciated area cannot well be indicated in a
single paragraph, the reader is referred for further information upon
this point to the general statements respecting them throughout the next
chapter.
CHAPTER V.
ANCIENT GLACIERS IN THE WESTERN HEMISPHERE.
_New England._
In North America all the indubitable signs of glacial action are found
over the entire area of New England, the southern coast being bordered
by a double line of terminal moraines. The outermost of these appears in
Nantucket, Martha's Vineyard, No Man's Land, Block Island, and through
the entire length of Long Island--from Montauk Point, through the centre
of the island, to Brooklyn, N. Y., and thence across Staten Island to
Perth Amboy in New Jersey. The interior line is nearly parallel with the
outer, and, beginning at the east end of Cape Cod, runs in a westerly
direction to Falmouth, and thence southwesterly through Wood's Holl, and
the Elizabeth Islands--these being, indeed, but the unsubmerged portions
of the moraine. On the mainland this interior line reappears near Point
Judith, on the south shore of Rhode Island, and, running slightly south
of west, serves to give character to the scenery at Watch Hill, and
thence crops out in the Sound as Fisher and Plum Islands, and farther
west forms the northern shore of Long Island to Port Jefferson.
[Illustration: MAP SHOWING
THE
GLACIAL GEOLOGY
OF THE
UNITED STATES.]
In these accumulations bordering the southern shore of New England, the
characteristic marks of glacial action can readily be detected even by
the casual observer, and prolonged examination will amply confirm the
first impression. The material of which they are composed is, for the
most part, foreign to the localities, and can be traced to outcrops
of rock at the north. The boulders scattered over the surface of Long
Island, for example, consist largely of granite, gneiss, hornblende, mica
slate, and red sandstone, which are easily recognised as fragments from
well-known quarries in Connecticut, Rhode Island, and Massachusetts; yet
they have been transported bodily across Long Island Sound, and deposited
in a heterogeneous mass through the entire length of the island. Not
only do they lie upon the surface, but, in digging into the lines of
hills which constitute the backbone of Long Island, these transported
boulders are found often to make up a large part of the accumulation.
Almost any of the railroad excavations in the city of Brooklyn present
an interesting object-lesson respecting the composition of a terminal
moraine.
All these things are true also of the lines of moraine farther east,
as just described. Professor Shaler has traced to its source a belt
of boulders occurring extensively over southern Rhode Island, and
found that they have spread out pretty evenly over a triangular area
to the southward, in accordance with the natural course to be pursued
by an ice-movement. Nearly all of Plymouth County, in southeastern
Massachusetts, is composed of foreign material, much of which can be
traced to the hills and mountains to the north. Even Plymouth Rock is a
boulder from the direction of Boston, and the "rock-bound" shores upon
which the Pilgrims are poetically conceived to have landed are known, in
scientific prose, as piles of glacial rubbish dumped into the edge of the
sea by the great continental ice-sheet.
The whole area of southeastern Massachusetts is dotted with conical
knolls of sand, gravel, and boulders, separated by circular masses of
peat or ponds of water, whose origin and arrangement can be accounted
for only by the peculiar agency of a decaying ice-front. Indeed, this
whole line of moraines, from the end of Cape Cod to Brooklyn, N. Y.,
consists of a reticulated network of ridges and knolls, so deposited by
the ice as to form innumerable kettle-holes which are filled with water
where other conditions are favourable. Those which are dry are so because
of their elevation above the general level, and of the looseness of the
surrounding soil; while many have been filled with a growth of peat, so
that their original character as lakelets is disguised.
As already described, these depressions, so characteristic of the
glaciated region, are, in the majority of cases, supposed to have
originated by the deposition of a great quantity of earthy material
around and upon the masses of ice belonging to the receding front of
the glacier, so that, when at length the ice melted away, a permanent
depression in the soil was left, without any outlet.
To some extent, however, the kettle-holes may have been formed by the
irregular deposition of streams of water whose courses have crossed each
other, or where eddies of considerable force have been produced in any
way. The ordinary formation of kettle-holes can be observed in progress
on the foot of almost any glacier, or, indeed, on a small scale, during
the melting away of almost any winter's snow. Where, from any cause, a
stratum of dirt has accumulated upon a mass of compact snow or ice, it
will be found to settle down in an irregular manner; furrows will be
formed in various directions by currents of water, so that the melting
will proceed irregularly, and produce upon a miniature scale exactly what
I have seen on a large scale over whole square miles of the decaying foot
of the great Muir Glacier in Alaska. The effects of similar causes and
conditions we can see on a most enormous scale in the ten thousand lakes
and ponds and peat-bogs of the whole glaciated area both in North America
and in Europe.
In addition to these two lines of evidence of glacial action in New
England, we should mention also the innumerable glacial grooves and
scratches upon the rocks which can be found on almost any freshly
uncovered surface. In New England the direction of these grooves is
ordinarily a little east of south. Upon the east coast of Massachusetts
and New Hampshire the scratches trend much more to the east than they
do over most of the interior. This is as it should be on the glacial
theory, since the ice would naturally move outwards in the line of least
resistance, which would, of course, be towards the open sea wherever
that is near. In the interior of New England the scratches upon the
rocks indicate a more southerly movement in the Connecticut Valley than
upon the mountains in the western part of Massachusetts. This also is as
it should be upon the glacial theory. The scratches upon the mountains
were made when the ice was at its greatest depth and when it moved
over the country in comparative disregard of minor irregularities of
surface, while in the valleys, at least in the later portion of the Ice
age, the movement would be obstructed except in one direction. In the
interpretation of the glacial grooves and scratches it should be borne in
mind that they often represent the work done during the closing stages
of the period. Just as the last shove of the carpenter's plane removes
the marks of the previous work, so the last rasping of a glacial movement
wears away the surfaces which have been previously polished and striated.
In various places of New England it is interesting as well as instructive
to trace the direction of the ice-movement by the distribution of
boulders. My own attention was early attracted to numerous fragments
of gneiss in eastern Massachusetts containing beautiful crystals
of feldspar, which proved to be peculiar to the region of Lake
Winnepesaukee, a hundred miles to the north, and to a narrow belt
stretching thence to the southwestward. In ascending almost any of the
lower summits of the White Mountains one's attention can scarcely
fail of being directed to the difference between the material of which
the mountains are composed and that of the numerous boulders which lie
scattered over the surface. The local geologist readily recognises these
boulders as pilgrims that have wandered far from their homes to the
northward.
Trains of boulders, such as those already described in Rhode Island, can
frequently be traced to some prominent outcrop of the rock in a hill or
mountain-peak from which they have been derived. One of the earliest
of these to attract attention occurs in the towns of Richmond, Lenox,
and Stockbridge, in the western part of Massachusetts. Here a belt of
peculiar boulders about four hundred feet wide is found to originate in
the town of Lebanon, N. Y., and to run continuously to the southeast
for a distance of nine miles. West of Fry's Hill, where the outcrop
occurs, no boulders of this variety of rock are to be found, while to
the southeast the boulders gradually diminish in size as their distance
from the outcrop increases. Near the outcrop boulders of thirty feet in
diameter occur, while nine miles away two feet is the largest diameter
observed.
Sir Charles Lyell endeavoured to explain this train of boulders by the
action of icebergs during a period of submergence--supposing that, as
icebergs floated past or away from this hill in Lebanon, N. Y., they
were the means of the regular distribution described. It is needless to
repeat the difficulties arising in connection with such a theory, since
now both by observation and experiment we have become more familiar
with the movement of glacial ice. What we have already said about the
transportation of boulders over Switzerland by the Alpine glaciers, and
what is open to observation at the present time upon the large glaciers
of Alaska, closely agree with the facts concerning this Richmond train of
boulders, and we have no occasion to look further for a cause.
Indeed, trains of boulders ought to appear almost everywhere over
the glaciated area; and so they do where all the circumstances are
favourable. But, readily to identify the train, requires that to furnish
the boulders there should be in the line of the ice-movement a projecting
mass of rock hard enough to offer considerable resistance to the abrading
agency of the ice and characteristic enough in its composition to be
readily recognised. Ship Rock, in Peabody, Mass., weighing about eleven
hundred tons, and Mohegan Rock, in Montville, Conn., weighing about ten
thousand tons, have ordinarily been pointed to as boulders illustrating
the power of ice-action. Their glacial character, however, has been
challenged from the fact that the variety of granite to which they
belong occurs in the neighbourhood, and indeed constitutes the bed-rock
upon which they rest.[AV] Some would therefore consider them, like some
of which we have already spoken, to be boulders which have originated
through the disintegration of great masses of rock, of which these were
harder nuclei that have longer resisted the ravages of the tooth of time.
It must be admitted that possibly this explanation is correct; but it
is scarcely probable that, in a region where there are so many other
evidences of glacial action, these boulders could have remained immovable
in presence of the onward progress of the ice-current that certainly
passed over them.
[Footnote AV: Popular Science Monthly, vol. xxxvii, pp. 196-201.]
However, as already seen, we are not left to doubt as to the movement
of some boulders of great size. That which now claims the reputation
of being the largest in New England is in Madison, N. H., and measures
thirty by forty by seventy-five feet. This can be traced to ledges of
Conway granite, about two miles away.[AW] Many boulders in the vicinity
of New Haven, Conn., can be identified, as from well-known trap-dykes,
sixteen miles or more to the north. The so-called Judge's Cave, on West
Rock, 365 feet above the adjoining valley and weighing a thousand tons,
is one of these. Professor Edward Orton[AX] describes a mass of Clinton
limestone near Freeport, Warren County, Ohio, as covering an area of
three-fourths of an acre, and as sixteen feet in thickness. It overlies
glacial clays and gravels, and must have been transported bodily from the
elevations containing this rock several miles to the northwest.
[Footnote AW: See W. 0. Crosby's paper in Appalachia, vol. vi, pp. 59-70.]
[Footnote AX: Geological Survey of Ohio, vol. iii, p. 385,]
[Illustration: Fig. 26.--Mohegan Rock.]
Portions of New England present the best illustrations anywhere afforded
in America of what are called "drumlins." These are "lenticular-shaped"
hills, composed of till, and containing, interspersed through their mass,
numerous scratched stones of all sizes. They vary in length from a few
hundred feet to a mile, and are usually from half to two-thirds as wide
as they are long. In height they vary from twenty-five to two hundred
feet.
But, according to the description of Mr. Upham, whatever may be their
size and height, they are singularly alike in outline and form, usually
having steep sides, with gently sloping, rounded tops, and presenting a
very smooth and regular contour. From this resemblance in shape to an
elliptical convex lens, Professor Hitchcock has called them lenticular
hills to distinguish these deposits of till from the broadly flattened or
undulating sheets which are common throughout New England.
[Illustration: Fig. 27.--Drumlins in Goffstown, N. H. (Hitchcock).]
The trend, or direction of the longer axis, of these lenticular hills is
nearly the same for all of them comprised within any limited area, and is
approximately like the course of the striæ or glacial furrows marked upon
the neighbouring ledges. In eastern Massachusetts and New Hampshire,
within twenty-five miles of the coast, it is quite uniformly to the
southeast, or east-southeast. Farther inland, in both of these States,
it is generally from north to south, or a few degrees east of south;
while in the valley of the Connecticut River it is frequently a little to
the west of south. In New Hampshire, besides its accumulation in these
hills, the till is frequently amassed in slopes of similar lenticular
form. These have their position almost invariably upon either the south
or north side of the ledgy hills against which they rest, showing a
considerable deflection towards the southeast and northwest in the east
part of the State. It cannot be doubted that the trend of the lenticular
hills, and the direction taken by these slopes, have been determined
by the glacial current, which produced the striæ with which they are
parallel.[AY]
[Footnote AY: Proceedings of the Boston Society of Natural History, vol.
xx, pp. 224, 225.]
Drumlins are abundant in the vicinity of Boston, and constitute nearly
all the islands in Boston Harbour. On the mainland, Beacon Hill, Bunker
Hill, Green Hill, Powderhorn Hill, Tufts College Hill, Winter Hill, Mount
Ida, Corey Hill, Parker Hill, Wollaston Heights, Prospect Hill, and
Telegraph Hill are specimens.
The northeastern corner of Massachusetts and the southeastern corner
of New Hampshire are largely covered with these peculiar-shaped
glacial deposits, while they are numerous as far west as Fitchburg,
in Massachusetts, and Ware, N. H., and in the northeastern part of
Connecticut. A little later, also, we shall refer to an interesting line
of them in central New York. Elsewhere in America, except in a portion of
Wisconsin, they rarely occur in such fine development as in New England.
In Europe they are best developed in portions of Ireland.
One's first impression in examining an exposed section of a drumlin
would lead him to think that the mass was entirely unstratified; but
closer examination shows that there is a coarse stratification, but
evidently not produced by water-action. The accumulation has probably
taken place gradually by successive deposits underneath the glacier
itself. Professor William M. Davis has suggested a plausible explanation
which we will briefly state.
[Illustration: Fig. 28.--Drumlins in the vicinity of Boston (Davis).]
The frequency with which drumlins are found to rest upon a mass of
projecting rock, the general co-ordination of the direction of their
axes with the direction of the scratches upon the underlying rock, and
the abundance of scratched stones in them, all support the theory that
drumlins are formed underneath the ice-sheet, somewhat in the way that
islands and bars of silt are formed in the delta of a great river. The
movement of ice seems to have been concentrated in pretty definite
lines, often determined by the contour of the bottom, leaving a slacker
movement in intervening areas, which were evidently protected in some
cases by projecting masses of rock. In these areas of slower movement
there was naturally an accumulation at the same time that there was
vigorous erosion in the lines of more rapid movement.
There was doubtless a continual transfer of material from the end of the
drumlin which abutted against the moving mass of ice to the lower end,
as there is in the formation of an island in a river. If time enough had
elapsed, the whole accumulation would have been levelled by the glacier
and spread over the broader area where the more rapid lines of movement
became confluent, and where the differential motion was less marked.
Drumlins are thus characteristic of areas in the glaciated region whose
floor was originally only moderately irregular, and where there was an
excessive amount of ground-moraine to be transported, and where the
movement did not continue indefinitely. It has been suggested, also,
that some of the long belts of territory in New England and central New
York covered by drumlins may represent old terminal moraines which were
subsequently surmounted by a readvance of the ice, and partially wrought
over into their present shape.
It is in New England, also, that kames are to be found in better
development than anywhere else in America. These interesting remnants of
the Glacial age are clearly described by Mr. James Geikie. His account
will serve as well for New England as for Scotland.
The sands and gravels have a tendency to shape themselves into mounds
and winding ridges, which give a hummocky and rapidly undulating outline
to the ground. Indeed, so characteristic is this appearance, that by it
alone we are often able to mark out the boundaries of the deposits with
as much precision as we could were all the vegetation and soil stripped
away and the various subsoils laid bare. Occasionally, ridges may be
tracked continuously for several miles, running like great artificial
ramparts across the country. These vary in breadth and height, some of
the more conspicuous ones being upward of four or five hundred feet
broad at the base, and sloping upward at an angle of twenty-five or even
thirty-five degrees, to a height of sixty feet and more above the general
surface of the ground. It is most common, however, to find mounds and
ridges confusedly intermingled, crossing and recrossing each other at all
angles, so as to enclose deep hollows and pits between. Seen from some
dominant point, such an assemblage of kames, as they are called, looks
like a tumbled sea--the ground now swelling into long undulations, now
rising suddenly into beautiful peaks and cones, and anon curving up in
sharp ridges that often wheel suddenly round so as to enclose a lakelet
of bright clear water.[AZ]
[Footnote AZ: The Great Ice Age, pp. 210, 211.]
[Illustration: Fig. 29.--Section of kame near Dover, New Hampshire.
Length, three hundred feet; height, forty feet; base, about forty feet
above the Cocheco River, or seventy-five feet above the sea. _a_, _a_,
gray clay; _b_, fine sand; _c_, _c_, coarse gravel containing pebbles
from six inches to one foot and a half in diameter; _d_, _d_, fine gravel
(Upham).]
[Illustration: Fig. 30.--Kames in Andover Mass.]
In New England attention was first directed to kames in 1842, by
President Edward Hitchcock, in a paper before the American Association
of Geologists and Naturalists, describing the gravel ridges in Andover,
Mass. In the accompanying plate is shown a portion of this kame system,
which has a double interest to me from the fact that it was while living
upon the banks of the Shawshin River, near where the kames and the river
intersect, that I began, in 1874, my special study of glacial deposits.
The Andover ridges are composed of imperfectly stratified water-worn
material, and are very sharply defined, from the town of Chelsea, back
from the coast into New Hampshire, for a distance of twenty-five miles.
The base of the ridges does not maintain a uniform level, but the system
descends into shallow valleys, and rises over elevations of one hundred
to two hundred feet, without interruption. This indifference to slight
changes of level is specially noticeable where the system crosses the
Merrimac River, just above the city of Lawrence. It is also represented
in the accompanying plate, where the base of the ridges in the immediate
valley of the Shawshin is fifty feet lower than the base of those a short
distance to the north, at the points marked _a_, _b_, and _c_. The ridges
here terminate at the surface in a sharp angle, and are above their base
forty-one feet at _a_, forty-nine feet at _b_, and ninety-one feet at
_c_. Between _c_ and _b_ there is an extensive peat-swamp, filling the
depression up to the level of an outlet through which the surplus water
has found a passage.
[Illustration: Fig. 31.--Longitudinal kames near Hingham, Massachusetts.
The parallel ridges of gravel in the foreground run nearly east and west,
and coalesce at each end, near the edges of the picture, to form an
elongated kettle-hole. The ridges from fifty to sixty feet in height. The
kame-stream was here evidently emptying into the ocean a few miles to the
east (Bouvé).]
Several systems of kames approximately parallel to this have been
traced out in Massachusetts and New Hampshire, while the remnants of
a very extensive system are found in the Connecticut Valley above the
Massachusetts line. But they abound in greatest profusion in the State
of Maine, where Professor George H. Stone has plotted them with much
care. The accompanying map gives only an imperfect representation of the
ramifying systems which he has traced out, and of the extent to which
they are independent of the present river-channels. One of the longest
of these extends more than one hundred miles, crossing the Penobscot
River nearly opposite Grand Lake, and terminating in an extensive delta
of gravel and sand in Cherryfield, nearly north of Mount Desert. This
is represented on our map by the shaded portion west of the Machias
River. Locally these ridges are variously designated as "horsebacks,"
"hogbacks," or "whalebacks," but that in Andover, Mass., was for some
reason called "Indian Ridge." Nowhere else in the world are these ridges
better developed than in New England, except it be in southern Sweden,
where they have long been known and carefully mapped.
[Illustration: Fig. 32.--The kames of Maine and southeastern New
Hampshire. (Stone.)]
The investigations of Mr. W. 0. Crosby upon the composition of till in
eastern Massachusetts is sufficiently important in its bearings upon the
question of glacial erosion to merit notice at this point.[BA] The object
of his investigations was to determine how much of the so-called ground
moraine, or till, consisted of material disintegrated by mechanical
action, and how much by chemical action. The "residuary clay," which has
arisen from chemical decomposition, would properly be attributed to the
disintegrating agencies of preglacial times, while the clay, which is
strictly mechanical in its origin, remains to represent the true "grist"
or "rock flour" of the Glacial period.
[Footnote BA: Proceedings of the Boston Society of Natural History, vol.
xxv (1890), pp. 115-140.]
The results of Mr. Crosby's investigations show that "not more than
one-third of the _detritus_ composing the till of the Boston Basin was in
existence before the Ice age, and that the remaining two-thirds must be
attributed to the mechanical action of the ice-sheet and its accompanying
torrents of water. In other words, if we assume the average thickness
of the drift as thirty feet, the amount of glacial erosion can scarcely
fall below twenty feet. After scraping away the residuary clays and
half-decomposed material, the ice-sheet has cut more than an equal depth
into the solid rocks."
Mr. Crosby's investigations also convinced him that the movement of the
till, or ground moraine, underneath the ice was not _en masse_, but that
"it must have experienced differential horizontal movements or flowing,
in which, normally, every particle or fragment slipped or was squeezed
forward with reference to those immediately below it, the velocity
diminishing downward through the friction of the underlying ledges....
The glaciation was not limited to masses which were firmly caught between
the ice and the solid ledges, and it was in every case essentially a
slipping and not a rolling movement.... These differential horizontal
movements mean that the till acted as a lubricant for the ice-sheet;
and the clayey element, especially, co-operating in many cases with the
pent-up subglacial waters, must have greatly facilitated the onward
progress of the ice." He concludes, therefore, that the onward movement
of the vast ice-sheet greatly exceeded that of the main part of the
ground moraine, the ice-sheet slipping over the till, the whole being
in some degree analogous to that of a great land-slip. "In both cases
the progress of a somewhat yielding and mobile mass is facilitated by an
underlying clayey layer saturated with water."
_New York, New Jersey, and Pennsylvania._
West of New England the glacial phenomena over the northern part of the
United States are equally marked all the way to the Missouri River, and
the boundary-line of the glaciated region can be traced with little
difficulty. It emerges from New York Bay on Staten Island and enters New
Jersey at Perth Amboy. A well-formed moraine covers the northern part
of Staten Island, and upon the mainland marks the boundary from Perth
Amboy, around through Raritan, Plainfield, Chatham, Morris, and Hanover,
to Rockaway, and thence in a southwesterly direction to Belvidere, on
the Delaware River. That portion of New Jersey lying north of this
serpentine line of moraine hills is characterised by the presence of
transported boulders, by numerous lakes of evident glacial origin, and by
every other sign of glacial action, while south of it all these peculiar
characteristics are absent. The observant passenger upon the railroad
trains between New York and Philadelphia can easily recognise the
moraine as it is passed through on the Pennsylvania Railroad at Metuchen
and on the Bound Brook Railroad at Plainfield. Near Drakestown, in
Morris County, there is a mass of blue limestone measuring, as exposed,
thirty-six by thirty feet, and which was quarried for years before
discovering that it was a boulder brought with other drift material from
many miles to the northwest and lodged here a thousand feet above the sea.
Across Pennsylvania the glacial boundary passes through Northampton,
Monroe, Luzerne, Columbia, Sullivan, Lycoming, Tioga, and Potter
Counties, where it enters the State of New York, running still in a
northwest direction through Allegany and Cattaraugus Counties to the
vicinity of Salamanca. Here it turns to the south nearly at a right
angle, running southwestward to Chautauqua County and re-entering
Pennsylvania in Warren County, and thence passing onward in the same
general direction through Crawford, Venango, Mercer, Butler, and Lawrence
Counties to the Ohio line in Columbiana County, about ten miles north of
the Ohio River.
The occurrence of a well-defined terminal moraine to mark the glacial
boundary eastward from Pennsylvania led Professor Lewis and myself, who
made the survey of that State in 1880, to be rather too sanguine in
our expectations of finding an equally well-marked moraine everywhere
along the southern margin of the glaciated area; still, the results are
even more interesting than would have been the exact fulfilment of our
expectations, since they more fully revealed to us the great complexity
of effect which is capable of being brought about by ice-action. Before
proceeding farther with the details, therefore, it will be profitable
at this point to pause in the narrative and briefly record a few
generalisations that have forced themselves into prominence during the
years in which field-work has been in progress.
Previous to our explorations in Pennsylvania it had been thought that the
indications of ice-action would extend much farther south in the valleys
than on the mountains, and this indeed would have been the case if the
glaciers in northern Pennsylvania had been of local origin; but our
experience very soon demonstrated that the great gathering-place of the
snows which produced the glacial movement in northern Pennsylvania could
not have been local, but that over the northern part of that State there
was distinct evidence of a continental movement of ice whose centre was
far beyond the Alleghanies.
For example, we found that the evidences of direct glacial action
extended farther south upon the hills and plateaus than they did in the
narrow valleys, while everywhere on the very southern border of glacial
indications we found boulders that had been brought from the granitic
region of northern New York or central Canada. In eastern Pennsylvania
we found indeed a terminal moraine more or less distinctly marking the
southern border over the highlands. This was more specially true in
Northampton and Monroe Counties.
In Northampton County it was very interesting to see long lines of hills,
a hundred or more feet in height and lying several hundred feet above
the Delaware River, composed entirely of glacial _débris_, much of which
had been brought bodily over the sharp summit of the Blue Ridge, or
Kittatinny Mountain, which rises as a continuous wall to the northwest
and is everywhere several hundred feet higher than the moraine in
Northampton County. The summit of Blue Ridge, also, as far south as the
glacial movement extended, shows evident signs of glacial abrasion, some
hundreds of feet evidently having been removed by that means, leaving a
well-defined shoulder, marking the limits of its southwestern border.
Resting upon the summit of the glaciated portion of the Blue Ridge, there
are also numerous boulders of Helderberg limestone, which must have been
brought from ledges at least five hundred feet lower than the places upon
which they now lie.
In Monroe County the terminal moraine marking there the extreme limit
of the ice-movement is upon an extensive plateau of Pocono sandstone,
about eighteen hundred feet above sea-level, and five or six hundred
feet lower than the crest of the Alleghany Mountains, a short distance
to the north. The moraine hills are here well marked by the occurrence
of circular lakelets and kettle-holes (such as have been described
as characteristic of the shores and islands bordering the south of
New England); by the occurrence of granitic boulders, which must have
been brought from the Adirondacks or Canada; and by the various other
indications referred to on a previous page.
As already intimated, the instructive point in our observations is the
fact that, between Kittatinny Mountain, in Northampton County, and Pocono
plateau, in Monroe County, there is a longitudinal depression, running
northeast by southwest, parallel with the ranges of the mountain system,
which is here about a thousand feet below the respective ridges on either
side. This, therefore, is one of the places where we should have expected
a considerable southern extension of the ice, if it had been largely due
to local causes. Now, while there is indeed a gradual southern trend down
the flanks of the mountain, yet, upon reaching the axis of the valley,
there appears at once a very marked change in the character of the
deposit, and the influence of powerful streams of water becomes manifest,
and it is evident, upon a slight inspection, that we have come upon a
line of drainage which sustained a peculiar relation to the continental
ice-sheet.
From Stroudsburg, near the Delaware Water-Gap, to Weissport, on the
Lehigh River, a distance of about thirty miles, the valley between the
mountains is continuous, and the elevation at each end very nearly the
same. But about half-way between the two places, near Saylorsburg, there
is a river-parting from which the water now runs on the one hand north
to Stroudsburg, and thence to the Delaware River, and on the other hand
south, through Big and Aquonchichola Creeks, to the Lehigh River. The
river-parting is formed by a great accumulation of gravel, whose summit
is about two hundred feet above the level of the valleys into which
the creeks empty at either end; and there are numerous kettle-holes and
lakelets in the vicinity, such as characterize the glacial region in
general.
In short, we are, without doubt, here on a well-marked terminal moraine
much modified by strong water-action in a valley of glacial drainage.
The gravel and boulders are all well water-worn, and the material is of
various kinds, including granite boulders from the far north, such as
characterise the terminal moraine on the highlands; but the pebbles are
not scratched, and the gravel is more or less stratified. It is evident
that we are here where a violent stream of water poured forth from that
portion of the ice-front which filled this valley, and which found its
only outlet in the direction of the Lehigh River. The gravel can be
traced in diminishing quantities to the southward, in accordance with
this theory, while to the northward there extends a series of gravel
ridges, or kames, such as we have shown naturally to owe their origin to
the accumulations taking place in ice-channels formed near the front of a
glacier as it slowly melts away.
From similar occurrences of vast gravel accumulations in other valleys
stretching southward from the glacial margin, we came to expect that,
wherever there was an open, line of drainage from the glaciated region
southward, the point of intersection between the glacial margin and
the drainage valley would be marked by an excessive accumulation of
water-worn gravel, diminishing in coarseness and abundance down the
valleys in proportion to the distance from the glacial margin.
For example, the Delaware River emerges from the glaciated region at
Belvidere, and there are there vast accumulations of gravel rising a
hundred or more feet above the present level of the river, while gravel
terraces, diminishing in height, mark the river below to tide-water at
Trenton. The Lehigh River leaves the glaciated region at Hickory Run, a
few miles above Mauch Chunk, but the gorge is so steep that there was
little opportunity either for the accumulation of gravel there or for its
preservation. Still, the transported gravel and boulders characteristic
of the melting floods pouring forth from a glacier, are found lining the
banks of the Lehigh all along the lower portion of its course. In the
Susquehanna River we have a better example at Beach Haven, in Luzerne
County, where there are very extensive accumulations of gravel resting
on the true glacial deposits of the valley, and extending down the river
in terraces of regularly diminishing height for many miles, and merging
into terraces of moderate elevation which line the Susquehanna Valley
throughout the rest of its course. Above Beach Haven the gravel deposits
in the trough of the river valley are more irregular, and betray the
modifying influence of the slowly decaying masses of ice which belonged
to the enveloping continental glacier.
Westward from the north fork of the Susquehanna, similar extensive
accumulations of gravel occur at the intersection of Fishing Creek in
Columbia County, Muncy, Loyalsock, Lycoming, and Pine Creeks in Lycoming
County, all tributary to the Susquehanna River, and all evidently being
channels through which the melting floods of the ice-sheet brought
vast quantities of gravel down to the main stream. Williamsport, on
the West Branch of the Susquehanna, is built upon an extensive terrace
containing much granitic material, brought down from the glaciated region
by Lycoming Creek, when it was flooded with the waters melted from the
continental ice-sheet which had here surmounted the Alleghanies and
invaded the valley of the Susquehanna.
Analogous deposits of unusual amounts of gravel, occurring in streams
flowing southward from the glaciated region, occur at Great Valley,
Little Valley, and Steamburg in Cattaraugus County, New York, and
at Russelburg and Garland in Warren County, Pennsylvania, also at
Titusville and Franklin in Venango County, and at Wampum in Lawrence
County, of the same State.
As a rule, Professor Lewis and myself found it more difficult to
determine with accuracy the exact point to which the ice extended in
the axis of these south-flowing valleys than we did upon the highlands
upon either side; and, in looking for the positive indications of direct
ice-action in these lines of drainage, we were almost always led up
the valley to a considerable distance inside of the line. This arose
from our inexperience in interpreting the phenomena, or rather from
our inattention to the well-known determining facts in the problem. On
further reflection it readily appeared that this was as it should be. The
ice-front, instead of extending farther down in a narrow valley than on
the adjoining highlands (where they are of only moderate elevation) ought
not to extend so far, for the subglacial streams would not only wear away
the ice of themselves, but would admit the air into the tunnels formed by
them so as to melt the masses both from below and from above, and thus
cause a recession of the front. If we had understood this principle at
the beginning of our survey, it would have saved us much perplexity and
trouble.
A single further illustration of this point will help to an understanding
of many references which will hereafter be made to the water deposits
which accumulated in the lines of drainage running southward from the
glaciated area. At Warren, Pa., Conewango Creek, which is the outlet
from Chautauqua Lake, enters the Alleghany River after flowing for a
number of miles in a deep valley with moderate slopes. In ascending the
creek from Warren, the gravel terraces, which rise twenty-five or thirty
feet above high-water mark, rapidly increase in breadth and height, and
the pebbles become more and more coarse. After a certain distance the
regular terraces begin to give place to irregular accumulations of gravel
in ridges and knobs. In the lower portion of the valley no pebbles
could be found which were scratched. Up the valley a few miles pebbles
were occasionally discovered which showed some slight indications of
having been scratched, but which had been subjected to such an amount of
abrasion by water-action as almost to erase the scratches. On reaching
Ackley's Station, the stream is found to be cutting through a regular
terminal moraine, extending across the valley and full of clearly marked
glaciated stones. Above this terminal moraine the terraces and gravel
ridges which had characterised the valley below disappear, giving place
to long stretches of level and swampy land, which had been subject to
overflow.
Something similar to this so often appears, that there can be no
question as to its meaning, which is, that during the farthest extent
of the ice the front rested for a considerable period of time along the
line marked by the terminal moraine. During this period there occurred
both the accumulation of the moraine and of the gravel terraces in the
valley below, due to the vast flow of water emerging from the ice-front,
especially during the period when it was most rapidly melting away. Upon
the retreat of the ice, the moraine constituted a dam which has not yet
been wholly worn away. For a while the water was so effectually ponded
back by this as to form a lake, which has since become filled up with
sediment and accumulations of peat. From this it is evident, also, that
when the ice began to retreat, the retreat was so continuous and rapid
that no parallel terminal moraines were formed for many miles.
Before leaving this section we will summarise the leading facts
concerning the glacial phenomena north of Pennsylvania and New Jersey.
From the observations of Professor Smock, it appears that, from the
southern margin the ascent to the summit of the ice-sheet was pretty
rapid; the depth one mile back from the margin being not much less
than a thousand feet. "Northward the angle of the slope diminished, and
the glacier surface approximated to a great level plain. The distance
between the high southwestern peaks of the Catskills and Pocono Knob
in Pennsylvania is sixty miles. The difference in the elevation of the
glacier could not have exceeded a thousand feet,"[BB] that is, the slope
of the surface was about seventeen feet to the mile.
[Footnote BB: American Journal of Science, vol. cxxv, 1883, p. 339 _et
seq._]
Professor Dana estimates the thickness of the ice in southern Connecticut
to have been between fifteen hundred and two thousand feet. Attempts to
calculate the thickness of the ice farther north, except from actual
discovery of glacial action on the summits of the mountains, are based
upon uncertain data with reference to the slope necessary to secure
glacial movement. In the Alps the lowest mean slopes down which glaciers
move are about two hundred and fifty feet to a mile; but in Greenland,
Jensen found the slope of the Frederickshaab Glacier to be only
seventy-five feet to the mile, while Helland found that of the Jakobshavn
Glacier to be only forty-five feet.
It is doubtful if even that amount is necessary to secure a continental
movement of ice, since, as already remarked, it is unsafe to draw
inferences concerning the movements of large masses of ice from those of
smaller masses in more constricted areas. We have seen, from the glacial
deposits on the top of Mount Washington, that over the northern part of
New England the ice was more than a mile in depth. We have no direct
evidence of the depth of the stream which surrounded the Adirondack
Mountains. Nor, on the other hand, are we certain that the Catskills
were not completely enveloped in ice, though most observers, reasoning
from negative evidence, have supposed that to be the case. But from the
facts stated concerning the boulders along the glacial boundary in
Pennsylvania, it is certain that the ice was deep enough to surmount
the ridge of the Alleghanies where they are two thousand and more feet
in height. At the least calculation the ice must have been five hundred
feet thick, in order to secure the movement of which there is evidence
across the Appalachian range. Supposing this to be the height of the ice
above the sea on the crest of the Alleghanies, and that the slope of the
surface of the ice-sheet was as moderate as Professor Smock has estimated
it (namely seventeen feet to the mile), the ice would be upwards of
six thousand feet in thickness in the latitude of the Adirondacks,
which corresponds closely with the positive evidence Ave have from the
mountains in New England.
A study of the map of New York will make it easy to understand the
distribution of some interesting glacial marks over the State. The
distance along the Hudson from the glacial boundary in the vicinity of
New York to the valley of the Mohawk is about one hundred and sixty
miles. Prom the glacial boundary at Salamanca, N. Y., to the same valley,
is not over eighty miles. It is easy to see, therefore, that when, in
advancing, the ice moved southward past the Adirondacks, the east end
of the valley of the Mohawk was reached and closed by the ice, while at
the west end of Lake Ontario the ice-front was still in Canada. Thus the
drainage, which naturally followed the course of the St. Lawrence, would
first be turned through the Mohawk. Afterwards, when the Mohawk had been
closed by ice, the vast amount of ponded water was compelled to seek a
temporary outlet over the lower passages leading into the Susquehanna or
into the Alleghany.
A number of such passages exist. One can be traced along the line of the
old canal from Utica to Binghamton, whose highest level is not far from
eleven hundred feet. Another lies in a valley leading south of Cayuga
Lake, whose highest point, at Wilseyville, is nine hundred and forty
feet above tide. Another leads south to the Chemung River from Seneca
Lake, whose highest point, at Horseheads, is less than nine hundred feet
above tide. The cols farther west are somewhat more elevated; the one at
Portage, leading from the Genesee River into the Canisteo, being upwards
of thirteen hundred feet, and that of Dayton, leading from Cattaraugus
Creek into the Conewango, being about the same. Of other southern outlets
farther west we will speak later on.
Fixing our minds now upon the region under consideration, in the southern
part of the State of New York, we can readily see that a glacial lake
must have existed in front of the ice while it was advancing, until it
had reached the river-partings between the Mohawk and the St. Lawrence
Rivers on the north and the Susquehanna and Alleghany Rivers on the
south. After the ice had attained its maximum extension, and was in
process of retreat, there would be a repetition of the phenomena, only
they would occur in the reverse order. The glacial markings which we see
are, of course, mainly those produced during the general retreat of the
ice.
The Susquehanna River stretching out its arms--the Chenango and Chemung
Rivers--to the east and the west, evidently serves as a line of drainage
for the vast glacial floods. These floods have left, along their courses,
extensive elevated gravel terraces, with much material in them which
is not local, but which has been washed out of the direct glacial
deposits from the far north. The east-and-west line of the water-parting
throughout the State is characterised by excessive accumulations of
glaciated material, forming something like a terminal moraine, and is
designated by President Chamberlin as "the terminal moraine of the second
Glacial epoch," corresponding, as he thinks, to the interior line already
described as characterising the south shore of New England.
In the central part of New York the remarkable series of "Finger Lakes,"
tributary to Lake Ontario and emptying into it through the Oswego and
Genesee Rivers, all have a glacial origin. Probably, however, they are
not due in any great degree to glacial erosion, but they seem to occupy
north-and-south valleys which had been largely formed by streams running
towards the St. Lawrence when there was, by some means (probably through
the Mohawk River), a much deeper outlet than now exists, but which has
been filled up and obliterated by glacial _débris_. The ice-movement
naturally centred itself more or less in these north-and-south valleys,
and hence somewhat enlarged them, but probably did not deepen them. The
ice, however, did prevent them from becoming filled with sediment, and on
its final retreat gave place to water.
Between these lakes and Lake Ontario, also, and extending east and west
nearly all the way from Syracuse to Rochester, there is a remarkable
series of hills, from one hundred to two or three hundred feet in height,
composed of glacial _débris_. But while the range extends east and west,
the axis of the individual hills lies nearly north and south. These are
probably remnants of a morainic accumulation which were made during
a pause in the first advance of the ice, and were finally sculptured
into their present shape by the onward movement of the ice. These are
really "drumlins," similar to those already described in northeastern
Massachusetts and southeastern New Hampshire. In the valley of central
New York these have determined the lines of drainage of the "Finger
Lakes," and formed dams across the natural outlets of nearly all of them.
North of the State of New York the innumerable lakes in Canada are all
of glacial origin, being mostly due to depressions of the nature of
kettle-holes, or to the damming up of old outlets by glacial deposits. A
pretty well-marked line of moraine hills, formed probably as terminal
deposits in the later stages of the Ice age, runs from near the eastern
end of Lake Ontario to the Georgian Bay, passing south of Lake Simcoe.
_The Mississippi Basin._
The physical geography of the glaciated region north of the Ohio River is
so much simpler than that of New England and the Middle States, that its
characteristics can be briefly stated. Ohio, Indiana, and Illinois are
covered with nearly parallel strata of rock mostly of the Carboniferous
age. In general, the surface slopes gently to the west; the average
elevation of Ohio being about a thousand feet above tide, while that of
the Great Lakes to the north and of the middle portion of the Mississippi
Valley is less than six hundred feet. The glacial deposits are spread in
a pretty even sheet over the area which was reached by the ice in these
States, and the lines of moraine, of which a dozen or more have been
partially traced in receding order, are much less clearly marked than
they are in New England, or in Michigan, and the States farther to the
northwest.
The line marking the southern limit attained by the ice of the Glacial
period in these three States is as follows: Entering Ohio in Columbiana
County, about ten miles north of the Ohio River, the glacial boundary
runs westward through New Lisbon to Canton in Stark County, and thence
to Millersburg in Holmes County. A few miles west of this place it
turns abruptly south, passing through Danville in Knox County, Newark
in Licking County, Lancaster in Fairfield County, to Adelphi in Ross
County. Thence bearing more westward it passes through Chillicothe
to southeastern Highland County and northwestern Adams, reaching the
Ohio River near Ripley, in Clermont County. Thence, following the
north bank of the Ohio River to Cincinnati, it crosses the river, and
after extending through the northern part of Boone County, Kentucky,
and recrossing the river to Indiana, not far from Rising Sun, it again
follows approximately the north bank of the river to within about ten
miles of Louisville, Ky., where it bends northward running through
Clarke, Scott, Jackson, Bartholomew, and Brown Counties to Martinsville,
in Morgan County, where it turns again west and south and follows
approximately the West Branch of the White River through Owen, Greene,
and Knox Counties, where it crosses the main stream of White River, and,
continuing through Gibson and Posey Counties, crosses the Wabash River
near New Harmony.
In Illinois the line still continues southwesterly through White,
Gallatin, Saline, and Williamson Counties, where it reaches its southern
limit near Carbondale, in latitude 37° 40', and from this point trends
northwestward, approximately following the northeastern bluff of the
Mississippi River, to the vicinity of Carondelet, Mo., a short distance
south of St. Louis.
Beyond the Mississippi the line follows approximately the course of the
Missouri River across Missouri, and continues westward to the vicinity of
Manhattan, in Kansas, where it turns northward, keeping about a hundred
miles west of the Missouri River, through eastern Kansas and Nebraska,
and striking the river near the mouth of the Niobrara, in South Dakota.
From there the line follows approximately the course of the Missouri
River to the vicinity of Fort Benton, in northwestern Montana, where the
line again bears more northward, running into British America.
It is still in dispute whether the ice extended from the eastern centre
far enough west to join the ice-movement from the Rocky Mountain
plateau. Dr. George M. Dawson[BC] is of the opinion that it did not, but
that there was a belt of a hundred miles or more, east of the Rocky
Mountains, which was never covered by true glacial ice. Mr. Upham[BD]
is equally confident that the two ice-movements became confluent,
and united upon the western plateau of Manitoba. The opportunity
for such a difference of opinion arises in the difficulty sometimes
encountered of distinguishing between a direct glacial deposit and a
deposit taking place in water containing boulder-laden icebergs. Where
Mr. Upham supposes the ice-fields of the east and of the west to have
been confluent in western Manitoba, Dr. Dawson supposes there was an
extensive subsidence of the land sufficient to admit the waters of the
ocean. Leaving this question for the present undetermined, we will now
rapidly summarise the glacial phenomena west of the third meridian
from Washington (which corresponds nearly with the western boundary of
Pennsylvania), and east of the Rocky Mountains.
[Footnote BC: Transactions of the Royal Society of Canada, vol. viii,
sec. iv, pp. 54-74.]
[Footnote BD: American Geologist, vol. vi, September, 1890; Bulletin of
the Geological Society of America, vol. ii, pp. 243-276.]
That the glacial movement extended to the southern boundary just
delineated is established by the presence down to that line of all the
signs of glacial action, and their absence beyond. Glacial groovings are
found upon the freshly uncovered rock surfaces at frequent intervals in
close proximity to the line all along its course, while granitic boulders
from the far north are scattered, with more or less regularity, over the
whole intervening space between this line and the Canadian highlands.
I have already referred to a boulder of jasper conglomerate found in
Boone County, Kentucky, which must have come from unique outcroppings of
this rock north of Lake Huron. Granitic boulders from the Lake Superior
region are also found in great abundance at the extreme margin mentioned
in southern Illinois. West of the Missouri River it is somewhat more
difficult to delineate the boundary with accuracy, on account of an
enveloping deposit of fine loam, technically called "loess." Loess is
very abundant in the whole valley of the Missouri River below Yankton,
South Dakota, being for a long distance in the vicinity of the river
a hundred feet or more in depth. Over northern Missouri and southern
Illinois the deposit is nearly continuous, but less in depth, and
everywhere in that region tends to hide from view the unstratified
glacial deposit continuously underlying it.
A single instance of personal experience will illustrate the condition of
things. While going south from Chicago, in search of the southern limit
of glacial action, I stopped off from the train at Du Quoin, about forty
miles north of where I subsequently found the boundary. Here the whole
surface was covered with loess, two or three feet in depth. Below this
was a gravelly soil, three or four feet in thickness, which contained
many scratched pebbles of granite. A well which had recently been dug,
reached the rock at a depth of twenty feet, and revealed a beautifully
polished and scratched surface, betraying, beyond question, the action
of glacial ice. As we shall show a little later, it is probable that,
about the time the ice of the Glacial period had reached its maximum
development, this area, which is covered with loess, was depressed in
level, and remained under water during a considerable portion of the
period when the ice-front was retreating.
[Illustration: Fig. 33.--Western face of the kettle-moraine, near Eagle,
Waukesha County, Wisconsin. (From a photograph by President T. C.
Chamberlain, United States Geological Survey.)]
To such an extent is this portion of the area included in southern
Iowa, northern Missouri, southern Illinois, and the extreme southern
portions of Indiana and Ohio covered with loess, that it has been
difficult to determine the relation of its underlying glacial deposits
to the more irregular deposits found farther north. At an early period
of recent investigations, while making a geological survey of the State
of Wisconsin, President T. C. Chamberlin fixed upon the line of moraine
hills, which can be seen upon our map, running southward between Green
Bay and Lake Michigan, and sweeping around in a curve to the right,
passing south of Madison and northward along the line of Wisconsin
River, and in another curve to the left, around the southern end of Lake
Michigan, as the "terminal moraine of the second Glacial epoch." In
Wisconsin the character of this line of moraine hills had been discovered
and described by Colonel Charles Whittlesey, in 1866. It was first
named the "kettle-moraine," because of the frequent occurrence in it of
"kettle-holes." This line of moraine hills has been traced with a great
degree of confidence across the entire glaciated area, as shown upon our
map, but it is not everywhere equally distinct, and, as will be observed,
follows a very irregular course.
Beginning in Ohio we find it coinciding nearly with the extreme glacial
boundary until it reaches the valley of the Scioto River, on the sixth
meridian west from Washington, where it begins to bear northward and
continues in that direction for a distance of sixty or seventy miles,
and then turns southward again in the valley of the Miami, having formed
between these two valleys a sort of medial moraine.[BE] A similar medial
moraine had also been noted by President Chamberlin between the valleys
of the Grand and Cuyahoga Rivers, in the eastern part of Ohio. Indeed,
for the whole distance across Ohio and Indiana, this moraine occurs in a
series of loops pointing to the south, corresponding in general to the
five gentle valleys which mark the territory, namely, those of the Grand
and Mahoning Rivers; the Sandusky and Scioto Rivers; the Great Miami
River; the White River; and the Maumee and Wabash Rivers. Everywhere,
however, over this area these morainic accumulations approximate pretty
closely to the extreme boundary of the glaciated region.
[Footnote BE: See map at the beginning of the chapter.]
In Illinois President Chamberlin's original determination of the moraine
fixed it near the southern end of Lake Michigan, as shown upon our map,
but Mr. Frank Leverett has subsequently demonstrated that there is a
concentric series of moraines south of this, reaching across the State,
(but somewhat obscured by superficial accumulations of loess referred to)
and extending nearly to the latitude of St. Louis.
West of Wisconsin President Chamberlin's "terminal moraine of the second
Glacial epoch" bends southward through eastern Minnesota, and, sweeping
down through central Iowa, forms, near the middle of the northern part
of that State, a loop, having its southern extremity in the vicinity of
Des Moines. The western arm of this loop runs through Minnesota in a
northwesterly direction nearly parallel with the upper portion of the
valley of the Minnesota, until reaching the latitude of the head-waters
of that river, where, in the vicinity of the Sisseton Agency, in Dakota,
it turns to the south by an acute angle, and makes a loop in that State,
extending to the vicinity of Yankton, and with the valley of the James
River as its axis. The western arm of this loop follows pretty closely
the line of the eastern edge of the trough of the Missouri River,
constituting what is called the "Missouri Coteau," which continues on as
a well-marked line of hills running in a northwesterly direction far up
into the Dominion of Canada.
One of the most puzzling glacial phenomena in the Mississippi Valley is
the driftless area which occupies the southeastern portion of Minnesota,
the southwestern part of Wisconsin, and the northwestern corner of Iowa,
as delineated upon our map. This is an area which, while being surrounded
on every side by all the characteristic marks of glaciation, is itself
conspicuous for their entire absence. Its rocks preserve no glacial
scratches and are covered by no deposits of till, while northern boulders
avoided it in their journey to more southern latitudes.
The reason for all this is not evident in the topography of the region.
The land is not higher than that to the north of it, nor is there any
manifest protection to it by the highlands south of Lake Superior. Nor
yet is there any reason to suppose that any extensive changes of level in
former times seriously affected its relations to the surrounding country.
Professor Dana, however, has called attention to the fact that even now
it is in a region of comparatively light precipitation, suggesting that
the snow-fall over it may always have been insignificant in amount. But
this could scarcely account for the failure of the great ice-wave of the
north to overrun it. We are indebted again to the sagacity of President
Chamberlin in suggesting the true explanation.
By referring to the map it will be noticed that this area sustains a
peculiar relation to the troughs of Lake Michigan and Lake Superior,
while from the arrangements of the moraines in front of these lakes it
will be seen that these lake basins were prominent factors in determining
the direction of the movement of the surplus ice from the north. It is
the more natural that they should do so because of their great depth,
their bottoms being in both cases several hundred feet below the present
water-level, reaching even below the level of the sea.
These broad, deep channels seem to have furnished the readiest outlet for
the surplus ice of the North, and so to have carried both currents of ice
beyond this driftless area before they became again confluent. The slight
elevation south of Lake Superior served to protect the area on account of
the feebleness of direct movement made possible by the strength of these
diverging lateral ice-currents. The phenomenon is almost exactly what
occurs where a slight obstruction in a river causes an eddy and preserves
a low portion of land below it from submergence. A glance at the map
will make it easily credible that an ice-movement south of Manitoba,
becoming confluent with one from Lake Superior, pushed far down into the
Missouri Valley and spread eastward to the Mississippi River, south of
the unglaciated driftless area, and there became confluent with a similar
movement which had been directed by the valleys of Lake Michigan and Lake
Erie. There can be little doubt that President Chamberlin's explanation
is in the main correct, and we have in this another illustration of the
analogy between the behaviour of moving ice and that of moving water.
[Illustration: Fig. 34.--Section of the east-and-west glacial furrows,
on Kelly's Island, preserved by Mr. Younglove. Fine sediment rests
immediately on the rock, with washed pebbles at the surface.]
The accompanying illustrations will give a better idea than words can
do of the celebrated glacial grooves on the hard limestone islands
near Sandusky, in the western part of Lake Erie. Through the interest
aroused in them by an excursion of the American Association for the
Advancement of Science, while meeting in Cleveland, Ohio, in 1888, the
Kelly Island Lime and Transport Company, of which Mr. M. C. Younglove is
the president, has been induced to deed to the Western Reserve Historical
Society for preservation a portion of one of the most remarkable of the
grooves still remaining.
The portion of the groove preserved is thirty-three feet across, and
the depth of the cut in the rock is seventeen feet below the line,
extending from rim to rim. Originally there was probably here a small
depression formed by preglacial water erosion, into which the ice crowded
the material, which became its graving-tool, and so the rasping and
polishing went on in increasing degree until this enormous furrow is
the result. The groove, however, is by no means simple, but presents a
series of corrugations merging into each other by beautiful curves. When
exposed for a considerable length it will resemble nothing else so much
as a collection of prostrate Corinthian columns lying side by side on a
concave surface.
The direction of these grooves is a little south of west, corresponding
to that of the axis of the lake. This is nearly at right angles to the
course of the ice-scratches on the summit of the water-shed south of
this, between the lake and the Ohio River. The reason for this change
of direction can readily be seen by a little attention to the physical
geography. The highlands to the south of the lake rise about seven
hundred feet above it. When the Ice period was at its climax and overran
these highlands, the ice took its natural course at right angles to
the terminal moraine and flowed southeast according to the direction
indicated by the scratches on the summit; but when the supply of ice was
not sufficient to overrun the highlands, the obstruction in front turned
the course and the resultant was a motion towards Toledo and the Maumee
Valley, where in the vicinity of Fort Wayne an extensive terminal moraine
was formed.
[Illustration: Fig. 35.--Same as the preceding. (Courtesy of M. C.
Younglove.)]
The much-mooted question of a succession of glacial epochs finds the
most of its supporting facts in the portion of the glaciated area lying
west of Pennsylvania. That there have been frequent oscillations of the
glacial front over this area is certain. But it is a question whether
the glacial deposits south of this distinct line of moraine hills are so
different from those to the north of it as to necessitate the supposition
of two entirely distinct glacial epochs. This can be considered most
profitably here.
The following are among the points with reference to which the phenomena
south of the moraine just delineated differ from those north of the line:
1. The glacial deposits to the south appear to be distributed more
uniformly than those to the north. To the north the drift is often
accumulated in hills, and is dotted over with kettle-holes, while to the
south these are pretty generally absent. Any one travelling upon a line
of railroad which traverses these two portions of the glaciated area as
indicated upon our map can easily verify these statements.
2. The amount of glacial erosion seems to be much less south of the line
of moraine hills delineated than north of them. Still, glacial striæ
are found, almost everywhere, close down to the extreme margin of the
glaciated area.
3. The gravel deposits connected with the drainage of the Glacial period
are much less abundant south of the so-called "terminal moraine of the
second Glacial period" than they are north of it. South of this moraine
the water deposits attributed to the Glacial period are of such fine
silt as to indicate slow-moving currents over a gentle low slope of the
surface.
4. The glacial deposits to the south are more deeply coloured than those
to the north, showing that they have been longer exposed to oxidising
agencies. Even the granitic boulders show the marks of greater age south
of this line, being disintegrated to a greater extent than those to the
north.
5. And, finally, there occur, over a wide belt bordering the so-called
moraine hills of the second Glacial epoch, extensive intercalated beds
of vegetal deposits. Among the earliest of these to be discovered were
those of Montgomery County, Ohio, where, in 1870, Professor Orton, of the
Ohio Survey, found at Germantown a deposit of peat fourteen feet thick
underneath ninety-five feet of till, and there seem also to be glacial
deposits underneath the peat as well as over it. The upper portion of the
peat contains "much undecomposed sphagnous mosses, grasses, and sedges,
and both the peat and the clayey till above it" contain many fragments
of coniferous wood which can be identified as red cedar (_Juniperus
Virginianus_). In numerous other places in that portion of Ohio
fresh-appearing logs, branches, and twigs of wood are found underneath
the till, or mingled with it, much as boulders are. Near Darrtown, in
Butler County, Ohio, red cedar logs were found under a covering of
sixty-five feet of till, and so fresh that the perfume of the wood is
apparently as strong as ever. Similar facts occur in several other
counties in the glaciated area of southern Ohio and southern Indiana.
Professor Collett reports that all over southwestern Indiana peat, muck,
rotted stumps, branches, and leaves of trees are found from sixty to one
hundred and twenty feet below the surface, and that these accumulations
sometimes occur to a thickness of from two to twenty feet.
[Illustration: Fig. 36.--Section of till near Germantown, Ohio, overlying
thick bed of peat. The man in the picture stands upon a shelf of peat
from which the till has been eroded by the stream. The dark spot at
the right hand of the picture, just above the water, is an exposure of
the peat. The thickness of the till is ninety-five feet. The partial
stratification spoken of in the text can be seen about the middle of the
picture. The furrows up and down had been made by recent rains. (United
States Geological Survey.) (Wright.)]
Farther to the northwest similar phenomena occur. Professor N. H.
Winchell has described them most particularly in Fillmore and Mower
Counties, Minnesota, from which they extend through a considerable
portion of Iowa. In the above counties of Minnesota a stratum of peat
from eighteen inches to six or eight feet in thickness, with much wood,
is pretty uniformly encountered in digging wells, the depth varying from
twenty to fifty feet. This county is near the highest divide in the State
of Minnesota, and from it "flow the sources of the streams to the north,
south, and east." The wood encountered in this stratum indicates the
prevalence f coniferous trees, and the peat mosses indicate a cool and
moist climate.
Nor are intercalated vegetable deposits absent from the vast region
farther north over the area that drains into Hudson Bay. At Barnesville,
in Clay County, Minnesota, which lies in the valley of the Red River of
the North, and also in Wilkin County in the same valley, tamarack wood
and sandy black mud containing many snail-shells have been found from
eight to twelve feet below a surface of till; and Dr. Robert Bell reports
the occurrence of limited deposits of lignite between layers of till, far
to the northwest, in Canada, and even upon the southern part of Hudson
Bay; while Mr. J. B. Tyrrell reports[BF] many indications of successive
periods of glaciation near the northern end of the Duck Mountain. The
most characteristic indications which he had witnessed consisted of
stratified beds of silt, containing fresh-water shells, with fragments of
plants and fish similar to those living in the lakes of the region at the
present time.
[Footnote BF: Bulletin of the Geological Society of America, vol. i, pp.
395-410.]
Reviewing these facts with reference to their bearing upon the point
under consideration, we grant, at the outset, that they do indicate a
successive retreat and readvance of the ice over extensive areas. This
is specially clear with respect to the vegetal deposits interstratified
with beds of glacial origin. But the question at issue concerning the
interpretation of these phenomena is, Do they necessarily indicate
absolutely distinct glacial epochs separated by a period in which the
ice had wholly disappeared from the glaciated area to the north? That
they do, is maintained by President Chamberlin and many others who have
wide acquaintance with the facts. That they do not certainly indicate a
complete disappearance of the ice during an extensive interglacial epoch,
is capable, however, of being maintained, without forfeiting one's rights
to the respect of his fellow-geologists. The opposite theory is thus
stated by Dr. Robert Bell: "It appears as if all the phenomena might be
referred to one general Glacial period, which was long continued, and
consequently accompanied by varying conditions of temperature, regional
oscillations of the surface, and changes in the distributions of sea and
land, and in the currents in the ocean. These changes would necessarily
give rise to local variations in the climate, and might permit of
vegetation for a time in regions which need not have been far removed
from extensive glaciers."[BG]
[Footnote BG: Bulletin of the Geological Society of America, vol. i, pp.
287-310.]
At my request, Professor J. E. Todd, of Iowa, whose acquaintance with the
region is extensive, has kindly written out for me his conclusions upon
this subject, which I am permitted to give in his own words:
"I am not prepared to write as I would like concerning the forest-beds
and old soils. I will, however, offer the following as a partial report.
I have come to think that there is considerable confusion on the subject.
I believe there are five or six different things classed under one head.
"1. _Recent Much and Soils._--The finest example I have found in the
whole Missouri Valley was twenty feet below silt and clay, in a basin
inside the outer moraine, near Grand View, South Dakota. From my
examination of the reported old soil near Albia, Iowa, I think the most
rational way of reconciling the conflicting statements concerning it is
that it also belongs to this class.
"2. _Peat or Soil under Loess._--This does not signify much if the loess
was formed in a lake subject to orographic oscillations, or if, as I am
coming to believe, it is a fluviatile deposit of an oscillating river
like the Hoang-Ho on the great Chinese plain. It at least does not mean
an interglacial epoch.
"3. _Wood and Dirt rearranged, not in situ._--This occurs either in
subaqueous or in subglacial deposits. I have found drift-wood in the
lower layers of the loess here, but not _in situ_. I have frequently
found traces of wood in till in Dakota, but always in an isolated
way. I think, from reading statements about the deposits in eastern
Iowa, that most if not all of the cases are of this sort. Two things
have conspired to lead to this error: one, the influence of Croll's
speculation; and the other, the easy inference of many well-diggers,
and especially well-borers, that what they pass through are always in
layers. In this way a log becomes a forest-bed. Scattered logs and muck
fragments occurring frequently in a region, though at different levels,
are readily imagined by an amateur geologist to be one continuous stratum
antedating the glacier or floods (as the case may be in that particular
region), when, in fact, it has been washed down from the margin of
the transporting agent and is contemporaneous with it. I suspect the
prevalence of wood in eastern Iowa may be traced to a depression of the
driftless region during the advance of the glacier, so as to bring the
western side of that area more into the grasp of glacial agencies.
"4. _Peat between Subglacial Tills._--If cases of this sort are found,
they are in Illinois, Indiana, and Ohio. Professor Worthen insisted that
there were no interglacial soils or forest-beds in Illinois; and in the
cases mentioned in the State reports he repeatedly explains the sections
given by his assistants, so as to harmonize them with that statement. I
think he usually makes his explanations plausible. He was very confident
in referring most of them, to preglacial times. His views, I suppose,
will be published in the long-delayed volume, now about to be issued.
"5. _Vegetable Matter between Glacial Till and Underlying Berg Till or
other Drift Deposits._--When one remembers that the front of the great
ice-sheet may have been as long in reaching its southern boundary as in
receding from it, and with as many advance and retrograde movements, we
can easily believe that much drift material would have outrun the ice and
have formed deposits so far ahead of it that vegetation would have grown
before the ice arrived to bury it.
"6. _Preglacial Soils, etc._--I believe that this will be found to
include most in southern Ohio, if not in Illinois, as Worthen claimed."
The phenomena of the Glacial period are too vast either to have appeared
or to have disappeared suddenly. By whatever cause the great accumulation
of ice was produced, the advance to the southward must have been slow
and its disappearance must have been gradual, though, as we shall show
a little later, the final retreat of the ice-front occupied but a short
time relatively to the whole period which has elapsed since. As we
shall show also, the advent of the Ice period was probably preceded and
accompanied by a considerable elevation of the northern part of the
continent Whether this elevation was contemporaneous upon both sides of
the continent is perhaps an open question; but with reference to the area
east of the Rocky Mountains, which is now under consideration, the centre
of elevation was somewhere south of Hudson Bay. Putting together what
we know, from the nature of the case, concerning the accumulation and
movement of glacial ice, and what we know from the relics of the great
glacial invasion, which have enabled us to determine its extent and the
vigour of its action, the course of events seems to have been about as
follows:
Throughout the Tertiary period a warm climate had prevailed over British
America, Greenland, and indeed over all the lands in proximity to the
north pole, so far as explorers have been able to penetrate them. The
vegetation characterizing these regions during the Tertiary period
indicates a temperature about like that which now prevails in North
Carolina and Virginia. Whatever may be said in support of the theory
that the Glacial period was produced by astronomical causes, in view of
present facts those causes cannot be regarded as predominant; at most
they were only co-operative. The predominant cause of the Glacial period
was probably a late Tertiary or post-Tertiary elevation of the northern
part of the continents, accompanied with a subsidence in the central
portion. Of such a subsidence in the Isthmus of Panama indications are
thought to be afforded by the occurrence of late Tertiary or, more
probably, post-Tertiary sea-shells at a considerable elevation on the
divide along the Isthmus of Panama, between the Atlantic and Pacific
Oceans. Of this we shall speak more fully in a later chapter.
Fixing our thoughts upon what is known as the Laurentian plateau, which,
though now in the neighbourhood of but two thousand feet above the sea,
was then much higher, we can easily depict in imagination the beginnings
of the great "Laurentide Glacier," which eventually extended to the
margin already delineated on the south and southwest in the United
States, and spread northward and eastward over an undetermined area.
Year after year and century after century the accumulating snows over
this elevated region consolidated into glacial ice and slowly pushed
outward the surplus reservoirs of cold. For a long time this process of
ice-accumulation may have been accompanied by the continued elevation of
the land, which, together with the natural effect of the enlarging area
of ice and snow, would tend to lower the temperature around the margin
and to increase still more the central area of accumulation.
The vigour of movement in any direction was determined partly by the
shape of the valleys opening southward in which the ice-streams would
naturally concentrate, and partly by those meteorological conditions
which determine the extent of snow-fall over the local centres of glacial
dispersion. For example, the general map of North America in the Ice
period indicates that there were two marked subcentres of dispersion
for the great Laurentide Glacier, the eastern one being in Labrador and
the western one north of Lake Superior. In a general way the southern
boundary of the glaciated region in the United States presents the
appearance of portions of two circumferences of circles intersecting each
other near the eastern end of Lake Erie. These circles, I am inclined
to believe, represent the areas over which a semi-fluid (or a substance
like ice, which flows like a semi-fluid) would disperse itself from the
subcentres above mentioned.
A study of the contour of the country shows that that also, in a general
way, probably had something to do with the lines of dispersion. The
western lobe of this glaciated area corresponds in its boundary pretty
closely with the Mississippi Valley, having the Ohio River approximately
as its eastern arm and the Missouri as its western, with the Mississippi
River nearly in its north and south axis. The eastern lobe has its
farthest extension in the axis of the Champlain and Hudson River Valleys,
its western boundary being thrown more and more northward as the line
proceeds to the west over the Alleghany Mountains until reaching the
longitude of the eastern end of Lake Erie; but this southern boundary is
by no means a water-level, nor is the contour of the country such that
it could ever have been a water-level. But it conforms in nearly every
particular to what would be the resultant arising from a pretty general
southward flow of a semi-fluid from the two subcentres mentioned, meeting
with the obstructions of the Adirondacks in northern New York and of the
broader Appalachian uplift in northern Pennsylvania.
How far south the area of glacial accumulation may have extended cannot
be definitely ascertained, but doubtless at an early period of the great
Ice age the northern portions of the Appalachian range in New York, New
England, New Brunswick, and Nova Scotia became themselves centres of
dispersion, while only at the height of the period did all their glaciers
become confluent, so that there was one continuous ice-sheet.
In the western portion of the area covered by the Laurentide Glacier, the
depression occupied by the Great Lakes, especially Lakes Michigan and
Superior, evidently had a marked influence in directing the flow of ice
during the stages which were midway between the culmination of the Ice
period and both its beginning and its end. This would follow from the
great depth of these lakes, the bottom of Lake Michigan being 286 feet
below sea-level, and that of Lake Superior 375 feet, making a total depth
of water of about 900 and 1,000 feet respectively. Into these oblong
depressions the ice would naturally gravitate until they were filled,
and they would become the natural channels of subsequent movement in the
direction of their longest diameters, while the great thickness of ice in
them would make them the conservative centres of glacial accumulation and
action after the ice had begun to retreat.
These deductions from the known nature of ice and the known topography of
the region are amply sustained by a study of the detailed map showing the
glacial geology in the United States. But on this we can represent indeed
only the marks left by the ice at various stages of its retreat, since,
as already remarked, the marks of each stage of earlier advance would be
obliterated by later forward movements. We may presume, however, that
in general the marks left by the retreating ice correspond closely with
those actually made and obliterated by the advancing movement.
From observations upon the glaciers of Switzerland and of Alaska, it
is found that neither the advance nor the retreat of these glaciers is
constant, but that, in obedience to meteorologic agencies not fully
understood, they advance and retreat in alternate periods, at one time
receding for a considerable distance, and at other times regaining the
lost ground and advancing over the area which has been uncovered by their
retreat.
"M. Forel reports, from the data which he has collected with much care,
that there have been in this century five periods in the Alpine glaciers:
of enlargement, from 1800 (?) to 1815; of diminution, from 1815 to 1830;
of enlargement, from 1830 to 1845; of diminution, from 1845 to 1875; and
of enlargement again, from 1875 onward. He remarks further that these
periods correspond with those deduced by Mr. C. Lang for the variations
for the precipitations and temperature of the air; and, consequently,
that the enlargement of the glaciers has gone forward in the cold and
rainy period, and the diminution in the warm and the dry."[BH]
[Footnote BH: American Journal of Science, vol. cxxxii, 1886, p. 77.]
When, now, we attentively consider the combination of causes necessary to
produce the climatic conditions of the great Ice age of North America, we
shall be prepared to find far more extensive variations in the progress
of the continental glacier, both during its advance and during its
retreat, than are to be observed in any existing local glaciers.
With respect to the arguments adduced in favor of a succession of glacial
epochs in America the following criticisms are pertinent:
1. So far as we can estimate, a temporary retreat of the front, lasting
a few centuries, would be sufficient to account for the vegetable
accumulations that are found buried beneath the glacial deposits in
southern Ohio, Indiana, central Illinois, and Iowa, while a temporary
readvance of the ice would be sufficient to bury the vegetable remains
beneath a freshly accumulated mass of till. Thus, as Dr. Bell suggested,
the interglacial vegetal deposits do not necessarily indicate anything
more than a temporary oscillation of the ice-front, and do not carry
with them the necessity of supposing a disappearance of the ice from the
whole glaciated area. Thus the introduction of a whole Glacial period to
account for such limited phenomena is a violation of the well-known law
of parsimony, which requires us in our explanations of phenomena to be
content with the least cause which is sufficient to produce them. In the
present instance a series of comparatively slight oscillations of the
ice-front during a single glacial period would seem to be sufficient to
account for all the buried forests and masses of vegetal _débris_ that
occur either in the United States or in the Dominion of Canada.
2. Another argument for the existence of two absolutely distinct glacial
periods in North America has been drawn from the greater oxidation of
the clays and the more extensive disintegration of certain classes of
the boulders found over the southern part of the glaciated area of the
Mississippi Valley, than has taken place in the more northerly regions.
Without questioning this statement of fact (which, however, I believe to
be somewhat exaggerated), it is not difficult to see that the effects
probably are just what would result from a single long glacial period
brought about by such causes as we have seen to be probably in operation
in America. For if one reflects upon the conditions existing when the
Glacial period began, he will see that, during the long ages of warm
climate which characterised the preceding period, the rocks must have
been extensively disintegrated through the action of subaërial agencies.
The extent to which this disintegration takes place can be appreciated
now only by those who reside outside of the glaciated area, where these
agencies have been in uninterrupted action. In the Appalachian range
south of the glaciated region the granitic masses and strata of gneiss
are sometimes found to be completely disintegrated to a depth of fifty or
sixty feet; and what seem to be beds of gravel often prove in fact to be
horizontal strata of gneiss from which the cementing material has been
removed by the slow action of acids brought down by the percolating water.
Now, there can be no question that this process of disintegration had
proceeded to a vast extent before the Glacial period, so that, when the
ice began to advance, there was an enormous amount of partially oxidised
and disintegrated material ready to be scraped off with the first advance
of ice, and this is the material which would naturally be transported
farthest to the south; and thus, on the theory of a single glacial
period, we can readily account for the greater apparent age of the
glacial _débris_ near the margin. This _débris_ was old when the Glacial
period began.
3. With reference to the argument for two distinct glacial periods drawn
from the smaller apparent amount of glacial erosion over the southern
part of the glaciated area, we have to remark that that would occur
in case of a single ice-invasion as well as in case of two distinct
ice-invasions, in which the later did not extend so far as the former.
From the very necessity of the case, glacial erosion diminishes as the
limit of the extent of the glaciation is approached. At the very margin
of the glacier, motion has ceased altogether. Back one mile from the
margin only one mile of ice-motion has been active in erosion, while ten
miles back from its front there has been ten times as much moving ice
actually engaged in erosion, and in the extreme north several hundred
times as much ice, Thus it is evident that we do not need to resort to
two glacial periods to account for the relatively small amount of erosion
exhibited over the southern portion of our glaciated area.
At the same time, it should be said that the indications of active
glacial erosion near the margin are by no means few or small. In Lawrence
County, Pennsylvania, on the very margin of the glaciated area, Mr. Max
Foshay[BI] has discovered very extensive glacial grooves, indicating much
vigour of ice-action even beyond the more extensive glacial deposits
which Professor Lewis and myself had fixed upon as the terminal moraine.
In Highland and Butler Counties, Ohio, and in southwestern Indiana and
southern Illinois, near the glacial margin, glacial grooves and striæ
are as clear and distinct in many cases as can anywhere be found; while
upon the surface of the limestone rocks within the limits of the city of
St. Louis, where the glacial covering is thin, and where disintegrating
agencies had had special opportunities to work, I found very clear
evidences of a powerful ice-movement, which had planed and scratched
the rock surface; and at Du Quoin, Illinois, as already related, the
fragments thrown up from the surface of the rock, fifty or sixty feet
below the top of the soil, were most beautifully planed and striated.
It should be observed, also, that this whole area is so deeply covered
with _débris_ that the extent of glacial erosion underneath is pretty
generally hid from view.
[Footnote BI: Bulletin of the Geological Society, vol. ii, pp. 457-464.]
4. The uniformity of the distribution of the glacial deposits over the
southern portion of the glaciated area in the Mississippi Valley is
partly an illusion, due to the fact that there was a vast amount of
deposition by water over that area during the earlier stages of the
ice-retreat. This has been due partly to the gentler slope which would
naturally characterise the borders of an area of elevation, and partly to
an extensive subsidence which seems to have begun soon after the ice had
reached its farthest extent of motion.
It should be borne in mind that at all times a glacier is accompanied
by the issue of vast streams of water from its front, and that these
of course increase in volume when the climax has been reached and the
ameliorating influences begin to melt away the accumulated mass of ice
and to add the volume of its water to that produced by ordinary agencies.
As these subglacial streams of water poured out upon the more gentle
slopes of the area in front of the ice, they would distribute a vast
amount of fine material, which would settle into the hollow places and
tend to obscure the irregularities of the previous direct glacial deposit.
Such an instance came clearly under my own observation in the vicinity of
Yankton, in South Dakota, where, upon visiting a locality some miles from
any river, and to which workmen were resorting for sand, I found that the
deposit occupied a kettle-hole, filling it to its brim, and had evidently
been superimposed by a temporary stream of water flowing over the region
while the ice was still in partial occupation of it. Thus, no doubt, in
many cases, the original irregularities of the direct glacial deposits
have been obliterated, even where there has been no general subsidence.
But, in the area under consideration, the loess, or loam, is so extensive
that it is perhaps necessary to suppose that the central portions of the
Mississippi Valley were subjected to a subsidence amounting to about five
hundred feet; so that the glacial streams from the retreating ice-front
met the waters of the ocean in southern Illinois and Indiana; thus
accounting for the extensive fine silt which has done so much over that
region to obscure the glacial phenomena.
_West of the Rocky Mountains._
The glacial phenomena in the United States west of the Rocky Mountains
must be treated separately, since American geologists have ceased to
speak of an all-pervading ice-cap extending from the north pole. But,
as already said, the glaciation of North America has proceeded from
two definite centres of ice-accumulation, one of which we have been
considering in the pages immediately preceding. The great centre of
glacial dispersion east of the Rocky Mountains is the region south of
Hudson Bay, and the vast ice-field spreading out from that centre is
appropriately named the Laurentide Glacier. The movement of ice in this
glacial system was outward in all directions from the Laurentian hills,
and extended west several hundred miles, well on towards the eastern foot
of the Rocky Mountains.
The second great centre of glacial dispersion occupies the vast
Cordilleran region of British Columbia, reaching from the Rocky Mountains
on the northeast to the Coast Range of the Pacific on the southwest, a
width of four hundred miles. The length is estimated by Dr. Dawson to
be twelve hundred miles. The principal centre of ice-accumulation lies
between the fifty-fifth and the fifty-ninth parallel. From this centre
the movement was in all directions, but chiefly to the northwest and to
the south. The movement of the Cordilleran glaciers extended northwest
to a distance of three hundred and fifty miles, leaving their moraines
far down in the Yukon Valley on the Lewes and Pelly Rivers.[BJ] Southward
the Cordilleran Glacier moved to a distance of six hundred miles,
extending to the Columbia River, in the eastern part of the State of
Washington.
[Footnote BJ: See George M. Dawson, in Science, vol. xi, 1888, p. 186,
and American Geologist, September, 1890, pp. 153-162.]
From this centre, also, the ice descended to the sea-level upon the
west, and filled all the channels between Vancouver's Island and the
mainland, as well as those in the Alexander Archipelago of Alaska. South
of Vancouver's Island a glacier pushed out through the straits of Juan de
Fuca to an unknown distance. All the islands in Puget Sound are composed
of glacial _débris_, resembling in every respect the terminal moraines
which have been described as constituting many of the islands south of
the New England coast. The ice-movement in Puget Sound, however, was
probably northward, resulting from glaciers which are now represented by
their diminutive descendants on the flanks of Mount Rainier.
South of the Columbia River the country was never completely enveloped
by the ice, but glaciers extended far down in the valleys from all the
lofty mountain-peaks. In Idaho there are glacial signs from the summit
of the Rocky Mountains down to the westward of Lake Pend d'Oreille. In
the Yellowstone Park there are clear indications that the whole area was
enveloped in glacial ice. An immense boulder of granite, resting upon
volcanic deposits, may be found a little west of Inspiration Point, on
the Yellowstone Cañon. Abundant evidences of glacial action are also
visible down the Yellowstone River to the vicinity of Livingston, showing
that that valley must have been filled with glacial ice to a depth of
sixteen hundred feet. To the west the glaciers from the Yellowstone
Park extended to the border of Idaho, where a clearly marked terminal
moraine is to be found in the Tyghee Pass, leading over from the western
fork of the Madison River into Lewis Fork of the Snake River. South of
Yellowstone Park the Teton Mountains were an important centre for the
dispersion of local glaciers, but they did not descend upon the western
side much below the 6,000-foot level, and only barely came to the edge
of the great Snake River lava plains. To the east the movement from the
Teton Mountains joined that from various other lofty mountains, where
altogether they have left a most intricate system of glacial deposits, in
whose reticulations Jackson's Lake is held in place.
[Illustration: Fig. 37.--Moraines of Grape Creek, Sangre del Cristo
Mountains, Colorado (after Stevenson).]
In Utah extensive glaciers filled all the northern valleys of the Uintah
Mountains, and extended westward in the Wahsatch range to the vicinity of
Salt Lake City. The mountain region of Colorado, also, had its glaciers,
occupying the head-waters of the Arkansas, the Platte, the Gunnison, and
the Grand Rivers. The most southern point in the Rocky Mountains at which
signs of local glaciers have been noted is near the summits of the San
Juan range, in southwestern Colorado. Here a surface of about twenty-five
square miles, extending from an elevation of 12,000 feet down to 8,000
feet, shows every sign of the former presence of moving ice. The greater
part of the glaciation in Colorado is confined to elevations above 10,000
feet.
The whole range of the Sierra Nevada through Oregon, and as far south as
the Yosemite Valley in California, formerly sustained glaciers of far
greater size than any which are now found in those mountains. In general
these glaciers were much longer on the western side of the Sierra Nevada
than on the eastern. On the eastern side glaciers barely came down to
Lake Tahoe and Lake Mono in California. The State of Nevada seems to
have been entirely free from glaciers, although it contains numerous
mountain-peaks more than ten thousand feet high. In the Yosemite Cañon
glaciers extended down the Merced River to the mouth of the cañon; while
in the Tuolumne River, a few miles to the north, the glaciers which still
linger about the peaks of Mount Dana filled the valley for a distance of
forty miles.
It is a question among geologists whether or not the glaciation west
of the Rocky Mountains was contemporaneous with that of the eastern
part of the continent. The more prevalent opinion among those who have
made special study of the phenomena is that the development of the
Cordilleran glaciers was independent of that of the Laurentide system.
At any rate, the intense glaciation of the Pacific coast seems to have
been considerably later than that of the Atlantic region. Of this we will
speak more particularly in discussing the questions of the date and the
cause of the Glacial period. It is sufficient for us here simply to say
that, from his extensive field observations throughout the Cordilleran
region, Dr. George M. Dawson infers that there have been several
successive alternations of level on the Pacific coast corresponding to
successive glacial and interglacial epochs, and that when there was a
period of elevation west of the Rocky Mountains there was a period of
subsidence to the east, and _vice versa_. In short, he supposes that the
east and west for a long time played a game of seesaw, with the Rocky
Mountains as the fulcrum. We give his scheme in tabulated form.
_Scheme of Correlation of the Phenomena of the Glacial Period in the
Cordilleran Region and in the Region of the Great Plains._
CORDILLERAN REGION. REGION OF THE GREAT PLAINS.
Cordilleran zone at a high Correlative subsidence and
elevation. Period of most severe submergence of the great plains,
glaciation and maximum development with possible contemporaneous
of the great Cordilleran Glacier. increased elevation of the
Laurentian axis and maximum
development of ice upon it.
Deposition of the lower
boulder-clay of the plains.
Gradual subsidence of the Correlative elevation of the
Cordilleran region and decay of the western part, at least, of the
great glacier, with deposition of great plains, which was probably
the boulder-clay of the interior more or less irregular and led to
plateau and the Yukon basin, of the the production of extensive lakes
lower boulder-clay of the littoral in which interglacial deposits,
and probably also, at a later stage including peat, were formed.
(and with greater submergence), of
the interglacial silts of the same
region.
Re-elevation of the Cordilleran Correlative subsidence of the
region to a level probably as high plains, which (at least in the
as or somewhat higher than the western part of the region)
present. Maximum of second period exceeded the first subsidence and
of glaciation. extended submergence to the base
of the Rocky Mountains near the
forty-ninth parallel. Formation of
second boulder-clay, and (at a
later stage) dispersion of large
erratics.
Partial subsidence of the Correlative elevation of the
Cordilleran region, to a level plains, or at least of their
about 2,500 feet lower than the western portion, resulting in a
present. Long stage of stability. condition of equilibrium as
Glaciers of the second period between the plains and the
considerably reduced. Upper Cordillera, their _relative_
boulder-clay of the coast probably levels becoming nearly as at
formed at this time, though perhaps present. Probable formation of the
in part during the second maximum Missouri coteau along a shore-line
of glaciation. during this period of rest.
Renewed elevation of the Simultaneous elevation of the great
Cordilleran region, with one plains to about their present
well-marked pause, during which the level, with final exclusion of
littoral stood about 200 feet lower waters in connection with the sea.
than at present. Glaciers much Lake Agassiz formed and eventually
reduced, and diminishing in drained towards the close of this
consequence of general amelioration period. This simultaneous movement
of climate towards the close of the in elevation of both great areas
Glacial period. may probably have been connected
with a more general northern
elevation of land at the close of
the Glacial period.
In New Zealand the marks of the Glacial period are unequivocal The
glaciers which now come down from the lofty mountains upon the South
Island of New Zealand to within a few hundred feet of the sea then
descended to the sea-level. The longest existing glacier in New Zealand
is sixteen miles, but formerly one of them had a length of seventy-eight
miles. One of the ancient moraines contains a boulder from thirty to
forty feet in diameter, and the amount of glacial _débris_ covering the
mountain-sides is said to be enormous. Reports have also been recently
brought of signs of ancient glaciers in Australia.
[Illustration: Fig. 38.--Generalised view of the whole glaciated region
of North America. The area of motionless ground-ice is shown by the white
lines in northern part of Alaska.]
According to Darwin, there are distinct signs of glaciation upon the
plains of Patagonia sixty or seventy miles east of the foot of the
mountains, and in the Straits of Magellan he found great masses of
unstratified glacial material containing boulders which were at least
one hundred and thirty miles away from their parent rock; while upon
the island of Chiloe he found embedded in "hardened mud" boulders which
must have come from the mountain-chains of the continent. Agassiz also
observed unquestionable glacial phenomena on various parts of the Fuegian
coast, and indeed everywhere on the continent south of latitude 37°.
Between Concepcion and Arauco, in latitude 37°, Agassiz observed, near
the sea-level, a glacial surface well marked with furrows and scratches,
and as well preserved, he says, "as any he had seen under the glaciers of
the present day."
[Illustration: Fig. 39.--Quartzite boulder of 45 cubic metres, on Mont
Lachat, 800 metres above the valley of the Belley, in Ain, France
(Falsan).]
CHAPTER VI.
ANCIENT GLACIERS IN THE EASTERN HEMISPHERE.
About two million square miles of northern Europe were covered with
perennial ice during the Glacial period. From the scratches upon the
rocks, and from the direction in which material has been transported,
it is evident that the main centre of radiation is to be found in the
mountains of Scandinavia, and that the glaciers still existing in Norway
are the lineal descendants of those of the great Ice age.
So shallow are the Baltic Sea and the German Ocean, that their basins
were easily filled with ice, upon which Scandinavian boulders could be
transported westward to the east shore of England, southward into the
plains of Germany, and eastward far out upon the steppes of Russia. The
islands north of Scotland bear marks also of an ice-movement from the
direction of Norway. If Scotland itself was not overrun with Scandinavian
glaciers, the reason was that it had ice enough of its own, and from
its highlands set up a counter-movement, which successfully resisted
the invasion from the Scandinavian Peninsula. But, elsewhere in Europe,
Scandinavian ice moved freely outward to the extent of its capacity.
Then, as now also, the Alps furnished centres for ice-movement, but the
glaciers were limited to the upper portions of the valleys of the Rhône,
the Rhine, and the Danube upon the west and north, and to a still smaller
area upon the southern side.
[Illustration: Fig. 40.
MAP showing
GLACIATED AREAS
in North America and Europe.]
_Central and Southern Europe._
The main centres of ice-movement in the Alps during the Glacial period
are the same as those which furnish the lingering glaciers of the present
time. From the water-shed between the Rhine, the Rhône, and the Aar,
glaciers of immense size descended all the valleys now occupied by those
streams. The valley of the Rhône between the Bernese and the Pennine
Alps was filled with a glacier of immense depth, which was maintained
by fresh supplies from tributaries upon either side as far down as
Martigny. Glacial markings at the head of the Rhône Valley are found upon
the Schneestock,[BK] at an elevation above the sea of about 11,500 feet
(3,550 metres), or about 1,500 feet above the present surface of the
Rhône Glacier. At Fiesch, about twenty miles below, where tributaries
from the Bernese Oberland snow-fields were received, the thickness of
the glacier was upwards of 5,000 feet (1,680 metres). Near Martigny,
about fifty miles farther down the valley, where the glacier was abruptly
deflected to the north, the depth of the ice was still upwards of 1,600
metres. From Martigny northward the thickness of the ice decreased
rapidly for a few miles, where, at the enlargement of the valley above
the head of Lake Geneva, it was less than 1,200 metres in thickness, and
spread out over the intervening plain as far as Chasseron, with a nearly
level surface, transporting, as we have before said, Alpine boulders
to the flanks of the Juras, and landing them about 3,000 feet (1,275
metres) above the level of Lake Geneva. The width of the main valley is
here about fifty miles, making the slope of the surface of the ice about
twenty feet to the mile.
[Footnote BK: A. Falsan's La Période Grlaciaire étudiée principalement en
France et en Suisse, chapitre xv.]
From its "vomitory," at the head of Lake Geneva, the ice of the ancient
Rhône Glacier spread to the right and to the left, while its northern
boundary was abruptly terminated by the line of the Jura Mountains. The
law of glacial motion was, however, admirably illustrated in the height
to which the ice rose upon the flanks of the Jura. At Chasseron, in the
direct line of its onward motion, it rose to its highest point, while
both to the southwest and to the northeast, along the line of the Juras,
the ice-action was limited to constantly decreasing levels.
Down the valley of the Rhône the direction of motion was determined by
the depression of Lake Geneva, at the lower end of which it received its
main tributary from Mont Blanc, which had come down from Chamouni through
the valley of the river Arve. From this point it was deflected by a spur
of the Jura Mountains more and more southward to the vicinity of Culoz,
near the mouth of Lake Bourget. Here the glacier coming down from the
western flanks of the Alps, through the upper valley of the Isère, past
Chambéry, became predominant, and deflected the motion to the west and
north, whither the ice extended to a line passing through Bourg, Lyons,
and Vienne, leaving upon one of the eminences on which Lyons is built a
boulder several feet in diameter, which is duly preserved and labelled
in the public park in that portion of the city. Farther south, glaciers
of less extent marked the Alps most of the way to the Mediterranean, but
they were not at all comparable in size to those from the central region.
To the right of Lake Geneva the movement started by the Rhône Glacier
spread eastward, being joined in the vicinity of Berne by the confluent
ice-stream which descended from the north flank of the Bernese Oberland,
through the valley of the Aar. These united streams filled the whole
valley with ice as far down as Soleure.[BL]
[Footnote BL: See map of Rhône Glacier, on p. 58.]
[Illustration: MAP OF
GLACIAL MOVEMENTS
IN FRANCE AND
SWITZERLAND.]
Farther eastward, other ice-streams from the Alps became predominant,
one of which, moving down the Reuss, deployed out upon the country lying
north of Lucerne and Zug. Still farther down, the ancient glacier which
descended the Limmatt spread itself out over the hills and lowlands about
Zürich, one of its moraines of retrocession nearly dividing the lake into
two portions.
Guyot and others have shown that the superficial deposits of this
portion of Switzerland are just such as would be distributed by glaciers
coming down from the above-mentioned Alpine valleys. Uniting together
north of Zürich, these glaciers pushed onward as far as the Rhine below
Schaffhausen. In Frickthal the glacial ice was still 1,200 feet thick,
and at Kaisterberg between 400 and 500 feet.
At Lucerne there is a remarkable exposure of pot-holes, and a glaciated
surface such as could be produced only by the combined action of moving
ice and running water; thus furnishing to tourists an instructive
object-lesson. Among the remarkable instances of boulders transported
a long distance in Switzerland, is that of a block of granite carried
from the Valais to the vicinity of Soleure, a distance of one hundred
and fifteen miles, which weighs about 4,100 tons. "The celebrated
Pierre-à-Bot, above Neufchâtel, measures 50' × 20' × 40', and contains
about 40,000 cubic feet of stone; while the Pierre-des-Marmettes, near
Monthey, contains no less than 60,840 cubic feet."
The ancient glacier of the Rhine, receiving its initial impulse in
the same centre as that of the Rhône, fully equalled it in all its
dimensions. Descending eastward from its source near the Schneestock
to Chur, a distance of fifty miles, it turned northward and continued
forty-five miles farther to the head of Lake Constance, where it spread
out in fan-shape, extending northwest to Thiengen, below Schaffhausen,
and covering a considerable area north and northeastward of the lake,
reaching in the latter direction Ulm, upon the Danube--the whole distance
of the movement being more than one hundred and fifty miles. Through
other valleys tributary to the Danube, glaciers descended upon the upper
plains of Bavaria, from the Tyrolese Alps to the vicinity of Munich.
From Gross Glockner as a centre in the Noric Alps, vast rivers of ice,
of which the Pasterzen Glacier is the remnant, poured far down into the
valleys of the Inn and the Enns on the north and into that of the Drave
on the southeast. Farther eastward in this part of Europe the mountains
seem to have been too low to have furnished centres for any general
dispersion of glacial ice.
[Illustration: Fig. 41.--Map showing the Lines of _Débris_ extending
from the Alps into the Plains of the Po (after Lyell). _A._ Crest of
the Alpine water-shed; _B._ Névé-fields of the ancient glaciers; _C._
Moraines of ancient glaciers.]
Upon the south side of the Alps the ancient glaciers spread far out
upon the plains of Lombardy, where moraines of vast extent and of every
description enable the student to determine the exact limits of the
ancient ice-action. From the southern flanks of Mont Blanc and Monte
Rosa, and from the snow-fields of the western Alps, glaciers of great
volume descended into the valley of Dora Baltea (vale of Aosta), and
on emerging from the mountain valley Spread Out over the plains around
Ivrea, leaving moraine hills in some instances 1,500 feet in height.
The total length of this glacier was as much as one hundred and twenty
miles. From the snow-fields in the vicinity of Mont Cenis, also, glaciers
extended down the Dora Ripera to the vicinity of Turin, and down other
valleys to a less extent. The lateral moraines of the Diore, on the south
side of Mont Blanc, at the head of the Dora Baltea, are 2,000 feet above
the present river, and extend upon the left bank for a distance of twenty
miles.
From the eastern Alps, glaciers descended through all the valleys of the
Italian lakes and deposited vast terminal moraines, which still obstruct
the drainage, and produce the charming lakes of that region. A special
historic interest pertains to the series of concentric moraines south of
Lake Garda, since it was in the reticulations of this glacial deposit
that the last great battle for Italian liberty was fought on June 24,
1859. Defeated in the engagements farther up the valley of the Po, the
Austrian general Benedek took his final stand to resist the united forces
of France and Italy behind an outer semicircle of the moraine hills south
of this lake (some of which are 500 or 600 feet above the surrounding
country), with his centre at Solferino, about ten miles from Peschera.
Here, behind this natural fortification, he awaited the enemy, who was
compelled to perform his manoeuvres on the open plain which spread out
on every side. But the natural fortifications furnished by the moraine
hills were too extensive to be defended by an army of moderate size.
The troops of Napoleon and Victor Immanuel concentrated at Solferino
and broke through the line. Thus the day was lost to the Austrians, and
they retired from Lombardy, leaving to Italy both the artificial and the
natural fortifications that guard the southern end of this important
entrance to the Tyrolese Alps. When once his attention is called to the
subject, the traveller upon the railroad cannot fail to notice this
series of moraines, as he enters it through a tunnel at Lonato on the
west, and emerges from it at Soma Campagna, eighteen or twenty miles
distant to the east. A monument celebrating the victory stands upon a
moraine hill about half-way between, at Martino della Battaglie.
In other portions of central and southern Europe the mountains were too
low to furnish important centres for glacial movements. Still, to a
limited extent, the signs of ancient glaciers are seen in the mountains
of the Black Forest, in the Harz and Erzgebirge, and in the Carpathians
on the east and among the Apennines on the south. In Spain, also, there
were limited ice-fields on the higher portions of the Sierra Nevada
and in the mountains of Estremadura, and perhaps in some other places.
In France, small glaciers were to be found in the higher portions
of the Auvergne, of the Morvan, of the Vosges, and of the Cevennes;
while, from the Pyrenees, glaciers extended northward throughout nearly
their whole extent. The ice-stream descending from the central mass of
Maladetta through the upper valley of the Garonne, was joined by several
tributaries, and attained a length of about forty-five miles.
_The British Isles._
During the climax of the Glacial period the Hebrides to the north of
Scotland were covered with ice to a depth of 1,600 feet. How far westward
of this it moved out to the sea, it is of course impossible to tell. But
in the channels between the Hebrides and Scotland it is evident that
the water was completely expelled by the ice, and that, from a height
of 1,600 feet above the Hebrides to the northern shores of Scotland,
there was a continuous ice-field sloping southward at the rate of about
twenty-five feet a mile.
Scotland itself was completely enveloped in glacial ice. Prevented by
the Scandinavian Glacier from moving eastward, the Scotch movement was
compelled to be westward and southward. On the southwest the ice-stream
reached the shores of Ireland, and became confluent with the glaciers
that enveloped that island, completely filling the Irish Sea.
There are so many controverted points respecting the glacial geology of
England, and they have such an important bearing upon the main question
of this volume, that a pretty full discussion of them will be necessary.
I have recently been over enough of the ground myself to become satisfied
of the general correctness of the views entertained by my late colleague,
the lamented Professor Henry Carvill Lewis, whose death in 1888 took
place before the publication of his most mature conclusions. But the
lines of investigation to which he gave so powerful an impulse have since
been followed out by an active body of scientific observers. To give the
statement of facts greater precision and authority, I have committed
the preparation of it to the Secretary of the Northwest of England
Boulder Committee, Percy F. Kendall, F. G. S., Lecturer on Geology at
the Yorkshire College, Leeds, and at the Stockport Technical School,
England.[BM]
[Footnote BM: Mr. Kendall's contribution extends to page 181.]
"All the characteristic evidences of the action of land-ice can be found
in the greatest perfection in many parts of England and Wales. Drumlins,
kames, _roches moutonnées_, far-travelled erratics, terminal moraines,
and perched blocks, all occur. There are, besides, in the wide-spread
deposits of boulder-clay which cover so many thousands of square miles on
the low grounds lying on either side of the Pennine chain, evidences of
the operation of ice-masses of a size far exceeding that of the grandest
of existing European glaciers. But, while the proofs of protracted
and severe glaciation are thus patent, there are, nevertheless, many
apparently anomalous circumstances which arrest the attention when the
whole country is surveyed. The glacial phenomena appear to be strictly
limited to the country lying to the northward of a line extending from
the Bristol Channel to the mouth of the Thames; and within the glaciated
area there are many extensive tracts of land devoid of 'drift' or other
indications of ice-action.
"By comparison with the phenomena displayed in the North American
continent, English glacial geology must seem puny and insignificant; but,
just as with the features of the 'Solid Geology,' we have compressed
within the narrow limits of our isles an epitome of the features which
across the Atlantic require a continent for their exposition. It has
resulted from this concentration that English geology requires a much
closer and more minute investigation. And the difficulty which has been
experienced by glacial geologists of dealing with an involved series of
facts has, in the absence of any clue leading to the co-ordination of a
vast series of more or less disconnected observations, resulted in the
adoption, to meet certain local anomalies, of explanations which were
very difficult if not impossible of reconciliation with facts observed
in adjacent areas. Thus, to account for shell-bearing drift extending up
to the water-shed on one side of a lofty range of hills, a submergence
of the land to a depth of 1,400 feet has been postulated; leaving for
independent explanation the fact, that the opposite slopes of the hills
and the low ground beyond were absolutely destitute of drift or of any
evidence of marine action.
"In the following pages I must adopt a somewhat dogmatic tone, in order
to confine myself within the limits of space which are imposed; and trust
rather to the cohesion and consistency of the explanations offered and
to a few pregnant facts than to the weighing and contrasting of rival
theories.
"The facts point conclusively to the action in the British Isles of
a series of glaciers radiating outward from the great hill chains or
clusters, and, as the refrigeration progressed, becoming confluent and
moving though in the same general direction, yet with less regard to the
minor inequalities of the ground. During these two stages many glaciers
must have debouched upon the sea-coast, with the consequent production of
icebergs, which floated off with loads of boulders and dispersed them in
the random fashion which is a necessary characteristic of transport by
floating ice.
"With a further accentuation of the cold conditions the discharge of
bergs from terminal fronts which advanced into the extremely shallow
seas surrounding the British shores would be quite inadequate to relieve
the great press of ice, and a further coalescence of separate elements
must have resulted. In the case of enclosed seas--as, for example, the
Irish Sea--the continued inthrust of glacier-ice would expel the water
completely; and the conjoined ice-masses would take a direction of flow
the resultant of the momentum and direction of the constituent elements.
In other cases--as, for example, in the North Sea--extraneous ice
approaching the shores might cause a deflection of the flow of the native
glaciers, even though the foreign ice might never actually reach the
shore.
"To such a system of confluent glaciers, and to the separate elements
out of which they grew, and into which, after the culmination, they were
resolved, I attribute the whole of the phenomena of the English and Welsh
drift. And only at one or two points upon the coast, and raised but
little above the sea-level, can I recognise any signs of marine action.
"_The Preglacial Level of the Land._--There is very little direct
evidence bearing upon this point. In Norfolk the famous forest bed, with
its associated deposits, stands at almost precisely the level which it
occupied in preglacial times. At Sewerby, near Flamborough Head, there
is an ancient beach and 'buried cliff' which the sea is now denuding of
its swathing of drift-deposits, and its level can be seen to be almost
absolutely coincident with the present beach. Mr. Lamplugh, whose
description of the 'Drifts of Flamborough Head,'[BN] constitutes one of
the gems of glacial literature, considers that there is clear evidence
that the land stood at this level for a long period. The beach is covered
by a rain-wash of small extent, and that in turn by an ancient deposit
of blown sand, while the lowest member of the drift series of Yorkshire
covers the whole. Mr. Lamplugh thinks that the blown sand may indicate
a slight elevation of the land; but the beach appears to me to be the
storm beach, and the reduction in the force of the waves such as would
result from the approach of an ice-front a few miles to the seaward would
probably produce the necessary conditions.
[Footnote BN: Quarterly Journal of the Geological Society, vol. xlvii.]
"Six miles to the northward of Flamborough, at Speeton, a bed of
estuarine silt containing the remains of mollusca in the position of life
occurs at an altitude of ninety feet above high-water mark. Mr. Lamplugh
inclines to the opinion that this bed is of earlier date than the 'buried
cliff'; he also admits the possibility that its superior altitude may be
due to a purely local upward bulging of the soft Lower Cretaceous clays
upon which the estuarine bed rests by the weight of the adjacent lofty
chalk escarpment.
"The evidence obtained from inland sections and borings in different
parts of England has been taken to indicate a greater altitude in
preglacial times. Thus, in Essex, deep-borings have revealed the
existence of deep drift-filled valleys, having their floors below
sea-level. The valley of the Mersey is a still better example. Numerous
borings have been made in the neighbourhood of Widnes and at other places
in the lower reaches of the river, making it clear that there is a
channel filled with drift and extending to 146 feet below mean sea-level.
This, with several other instances, has been taken to indicate a greater
altitude for the land in preglacial times, since a river could not
erode its channel to such a depth below sea-level. The argument appears
inconclusive for one principal reason: no mention is made of any river
gravels or other alluvium in the borings. Indeed, there is an explicit
statement that the deposits are all glacial, showing that the channel
must have been cleared out by ice. This, therefore, leaves open the
vital question, whether the deposits removed were marine or fluviatile.
It may be remarked that the great estuary of the Mersey has undoubtedly
been produced by a post-glacial (and probably post-Roman) movement of
depression.
"_The Preglacial Climate._--In all speculations regarding the cause
of the Glacial epoch, due account must be taken of the undoubted fact
that it came on with extreme slowness and departed with comparative
suddenness. In the east of England an almost perfect and uninterrupted
sequence of deposits is preserved, extending from the early part of the
Pliocene period down to the present day.
"These in descending order are:
"1. Post-glacial sands, gravels, etc.
"2. Glacial series.
"3. The 'Forest Bed' and associated marine deposits.
"4. Chillesford clay and sand.
"5. The many successive stages of the Red Crag. (The Norwich Crag is a
local variation of the upper part of the Red Crag.)
"6. The Coralline Crag.
"The fossils preserved in these deposits, apart from the physical
indications, exhibit the climatal changes which accompanied their
deposition. The Coralline Crag contains a fauna consisting mainly
of species which now range to the Mediterranean, many of them being
restricted to the warm southern waters. Associated with these are a few
boreal forms, but they are represented in general by few individuals.
Here and there in the deposits of this age far-travelled stones are to
be found, but they are always accounted great rarities.
"The Red Crag consists of an irregular assemblage of beaches and
sand-banks of widely different ages, but their sequence can be made out
with ease by a study of the fauna. In the oldest deposits, Mediterranean
species are very numerous, while the boreal forms are comparatively rare;
but in successive later deposits the proportions are very gradually
reversed, and from the overlying Chillesford series the Mediterranean
species are practically absent. The physical indications run _pari
passu_ with the paleontological, and in the newer beds of the Red Crag
far-travelled stones are common.
"In the Forest Bed series there is a marine band--the _Leda myalis_
bed--which contains an almost arctic assemblage of shells; while at about
the same horizon plant remains have been found, including such high
northern species as _Salix polaris_ and _Betula nana_.
"The glacial deposits do not, in my opinion, contain anywhere in England
or Wales a genuine intrinsic fauna, such shells as occur in the East
Anglian glacial deposits having been derived in part from a contemporary
sea-bed, and, for the rest, from the older formations, down perhaps to
the Coralline Crag. In the post-glacial deposits we have hardly any trace
of a survival of the boreal forms, and I consider that the whole marine
fauna of the North Sea was entirely obliterated at the culmination of the
Glacial epoch, and that the repeopling in post-glacial times proceeded
mainly from the English Channel, into which the northern forms never
penetrated.
"_The Great Glacial Centres._
"Where such complex interactions have to be described as were produced
by the conflicting glaciers of the British Isles it is difficult to
deal consecutively with the phenomena of any one area, but with short
digressions in explanation of special points it may be possible to
accomplish a clear presentation of the facts.
"_Wales._--The phenomena of South Wales are comparatively simple. Great
glaciers travelled due southward from the lofty Brecknock Beacons,
and left the characteristic _moutonnée_ appearance upon the rocky bed
over which they moved. The boulder-transport is in entire agreement
with the other indications, and there are no shells in the drift. The
facts awaiting explanation are the occurrence in the boulder-clays of
Glamorganshire, at altitudes up to four hundred feet, of flints, and of
igneous rocks somewhat resembling those of the Archæan series of the
Wrekin. At Clun, in Shropshire, a train of erratics (see map) has been
traced back to its source to the westward. On the west coast, in Cardigan
Bay, the boulders are all such as might have been derived from the
interior of Wales. At St. David's Peninsula, Pembrokeshire, striæ occur
coming in from the northwest, and, taken with the discovery of boulders
of northern rocks, may point to a southward extension of a great glacier
produced by confluent sheets that choked the Irish Sea. Information
is very scanty regarding large areas in mid-Wales, but such as can be
gathered seems to point to ice-shedding having taken place from a north
and south parting line. In North Wales, much admirable work has been done
which clearly indicates the neighbourhood of Great Arenig (Arenig Mawr)
as the radiant point for a great dispersal of blocks of volcanic rock of
a characteristic Welsh type.
"_Ireland._--A brief reference must be made to Ireland, as the ice which
took origin there played an important part in bringing about some strange
effects in English glaciation, which would be inexplicable without a
recognition of the causes in operation across the Irish Sea. Ireland
is a great basin, surrounded by an almost continuous girdle of hills.
The rainfall is excessive, and the snow-fall was probably more than
proportionately great; therefore we might expect that an ice-sheet of
very large dimensions would result from this combination of favouring
conditions. The Irish ice-sheet appears to have moved outward from about
the centre of the island, but the main flow was probably concentrated
through the gaps in the encircling mountains.
"_Galloway._--The great range of granite mountains in the southwestern
corner of Scotland seems to have given origin to an immense mass of ice
which moved in the main to the southward, and there are good grounds
for the belief that the whole ice-drainage of the area, even that which
gathered on the northern side of the water-shed, ultimately found its
way into the Irish Sea basin and came down coastwise and across the low
grounds of the Rinns of Galloway, being pushed down by the press of
Highland ice which entered the Firth of Clyde. It is a noteworthy fact
that marine shells occur in the drift in the course taken by the ice
coming on to the extremity of Galloway from the Clyde.
"_The Lake District._--A radial flow of ice took place down the valleys
from about the centre of the Cumbrian hill-plexus, but movement to the
eastward was at first forbidden by the great rampart of the Cross Fell
escarpment, which stretches like a wall along the eastern side of the
Vale of Eden.
"During the time when the Cumbrian glaciers had unobstructed access
to the Solway Frith, to the Irish Sea, and to Morecambe Bay, the
dispersal of boulders of characteristic local rocks would follow the
ordinary drainage-lines; but, as will be shown later, a state of affairs
supervened in the Irish Sea which resulted, in many cases, in a complete
reversal of the ice-flow.
"_The Pennine Chain_ was the source of glaciers of majestic dimensions
upon both its flanks in the region north of Skipton, but to the southward
of that breach in the chain (see map) no evidence is obtainable of any
local glaciers.
"_The Confluent Glaciers._
"With the growth of ice-caps upon the great centres a condition of
affairs was brought about in the Irish Sea productive of results which
will readily be foreseen. The enormous volumes of ice poured into
the shallow sea from north, south, east, and west, resulted in such
a congestion as to necessitate the initiation of some new systems of
drainage.
"_The Irish Sea Glacier._--The ice from Galloway, Cumbria, and Ireland
became confluent, forming what the late Professor Carvill Lewis termed
'the Irish Sea Glacier,' and took a direction to the southward. Here it
came in diametrical conflict with the northward-flowing element of the
Welsh sheet, which it arrested and mastered; and the Irish Sea Glacier
bifurcated, probably close upon the precipitous Welsh coast to the
eastward of the Little Orme's Head, and the two branches flowed coastwise
to eastward and westward, keeping near the shore-line.
"The westerly branch swept round close to the coast in a southwesterly
direction, and completely overrode Anglesea; striating the rock-surfaces
from northeast to southwest (see map), and strewing the country with
its bottom-moraine, containing characteristic northern rocks, such
as the Galloway granites, the lavas and granites of the central and
western portions of the Lake District, and fragments of shells derived
from shell-banks in the Irish Sea. One episode of this phase of the
ice-movement was the invasion of the first line of hills between the
Menai Straits and Snowdon. The gravels and sands of Fridd-bryn-mawr,
Moel Tryfaen, and Moel-y-Cilgwyn, are the coarser washings of the
bottom-moraine, and consequently contain such rock-fragments and shells
as characterise it. From Moel-y-Cilgwyn southward, evidence is lacking
regarding the course taken by the glacier, but it probably passed over or
between the Rivals Mountains (Yr Eifl), and down Cardigan Bay at some
distance from the coast in confluence with the ice from mid-Wales; and,
as I have suggested, may have passed over St. David's Head.
"Returning now towards the head of the glacier we may follow with
advantage its left bank downward. The ice-flow on the Cumberland coast
appears to have resembled very much that in North Wales. A great press of
ice from the northward (Galloway) seems to have had a powerful 'easting'
imparted to it by the conjoint influences of the thrust of the Irish ice
and the inflow of ice from the Clyde. Whatever may have been the cause,
the effect is clear: about Ravenglass cleavage took place, and a flow to
northward and to southward, each bending easterly. By far the larger mass
took a southerly course and bent round Black Combe, over Walney, and a
strip of the mainland about Barrow in Furness, and out into and across
Morecambe Bay. Its limits are marked in the field by the occurrence of
the same rocks which characterise it in Anglesea, viz., the granites of
Galloway and of west and central Cumbria.
"The continued thrust shouldered in the glacier upon the mainland of
Lancashire, but the precise point of emergence has not yet been traced,
though it cannot be more than a few miles from the position indicated on
the map. I should here remark, that all along the boundaries the Irish
Sea Glacier was confluent with local ice, except, probably, in that part
of the Pennine chain to the southward of Skipton. Down to Skipton there
was a great mass of Pennine ice which was compelled to take an almost
due southerly course, and thus to run directly athwart the direction of
the main hills and valleys. A sharp easterly inflection of the Irish Sea
Glacier carried it up the valley of the Ribble, and thence, under the
shoulder of Pendle, to Burnley, where Scottish granites are found in the
boulder-clay.
"On the summit of the Pennine water-shed, at Heald Moor, near Todmorden
(1,419 feet), boulder-clay has been found containing erratics belonging
to this dispersion; while in the gorge of the Yorkshire Calder, which
flows along the eastern side of the same hill, not a vestige of such a
deposit is to be found, saving a few erratic pebbles at a distance of
eight or ten miles, which were probably carried down by flood-wash from
the edge of the ice.
"From this point the limits of the ice may be traced along the flanks of
the Pennine chain at an average altitude of about 1,100 feet.
"At one place the erratics can be traced to a position which would
indicate the formation of an extra-morainic lake having its head at a
col about 1,000 feet above sea-level, separating it from the valley of
an eastward-flowing stream, the Wye, about twelve miles down which a few
granite blocks have been found. Other extra-morainic lakes must have
been formed, but very little information has been collected regarding
them. The Irish Sea Glacier can be shown to have spread across the whole
country to the westward of the line I have traced, and beyond the estuary
of the Dee.
"I may now follow its boundaries on the Welsh coast, and pursue the line
to the final melting-place of the glacier. From the Little Orme's Head
the line of confluence with the native ice is pretty clearly defined. It
runs in, perhaps, half a mile from the shore, until the broad low tract
of the Vale of Clwyd is reached. Here the northern ice obtained a more
complete mastery, and pushed in even as far as Denbigh. This extreme
limit was probably attained as a mere temporary episode. Horizontal striæ
on a vertical face of limestone on the crags dominating the mouth of the
vale on the eastern side attest beyond dispute the action of a mass of
land-ice moving in from the north.
"I may here remark, that in this district the deposits furnish a very
complete record of the events of the Glacial period. In the cliffs on
the eastern side of the Little Orme's Head, and at several other points
along the coast towards the east, a sequence may be observed as follows:
"4. Boulder-clay with northern erratics and shells.
"3. Sands and gravels with northern erratics and shells.
"2. Boulder-clay with northern erratics and shells.
"1. Boulder-clay with Welsh erratics and no shells.
"A similar succession is to be seen in the Vale of Clwyd. The
interpretation is clear: In the early stages of glaciation the Welsh
ice spread without hindrance to, and laid down, bed No. 1; then the
northern ice came down, bringing its typical erratics and the scourings
of the sea-bottom, and laid down the variable series of clays, sands, and
gravels which constitute Nos. 2, 3, and 4 of the section.
[Illustration: Fig. 42.--The Cefn Cave, in Vale of Clwyd. (Trimmer.) _a_,
Entrance; _b_, mud with pebbles and wood covered with stalagmite; _c_,
mud, bones, and angular fragments of limestone; _d_, sand and silt, with
fragments of marine shells; _e_, fissure; _f_, northern drift; _g_, cave
cleared of mud; _h_, river Elwy, 100 feet below; _i_, limestone rock.]
"In the Vale of Clwyd an additional interest is imparted to the study of
the drift from the circumstance that the remains of man have been found
in deposits in caves sealed with drift-beds. The best example is the Cae
Gwyn caves, in which flint implements and the bones and teeth of various
extinct animals were found embedded in 'cave-earth' which was overlaid
by bedded deposits of shell-bearing drift, with erratics of the northern
type.
"It has been supposed that the drift-deposits were marine accumulations;
but it is inconceivable that the cave could ever have been subjected to
wave-action without the complete scouring out of its contents.
"To resume the delineation of the limits of the great Irish Sea Glacier:
From the Vale of Clwyd the boundary runs along the range of hills
parallel to the estuary of the Dee at an altitude of about nine hundred
feet. As it is traced to the southeast it gradually rises, until at
Frondeg, a few miles to the northward of the embouchure of the Yale of
Llangollen, it is at a height of 1,450 feet above sea-level. Thence it
falls to 1,150 feet at Gloppa, three miles to the westward of Oswestry,
and this is the most southerly point to which it has been definitely
traced on the Welsh border, though scattered boulders of northern rocks
are known to occur at Church Stretton.
"Along the line from the Vale of Clwyd to Oswestry the boundary is
marked by a very striking series of moraine-mounds. They occur on the
extreme summits of lofty hills in a country generally almost driftless,
and their appearance is so unusual that one--Moel-y-crio--at least
has been mistaken for an artificial tumulus. The limitation of the
dispersal of northern erratics by these mounds is very clear and
sharp; and Mackintosh, in describing those at Frondeg, remarked that,
while no northern rocks extended to the westward of them, so no Welsh
erratics could be found to cross the line to the eastward. There are
Welsh erratics in the low grounds of Cheshire and Shropshire, but their
distribution is sporadic, and will be explained in a subsequent section.
"Having thus followed around the edges of this glacier, it remains to
describe its termination. It is clear that the ice must have forced its
way over the low water-shed between the respective basins of the Dee and
the Severn. So soon as this ridge (less than 500 feet above the sea)
is crossed, we find the deposits laid down by the glacier change their
character, and sands and gravels attain a great predominance.[BO] Near
Bridgenorth, and, at other places, hills composed of such materials
attain an altitude of 200 feet. From Shrewsbury _via_ Burton, and thence,
in a semicircular sweep, through Bridgenorth and Enville, there is an
immense concentration of boulders and pebbles, such as to justify the
designation of a terminal moraine. To the southward, down the valley
of the Severn, existing information points to the occurrence merely of
such scattered pebbles as might have been carried down by floods. In the
district lying outside this moraine there is a most interesting series of
glacial deposits and of boulders of an entirely different character. (See
map.)
[Footnote BO: Mackintosh, Q. J. G. S.]
"From the neighbourhood of Lichfield, through some of the suburbs of
Birmingham, and over Frankley Hill and the Lickey Hills to Bromsgrove,
there is a great accumulation of Welsh erratics, from the neighbourhood,
probably, of Arenig Mawr.
"The late Professor Carvill Lewis suggested that these Arenig rocks
might have been derived from some adjacent outcrop of Palæozoic rocks--a
suggestion having its justification in the discoveries that had been made
of Cumbrian rocks in the Midlands. To test the matter, an excavation was
made at a point selected on Frankley Hill, and a genuine boulder-clay
was found, containing erratics of the same type as those found upon the
surface.
"The explanation has since been offered that this boulder-clay was a
marine deposit laid down during a period of submerge nee.[BP] Apart
from the difficulty that the boulder-clay displays none of the ordinary
characteristics of a marine deposition, but possesses a structure,
or rather absence of structure, in many respects quite inconsistent
with such an origin, and contains no shells or other remains of marine
creatures, it must be pointed out that no theory of marine notation
will explain the distribution of the erratics, and especially their
concentration in such numbers at a station sixty or seventy miles from
their source.
[Footnote BP: Proceedings of the Birmingham Philosophical Society, vol.
vi, Part I, p. 181.]
"Upon the land-ice hypothesis this difficulty disappears. During the
early stages of the Glacial period the Welsh ice had the whole of
the Severn Valley at its mercy, and a great glacier was thrust down
from Arenig, or some other point in central Wales, having an _initial
direction_, broadly speaking, from west to east. This glacier extended
across the valley of the Severn, sweeping past the Wrekin, whence it
carried blocks of the very characteristic rocks to be lodged as boulders
near Lichfield; and it probably formed its terminal moraine along the
line indicated. (See lozenge-shaped marks on the map.) As the ice in
the north gathered volume it produced the great Irish Sea Glacier,
which pressed inland and down the Vale of Severn in the manner I have
described, and brushed the relatively small Welsh stream out of its path,
and laid down its own terminal moraine in the space between the Welsh
border and the Lickey Hills. It seems probable that the Welsh stream
came mainly down the Vale of Llangollen, and thence to the Lickey Hills.
Boulders of Welsh rocks occur in the intervening tract by ones and twos,
with occasional large clusters, the preservation of any more connected
trail being rendered impossible by the great discharge of water from
the front of the Irish Sea Glacier, and the distributing action of the
glacier itself.
"Within the area in England and Wales covered by the Irish Sea Glacier
all the phenomena point to the action of land-ice, with the inevitable
concomitants of subglacial streams, extra-morainic lakes, etc. There is
nothing to suggest marine conditions in any form except the occurrence
of shells or shell fragments; and these present so many features of
association, condition, and position inconsistent with, what we should
be led to expect from a study of recent marine life, that conchologists
are unanimous in declaring that not one single group of them is on the
site whereon the shells lived. It is a most significant fact--one out of
a hundred which could be cited did space permit--that in the ten thousand
square miles of, as it is supposed, recently elevated sea-bottom, not a
single example of a bivalve shell with its valves in apposition has ever
been found! Nor has a boulder or other stone been found encrusted with
those ubiquitous marine parasites, the barnacles.
"The evidences of the action of land-ice within the area are everywhere
apparent in the constancy of direction of-- (1.) Striæ upon rock
surfaces. (2.) The terminal curvature of rocks. (3.) The 'pull-over' of
soft rocks. (4.) The transportal of local boulders. (5.) The orientation
of the long axes of large boulders. (6.) The false bedding of sands
and gravels. (7.) The elongation of drift-hills. (8.) The relations
of 'crag and tail.' There is a similar general constancy, too, in the
directions of the striæ upon large boulders. Upon the under side they run
longitudinally from southeast (or thereabouts) to northwest, while upon
the upper surface they originate at the opposite end, showing that the
scratches on the under side were produced by the stone being dragged from
northwest to southeast, while those on the top were the product of the
passage of stone-laden ice over it in the same direction.
"Such an agreement cannot be fortuitous, but must be attributed to the
operation of some agent acting in close parallelism over the whole
area. To attribute such regularity to the action of marine currents is
to ignore the most elementary principles of marine hydrology. Icebergs
must, in the nature of things, be the most erratic of all agents, for
the direction of drift is determined--among other varying factors--by
the draught of the berg. A mass of small draught will be carried by
surface currents, while one of greater depth will be brought within the
influence of under-currents; and hence it not infrequently happens that
while floe-ice is drifting, say, to the southeast, giant bergs will go
crashing through it to the northwest. There are tidal influences also to
be reckoned with, and it is matter of common knowledge that flotsam and
jetsam travel back and forth, as they are alternately affected by ebb and
flood tide.
"Bearing these facts in mind, it is surely too much to expect that
marine ice should transport boulders (how it picked up many of them also
requires explanation) with such unfailing regularity that it can be said
without challenge,[BQ] 'boulders in this district [South Lancashire and
Cheshire] never occur to the north or west of the parent rock.' The
same rule applies without a single authentic exception to the whole
area covered by the eastern branch of the Irish Sea Glacier; and hence
it comes about that not a single boulder of Welsh rock has ever been
recorded from Lancashire.
[Footnote BQ: Brit. Assoc. Report, 1890, p. 343.]
"_The Solway Glacier._--The pressure which forced much of the Irish Sea
ice against the Cumbrian coast-line caused, as has been described, a
cleavage of the flow near Ravenglass, and, having followed the southerly
branch to its termination in the midlands, the remaining moiety demands
attention.
"The 'easting' motion carried it up the Solway Frith, its right flank
spreading over the low plain of northern Cumberland, which it strewed
with boulders of the well-known 'syenite' (granophyre) of Buttermere.
When this ice reached the foot of the Cross Fell escarpment, it suffered
a second bifurcation, one branch pushing to the eastward up the valley
of the Irthing and over into Tyneside, and the other turning nearly due
southward and forcing its way up the broad Vale of Eden.
"Under the pressure of an enormous head of ice, this stream rose from
sea-level, turned back or incorporated the native Cumbrian Glacier
which stood in its path, and, having arrived almost at the water-shed
between the northern and the southern drainage, it swept round to the
eastward and crossed over the Pennine water-shed; not, however, by the
lowest pass, which is only some 1,400 feet above sea-level, but by the
higher pass of Stainmoor, at altitudes ranging from 1,800 to 2,000
feet. The lower part of the course of this ice-flow is sufficiently
well characterised by boulders of the granite of the neighbourhood of
Dalbeattie in Galloway; but on its way up the Vale of Eden it gathered
several very remarkable rocks and posted them as way-stones to mark its
course. One of these rocks, the Permian Brockram, occurs nowhere _in
situ_ at altitudes exceeding 700 feet, yet in the course of its short
transit it was lifted about a thousand feet above its source. The Shap
granite (see radiant point on map) is on the northern side of the east
and west water-sheds of the Lake District, and reaches its extreme
elevation, (1,656 feet) on Wasdale Pike; yet boulders of it were carried
over Stainmoor, at an altitude of 1,800 feet literally by tens of
thousands.
"This Stainmoor Glacier passed directly over the Pennine chain, past the
mouths of several valleys, and into Teesdale, which it descended and
spread out in the low grounds beyond. Pursuing its easterly course, it
abutted upon the lofty Cleveland Hills and separated into two streams,
one of which went straight out to sea at Hartlepool, while the other
turned to the southward and flowed down the Vale of York, being augmented
on its way by tributary glaciers coming down Wensleydale. The final
melting seems to have taken place somewhere a little to the southward
of York; but boulders of Shap granite by which its extension is
characterised have been found as far to the southward as Royston, near
Barnsley.
"The other branch of the Solway Glacier--that which travelled due
eastward--passed up the valley of the Irthing, and over into that of the
Tyne, and out to sea at Tynemouth. It carried the Scottish granites with
it, and tributary masses joined on either hand, bringing characteristic
boulders with them.
"The fate of those elements of the Solway Frith Glacier which reached
the sea is not left entirely to conjecture. The striated surfaces near
the coast of Northumberland indicate a coastwise flow of ice from the
northward--probably from the Frith of Forth--and the glaciers coming out
from the Tyne and Tees were deflected to the southward.
"There is conclusive evidence that this ice rasped the cliffs of the
Yorkshire coast and pressed up into some of the valleys. Where it passed
the mouth of the Tees near Whitby it must have had a height of at least
800 feet, but farther down the coast it diminished in thickness. It
nowhere extended inland more than a mile or two, and for the most part
kept strictly to the coast-line. Along the whole coast are scattered
erratics derived from Galloway and the places lying in the paths of the
glaciers. In many places the cliffs exhibit signs of rough usage, the
rocks being crumpled and distorted by the violent impact of the ice. At
Filey Brigg a well-scratched surface has been discovered, the striation
being from a few degrees east of north.
"At Speeton the evidence of ice-sheet or glacier-work is of the most
striking character. On the top of the cliffs of Cretaceous strata a line
of moraine-hills has been laid down, extending in wonderful perfection
for a distance of six miles. They consist of a mixture of sand,
gravel, and a species of clay-rubble, with occasional masses of true
boulder-clay, the whole showing the arched bedding so characteristic
of such accumulations. At the northerly end the moraine keeps close to
the edge of the chalk cliffs, which are there 400 feet high, and the
hills are frequently displayed in section; but as the elevation of the
cliffs declines they fall back from the edge of the cliffs and run quite
across the headland of Flamborough, and are again exposed in section in
Bridlington Bay. One remarkable and significant fact is pointed out,
namely, that behind this moraine, within half a mile and at a lower
level, the country is almost absolutely devoid of any drift whatever.
[Illustration: Fig. 43.--Moraine between Speeton and Flamborough
(Lamplugh).]
"The interpretation of these phenomena is as follows: When the
valley-glaciers reached the sea they suffered the deflection which has
been mentioned, partly as the result of the interference of ice from
the east of Scotland, but also influenced directly by the cause which
operated upon the Scottish ice and gave direction to it--that is, the
impact of a great glacier from Scandinavia, which almost filled the North
Sea, and turned in the eastward-flowing ice upon the British coast.
"It is easy to see how this pressure must have forced the glacier-ice
against the Yorkshire coast, but vertical chalk cliffs 400 feet in
height are not readily surmounted by ice of any thickness, however
great, and so it coasted along and discharged its lateral moraine upon
the cliff-tops. As the cliffs diminished in height we find the moraine
farther inland, and, as I have pointed out, the ice completely overrode
Flamborough Head. Amongst the boulders at Flamborough are many of Shap
granite, a few Galloway granites, a profusion of Carboniferous rocks,
brought by the Tyne branch of the Sol way Glacier as well as by that of
Stainmoor, and, besides many torn from the cliffs of Yorkshire, a few
examples of unquestionable Scandinavian rocks, such as the well-known
_Rhomben-porphyr_. It is important to note that about ten to twenty
miles from the Yorkshire coast there is a tract of sea-bottom called
by trawlers 'the rough ground,' in allusion to the fact that it is
strewn with large boulders, amongst which are many of Shap granite. This
probably represents a moraine of the Teesdale Glacier, laid down at a
time when the Scandinavian Glacier was not at its greatest development.
"On the south side of Flamborough Head the 'buried cliff' previously
alluded to occurs. The configuration of the country shows--and the
conclusion is established by numerous deep-borings--that the preglacial
coast-line takes a great sweep inland from here, and that the plain of
Holderness is the result of the banking-up of an immense thickness of
glacial _débris_. In the whole country reviewed, from Tynemouth to
Bridlington, wherever the ice came on to the land from the seaward, it
brought in shells and fragmentary patches of the sea-bottom involved in
its ground moraine. Space does not permit of a detailed description of
the several members of the Yorkshire Drift, and I pass on to deal in a
general way with the glacial phenomena of the eastern side of England.
"_The East Anglian Glacier._--The influence of the Scandinavian ice is
clearly seen in the fact that the entire ice-movement down the east
coast south of Bridlington was all from the _seaward_. Clays, sands, and
gravels, the products of a continuous mass of land-ice coming from the
northeast are spread over the whole country, from the Trent to the high
grounds on the north of London overlooking the Thames.
"The line of extreme extension of these drift-deposits runs from Finchley
(near London), in the south across Hertfordshire, through Cambridgeshire,
with outlying patches at Gogmagog and near Buckingham, and northwestward
over a large portion of Leicestershire into the upper waters of the
Trent, embracing the elevated region of Palæozoic rocks at Charnwood
Forest, near Leicester.
"Reserving the consideration of the very involved questions connected
with the drifts of the upper part of the Trent Valley, I may pass
on to join the phenomena of the southeastern counties with those at
Flamborough Head. From Nottinghamshire the limits of the drift of the
East Anglian Glacier seem to run in a direction nearly due west to east,
for the great oolitic escarpment upon which Lincoln Cathedral is built
is absolutely driftless to the northward of the breach about Sleaford.
However, along the western flank of the oolitic range true boulder-clay
occurs, bordering and doubtless underlying the great fen-tract of
mid-Lincolnshire; and the great Lincolnshire Wolds appear to have been
completely whelmed beneath the ice.
"The most remarkable of the deposits in this area is the Great Chalky
Boulder-Clay, which consists of clay containing much ground-up chalk,
and literally packed with well-striated boulders of chalk of all sizes,
from minute pebbles up to blocks a foot or more in diameter. Associated
with them are boulders of various foreign rocks, and many flints in a
remarkably fresh condition, and still retaining the characteristic white
coat, except where partially removed by glacial attrition.
"One of the perplexing features of the glacial phenomena in the eastern
counties of England is the extension of true chalky boulder-clay to the
north London heights at Finchley and elsewhere; for only the faintest
traces are to be found in the gravel deposits of the Thames Valley of any
wash from such a deposit, or from a glacier carrying such materials.
"It has been suggested that the deposit may have been laid down in an
extra-morainic lake, or in an extension of the North. Sea, but these
suggestions leave the difficulty just where it was. If a lake or sea
could exist without shores, a glacier-stream might equally dispense with
banks. Within the area of glaciation, defined above, abundant evidence
of the action of land-ice is obtainable, though striated surfaces are
extremely rare--a fact attributable to the softness of the chalk and
clays which occupy almost the whole area. Well-striated surfaces are
found on the harder rocks, as, for example, on the oolitic limestone at
Dunston, near Lincoln.
"Mr. Skertchly has remarked that the proofs of the action of land-ice
are irrefragable. The Great Chalky Boulder-Clay covers an area of
3,000 square miles, and attains an altitude of 500 feet above the
sea-level, thus bespeaking, if the product of icebergs, 'an extensive
gathering-ground of chalk, having an elevation of more than 500 feet.
But where is it? Certainly not in Western Europe, for the chalk does not
attain so great an elevation except in a few isolated spots.'[BR]
[Footnote BR: Geikie's Great Ice Age, p. 360.]
[Illustration: Fig. 44.--Diagram-section near Cromer (Woodward). 6.
Gravel and sand (Middle Glacial) resting on contorted drift (loam, sand,
and marl, with large included boulders of chalk); 5. Cromer till: 4.
Laminated clay and sands (Leda myalis bed); 3. Fresh-water loams and
sands: 3_a_. Black fresh-water bed of Runton (upper fresh-water bed); 2.
Forest bed--laminated clays and sands, with roots and _débris_ of wood,
bones of mammalia, estuarine mollusca, etc., the upper part in places
penetrated by rootlets (rootlet bed); 2_a_. Weybourn crag; 1. Chalk with
flints; * Large included boulder of chalk.]
"It has been further pointed out by Mr. Skertchly, that the condition of
the flints in this deposit furnishes strong evidence that they could not
have been carried by floating ice nor upon a glacier, for, in either of
the latter events, there must have been some exposure to the weather,
which, as he remarks, would have rendered them worthless to the makers of
gun-flints, whereas they are now regularly collected for their use.
"The way in which the boulder-clay is related to the rocks upon which
it rests is a conclusive condemnation of any theory of floating ice;
for example, where it rests upon Oxford Clay, it contains the fossils
characteristic of that formation, as it is largely made up of the clay
itself. The exceptions to this rule are as suggestive as those cases
which conform to it. Each outcrop yields material to the boulder-clay to
the south westward, showing a pull-over from the northeast.
"One of the most remarkable features of the drift of this part of
England is the inclusion of gigantic masses of rock transported for
a short distance from their native outcrop, very often with so small
a disturbance that they have been mapped as _in situ_. Examples of
chalk-masses 800 feet in length, and of considerable breadth and
thickness, have been observed in the cliffs near Cromer, in Norfolk, but
they are by no means restricted to situations near the coast. One example
is mentioned in which quarrying operations had been carried on for some
years before any suspicion was aroused that it was merely an erratic.
The huge boulders were probably dislodged from the parent rock by the
thrust of a great glacier, which first crumbled the beds, then sheared
off a prominent fold and carried it along. This explanation we owe to Mr.
Clement Reid.[BS] The drift-deposits of this region frequently contain
shells, but they rarely constitute what may be termed a consistent fauna,
usually showing such an association as could only be found where some
agent had been at work gathering together shells of different habitats
and geological age.
[Footnote BS: See Geology of the Country around Cromer, and Geology of
Holderness, Memoirs of Geological Survey of England and Wales.]
[Illustration: Fig. 45.--Section at right angles to the cliff through
the westerly chalk bluff at Trimingham, Norfolk, showing the manner in
which chalk masses are incorporated into the till (Clement Reid). Scale,
250 fret to an inch. A. Level of low-water spring-tides; B. Chalk, with
sandy bed at *; C. Forest-bed series, etc., seen in the cliffs a few
yards north and south of this point; D. Cromer till, stiff lead-colored
boulder-clay; E. Fine, chalky sands, much false-bedded; F. Contorted
drift, brown bouldery-clay with marked bedding- or fluxion-structure; G.
The bed, above the white line were seen and measured by more snow and
measured by Mr. Reid; * Chalk seen _in situ_ on beach.
"If the ice-sheet, instead of flowing over the beds, happens to plough
into them or abut against them, it would bend up a boss of chalk, as at
Beeston. A more extensive disturbance, like that at Trimingham drives
before it a long ridge of the bads, and nips up the chalk, till, like
a cloth creased by the sliding of a heavy book, it is folded into an
inverted anticlinal. A slight increase of pressure, and the third stage
is reached--the top of the anticlinal being entirely sheared off, the
chalk boulder driven up an incline, and forced into the overlying
boulder-clays." (Clement Reid.)]
"Attempts have been made to correlate the deposits over the whole area,
but with very indifferent success. A consideration of the consequences
of the invasion of the country by an ice-stream from the northeast will
prepare us for any conceivable complication of the deposits.
"The main movement was against the drainage of the country, so that
the ice-front must have been frequently in water. There would be
aqueous deposition and erosion; the kneading up of morainic matter into
ground-moraine; irregularities of distribution and deposition due to ice
floating in an extra-morainic lake; flood-washes at different points of
overflow; and other confusing causes, which make it rather matter for
surprise that any order whatever is traceable.
"I now turn to the valley of the Trent. We find that it occupies such a
position that it would be exposed, successively or simultaneously, to
the action of ice-streams of most diverse origin. I have shown that the
area to the westward of Lichfield was invaded at one period by a Welsh
glacier, and at a subsequent one by the Irish Sea Glacier, and both of
these streams entered the valley of the Trent or some of its affluents.
From the eastward, again, the great North Sea Glacier encroached in like
manner, carrying the Great Chalky Boulder-Clay even into the drainage
area of the westward-flowing rivers near Coventry.
"The glacial geology of the Trent Valley from Burton to Nottingham has
been ably dealt with by Mr. R. M. Deeley,[BT] who recognises a succession
which may be generalised as follows: (1.) A lower series containing rocks
derived from the Pennine chain; (2.) A middle series containing rocks
from the eastward (chalky boulder-clay, etc.); and (3.) An upper series
with Pennine rocks. Mr. Deeley thinks the Pennine _débris_ may have
been brought by glaciers flowing down the valleys of the Dove, the Wye,
and the Derwent; but, while recognising the importance of the testimony
adduced, especially that of the boulders, I am compelled to reserve
judgment upon this point until something like moraines or other evidences
of local glaciers can be shown in those valleys. In their upper parts
there is not a sign of glaciation. Some of the deposits described must
have been laid down by land-ice; while the conformation of the country
shows that during some stages of glaciation a lake must have existed
into which the different elements of the converging glaciers must have
projected. This condition will account for the remarkable commingling of
boulders observed in some of the deposits. Welsh, Cumbrian, and Scottish
rocks occur in the western portion of the Trent Valley. The overflow of
the extra-morainic lake would find its way into the valleys of the Avon
and Severn, and may be taken to account for the abundance of flints in
some of the gravels.
[Footnote BT: Quarterly Journal Geological Society, vol. xlii, p. 437.]
"_The Isle of Man._--This little island in mid-seas constituted in the
early stages of the Glacial epoch an independent centre of glaciation,
and from some of its valleys ice-streams undoubtedly descended to the
sea; but with the growth of the great Irish Sea Glacier the native ice
was merged in the invading mass, and at the climax of the period the
whole island was completely buried, even to its highest peak (Snae Fell,
2,054 feet), beneath the ice. The effects of this general glaciation
are clearly seen in the mantle of unstratified drift material which
overspread the hills; in the _moutonnée_ appearance of the entire
island; and in the transport of boulders of local rocks. The striations
upon rock surfaces show a constancy of direction in agreement with the
boulder-transport which can be ascribed to no other agency than a great
continuous sheet of such dimensions as to ignore minor hills and valleys.
"The disposition of the striæ is equally conclusive, for we find that on
a stepped escarpment of limestone both the horizontal and the vertical
faces are striated continuously and obliquely from the one on to the
other, showing that the ice had a power of accommodating itself to the
surface over which it passed that could not be displayed by floating ice.
There is a remarkable fact concerning the distribution of boulders on
this island which would strike the most superficial observers, namely,
that foreign rocks are confined to the low grounds. It might be argued
that the local ice always retained its individuality, and so kept the
foreign ice with its characteristic boulders at bay. But, apart from
the _a priori_ improbability of so small a hill-cluster achieving what
the Lake District could not accomplish, the fact that Snae Fell, an
isolated _conical_ hill, is swathed in drift from top to bottom, is
quite conclusive that the foreign ice must have got in. Why, then, did
it carry no stones with it? The following suggestion I make not without
misgivings, though there are many facts to which I might appeal that seem
strongly corroborative:
"The hilly axis of the island runs in a general northeast and southwest
direction, and it rises from a great expanse of drift in the north with
singular abruptness, some of the hills being almost inaccessible to a
direct approach without actual climbing. I imagine that the ice which
bore down upon the northern end of the island was, so far as its lower
strata were concerned, unable to ascend so steep an acclivity, and was
cleft, and flowed to right and left. The upper ice, being of ice-sheet
origin, would be relatively clean, and this flowing straight over the
top of the obstruction would glaciate the country with such material as
was lying loose upon the ground or could be dislodged by mere pressure.
It would appear from published descriptions that the Isle of Arran
offers the same problem, and I would suggest the application of the same
solution to it.
"Marine shells occur in the Manx drift, but only in such situations
as were reached by the ice-laden with foreign stones. They present
similar features of association of shells of different habitat, and
perhaps of geological age, to those already referred to as being common
characteristics of the shell-faunas of the drift of the mainland. Four
extinct species of mollusca have been recognised by me in the Manx drift.
"The Manx drift is of great interest as showing, perhaps better than any
locality yet studied, those features of the distribution of boulders of
native rocks which attest so clearly the exclusive action of land-ice.
There are in the island many highly characteristic igneous rocks, and I
have found that boulders of these rocks never occur to the northward of
the parent mass, and very rarely in any direction except to the southwest.
"Cumming observed in regard to one rock, the Foxdale granite, that
whereas the highest point at which it occurs _in situ_ was 657 feet
above sea-level, boulders of it occurred in profusion within 200 feet of
the summit of South Barrule (1,585 feet), a hill two miles only, in a
southwesterly direction, from the granite outcrop.
"They also occur on the summit of Cronk-na-Irrey-Lhaa, 1,449 feet above
sea-level. The vertical uplift has been 728 and 792 feet respectively.
"In the low grounds of the north of the island a finely developed
terminal moraine extends in a great sweep so as to obstruct the drainage
and convert thousands of acres of land into lake and morass, which is
only now yielding to artificial drainage. Many fine examples of drumlin
and esker mounds occur at low levels in different parts of the island;
and it was remarked nearly fifty years ago by Cumming, that their long
axes were parallel to the direction of ice-movement indicated by the
striated surfaces and the transport of boulders.
"The foreign boulders are mainly from the granite mountains of Galloway,
but there are many flints, presumably from Antrim, a very small number
of Lake District rocks, and a remarkable rock containing the excessively
rare variety of hornblende, Riebeckite. This has now been identified with
a rock on Ailsa Crag, a tiny islet in the Frith of Clyde; and a Manx
geologist, the Rev. S. N. Harrison, has discovered a single boulder of
the highly characteristic pitchstone of Corriegills, in the Isle of Arran.
"_The So-called Great Submergence._
"It may be convenient to adduce some additional facts which render the
theory of a great submergence of the country south of the Cheviots
untenable.
"The sole evidence upon which it rests is the occurrence of shells,
mostly in an extremely fragmentary condition, in deposits occurring at
various levels up to about 1,400 feet above sea-level: A little space may
profitably be devoted to a criticism of this evidence.
"_Moel Tryfaen_ ('The Hill of the Three Rocks').--This celebrated
locality is on the first rise of the ground between the Menai Straits and
the congeries of hills constituting 'Snowdonia'; and when we look to the
northward from the top of the hill (1,350 feet) we see the ground rising
from the straits in a series of gentle undulations whose smooth contours
would be found from a walk across the country to be due to the thick
mask of glacial deposits which obliterates the harsher features of the
solid rocks.
"The deposits on Moel Tryfaen are exposed in a slate-quarry on the
northern aspect of the hill near the summit, and consist of two wedges
of structureless boulder-clay, each thinning towards the top of the
hill. The lower mass of clay, wherever it rests upon the rock, contains
streaks and irregular patches of eccentric form, of sharp, perfectly
angular fragments of slate; and the underlying rock may be seen to be
crushed and broken, its cleavage-laminæ being thrust over from northwest
to southeast--that is, _up-hill_. The famous 'shell-bed' is a thick
series of sands and gravels interosculated with the clays on the slope of
the hill, but occupying the entire section above the slate towards the
top. The bedding shows unmistakable signs of the action of water, both
regular stratification and false bedding being well displayed. The stones
occurring in the clays are mainly if not entirely Welsh, including some
from the interior of the country, and they are not infrequently of large
size--two or three tons' weight--and well scratched.
"The stones found in the sands and gravels include a great majority of
local rocks, but besides these there have been recorded the following:
Rock. Source. Highest Minimum
point uplift
_in situ_. in feet.
Granite Eskdale, Cumberland 1,286 64
Granite Criffel, Galloway ..... ...
Flint Antrim (?) 1,000 350
To these I can add:
Granophyre Buttermere, Cumberland ..... ...
Eurite [BU] Ailsa Craig, Frith of Clyde 1,097 253
[Footnote BU: The altitude at which this rock occurs on Ailsa Craig
has not been announced, so 1 have put it as the extreme height of the
island.]
"The shells in the Moel Tryfaen deposit have been fully described, so far
as the enumeration of species and relative frequency are concerned, but
little has been said as to their absolute abundance and their condition.
The shells are extremely rare, and daring a recent visit a party of five
persons, in an assiduous search of about two hours, succeeded in finding
_five whole shells_ and about two ounces of fragments. The opportunities
for collecting are as good as could be desired. The sections exposed have
an aggregate length of about a quarter of a mile, with a height varying
from ten to twenty feet of the shelly portion; and besides this there are
immense spoil-banks, upon whose rain-washed slopes fossil-collecting can
be carried on under the most favorable conditions.
"I would here remark, that the occurrence of small seams of shelly
material of exceptional richness has impressed collectors with the idea
that they were dealing with a veritable shell-bed, when the facts would
bear a very different interpretation. A fictitious abundance is brought
about by a process of what may be termed 'concentration,' by the action
of a gently flowing current of water upon materials of different sizes
and different specific gravities. Shells when but recently vacated
consist of materials of rather high specific gravity, penetrated by pores
containing animal matter, so that the density of the whole mass is far
below that of rocks in general, and hence a current too feeble to move
pebbles would yet carry shells. Illustrations of this process may be
observed upon any shore in the concentration of fragments of coal, corks,
or other light material.
"Regarding the interpretation of these facts: The commonly received
idea is, that the beds were laid down in the sea during a period of
submergence, and that the shells lived, not perhaps on the spot, but
somewhere near, and that the terminal curvature of the slate was produced
by the grounding of icebergs which also brought the boulders. But if
this hypothesis were accepted, it would be necessary to invest the
flotation of ice with a constancy of direction entirely at variance with
observed facts, for the phenomena of terminal curvature is shown" with
perfect persistence of direction wherever the boulder-clay rests upon the
rock; and, further, there is the highly significant fact, that neither
the sands and gravels nor the rock upon which they rest show any signs of
disturbance or contortion, such as must have been produced if floating
ice had been an operative agent.
"The uplift of foreign rocks is equally significant; and when we take
into account the great distances from which they have been borne and
the frequency with which such an operation must have been repeated, the
inadequacy becomes apparent of Darwin's ingenious suggestion, that it
might have been effected by a succession of uplifts by shore-ice during
a period of slow subsidence; while the character and abundance of the
molluscan remains invest with a species of irony the application of the
term 'shell-bed' to the deposit.
"I now turn to the alternative explanation (see _ante_, p. 145), viz.,
that the whole of the phenomena were produced by a mass of land-ice which
was forced in upon Moel Tryfaen from the north or northwest, overpowering
any Welsh ice which obstructed its course. This view is in harmony with
the observations regarding the 'terminal curvature' of the slates, the
occurrence of sharp angular chips of slate in the boulder-clay, and the
coincidence of direction of these indications of movement with the carry
of foreign stones. The few shells and shell-crumbs in the sands and
gravels would, upon this hypothesis, be the infinitesimal relics of huge
shell-banks in the Irish Sea which were destroyed by the glacier and in
part incorporated in its ground-moraine or involved in the ice itself.
The sands and gravels would represent the wash which would take place
wherever, by the occurrence of a 'nunatak' or by approach to the edge of
the ice, water could have a free escape.
"Two principal objections have been urged to the land-ice explanation
of the Moel Tryfaen deposits. An able critic asks, 'Can, then, ice walk
up-hill?' To this we answer, Given a sufficient 'head' behind it, and
ice can certainly achieve that feat, as every _roche moutonnée_ proves.
If it be granted that ice on the small scale can move up-hill, there is
no logical halting-place between the uplift of ten or twenty feet to
surmount a _roche moutonnée_, and an equally gradual elevation to the
height of Moel Tryfaen. Furthermore, the inland ice of Greenland is known
to extrude its ground-moraine on the 'weather-side' of the nunataks, and
the same action would account for the material uplifted on Moel Tryfaen.
"The second objection brought forward was couched in somewhat these
terms: 'If the Lake District had its ice-sheet, surely Wales had one
also. Could not Snowdonia protect the heart of its own domain?' Of
course, Wales had its ice-sheet, and the question so pointedly raised
by the objector needs an answer; and though it is merely a question
of how much force is requisite to overcome a certain resistance (both
factors being unknown), still there are features in the case which render
it specially interesting and at the same time comparatively easy of
explanation. It seems rather like stating a paradox, yet the fact is,
that it was the proximity of Snowdon which, in my opinion, enabled the
foreign ice to invade Wales at that point.
"A glance at the map will show that the 'radiant point' of the Welsh ice
was situated on or near Arenig Mawr, and that the great mass of Snowdon
stands quite on the periphery of the mountainous regions of North Wales,
so that it would oppose its bulk to fend off the native ice-sheet and
prevent it from extending seaward in that direction.
[Illustration: Fig. 46.--Section across Wales to show the relationship of
native to foreign ice.]
"As a consequence, the only Welsh ice in position to obstruct the onward
march of the invader would be such trifling valley-glaciers as could form
on the western slopes of Snowdon itself.
"The peak of Snowdon is 3,570 feet above sea-level, and Arenig Mawr,
2,817 feet high, is eighteen miles to the eastward, and a broad, deep
valley with unobstructed access to Cardigan Bay intervenes; so, if any
ice from the central mass made its way over the Snowdonian range, it
performed a much more surprising feat than that involved in the ascent of
Moel Tryfaen from the westward.
"The profile shows in diagrammatic form the probable relations of the
foreign to the native ice at the time when the Moel Tryfaen deposits were
laid down.
"From what has been said regarding the great glaciers, it would seem
that ice advanced upon the land from the seaward in several parts of the
coast of England, Wales, and the Isle of Man. Now, it is in precisely
those parts of the country, and those alone, that the remains of marine
animals occur in the glacial deposits. If the dispersal of the shells
found in the drift had been effected by the means I have suggested, it
would follow, as an inevitable consequence, that wherever shells occur
there should also be boulders which have been brought from beyond the
sea. This I find to be the case, and in two instances the discovery of
shells was preliminary to the extension of the boundaries of the known
distribution of boulders of trans-marine origin.
"The officers of the Geological Survey some years ago observed the
occurrence of 'obscure fragments of marine shells' in a deposit at
Whalley, Lancashire, in which they could find only local rocks. One case
such as this would be fatal to the theory of the _remanié_ origin of the
shells, but on visiting the section with Mr. W. A. Downham, I found,
amongst the very few stones which occurred in the shell-bearing sand at
the spot indicated, two well-marked examples of Cumbrian volcanic rocks,
and, at a little distance, large boulders of Scottish granites.
"The second case is more striking. The announcement was made that shells
had been found on a hill called Gloppa near Oswestry, in Shropshire, and,
as it lay about five miles to the westward of Mackintosh's boundary of
the Irish Sea Glacier, and therefore well within the area of exclusively
Welsh boulders, it furnished an excellent opportunity of putting the
theory to the test. An examination of the boulders associated with the
shells showed that the whole suite of Galloway and Cumbrian erratics
such as belong to the Irish Sea Glacier were present in great abundance.
Not only this, but in the midst of the series of shell-bearing gravels I
observed a thin lenticular bed of greenish clay, which upon examination
was found to be crowded with well-scratched specimens of Welsh rocks; but
neither a morsel of shell nor a single pebble of a foreign rock could be
found, either by a careful examination in the field or by washing the
clay at home, and examining with a lens the sand and stones separated out.
"The fact that predictions such as these have been verified affords a
very striking corroboration of the theory put forward; and, though shells
cannot be found in every deposit in which they might, _ex hypothesi_,
be found, yet the strict limitation of them to situations which conform
to those assigned upon theoretical grounds cannot be ascribed to mere
coincidence. If the land had ever been submerged during any part of
the Glacial epoch to a depth of 1,400 feet, it is inconceivable that
clear and indisputable evidence should not be found in abundance in the
sheltered valleys of the Lake District and Wales, which would have been
deep, quiet fiords, in which vast colonies of marine creatures would have
found harbour, as they do in the deep lochs of Scotland to-day.
"It has been urged, in explanation of this absence of marine remains
in the great hill-centres, that the 'second glaciation' might have
destroyed them; but to do this would require that the ice should make a
clean and complete sweep of all the loose deposits both in the hollows
of the valleys and on the hill-sides, and further that it should destroy
all the shells and all the foreign stones which floated in during the
submergence. At the same time we should have to suppose that the drift
which lay in the paths of the great glaciers was not subjected to any
interference whatever. But, assuming that these difficulties were
explained, there would still remain the fact that the valleys which have
never been glaciated--as, for example, those of Derbyshire--show no
signs whatever of any marine deposits, nor of marine action in any form
whatever.
"The sea leaves other traces also, besides shells, of its presence
in districts that have really been submerged, yet there are no signs
whatever to be found of them in all England, except the _post_-glacial
raised beaches. Furthermore, in all the area occupied by glacial
deposits there are no true sea-beaches, no cliffs nor sea-worn caves,
no barnacle-encrusted rocks, nor rocks bored by Pholas or Saxicava. Are
we to believe that these never existed; or that, having existed, they
have been obliterated by subsequent denudations? To make good the former
proposition, it would be necessary as a preliminary to show that the
movement of subsidence and re-elevation was so rapid, and the interval
between so brief, that no time was allowed for any marine erosion to
take place. If this were so, it would be the most stupendous catastrophe
of which we have any geological record; but we are not left in doubt
regarding the duration of the submerged condition, for the occurrence
of forty feet of gravel upon the summits of the hills indicates plainly
that, if they were accumulated by the sea, the land must have stood at
that level for a very long period, amply sufficient for the formation of
a well-marked coast-line.
"The alternative proposition, that post-glacial denudation had removed
the traces of subsidence, is equally at variance with the evidence.
Post-glacial denudation has left kames and drumlins, and all the other
forms of glacial deposits, in almost perfect integrity; the small
kettle-holes are not yet filled up; and it is therefore quite out of the
question that the far more enduring features, such as sea-cliffs, shore
platforms, and beaches, should have been destroyed.
"The only reasonable conclusion is, that these evidences of marine action
never existed, because the land in glacial times was never depressed
below its present level. If the level were different at all (as I think
may have been the case on the western side of England), it was higher,
and not lower.
"The details of the submergence hypothesis have, so far as I am aware,
never been dealt with by its advocates, otherwise I cannot but think that
it would have been abandoned long since. It has been stated in general
terms that the subsidence was greatest in the north and diminished to
zero in the south, but no attempt was made to trace the evidence of
extreme subsidence across country and along the principal hill-ranges--in
fact, to see how it varied in every direction.
"If we take a traverse of England, say from Flamborough Head upon the
east to Moel Tryfaen on the west, and accept as evidence of submergence
any true glacial deposits (except, as in the case of the interior of
Wales, the deposits are obviously the effects of purely local glaciers
and contain, therefore, no shells), we shall find that the subsidence, if
any, must have been not simply differential but sporadic.
[Illustration: Fig. 47.--Section of the cliff on the east side of South
Sea Landing, Flamborough Head. Scale, 120 feet to 1 inch; length of
section 290 yards; average height, 125 feet. (See above map of moraine
between Speeton and Flamborough.)
Explanation.--_4._ Brownish boulder-clay, a band of pebbles; _4a_,
in places about seven feet from top. _3._ Washed gravel, with thin
sand-seams, well-bedded, pebbles chiefly erratics. _2._ "Basement"
boulder-clay, with many included patches of sand, gravel, and silt; _2a_,
at _B_, one of these _2b_ contain shells. _1b_. Sand and silt, overlying
and in places interbedded with _1_. _1._ Rubble of angular and subangular
chalk-blocks and gravel, with occasional erratic, passes partly into
chalky boulder-clay, _1a_. _x_. White chalk, without flints, surface much
shaken.]
"At Flamborough Head shelly drift attains an altitude of 400 feet,
but half a mile from the coast the country is practically driftless
even at lower levels. The Yorkshire Wolds were not submerged. On the
western flanks of the wolds drift comes in at about 100 to 150 feet, and
persists, probably, under the post-glacial warp, from which it again
protrudes on the western side of the valley of the Ouse, and however the
drift between there and the Pennine water-shed may be interpreted, it
shows not a sign of marine origin; but, even granting that it did, we
find that it does not reach within a thousand feet of the water-shed.
When the water-shed is crossed, however, abundant glacial deposits are
met with which are not to be differentiated from others at slightly lower
levels which contain shells.
[Illustration: Fig. 48.--Enlarged section of the shelly sand and
surrounding clay at _B_ in preceding figure. Scale, 4 feet to 1 inch.
Explanation.--_2._ "Basement" boulder-clay. _2a_. Pure compact blue and
brown clay of aqueous origin, bedding contorted and nearly obliterated,
but the mass is cut up by shearing planes. _2b_. Irregular seam, and
scattered streaks, of greenish-yellow sand with many marine shells. _2c_.
Patch of pale-yellow sand, different from _2b_, without trace of fossils.]
"If we suppose that the line of our traverse crosses the Pennine Chain
at Heald Moor, we shall find that on the eastern side no traces of drift
occur above about 300 feet; while the very summit of the water-shed is
occupied by boulder-clay, and thence downward the trace is practically
continuous, and at about 1,000 feet and downward the drift contains
marine shells. Across the great plain of Lancashire and Cheshire
the 'marine' drift is fully developed--though it may be remarked in
parentheses that it contains a shallow-water fauna, albeit _ex hypothesi_
deposited, in part at least, in a depth of 200 fathoms of water--and to
the Welsh border at Frondeg, where it again reaches a water-shed at an
altitude of 1,450 feet; but at 100 yards to the westward of the summit
all traces of subsidence disappear, and through the centre of Wales no
sign is visible; then we emerge on the western slopes at Moel Tryfaen,
and they assume their fullest dimensions, though only to finish abruptly
on the hill-top, and put in no appearance in the lower grounds which
extend from there to the sea.
"The conclusions pointed to by the evidence (and, as I have endeavoured
to show, all the evidence which existed at the close of the Glacial
period is there still) are, that a subsidence of the Yorkshire Wolds
took place on the east, but not in the centre or west; that the Pennine
Chain was submerged on the western side to a depth of 1,400 feet, and
on the east to not more than 300 feet, even on opposite sides of the
same individual hill; that all the lowlands between, say, Bacup and the
Welsh border, were submerged, and that the hills near Frondeg partook of
this movement, but only on their eastern sides; that the centre of Wales
was exempt, but that the summit of Moel Tryfaen forms an isolated spot
submerged, while the surrounding country escaped. These absurdities might
be indefinitely multiplied, and they must follow unless it be admitted
that the phenomena are the results of glacial ice, and that ice can move
'up-hill.'
"The south of England certainly has partaken of no movement of
subsidence. A line drawn from Bristol to London will leave all the true
glacial deposits to the northward, except a bed of very questionable
boulder-clay at Watchet, and a peculiar deposit of clayey rubble which
has been produced on the flanks of the Cornish hills probably, as the
late S. V. Wood, Jr, suggested, by the slipping of material over a
permanently frozen subsoil.
"For the remainder of the southern area the evidence is plain that there
has been no considerable subsidence during glacial times. The presence
over large areas of chalk country of the 'clay with flints'--a deposit
produced by the gradual solution of the chalk and the accumulation in
situ of its insoluble residue--is absolute demonstration that for immense
periods of time the country has been exempt from any considerable aqueous
action. The enormous accumulations of china clay upon the granite bosses
of Cornwall and Devon tell the same tale. A few erratics have been found
at low levels at various points on the southern coasts, usually not
above the reach of the waves. These consist of rocks which may have been
floated by shore-ice from the Channel Islands or the French coast.
"This imperfect survey of the evidence against the supposed submergence
has been rendered the more difficult by the fact that it is not
considered necessary to produce the evidence of marine shells in all
cases. Indeed, it has been argued that post-Tertiary beds covering
thousands of square miles might be absolutely destitute of shells without
prejudice to the theory of their formation in the sea.
"But such a suggestion, one would think, could hardly come from anyone
familiar with marine Tertiary deposits, or even with the appearance of
modern sea-beaches. Admitting, however, for the purposes of argument,
that the beaches along a great extent of coast might be devoid of shells,
it cannot be argued that the deep waters were destitute of life; and
hence the boulder-clays, if of marine origin, should contain a great
abundance of shells and other remains, and, once entombed, it is beyond
belief that they could all be removed from such a deposit in the short
lapse of post-glacial time.
"Now, some of the boulder-clays--as, for example, those of Lancashire
and Cheshire--are held to be of marine origin, and this is indeed
a vital necessity to the submergence theory; for, if these are not
marine deposits, neither are the other shelly deposits; but these
boulder-clays are absolutely indistinguishable from those lying within
the hill-centres, and, as it passes belief that such deposits could be of
diverse origin and yet possess an identical structure and arrangement,
then we should have a right to demand that these clays should have
enclosed shells and should still contain them, but they do not.
"I may here mention that I am informed by Mr. W. Shone, F. G. S.--and
he was good enough to permit me to quote the statement--that the
boulder-clay of Cheshire and the shelly boulder-clay of Caithness are 'as
like as two peas.' The importance of this comparison lies in the fact
that, since Croll's classical description, all observers have agreed
that it was the product of land-ice which moved in upon the land out of
the Dornoch Firth. It was pointed out then, as since has been done for
England, that it was only where the direction of ice-movement was from
the seaward that any shells occur in the boulder-clay.
"_The Dispersion of Erratics of Shap Granite._--So great a significance
attaches to the peculiar distribution of this remarkable rock, that I
may add a few details here which could not be conveniently introduced
elsewhere.
"This granite occupies an area which lies just to the northward of the
water-shed between the basins of the Lime and the Eden, and its extreme
elevation is 1,656 feet. Boulders occur in large numbers as far to the
northward as Cross Fells, while, as already described, they pass over
Stainmoor and are dispersed in great numbers along the route taken by the
great Stainmoor branch of the Solway Glacier. But a considerable number
of the boulders also found their way to the southward, and a well-marked
trail can be followed down into Morecambe Bay; and at Hest Bank, to the
north of Lancaster, the boulder-clay contains many examples, together
with the 'mica-trap' of the Kendal and Sedbergh dykes and other local
rocks, but no shells or erratics from other sources than the country
draining into Morecambe Bay. To the southward the ice which bore these
rocks was deflected by the great Irish Sea Glacier, and, so far as
present information enables me to state, the Shap granite blocks mark the
course of the medial moraine between these two ice-streams. It has been
found near Garstang, at Longridge, and at Whalley, this being the exact
line of junction of the Irish Sea Glacier with the ice from Morecambe Bay
and the Pennine Chain.
"It is a very remarkable and significant fact, that not a single
authentic occurrence of the rock across the boundary indicated has yet
been recorded."
_Northern Europe._
On passing over the shallow German Sea from England to the Continent,
the southern border of the Scandinavian ice-field is found south of
the Zuyder Zee, between Utrecht and Arnhem--the moraine hills in the
vicinity of Arnhem being quite marked, and a barren, sandy plain dotted
with boulders and irregular moraine hills extending most of the way to
the Zuyder Zee. From Arnhem the southern boundary of the great ice-field
runs "eastward across the Rhine Valley, along the base of the Westphalian
Hills, around the projecting promontory of the Hartz, and then southward
through Saxony to the roots of the Erzgebirge. Passing next southeastward
along the flanks of the Riesen and Sudeten chain, it sweeps across Poland
into Russia, circling round by Kiev, and northward by Nijni-Novgorod
towards the Urals."[BV] Thence the boundary passes northward to the
Arctic Ocean, a little east of the White Sea.
[Footnote BV: A. Geikie's Text-Book of Geology, p. 885.]
The depth of this northern ice-sheet is proved to have been upwards
of 1,400 feet where it met the Hartz Mountains, for it has deposited
northern _débris_ upon them to that height; while, as already shown, it
must have been over 2,000 feet in the main valley of Switzerland. In
Norway it is estimated that the ice was between 6,000 and 7,000 feet
thick.
The amount of work done by the continental glaciers of Europe in the
erosion, transportation, and deposition of rock and earthy material is
immense. According to Helland, the average depth of the glacial deposits
over North Germany and northwestern Russia is 150 German feet, i. e.,
about 135 English feet. As the deposition towards the margin of a glacier
must be commensurate with its erosion near the centre of movement, this
vast amount implies a still greater proportionate waste in the mountains
of Scandinavia, where the area diminishes with every contraction of
the circle. Two hundred and fifty feet is therefore not an extravagant
calculation for the amount of glacial erosion in the Scandinavian
Peninsula.
It is not difficult to see how the Scandinavian mountains were able
to contribute so much soil to the plains of northern Germany and
northwestern Russia. Previous to the Glacial period, a warm climate
extended so far north as to permit the growth of semi-tropical vegetation
in Spitsbergen, Greenland, and the northern shores of British America.
Such a climate, with its abundant moisture and vegetation, afforded most
favourable conditions for the superficial disintegration of the rocks.
When, therefore, the cold of the Glacial period came on, the moving
currents of ice would have a comparatively easy task in stripping the
mantle of soil from the hills of Norway and Sweden, and transporting it
towards the periphery of its movement. Of course, erosion in Scandinavia
meant subglacial deposition beyond the Baltic. Doubtless, therefore, the
plains of northern Germany, with their great depth of soil, are true
glacial deposits, whose inequalities of surface have since been much
obliterated, through the general influences of the lapse of time, and by
the ceaseless activity of man.
An interesting series of moraines in the north of Germany, bordering the
Baltic Sea, was discovered in 1888 by Professor Salisbury, of the United
States Geological Survey. Its course lies through Schleswig-Holstein,
Mecklenburg, Potsdam (about forty miles north of Berlin), thence swinging
more to the north, and following nearly the line between Pomerania and
West Prussia, crossing the Vistula about twenty miles south of Dantzic,
thence easterly to the Spirding See, near the boundary of Poland.
Among the places where this moraine can be best seen are--"1. In Province
Holstein, the region about (especially north of) Eutin; 2. Province
Mecklenburg, north of Crivitz, and between Bütow and Kröpelin; 3.
Province Brandenburg, south of Reckatel, between Strassen and Bärenbusch,
south of Fürstenberg and north of Everswalde, and between Pyritz and
Solden; 4. Province Posen, east of Locknitz, and at numerous points to
the south, and especially about Falkenburg, and between Lompelburg and
Bärwalde. This is one of the best localities. 5. Province West Preussen,
east of Bütow; 6. Province Ost Preussen, between Horn and Widikin."
Comparing these with the moraines of America, Professor Salisbury remarks:
"In its composition from several members, in its variety of development,
in its topographic relations, in its topography, in its constitution, in
its associated deposits, and in its wide separation from the outermost
drift limit, this morainic belt corresponds to the extensive morainic
belt of America, which extends from Dakota to the Atlantic Ocean. That
the one formation corresponds to the other does not admit of doubt. In
all essential characteristics they are identical in character. What may
be their relations in time remains to be determined."
[Illustration: Fig. 49.--Map showing the glaciated area of Europe
according to J. Geikie, and the moraines in Britain and Germany according
to Lewis and Salisbury.]
The physical geography of Europe is so different from that of America,
that there was a marked difference in the secondary or incidental effects
of the Glacial period upon the two regions. In America the continental
area over which the glaciers spread is comparatively simple in its
outlines. East of the Rocky Mountains, as we have seen, the drainage
of the Glacial period was, for a time, nearly all concentrated in the
Mississippi basin, and the streams had a free course southward.
But in Europe there was no free drainage to the south, except over
a small portion of the glaciated area in central Russia, about the
head-waters of the Dnieper, the Don, and the Volga; though the Danube
and the Rhône afforded free course for the waters of a portion of the
great Alpine glaciers. But all the great rivers of northern Europe
flow to the northward, and, with the exception of the Seine, they all
for a time encountered the front of the continental ice-sheet. This
circumstance makes it difficult to distinguish closely between the direct
glacial deposits in Europe and those which are more or less modified
by water-action. At first sight it would seem also somewhat hazardous
to attempt to correlate with any portion of the Glacial period the
deposition of the gravelly and loamy deposits in valleys, which, like
those of the Seine and Somme, lie entirely outside of the glaciated area.
Upon close examination, however, the elements of doubt more and more
disappear. The Glacial period was one of great precipitation, and it
is natural to suppose that the area of excessive snow-fall extended
considerably beyond the limit of the ice-front. During that period
therefore, the rivers of central France must have been annually flooded
to an extent far beyond anything which is known at the present time.
Since these rivers flowed to the northward, at a period when, during
the long and severe winters, the annual accumulation of ice near their
mouths was excessive, ice-gorges of immense extent, such as now form
about the mouths of the Siberian rivers, would regularly occur. We are
not surprised, therefore, to find, even in these streams, abundant
indications of the indirect influence of the great northern ice-sheet.
The indications referred to consist of high-level gravel terraces
occasionally containing boulders, of from four to five tons weight, which
have been transported for a considerable distance. The elevation of the
terraces above the present flood-plains of the Seine and Somme reaches
from 100 to 150 feet. We are not to suppose, however, that even in
glacial times the floods of the river Seine could have filled its present
valley to that height. The highest flood in this river known in historic
times rose only to a height of twenty-nine feet. Mr. Prestwich estimates
that, without taking into consideration the more rapid discharge, a flood
of sixty times this magnitude would be required to fill the present
valley to the level of the ancient gravels, while at Amiens the shape of
the valley of the Somme is such that five hundred times the mean average
of the stream would be required to reach the high-level gravels. The
conclusion, therefore, is that the troughs of these streams have been
largely formed by erosion since the deposition of the high-level gravels.
Connected with these terrace gravels in northern France is a loamy
deposit, corresponding to the loess in other parts of Europe, and to a
similar deposit to which we have referred in describing the southwestern
part of the glaciated area in North America. In northern France this fine
silt overlies the high-level gravel deposits, and, as Mr. Prestwich has
pretty clearly shown, was deposited contemporaneously with them during
the early inundations and before the stream had eroded its channel to its
present level.
The distribution of loess in Europe was doubtless connected with the
peculiar glacial conditions of the continent. Its typical development
is in the valley of the Rhine, where it is described by Professor
James Geikie "as a yellow or pale greyish-brown, fine-grained, and
more or less homogeneous, consistent, non-plastic loam, consisting of
an intimate admixture of clay and carbonate of lime. It is frequently
minutely perforated by long, vertical, root-like tubes which are lined
with carbonate of lime--a structure which imparts to the loess a strong
tendency to cleave or divide in vertical planes. Thus it usually presents
upright bluffs or cliffs upon the margins of streams and rivers which
intersect it. Very often it contains concretions or nodules of irregular
form.... Land-shells and the remains of land animals are the most common
fossils of the loess, but occasionally fresh-water shells and the bones
of fresh-water fish occur."
"From the margins of the modern alluvial flats which form the bottoms
of the valleys it rises to a height of 200 or 300 feet above the
streams--sweeping up the slopes of the valleys, and imparting a rich
productiveness to many districts which would otherwise be comparatively
unfruitful. From the Rhienthal itself it extends into all the tributary
valleys--those of the Neckar, the Main, the Lahn, the Moselle, and the
Meuse, being more or less abundantly charged with it. It spreads, in
short, like a great winding-sheet over the country--lying thickly in the
valleys and dying off upon the higher slopes and plateaux. Wide and deep
accumulations appear likewise in the Rhône Valley, as also in several
other river-valleys of France, as in those of the Seine, the Saône, and
the Garonne, and the same is the case with many of the valleys of middle
Germany, such as those of the Fulda, the Werra, the Weser, and the upper
reaches of the great basin of the Elbe. It must not be supposed that the
loess is restricted to valleys and depressions in the surface of the
ground.
"It is true that it attains in these its greatest thickness, but
extensive accumulations may often be followed far into the intermediate
hilly districts and over the neighbouring plateaux. Thus the Odenwald,
the Taunus, the Vogelgebirge, and other upland tracts, are cloaked with
loess up to a considerable height. Crossing into the drainage system of
the Danube, we find that this large river and many of its tributaries
flow through vast tracts of loess. Lower Bavaria is thickly coated with
it, and it attains a great development in Bohemia, Upper and Lower
Austria, and Moravia--in the latter country rising to an elevation of
1,300 feet. It is equally abundant in Hungary, Galicia, Bukowina, and
Transylvania. From the Danubian flat lands and the low grounds of Galicia
it stretches into the valleys of the Carpathians, up to heights of 800
and 2,000 feet. In some cases it goes even higher--namely, to 3,000
feet, according to Zeuschner, and to 4,000 or 5,000 feet, according to
Korzistka. These last great elevations, it will be understood, are in
the upper valleys of the northern Carpathians. In Roumania loess is
likewise plentiful, but it has not been observed south of the Balkans.
East of the Carpathians--that is to say, in the regions watered by the
Dniester, the Dnieper, and the Don--loess appears also to be wanting,
and to be represented by those great steppe-deposits which are known as
_Tchernozen_, or black earth."[BW]
[Footnote BW: Prehistoric Europe, pp. 144-146.]
The shells found in the loess indicate both a colder and a wetter climate
during its deposition than that which now exists. The relics of land
animals are infrequently found in the deposit, yet they do occur, but
mostly in fragmentary condition--the principal animals represented being
the mammoth, the rhinoceros, the reindeer, and the horse; which is about
the same variety as is found in the gravel deposits of the Glacial
period, both in western Europe and in America.
A species of loess--differing, however, somewhat in color from that on
the Rhine--covers the plains of northeastern France up to an elevation of
700 feet above the the sea, where, as we have already said, it overlies
the high-level gravels of the Seine and the Somme. Above this height
the superficial soil in France is evidently merely the decomposed upper
surface of the native rock.
The probable explanation of all these deposits, included under the term
"loess," is the same as that already given by Prestwich of the loamy
deposits of northern France. But in case of rivers, which, like the
Rhine, encountered the ice-front in their northward flow, a flooded
condition favouring the accumulation of loess was doubtless promoted by
the continental ice-barrier. In the case of the Danube and the Rhône,
however, where there was a free outlet away from the glaciated region,
the loess in the upper part of the valleys must have accumulated in
connection with glacial floods quite similar to those which we have
described as spreading over the imperfectly formed water-courses of the
Mississippi basin during the close of the Ice age. That the typical loess
is of glacial origin is pretty certainly shown, both by its distribution
in front of glaciers and by its evident mechanical origin when studied
under the microscope. It is, in short, the fine sediment which gives the
milky whiteness to glacial rivers.
In central Russia there is a considerable area in which the glacial
conditions were, in one respect, similar to those in the northern part
of the Mississippi Valley in the United States. In both regions the
continental ice-sheet surmounted the river partings, and spread over the
upper portion of an extensive plain whose drainage was to the south. The
Dnieper, the Don, and the western branch of the Volga, like the Ohio
and the Mississippi, have their head-waters in the glaciated region. In
some other respects, also, there is a resemblance between the plains
bordering the glaciated region in central Russia and those which in
America border it in the Mississippi Valley. Mr. James Geikie is of the
opinion that the extensive belt of black earth adjoining the glaciated
area in Russia, and constituting the most productive agricultural portion
of the country, derives its fertility, as does much of the Mississippi
Valley, from the blanket of glacial silt spread pretty evenly over it.
Thus it would appear that in Europe, as in America, the ice of the
Glacial period was a most beneficent agent, preparing the face of the
earth for the permanent occupation of man. On both continents the seat
of empire is in the area once occupied by the advance of the great
ice-movements of that desolate epoch.
_Asia._
East of the Urals, in northern Asia, there is no evidence of moving ice
upon the land during the Glacial period; but at Yakutsk, in latitude 62°
north, the soil is frozen at the present time to an unknown depth, and
many of the Siberian rivers, as they approach and empty into the Arctic
Sea, flow between cliffs of perpetual ice or frozen ground. The changes
that came over this region during the Glacial period are impressively
indicated by the animal remains which have been preserved in these
motionless icy cliffs. In the early part of the period herds of mammoth
and woolly rhinoceros roamed over the plains of Siberia, and waged an
unequal warfare with the slowly converging and destructive forces. The
heads and tusks of these animals were so abundant in Siberia that they
long supplied all Russia with ivory, besides contributing no small
amount for export to other countries. "In 1872 and 1873 as many as 2,770
mammoth-tusks, weighing from 140 to 160 pounds each, were entered at the
London clocks."[BX] So perfectly have the carcasses of these extinct
animals been preserved in the frozen soil of northern Siberia that when,
after the lapse of thousands of years, floods have washed them out from
the frozen cliffs, dogs and wolves and bears have fed upon their flesh
with avidity. In some instances even "portions of the food of these
animals were found in the cavities of the teeth. Microscopic examination
showed that they fed upon the leaves and shoots of the coniferous trees
which then clothed the plains of Siberia." A skeleton and parts of
the skin, and some of the softer portions of the body of a mammoth,
discovered in 1799 in the frozen cliff near the mouth of the Lena, was
carried to St. Petersburg in 1806, from which it was ascertained that
this huge animal was "covered with alight-coloured, curly, very thick-set
hair one to two inches in length, interspersed with darker-colored hair
and bristles from four to eighteen inches long."[BY]
[Footnote BX: Prestwich's Geology, vol. ii, p. 460.]
[Footnote BY: Prestwich's Geology, vol. ii, p. 460.]
In the valleys of Sikkim and eastern Nepaul, in northern India, glaciers
formerly extended 6,000 feet lower than now, or to about the 5,000-foot
level, and in the western Himalayas to a still lower level. The higher
ranges of mountains in other portions of Asia also show many signs of
former glaciation. This is specially true of the Caucasus, where the
ancient glaciers were of vast extent. According, also, to Sir Joseph
Hooker, the cedars of Lebanon flourish upon an ancient moraine. Of the
glacial phenomena in other portions of Asia little is known.
_Africa._
Northern and even central Africa must likewise come in for their share
of attention. The Atlas Mountains, rising to a height of 13,000 feet,
though supporting none at the present time, formerly sustained glaciers
of considerable size. Moraines are found in several places as low as the
4,000-foot level, and one at an altitude of 4,000 feet is from 800 to 900
feet high, and completely crosses and dams up the ravine down which the
glacier formerly came.
Some have supposed that there are indubitable evidences of former
glaciation in the mountain-ranges of southwestern Africa between latitude
30° and 33°, but the evidence is not as unequivocal as we could wish, and
we will not pause upon it.
The mountains of _Australia_, also, some of which rise to a height of
more than 7,000 feet, are supposed to have been once covered with glacial
ice down to the level of 5,800 feet, but the evidence is at present too
scanty to build upon. But in _New Zealand_ the glaciers now clustering
about the peaks in the middle of the South Island, culminating in Mount
Cook, are but diminutive representatives of their predecessors. This is
indicated by extensive moraines in the lower part of the valleys and by
the existence of numerous lakes, attributable, like so many in Europe and
North America, to the irregular deposition of morainic material by the
ancient ice-sheet.[BZ]
[Footnote BZ: See With Axe and Rope in the New Zealand Alps, by G. E.
Mannering, 1891.]
CHAPTER VII.
DRAINAGE SYSTEMS AND THE GLACIAL PERIOD.
We will begin the consideration of this part of our subject, also, with
the presentation of the salient facts in North America, since that field
is simpler than any field in the Old World.
The natural drainage basins of North America east of the Rocky Mountains
are readily described. The Mississippi River and its branches drain
nearly all the region lying between the Appalachian chain and the Rocky
Mountains and south of the Dominion of Canada and of the Great Lakes.
All the southern tributaries to the Great Lakes are insignificant, the
river partings on the south being reached in a very short distance. The
drainage of the rather limited basin of the Great Lakes is northeastward
through the St. Lawrence River, leaving nearly all of the Dominion of
Canada east of the Rocky Mountains to pour its surplus waters northward
into Hudson Bay and the Arctic Ocean. With the exception of the St.
Lawrence River, these are essentially permanent systems of drainage. To
understand the extent to which the ice of the Glacial period modified
these systems, we must first get before our minds a picture of the
country before the accumulation of ice began.
_Preglacial Erosion._
Reference has already been made to the elevated condition of the northern
and central parts of North America at the beginning of the Glacial
period. The direct proof of this preglacial elevation is largely derived
from the fiords and great lake basins of the continent. The word "fiord"
is descriptive of the deep and narrow inlets of the sea specially
characteristic of the coasts of Norway, Denmark. Iceland, and British
Columbia. Usually also fiords are connected with valleys extending still
farther inland, and occupied by streams.
Fiords are probably due in great part to river erosion when the shores
stood at considerably higher level than now. Slowly, during the course
of ages, the streams wore out for themselves immense gorges, and were
assisted, perhaps, to some extent by the glaciers which naturally came
into existence during the higher continental elevation. The present
condition of fiords, occupied as they usually are by great depths of
sea-water, would be accounted for by recent subsidence of the land. In
short, fiords seem essentially to be submerged river gorges, partially
silted up near their mouths, or perhaps partially closed by terminal
moraines.
It is not alone in northwestern Europe and British Columbia that fiords
are found, but they characterize as well the eastern coast of America
north of Maine, while even farther south, both on the Atlantic and on
the Pacific coast, some extensive examples exist, whose course has been
revealed only to the sounding-line of the Government survey.
The most remarkable of the submerged fiords in the middle Atlantic region
of the United States is the continuation of the trough of Hudson River
beyond New York Bay. As long ago as 1844 the work of the United States
Coast Survey showed that there was a submarine continuation of this
valley, extending through the comparatively shallow waters eighty miles
or more seaward from Sandy Hook.
[Illustration: Fig. 50.--Map showing old channel and mouth of the Hudson
(dewberry).]
The more accurate surveys conducted from 1880 to 1884 have brought to
our knowledge the facts about this submarine valley almost as clearly
as those relating to the inland portion of it above New York city.
According to Mr. A. Lindenkohl,[CA] this submarine valley began to be
noticeable in the soundings ten miles southeast of Sandy Hook. The depth
of the water where the channel begins is nineteen fathoms (114 feet).
Ten miles out the channel has sunk ninety feet below the general depth
of the water on the bank, and continues at this depth for twenty miles
farther. This narrow channel continues with more or less variation for
a distance of seventy-five miles, where it suddenly enlarges to a width
of three miles and to a depth of 200 fathoms, or 1,200 feet, and extends
for a distance of twenty-five miles, reaching near that point a depth
of 474 fathoms, or 2,844 feet. According to Mr. Lindenkohl, this ravine
maintains for half its length "a vertical depth of more than 2,000 feet,
measuring from the top of its banks, and the banks have a nearly uniform
slope of about 14°." The mouth of the ravine opens out into the deep
basin of the central Atlantic.
[Footnote CA: Bulletin of the Geological Society of America, vol. i, p.
564; American Journal of Science, June, 1891.]
With little question there is brought to light in these remarkable
investigations a channel eroded by the extension of the Hudson River,
into the bordering shelf of the Atlantic basin at a time when the
elevation of the continent was much greater than now. This is shown to
have occurred in late Tertiary or post-Tertiary times by the fact that
the strata through which it is worn are the continuation of the Tertiary
deposits of New Jersey. The subsidence to its present level has probably
been gradual, and, according to Professor Cook, is still continuing at
the rate of two feet a century.
Similar submarine channels are found extending out from the present
shore-line to the margin of the narrow shelf bordering the deep water of
the central Atlantic running from the mouth of the St. Lawrence River,
through St. Lawrence Bay, and through Delaware and Chesapeake Bays.[CB]
All these submerged fiords on the Atlantic coast were probably formed
during a continental elevation which commenced late in the Tertiary
period, and reached the amount of from 2,000 to 3,000 feet in the
northern part of the continent.
[Footnote CB: See Lindenkohl in American Journal of Science, for June,
1891.]
[Illustration: Fig. 51.--New York harbor in preglacial times looking
south, from south end of New York Island (Newberry).]
To this period must probably be referred also the formation of the gorge,
or more properly fiord, of the Saguenay, which joins the St. Lawrence
below Quebec. The great depth of this fiord is certainly surprising,
since, according to Sir William Dawson, its bottom, for fifty miles above
the St. Lawrence, is 840 feet below the sea-level, while the bordering
cliffs are in some places 1,500 feet above the water. The average width
is something over a mile.
It seems impossible to account for such a deep gorge extending so far
below the sea-level, except upon the supposition of a long-continued
continental elevation, which should allow the stream to form a cañon to
an extent somewhat comparable with that of the cañons of the Colorado and
other rivers in the far West. Then, upon the subsidence of the continent
to the present level, it would remain partially or wholly submerged,
as we find it at the present time. During the Glacial period it was so
filled with ice as to prevent silting up. The rivers entering the Pacific
Ocean, both in the United States and in British Columbia, are also lost
in submerged channels extending out to the deeper waters of the Pacific
basin in a manner closely similar to the Atlantic streams which have been
mentioned.
During this continental elevation which preceded, accompanied, and
perhaps brought on the Glacial period, erosion must have proceeded with
great intensity along all the lines of drainage, and throughout the whole
region which is now covered, and to a considerable extent smoothed over,
by glacial deposits, and the whole country must have presented a very
different appearance from what it does now.
A pretty definite idea of its preglacial condition can probably be formed
by studying the appearance of the regions outside of and adjoining that
which was covered by the continental glacier. The contrast between the
glaciated and the unglaciated region is striking in several respects
aside from the presence and absence of transported rocks and other
_débris_, but in nothing is it greater than in the extent of river
erosion which is apparent upon the surface. For example, upon the
western flanks of the Alleghanies the regions south of the glacial limit
is everywhere deeply channeled by streams. Indeed, so long have they
evidently been permitted to work in their present channels that, wherever
there have been waterfalls, they have receded to the very head-waters,
and no cataracts exist in them at the present time. Nor are there in the
unglaciated region any lakes of importance, such as characterize the
glaciated region. If there have been lakes, the lapse of time has been
sufficient for their outlets to lower their beds sufficiently to drain
the basins dry.
On entering the glaciated area all this is changed. The ice-movement
has everywhere done much to wear down the hills and fill the valleys,
and, where there was _débris_ enough at command, it has obliterated the
narrow gorges originally occupied by the preglacial streams. Thus it has
completely changed the minor lines of superficial drainage, and in many
instances has produced most extensive and radical changes in the whole
drainage system of the region. In the glaciated area, channels buried
beneath glaciated _débris_ are of frequent occurrence, while many of the
streams which occupy their preglacial channels are flowing at a very much
higher level than formerly, the lower part of the channel having been
silted up by the superabundant _débris_ accessible since the glacial
movement began.
_Buried Outlets and Channels._
It is easy to see how the great number of shallow lakes which frequent
the glaciated region were formed by the irregular deposition of glacial
_débris_, but it is somewhat more difficult to trace out the connection
between the Glacial period and the Great Lakes of North America, several
of which are of such depth that their bottoms are some hundreds of feet
below the sea-level, Lake Erie furnishing the only exception. This
lake is so shallow that it is easy to see how its basin may have been
principally formed by river erosion, while it is evident that such
must have been the mode of its formation, since it is surrounded by
sedimentary strata lying nearly in a horizontal position.
[Illustration: Fig. 52.--Section across the valley of the Cuyahoga River,
twenty miles above its mouth (Claypole).]
That Lake Erie is really nothing but a "glacial mill-pond" is proved
also by much direct evidence, especially that derived from the depth of
the buried channels of the streams flowing into it from the south. Of
these, the Cuyahoga River, which enters the lake at Cleveland, has been
most fully investigated. In searching for oil, some years ago, borings
were made at many places for twenty-five miles above the mouth of the
river. As a result, it appeared that for the whole distance the rocky
bottom of the gorge was about two hundred feet below the present bottom
of the river, while the river itself is two or three hundred feet below
the general level of the country, occupying a trough about half a mile in
width, with steep, rocky sides. These facts indicate that at one time the
river must have found opportunity to discharge its contents at a level
two hundred feet below that of the present lake, while an examination
of the material filling up the bottom of the gorge to its present level
shows it to be glacial _débris_, thus proving that the silting up was
accomplished during the Glacial period.
As the water of Lake Erie is for the most part less than one hundred
feet in depth, and is nowhere much more than two hundred feet deep, it
is clear that the preglacial outlet which drained it down to the level
of the rocky bottom of the Cuyahoga River must have destroyed the lake
altogether. Hence Ave may be certain that, before the Glacial period, the
area now covered by the lake was simply a broad, shallow valley through
which there coursed a single river of great magnitude, with tributary
branches occupying deep gorges. Professor J. W. Spencer has shown with
great probability that the old line of drainage from Lake Erie passed
through the lower part of the valley of Grand River, in Canada, and
entered Lake Ontario at its western extremity, and that during the great
Ice age this became so completely obstructed with glacial _débris_ as to
form an impenetrable dam, and to cause the pent-up water to flow through
the Niagara Valley, which chanced to furnish the lowest opening.
In speaking of the present area of Lake Erie, however, as being then
occupied by a river valley, we do not mean to imply that it was not
afterwards greatly modified by glacial erosion; for undoubtedly this was
the case, whatever views we may have as to the relative efficiency of ice
and water in scooping out lake basins.
In the case of Lake Erie, we need suppose no change of level to account
for the erosion of its basin, but only that, since the strata in which it
is situated were deposited, time enough had elapsed for a great river to
cut a gorge extending from the western end of Lake Ontario through to the
present bed of Lake Erie, and that here a great enlargement of the valley
was occasioned by the existence of deep beds of soft shale which could
easily be worn away by a ramifying system of tributary streams. Rivers
acting at present relative levels would be amply sufficient to produce
the results which are here manifest.
But in the case of Lakes Ontario, Huron, Michigan, and Superior, whose
depths descend considerably below the sea-level, we must suppose that
they were, in the main, eroded when the continent was so much elevated
that their bottoms were brought above tide-level. The depth of Lake
Ontario implies the existence of an outlet more than four hundred feet
lower than at present, which, of course, could exist only when the
general elevation was more than four hundred feet greater than now.
The existence of an outlet at that depth seems to be proved also by the
fact that at Syracuse, where numerous wells have been sunk to obtain
brine for the manufacture of salt, deposits of sand, gravel, and rolled
stones, four hundred and fifty feet thick, are penetrated without
reaching rock. Since this lies in the basin of Lake Ontario, it follows
that if the basin itself has been produced by river erosion, the land
must have been of sufficient height to permit an outlet through a valley,
or cañon, of the required depth, and this outlet must now be buried
beneath the abundant glacial _débris_ that covers the region.
Professor Newberry, who has studied the vicinity carefully, is of the
opinion that there is ample opportunity for such a line of drainage
to have extended through the Mohawk Valley to the Hudson River. But,
at Little Falls, a spur of the Adirondack Mountains projects into the
valley, and the Archæan rocks over which the river runs are so prominent
and continuous that some have thought it impossible for the requisite
channel to have ever existed there. Extensive deposits of glacial
_débris_, however, are found in the vicinity, especially in places some
distance to the north, and in Professor Newberry's opinion the existence
of a buried channel around the obstruction upon the north side is by no
means improbable.
The preglacial drainage of Lake Huron has not been determined with any
great degree of probability. Professor Spencer formerly supposed that it
passed from the southern end of the lake through London, in the western
part of Ontario, and reached the Erie basin near Port Stanley, and so
augmented the volume of the ancient river which eroded the buried cañon
from Lake Erie to Lake Ontario. But he now supposes, though the evidence
is by no means demonstrative, that the waters of Lake Huron passed into
Lake Ontario by means of a channel extending from Georgian Bay to the
vicinity of Toronto.
With a fair degree of probability, the basin of Lake Superior is
supposed by Professor Newberry to have been joined to that of Lake
Michigan by some passage, now buried, considerably to the west of the
Strait of Mackinac, and thence to have had an outlet southward from the
vicinity of Chicago directly into the Mississippi River. Of this there
is considerable evidence furnished by deeply buried channels which have
been penetrated by borings in various places in Kankakee, Livingston,
and McLean Counties, Illinois; but the whole area extending from Lake
Michigan to the Mississippi is so deeply covered with glacial _débris_
that the surface of the country gives no satisfactory indication of the
exact lines of preglacial drainage.
Some of the most remarkable instances of ancient river channels buried
by the glacial deposits have been brought to light in southwestern Ohio,
where there has been great activity in boring for gas and oil. At St.
Paris, Champaign County, for example, in a locality where the surface
of the rock near by was known to be not far below the general level, a
boring was begun and continued to a depth of more than five hundred feet
without reaching rock, or passing out of glacial _débris_.
Many years ago Professor Newberry collected sufficient facts to show that
pretty generally the ancient bed of the Ohio River was as much as 150
feet below that over which it now flows. During a continental elevation
the erosion had proceeded to that extent, and then the channel had been
silted up during the Glacial period with the abundant material carried
down by the streams from the glaciated area. One of the evidences of
the preglacial depth of the channel of the Ohio was brought to light at
Cincinnati, where "gravel and sand have been found to extend to a depth
of over one hundred feet below low-water mark, and the bottom of the
trough has not been reached." In the valley of Mill Creek, also, "in the
suburbs of Cincinnati, gravel and sand were penetrated to the depth of
120 feet below the stream before reaching rock." But from the general
appearance of the channel, Professor J. F. James was led to surmise
that a rock bottom extended all the way across the present channel of
the Ohio, between Price Hill and Ludlow, Ky., a short distance below
Cincinnati, which would preclude the possibility of a preglacial outlet
at the depth disclosed in that direction. Mr. Charles J. Bates (who was
inspector of the masonry for the Cincinnati Southern Railroad while
building the bridge across the Ohio at this point) informs me that Mr.
James's surmise is certainly correct, and that his "in all probability"
may be displaced by "certainly," since the bedded rocks supposed by
Professor James to extend across the river a few feet below its present
bottom were found by the engineers to be in actual existence.
In looking for an outlet for the waters of the upper Ohio which should
permit them to flow off at the low level reached in the channel at
Cincinnati, Professor James was led to inspect the valley extending
up Mill Creek to the north towards Hamilton, where it joins the Great
Miami. The importance of Mill Creek Valley is readily seen in the fact
that the canal and the railroads have been able to avoid heavy grades
by following it from Cincinnati to Hamilton. As a glance at a map will
show, it is also practically but a continuation of the northerly course
pursued by the Ohio for twenty miles before reaching Cincinnati. This,
therefore, was a natural place in which to look beneath the extensive
glacial _débris_ for the buried channel of the ancient Ohio, and here
in all probability it has been found. The borings which have been made
in Milk Creek Valley north of Cincinnati, show that the bedded rock
lies certainly thirty-four feet below the low-water mark of the Ohio
just below Cincinnati, while at Hamilton, twenty-five miles north of
Cincinnati, where the valley of the Great Miami is reached, the bedded
rock of the valley lies as much as ninety feet below present low-water
mark in the Ohio.
Other indications of the greater depth of the preglacial gorge of the
Ohio are abundant. "At the junction of the Anderson with the Ohio, in
Indiana, a well was sunk ninety-four feet below the level of the Ohio
before rock was found." At Louisville, Ky., the occurrence of falls
in the Ohio seemed at first to discredit the theory in question, but
Professor Newberry was able to show that the falls at Louisville are
produced by the water's being now compelled to flow over a rocky point
projecting from the north side into the old valley, while to the south
there is ample opportunity for an old channel to have passed around this
point underneath the city on the south side. The lowlands upon which the
city stands are made lands, where glacial _débris_ has filled up the old
channel of the Ohio.
Above Cincinnati the tributaries of the Ohio exhibit the same phenomena.
At New Philadelphia, Tuscarawas County, the borings for salt-wells show
that the Tuscarawas is running 175 feet above its ancient bed. The
Beaver, at the junction of the Mahoning and Shenango, is flowing 150 feet
above the bottom of its old trough, as is demonstrated by a large number
of oil-wells bored in the vicinity. Oil Creek is shown by the same proofs
to run from 75 to 100 feet above its old channel, and that channel had
sometimes vertical and even overhanging walls.[CC]
[Footnote CC: Geological Survey of Ohio, vol. ii, pp. 13, 14.]
The course of preglacial drainage in the upper basin of the Alleghany
River is worthy of more particular mention. Mr. Carll, of the
Pennsylvania Geological Survey, has adduced plausible reasons for
believing that previous to the Glacial period the drainage of the
valley of the upper Alleghany north of the neighbourhood of Tidioute,
in Warren County, instead of passing southward as now, was collected
into one great stream flowing northward through the region of Cassadaga
Lake to enter the Lake Erie basin at Dunkirk, N. Y. The evidence is
that between Tidioute and Warren the present Alleghany is shallow, and
flows over a rocky basin; but from Warren northward along the valley
of the Conewango, the bottom of the old trough lies at a considerably
lower level, and slopes to the north. Borings show that in thirteen
miles the slope of the preglacial floor of Conewango Creek to the north
is 136 feet. The actual height above tide of the old valley floor at
Fentonville, where the Conewango crosses the New York line, is only 964
feet; while that of the ancient rocky floor of the Alleghany at Great
Bend, a few miles south of Warren, was 1,170 feet. Again, going nearer
the head-waters of the Alleghany, in the neighbourhood of Salamanca,
it is found that the ancient floor of the Alleghany is, at Carrollton,
70 feet lower than the ancient bed of the present stream at Great
Bend, about sixty miles to the south; while at Cole's Spring, in the
neighbourhood of Steamburg, Cattaraugus County, N. Y., there has been
an accumulation of 315 feet of drift in a preglacial valley whose rocky
floor is 155 feet below the ancient rocky floor at Great Bend. Unless
there has been a great change in levels, there must, therefore, have
been some other outlet than the present for the waters collecting in the
drainage basin to the north of Great Bend.[CD]
[Footnote CD: For a criticism of Mr. Carll's views, see an article
on Pleistocene Fluvial Planes of Western Pennsylvania, by Mr. Frank
Leverett, in American Journal of Science, vol. xlii, pp. 200-212.]
While there are numerous superficial indications of buried channels
running towards Lake Erie in this region, direct exploration has not
been made to confirm these theoretical conclusions. In the opinion of Mr.
Carll, Chautauqua Lake did not flow directly to the north, but, passing
through a channel nearly coincident with that now occupied by it, joined
the northerly flowing stream a few miles northeast from Jamestown.[CE] It
is probable, however, that Chautauqua did not then exist as a lake, since
the length of preglacial time would have permitted its outlet to wear a
continuous channel of great depth corresponding to that known to have
existed in the Conewango and upper Alleghany.
[Footnote CE: Second Geological Survey of Pennsylvania, vol. iii.]
The foregoing are but a few of the innumerable instances where the local
lines of drainage have been disturbed, and even permanently changed,
by the glacial deposits. Almost every lake in the glaciated region is
a witness to this disturbance of the established lines of drainage by
glacial action, while in numerous places where lakes do not now exist
they have been so recently drained that their shore-lines are readily
discernible.
An interesting instance of the recent disappearance of one of these
glacial lakes is that of Runaway Pond, in northern Vermont. In the early
part of the century the Lamoille River had its source in a small lake
in Craftsbury, Orleans County. The sources of the Missisquoi River were
upon the same level just to the north, and the owner of a mill privilege
upon this latter stream, desiring to increase his power by obtaining
access to the water of the lake, began digging a ditch to turn it into
the Missisquoi, but no sooner had he loosened the thin rim of compact
material which formed the bottom and the sides of the inclosure, than the
water began to rush out through the underlying and adjacent quicksands.
This almost instantly enlarged the channel, and drained the whole body of
water oft 3 in an incredibly short time. As a consequence, the torrent
went rushing down through the narrow valley, sweeping everything before
it; and nothing but the unsettled condition of the country prevented a
disaster like that which occurred in 1889 at Johnstown, Pa. Doubtless
there are many other lakes held in position by equally slender natural
embankments. Artificial reservoirs are by no means the only sources of
such danger.
The buried channel of the old Mississippi River in the vicinity of
Minneapolis is another instructive example of the instability of many
of the present lines of drainage. The gorge of the Mississippi River
extending from Fort Snelling to the Falls of St. Anthony at Minneapolis
is of post-glacial origin. One evidence of this is its narrowness when
contrasted with the breadth of the valley below Fort Snelling. Below
this point the main trough of the Mississippi has a width of from two to
eight miles, and the faces of the bluffs on either side show the marks
of extreme age. The tributary streams also have had time to wear gorges
proportionate to that of the main stream, and the agencies which oxidise
and discolor the rocks have had time to produce their full effects. But
from Fort Snelling up to Minneapolis, a distance of about seven miles,
the gorge is scarcely a quarter of a mile in width, and the faces of
the high, steep bluffs on either side are remarkably fresh looking by
comparison with those below; while the tributary gorges, of which that of
the Minnehaha River is a fair specimen, are very limited in their extent.
Upon looking for the cause of this condition of things we observe that
the broad trough of the Mississippi River, which had characterised it all
the way below Fort Snelling, continues westward, without interruption, up
the valley of the present Minnesota River, and, what seems at first most
singular, it does not cease at the sources of the Minnesota, but, through
Lake Traverse and Big Stone Lake, is continuous with the trough of the
Red River of the North.
[Illustration: Fig. 53.--Map of Mississippi River from Fort Snelling to
Minneapolis and the vicinity, showing the extent of the recession of the
Falls of St. Anthony since the great Ice age. Notice the greater breadth
of the valley of the Minnesota River as described in the text (Winchell).]
Deferring, however, for a little the explanation of this, we will go
back to finish the history of the preglacial channel around the Falls
of St. Anthony. As early as the year 1876 Professor N. H. Winchell had
collected sufficient evidence from wells, one of which had been sunk to a
depth of one hundred and seventy-five feet, to show that the preglacial
course of the stream corresponding to the present Mississippi River ran
to the west of Minneapolis and of the Falls of Minnehaha, and joined
the main valley some distance above Fort Snelling, as shown in the
accompanying map.
This condition of things was at one time very painfully brought to the
notice of the citizens of Minneapolis. A large part of the wealth of the
city at that time consisted of the commercial value of the water-power
furnished by the Falls of St. Anthony. To facilitate the discharge of
the waste water from their wheels, some mill-owners dug a tunnel through
the soft sandstone underlying the limestone strata over which the river
falls; but it very soon became apparent that the erosion was proceeding
with such rapidity that in a few years the recession of the falls would
be carried back to the preglacial channel, when the river would soon
scour out the channel and destroy their present source of wealth. The
citizens rallied to protect their property, and spent altogether as
much as half a million dollars in filling up the holes that had been
thoughtlessly made; but so serious was the task that they were finally
compelled to appeal for aid to the United States Government. Permanent
protection was provided by running a tunnel, some ways back from the
falls, completely across the channel, through the soft sandstone
underlying the limestone, and filling this up with cement hard enough
and compact enough to prevent the further percolation of the water from
above.
_Ice-Dams._
The foregoing changes in lines of drainage due to the Glacial period were
produced by deposits of earthy material in preglacial channels. Another
class of temporary but equally interesting changes were produced by the
ice itself acting directly as a barrier.
Many such lakes on a small scale are still in existence in various parts
of the world. The Merjelen See in Switzerland is a well-known instance.
This is a small body of water held back by the great Aletsch Glacier,
in a little valley leading to that of the Fiesch Glacier, behind the
Eggischorn. At irregular intervals the ice-barrier gives way, and allows
the water to rush out in a torrent and flood the valley below. Afterwards
the ice closes up again, and the water reaccumulates in preparation for
another flood.
Other instances in the Alps are found in the Mattmark See, which fills
the portion of the Saas Valley between Monte Rosa and the Rhône. This
body of water is held in place by the Allalin Glacier, which here crosses
the main valley. The Lac du Combal is held back by the Glacier de Miage
at the southern base of Mont Blanc. "A more famous case is that of the
Gietroz Glacier in the valley of Bagnes, south of Martigny. In 1818
this lake had grown to be a mile long, and was 700 feet wide and 200
feet deep. An attempt was made to drain it by cutting through the ice,
and about half the water was slowly drawn off in this way; but then the
barrier broke, and the rest of the lake was emptied in half an hour,
causing a dreadful flood in the valley below. In the Tyrol, the Vernagt
Glacier has many times caused disastrous floods by its inability to hold
up the lake formed behind it. In the northwestern Himalaya, the upper
branches of the Indus are sometimes held back in this way. A noted flood
occurred in 1835; it advanced twenty-five miles in an hour, and was felt
three hundred miles down-stream, destroying all the villages on the lower
plain, and strewing the fields with stones, sand, and mud."[CF]
[Footnote CF: Professor William M. Davis in. Proceedings of the Boston
Society of Natural History, vol. xxi, pp. 350, 351.]
In Greenland such temporary obstructions are frequent, forming lakes of
considerable size. Instances occur, in connection with the Jakobshavn and
the Frederickshaab Glaciers, and in the North Isortok and Alangordlia
Fiords.
Frequently, also, bodies of water of considerable size are found in
depressions of the ice itself, even at high levels. I have myself seen
them covering more than an acre, and as much as a thousand feet above
the sea-level, upon the surface of the Muir Glacier, Alaska. They are
reported by Mr. I. C. Russell[CG] of larger size and at still higher
elevations upon the glaciers radiating from Mount St. Elias; while the
explorers of Greenland mention them of impressive size upon the surface
of its continental ice-sheet.
[Footnote CG: See National Geographic Magazine, vol. iii, pp. 116-120.]
With these facts in mind we can the more readily enter into the
description which will now be given of some temporary lakes of vast size
which were formed by direct ice-obstructions during portions of the
period.
One of the most interesting of these is illustrated upon the accompanying
map, which will need little description.
[Illustration: Fig. 54.--Map showing the effect of the glacial dam at
Cincinnati (Claypole). (From Transactions of the Edinburgh Geological
Society.)]
While tracing the boundary-line of the glaciated area in the Mississippi
Valley during the summer of 1882, I discovered the existence of
unmistakable glacial deposits in Boone County, Kentucky, across the Ohio
River, from Cincinnati.[CH]; These deposits were upon the height of land
550 feet above the Ohio River, or nearly 1,000 feet above the sea, which
is about the height of the water-shed between the Licking and Kentucky
Rivers. As the Ohio River occupies a trough of erosion some hundreds of
feet in depth, and extending all the way from this point to the mountains
of western Pennsylvania, it would follow that the ice which conveyed
boulders across the Ohio River at Cincinnati, and deposited them upon
the highlands between the Licking and Kentucky Rivers, would so obstruct
the channel of the Ohio as to pond the water back, and hold it up to
the level of the lowest pass into the Ohio River farther down. Direct
evidences of obstruction by glacial ice appear also for a distance of
fifty or sixty miles, extending both ways, from Cincinnati.
[Footnote CH: The existence of portions of this evidence had previously
been pointed out by Mr. Robert B. Warder and Dr. George Sutton (see
Geological Reports of Indiana, 1872 and 1878).]
The consequences connected with this state of things are of the most
interesting character.
The bottom of the Ohio River at Cincinnati is 432 feet above the
sea-level. A dam of 550 feet would raise the water in its rear to a
height of 982 feet above tide. This would produce a long, narrow lake,
of the width of the eroded trough of the Ohio, submerging the site
of Pittsburg to a depth of 281 feet, and creating slack water up the
Monongahela nearly to Grafton, West Virginia, and up the Alleghany as far
as Oil City. All the tributaries of the Ohio would likewise be filled
to this level. The length of this slack-water lake in the main valley,
to its termination up either the Alleghany or the Monongahela, was not
far from one thousand miles. The conditions were also peculiar in this,
that all the northern tributaries rose within the southern margin of the
ice-front, which lay at varying distances to the north. Down these there
must have poured during the summer months immense torrents of water to
strand boulder-laden icebergs on the summits of such high hills as were
lower than the level of the dam.
Naturally enough, this hypothesis of a glacial dam at Cincinnati aroused
considerable discussion, and led to some differences of opinion.
Professors I. C. White and J. P. Lesley, whose field work has made them
perfectly familiar with the upper Ohio and its tributaries, at once
supported the theory, with a great number of facts concerning certain
high-level terraces along the Alleghany and Monongahela Rivers; while
additional facts of the same character have been brought to light by
myself and others. In general, it may be said that in numerous places
terraces occur at a height so closely corresponding to that of the
supposed dam at Cincinnati, that they certainly strongly suggest direct
dependence upon it. The upward limit of these terraces in the Monongahela
River is 1,065 feet, and they are found in various places in situations
which indicate that they were formed in still water of such long standing
as would require an obstruction below of considerable permanence.
One of the most decisive cases adduced by Professor White occurs near
Morgantown, in West Virginia, of which he gives the following description:
"Owing to the considerable elevation--275 feet--of the fifth terrace
above the present river-bed in the vicinity of Morgantown, its deposits
are frequently found far inland from the Monongahela, on tributary
streams. A very extensive deposit of this kind occurs on a tributary one
mile and a half northeast of Morgantown; and the region, which includes
three or four square miles, is significantly known as the 'Flats.' The
elevation of the 'Flats' is 275 feet above the river, or 1,065 feet above
tide. The deposits on this area consist almost entirely of clays and
fine, sandy material, there being very few boulders intermingled. The
depth of the deposit is unknown, since a well sunk on the land of Mr.
Baker passed through alternate beds of clay, fine sand, and muddy trash,
to a depth of sixty-five feet without reaching bed-rock. In some portions
of the clays which make up this deposit, the leaves of our common
forest-trees are found most beautifully preserved.
"At Clarksburg, where the river unites with Elk Creek, there is a wide
stretch of terrace deposits, and the upper limit is there about 1,050
feet above tide, or only 130 feet above low-water (920 feet); while at
Weston, forty miles above (by the river), these deposits cease at seventy
feet above low water, which is there 985 feet above tide. It will thus
be observed that the upper limit of the deposits retains a practical
horizontality from Morgantown to Weston, a distance of one hundred miles,
since the upper limit has the same elevation above tide (1,045 to 1,065
feet) at every locality.
"These deposits consist of rounded boulders of sandstone, with a large
amount of clay, quicksand, and other detrital matter. The country rock
in this region consists of the soft shales and limestones of the upper
coal-measures, and hence there are many 'low gaps' from the head of one
little stream to that of another, especially along the immediate region
of the river; and in every case the summits of these divides, where they
do not exceed an elevation of 1,050 feet above tide, are covered with
transported or terrace material; but where the summits go more than a
few feet above that level we find no transported material upon them, but
simply the decomposed country rock."
Other noteworthy terraces naturally attributable to the Cincinnati
ice-dam are to be found in the valley of the Kanawha, in West Virginia,
and one of special significance on the pass between the valleys of the
Ohio and Monongahela, west of Clarksburg, West Virginia. According to
Professor White, there is at this latter place "a broad, level summit,
having an elevation of 1,100 feet, in a gap about 300 feet below the
enclosing hills. This gap, or valley, is covered by a deposit of fine
clay. The cut through it is about thirty feet, and one can observe the
succession of clays of all kinds and of different colours, from yellow on
the surface down to the finest white potter's clay at the level of the
railway, where the cut reaches bed-rock, thus proving that the region has
been submerged."[CI]
[Footnote CI: Bulletin of the Geological Society of America, vol. i, p.
478.]
Another crucial case I have myself described at Bellevue, in the angle
of the Ohio and Alleghany Rivers, about five miles below Pittsburg,
where the gravel terrace is nearly 300 feet above the river, making it
about 1,000 feet above the sea. A significant circumstance connected
with this terrace is that not only does its height correspond with that
of the supposed obstruction at Cincinnati, but it contains many pebbles
of Canadian origin, which could not have got into the valley of the
Alleghany before the Glacial period, and could only have reached their
present position by being brought down the Alleghany River upon floating
ice, or by the ordinary movement of gravel along the margin of a river.
Thus this terrace, while corresponding closely with the elevation of
those on the Monongahela River, is directly connected with the Glacial
period, and furnishes a twofold argument for our theory.
A still stronger case occurs at Beech Flats, at the head of Ohio
Brush Creek, in the northwest corner of Pike County, Ohio, where, at
an elevation of about 950 feet above the sea, there is an extensive
flat-topped terrace just in front of the terminal moraine. This terrace
consists of fine loam, such as is derived from the glacial streams, but
which must have been deposited in still water. The occurrence of still
water at that elevation just in front of the continental ice-sheet is
best accounted for by the supposed dam at Cincinnati. Indeed, it is
extremely difficult to account for it in any other way.
There are, however, two other methods of attempting to account for the
class of facts above cited in support of the ice-dam theory, of which the
most plausible is, that in connection with the Glacial period there was
a subsidence of the whole region to an extent of 1,100 feet.
The principal objection heretofore alleged against this supposition is
that there are not corresponding signs of still-water action at the same
level on the other side of the Alleghany Mountains. This will certainly
be fatal to the subsidence theory, if it proves true. But it is possible
that sufficient search for such marks has not yet been made on the
eastern side of the mountains.
The other theory to account for the facts is, that the terraces adduced
in proof of the Cincinnati ice-dam were left by the streams in the slow
process of lowering their beds from their former high levels. This is
the view advocated by President T. C. Chamberlin. But the freshness
of the leaves and fragments of wood, such as were noted by Professor
White at Morgantown, and the great extent of fine silt occasionally
resting upon the summits of the water-sheds, as described above, near
Clarksburg, bear strongly against it. Furthermore, to account for the
terrace described at Bellevue, which contains Canadian pebbles, President
Chamberlin is compelled to connect the deposit with his hypothetical
first Glacial epoch, and to assume that all the erosion of the Alleghany
and Monongahela Rivers, and indeed of the whole trough of the Ohio River,
took place in the interval between the "first" and the "second" Glacial
periods (for he would connect the glacial deposits upon the south side of
the river at Cincinnati with the first Glacial epoch)--all of which, it
would seem, is an unnecessary demand upon the forces of Nature, when the
facts are so easily accounted for by the simple supposition of the dam at
Cincinnati.[CJ]
[Footnote CJ: See matter discussed more at length in the lee Age, pp.
326-350, 480-500; Bulletin of the United States Geological Survey, No.
58, pp. 76-100; Popular Science Monthly, vol. xlv, pp. 184-199. _Per
contra_, Mr. Frank Leverett, in American Geologist, vol. x, pp. 18-24.]
[Illustration: Fig. 55.--Map showing the condition of things when the
ice-front had withdrawn about on hundred and twenty miles, and while
it still filled the valley of the Mohawk. The outlet was then through
the Wabash. Niagara was not yet born (Claypole). (Transactions of the
Edinburgh Geological Society.)]
We have already described[CK] the various temporary lakes and lines of
drainage caused by the direct obstruction of the northward outlets to
the basin of the Great Lakes. In connection with the map, it will be
unnecessary to do anything more here than add a list of such temporary
southern outlets from the Erie-Ontario basin.[CL] The first is at Fort
Wayne, Indiana, through a valley connecting the Maumee River basin with
that of the Wabash. The channel here is well defined, and the high-level
gravel terraces down the Wabash River are a marked characteristic of the
valley. The elevation of this col above the sea is 740 feet. Similar
temporary lines of drainage existed from the St. Mary's River to the
Great Miami, at an elevation of 942 feet; from the Sandusky River to
the Scioto, through the Tymochtee Gap, at an elevation of 912 feet;
from Black River to the Killbuck (a tributary of the Muskingum) through
the Harrisville Gap, at 911 feet; from the Cuyahoga into the Tuscarawas
Valley, through the Akron Gap, at 971 feet; from Grand River into the
Mahoning, through the Orwell Gap, 938 feet; from Cattaraugus Creek, N.
Y., into the Alleghany Valley through the Dayton Gap, about 1,300 feet;
between Conneaut Creek and Shenango River, at Summit Station, 1,141 feet;
from the Genesee River, N. Y., into the head-waters of the Canisteo, a
branch of the Susquehanna, at Portageville, 1,314 feet; from Seneca Lake
to Chemung River, at Horseheads, 879 feet; from Cayuga Lake to the valley
of Cayuga Creek, at Spencer, N. Y., 1,000 feet; from Utica, N. Y., into
the Chenango Valley at Hamilton, about 900 feet.
[Footnote CK: See pp. 92 seq., 199 _seq._]
[Footnote CL: See also accompanying map.]
[Illustration: Fig. 56.--Map illustrating a stage in the recession of the
ice in Ohio. For a section of the deposit in the bed of this lakelet, see
page 200. The gravel deposits formed at this stage along the outlet into
the Tuscarawas River are very clearly marked (Claypole). (Transactions of
the Edinburgh Geological Society.)]
Perhaps it would have been best to give this list in the reverse order,
which would be more nearly chronological, since it is clear that the
highest outlets are the oldest. We should then have to mention, after the
Fort Wayne outlet, two others at lower levels which are pretty certainly
marked by distinct beach ridges upon the south side of Lake Erie. The
first was opened when the ice had melted back from the south peninsula of
Michigan to the water-shed across from the Shiawassee and Grand Rivers,
uncovering a pass which is now 729 feet above the sea. This continued to
be the outlet of Lake Erie-Ontario until the ice had further retreated
beyond the Strait of Mackinac, when the water would fall to the level of
the old outlet from Lake Michigan into the Illinois River, which is a
little less than 600 feet, where it would remain until the final opening
of the Mohawk River in New York attracted the water in that direction,
and lowered the level to that of the pass from Lake Ontario to the Mohawk
at Rome.[CM]
[Footnote CM: Mr. Warren Upham, in the Bulletin of the Geological Society
of America, vol. ii, p. 259.]
A study of these lines of temporary drainage during the Glacial period
sheds much light upon the long lines of gravel ridges running parallel
with the shores of Lake Erie and Lake Ontario. South of Lake Erie a
series of four ridges of different elevations can be traced. In Lorain
County, Ohio, the highest of these is 220 feet above the lake; the next
160 feet; the next 118 feet; and the lower one 100 feet, which would make
them respectively 795, 755, 715, and 700 feet above tide.
These gravel ridges are evidently old beach lines, and indicate the
different levels up to which the water was held by ice-obstructions
across the various outlets of the drainage valley. The material in the
ridges is water-worn and well assorted, and in coarseness ranges from
fine sand up to pebbles several inches in diameter. The predominant
material in them is of local origin. Where the rocks over which they run
are sandstone, the material is chiefly sand, and where the outcropping
rock is shale, the ridges consist chiefly of the harder nodules of that
formation which have successfully resisted the attrition of the waves.
Ordinarily these ridges are steepest upon the side facing the lake.
According to Mr. Upham, who has driven over them with me, the Lake Erie
ridges correspond, both in general appearance and in all other important
respects, to those which he has so carefully surveyed around the shores
of the ancient Lake Agassiz in Minnesota and Manitoba, an account of
which will be given a little farther on in this chapter.
[Illustration: Fig. 57.--Section of the lake ridges near Sandusky, Ohio.]
We are not permitted, however, to assume that there have been no changes
of level since the deposition of these beaches surrounding the ancient
glacial Lake Erie-Ontario. On the contrary, there appears to have been
a considerable elevation towards the east and northeast in post-glacial
times. The highest ridge south of Lake Erie, which at Fort Wayne is about
780 feet high, is now about 795 feet in Lorain County. The second of the
ridges above-mentioned, which is about 740 feet above tide at Cleveland,
Ohio, rises to 870 feet where the last traces of it have been discovered
at Hamburg, N. Y. The third ridge, which is 673 feet at Cleveland, has
risen to the height of 860 feet at Crittenden, about one hundred miles to
the east of Buffalo, N. Y.
A similar eastern increase of elevation is discoverable in the main ridge
surrounding Lake Ontario. What Professor Spencer calls the Iroquois
beach, which is 363 feet above tide at Hamilton, Ontario, has risen to a
height of 484 feet near Syracuse, N. Y.; while farther to the northeast,
in the vicinity of Watertown, it is upwards of 800 feet above tide.
There is also a similar northward increase of elevation in the beaches
surrounding the higher lands of Ontario eastward of Lake Huron and
Georgian Bay.
All this indicates that at the close of the Glacial period there
was a subsidence of several hundred feet in the area of greatest
ice-accumulation lying to the east and north of the Great Lake region.
The formation of these ridges occurred during that period of subsidence.
The re-elevation which followed the disappearance of the ice of course
carried with it these ridges, and brought them to their present
position.[CN]
[Footnote CN: See Spencer, in Bulletin of the Geological Society of
America, vol. ii, pp. 465-476.]
In returning to consider more particularly the remarkable gorge joining
the Minnesota with the Red River of the North, we are brought to the
largest of the glacial lakes of this class, and to the typical place in
America in which to study the temporary changes of drainage produced by
the ice itself daring the periods both of its advance and of its retreat.
[Illustration: Fig. 58.--Map showing the stages of recession of the ice
in Minnesota as described in the text (Upham).]
By turning to our general map of the glaciated region of the United
States,[CO] one can readily see the relation of the valley between
Lake Traverse and Big Stone Lake to an area marked as the bed of what
is called Lake Agassiz. During the Glacial period Brown's Valley, the
depression joining these two lakes, was the outlet of an immense body of
water to the north, whose natural drainage was towards Hudson Bay or the
Arctic Ocean, but which was cut off, by the advancing ice, from access to
the ocean-level in that direction, and was compelled to seek an exit to
the south.
[Footnote CO: See page 66.]
Thus for a long period the present Minnesota River Valley was occupied
by a stream of enormous dimensions, and this accounts for the great
size of the trough--the present Minnesota being but an insignificant
stream winding about in this deserted channel of the old "Father of
Waters," and having as much room as a child of tender age would have in
his parent's cast-off garments. This glacial stream has been fittingly
named River Warren, after General Warren, who first suggested and proved
its existence, and so we have designated it on the accompanying map of
Minnesota.
Lake Traverse is fifteen miles long, and the water is nowhere more than
twenty feet deep. Big Stone Lake is twenty-six miles long, and of about
the same depth. Brown's Valley, which connects the two, is five miles
long, and the lakes are so nearly on a level that during floods the water
from Lake Traverse sometimes overflows and runs to the south as well as
to the north.
[Illustration: Fig. 59.--Glacial terrace near the boundary of the
glaciated area, on Raccoon Creek, a tributary of the Licking River, in
Granville, Licking County, Ohio. Height about fifty feet.]
The trough occupied by these lakes and valley is from one mile to one
mile and a half in width and about 120 feet in depth. If we had been
permitted to stand upon the bluffs overlooking it during the latter
part of the Glacial period, we should have seen the whole drainage of
the north passing by our feet on its way to the Gulf of Mexico. As lie
follows down the valley of the Minnesota River, the observant traveller,
even now, cannot fail to see in the numerous well-preserved gravel
terraces the high-water marks of that stream when flooded with the joint
product of the annual precipitation over the vast area to the north, and
of the still more enormous quantities set free by the melting of the
western part of the great Laurentide Glacier.
Numerous other deserted water-ways in the northwestern part of the
valley of the Mississippi have been brought to light in the more
recent geological surveys, both in the United States and in Canada.
During a considerable portion of the Glacial period the Saskatchewan,
the Assiniboine, the Pembina, and the Cheyenne Rivers, whose present
drainage is into the Red River of the North, were all turned to the
south, and their temporary channels can be distinctly traced by deserted
water-courses marked by lines of gravel deposits.[CP]
[Footnote CP: For further particulars, see Ice Age, pp. 293 _et seq._]
In Dakota, Professor J. E. Todd has discovered large deserted channels
on the southwestern border of the glaciated region near the Missouri
River, where evidently streams must have flowed for a long distance in
ice-channels when the ice still continued to occupy the valley of the
James River. From these channels of ice in which the water was held up
to the level of the Missouri Coteau the water debouched directly into
channels with sides and bottom of earthy material, which still show every
mark of their former occupation by great streams.[CQ]
[Footnote CQ: For particulars, see Ice Age, p. 292.]
In Minnesota, also, there is abundant evidence that while the
northeastern part of the valley from Mankato to St. Paul was occupied by
ice, the drainage was temporarily turned directly southward across the
country through Union Slough and Blue Earth River into the head-waters of
the Des Moines River in Iowa.
_Ancient River Terraces._
The interest of the whole inquiry respecting the relation of man to
the Glacial period in America concentrates upon these temporary lines
of southern drainage. Wherever they existed, the swollen floods of the
Glacial period have left their permanent marks in the deposition of
extensive gravel terraces. The material thus distributed is derived
largely from the glacial deposits through which they run and out of which
they emerge. While the height of the terraces depended upon various
conditions which must be studied in detail, in general it may be said
that it corresponds pretty closely with the extent of the area whose
drainage was turned through the channel during the prevalence of the ice.
The height of the terraces and the coarseness of the material seem also
to have been somewhat dependent upon the proximity of their valleys to
the areas of most vigorous ice-action, and this, in turn, seems to lie in
the rear of the moraines which President Chamberlin has attributed to the
second Glacial epoch. Southward from this belt of moraines the terraces
uniformly and gradually diminish both in height and in the coarseness of
their gravel, until they finally disappear in the present flood-plain of
the Mississippi River.
[Illustration: Fig. 60.--Ideal section across a river-bed in drift
region: _b b b_, old river-bed; _R_, the present river; _t t_, upper or
older terraces; _t' t'_, lower terraces.]
An interesting illustration of this principle is to be observed in the
continuous valley of the Alleghany and Ohio Rivers. The trough of this
valley was reached by the continental glacier at only a few points,
the ice barely touching it at Salamanca, N. Y., Franklin, Pa., and
Cincinnati, Ohio. But throughout its whole length the ice-front was
approximately parallel to the valley, and occupied the head-waters of
nearly all its tributaries. Now, wherever tributaries which could be fed
by glacial floods, enter the trough of the main stream, they brought down
an excessive amount of gravel, and greatly increased the size of the
terrace in the trough itself, and from the mouth of each such tributary
to that of the next one below there is a gradual decrease in the height
of the terrace and in the coarseness of the material.
This law is illustrated with special clearness in Pennsylvania between
Franklin and Beaver. Franklin is upon the Alleghany River, at the last
point where it was reached directly by the ice. Below this point no
tributary reaches it from the glaciated region, and none such reaches the
Ohio after its junction with the Alleghany until we come to the mouth of
Beaver Creek, about twenty-five miles below Pittsburg.
But at this point the Ohio is joined by a line of drainage which emerges
from the glaciated area only ten or twelve miles to the north, and whose
branches occupy an exceptionally large glaciated area. Accordingly, there
is at Beaver a remarkable increase in the size of the glacial terrace
on the Ohio. In the angle down-stream between the Beaver and the Ohio
there is an enormous accumulation of granitic pebbles, many of them
almost large enough to be called boulders, forming the delta terrace,
upon which the city is built and rising to a height of 135 feet above
the low-water mark in the Ohio. In striking confirmation of our theory,
also, the terrace in the Ohio Valley upon the upper side of Beaver Creek
is composed of fine material, largely derived from local rocks and
containing but few granitic pebbles.
From the mouth of Beaver Creek, down the Ohio, the terrace is constant
(sometimes upon one side of the river and sometimes upon the other),
but, according to rule, the material of which it is composed gradually
grows finer, and the elevation of the terrace decreases. According to
rule, also, there is a notable increase in the height of the terrace
below each affluent which enters the river from the glaciated region.
This is specially noticeable below Marietta, at the mouth of the
Muskingum, whose head-waters drain an extensive portion of the glaciated
area. From the mouth of the Little Beaver to this point the tributaries
of the Ohio are all small, and none of them rise within the glacial
limit. Hence they could contribute nothing of the granitic material which
enters so largely into the formation of the river terrace; but below the
mouth of the Muskingum the terrace suddenly ascends to a height of nearly
one hundred feet above low-water mark.
Again, at the mouth of the Scioto at Portsmouth, there is a marked
increase in the size of the terrace, which is readily accounted for by
the floods which came down the Scioto Valley from the glaciated region.
The next marked increase is at Cincinnati, just below the mouth of the
Little Miami, whose whole course lay in the glaciated region, and whose
margin is lined by very pronounced terraces. At Cincinnati the upper
terrace upon which the city is built is 120 feet above the flood-plain.
Twenty-five miles farther down the river, near Lawrenceburg, these
glacial terraces are even more extensive, the valley being there between
three and four miles wide, and being nearly filled with gravel deposits
to a height of 112 feet above the flood-plain. Below this point the
terraces gradually diminish in height, and the material becomes finer
and more water-worn, until it merges at last in the flood-plain of the
Mississippi. The course of the Wabash River is too long to permit it to
add materially to the size of the terraces which characterise the broader
valley of the Ohio below the Illinois line.
It is in terraces such as these just described that we find the imbedded
relics of man which definitely connect him with the great Ice age. These
have now been found in the glacial terraces of the Delaware River at
Trenton, N. J.; in similar terraces in the valley of the Tuscarawas River
at New Comerstown, and in the valley of the Little Miami at Loveland and
Madisonville, in Ohio; on the East Fork of White River, at Medora, Ind.;
and still, again, at Little Falls, in the trough of the Mississippi, some
distance above Minneapolis, Minn.
I append a list of the points at which various streams from the Atlantic
Ocean to the Mississippi River emerge from the glacial boundary, and
below which the terraces are specially prominent. Of course, with the
retreat of the ice, the formation of the terraces continued northward
in the glaciated area to a greater or less distance, according to the
extent of the valley or to the length of time during which the drainage
was temporarily turned into it. These points of emergence are: In the
Delaware Valley, at Belvidere, N. J.; in the Susquehanna, at Beach Haven,
Pa.; in the Conewango, at Ackley, Warren County; in Oil Creek, above
Titusville: in French Creek, a little above Franklin; in Beaver Creek,
at Chewtown, Lawrence County; on the Middle Fork of Little Beaver, near
New Lisbon, Ohio; on the east branch of Sandy Creek, at East Rochester,
Columbiana County; on the Nimishillin, at Canton, Stark County; on the
Tuscarawas, at Bolivar; on Sugar Creek, at Beech City; on the Killbuck,
at Millersburg, Holmes County; on the Mohican, near the northeast corner
of Knox County; on the Licking River, at Newark; on Jonathan Creek, Perry
County; on the Hocking, at Lancaster; on the Scioto, at Hopetown, just
above Chillicothe; on Paint Creek, and its various tributaries, between
Chillicothe and Bainbridge; and on the Wabash, above New Harmony, Ind.;
to which may be added the Ohio River itself, at its junction with the
Miami, near Lawrenceburg.
Another class of terraces having most interesting connection with the
Glacial period is found in the arid basins west of the Rocky Mountains.
Over wide areas in Utah and Nevada the evaporation now just balances
the precipitation, and all the streams disappear in shallow bodies of
salt water of moderate dimensions, of which Great Salt Lake in Utah, and
Mono, Pyramid, and North Carson Lakes in Nevada, are the most familiar
examples. These occupy the lowest sinks of enclosed basins of great depth.
But there is abundant evidence that in consequence of the increased
precipitation and diminished evaporation of the Glacial period one of
these basins was filled to the brim and the other to a depth of several
hundred feet. These former enlargements have been named after the first
explorers of the region, Captains Lahontan and Bonneville, and are shown
on the accompanying sketch map by the shading surrounding the existing
lakes.
Lake Lahontan has been carefully studied by Mr. I. C. Russell, and has
been found to extend from the boundary of Oregon to latitude 38° 30'
south, a distance of two hundred and sixty miles. The Central Pacific
Railroad runs through its dried-up bed from Golconda to Wadsworth, a
distance of one hundred and sixty-five miles. The terraces of the former
lake are distinctly traceable at a height of 700 feet above the present
level of Lake Mono.
Lake Bonneville, whose present representative is Great Salt Lake, is the
subject of a recent monograph by Mr. G. K. Gilbert, from which it appears
that this ancient body of water occupied 19,750 square miles--an area
about ten times that of the present lake. At the time of its maximum
extension its depth was 1,000 feet, while Great Salt Lake ranges only
from fifteen to fifty feet in depth.
The pass through which the discharge finally took place is at Red Rock,
on the Utah and Northern Railroad, at the head of Cache Valley on the
south and the lower part of Marsh Creek Valley on the north. During
the long period preceding and accompanying the gradual rise of water in
the Utah basin to the level of the highest terrace, Marsh Creek (the
upper portion of which comes from the mountains on the east and turns
at right angles) had been at work depositing a delta of loose material
in the col which separates the two valleys. This deposit rested upon
a stratum of limestone at the bottom of the pass, and covered it with
sand, clay, and gravel to a depth of 375 feet. Thus, when the water was
approaching its upper level, the only barrier to prevent its escape was
this unstable accumulation of loose material upon top of the rock. It
would have required, therefore, no prophet's eye to predict that the way
was preparing for a tremendous _débâcle_.
[Illustration: Fig. 61.--Map of the Quaternary Lakes. Bonneville and
Lahontan (after Gilbert and Russell).]
The critical point at length was reached. After remaining nearly at
the elevation of the pass for a considerable period, during which the
1,000-foot shore-line was formed, the crisis came when the water began
to flow northward towards Snake River. Once begun in such loose material,
the channel rapidly enlarged until soon a stream equal to Niagara, and
at times probably much larger, was pouring northward through the valley
heretofore occupied by the insignificant rivulets of Marsh Creek and
the Port Neuf. It is impossible to tell how rapidly the loose barrier
wore away, but there is abundant evidence in the valley below that not
only the present channel of the lower part of Marsh Creek, but the whole
bottom of the valley for a mile or more in width, was for a considerable
time covered by a rapid stream from ten to twenty feet in depth, and
descending at the rate of thirteen feet to the mile.
The continuance of this flood was dependent upon the amount of water to
be discharged, which, as we have seen, was that contained in an area of
20,000 square miles, with a depth of 375 feet. A stream of the size of
Niagara would occupy about twenty-five years in the discharge of such a
mass, and this may fairly be taken as a measure of the time through which
it lasted. When the loose material lying above the strata of limestone
in Red Rock Pass had been washed away, the lake then continued at that
level for an indefinite period, with an overflow regulated by the annual
precipitation of the drainage basin. This stage of the lake, during which
it occupied 13,000 square miles and was 625 feet above its present level,
is also marked by an extensive and persistent shore-line all around
the basin. But, finally, the balance again turned when the evaporation
exceeded the precipitation, and the vast body of water has since dwindled
to its present insignificant dimensions.
My own interest in this discovery of Mr. Gilbert is enhanced by the
explanation it gives of a phenomenon in the Snake River Valley which I
was unable to solve when on the ground in 1890. The present railroad
town of Pocatello is situated just where this flood emerged from the
narrower valley of Marsh Creek and the Port Neuf, and spread itself out
upon the broad plain of the Snake River basin. The southern edge of the
plain upon which the city is built is a vast boulder-bed covered with a
thin stratum of sand and gravel. Everywhere, in sinking wells and digging
ditches on the vacant lots and in the streets of the city, water-worn
boulders of a great variety of material and sometimes three or four feet
in diameter are encountered. I was debarred from regarding this as a
terminal moraine, both by the water-worn character of the boulders and by
the absence of any sign of ice-action in the surrounding mountains, and I
was equally debarred from attributing it to any ordinary stream of water,
both by the size of the boulders and the fact that for a mile or more up
the Port Neuf Valley there is an intervale, forty or fifty feet below the
surface at Pocatello, and occupying the whole width of the valley, in
which there is only gravel and fine sand, through which the present Port
Neuf pursues a meandering course. The upper end of this short intervale
is bounded by the terminus of a basaltic stream which had flowed down the
valley and filled it to a considerable depth, but had subsequently been
much eroded by violent water-action.
In the light of Mr. Gilbert's discoveries, however, everything is clear.
The tremendous _débâcle_ which he has brought within the range of
scientific vision would naturally produce just the condition of things
which is so puzzling at Pocatello. Coming down through the restricted
channel with sufficient force to roll along boulders of great size and
to clear them all out from the upper portion of the valley, the torrent
would naturally deposit them where the current was first checked, a mile
below the lava cliffs. The plunge of the water over these cliffs would
keep a short space below clear from boulders, and the more moderate
stream of subsequent times would fill in the depression with the sand
and gravel now occupying it.
What other effects of this remarkable outburst may be traced farther down
in the Snake River Valley I cannot say, but it will be surprising if
they do not come to light and help to solve some of the many geological
problems yet awaiting us in this interesting region.
It should have been said that during the formation of the 625-foot, or
so-called Provo shore-line, glaciers descended from the cañons on the
west flank of the Wahsatch Mountains, and left terminal moraines to mark
the coincidence of the Glacial period with that stage of the enlargement
of the lake. Evidences of a similar coincidence are to be found on the
high-level terraces surrounding Lake Mono, to which glaciers formerly
descended from the western flanks of the Sierra Nevada.
The ancient shore-lines surrounding Lakes Bonneville and Lahontan bear
evidence also of various other episodes in the Glacial period. Evidently
there were two periods of marked increase in the size of the lakes, with
an arid period intervening. During the first rise the level of Bonneville
attained to within ninety feet of the second, and numerous beaches were
formed, and a large amount of yellow clay deposited. Then it seems
to have been wholly evaporated, while its soluble mineral matter was
precipitated, and so mingled with silt that it did not readily redissolve
during the second great rise of water. Partly on this account, and partly
through the influence of the outlet into the Snake River, the lake was
nearly fresh during its second enlargement.
_European Facts._
In Chapter VI it came in place to mention many of the facts connected
with the influence of the Glacial period upon the drainage systems
of Europe. We there discussed briefly the probable influence of the
ice-obstructions that extended across the mouths of the Dwina, the
Vistula, the Oder, the Elbe, the Weser, and the Rhine. The drainage of
the obstructed rivers in Russia was perhaps turned southward into the
Caspian and Black Seas, and then assisted in forming the fertile soil of
the plains in the southern part of that empire.
The obstructed drainage of the German rivers was probably turned westward
in front of the ice through the Straits of Dover or across the southern
part of England. This was during the climax of the Glacial period; but
later, according to Dawkins, during a period in which the land of the
British Isles stood about 600 feet above its present level, the streams
of the eastern coast--namely, "the Thames, Medway, Humber, Tyne, and
others, joined the Rhine, the Weser, and the Elbe, to form a river
flowing through the valley of the ocean. In like manner, the rivers of
the south of England and of the north of France formed a great river
flowing past the Channel Islands due west into the Atlantic, and the
Severn united with the rivers of the south of Ireland; while those to the
east of Ireland joined the Dee, Mersey Ribble, and Lune, as well as those
of western Scotland, ultimately reaching the Atlantic to the west of the
Hebrides. The water-shed between the valleys of the British Channel and
the North Sea is represented by a ridge passing due south from Folkestone
to Dieppe, and that between the drainage area and the Severn and its
tributaries on the one hand, and of the Irish Channel on the other, by a
ridge from Holyhead westward to Dublin.
"This tract of low, undulating land which surrounded Britain and Ireland
on every side consisted not merely of rich hill, valley, and plain, but
also of marsh-land studded with lakes, like the meres of Norfolk, now
indicated by the deeper soundings. These lakes were very numerous to the
south of the Isle of Wight and off the coast of Norfolk and Suffolk."[CR]
[Footnote CR: Early Man in Britain, p. 151.]
The evidence first regarded by scientific men to be demonstrative of the
formation of extensive lakes during the Glacial period by the direct
influence of ice-dams exists in the Parallel Roads of Glen Roy in
Scotland.
[Illustration: Fig. 62.--Parallel roads of Glen Roy.]
According to the description of Sir Charles Lyell, "Glen Roy is situated
in the western Highlands, about ten miles north of Fort William, near the
western end of the great glen of Scotland, or Caledonian Canal, and near
the foot of the highest of the Grampians, Ben Nevis. Throughout nearly
its whole length, a distance of more than ten miles, three parallel
roads or shelves are traced along the steep sides of the mountains, each
maintaining a perfect horizontality, and continuing at exactly the same
level on the opposite sides of the glen. Seen at a distance they appear
like ledges, or roads, cut artificially out of the sides of the hills;
but when we are upon them, we can scarcely recognize their existence, so
uneven is their surface and so covered with boulders. They are from ten
to sixty feet broad, and merely differ from the side of the mountain by
being somewhat less steep.
"On closer inspection, we find that these terraces are stratified in
the ordinary manner of alluvial or littoral deposits, as may be seen at
those points where ravines have been excavated by torrents. The parallel
shelves, therefore, have not been caused by denudation, but by the
deposition of detritus, precisely similar to that which is dispersed in
smaller quantities over the declivities of the hills above. These hills
consist of clay-slate, mica-schist, and granite, which rocks have been
worn away and laid bare at a few points immediately above the parallel
roads. The lowest of these roads is about 850 feet above the level of the
sea, and the next about 212 feet higher, and the third 82 feet above the
second. There is a fourth shelf, which occurs only in a contiguous valley
called Glen Gluoy, which is twelve feet above the highest of all the Glen
Roy roads, and consequently about 1,156 feet above the level of the sea.
One only, the lowest of the three roads of Glen Roy, is continued through
Glen Spean, a large valley with which Glen Roy unites. As the shelves,
having no slope towards the sea like ordinary river terraces, are always
at the same absolute height, they become continually more elevated above
the river in proportion as we descend each valley; and they at length
terminate very abruptly, without any obvious cause, or any change either
in the shape of the ground or in the composition or hardness of the
rocks."[CS]
[Footnote CS: Antiquity of Man, pp. 252, 253.]
Early in his career Charles Darwin studied these ancient beaches, and
ascribed them to the action of the sea during a period of continental
subsidence. In this view he was supported by the majority of geologists
until the region was visited by Agassiz, who saw at once the true
explanation. If these were really sea-beaches, similar deposits should
be found at the same elevation on other mountains than those surrounding
Glen Roy. Their absence elsewhere points, therefore, to some local cause,
which was readily suggested to the trained eye of one like Agassiz, then
fresh from the study of Alpine glaciers, who saw that these beaches were
formed upon the margin of temporary lakes, held back during the Glacial
period (as the Merjelen See now is) by a glacier which came out of one
glen and projected itself directly across the course of another, and thus
obstructed its drainage. The glacier of Glen Spean had pushed itself
across Glen Roy, as the great Aletsch Glacier in Switzerland now pushes
itself across the little valley behind the Eggishorn.
CHAPTER VIII.
RELICS OF MAN IN THE GLACIAL PERIOD.
_In Glacial Terraces of the United States._
Although the first clear evidence of glacial man was discovered in
Europe, the problem is so much simpler on the Western Continent that
we shall find it profitable to study the American facts first. We will
therefore present a summary of them at once, and then proceed to the more
obscure problems of European archæology.
The first definite discovery of human relics clearly connected with,
glacial deposits in America, and of the same age with them, was made
by Dr. C. C. Abbott, at Trenton, N. J., in the year 1875. The city of
Trenton is built upon a delta terrace about three miles wide which
occurs at the head of tide-water on the Delaware River. This terrace
bears every mark of having been deposited by a torrential stream which
came down the valley during the closing period of the great Ice age. The
material of which the terrace consists is all water-worn. According to
the description of Professor N. S. Shaler:
[Illustration: Fig. 63.--The glaciated portion is shaded. The shading
on the Lehigh and Delaware Rivers indicates glacial terraces, which are
absent from the Schuylkill.]
"The general structure of the mass is neither that of ordinary
boulder-clay nor of stratified gravels, such as are formed by the
complete rearrangement by water of the elements of simple drift-deposits.
It is made up of boulders, pebbles, and sand, varying in size from masses
containing one hundred cubic feet or more to the finest sand of the
ordinary sea-beaches. There is little trace of true clay in the deposit;
there is rarely enough to give the least trace of cementation to the
masses. The various elements are rather confusedly arranged; the large
boulders not being grouped on any particular level, and their major
axes not always distinctly coinciding with the horizon. All the pebbles
and boulders, so far as observed, are smooth and water-worn, a careful
search having failed to show evidence of distinct glacial scratching
or polishing on their surfaces. The type of pebble is the subovate or
discoidal, and though many depart from this form, yet nearly all observed
by me had been worn so as to show that their shape had been determined by
running water. The materials comprising the deposit are very varied, but
all I observed could apparently with reason be supposed to have come from
the extensive valley of the river near which they lie, except perhaps the
fragments of some rather rare hypogene rocks."
[Illustration: Fig. 64.--Palæolith found by Abbott in New Jersey,
slightly reduced.]
A conclusive proof of the relation of this Trenton delta terrace to the
Glacial period is found in the fact that the gravel deposit is continuous
with terraces extending up the trough of the valley of the Delaware to
the glaciated area and beyond. As, however, the descent of the river-bed
is rapid (about four feet to the mile) from the glacial border down to
tide-water, the terrace is not remarkably high, being only about fifteen
or twenty feet above the present flood-plain. But it is continuous,
and similar in composition with the great enlargement in the delta at
Trenton. Without doubt, therefore, the deposit represents the overwash
gravel of the Glacial period.
Fortunately for science, Dr. C. C. Abbott, whose tastes for archæological
investigations were early developed, had his residence upon the border
of this glacial delta terrace at Trenton, and as early as 1875 began
to find rough-stone implements of a peculiar type in the talus of
the bank where the river was undermining the terrace. In turning his
attention to the numerous fresh exposures of gravel made by railroad and
other excavations during the following year, he found several of the
implements in undisturbed strata, some of which were sixteen feet below
the surface. Since that time he has continued to make discoveries at
various intervals. In 1888 he had found four hundred implements of the
palæolithic type at Trenton, sixty of which had been taken from recorded
depths in the gravel, two hundred and fifty from the talus at the bluff
facing the river, and the remainder from the surface, or derived from
collectors who did not record the positions or circumstances under which
they were found.
[Illustration: Fig. 65.--Section across the Delaware River at Trenton.
New Jersey: _a_, _a_, Philadelphia red gravel and brick-clay (McGee's
Columbia deposit); _b_. _b_, Trenton gravel, in which the implements are
found: _c_, present flood-plain of the Delaware River (after Lewis).
(From Abbott's Primitive Industry.)]
The material from which the implements at Trenton are made is
argillite--that is, a clay slate which has been so metamorphosed as to
be susceptible of fracture, almost like flint. It is, however, by no
means capable of being worked into such delicate forms as flint is. But
as it is the only material in the vicinity capable of being chipped,
prehistoric men of that vicinity were compelled to make a virtue of
necessity and use the inferior material. Of all the implements found by
Dr. Abbott in the gravel, only one was flint; while upon the surface
innumerable arrow-heads of flint have been found. The transition, also,
in the type of implements is as sudden as that in the kind of material
of which they are made. Below the superficial deposit of black soil,
extending down to the depth of about one foot, the modern Indian flint
implements entirely disappear, and implements of palæolithic type only
are found.
[Illustration: Fig. 66.--Section of the Trenton gravel in which the
implements described in the text are found. The shelf on which the man
stands is made in process of excavation. The gravel is the same above and
below (photograph by Abbott).]
[Illustration: Fig. 67.--Face view of argillite implement, found by Dr.
C. C. Abbott, in 1876, at Trenton, New Jersey, in gravel, three feet
from face of bluff, and twenty-two feet from the surface (No. 10,985)
(Putnam).]
In the year 1882, after I had traced the glacial boundary westward from
the Delaware River, across the States of Pennsylvania, Ohio, and Indiana,
I was struck with the similarity between the terrace at Trenton and
numerous terraces which I had attributed to the Glacial age in Ohio and
the other States. It adds much to the interest of subsequent discoveries
to note that in 1884, in my report to the Western Reserve Historical
Society upon the glacial boundary of Ohio, I wrote as follows:
[Illustration: Fig. 68.--Argillite implement found by Dr. C. C Abbott,
March, 1879, at A. K. Rowan's farm, Trenton, New Jersey, in gravel
sixteen feet from surface: a, face view; b, side view (No. 11,286)
(Putnam).]
"The gravel in which they [Dr. Abbott's implements] are found is glacial
gravel deposited upon the banks of the Delaware when, during the last
stages of the Glacial period, the river was swollen with vast floods of
water from the melting ice. Man was on this continent at that period
when the climate and ice of Greenland extended to the mouth of New York
Harbor. The probability is, that if he was in New Jersey at that time, he
was also upon the banks of the Ohio, and the extensive terrace and gravel
deposits in the southern part of our State should be closely scanned
by archæologists. When observers become familiar with the rude form of
these palæolithic implements, they will doubtless find them in abundance.
But whether we find them or not in this State [Ohio], if you admit, as
I am compelled to do, the genuineness of those found by Dr. Abbott, our
investigation into the glacial phenomena of Ohio must have an important
archæological significance, for they bear upon the question of the
chronology of the Glacial period, and so upon that of man's appearance in
New Jersey."
[Illustration: Fig. 69.--Chipped pebble of black chert, found by Dr. C.
L. Metz. October, 1885, at Madisonville, Ohio, in gravel eight feet from
surface under clay: _a_, face view; _b_, side view.]
The expectation of finding evidence of preglacial man in Ohio was
justified soon after this (in 1885), when Dr. C L. Metz, while
co-co-operating with Professor F. W. Putnam, of the Peabody Museum,
Cambridge, Mass., in field work, discovered a flint implement of
palæolithic type in undisturbed strata of the glacial terrace of the
Little Miami River, near his residence at Madisonville, Ohio. In 1887
Dr. Metz found another implement in the terrace of the same river, at
Loveland, about twenty-five miles farther up the stream. The implement
at Madisonville occurred eight feet below the surface, and about a mile
back from the edge of the terrace; while that at Loveland was found in a
coarser deposit, about a quarter of a mile back from the present stream,
and thirty feet below the surface. Mastodon-bones also were discovered in
close proximity to the implement at Loveland.
[Illustration: Fig. 70.]
Interest in these investigations was still further increased by the
report of Mr. Hilborne T. Cresson, of Philadelphia, that in 1886, with
my map of the glaciated region in hand, he had found an implement of
palæolithic type in undisturbed strata of the glacial terrace bordering
the East Branch of White River, near the glacial boundary at Medora,
Jackson County, Ind. The terrace was about fifty feet above the
flood-plain of the river.
Later still, in October, 1889, Mr. W. C. Mills, of Newcomerstown,
Tuscarawas County, Ohio, found in that town a finely shaped flint
implement sixteen feet below the surface of the terrace of glacial
gravel which lines the margin of the Tuscarawas Valley.[CT] Mr. Mills
was not aware of the importance of this discovery until meeting with
me some months later, when he described the situation to me, and soon
after sent the implement for examination. In company with Judge C.
C. Baldwin, President of the Western Reserve Historical Society, and
several others, a visit was made to Mr. Mills, and we carefully examined
the gravel-pit in which the implement occurred, and collected evidence
which was abundant to corroborate all his statements. The implement
in question is made from a peculiar flint which is found in the Lower
Mercer limestone, of which there are outcrops a few miles distant, and
it resembles in so many ways the typical implements found by Boucher de
Perthes, at Abbeville, that, except for the difference in the material
from which it is made, it would be impossible to distinguish it from
them. The similarity of pattern is too minute to have originated except
from imitation.
[Footnote CT: For typical section of a glacial terrace in Ohio, see p.
227.]
[Illustration: Fig. 71.--The smaller is the palæolith from Newcomerstown,
the larger from Amiens (face view), reduced one half in diameter.]
In 1877, a year after the discoveries by Dr. Abbott in New Jersey, some
rude quartz implements were discovered by Professor N. H. Winchell in
the glacial terraces of the upper Mississippi, in the vicinity of Little
Falls, Morrison County, Minn. This locality was afterwards more fully
explored by Miss Franc E. Babbitt, who succeeded in finding so large a
number of the implements as to set at rest all question concerning their
human origin. According to Mr. Warren Upham, the glacial flood-plain
of the Mississippi is here about three miles wide, with an elevation
of from twenty-five to thirty feet above the river. It is in a stream
near the bottom of this glacial terrace that the most of Miss Babbitt's
discoveries were made, and Mr. Upham has pretty clearly shown that the
gravel of the terrace overlying them was mostly deposited while the
ice-front was still lingering about sixty miles farther north, in the
vicinity of Itasca Lake.[CU]
[Footnote CU: For a general map, see p. 66; also p. 225.]
[Illustration: Fig. 72.--Edge view of the preceding.]
[Illustration: Fig. 73.--Section across the Mississippi Valley at Little
Falls, Minnesota, showing the stratum in which chipped quartz fragments
were found by Miss F. E. Babbitt, as described in the text (Upham).]
Up to this time the above are all the instances in which the relics
of man are directly and indubitably connected with deposits of this
particular period east of the Rocky Mountains. Probably it is incorrect
to speak of these as preglacial, for the portion of the period at which
the deposits incorporating human relics were made is well on towards the
close of the great Ice age, since these terraces were, in some cases, and
may have been in all cases, deposited after the ice-front had withdrawn
nearly, if not quite, to the water-shed of the St Lawrence basin. It may
be difficult to demonstrate this with reference to the gravel deposits at
Trenton, Madisonville, and Medora, but it is evident at a glance in the
case of Newcomerstown and Little Falls.
That the implement-bearing gravel of Trenton, N. J., belongs to the
later stages of the Glacial period is evident from its relation to what
Professor H. Carvill Lewis called "the Philadelphia red gravel and
brick-clay," but which, from its large development in the District of
Columbia at Washington, is called by Mr. McGee the "Columbia deposit."
The city of Philadelphia is built upon this formation in the Delaware
Valley, and the brick for its houses is obtained from it; the cellar
of each house ordinarily furnishing clay enough for its brick walls.
This clay is of course a deposit in comparatively still water, which
would imply deposition during a period of land subsidence. But that it
was ice-laden water which flooded the banks is shown by the frequent
occurrence of large blocks of stone in the deposits, such as could have
been transported only in connection with floating ice. The boulders in
the Columbia formation clearly belong to the individual river valleys in
which they are found, and doubtless are to be connected with the flooded
condition of those valleys when, by means of a northerly subsidence, the
gradient of the streams was considerably less than now.
[Illustration: Fig. 74.--Quartz implement, found by Miss F. E. Babbitt,
1878, at Little Falls, Minnesota, in modified drift, fifteen feet below
surface: _a_, face view; _b_, profile view. The black represented on the
cut is the matrix of the quartz vein (No. 31,323) (Putnam).]
There is some difference of opinion in respect to the extent of
this subsidence, and, indeed, respecting the height attained by the
Philadelphia brick-clay, or McGee's Columbia deposit. Professor Lewis
(whose residence was at Philadelphia, and who had devoted much time to
field observations) insisted that the deposit could not be found higher
than from 180 to 200 feet above the immediate flood-plain of the river
valleys where they occur. But, without entering upon this disputed
question, it is sufficient to consider the bearing of the facts that are
accepted by all--namely, that towards the close of the Glacial period
there was a marked subsidence of the land on the eastern coast of North
America, increasing towards the north.
Fully to comprehend the situation, we need to bring before the mind some
of the indirect effects of the Glacial period in this region. The most
important of these was the necessary projection of subglacial conditions
over a considerable belt of territory to the south of that actually
reached by glacial ice; so that, while there are no clear indications of
the existence of local glaciers in the Appalachian Mountains south of the
central part of Pennsylvania, there are many indications of increased
snow-fall upon the mountains, connected with prolonged winters and with a
great increase of spring floods and ice-gorges upon the annual breaking
up of winter.
These facts have been stated in detail by Mr. McGee,[CV] from whose
report it appears that, on the Potomac at Washington, the surface of
the Columbia deposit is 150 feet above tide, and that the deposit itself
contains many boulders, some of which are as much as two or three feet in
diameter. These are mingled with the gravel in such a way as to show that
they must have been brought down by floating ice from the head-waters of
the Potomac when the winters were much more severe than now. That this
deposit is properly the work of the river is shown by the entire absence
of marine shells.
[Footnote CV: Seventh Annual Report of the United States Geological
Survey for 1885 and 1886, pp. 537-646.]
According to Mr. McGee, also, there is a gradual decrease in the height
of these delta terraces of the Columbia period as they recede from the
glacial boundary--that at the mouth of the Susquehanna being 245 feet,
that of the Potomac 140 feet, that on the Rappahannock 125, that on the
James 100, and that on the Roanoke 75; while the size of the transported
boulders along the streams also gradually diminishes in the same order.
During the Columbia period the Susquehanna River transported boulders
fifty times the size now transported, while the Potomac transported them
only up to twenty times, the Rappahannock only ten times, the James
only five, and the Roanoke only two or three times the size of those
now transported. This progressive diminution, both in the extent of the
deposit and in the coarseness of the material deposited by these rivers
at about the time of the maximum portion of the Glacial period, is what
would naturally be expected under the conditions supposed to exist in
connection with the great Ice age, and is an important confirmation of
the glacial theory.
That the period of subsidence and more intense glacial conditions during
which the Columbia deposits took place, preceded, by a long interval, the
deposition of the gravel terraces at Trenton, N. J., and the analogous
deposits in the Mississippi Valley where palæolithic implements have been
found, is evident enough. The Trenton gravel was deposited in a recess in
the Columbia deposit which had been previously worn out by the stream.
Indeed, in every place where opportunity offers for direct observation
the Trenton gravel is seen to be distinctly subsequent to the other. It
was not _buried by_ the Philadelphia red gravel and brick-clay, but to a
limited degree overlies and _buries_ it.
The data for measuring the absolute length of time between these two
stages of the Glacial period are very indefinite. Mr. McGee, however,
supposes that since the Columbia period a sufficient time has elapsed
for the falls of the Susquehanna to recede more than twenty miles and
for those of the Potomac eighteen miles, and this through a rock which
is exceedingly obdurate. But, in channels opening, as these do, freely
outward, it is difficult to tell in what epochs the erosion has been
principally performed, since there are no buried channels, as in the
glaciated area, enabling us to determine whether or not much of the
eroding work of the river may have been accomplished in preglacial times.
The lapse of time which, upon the least calculation, separates the
Columbia epoch from the Trenton, gives unusual importance to any
discovery of palæolithic implements which may be made in the earlier
deposits. We are bound, therefore, to consider with special caution
the reported discovery of an implement in these deposits at Claymont,
Delaware. The discovery was made by Dr. Hilborne T. Cresson, on July 13,
1887, during the progress of an extensive excavation in constructing the
Baltimore and Ohio Railroad, nineteen miles south of Philadelphia. The
implement was from eight to nine feet below the surface. As there is so
much chance for error of judgment respecting the undisturbed condition
of the strata, and as there was so little opportunity for Dr. Cresson to
verify his conclusion, we may well wait for the cumulative support of
other discoveries before building a theory upon it; still, it will be
profitable to consider the situation.
[Illustration: Fig. 75.--Argillite implement, found by H. T. Cresson,
1887, in Baltimore and Ohio Railroad cut, one mile from Claymont,
Delaware, in Columbia gravel, eight to nine feet below the overlying clay
bed: _a_, face view; _b_, side view (No. 45,726) (Putnam).]
Both Mr. McGee and myself have visited the locality with Dr. Cresson, and
there can be no doubt that the implement occurred underneath the Columbia
gravel. The line of demarcation is here very sharp between that gravel
and the decomposed strata of underlying gneiss rock, which appears in
our illustration as a light band in the middle of the section exposed.
Some large boulders which could have been moved only in connection with
floating ice are found in the overlying deposit near by. This excavation
is about one mile and a half west of the Delaware River, and about 150
feet above it, being nearly at the uppermost limit of the Columbia
deposit in that vicinity.
[Illustration: Fig. 76.--General section of Baltimore and Ohio cut,
near Claymont, Delaware, where Mr. Cresson found palæolithic implements
figured in the text (from photograph by Cresson).]
The age of these deposits in which implements have been found at
Claymont and at Trenton will be referred to again when we come to the
specific discussion of the date of the Glacial period. It is sufficient
here to bring before our minds clearly, first, the fact that this at
Claymont is connected with the river floods accompanying the ice at its
time of maximum extension, and when there was a gradually increasing
or differential depression of the country to an unknown extent to the
northward.
Two radically different theories are presented to account for the
deposits variously known as the Columbia gravel and the Philadelphia
brick-clay. Mr. McGee, in the monograph above referred to, supposes them
to have been deposited during a period of a general subsidence of the
coast-line; so that they took place at about tide-level. Mr. Upham, on
the other hand, supposes them to have been deposited during the period
of general elevation to whose influence he mainly attributes the Glacial
period itself. In his view much of the shallow sea-bottom adjoining
the present shore off from Delaware and Chesapeake Bays was then a
land-surface, and the Hudson, the Delaware, and the Susquehanna Rivers,
coming down from the still higher elevations of the north, flowed through
extensive plains so related to the northern areas of elevation that
deposition was occurring in their valleys, owing in part to the flooded
condition of the streams, in part to the differential elevation, and in
part to the superabundance of silt and other _débris_ furnished by the
melting ice-sheet in the head-waters of these streams.
The deposits of Trenton gravel occurred much later, at a time when the
ice had melted far back towards the head-waters of the Delaware, and
after the land had nearly resumed its present relations of level, if
indeed it had not risen northward to a still greater relative height.
As would be expected from the climatic conditions accompanying the
Glacial epoch, man's companions in the animal world were very different
during the period when the high-level river gravels of America were
forming from those with which he is now associated. From the remains
actually discovered, either in these gravels or in close proximity to
them, we infer that, while the mastodon was the most frequent of the
extinct quadrupeds with which man then had to contend in that region, he
must have been familiar also with the walrus, the Greenland reindeer, the
caribou, the bison, the moose, and the musk ox.
_In the Glacial Terraces of Europe._
The existence of glacial man in Europe was first determined in connection
with the high-level river gravels already described in the valley of the
Somme, situated in Picardy in the northern part of France. Here in 1841
Boucher de Perthes began to discover rudely fashioned stone implements
in undisturbed strata of the gravel terraces, whose connection with
the Glacial period we have already made clear. But for nearly twenty
years his discoveries were ignored by scientific men, although he made
persistent efforts to get the facts before them, and published a full
account of them with illustrations as early as 1847. Some suggested fraud
on the part of the workmen; others without examination declared that the
gravel must have been disturbed; while others, still, denied altogether
the artificial character of the implements.
[Illustration: Fig. 77.--Section across valley of the Somme: 1, peat,
twenty to thirty feet thick, resting on gravel, _a_; 2, lower-level
gravels, with elephant-bones and flint implements, covered with
river-loam twenty to forty feet thick; 3, upper-level gravels, with
similar fossils covered with loam, in all, thirty feet thick; 4,
upland-loam, five to six feet thick; 5, Eocene-Tertiary.]
At length, Dr. Regillout, an eminent physician residing at Amiens,
about forty miles higher up the Somme than Abbeville, visited Boucher
de Perthes, and, upon seeing the similarity between the gravel terraces
at Abbeville and Amiens, returned home to look for similar implements
in the high-level gravel-pits at St. Acheul, a suburb of Amiens. Almost
immediately he discovered flint implements there of the same pattern with
those at Abbeville, and in undisturbed strata of the gravel terrace,
where it rested on the original chalk formation, at a height of 90 feet
above the river. In the course of four years, Dr. Regillout found several
hundred of these implements, and in 1854 published an illustrated report
upon the discoveries.
Still the scientific world remained incredulous until the years 1858 and
1859, when Dr. Falconer, Mr. Prestwich, Mr. John Evans, Mr. Flower, Sir
Charles Lyell, of England, and MM. Pouchet and Gaudry, of France, visited
Abbeville and Amiens, and succeeded in making similar discoveries for
themselves. Additional discoveries at St. Acheul have continued up to
the present time whenever excavations have gone on at the gravel-pits.
Mr. Prestwich estimates that there is an implement to every cubic metre
of gravel, and says that he himself has brought away at different times
more than two hundred specimens, and that the total number found in this
one locality can hardly be under four thousand. "The gravel-beds are on
the brow of a hill 97 feet above the river Somme," and besides the relics
of man contain numerous fluviatile and land shells together with "teeth
and bones of the mammoth, rhinoceros, horse, reindeer, and red deer, but
not of the hippopotamus,"[CW] bones of the latter animal being found here
only in the gravels of the lower terraces, where they are less than
thirty feet above the river, and mark a considerably later stage in the
erosion of the valley. While many of the implements found at Amiens seem
to have been somewhat worn and rolled, "others are as sharp and fresh
as when first made.... The bedding of the gravel is extremely irregular
and contorted, as though it had been pushed about by a force acting from
above; and this, together with the occurrence of blocks of Tertiary
sandstone of considerable size, leads to the inference that both are due
to the action of river-ice. In the Seine Valley blocks of still larger
size, and transported from greater distances, are found in gravels of the
same age."
[Footnote CW: Prestwich's Geology, vol. ii, p. 481.]
"Flint implements are found under similar conditions in many of the
river-valleys of other parts of France, especially in the neighbourhood
of Paris; of Mons in Belgium; in Spain, in the neighbourhood of
Madrid, in Portugal, in Italy, and in Greece; but they have not been
discovered in the drift-beds of Denmark, Sweden, or Russia, nor is there
any well-authenticated instance of the occurrence of palæoliths in
Germany."[CX]
[Footnote CX: Prestwich's Geology, vol. ii, pp. 481, 482.]
When once the fact had been established that man was in northern France
at the time of the deposition of the high-level gravels of the Somme and
the Seine, renewed attention was directed to terraces of similar age in
southern England. One of these is that upon which the city of London is
built, and which, according to Lyell's description, "extends from above
Maidenhead through the metropolis to the sea, a distance from west to
east of fifty miles, having a width varying from two to nine miles. Its
thickness ranges commonly from five to fifteen feet."[CY]
[Footnote CY: Antiquity of Man, pp. 154, 155.]
For a long time geologists had been familiar with the fact that these
terraces of the Thames contain the remains of numerous extinct animals,
among which are included the mammoth and a species of rhinoceros.
Upon directing special attention to the subject, it was found that, at
various intervals, the remains of man, also, had been reported from the
same deposits. As long ago as 1715 Mr. Conyers discovered a palæolithic
implement, in connection with the skeleton of an elephant, at Black
Mary's, near Gray's Inn Lane, London. This implement is preserved in the
British Museum, and closely resembles typical specimens from the gravel
at Amiens. Other implements of similar character have been found in
the valley of the Wey near Guilford, also in the valley of the Darent,
near Whitstable in Kent, and between Heme Bay and the Reculvers. While
the exact position of these implements in the gravel had not been so
positively noted as in the case of those found at Amiens and Abbeville,
there can be little doubt that man, in company with the extinct animals
mentioned, inhabited the valley of the Thames at a period when its annual
floods spread over the whole terrace-plain upon which the main part of
London is built.
In the valley of the Ouse, however, near Bedford, the discovery of
palæolithic implements in the gravel terraces connected with the
Glacial period and in intimate association with bones of the elephant,
rhinoceros, hippopotamus, and other extinct animals, has been as fully
established as in the valley of the Somme. The discoveries here were
first made in the year 1860, by Mr. James Wyatt, in a gravel-pit at
Biddenham, two miles northwest of Bedford. Two flint implements were
thrown out by workmen in one day from undisturbed strata thirteen feet
below the surface, and numerous other specimens have since been found in
a similar situation.
The valley of the Ouse is bordered on either side by sections of a
superficial blanket of glacial drift containing many transported boulders
of considerable size. The valley is here about two miles wide, and ninety
feet deep. The gravel deposit, however, in which the implements were
found, is only about thirty feet above the present level of the river,
and hence represents the middle period of the work of the river in
erosion.
Another locality in England in which similar discoveries have been made,
is at Hoxne, about five miles from Diss, in Suffolk County. Like that
in the valley of the Thames, however, the implements were found a long
time before the significance of the discovery was recognized. Mr. John
Frere reported the discovery to the Society of Antiquaries in 1801,
and gave some of the implements both to the society and to the British
Museum, in whose collections they are still preserved. The implements are
of the true palæolithic type, and existed in such abundance, and were
so free from signs of wear, that the conclusion seemed probable that a
manufactory of them had been uncovered. As many as five or six to the
square yard are said to have been found. Indeed, their numbers were so
great that the workmen "had emptied baskets of them into the ruts of the
adjoining road before becoming aware of their value."
The deposit in which they are found is situated in the valley of Gold
Brook, a tributary of the Waveney. The implements occurred about twelve
feet below the surface, in fresh-water deposits, filling a hollow eroded
in the glacial deposit covering that part of England. This, therefore, is
clearly either of post-glacial or of late glacial age.
Still another locality in which similar palæolithic implements were found
in undisturbed gravel of this same age in eastern England is Icklingham,
in the valley of the Lark, where the situation is quite similar to that
already described at Bedford, on the Ouse.
The last place we will stop to mention in England which was visited
by palæolithic man, during or soon after the Glacial epoch, is to be
found in the vicinity of Southampton. At this time the Isle of Wight
was joined to the mainland, and not improbably England itself to the
Continent. The river, then flowing through the depression of the Solent
and the Southampton Water, occupied a much higher level than now, leaving
terraces along the shore at various places, in which the tools of
palæolithic man have been discovered.
Though these are the best authenticated discoveries connecting man with
the Glacial period in England, they are by no means the only probable
cases. Almost every valley of southern England furnishes evidence of a
similar but less demonstrative character.
_In Cave Deposits._
The discovery of the remains of man in the high-level river-gravels
deposited near the close of the Glacial period led to a revision of the
evidence which had from time to time been reported connecting the remains
of man with those of various extinct animals in cave deposits both in
England and upon the Continent.
_The British Isles._
As early as 1826, Rev. J. MacEnery, a Roman Catholic priest residing
near Torquay, in Devonshire, England, had made some most remarkable
discoveries in a cavern at Kent's Hole, near his home; but, owing to his
early death, and to the incredulity of that generation of scientific
men, his story was neither credited nor published till 1859. About this
time, a new cave having been discovered not far away, at Brixham, the
best qualified members of the Royal Society (Lyell, Phillips, Lubbock,
Evans, Vivian, Pengelly, Busk, Dawkins, and Sanford) were deputed to see
that it was carefully explored. Mr. Pengelly, who had had twenty years'
experience in similar explorations, directed and superintended the work.
Every portion of the contents was examined with minutest care. Kent's
Hole is "180 to 190 feet above the level of mean tide, and about 70 feet
above the bottom of the valley immediately adjacent."[CZ] In one chamber
the excavation was about sixty feet square. The contents were arranged in
the following order:
[Footnote CZ: Dawkins's Cave-Hunting, p. 325.]
[Illustration: Fig. 78.--Mouth of Kent's Hole.]
1. A surface of dark earth a few inches thick, containing Roman pottery,
iron and bronze spear-heads, together with polished stone weapons. There
were, too, in this stratum bones of cows, goats, and horses, mingled with
large quantities of charcoal.
2. Below this was a stalagmite floor from one to three feet thick, formed
by the dripping of lime-water from the roof.
3. Under this crust of stalagmite was a compact deposit of red earth,
from two to thirteen feet thick.[DA] Flint implements of various kinds
and charcoal were also found at different depths; also an awl, or
piercer; a needle with the eye large enough to admit small pack-thread;
and three harpoon-heads made out of bone and deer's horn.
[Footnote DA: Dawkins's Cave-Hunting, p. 326; Lyell's Antiquity of Man,
p. 101.]
4. Flint implements were also obtained in a conglomerate (breccia) still
below this. The fossil bones in this cave belonged to the same species of
animals as those discovered in a cave near Wells.
The Brixham cave occurs near the small village of that name, not far from
Torquay. The entrance to it is about ninety-five feet above high water.
Its deposits, in descending order, are: 1. Stalagmitic floor from six to
twelve or fifteen inches in thickness. 2. A thin breccia of limestone
fragments cemented together by carbonate of lime. This had accumulated
about the mouth, so as to fill up the entrance. 3. A layer of blackish
earth about one foot in thickness 4. A deposit of from two to four feet
thick, consisting of clayey loam, mingled with fragments of limestone,
from small bits up to rocks weighing a ton. Bounded pebbles of other
material were also occasionally met with. 5. Shingle consisting of
rounded pebbles largely of foreign material.
All these strata, except the third, contained fossils of some kind, but
the fourth was by far the richest repository. Among the bones found are
those of the mammoth, the woolly rhinoceros, the horse, the ox, the
reindeer, the cave-lion, the cave-hyena, and the cave-bear. Associated
with these remains a number of worked flints was found. In one place
the bones of an entire leg of a cave-bear occurred in such a position as
to show that they must have been bound together by the ligaments when
they were buried. Immediately below these bones a flint implement was
found.[DB]
[Footnote DB: See Pengelly's Reports to the Devonshire Association, 1867.]
The hyena's den, at Wookey Hole, near Wells, in Somerset, was carefully
explored by Professor Boyd Dawkins, who stood by and examined every
shovelful of material as it was thrown out.
This cave alone yielded 35 specimens of palæolithic art, 467 jaws and
teeth of the cave-hyena, 15 of the cave lion, 27 of the cave-bear, 11 of
the grizzly bear, 11 of the brown bear, 7 of the wolf, 8 of the fox, 30
of the mammoth, 233 of the woolly rhinoceros, 401 of the horse, 16 of the
wild ox, 30 of the bison, 35 of the Irish elk, and 30 of the reindeer
(jaws and teeth only).
In Derbyshire numerous caves were explored by Professor Dawkins at Cress
well Crags, which, in addition to flint implements and the remains of
the animals occurring in the Brixham cave, yielded the bones of the
machairodus, an extinct species of tiger or lion which lived during the
Tertiary period.
The Victoria cave, near Settle, in west Yorkshire, is the only other one
in England which we need to mention. In this there were no remains found
which could be positively identified as human, but the animal remains
in the lower strata of the cave deposit were so different from those in
the upper bed as to indicate the great lapse of time which separated the
two. This cave is 1,450 feet above the sea-level, and there were found in
the upper strata of the floor, down to a depth of from two to ten feet,
many remains of existing animals. Then, for a distance of twelve feet,
there occurred a clay deposit, containing no organic remains whatever,
but some well-scratched boulders. Below this was a third stratum of earth
mingled with limestone fragments, at the base of which were numerous
remains of the mammoth, rhinoceros, hippopotamus, bison, hyena, etc.
One bone occurred which was by some supposed to be human, but by others
to have belonged to a bear. This lower stratum is, without much doubt,
preglacial, and the thickness of the deposit intervening between it and
the upper fossiliferous bed is taken by some to indicate the great lapse
of time separating the period of the mammoth and rhinoceros in England
from the modern age. The scratched boulders in the middle stratum of
laminated clay, would indicate certainly that the material found its way
into the cave during the Glacial epoch, when ice filled the whole valley
of the Ribble, which flows past the foot of the hill, and whose bed is
900 feet below the mouth of the cave.
In North Wales the Vale of Clwyd contains numerous caves which were
occupied by hyenas in preglacial times and with their bones are
associated those of the mammoth, the rhinoceros, the hippopotamus, the
cave-lion, the cave-bear, and various other animals. Flint implements
also were found in the cave at Cae Gwyn, near the village of Tremeirchon,
on the eastern side of the valley, opposite Cefn, and about four miles
distant. We have already given an illustration of the Cefn cave (see
page 148). It will be observed that this valley of the Clwyd opens to
the north, and has a pretty rapid descent to the sea from the Welsh
mountains, and was in position to be obstructed by the Irish Sea glacier,
so as to have been occupied at times by one of the characteristic
marginal lakes of the Glacial period. It is evident also that the
northern ice prevailed over the Welsh ice for a considerable portion
of the lower part of the valley; for northern drift is the superficial
deposit upon the hills on the sides of the valley up to a height of over
500 feet. From the investigations of Mr. C. E. De Rance, F. G. S.,[DC]
it is equally clear also that the northern drift, which until lately
sealed up the entrance of the cave, was subsequent to its occupation by
man, and this was the opinion formed by Sir Archibald Geikie, Director
General of the Geological Survey of the United Kingdom, as the result of
special investigations which he made of the matter.[DD]
[Footnote DC: Proceedings of the Yorkshire Geological Society for 1888,
pp. 1-20.]
[Footnote DD: See De Ranee, as above, p. 17; and article by H. Hicks,
in Quarterly Journal of Geological Society, vol. xlii, p. 3; Geological
Magazine, May, 1885, p. 510.]
From the caves in the Vale of Clwyd as many as 400 teeth of rhinoceros,
500 of horse, 180 of hyena, and 15 of mammoth have been taken. A section
of the cave deposits in the cave at Cae Gwyn is as follows:
"Below the soil for about eight feet a tolerably stiff boulder-clay,
containing many ice-scratched boulders and narrow bands and pockets of
sand. Below this about seven feet of gravel and sand, with here and
there bands of red clay, having also many ice-scratched boulders. The
next deposit was a laminated brown clay, and under this was found the
bone-earth, a brown, sandy clay with small pebbles and with angular
fragments of limestone, stalagmites, and stalactites. During the
excavations it became clear that the bones had been greatly disturbed by
water action; that the stalagmite floor, in parts more than a foot in
thickness, and massive stalactites, had also been broken and thrown about
in all positions; and that these had been covered afterwards by clays and
sand containing foreign pebbles. This seemed to prove that the caverns,
now 400 feet above ordnance datum, must have been submerged subsequently
to their occupation by the animals and by man. In Dr. Hicks's opinion,
the contents of the cavern must have been disturbed by marine action
during the great submergence in mid-glacial times, and afterwards
covered by marine sands and by an upper boulder-clay, identical in
character with that found at many points in the Vale of Clwyd. The
paleontological evidence suggests that the deposits in question are not
preglacial, but may be equivalent to the Pleistocene deposits of our
river-valleys."[DE]
[Footnote DE: H. B. Woodward's Geology of England and Wales, pp. 543, 544]
If the views of Professor Lewis and Mr. Kendall are correct concerning
the unity of the Glacial period in England, the shelly and sandy deposits
connected with these Clwydian caves at an elevation of 400 feet or more
would be explained in connection with the marginal lakes which must
have occupied the valley during both the advance and the retreat of
the ice-front; the shells having been carried up from the sea-bottom
by the ice-movement, after the manner supposed in the case of those at
Macclesfield and Moel Tryfaen. If, therefore, the statements concerning
the discovery of flint implements in this Cae Gwyn cave can be relied
upon, this is the most direct evidence yet obtained in Europe of man's
occupation of the island during the continuance of the Glacial period.
In all these caves it is to be noted that there is a sharp line of
demarcation between the strata containing palæolithic implements and
those containing only the remains of modern animals. Palæolithic
implements are confined to the lower strata, which in some of the caves
are separated from the upper by a continuous bed of stalagmite, to which
reference will be made when discussing the chronology of the Glacial
period. The remains of extinct animals also are confined to the lower
beds.
The caves which we have been considering in England are all in limestone
strata, and have been formed by streams of water which have enlarged some
natural fissures both by mechanical action in wearing away the rocks, and
by chemical action in dissolving them. Through the lowering of the main
line of drainage, caverns with a dry floor are at length left, offering
shelter and protection both to man and beast. Oftentimes, but not always,
some idea of the age of these caverns may be obtained by observing the
depth to which the main channel of drainage to which they were tributary
has been lowered since their formation. But to this subject also we will
return when we come specifically to discuss the chronological question.
_The Continent._
Systematic explorations in the caves of Belgium were begun in 1833 by
Dr. Schmerling, in the valley of the Meuse, near his residence in Liége.
The Meuse is here bordered by limestone precipices 200 or more feet in
height. Opening out from these rocky walls are the entrances to the
numerous caverns which have rendered the region so famous. To get access
to the most important of these, Dr. Schmerling had to let himself down
over a precipice by a rope tied to a tree, and then to creep along on
all-fours through intricate channels to reach the larger chambers which
it was his object to explore. In the cave at Engis, on the left bank of
the Meuse, about eight miles above Liége, he found a human skull deeply
buried in breccia in company with many bones of the extinct animals
previously stated to have been associated with man during the Glacial
period. This so-called "Engis skull" was by no means apelike in its
character, but closely resembled that of the average Caucasian man. But
this established the association upon the Continent of man with some of
the extinct animals of the Glacial period.
[Illustration: Fig. 79.--Engis skull, reduced (after Lyell.)]
The vicinity of Liége has also furnished us another cavern whose
contents are of the highest importance, ranking indeed as perhaps the
most significant single discovery yet made. The cave referred to is
on the property of the Count of Beauffort, in the commune of Spy, in
the province of Namur in Belgium. For the facts relating to it we are
indebted to Messrs: Lohest and Fraipont, the former Professor of Geology
and the latter of Anatomy in the University of Liége. The exploration
of the cave was made in 1886, and the full report with illustrations
published in the following year in Archives de Biologie.[DF] The
significance of this discovery is enhanced by the light it sheds upon and
the confirmation it brings to the famous Neanderthal skull and others of
similar character, which for a long time had been subjects of vigorous
discussion. Before describing it, therefore, we will give a brief account
of the previous discoveries.
[Footnote DF: See pp. 587, 757.]
The famous Neanderthal skull was brought to light in 1857 by workmen in a
limestone-quarry, near Düsseldorf, in the valley of the Neander, a small
tributary to the Rhine. By these workmen a cavern was opened upon the
southern side of the winding ravine, about sixty feet above the stream
and one hundred feet below the top of the cliff. The skull attracted much
attention from its supposed possession of many apelike characteristics;
indeed, it was represented by some to be a real intermediate link between
man and the anthropoid apes. The accompanying cut enables one to compare
the outline of the Neanderthal skull with that of a chimpanzee on the
one hand and of the highly developed European on the other. The apelike
peculiarities of this skull appear in its vertical depression, in the
enormous thickness of the bony ridges just above the eyes, and in the
gradual slope of the back part of the head, together with some other
characteristics which can only be described in technical language; so
that it was pronounced by the highest authorities the most apelike of
human crania which had yet been discovered. Unfortunately, the jaw was
not found. The capacity of the skull, however, was seventy-five cubic
inches, which is far above that of the highest of the apes, being indeed
equal to the average capacity of Polynesian and Hottentot skulls.[DG]
Huxley well remarks that "so large a mass of brain as this would alone
suggest that the pithecoid tendencies indicated by this skull did not
extend deep into the organization."
[Footnote DG: Huxley's Man's Place in Nature, p. 181.]
[Illustration: Fig. 80.--Comparison of forms of skulls: _a_, European;
_b_, the Neanderthal man; c, a chimpanzee (after Lyell).]
[Illustration: Fig. 81.--Skull of the Man of Spy. (From photograph.)]
Upon extending inquiries, it was found that the Neanderthal type of
skull is one which still has representatives in all nations; so that it
is unsafe to infer that the individual was a representative of all the
individuals living in his time. The skull of Bruce, the celebrated Scotch
hero, was a close reproduction of the Neanderthal type; while, according
to Quatrefages,[DH] the skull of the Bishop of Toul in the fourth century
"even exaggerates some of the most striking features of the Neanderthal
cranium. The forehead is still more receding, the vault more depressed,
and the head so long that the cephalic index is 69-41." The discovery of
Messrs. Fraipont and Lohest adds much to our definite knowledge of the
Neanderthal type of man, since the Belgic specimens are far more complete
than any others heretofore found, there being in their collection two
skulls, together with the jawbones and most of the other parts of the
frame. In this case also there is no suspicion that the deposits had been
disturbed, so as to admit any intrusion of human relics into the company
of relics of an earlier age. According to M, Lohest, there were three
distinct ossiferous beds, separated by layers of stalagmite. All the
ossiferous beds contained the remains of the mammoth, but in the upper
stratum they were few, and probably intrusive. The implements found in
this were also of a more modern type. In the second stratum from the top
numerous hearths were found with burnt wood and ashes, together with the
bones of the rhinoceros, the horse, the mammoth, the cave-bear, and the
cave-hyena, all of which were abundant, while there were also specimens
of the Irish elk, the reindeer, the bison, the cave-lion, and several
other species. In this layer also there were numerous implements of
ivory, together with ornaments and some faint indications of carving upon
the rib of a mammoth, besides a few fragments of pottery.
[Footnote DH: Human Species, p. 310,]
It was in the third, or lowest, of these beds that the skeletons
were found. Here they were associated with abundant remains of the
rhinoceros, the horse, the bison, the mastodon, the cave-hyena, and a
few other extinct species. Flint implements also, of the "Mousterien"
pattern (which, according to the opinion of the French archæologists, is
characteristic of middle palæolithic times), were abundant Neither of the
skeletons was complete, but they were sufficiently so to give an adequate
idea of the type to which they belong, and one of the skulls is nearly
perfect. According to M. Fraipont, "one of these skulls is apparently
that of an old woman, the other that of a middle-aged man. They are both
very thick; the former is clearly dolichocephalic (long-headed, index
70), the other less so. Both have very prominent eyebrows and large
orbits, with low, retreating foreheads, excessively so in the woman. The
lower jaws are heavy. The older has almost no projecting chin. The teeth
are large, and the last molar is as large as the others. These points
are characteristic of an inferior and the oldest-known race. The bones
indicate, like those of the Neanderthal and Naulette specimens, small,
square-shouldered individuals." They were "powerfully built, with strong,
curiously curved thigh-bones, the lower ends of which are so fashioned
that they must have walked with a bend at the knees."[DI]
[Footnote DI: Huxley, Nineteenth Century, vol. xxviii (November, 1890),
p. 774.]
Other crania from various Quaternary deposits in Europe seem to warrant
the inference that this type of man was the prevalent one during the
early part of the Palæolithic age. As long ago as 1700 a skull of
this type was exhumed in Canstadt, a village in the neighbourhood
of Stuttgart, in Würtemberg. This was found in coexistence with the
extinct animals whose bones we have described as so often appearing in
the high-level river-gravel of the Glacial age. But the importance of
the discovery at Canstadt was not appreciated until about the middle
of the present century. From the priority of the discovery, and of the
discussion among German anthropologists concerning it, it has been
thought proper, however, by some to give the name of this village to the
race and call it the "Canstadt race." But, whatever name prevails, it
is important in our reading to keep in mind that the man of Canstadt,
the man of Neanderthal, and the man of Spy are identical in type, and
probably in age. Similar discoveries have been made in various other
places. Among these are a lower jaw of the same type discovered in 1865
by M. Dupont, at Naulette, in the valley of the Lesse, in Belgium, and
associated with the remains of extinct animals; a jawbone found in a
grotto at Arcy; a fragment of a skull found in 1865 by Faudel, in the
loess of Eguisheim, near Colmar; a skull at Olmo, discovered in 1863, in
a compact clayey deposit forty-five feet below the surface; and a skull
discovered in 1884 at Marcilly.
M. Dupont has brought to light much additional testimony to glacial man
from other caves in different parts of Belgium. In all he has explored as
many as sixty. Three of these, in the valley of the Montaigle, situated
about one hundred feet above the river, contained both remains of man
and many bones of the mammoth and other associated animals, which had
evidently been brought in for food.
In the hilly parts of Germany, also, and in Hungary, and even in the
Ural Mountains in Russia, and in one of the provinces of Siberia, the
remains of the rhinoceros, and most of the other animals associated with
man in glacial times, have been found in the cave deposits which have
been examined. Though it can not be directly proved that these animals
were associated with man in any of these places, still it is interesting
to see how wide-spread the animals were in northern Europe and Asia
during the Glacial period.
Some northern animals, also, spread at this time into southern
Europe--remains of the reindeer having been discovered on the south slope
of the Pyrenees, but the remains of the mammoth, the woolly rhinoceros,
and the musk ox, have not been found so far south.
African species of the elephant, however, seem at one time to have had
free range throughout Spain, and the hippopotamus roamed in vast herds
over the valleys of Sicily, while several species of pygmy elephants seem
to be peculiar to the island of Malta.
In the case of all the cave deposits referred to (with possibly the
exception of those of Victoria, England, and Cae Gwyn, Wales), the
evidence of man's existence during the Glacial period is inferential,
and consists largely in the fact that he was associated with various
extinct animals which did not long survive that period, or with animals
that have since retired from Europe to their natural habitat in
mountain-heights or high latitudes. The men whose remains are found in
the high-level river-drift, and in the caverns described, were evidently
not in possession of domestic animals, as their bones are conspicuous for
their absence in all these places. The horse, which would seem to be an
exception, was doubtless used for food, and not for service.
If we were writing upon the general subject of the antiquity and
development of the human race, we should speak here in detail of several
other caves and rock shelters in France and southern Europe, where
remains of man belonging to an earlier period have been found. We should
mention the rock shelter of Cro-Magnon in the valley of Vezère, as well
as that of Mentone, where entire human skeletons were found. But it is
doubtful if these and other remains from caves which might be mentioned
belong in any proper sense to the Glacial period. The same remarks should
be made also with reference to the lake-dwellings in Switzerland, of
which so much has been written in late years. All these belong to a much
later age than the river-drift man of whom we are speaking, and of whom
we have such abundant evidence both in Europe and in America.
[Illustration: Fig. 82.--Tooth of Machairodus neogæus, × 1/6 (drawn from a
cast).]
[Illustration: Fig. 83.--Perfect tooth of an Elephas, found in Stanislaus
County, California, 1/8 natural size.]
_Extinct Animals associated with Man during the Glacial Period._
This is the proper place in which to speak more fully of the extinct
animals which accompanied man in his earliest occupation of Europe and
America, and whose remains are so abundant in the river-drift gravel and
in the caves of England, in connection with the relics of man. Among
these animals are
The Lion, which is now confined, to Africa and the warmer portions of
Asia. But in glacial times a large species of this genus ranged over
Europe from Sicily to central England.
The saber-toothed Tiger, with tusks ten inches long: (Machairodus
latidens), is now extinct. This species was in existence during the
latter part of the Tertiary period, but continued on until after man's
appearance in the Glacial period. The presence of this animal would seem
to indicate a warm climate.
The Leopard (_Felis pardus_) is now confined to Africa and southern Asia,
and the larger islands adjoining; but during man's occupation of Europe
in the Glacial epoch he was evidently haunted at every step by this
animal; for his bones are found as far north in England as palæolithic
man is known to have ranged.
The Hyena. Two species of this animal are found in the bone-caves of
Europe. During the Glacial epoch they ranged as far up as northern
England, but they are now limited to Africa and southwestern Asia.
[Illustration: Fig. 84.--Skull of _Hyena spelæa_, × 1/4.]
The Elephant is represented in the Preglacial and Glacial epochs by
several species, some of which ranged as far north as Siberia. The
African elephant is not now found north of the Pyrenees and the Alps.
But a species of dwarf elephant, but four or five feet in height,
has already been referred to as having occupied Malta and Sicily; and
still another species has been found in Malta, whose average height
was less than three feet. An extinct species (Elephas antiquus), whose
remains are found in the river-drift and in the lower strata of sediment
in many caverns as far north as Yorkshire, England, was of unusual
size, and during the Glacial period was found on both sides of the
Mediterranean. But the species most frequently met with in palæolithic
times was the mammoth (_Elephas primigenius_). This animal, now extinct,
accompanied man in nearly every portion both of Europe and North America,
and lingered far down into post-glacial times before becoming extinct.
This animal was nearly twice the weight of the modern elephant, and one
third taller. Occasionally his tusks were more than twelve feet long,
and curved upward in a circle. It is the carcasses of this animal which
have been found in the frozen soil of Siberia and Alaska. It had a thick
covering of long, black hair, with a dense matting of reddish wool at the
roots. During the Glacial period these animals must have roamed in vast
herds over the plains of northern France and southern England, and the
northern half of North America.
[Illustration: Fig. 85.--Celebrated skeleton of mammoth, in St.
Petersburg museum.]
[Illustration: Fig. 86.--Molar tooth of mammoth (_Elephas primigenius_):
_a_, grinding surface; _b_, side view.]
The Hippopotamus is at present a familiar animal in the larger rivers
of Africa, but is not now found in Europe. During the Glacial period,
however, he ranged as far north as Yorkshire, England, and his remains
were found in close association with those of man, both in Europe and on
the Pacific coast in America. Twenty tons of their bones have been taken
from a single cave in Sicily.[DJ]
[Footnote DJ: Prestwich's Geology, vol. ii, p. 508.]
[Illustration: Fig. 87.--Tooth of _Mastodon Americanus_.]
The mammoth and the rhinoceros we know to have been adapted to cold
climates by the possession of long hair and thick fur, but the
hippopotamus by its love for water would seem to be precluded from the
possession of this protective covering. It is suggested, however, by
Sir William Dawson, that he may have been adapted to arctic climates by
a fatty covering, as the walrus is at the present time. A difficulty in
accounting for many of the remains of the hippopotamus in some of the
English caverns is that they are so far away from present or possible
water-courses. But it would seem that due credit has not been ordinarily
given to the migratory instincts of the animal. In southern Africa they
are known to "travel speedily for miles over land from one pool of a
dried-up river to another; but it is by water that their powers of
locomotion are surpassingly great, not only in rivers, but in the sea....
The geologist, therefore, may freely speculate on the time when herds
of hippopotami issued from North African rivers, such as the Nile, and
swam northward in summer along the coasts of the Mediterranean, or even
occasionally visited islands near the shore. Here and there they may have
landed to graze or browse, tarrying awhile, and afterwards continuing
their course northward. Others may have swum in a few summer days from
rivers in the south of Spain or France to the Somme, Thames, or Severn,
making timely retreat to the south before the snow and ice set in."[DK]
[Footnote DK: Lyell, Antiquity of Man, p. 180,]
The Mastodon (_Mastodon Americanus_), (Fig. 88), "is probably the largest
land mammal known, unless we except the Dinotherium. It was twelve to
thirteen feet high, and, including the tusks, twenty-four to twenty-five
feet long. It differed from the elephant chiefly in the character of its
teeth. The difference is seen in Figs. 86 and 87. The elephant's tooth
given above (Fig. 86) is sixteen inches long, and the grinding surface
eight inches by four."
[Illustration: Fig. 88.--_Mastodon Americanus_ (after Owen).]
The mastodon, together with the mammoth, made their appearance about
the middle of the Miocene epoch. At the close of the Tertiary period
the mastodon became extinct on the Eastern Continent, but continued in
North America to be a companion of man well on toward the close of the
Glacial period. Many perfect skeletons have been found in the deposits
of this period in North America. "One magnificent specimen was found in
a marsh near Newburg, New York, with its legs bent under the body, and
the head thrown up, evidently in the very position in which it mired. The
teeth were still filled with the half-chewed remnants of its food, which
consisted of twigs of spruce, fir, and other trees; and within the ribs,
in the place where the stomach had been, a large quantity of similar
material was found."[DL]
[Footnote DL: Le Conte's Geology (edition of 1891), p. 582.]
The Rhinoceros is now confined to Africa and southern Asia; but the
remains of four species have been found in America, Europe, and northern
Asia, in deposits of the Glacial period. In company with that of the
mammoth, already spoken of, a carcass of the woolly rhinoceros was found
in 1771 in the frozen soil of northern Siberia. The bones of other
species have been found as far north as Yorkshire, England. In the valley
of the Somme there was found "the whole hind limb of a rhinoceros, the
bones of which were still in their true relative position. They must
have been joined together by ligaments and even surrounded by muscles
at the time of their interment." An entire skeleton was found near by.
The gravel terrace in which these occurred is about forty feet above the
floor of the valley, and must have been formed subsequent to some of the
strata which contained the remains of human art. In America the bones are
found in the gold-bearing gravels of California, in connection with human
remains.
[Illustration: Fig. 89.--Skeleton of _Rhinoceros tichorhinus_.]
[Illustration: Fig. 90.--Skull of cave-bear (_Ursus spelæus_),]
The Bear was represented in Europe in palæolithic times by three species,
of which only one exists there at the present time. But during the
Glacial period the grizzly bear, now confined to the western part of
America, and the extinct cave-bear were companions, or enemies as the
case may be, of man throughout Europe. The cave-bear was of large size,
and his bones occur almost everywhere in the lower strata of sediment in
the caves of England.
The Great Irish Elk, or deer, is now extinct, though it is supposed by
some to have lingered until historic times. Its remains are found widely
distributed over middle Europe in deposits of palæolithic age.
[Illustration: Fig. 91.--Skeleton of the Irish elk (_Cervus megaceros_).]
The Horse was also, as we have seen, a very constant associate of man
in middle Europe during the Palæolithic age, but probably not as a
domesticated animal. The evidence is pretty conclusive that he was
prized chiefly for food. About some of the caves in France such immense
quantities of their bones are found that they can be accounted for best
as refuse-heaps into which the useless bones had been thrown after their
feasts, after the manner of the disposal of shells of shell-fish. In
America the horses associated with man were probably of a species now
extinct. The skull of one (_Equus excelsus_) recently found in Texas, in
Pleistocene deposits, associated with human implements, is, according
to Cope, intermediate in character between the horse and quagga.[DM]
The frontal bone was crushed in in a manner to suggest that it had been
knocked in the head with a stone hammer, such as was found in the same
bed. Possibly, therefore, man's love of horse-flesh may have been an
important element in securing the extinction of the species in America.
[Footnote DM: American Naturalist, vol. xxv (October, 1891), p. 912.]
Besides these animals there were associated with man at this time the
Musk Sheep and the Reindeer, both now confined to the regions of the far
north, but during the Glacial period ranging into southern France, and
mingling their bones with those both of man and of the southern species
already enumerated.
[Illustration: Fig. 92.--Musk-sheep (_Ovibos moschatius_).]
The Wolverine, the Arctic Fox, the Marmot, the Lemming--all now confined
to colder regions--at that time mingled on the plains of central Europe
with the species mentioned as belonging now to Africa and southern Asia.
The Ibex, also, and the Snowy Vole and Chamois descended to the plains
from their mountain-heights, and joined in the strange companionship of
animals from the north and from the south.
Besides these extremes there were associated with man during the Glacial
period numerous representatives of the temperate group of existing
animals, such as the bison, the horse, the stag, the beaver, the hare,
the rabbit, the otter, the weasel, the wild-cat, the fox, the wolf, the
wild boar, and the brown bear.
[Illustration: Fig. 93.--Reindeer.]
To account for this strange intermingling of arctic and torrid species
of animals, especially in Europe, during man's occupancy of the region
in glacial times, various theories have been resorted to, but none of
them can be said to be altogether satisfactory. One hypothesis is that
the bones of these diverse animals became mingled by reason of the great
range of the annual migration of the species. The reindeer, for example,
still performs extensive annual migrations. In summer it ventures far out
upon the _tundras_ of North America and Siberia to feed upon the abundant
vegetation that springs up like magic under the influence of the long
days of sunshine; while, as winter approaches, it returns to the forests
of the interior. Or in other places this animal and his associates,
like birds of passage, move northward in summer to escape the heat, and
southward in the winter to escape the extreme cold. Many of the other
animals also are more or less migratory in their habits.
Thus it is thought that during the Glacial period, when man occupied
northern France and southern England, the reindeer, the musk sheep, the
arctic fox, and perhaps the hippopotamus and some other animals, annually
vibrated between northern England and southern France, a slight elevation
of the region furnishing a land passage from England to the continent;
while the chamois and other Alpine species vibrated as regularly between
the valleys in winter and the mountain-heights in summer. The habits of
these species are such that it is not difficult to see how in their case
this migration could have taken place.
Professor Boyd Dawkins attempts to reduce the difficulty by supposing
that the Glacial epoch was marked by the occurrence of minor periods of
climatic variation, during which, in comparatively short periods, the
isothermal lines vibrated from north to south, and _vice versa_. In this
view the southern species gradually crowded upon the northern during
the periods of climatic amelioration, until they reached their limit in
central England, and then in turn, as the climate became more rigorous,
slowly retreated before the pressure of their northern competitors.
Meanwhile the hyena sallied forth from his various caves, over this
region, at one time of the year to feed upon the reindeer, and at another
time of the year upon the flesh of the hippopotamus, in both cases
dragging their bones with him to his sheltered retreat in the limestone
caverns[DN] which he shared at intervals with palæolithic man.
[Footnote DN: Early Man in Britain, p. 114.]
The theory of Mr. James Geikie is that the period, while one of great
precipitation, was characterised by a climate of comparatively even
temperature, in which there was not so great a difference as now between
the winters and the summers, the winters not being so cold and the
summers not so hot as at present. This is substantially the condition of
things in southern Alaska at the present time, where extensive glaciers
come down to the sea-level, even though the thermometer at Sitka rarely
goes below zero (Fahrenheit). It is, therefore, easy to conceive that if
there were extensive plains bordering the Alaskan archipelago, so as to
furnish ranging grounds for more southern species, the animals of the
north and the animals of the south might partially occupy the same belt
of territory, and their bones become mingled in the same river deposits.
In order to clear the way for either of these hypotheses to account
for the mingling of arctic and torrid species characteristic of the
period under consideration in Europe, we must probably suppose such an
elevation of the region to the south as to afford land connection between
Europe and Africa. This would be furnished by only a moderate amount of
elevation across the Strait of Gibraltar and from the south of Italy to
the opposite shore in Africa; and there are many indications, in the
distribution of species, of the existence in late geological times of
such connection.
It should also be observed that the present capacities and habits of
species are not a certain criterion of their past habits and capacities.
As already remarked, both the rhinoceros and the mammoth of glacial
times were probably furnished with a woolly protection, which enabled
them to endure more cold than their present descendants could do, while
the elephant is even now known to be able to endure the rigors of the
climate at great elevations upon the Himalaya Mountains. We can easily
imagine these species to have been adjusted to quite different climatic
conditions from those which now seem necessary to their existence. In
the case of the hippopotamus, also, it is quite possible, as already
suggested, that it is more inclined to migration than is generally
supposed.
Geikie's theory of the prevalence of an equable climate during a portion
of the Glacial period in Europe is thought to be further sustained
by the character of the vegetation which then covered the region, as
well as by the remains of the mollusks which occupied the waters. Then
"temperate and southern species like the ash, the poplar, the sycamore,
the fig-tree, the Judas-tree, the laurel, etc., overspread all the low
ground of France, as far north at least as Paris.... It was under such
conditions," continues Geikie, "that the elephants, rhinoceroses, and
hippopotamuses, and the vast herds of temperate cervine and bovine
species ranged over Europe, from the shores of the Mediterranean up to
the latitude of Yorkshire, and probably even farther north still; and
from the borders of Asia to the Western Ocean. Despite the presence of
numerous fierce carnivora--lions, hyenas, tigers, and others--Europe at
that time, with its shady forests, its laurel-margined streams, its broad
and deep-flowing rivers, a country in every way suited to the needs of a
race of hunters and fishers--must have been no unpleasant habitation for
palæolithic man.
"This, however, is only one side of the picture. There was a time when
the climate of Pleistocene Europe presented the strongest contrast to
those genial conditions--a time when the dwarf birch of the Scottish
Highlands, and the arctic willow, with their northern congeners, grew
upon the low grounds of middle Europe. Arctic animals, such as the musk
sheep and the reindeer, lived then, all the year round, in the south of
France; the mammoth ranged into Spain and Italy; the glutton descended to
the shores of the Mediterranean; the marmot came down to the low grounds
at the foot of the Apennines; and the lagomys inhabited the low-lying
maritime districts of Corsica and Sardinia. The land and fresh-water
shells of many Pleistocene deposits tell a similar tale; boreal, high
alpine, and hyperborean forms are characteristic of these accumulations
in central Europe; even in the southern regions of our continent the
shells testify to a former colder and wetter climate."[DO]
[Footnote DO: Prehistoric Europe, p. 67.]
In Mr. Geikie's view these facts indicate two Glacial periods, with an
intervening epoch of mild climate. In the opinion of others they are
readily explainable by the coming on and departure of a single Ice age,
with its various minor episodes.
_Earliest Remains of Man on the Pacific Coast of North America._
Most interesting evidence concerning the antiquity of man in America,
and his relation to the Glacial period, has come from the Pacific coast.
During the height of the mining activity in California, from 1850 to
1860, numerous reports were rife that human remains had been discovered
in the gold-bearing gravel upon the flanks of the Sierra Nevada
Mountains. These reports did not attract much scientific attention until
they came to relate to the gravel deposits found deeply buried beneath
a flow of lava locally known as the Sonora or Tuolumne Table Mountain.
This lava issued from a vent near the summit of the mountain-range, and
flowed down the valley of the Stanislaus River for a distance of fifty or
sixty miles, burying everything in the valley beneath it, and compelling
the river to seek another channel. The thickness of the lava averages
about one hundred feet, and so long a time has elapsed since the eruption
that the softer strata on either side of the valley down which it flowed
have been worn away to such an extent that the lava now rises nearly
everywhere above the general level, and has become a striking feature in
the landscape, stretching for many miles as a flat-topped ridge about
half a mile in width, and presenting upon the sides a perpendicular face
of solid basalt for a considerable distance near the lower end of the
flow.
[Illustration: Fig. 94.--Section across Table Mountain, Tuolumne County,
California: _L_, lava; _G_, gravel; _S_, slate; _R_, old river-bed; _R'_,
present river-bed.]
[Illustration: Fig. 95.--Calaveras Skull. (From Whitney.)]
It was under this mountain of lava that the numerous implements and
remains of man occurred which were reported to Professor J. D. Whitney
when he was conducting the geological survey of California between 1860
and 1870. The implements consisted of stone mortars and pestles, suitable
for use in grinding acorns and other coarse articles of food. There were,
however, some rude articles of ornament. In one of the mining shafts
penetrating the gravel underneath Table Mountain, near Sonora, there was
reported to have been discovered, in 1857, a human jawbone, one portion
of which was sent by responsible parties to the Boston Society of Natural
History, and another part to the Philadelphia Academy of Sciences, in
whose collections the fragments can now be seen.
Interest reached a still higher pitch when, in 1860, an entire human
skull with some other human bones was reported to have been discovered
under this same lava deposit, a few miles from Sonora, at Altaville, in
Calaveras County, and hence known as the "Calaveras skull." Persistent
efforts were made soon after to discredit the genuineness of this
discovery. Bret Harte showered upon it the shafts of his ridicule, and
various other persons gave currency to the story that the whole report
originated in a joke played by the miners upon unsuspecting geologists.
These attacks were so successful that many conservative archæologists and
men of science have refused to accept the skull as genuine.
Recent events, however, have brought such additional evidence[DP] to the
support of this discovery that it would seem unreasonable any longer to
refuse to credit the testimony. At the meeting of the Geological Society
of America, at Washington, in January, 1891, Mr. George P. Becker, of
the United States Geological Survey, who for some years has had charge
of investigations relating to the gold-bearing gravels of the Pacific
coast, presented the affidavit of Mr. J. H. Neale, a well-known mining
engineer of unquestionable character, stating that he had taken a stone
mortar and pestle, together with some spear-heads (which through Mr.
Becker he presented to the Society), from undisturbed strata of gravel
underneath the lava of Table Mountain, near Rawhide Gulch, a few miles
from Sonora. At the same meeting Mr. Becker presented a pestle which
Mr. Clarence King, the first director of the United States Geological
Survey, took with his own hands out of undisturbed gravel under this same
lava deposit, near Tuttletown, a mile or two from the preceding locality
mentioned.
[Footnote DP: See Bulletin Geological Society of America, 1891, pp.
189-200.]
I was so fortunate, also, as to be able to report to the Society at the
same meeting the discovery, in 1887, of a small stone mortar by Mr. C.
McTarnahan, the assistant surveyor of Tuolumne County. This mortar was
found by Mr. McTarnahan in the Empire mine, which penetrates the gravel
underneath Table Mountain, about three miles from Sonora, and not far
from the other localities above mentioned. The place where the mortar was
found is about one hundred and seventy-five feet in from the edge of the
superincumbent lava, which is here about one hundred feet in thickness.
At my request, this mortar was presented by its owner, Mrs. M. J. Darwin,
to the Western Reserve Historical Society of Cleveland, Ohio, in whose
collection it can now be seen.
These three independent instances, each of them authenticated by the best
of evidence, have such cumulative force that probably few men of science
will longer stand out against it.
Associated with these discoveries, there is to be mentioned another,
which was brought to my notice by Mr. Charles Francis Adams in October,
1889.[DQ] This was a miniature clay image of a female form, about one
inch and a half in length, and beautifully formed, which was found, in
August, 1889, by Mr. M. A. Kurtz, while boring an artesian well at Nampa,
Ada County, Idaho. The strata passed through included, near the surface,
fifteen feet of lava. Underneath this, alternating beds of clay and
quicksand occurred to a depth of three hundred and twenty feet, where
there appeared indications of a former surface soil lying just above the
bed-rock, from which the clay image was brought up in the sand-pump.
[Footnote DQ: See Proceedings Boston Society Natural History, January,
1890, and February, 1891.]
[Illustration: Fig. 96.--Three views of Nampa image drawn to scale. The
middle one is from a photograph.]
I devoted the summer of 1890 to a careful study of the lava deposits both
in Idaho and in California, with a view to learning their significance
with reference to these discoveries. The main facts brought to light by
this investigation are that in the Snake River Valley, Idaho, there are
not far from twelve thousand square miles of territory covered with a
continuous stratum of basaltic lava, extending nearly across the entire
diameter of the State from east to west. Nampa, where the miniature
image was discovered, is within five miles of the western limit of this
lava-flow, and where it had greatly thinned out. The relative age of the
lava is shown by its relation to Tertiary beds of shale and sandstone,
containing numerous fossils of late Pliocene species. These are overlaid
in this vicinity by the lava, thus determining its post-Tertiary
character. Examination with reference to the more precise determination
of age reveals channels of erosion formed since the lava-flow took
place, which, when studied sufficiently, will probably lead to valuable
approximate results. At present I can only say that the amount of
erosion since the lava eruptions of western Idaho is not excessive, and
very likely may be brought within a period of from ten thousand to twenty
thousand years. The enormous erosion in the cañon of the Snake River,
near Shoshone Falls, in central Idaho, is doubtless of a much earlier
date than that in the Boise River, near Nampa.
[Illustration: Fig. 97.--Map showing Pocatello, Nampa, and the valley of
Snake River.]
The disturbances created in this part of the valley by the bursting of
the barriers between the glacial Lake Bonneville and the Snake River,
already described (see above, page 233), have not been worked out. There
can be no doubt, however, that interesting results will come to light
in connection with the problem; for Pocatello, the point at which the
_débâcle_ reached the Snake River plain, is about 2,000 feet higher than
Nampa, and 350 miles distant, and the water must have poured into the
valley faster than the river in its upper portion could have discharged
it. By just what channels the mighty current worked down to the lower
levels on the western borders of the State it would be most interesting
as well as instructive to know.
A study of the situation in Tuolumne and Calaveras Counties, California,
reveals a state of things closely resembling, in important respects,
that in western Idaho. At first sight the impression is made that an
immense lapse of time must have occurred since the volcanic eruption
which furnished the lava of Table Mountain. The Stanislaus River flows
in a channel of erosion a thousand feet or more lower than the ancient
channel filled by lava, and in two or three places cuts directly across
it. An immense amount of time, also, would seem to be required to permit
the smaller local streams to have worn away so much of the sides of the
ancient valley as to allow the lava deposit now so continuously to rise
above the general surface. Still, the question of absolute time cannot
be considered separately without much further study. It is by no means
certain that, when the lava-stream poured down the mountain, it always
followed the lowest depressions; but at certain points it may have been
dammed up in its course by its own accumulations so as to be turned off
into what was then an ancient abandoned channel.
[Illustration: Fig. 98.--Section along the line, north and south:
_r' r'_, old river-beds; _r r_, present river-beds; _L_, lava;
_sl_, slate.]
The forms of animal and vegetable life with which the remains of man
under Table Mountain are associated, are, indeed, to a considerable
extent, species now extinct in California, and some of them no longer
exist anywhere in the world. But a suggestion of Professor Prestwich,
in England, made with reference to the extinct forms of life associated
with human remains in the glacial deposits in Europe, is revived by
Mr. Becker, of the Geological Survey, with reference to the California
discoveries; his inference being, not that man is so extremely ancient
in California, but that many of these plants and animals have continued
to a more recent date than has ordinarily been supposed.
The connection of these lava-flows on the Pacific coast with the Glacial
period is unquestionably close. For some reason which we do not fully
understand, the vast accumulation of ice in North America during the
Glacial period is correlated with enormous eruptions of lava west of the
Rocky Mountains, and, in connection with these events, there took place
on the Pacific coast an almost entire change in the plants and animals
occupying the region. Mr. Warren Upham is of the opinion that on the
Pacific coast they lingered much later than in the region east of the
Rocky Mountains. Indeed, it is pretty certain that not many centuries
have elapsed since the glacial phenomena of the Sierra Nevada Mountains
were much more pronounced than they are at the present time, and it is
equally certain that there have been vast eruptions of lava in California
within three hundred years.
From these data, therefore, Mr. Becker has real foundation for his
suggestion that perhaps in the Glacial period California was a kind of
health resort for Pliocene animals, as it is at the present time for man;
or, at any rate, that the later date of the accumulations permitted the
animals to survive there much longer than in the region east of the Rocky
Mountains.
Further discussion of the preceding facts will profitably be deferred
until, in the next two chapters, the questions of the cause and date of
the Glacial period have been considered.
CHAPTER IX.
THE CAUSE OF THE GLACIAL PERIOD.
In searching for the cause of the Glacial period, it is evident that we
must endeavor to find conditions which will secure over the centre of the
glaciated area either a great increase of snow-fall or a great decrease
in the mean annual temperature, or both of these conditions combined in
greater or less degree. As can be seen, both from the nature of the case
and from the unglaciated condition of Siberia and northern Alaska, a low
degree of temperature is not sufficient to produce permanent ice-fields.
If the snow-fall is excessively meagre, even the small amount of heat in
an arctic summer will be sufficient to melt it all away.
From the condition of Greenland, however, it appears that a moderate
amount of precipitation where it is chiefly in the form of snow may
produce enormous glaciers if at the same time the average temperature
is low. In southeastern Alaska, on the other hand, the glaciers are of
enormous size, though the mean annual temperature is by no means low,
for there the great amount of snow-fall amply compensates for the higher
temperature.
Snow stores the cold and keeps it in a definite place. If the air becomes
chilled, circulation at once sets in, and the cold air is transferred to
warmer regions; but if there is moisture in the air, so that snow forms,
the cold becomes locked up, as it were, and falls to the earth.
The amount of cold thus locked up in snow is enormous. To melt one
cubic foot of ice requires as much heat as would raise the temperature
of a cubic foot of water 176° Fahrenheit. To melt a "layer of ice only
one inch and a half thick would require as much heat as would raise a
stratum of air eight hundred feet thick from the freezing-point to the
tropical heat of 88° Fahrenheit." It is the slowness with which ice melts
which enables it to accumulate as it does, both in winter and upon high
mountains and in arctic regions. Captain Scoresby relates that when near
the north pole the sun would sometimes be so hot as to melt the pitch on
the south side of his vessel, while water was freezing on the north side,
in the shade, owing to the cooling effect of the masses of ice with which
he was surrounded.
Thus it will appear that a change in the direction of the moist winds
blowing from the equator towards the poles might produce a Glacial
epoch. If snow falls upon the ocean it cools the water, but through the
currents, everywhere visible in the sea, the temperature in the water in
the different parts soon becomes equalized. If, however, the snow falls
upon the land, it must be melted by the direct action of the sun and
wind upon the spot where it is. If the heat furnished by these agencies
is not sufficient to do it year by year, there will soon be such an
accumulation that glaciers will begin to form. It is clear, therefore,
that the conditions producing a Glacial period are likely to prove very
complicated, and we need not be surprised if the conclusions to which we
come are incapable of demonstration.
Theories respecting the cause of the Glacial period may be roughly
classified as astronomical and geological. Among the astronomical
theories, one which has sometimes been adduced is that the solar system
in its movement through space is subjected to different degrees of heat
at different times. According to this theory, the temperate climate
which characterised the polar regions during the Tertiary period, and
continued up to the beginning of the Glacial epoch, was produced by the
influence of the warmer stretches of space through which the whole solar
system was moving at that time; while the Glacial period resulted from
the influence upon the earth of the colder spaces through which the
system subsequently moved.
While it is impossible absolutely to disprove this hypothesis, it labors
under the difficulty of having little positive evidence in its favor,
and thus contravenes a fundamental law of scientific reasoning, that we
must have a real cause upon which to rest our theories. In endeavouring
to explain the unknown, we should have something known to start with.
But in this case we are not sure that there are any such variations in
the temperature of the space through which the solar system moves. This
theory, therefore, cannot come in for serious consideration until all
others have been absolutely disproved. As we shall also more fully see,
in the subsequent discussion, the distribution of the ice during the
Glacial period was not such as to indicate a gradual extension of it from
the north pole, but rather the accumulation upon centres many degrees to
the south.
Closely allied with the preceding theory is the supposition broached
by some astronomers that the sun is a variable star, dependent to some
extent for its heat upon the impact of meteorites, or to the varying
rapidity with which the contraction of its volume is proceeding.
It is well known that when two solid bodies clash together, heat is
produced proportionate to the momentum of the two bodies. In other
words, the motion which is arrested is transformed into heat. Mr. Croll,
in his last publication[DR] upon the subject, ingeniously attempted to
account for the gaseous condition of the nebulæ and the heat of the sun
and other fixed stars by supposing it to be simply transformed motion.
According to this theory, the original form of force imparted to the
universe was that exerted in setting in motion innumerable dark bodies,
which from time to time have collided with each other. The effects of
such collisions would be to transform a large amount of motion into
heat and its accompanying forms of molecular force. The violence of the
compact of two worlds would be so great as to break them up into the
original atoms of which they are composed, and the heat set free would
be sufficient to keep the masses in a gaseous condition and cause them
to swell out into enormous proportions. From that time on, as the heat
radiated into space, there would be the gradual contraction which we
suppose is going on in all the central suns, accompanied, of course, with
a gradual decline of the heat-energy in the system.
[Footnote DR: Stellar Evolution and its Relation to Geological Time.]
Now, it is well known that the earth and the solar system in their
onward progress pass through trains of meteorites. The tails of some of
the comets are indeed pretty clearly proved to be streams of ponderable
matter, through which, from time to time, the minor members of the solar
system plunge, and receive some accession to their bulk and weight. The
shooting-stars, which occasionally attract our attention in the sky,
mark the course of such meteorites as they pass through the earth's
atmosphere, and are heated to a glow by the friction with it. It has been
suggested, therefore, that the sun itself may at times have its amount
of heat sensibly affected by such showers of meteorites or asteroids.
Upon this theory the warm period of the Tertiary epoch, for instance,
may have been due to the heat temporarily added to the sun by impact
with minor astronomical bodies. When, afterwards, it gradually cooled
down, receiving through a long period no more accessions of heat from
that source, the way was prepared for the colder epoch of the Glacial
period, which, in turn, was dispelled by fresh showers of meteorites
upon the sun, sufficient to produce the amelioration of climate which we
experience at the present time.
As intimated, this theory is closely allied to the preceding, the
principal difference being that it limits the effects of the supposed
cause to the solar system, and looks to our sun as the varying source of
heat-supply. It has the advantage over that, however, of possessing a
more tangible _vera causa_. Meteorites, asteroids, and comets are known
to be within this system, and have occasional collisions with other
members of it. But the principal objection urged against the preceding
theory applies here, also, with equal force. The accumulations of ice
during the Glacial period were not determined by latitude. In North
America the centre of accumulation was south of the Arctic Circle--a fact
which points clearly enough to some other cause than that of a general
lowering of the temperature exterior to the earth.
The same objections would bear against the theory ably set forth by Mr.
Sereno E. Bishop, of Honolulu, which, in substance, is that there may
be considerable variability in the sun's emission of heat, owing to
fluctuations in the rate of the shrinkage of its diameter, brought about
by the unequal struggle between the diminishing amount of heat in the
interior and the increasing force of the gravitation of its particles,
and by the changes in the enveloping atmosphere of the sun, which, like
an enswathing blanket, arrests a large portion of the radiant heat from
the nucleus, and is itself evidently subject to violent movements, some
of which seem to carry it down to the sun's interior. Unknown electrical
forces, he thinks, may also combine to add an element of variability.
These supposed changes may be compared to those which take place upon
the surface of the earth when, at irregular intervals, immense sheets of
lava, like those upon the Pacific coast of North America, are exuded in a
comparatively brief time, to be succeeded by a long period of rest. The
heat thus brought to the surface of the earth would add perceptibly to
that radiated from it into space in ordinary times. Something similar to
this upon the sun, it is thought, might produce effects perceptible upon
the earth, and account for alternate periods of heat and cold.
A fourth astronomical theory is that there has been a shifting of the
earth's axis; that at the time of the Glacial period the north pole,
instead of being where it now is, was somewhere in the region of central
Greenland. This attractive theory has been thought worthy of attention
by President T. C. Chamberlin and by Professor G. C. Comstock,[DS] but
it likewise labours under a twofold difficulty: First, the shifting of
the poles observed (450 feet per year) is too slight to have produced the
changes within any reasonable time, and it is not likely to have been
continuous for a long period. But still more fatal to the theory is the
fact that the warm climate preceding the Glacial period seems to have
extended towards the present north pole upon every side; a temperate
flora having been found in the fossil plants of the Tertiary beds in
Greenland and northern British America, as well as upon Nova Zembla and
Spitzbergen.
[Footnote DS: See papers by these gentlemen read at the meeting of the
American Association for the Advancement of Science, in Washington, in
August, 1891. Professor Comstock's paper appeared in the American Journal
of Science for January, 1893.]
A fifth astronomical theory, and one which has of late years been
received with great favour, is that so ably advocated by the late Dr.
James Croll and by Professor James Geikie. Following the suggestions
of the astronomer Adhémar, these writers have attempted to show that
not only one Glacial epoch, but a succession of such epochs, has been
produced in the world by the effect of the changes which are known to
have taken place in the eccentricity of the earth's orbit when combined
with the precession of the equinoxes--another calculable astronomical
cause.
[Illustration: Fig. 99.--Diagram showing effect of precession: _A._
condition of things now; _B._ as it will be 10,500 years hence. The
eccentricity is of course greatly exaggerated.]
It is well known that the earth's orbit is elliptical; that is, it is
longer in one direction than in the other, so that the sun is one side
of the centre. During the winter of the northern hemisphere the earth
is now about three million miles nearer the sun than in the summer; but
the summer makes up for this distance by being about seven days longer
than the winter. Through the precession of the equinoxes this state of
things will be reversed in ten thousand five hundred years; at which time
we shall be nearer the sun during our northern summer, and farther away
in winter, our winter then being also longer than our summer. Besides,
through the unequal attraction of the planets the eccentricity of the
earth's orbit periodically increases and diminishes, so that there have
been periods when the earth was ten million five hundred thousand miles
farther from the sun in winter than in summer; at which times, also,
the winter was nearly twenty-eight days longer than the summer. Such an
extreme elongation of the earth's orbit occurred about two hundred and
fifty thousand years ago.
It is easy to assume that such a change in astronomical conditions would
produce great effects upon the earth's climate; and equally easy to
connect with those effects the vast extension of ice during the Glacial
period. Since, also, this period of extreme eccentricity terminated
only eighty thousand years ago, the close of the Glacial period would,
perhaps, upon Mr. Croll's theory, be comparatively a recent event; for
if the secular summer of the earth's eccentricity lags relatively as
far behind the secular movements as the annual summer does behind the
vernal equinox, we should, as Professor Charles H. Hitchcock suggests,
have to place the complete breaking up of the Ice period as late as forty
thousand years ago.[DT]
[Footnote DT: Geology of New Hampshire, vol. iii, p.327.]
We have no space to indicate, as it deserves, the comparative merits
and demerits of this ingenious theory. It would, however, be a great
calamity to have geologists accept it without scrutiny. It is, indeed,
a part of the business of geologists to doubt such theories until they
are verified by a thorough examination of all accessible _terrestrial_
evidence bearing upon the subject. There is no reason to question the
reality of the variations in the relative positions of the earth and the
sun assumed by Mr. Croll; though there may be serious doubt whether the
effects of those changes upon climate would be all that is surmised,
since equal amounts of heat would fall upon the earth during summer,
whether made longer or shorter by the cause referred to. During the short
summers the earth is so much nearer the sun that it receives each season
absolutely as much heat as it does during the longer summers, when it
is so much farther away from the sun. Thus the theory rests at last upon
the question what would become of the heat reaching the earth in these
differing conditions. It is plausibly urged by Mr. Croll that when a
hemisphere of the earth is passing through a period of long winters the
radiation of heat will be so excessive that the temperature would fall
much below what it would during the shorter winters; and so ice and snow
would accumulate far beyond the usual amount. It is also supposed that
the effect of the summer's sun in melting the ice during the short summer
would be diminished through natural increase of the amount of foggy and
cloudy weather.
Adhémar's theory is supposed by Sir Robert Ball, Royal Astronomer of
Ireland, to be considerably re-enforced by a discovery which he has made
concerning the distribution of heat upon the earth during the seasons
culminating in the summer and winter solstices. Croll had assumed,
on the authority of Herschel, that a hemisphere of the earth during
the longer winter in aphelion would receive the same actual amount of
heat which would fall upon it during the shorter summer in perihelion;
whereas, according to Dr. Ball's discovery, "of the total amount of heat
received from the sun on a hemisphere of the earth in the course of a
year, sixty-three per cent is received during the summer and thirty-seven
per cent during the winter."[DU] When, therefore, the summers occur in
perihelion the heat is more intense than Croll had supposed, and, at
the same time, the winters occurring in aphelion are more deficient in
heat than he had assumed. This discovery of Dr. Ball will not, however,
materially affect the discussion of Croll's theory upon its inherent
merits, since it is simply an intensification of the causes invoked by
him. We will therefore let it stand or fall in the light of the general
considerations hereafter to be adduced.
[Footnote DU: Cause of an Ice Age, p. 90.]
The aid of theoretical consequent changes in the volume of the Gulf
Stream, and in the area of the trade-winds, has also to be invoked by
Mr. Croll. The theory likewise receives supposed confirmation from facts
alleged concerning the present climate of the southern hemisphere which
is passing through the astronomical conditions thought to be favourable
to its glaciation. The antarctic continent is completely enveloped in
ice, even down to the sixty-seventh degree of latitude. A few degrees
nearer the pole Sir J. C. Boss describes the ice as rising from the water
in a precipitous wall one hundred and eighty feet high. In front of such
a wall, and nearly twenty degrees from the south pole, this navigator
sailed four hundred and fifty miles! Voyagers, in general, are said to
agree that the summers of the antarctic zone are much more foggy and cold
than they are in corresponding latitudes in the northern hemisphere; and
this, even though the sun is 3,000,000 miles nearer the earth during the
southern summer than it is during the northern.
Another direction from which evidence is invoked in confirmation of Mr.
Croll's theory is the geological indications of successive Glacial epochs
in times past. If there be a recurring astronomical cause sufficient of
itself to produce Glacial periods, such periods should recur as often as
the cause exists; but glaciation upon the scale of that which immediately
preceded the historic era could hardly have occurred in early geological
time without leaving marks which geologists would have discovered. Were
the "till" now covering the glaciated region to be converted into rock,
its character would be unmistakable, and the deposit is so extensive that
it could not escape notice.
In his inaugural address before the British Association in 1880,
Professor Ramsey, Director-General of the Geological Survey of Great
Britain, presented a formidable list of glacial observations in
connection with rocks of a remote age.[DV] Beginning at the earliest
date, he cites Professor Archibald Geikie, one of the most competent
judges, as confident that the rounded knobs and knolls of Laurentian
rocks exposed over a large region in northwestern Scotland, together
with vast beds of coarse, angular, unstratified conglomerates, are
unquestionable evidences of glacial action at that early period. Masses
of similar conglomerates, resembling consolidated glacial boulder-beds,
occur also in the Lower Silurian formation at Corswall, England. In
Dunbar, Scotland, Professor Forbes also found, in formations of but
little later age than the Coal period, "brecciated conglomerates,
consisting of pebbles and large blocks of stone, generally angular,
embedded in a marly paste, in which some of the pebbles are as well
scratched as those found in medial moraines." In formations of
corresponding antiquity the geologists of India have found similar
boulder-beds, in which some of the blocks are polished and striated.
[Footnote DV: Nature (August 26, 1880), vol. xxii, pp. 388, 389.]
Still, this evidence is less abundant than we should expect, if there had
been the repeated Glacial epochs supposed by Mr. Croll's astronomical
theory; and it is by no means impossible that the conglomerates of
scratched stones described by Professor Ramsey in Great Britain, and
by Messrs. Blandford and Medlicott in India, may have resulted from
local glaciers coming down from mountain-chains which have been since
removed by erosion or subsidence. We are not aware that any incontestable
evidence has been presented in America of any glaciation previous to that
of _the_ Glacial period.
Upon close consideration, also, it appears that Mr. Croll's theory has
not properly taken into account the anomalous distribution of heat which
we actually find to take place on the surface of the earth. He has done
good service in showing what an enormous transfer of heat there is
from the southern to the northern Atlantic by means of the Gulf Stream,
estimating that the heat conveyed by the Gulf Stream into the Atlantic
Ocean is equal to one fifth of all possessed by the waters of the North
Atlantic; or to the heat received from the sun upon a million and a half
square miles at the equator, or two million square miles in the temperate
zone. "The stoppage of the Gulf Stream would deprive the Atlantic of
77,479,650,000,000,000,000 foot-pounds of energy in the form of heat per
day."
Among the objections which bear against this ingenious theory is one
which will appear with great force when we come to discuss the date of
the Glacial period, when we shall show that even Professor Hitchcock's
supposition that the lingering effects of the last great eccentricity of
the earth's orbit, continued down to forty thousand years ago, is not
sufficient to account for the recentness of the close of the period as
shown by abundant geological evidence. It is certainly not more than ten
or fifteen thousand years ago that the ice finally melted off from the
Laurentian highlands; while on the Pacific coast the period of glaciation
was still more recent.
From inspection of the accompanying map the main point of Mr. Croll's
reasoning may be understood. It will be seen that the direction of the
currents in the central Atlantic is largely determined by the contour of
the northeastern coast of South America. From some cause the southeast
trade-winds are stronger than the northeast, and their force is felt in
pushing the superficial currents of warm water farther north than Cape
St. Roque, the eastern extremity of Brazil. As the direction of the South
American coast trends rapidly westward from this point to the Isthmus of
Panama, the resultant of the forces is a strong current northwestward
into the _cul-de-sac_ of the Gulf of Mexico, from which there is only the
one outlet between Cuba and the peninsula of Florida. Through this the
warm water is forced into the region where westerly winds prevail, and
spreads its genial influence far to the northward, modifying the climate
of the British Isles, and even of far-off Norway.
[Illustration: Fig. 100.--Map showing course of currents in the Atlantic
Ocean: _b_ and _b'_ are currents set in motion by opposite trade-winds;
meeting, they produce the equatorial current, which divides into _c_ and
_c'_, continuing on as _a_ and _a'_ and _e_.]
But why are the southeast trade-winds of the Atlantic stronger than
the northeast? The ultimate reason, of course, is to be found in the
fact that the northern hemisphere is warmer than the southern. The
atmosphere over the northern-central portion of the Atlantic region is
more thoroughly rarefied by the sun's heat than is that over the region
south of the equator. The strong southeast trades are simply the rush of
atmosphere from the South Atlantic to fill the vacuum caused by the heat
of the sun north of the equator.
But, again, why is this? Because, says Mr. Croll, we are now in that
stage of astronomical development favourable to the increased warmth
of the northern hemisphere. In the northern hemisphere the summers are
longer than the winters. Perihelion occurs in winter and aphelion in
summer. This is the reason why the North Atlantic is warmer than the
South Atlantic, and why the trade-winds of the south are drawn to the
north of the equator. Ten thousand five hundred years ago, however, the
conditions were reversed, and the greater rarefaction of the atmosphere
would have taken place south of the equator, thus drawing the trade-winds
in that direction.
By again inspecting the map, one will see how far-reaching the effect on
the climate of northern countries this change in the prevalences of the
trades would have been. Then, instead of having the northwest current
leading along the northeast coast of South America into the Gulf of
Mexico augmented by the warm currents circulating south of the equator,
the warm currents of the north would have been pushed down so far that
they would augment the current running to the southwest beyond Cape St.
Roque, along the southeast shore of South America; thus the northern
portion of the Atlantic, instead of robbing the southern portion of
heat, would itself be robbed of its warm currents to contribute to the
superfluous heat of the South Atlantic.
This theory is certainly very ingenious. There is a weak point in
it, however. Mr. Croll assumes that when the winters of the northern
hemisphere occur in aphelion, they must necessarily be colder than now.
But, evidently, this assertion implies a fuller knowledge than we possess
of the laws by which the heat received from the sun is distributed over
the earth.
For it appears from observation that the equator is by no means so
hot now as, theoretically, it ought to be, and that the arctic regions
are not so cold as, according to theory, they should be, and this in
places which could not be affected by oceanic currents. For example,
at Iquitos, on the Amazon, only three hundred feet above tide, three
degrees and a half south of the equator, and more than a thousand miles
from the Atlantic (so that ocean-currents cannot abstract the heat from
its vicinity), the mean yearly temperature is but 78° Fahr.; while at
Verkhojansk, in northeast Siberia, which is 67° north of the equator, and
is situated where it is out of the reach of ocean-currents, and where
the conditions for the radiation of heat are most favourable, and where,
indeed, the winter is the coldest on the globe (January averaging--56°
Fahr.), the mean yearly temperature is two degrees and a half above zero;
so that the difference between the temperature upon the equator and that
at the coldest point on the sixty-seventh parallel is only about 75°
Fahr.; whereas, if temperature were in proportion to heat received from
the sun, the difference ought to be 172°. Again, the difference between
the actual January temperature on the fiftieth parallel and that upon the
sixtieth is but 20° Fahr., whereas, the quantity of solar heat received
on the fiftieth parallel during the month of January is three times that
received upon the sixtieth, and the difference in temperature ought to be
about 170° Fahr. upon any known law in the case.
Woeikoff, a Russian meteorologist, and one of the ablest critics of Mr.
Croll's theory, and to whom we are indebted for these facts, ascribes
the greater present warmth of the northern Atlantic basin, not to the
astronomical cause invoked by Mr. Croll, but to the relatively small
extent of sea in the middle latitudes of the northern hemisphere. The
extent and depth of the oceans of the southern hemisphere would of
themselves give greater steadiness and force to its trade-winds, and
lead to a general lowering of the temperature; so that it is doubtful
if the astronomical causes introduced by Mr. Croll, even with Dr.
Ball's re-enforcement, would produce any appreciable effect while the
distribution of land and water remains substantially what it is at the
present time.
Still another variation in the astronomical theory has been set forth
and defended by Major-General A. W. Drayson, F. R. A. S., instructor
in the Royal Military School at Woolwich, England. He contends that
what has been called the precession of the equinoxes, and supposed to
be "a conical movement of the earth's axis in a circle around a point
as a centre, from which it continually decreases its distance,"[DW] is
really a second rotation of the earth about its centre. As a consequence
of this second rotation, he endeavours to show that the inclination of
the earth's axis varies as much as 12°; so that, whereas the Arctic and
Antarctic Circles and the tropics extend to only about 23° from the poles
and the equator, respectively, about thirteen thousand five hundred years
ago they extended more than 35°; thus bringing the frigid zones in both
cases 12° nearer the equator than now. This, he contends, would have
produced the Glacial period at the time now more generally assigned to it
by direct geological evidence.
[Footnote DW: Untrodden Ground in Astronomy and Geology, p. 26.]
The difficulty with this theory, even if the mathematical calculations
upon which it is based are correct, would be substantially the same as
those already urged against that of Mr. Croll. It is specially difficult
to see how General Drayson would account for the prolonged temperate
climate in high northern latitudes during the larger part of the Tertiary
epoch.
It will be best to turn again to the map to observe the possible effect
upon the Gulf Stream of a geological event of which we have some definite
evidence, and which is adduced by Mr. Upham and others as one of the
important probable causes of the Glacial period, namely, the subsidence
of the Isthmus of Panama and the adjacent narrow neck of land connecting
North with South America. It will be seen at a glance that a subsidence
sufficient to allow the northwest current of warm water, pushed by the
trade-winds along the northeast shore of South America, to pass into
the Pacific Ocean, instead of into the Gulf of Mexico, would be a cause
sufficient to produce the most far-reaching results; it would rob the
North Atlantic of the immense amount of heat and moisture now distributed
over it by the Gulf Stream, and would add an equal amount to the northern
Pacific Ocean, and modify to an unknown extent the distribution of heat
and moisture over the lands of the northern hemisphere.
The supposition that a subsidence of the Isthmus of Panama was among
the contributing causes of the Glacial period has been often made, but
without any positive proof of such subsidence. From evidence which
has recently come to light, however, it is certain that there has
actually been considerable subsidence there in late Tertiary if not in
post-Tertiary times. This evidence is furnished by Dr. G. A. Maack and
Mr. William M. Gabb in their report to the United States Government in
1874 upon the explorations for a ship-canal across the isthmus, and
consists of numerous fossils belonging to existing species which are
found at an elevation of 150 feet above tide. As the dividing ridge is
more than 700 feet above tide, this does not positively prove the point,
but so much demonstrated subsidence makes it easy to believe, in the
absence of contradictory evidence, that there was more, and that the
isthmus was sufficiently submerged to permit a considerable portion of
the warm equatorial current which now passes northward from the Caribbean
Sea and the Gulf of Mexico to pass into the Pacific Ocean.
[Illustration: Fig. 101.--Map showing how the land clusters about the
north pole.]
An obvious objection to the theory of a late Tertiary or post-Tertiary
subsidence of the Isthmus of Panama presents itself in the fact that
there is at present a complete diversity of species between the fish
inhabiting the waters upon the different sides of the isthmus. If
there had been such a subsidence, it seems natural to suppose that
Atlantic species would have migrated to the Pacific side and obtained
a permanent lodgment there, and that Pacific species would have found
a congenial home on the Atlantic side. It must be confessed that this
is a serious theoretical difficulty, but perhaps not insuperable. For
it is by no means certain that colonists from the heated waters of the
Caribbean Sea would become so permanently established upon the Pacific
side that they could maintain themselves there upon the re-establishment
of former conditions. On the contrary, it seems reasonable to suppose
that upon the re-elevation of the isthmus the northern currents, which
would then resume their course, would bring back with them conditions
unfavourable to the Atlantic species, and favourable to the competing
species which had only temporarily withdrawn from the field, and which
might now be better fitted than ever to renew the struggle with their
Atlantic competitors. It is by no means certain, therefore, that with
the re-establishment of the former conditions there would not also be a
re-establishment of the former equation of life upon the two sides of the
isthmus.
Mr. Upham's theory involves also extensive elevations of land in the
northern part of America; in this respect agreeing with the opinions
early expressed by Professors J. D. Dana and J. S. Newberry. Of the
positive indications of such northward elevations of land we have already
spoken when treating in a previous chapter of the fiords and submerged
channels which characterise northern Europe and both the eastern and
the western coasts of North America. But in working out the problem the
solution is only half reached when we have got the Gulf Stream into
the Pacific Ocean, and the land in the northern part of the continents
elevated to some distance above its present level. There is still the
difficulty of getting the moisture-laden currents from the Pacific Ocean
to carry their burdens over the crest of the Sierra Nevada and Rocky
Mountains and to deposit them in snow upon the Laurentian highlands.
An ingenious supplement to the theory, therefore, has been brought
forward by Professor Carpenter, who suggests that the immense Tertiary
and post-Tertiary lava-flows which cover so much of the area west of
the Rocky Mountains were the cause of the accumulations of snow which
formed the Laurentide Glacier. This statement, which at first seems so
paradoxical as to be absurd, appears less so upon close examination.
The extent of the outflows of lava west of the Rocky Mountains is almost
beyond comprehension. Literally, hundreds of thousands of square miles
have been covered by them to a depth in many places of thousands of feet.
These volcanic eruptions are mostly of late date, beginning in the middle
of the Tertiary and culminating probably about the time of the maximum
extent of the Laurentide Glacier. Indeed, so nearly contemporaneous was
the growth of the Laurentide Glacier with these outflows that Professor
Alexander Winchell had, with a good deal of plausibility, suggested that
the outflows of the eruptions of lava were caused by the accumulation
of ice over eastern British America. His theory was that the three
million cubic miles of ice which is proved to have been abstracted from
the ocean and piled up over that area was so serious a disturbance of
the equilibrium of the earth's crust that it caused great fissures to
be opened along the lines of weakness west of the Rocky Mountains, and
pressed the liquid lava out, as the juice is pressed out of an orange in
one place by pressing upon the rind in another.
Professor Carpenter's view is the exact reverse of Professor Winchell's.
Going back to those orographic changes which produced the lava-flows
and the elevation of the northern part of British America, he thinks
the problem of getting the moisture transferred from the Pacific Ocean
to the Canadian highlands is solved by the lava-flows west of the Rocky
Mountains. This immense exudation of molten matter was accompanied by an
enormous liberation of heat, which must have produced significant changes
in the meteorological conditions.
The moisture of the atmosphere is precipitated by means of the
condensation connected with a lowering of its temperature. Ordinarily,
therefore, when moist winds from an oceanic area pass directly over a
lofty mountain-chain, the precipitation takes place immediately, and
the water finds its way back by a short course to the sea. This is what
now actually occurs on the Pacific coast. The Sierra Nevada condense
nearly all the moisture; so that very little falls on the vast area
extending from their summits eastward to the Rocky Mountains. All that
region is now practically a desert land, where the evaporation exceeds
the precipitation. In Professor Carpenter's view the heat radiated from
the freshly exuded lava is supposed to have prevented the precipitation
near the coast-line, and to have helped the winds in carrying it farther
onward to the northeast, where it would be condensed upon the elevated
highlands, upon which the snows of the great Laurentide Glacier were
collected.
It is not necessary for us to attempt to measure the amount of truth in
this subsidiary hypothesis of Professor Carpenter, but it illustrates
how complicated are the conditions which have to be considered before we
rest securely upon any particular hypothesis. The unknown elements of the
problem are so numerous, and so far-reaching in their possible scope,
that a cautious attitude of agnosticism, with respect to the cause of
the Glacial period, is most scientific and becoming. Still, we are ready
to go so far as to say that Mr. Upham's theory comes nearest to giving
a satisfactory account of all the phenomena, and it is to this that
Professor Joseph Le Conte gives his cautious approval.
Summarily stated, this theory is, that the passage from the Tertiary
to the Quaternary or Glacial period was characterised by remarkable
oscillations of land-level, and by corresponding changes of climate, and
of ice-accumulation in northern regions; that the northern elevation
was connected with subsidence in the equatorial regions; that these
changes of land-level were both initiated and, in the main, continued
by the interior geological forces of the globe; but that the very
continental elevation which mainly brought on the Glacial period added
at length, in the weight of the ice which accumulated over the elevated
region, a new force to hasten and increase the subsidence, which would
have taken place in due time in the natural progress of the orographic
oscillations already begun. Professor Le Conte illustrates the subject by
the following diagram, which, for simplicity's sake, treats the Glacial
epoch as one; the horizontal line, A B, represents time from the later
Pliocene until now; but it also represents the present condition of
things both as to land-level and as to ice-accumulation. The full line, c
d e, represents the oscillations of land (and presumably of temperature)
above and below the present condition. The broken line represents the
rise, culmination, and decline of ice-accumulation. The dotted line
represents the crust-movement as it would have been if there had been no
ice-accumulation.
[Illustration: Fig. 102.]
_Succession of Epochs, Glacial and Fluvial Deposits, and_
Eastern Provinces and Middle and Southern
Epochs. New England. Atlantic States.
Recent or Rise of the land to its Continued subsidence of
Terrace. present height, or coast at New York and
(Mostly within somewhat higher, soon southward, and rise of
the period of after the departure of the mountainous belt, by
traditional the ice. Rivers eroding displacement along the
and written their glacial fall line of the rivers.
history.) flood-plains, leaving Much erosion of the
remnants as terraces. Columbia formation since
Warmer climate than now, culmination of second
probably due to greater Glacial epoch;
Gulf Stream, formerly sedimentation in bays,
permitted southern sounds, and estuaries.
mollusks to extend to
Gulf of St. Lawrence, now
represented by isolated
colonies.
Glacial Period of Ice Age. Pleistocene Period.
Champlain. Land depressed under Less subsidence in
ice-weight; glacial latitude of New York and
(Close of the recession; continued southward than at north;
second Glacial deposition of upper till lower Hudson Valley, and
epoch.) and deep flood-plains of part of its present
gravel, sand and clay submarine continuation,
(modified drift). above sea-level. Gravel
Terminal moraines marking and sand deposits from
pauses or readvance englacial drift in
during general retreat of Delaware and Susquehanna
ice. Marine submergence. Valleys, inclosing
150 to 230 feet on coast abundant human implements
of Maine, to 520 feet in at Trenton, N.J.
Gulf and valley of St.
Lawrence.
Second Glacial. Second great uplift of Renewal of great
the land, 3.000 to 4,000 continental elevation
feet higher than now; (3.000 feet in latitude
snow-fall again all the of New York and
year; ice probably two Philadelphia), of
miles thick on Laurentide excessive snow-fall and
highlands, and extending rains, and of wide-spread
somewhat farther south fluvial deposits, the
here than in first Columbia formation, on
glaciation. Lower till the coastal plain, during
(ground moraine), and early part of this epoch.
upper till (englacial Implements of man at
drift). Terminal Claymont, Del.
moraines, kames, osars,
valley drift.
Inter-glacial. Ice-sheet melted here; Depression, but generally
probably not more ice in not to the present level.
(Longest epoch arctic regions than now. Deep channels cut in the
of this era.) bed-rocks by the
Fluvial and lacustrine Delaware, Susquehanna,
deposits of this time, Potomac, and other
with those of the first rivers. The Appomattox
Glacial epoch, were deposits much eroded.
eroded by the second
glaciation. Relative length of this
epoch made known by McGee
from study of this
region.
First Glacial. Begun by high continental Continental elevation;
uplift, cool climate and erosion of Delaware and
snow-fall throughout the Chesapeake Bays, and of
year, producing Albemarle and Pamlico
ice-sheet. Much glacial Sounds. Plentiful
erosion and snow-fall on the southern
transportation; till and Appalachian Mountains;
stratified deposits. snows melted in summer,
Ended by depression of and heavy rains,
land; return of warm producing broad
climate, with rain; final river-floods, with
melting of the ice. deposition of the
Isthmus of Panama Appomattox formation.
probably submerged (Gulf
Stream smaller), and
again in second Glacial
epoch.
_Changes in Altitude and Climate, during the Quaternary Era._
Mississippi Basin and Cordilleran Region. Europe and Asia.
northward.
Terracing of river Including a stage of Erosion and terracing
valleys. Northward rise considerable uplift, of stratified drift in
of area of Lake Agassiz with return of humid river valleys. Land
nearly complete before conditions, Alpine passage of European
the ice was melted on glaciation (third flora to Greenland;
the country crossed by Glacial epoch), and succeeded by subsidence
Nelson River; but rise the second great rise there, admitting warm
about Hudson Bay is still of Lakes Bonneville currents to Arctic Sea.
going on; 7,000 to 8,000 and Lahontan. Very Minor climatic changes,
years since ice-melting recent subsidence including a warmer
uncovered Niagara and and change to present stage than now. Upper
falls of St. Anthony. aridity. and outer portions of
Indo-Gangetic alluvial
plain; extensive
deposits of Hwang Ho,
and destructive changes
of its course.
Abundant deposition of Depression probably Final departure of the
englacial drift. Stone almost to the present ice-sheets; glacial
implements in river level. Restoration of rivers forming eskers
gravels of Ohio, Ind., arid climate; nearly or and kames. Loess
and Minn. Laurentian quite complete deposited while the
lakes held at higher evaporation of Lakes region of the Alps was
levels, and Lake Bonneville and Lahontan.depressed lower than
Agassiz formed in Red Formation of the "adobe"now. Upper (englacial)
River basin, by continuing through the till, and asar, of
barrier of retreating second Glacial, Sweden. Marine
ice, with outlets over Champlain, and Recent submergence 500 to 600
lowest points of their epochs. feet in Scotland,
present southern Scandinavia, and
water-shed. Marine Spitzbergen.
submergence 300 to 500
feet on southwest
side of Hudson Bay.
Ice-sheet here less Probable uplift 3,0 Second elevation and
extensive than in the feet, shown by general glaciation of
first Glacial epoch, and submerged valleys near northwestern Europe;
not generally bordered Cape Mendocino. Second the ice-sheets of Great
as then by lakes in ice-sheet on British Britain probably more
valleys which now drain Columbia and Vancouver extensive than in first
southward. Island; local Glacial epoch.
glaciation of Rocky Oscillations of
Terminal moraines at Mountains, Cascade and ice-front; British
extreme limit of the Sierra range, Nevada, Lower and Upper
ice-advance, and at ten south to latitude 37°. the Chalky, Purple, and
or more stages of halt or First great rise of bowlder-clays, Hessle
readvance in its retreat. Lakes Bonneville bowlder-clays. Terminal
and Lahontan. moraines in Germany.
Depression nearly to Continental depression. Recession, or probably
present level southward; Arid climate. Long- complete departure, of
more northward, but continued denudation of the ice-sheets.
followed there, by the mountains:
differential uplift of resulting very thick Land connection between
800 or 1,000 feet. subaërial deposits of Europe and Africa,
Great erosion of loess the "adobe." permitting southern
and other modified animals to extend far
drift, and of "Orange Intermittent volcanic northward.
Sand." Valleys of this action in various parts
epoch, partly filled of this region, Erosion of the Somme
with later till, are throughout the Valley below its oldest
marked by chains of Quaternary era to very implement-bearing
lakes in southern recent times, and gravels.
Minnesota. liable to break forth
again.
Pliocene elevation of Latest rise (3.000 Uplift and glaciation
continent brought to feet) of the Colorado of northwestern Europe:
culmination at Cañon district. Sierra maximum elevation.
beginning of Nevada and other Great 2,500 feet or more
Quaternary era; this Basin mountain-ranges (depth of the Skager
whole basin probably formed by immense Rack); France and
then uplifted 3.000 uplifts, with faulting. Britain united with the
feet; excessive California river- Färöe Islands, Iceland,
snow-fall and rain; courses changed; human and Greenland. Uplifts
deposition of the bones and implements in of the Himalayas and
"Orange Sand." Ice- the old river gravels, other mountain-ranges
sheet south to lava-covered. Ice-sheet attendant on both
Cincinnati and St. on British Columbia; Glacial epochs.
Louis, at length local glaciers
depressing the earth's southward.
crust beneath it;
slackened river floods
and shallow lakes,
forming the loess.
It is seen from the diagram that the ice-accumulation culminated at a
time when the land, under the pressure of the ice-load, had already
commenced to subside; and that the subsidence was greatest at a time when
the pressure had already begun to diminish. But the fact that the land,
after the removal of the ice-load, did not return again to its former
height in the Pliocene, is proof positive that there were other and
more fundamental causes of crust-movement at work besides weighting and
lightening. The land did not again return to its former level because the
cycle of elevation, whatever its cause, which commenced in the Pliocene
and culminated in the early Quaternary, had exhausted itself. If it had
not been for the ice-load interfering with and modifying the natural
course of the crust-movement determined previously and primarily by other
and probably internal causes, the latter would probably have taken the
course represented by the dotted line. It would have risen higher and
culminated later, and its curve would have been of simpler form.
We append a carefully prepared table by Mr. Warren Upham, showing the
probable changes in altitude and climate during the Quaternary era.[DX]
[Footnote DX: On page 106 and sequel I have summarised the reasons which
lead me to discard the Inter-Glacial epoch, and to look upon the whole
Glacial period as constituting a grand unity with minor episodes. It
does not yet seem to me that the duality of the period is proved. On the
contrary, Mr. Kendall's chapter on the Glacial phenomena of Great Britain
strongly confirms my view.]
On the part of many the theory here provisionally adopted will be
regarded with disfavour by reason of a disinclination to supposing
any great recent changes of level in the continental areas. So firmly
established do the continents appear to be, that it seems like invoking
an inordinate display of power to have them exalted for the sake of
producing a Glacial period. Due reflection, however, will make it
evident that within certain limits the continents are exceedingly
unstable, and that they have displayed this instability to as great an
extent in recent geological times as they have done in any previous
geological periods. When one reflects, also, upon the size of the earth,
a continental elevation of 3,000 or 4,000 feet upon a globe whose
diameter is more than 40,000,000 feet is an insignificant trifle. On a
globe one foot in diameter it would be represented by a protuberance of
barely one thousandth of an inch. A corresponding wrinkle upon a large
apple would require a magnifying-glass for its detection. Moreover, the
activity of existing volcanoes, the immense outflows of lava which have
taken place in the later geological periods, together with the uniform
increase of heat as we penetrate to deeper strata in the crust of the
earth--all point to a condition of the earth's interior that would
make the elevations of land which we have invoked for the production
of the Glacial period easily credible. Physicists do not, indeed, now
hold to the entire fluidity of the earth's interior, but rather to a
solid centre, where gravity overcomes the expansive power of heat, and
maintains solidity even when the heat is intense. But between the cooling
crust of the earth's exterior and a central solid core there is now
believed to be a film where the influences of heat and of the pressure
of gravity are approximately balanced, and the space is occupied by a
half-melted or viscous magma, capable of yielding to a slow pressure, and
of moving in response to it from one portion of the enclosed space to
another where the pressure is for any cause relieved.
As a result of prolonged enquiries respecting the nature of the forces
at work both in the interior and upon the exterior of the earth, and
of a careful study of the successive changes marking the geological
period, we are led to believe that the continental elevations necessary
to produce the phenomena of the Glacial period are not only entirely
possible but easily credible, and in analogy with the natural progress
of geological history. In the first place, it is easy to see that
two causes are in operation to produce a contraction of the earth's
volume and a shortening of its diameter. Heat is constantly being
abstracted from the earth by conduction and radiation, but perhaps to
a greater extent through ceaseless volcanic eruptions which at times
are of enormous extent. It requires but a moment's thought to see that
contraction of the volume of the earth's interior means that the hardened
exterior crust must adjust itself by wrinkles and folds. For a long
period this adjustment might show itself principally in gentle swells,
lifting portions of the continents to a higher level, accompanied by
corresponding subsidence in other places. This gradually accumulating
strain would at length be relieved along some line of special weakness in
the crust by that folding process which has pushed up the great mountain
systems of the world.
Careful study of the principal mountain systems shows that all the
highest of them are of late geological origin. Indeed, the latter part
of the Tertiary period has been the great mountain-building epoch in the
earth's history. The principal part of the elevation of the Andes and
the Rocky Mountains has taken place since the middle of the Tertiary
period. In Europe there is indubitable evidence that the Pyrenees have
been elevated eleven thousand feet during the same period, and that the
western Alps have been elevated thirteen thousand feet in the same time.
The Carpathians, the western Caucasus, and the Himalayas likewise bear
explicit evidence to the fact that a very considerable portion of their
elevation, amounting to many thousand feet, has been effected since the
middle of the Tertiary period, while a considerable portion of this
elevation of the chiefest mountain systems of the world has occurred in
what would be called post-Tertiary time--that is, has been coincident
with a portion of the Glacial period.
The Glacial period, however, we suppose to have been brought about, not
by the specific plications in the earth's crust which have produced the
mountain-chains, but by the gentler swells of larger continental areas
whose strain was at last relieved by the folding and mashing together
of the strata along the lines of weakness now occupied by the mountain
systems. The formation of the mountains seems to have relieved the
accumulating strain connected with the continental elevations, and to
have brought about a subsequent subsidence.
Doubtless, also, correlated subsidences and elevations of the earth's
crust have been aided by the transfer of the sediment from continental
to oceanic areas, and, as already suggested, during the Glacial period
by the transfer of water evaporated from the surface of the ocean to
the ice-fields of the glaciated area. For example, present erosive
agencies are lowering the level of the whole Mississippi basin from
the Alleghanies to the Rocky Mountains at the rate of a foot in five
thousand years. All this sediment removed is being transferred to the
ocean-bed. Present agencies, therefore, if not counteracted, would
remove the whole continent of America (whose average elevation above the
sea is only 748 feet) in less than four million years; while the great
rivers which descend in all directions from the central plateau of Asia
are transferring sediment to the ocean from two to four times as fast
as the Mississippi is, and the Po is transferring it from the Alps to
the Adriatic fully seven times as fast as the Mississippi is from its
basin to the Gulf of Mexico. This rapid transfer of sediment from the
continents to the ocean is producing effects in disturbing the present
equilibrium of the earth's crust, which are too complicated for us fully
to calculate; but it is by no means improbable that when accumulating for
a considerable length of time, the ultimate results may be very marked
and perhaps sudden in their appearance.
The same may also be said of the accumulation of ice during the Glacial
period. The glaciated areas of North America and Europe combined
comprise about six million square miles. At a moderate estimate,
the ice was three-quarters of a mile deep. Here, therefore, there
would be between four and five million cubic miles of water, which
had first relieved the ocean-beds of the pressure of its weight, and
then concentrated its force over the elevated areas of the northern
hemisphere. This disturbance of the equilibrium, by the known transfer
of force from one part of the earth's crust to another, certainly gives
much plausibility to the theory of Jamieson, Winchell, Le Conte, and
Upham, that the Glacial period partly contained in itself its own cure,
and by the weight of its accumulated weight of ice helped to produce
that depression over the glaciated area which at length rendered the
accumulation of ice there impossible.
This general view of the known causes in operation during the Glacial
period will go far towards answering an objection that has probably
before this presented itself to the reader's mind. It seems clear
that the Glacial period in the southern hemisphere has been nearly
contemporaneous with that of the northern. The Glacial period proper of
the southern hemisphere is long since passed. The existing glaciers of
New Zealand, of the southern portion of the Andes Mountains, and of the
Himalaya Mountains are but remnants of those of former days. In the light
of the considerations just presented, it would not seem improbable that
the same causes should produce these similar effects in the northern and
the southern hemisphere contemporaneously. At any rate, it would not
seem altogether unlikely that the pressure of ice during the climax of
the Glacial period upon the northern hemisphere (which, as we have seen,
there is reason to believe aided in the depression of the continent to
below its present level in the latter part of the Glacial period) should
have contributed towards the elevation of mountains in other parts of the
world, and so to the temporary enlargement of the glaciers about their
summits.
Nor are we wholly without evidence that these readjustments of land-level
which have been carried on so Vigorously since the middle of the Tertiary
period are still going on with considerable though doubtless with
diminished rapidity. There has been a re-elevation of the land in North
America since the Glacial period amounting to 230 feet upon the coast of
Maine, 500 feet in the vicinity of Montreal, from 1,000 to 1,600 feet in
the extreme northern part of the continent, and in Scandinavia to the
extent of 600 feet. In portions of Scandinavia the land is now rising
at the rate of three feet in a century. Other indications of even the
present instability of the earth's surface occur in numbers too numerous
to mention.[DY]
[Footnote DY: For a convincing presentation of the views here outlined,
together with abundant references to literature, see Mr. Warren Upham's
Appendix to the author's Ice Age in North America.]
But, while we are increasingly confident that the main causes of the
Glacial period have been changes in the relative relation of land-levels
connected with diversion of oceanic currents, it is by no means
impossible, as Wallace[DZ] and others have suggested, that these were
combined with the astronomical causes urged by Drs. Croll and Geikie.
By some this combination is thought to be the more probable, because
of the extreme recentness of the close of the Glacial period, as shown
by the evidence which will be presented in the following chapter. The
continuance of glaciers in the highlands of Canada, down to within a few
thousand years of the present time, coincides in a remarkable manner with
the last occurrence of the conditions favourable to glaciation upon Mr.
Croll's theory, which took place about eleven thousand years ago.
[Footnote DZ: See Island Life, chapters viii and ix.]
CHAPTER X.
THE DATE OF THE GLACIAL PERIOD.
In approaching the subject of glacial chronology, we are compelled
to recognise at the outset the approximate character of all our
calculations. Still, we shall find that there are pretty well-defined
limits of time beyond which it is not reasonable to place the date of
the close of the Glacial period; and, where exact figures cannot be
determined, it may yet be of great interest and importance to know
something near the limits within which our speculations must range.
For many years past Mr. Croll's astronomical theory as to the cause of
the Glacial period has been considered in certain circles as so nearly
established that it has been adopted by them as a chronological table in
which to insert a series of supposed successive Glacial epochs which are
thought to have characterised not merely the Quaternary epoch but all
preceding geological eras. What we have already said, however, respecting
the weakness of Mr. Croll's theory is probably sufficient to discredit it
as a chronological apparatus. We will therefore turn immediately to the
more tangible evidences bearing upon the subject.
The data directly relating to the length of time which separates the
present from the Glacial period are mainly connected with two classes of
facts:
1. The amount of erosion which has been accomplished by the river systems
since the Glacial period; and 2. The amount of sedimentation which
has taken place in lakes and kettle-holes. We will consider first the
evidence from erosion.
[Illustration: Fig. 103.--Diagram of eccentricity and precession:
Abscissa represents time and ordinates, degrees of eccentricity and also
of cold. The dark and light shades show the warmer and colder winters,
and therefore indicate each 10,500 years, the whole representing a period
of 300,000 years.]
The gorge below Niagara Falls affords an important chronometer for
measuring the time which has elapsed since a certain stage in the
recession of the great North American ice-sheet. As already shown, the
present Niagara River is purely a post-glacial line of drainage;[EA] the
preglacial outlet to Lake Erie having been filled up by glacial deposits,
so that, on the recession of the ice, the lowest level between Lake Erie
and Lake Ontario was in the line of the trough of the present outlet.
But, from what has already been said, it also appears that the Niagara
River did not begin to flow until considerably after the ice-front had
withdrawn from the escarpment at Queenston, where the river now emerges
from its cañon to the low shelf which borders Lake Ontario. For a
considerable period afterwards the ice continued to block up the easterly
and northerly outlets through the valleys of the Mohawk and of the St.
Lawrence, and held the water in front of the ice up to the level of the
passes leading into the Mississippi Valley. Niagara River, of course, was
not born until these ice-barriers on the east and northeast melted away
sufficiently to allow the drainage to take its natural course.
[Footnote EA: See above, p. 200 _et seq._]
[Illustration: Fig. 104.--Map of the Niagara River below the falls,
showing the buried channel from the whirlpool to St. Davids. Small
streams, _a_, _b_, _c_, fall into the main gorge over a rocky escarpment.
No rock appears in the channel at _d_, but the rocky escarpment reappears
at _e_.]
Of these barriers, that across the Mohawk Valley doubtless gave way
first. This would allow the confluent waters of this great glacial lake
to fall down to the level of the old outlet from the basin of Lake
Ontario into the Mohawk Valley, in the vicinity of Home, N. Y. The
moment, however, that the water had fallen to this level, the plunging
torrents of Niagara would begin their work; and the gorge extending from
Queenston up to the present falls is the work done by this great river
since that point of time in the Glacial period when the ice-barrier
across the Mohawk Valley broke away.
The problem is therefore a simple one. Considering the length of
this gorge as the dividend, the object is to find the rate of annual
recession; this will be the divisor. The quotient will be the number of
years which have elapsed since the ice first melted away from the Mohawk
Valley. We are favoured in our calculation by the simplicity of the
geologic arrangement.
The strata at Niagara dip slightly to the south, but not enough to make
any serious disturbance in the problem. That at the surface, over which
the water now plunges, consists of hard limestone, seventy or eighty
feet in thickness, and this is continuous from the falls to the face of
the escarpment at Queenston, where the river emerges from the gorge.
Immediately underneath this hard superficial stratum there is a stratum
of soft rock, of about the same thickness, which disintegrates readily.
As a consequence, the plunging water continually undermines the hard
stratum at the surface, and prepares the way for it to fall down, from
time to time, in huge blocks, which are, in turn, ground to powder by
the constant commotion in which they are kept, and thus the channel is
cleared of _débris_.
[Illustration: Fig. 105.--Section of strata along the Niagara gorge from
the falls to the lake: 1, 3, strata of hard rock; 2, 4, of soft rock.]
Below these two main strata there is considerable variation in the
hardness of the rock, as shown in the accompanying diagram, where 3 and
5 are hard strata separated by a soft stratum. In view of this fact it
seems probable that, for a considerable period in the early part of the
recession, instead of there being simply one, there was a succession of
cataracts, as the water unequally wore back through the harder strata,
numbered 5, 3, and 1; but, after having receded half the distance, these
would cease to be disturbing influences, and the problem is thus really
the simple one of the recession through the strata numbered 1 and 2,
which are continuous. So uniform in consistency are these throughout the
whole distance, that the rate of recession could never have been less
than it is now. We come, therefore, to the question of the rapidity with
which the falls are now receding.
In 1841 Sir Charles Lyell and Professor James Hall (the State Geologist
of New York) visited the falls together, and estimated that the rate of
recession could not be greater than one foot a year, which would make the
time required about thirty-five thousand years. But Lyell thought this
rate was probably three times too large; so that he favoured extending
the time to one hundred thousand years. Before this the eminent French
geologist Desor had estimated that the recession could not have been
more than a foot in a century, which would throw the beginning of the
gorge back more than three million years. But these were mere guesses
of eminent men, based on no well-ascertained facts; while Mr. Bakewell,
an eminent English geologist, trusting to the data furnished him by the
guides and the old residents of Niagara, had, even then, estimated that
the rate of recession was as much as three feet a year, which would
reduce the whole time required to about ten thousand years.
But the visit of Lyell and Hall in 1841 led to the beginning of more
accurate calculations. Professor Hall soon after had a trigonometrical
survey of the falls made, from which a map was published in the State
geological report. From this and from the monuments erected, we have had
since that time a basis of comparison in which we could place absolute
confidence.
In recent years three surveys have been made: the first by the New
York State Geologists, in 1875; and the third by Mr. R. S. Woodward,
the mathematician of the United States Geological Survey, in 1886. The
accompanying map shows the outlines of the falls at the time of these
three measurements, from 1842 to 1886. According to Mr. Woodward, "the
length of the front of the Horseshoe Fall is twenty-three hundred feet.
Between 1842 and 1875 four and a quarter acres of rock were worn away by
the recession of the falls. Between 1875 and 1886 a little over one acre
and a third disappeared in a similar manner, making in all, from 1842 to
1886, about five and a half acres removed, and giving an annual rate of
recession of about two feet and a half per year for the last forty-five
years. But in the central parts of the curve, where the water is deepest,
the Horseshoe Fall retreated between two hundred and two hundred and
seventy-five feet in the eleven years between 1875 and 1886."
[Illustration: Fig. 106.--Map showing the recession of the Horseshoe
Falls since 1842, as by survey mentioned in the text (Pohlman). (by
courtesy of the American Institute of Mining Engineers.)]
It will be perceived that the recession in the centre of the Horseshoe is
very much more rapid than that nearer the margin; yet this rate at the
centre is more nearly the standard of calculation than is that near the
margin, for the gorge constantly tends to enlarge itself below the falls,
and so gradually to bring itself into line with the full-formed channel.
Taking all things into account, Mr. Woodward and the other members of
the Geological Survey thought it not improbable that the average rate
of actual recession in the Horseshoe Fall was as great as five feet per
annum; and that, if we can rely upon the uniformity of the conditions in
the past, seven thousand years is as long a period as can be assigned to
its commencement.
The only condition in the problem about which there can be much chance of
question relates to the constancy of the volume of water flowing in the
Niagara channel. Mr. Gilbert had suggested that, as a consequence of the
subsidence connected with the closing portions of the Glacial period, the
water of the Great Lakes may have been largely diverted from its present
outlet in Niagara River and turned northeastward, through Georgian Bay,
French River, and Lake Nipissing, into a tributary of the Ottawa River,
and so carried into the St. Lawrence below Lake Ontario. Of this theory
there is also much direct evidence. A well-defined shore line of rounded
pebbles extends, at an elevation of about fifty feet, across the col
from Lake Nipissing to the head-waters of the Mattawa, a tributary of
the Ottawa; while at the junction with the Ottawa there is an enormous
delta terrace of boulders, forming a bar across the main stream just such
as would result from Mr. Gilbert's supposed outlet. But this outlet was
doubtless limited to a comparatively few centuries, and Dr. Robert Bell
thinks the evidence still inconclusive.[EB]
[Footnote EB: See Bul. Geol. Soc. Am., vol. iv, pp. 423-427, vol. v, pp.
620-626.]
A second noteworthy glacial chronometer is found in the gorge of
the Mississippi River, extending from the Falls of St. Anthony, at
Minneapolis, to its junction with the preglacial trough of the old
Mississippi, at Fort Snelling, a distance likewise of about seven miles.
Above Fort Snelling the preglacial gorge is occupied by the Minnesota
River, and, as we have before stated, extends to the very sources of
this river, and is continuous with the southern portion of the valley of
the trough of the Red River of the North. Before the Glacial period the
drainage of the present basin of the upper Mississippi joined this main
preglacial valley, not at Fort Snelling, but some little distance above,
as shown upon our map.[EC] This part of the preglacial gorge became
partially filled up with glacial deposits, but it can be still traced
by the lakelets occupying portions of the old depression, and by the
records of wells which have been sunk along the line. When the ice-front
had receded beyond the site of Minneapolis, the only line of drainage
left open for the water was along the course of the present gorge from
Minneapolis to Fort Snelling.
[Footnote EC: See above, p. 209.]
Here, as at Niagara, the problem is comparatively simple. The upper
strata of rock consist of hard limestone, which is underlaid by a soft
sandstone, which, like the underlying shale at Niagara, is eroded faster
than the upper strata, and so a perpendicular fall is maintained. The
strata are so uniform in texture and thickness that, with the present
amount of water in the river, the rate of recession of the falls must
have been, from the beginning, very constant. If, therefore, the rate can
be determined, the problem can be solved with a good degree of confidence.
Fortunately, the first discoverer of the cataract--the Catholic
missionary Hennepin--was an accurate observer, and was given to
recording his observations for the instruction of the outside world and
of future generations. From his description, printed in Amsterdam in
1704, Professor N. H. Winchell is able to determine the precise locality
of the cataract when discovered in 1680.
Again, in 1766 the Catholic missionary Carver visited the falls, and not
only wrote a description, but made a sketch (found in an account of his
travels, published in London in 1788) which confirms the inferences drawn
from Hennepin's narrative. The actual period of recession, however (which
Professor Winchell duly takes into account), extends only to the year
1856, at which time such artificial changes were introduced as to modify
the rate of recession and disturb further calculations. But between 1680
and 1766 the falls had evidently receded about 412 feet. Between 1766 and
1856 the recession had been 600 feet. The average rate is estimated by
Professor Winchell to be about five feet per year, and the total length
of time required for the formation of the gorge above Fort Snelling
is a little less than eight thousand years, or about the same as that
calculated by Messrs. Woodward and Gilbert for the Niagara gorge.
To these calculations of Professor Winchell it does not seem possible
to urge any valid objection. It does not seem credible that the amount
of water in the Mississippi should ever have been less than now, while
during the continuance of the ice in the upper portion of the Mississippi
basin the flow of water was certainly far greater than now.
If any one is inclined to challenge Professor Winchell's interpretation
of the facts, even a hasty visit to the locality will suffice to produce
conviction. The comparative youth of the gorge from Fort Snelling up to
Minneapolis is evident: 1. From its relative narrowness, when compared
with the main valley below. This is represented by the shading upon
the map. The gorge from Fort Snelling up is not old enough to have
permitted much enlargement by the gradual undermining of the superficial
strata on either side, which slowly but constantly goes on. 2. From
the abruptness with which it merges into the preglacial valley of the
Minnesota-Mississippi. The opening at Fort Snelling is not Y-shaped,
as in gorges where there has been indefinite time for the operation of
erosive agencies. 3. Furthermore, the precipices lining the post-glacial
gorge above Fort Snelling are far more abrupt than those in the
preglacial valley below, and they give far less evidence of weathering.
4. Still, again, the tributary streams, like the Minnehaha River, which
empty into the Mississippi between Fort Snelling and Minneapolis,
flow upon the surface, and have eroded gorges of very limited extent;
whereas, below Fort Snelling, the small streams have usually either found
underground access to the river or occupy gorges of indefinite extent.
The above estimates, setting such narrow limits to post-glacial time
in America, will seem surprising only to those who have not carefully
considered the glacial phenomena of various kinds to be observed all
over the glaciated area. As already said, the glaciated portion of
North America is a region of waterfalls, caused by the filling up of
old channels with glacial _débris_, and the consequent diversion of the
water-courses. By this means the streams in countless places have been
forced to fall over precipices, and to begin anew their work of erosion.
Waterfalls abound in the glaciated region because post-glacial time is
so short. Give these streams time enough, and they will wear their way
back to their sources, as the preglacial streams had done over the same
area, and as similar streams have done outside the glaciated region. Upon
close observation, it will be found that the waterfalls in America are
nearly all post-glacial, and that their work of erosion has been confined
to a very limited time. A fair example is to be seen at Elyria, Ohio,
in the falls of Black River, one of the small streams which empty into
Lake Erie from the south. Its post-glacial gorge, worn in sandstone which
overlies soft shale, is only about two thousand feet in length, and it
has as yet made no approach toward a V-shaped outlet.
The same impression of recent age is made by examining the outlets of
almost any of the lakes which dot the glaciated area. The very reason of
the continued existence of these lakes is that they have not had time
enough to lower their outlets sufficiently to drain the water off, as has
been done in all the unglaciated region. In many cases it is easy to see
that the time during which this process of lowering the outlets has been
going on cannot have been many thousand years.
The same impression is made upon studying the evidences of post-glacial
valley erosion. Ordinary streams constantly enlarge their troughs by
impinging against the banks now upon one side and now upon the other, and
transporting the material towards the sea. It is estimated by Wallace
that nine-tenths of the sedimentary material borne along by rivers is
gathered from the immediate vicinity of its current, and goes to enlarge
the trough of the stream. Upon measuring the cubical contents of many
eroded troughs of streams in the glaciated region, and applying the
tables giving the average amount of annual transportation of sediment
by streams, we arrive at nearly the same results as by the study of the
recession of post-glacial waterfalls.
Professor L. E. Hicks, of Granville, Ohio, has published the results
of careful calculations made by him, concerning the valley of Raccoon
Creek in Licking County, Ohio.[ED] These show that fifteen thousand
years would be more than abundant time for the erosion of the immediate
valley adjoining that small stream. I have made and published similar
calculations concerning Plum Creek, at Oberlin, in Lorain County,
Ohio.[EE] Like Raccoon Creek, this has its entire bed in glacial
deposits, and has had nothing else to do since its birth but to enlarge
its borders. The drainage basin of the creek covers an area of about
twenty-five square miles. Its main trough averages about twenty feet in
depth by five hundred in width, along a distance of about ten miles. From
the rate at which the stream is transporting sediment, it is incredible
that it could have been at work at this process more than ten thousand
years without producing greater results.
[Footnote ED: See Baptist Quarterly for July. 1884.]
[Footnote EE: See Ice Age in North America, p. 469.]
Calculations based upon the amount of sediment deposited since the
retreat of the ice-sheet point to a like moderate conclusion. When one
looks upon the turbid water of a raging stream in time of flood, and
considers that all the sediment borne along will soon settle down upon
the bottom of the lake into which the stream empties, he can but feel
surprised that the "wash" of the hills has not already filled up the
depression of the lake. It certainly would have done so had the present
condition of things existed for an indefinite period of time.
Naturally, while prosecuting the survey of the superficial geology of
Minnesota, Mr. Upham was greatly impressed by the continued existence
of the innumerable lakelets that give such a charm to the scenery of
that State. Every day's investigations added to the evidence that the
lapse of time since the Ice age must have been comparatively brief,
since, otherwise, the rains and streams would have filled these basins
with sediment, and cut outlets low enough to drain them dry, for in many
instances he could see such changes slowly going forward.[EF]
[Footnote EF: Minnesota Geological Report for 1879, p. 73.]
[Illustration: Fig. 107.--Section of kettle-hole near Pomp's Pond,
Andover, Massachusetts (see text). (For general view of the situation,
see Fig. 30, p. 78.)]
Some years ago I myself made a careful estimate of the amount of
deposition and vegetable accumulation which had taken place in a
kettle-hole near Pomp's Pond, in Andover, Mass. The diameter of the
depression at the rim was 276 feet. The inclination of the sides was
such that the extreme depression of the apex of the inverted cone could
not have been more than seventy feet; yet the accumulation of peat and
sediment only amounted to a depth of seventeen feet. The total amount of
material which had accumulated would be represented by a cone ninety-six
feet in diameter at the base and seventeen feet at the apex, which would
equal only a deposit of about five feet over the present surface of the
bottom. It is easy to see that ten thousand years is a liberal allowance
of time for the accumulation of five feet of sediment in the bottom
of an enclosure like a kettle-hole, for upon examination it is clear
that whatever insoluble material gets into a kettle-hole must remain
there, since there is no possible way by which it can get out. Now five
feet is sixty inches, and if this amount has been six thousand years
in accumulating, that would represent a rate of an inch in one hundred
years, while, if it has been twelve thousand years in accumulation, the
rate will be only one two-hundredth of an inch per year, a film so small
as to be almost inappreciable. If we may judge from appearance, the
result would not be much different in the case of the tens of thousands
of kettle-holes and lakelets which dot the surface of the glaciated
region.
In the year 1869 Dr. E. Andrews, of Chicago, made an important series of
calculations concerning the rate at which the waters of Lake Michigan are
eating into the shores and washing the sediment into deeper water or
towards the southern end of the lake. With reference to the erosion of
the shores, it appears from the work of the United States Coast Survey
that a shoulder, covered with sixty feet of water, representing the
depth at which wave-action is efficient in erosion, extends outward from
the west shore a distance of about three miles, where the sounding line
reveals the shore of the deeper original lake as it appeared upon the
first withdrawal of the ice.
From a variety of observations the average rate at which the erosion of
the bluffs is proceeding is found to be such that the post-glacial time
cannot be more than ten thousand years, and probably not more than seven
thousand.
An independent mode of calculating this period is afforded by the
accumulations of sand at the south end of the lake, to which it is
constantly drifting by the currents of water propelled against the shores
by the wind; for the body of water in the lake is moving southward
along the shores towards the closed end in that direction, there being
a returning current along the middle of the lake. All the railroads
approaching Chicago from the east pass through these sand deposits, and
few of the observant travellers passing over the routes can have failed
to notice the dunes into which the sand has been drifted by the wind.
Now, all the material of these dunes and sand-beaches has been washed out
of the bluffs to the northward by the process already mentioned, and has
been slowly transferred by wave-action to its present position. It is
estimated that south of Chicago and Grand Haven, this wave-transported
sand amounts to 3,407,451,000 cubic yards. This occupies a belt curving
around the south end about ten miles wide and one hundred miles long.
The rate at which the sand is moving southward along the shore is found
by observing the amount annually arrested by the piers at Chicago, Grand
Haven, and Michigan City. This equals 129,000 cubic yards for a year,
which can scarcely be more than one quarter or one fifth of the total
amount in motion. At this rate, the sand accumulations at the southern
end of the lake would have been produced in a little less than seven
thousand years.
"If," says Dr. Andrews, "we estimate the total annual sand-drift at
only twice the amount actually stopped by the very imperfect piers
built--which, in the opinion of the engineers, is setting it far too
low--and compare it with the capacity of the clay-basin of Lake Michigan,
we shall find that, had this process continued one hundred thousand years
the whole south end of Lake Michigan, up to the line connecting Chicago
and Michigan City, would have been full and converted into dry land
twenty-five thousand years ago, and the coast-line would now be found
many miles north of Chicago."[EG]
[Footnote EG: Southall's Recent Origin of Man, p. 502.]
It is proper to add a word in answer co an objection which may arise
in the reader's mind, for it will doubtless occur to some to ask why
this sand which is washed out by the waves from the bluffs is not
carried inward towards the deeper portion of the trough of the lake,
thus producing a waste which would partly counteract the forces of
accumulation at the south end. The answer is found in the fact that the
south end of Lake Michigan is closed, and that the currents set in motion
by the wind are such that there is no off-shore motion sufficient to move
sand, and, as a matter of fact, dredgings show that the sand is limited
to the vicinity of the shore.
By comparing the eroded cliffs upon Michigan and the other Great Lakes
with what occurs in similar situations about the glacial Lake Agassiz, we
obtain an interesting means of estimating the comparative length of time
occupied by the ice-front in receding from the Canadian border to Hudson
Bay.
As we have seen, Lake Agassiz occupied a position quite similar in most
respects to Lake Michigan. Its longest diameter was north and south, and
the same forces which have eroded the cliffs of Lake Michigan and piled
up sand-dunes at its southern end would have produced similar effects
upon the shores of Lake Agassiz, had its continuance been anywhere near
as long as that of the present Lake Michigan has been. But, according
to Mr. Upham, who has most carefully surveyed the whole region, there
are nowhere on the shores of the old Lake Agassiz any evidence of eroded
cliffs at all to be compared with those found upon the present Great
Lakes, while there is almost an entire lack of sand deposits about the
south end such as characterise the shore of Lake Michigan. "The great
tracts of dunes about the south end of Lake Michigan belong," as Upham
well observes, "wholly to beach accumulations, being sand derived from
erosion of the western and eastern shores of the lake.... But none of
the beaches of our glacial lakes are large enough to make dunes like
those on Lake Michigan, though the size and depth of Lake Agassiz, its
great extent from north to south, and the character of its shores, seem
equally favorable for their accumulation. It is thus again indicated that
the time occupied by the recession of the ice-sheet was comparatively
brief."[EH]
[Footnote EH: Proceedings of the Boston Society of Natural History,
vol. xxiv, p. 454; Upham's Glacial Lakes in Canada, in Bulletin of the
Geological Society of America, vol. ii, p. 248.]
From Mr. Upham's conclusions it would seem that if ten thousand years
be allowed for the post-glacial existence of Lake Michigan, one tenth
of that period would be more than sufficient to account for the cliffs,
deltas, beaches, and other analogous phenomena about Lake Agassiz. In
other words, the duration of Lake Agassiz could not have been more
than a thousand years, which gives us a measure of the rate at which
the recession of the ice-front went on after it had withdrawn to the
international boundary. The distance from there to the mouth of Nelson
River is about 600 miles. The recession of the ice-front over that area
proceeded, therefore, at the average rate of about half a mile per year.
There are many evidences that the main period of glaciation west of the
Rocky Mountains was considerably later than that in the eastern part of
the continent. A portion of the facts pointing to this conclusion have
been well stated by Mr. George F. Becker, of the United States Geological
Survey.
"No one," he says, "who has examined the glaciated regions of the
Sierra can doubt that the great mass of the ice disappeared at a very
recent period. The immense areas of polished surfaces fully exposed
to the severe climate of say from 7,000 to 12,000 feet altitude, the
insensible erosion of streams running over glaciated rocks, and the
freshness of erratic boulders are sufficient evidence of this. There
is also evidence that the glaciation began at no very distant geologic
date. As Professor Whitney pointed out, glaciation is the last important
geological phenomenon and succeeded the great lava flows. There is also
much evidence that erosion has been trifling since the commencement of
glaciation, excepting under peculiar circumstances. East of the range,
for example, at Virginia City, andesites which there is every reason to
suppose preglacial have scarcely suffered at all from erosion, so that
depressions down which water runs at every shower are not yet marked with
water-courses, while older rocks, even of Tertiary age and close by,
are deeply carved. The rainfall at Virginia City is, to be sure, only
about ten inches, so that rock would erode only say one third as fast
as on the California coast; but even when full allowance is made for
this difference, it is clear that these andesites must be much younger
than the commencement of glaciation in the northeastern portion of the
continent as usually estimated. So, too, the andesites near Clear Lake,
in California, though beyond a doubt preglacial, have suffered little
erosion, and one of the masses, Mount Konocti (or Uncle Sam), has nearly
as characteristic a volcanic form as Mount Vesuvius."[EI]
[Footnote EI: Bulletin of the Geological Society of America, vol. ii, pp.
196, 197.]
This view of Mr. Becker is amply sustained by many other obvious facts,
some of which may be easily observed by tourists who visit the Yosemite
Park. The freedom of the abutting walls of this cañon from talus, as well
as the freshness of the glacial scratches upon both the walls and the
floor of the tributary cañons, all indicate a lapse of centuries only,
rather than of thousands of years, since their occupation by glacial ice.
The freshness of the high-level terraces surrounding the valleys of Great
Salt Lake, in Utah, and of Pyramid and North Carson Lakes, in Nevada, and
the small amount of erosion which has taken place since the formation of
these terraces, point in the same direction--namely, to a very recent
date for the glaciation of the Pacific coast.
We have already detailed the facts concerning the formation of these
terraces and the evidence of their probable connection with the Glacial
period. It is sufficient, therefore, here to add that, according to Mr.
Russell and Mr. Gilbert (two of the most eminent members of the United
States Geological Survey, who have each published monographs minutely
embodying the results of their extensive observations in this region),
the erosion of present streams in the beds which were deposited during
the enlargement of the lakes is very slight, and the modification of the
shores since the formation of the high terraces has been insignificant.
According to Mr. Gilbert: "The Bonneville shores are almost unmodified.
Intersecting streams, it is true, have scored them and interrupted their
continuity for brief spaces; but the beating of the rain has hardly
left a trace. The sea-cliffs still stand as they first stood, except
that frost has wrought upon their faces so as to crumble away a portion
and make a low talus at the base. The embankments and beaches and bars
are almost as perfect as though the lake had left them yesterday, and
many of them rival in the symmetry and perfection of their contours the
most elaborate work of the engineer. There are places where boulders of
quartzite or other enduring rock still retain the smooth, glistening
surfaces which the waves scoured upon them by clashing against them the
sands of the beach.
"When this preservation is compared with that of the lowest Tertiary
rocks of the region--the Pliocene beds to which King has given the name
Humboldt--the difference is most impressive. The Pliocene shore-lines
have disappeared.
"The deposits are so indurated as to serve for building-stone. They have
been upturned in many places by the uplifting of mountains. Elsewhere
they have been divided by faults, and the fragments, dissevered from
their continuation in the valley, have been carried high up on the
mountain-flanks, where erosion has carved them in typical mountain
forms.... The date of the Bonneville flood is the geologic yesterday,
and, calling it yesterday, we may without exaggeration refer the Pliocene
of Utah to the last decade; the Eocene of the Colorado basin to the last
century, and relegate the laying of the Potsdam sandstone to prehistoric
times."[EJ]
[Footnote EJ: Second Annual Report of the United States Geological
Survey, p. 188.]
Mr. Russell adds to this class of evidence that of the small extent to
which the glacial striæ have been effaced since the withdrawal of the
ice from the borders of these old lakes: "The smooth surfaces are still
scored with fine, hair-like lines, and the eye fails to detect more
than a trace of disintegration that has taken place since the surfaces
received their polish and striation.... It seems reasonable to conclude
that in a severe climate like that of the high Sierra it" (the polish)
"could not remain unimpaired for more than a few centuries at the
most."[EK]
[Footnote EK: See also Mr. Upham in American Journal of Science, vol.
xli, pp. 41, 51.]
Europe does not seem to furnish so favourable opportunities as America
for estimating the date of the Glacial period; still it is not altogether
wanting in data bearing upon the subject.
Some of the caves in which palæolithic implements were found associated
with the bones of extinct animals in southern England contain floors
of stalagmite which have been thought by some to furnish a measure of
the time separating the deposits underneath from those above. This is
specially true in the case of Kent's Cavern, near Torquay, which contains
two floors of stalagmite, the upper one almost continuous and varying in
thickness from sixteen inches to five feet, the lower one being in places
twelve feet thick, underneath which human implements were found.
But it is difficult to determine the rate at which stalagmite
accumulates. As is well known, this deposit is a form of carbonate of
lime, and accumulates when water holding the substance in solution drops
down upon the surface, where it is partially evaporated. It then leaves a
thin film of the substance upon the floor. The rate of the accumulation
will depend upon both the degree to which the water is saturated with the
carbonate and upon the quantity of the water which percolates through the
roof of the cavern. These factors are so variable, and so dependent upon
unknown conditions in the past, that it is very difficult to estimate the
result for any long period of time. Occasionally a quarter of an inch of
stalagmite accretion has been known to take place in a cavern in a single
year, while in Kent's Cavern, over a visitor's name inscribed in the
year 1688, a film of stalagmite only a twentieth of an inch in thickness
has accumulated. If, therefore, we could reckon upon a uniformity of
conditions stretching indefinitely back into the past, we could determine
the age of these oldest remains of man in Kent's Hole by a simple sum in
arithmetic, and should infer that the upper layer of stalagmite required
240,000 years, and the lower 576,000 years, for their growth, which would
carry us back more than 700,000 years, and some have not hesitated to
affix as early a date as this to these lowest implement-bearing gravels.
But other portions of the cave show an actual rate of accretion very much
larger. Six inches of stalagmite is there found overlying some remains of
Romano-Saxon times which cannot be more than 2,000 years old. Assuming
this as the uniform rate, the total time required for the deposit of the
stalagmitic floors would still be about 70,000 years. But, as we have
seen, the present rates of deposition are probably considerably less than
those which took place during the moister climate of the Glacial epoch.
Still, even by supposing the rate to be increased fourfold, the age of
this lower stratum would be reduced to only 12,000 years. So that, as Mr.
James Geikie well maintains, "Even on the most extravagant assumption as
to the former rate of stalagmitic accretion, we shall yet be compelled
to admit a period of many thousands of years for the formation of the
stalagmitic pavements in Kent's Cavern."[EL] We should add, however,
that there is much well-founded doubt whether the implements found
in the lowest stratum were really in place, since, according to Dr.
Evans, "Owing to previous excavations and to the presence of burrowing
animals, the remains from above and below the stalagmite have become
intermingled."[EM]
[Footnote EL: Prehistoric Europe, p. 83.]
[Footnote EM: Stone and Flint Implements, p. 446.]
An attempt was made by M. Morlot in Switzerland to obtain the chronology
of the Glacial period by studying the deltas of the streams descending
the glaciated valleys. He paid special attention to that of the Tinière,
a stream which flows into Lake Geneva near Villeneuve. The modern delta
of this stream consists of gravel and sand deposited in the shape of a
flattened cone, and investigations upon it were facilitated by a long
railroad cutting through it. "Three layers of vegetable soil, each of
which must at one time have formed the surface of the cone, have been
cut through at different depths."[EN] In the upper stratum Roman tiles
and a coin were found; in the second stratum, unvarnished pottery and
implements of bronze; while in the lower stratum, at a depth of nineteen
feet from the surface, a human skull was found, to which Morlot assigned
an age of from 5,000 to 7,000 years.
[Footnote EN: Lyell's Antiquity of Man, p. 28.]
But Dr. Andrews, after carefully revising the data, felt confident that
the time required for the whole deposit of this lower delta was not more
than 5,000 years, and that the oldest human remains in it, which were
about half way from between the base and the surface of the cone, were
probably not more than 3,000 years old.
Still, the significance of this estimate principally arises from the
relation of the modern delta to older deltas connected with the Glacial
period. Above this modern delta, formed by the river in its present
proportions, there is another, more ancient, about ten times as large,
whose accumulation doubtless took place upon the final retreat of the
ice from Lake Geneva. No remains of man have been found in this, but it
doubtless corresponds in age with the high-level gravels in the valley
of the Somme, in which the remains of man and the mammoth, together with
other extinct animals, have been found.
We do not see, however, that any very definite calculation can be made
concerning the time required for its deposition. Lyell was inclined to
consider it ten times as old as the modern delta, simply upon the ground
of its being ten times as large. On Morlot's estimate of the age of the
modern delta, therefore, the retreat of the ice whose melting torrents
deposited the upper delta would be fixed at 100,000 years ago, and upon
Dr. Andrews's calculation, at about 20,000.
But it is evident that the problem is not one of simple multiplication.
The floods of water which accompanied the melting back of the ice from
the upper portions of this valley must have been immensely larger than
those of the present streams, and their transporting power immensely
greater still. Hence we do not see that any conclusions can be drawn from
the deltas of the Tinière to give countenance to extreme views concerning
the date of the close of the Glacial period.[EO]
[Footnote EO: Lyell's Antiquity of Man, p. 321.]
In the valley of the Somme the chronological data relating to the Glacial
period, and indicating a great antiquity for man, have been thought to
be more distinct than anywhere else in Europe. As already stated, it
is the prevalent opinion that since man first entered the valley, in
connection with the mammoth and the other extinct animals characteristic
of the Glacial period, the trough of the Somme, about a mile in width and
a hundred feet in depth, has been eroded by the drainage of its present
valley. An extensive accumulation of peat also has taken place along the
bottom of the trough of the river since it was originally eroded to its
present level. This substance occurs all along the bottom of the valley
from far above Amiens to the sea, and is in some places more than thirty
feet in depth. The animal and vegetable remains in it all belong to
species now inhabiting Europe.
The depth of the peat indicates that when it was formed the land stood
at a slightly higher elevation than now, for the base of the stratum is
now below the sea-level, while the peat is of fresh-water origin, and,
according to Dr. Andrews,[EP] is formed from the vegetable accumulations
connected with forest growths. When, therefore, the country was covered
with forests, as it was in prehistoric times, the accumulation must have
proceeded with considerable rapidity. This inference is confirmed by the
occurrence in the peat of prostrate trunks of oak, four feet in diameter,
so sound that they were manufactured into furniture. The stumps of trees,
especially of the birch and alder, were also found in considerable
number, standing erect where they grew, sometimes to a height of three
feet. Now, as Dr. Andrews well remarks, it is evident that, in order
to prevent these stumps and prostrate trunks from complete decay, the
accumulation of peat must have been rapid. From certain Roman remains
found six feet and more beneath the surface, he estimates that the
accumulation since the Roman occupation has been as much as six inches a
century, at which rate the whole would take place in somewhat over 5,000
years.
[Footnote EP: American Journal of Science, October, 1868.]
Still, if we accept this estimate, we have obtained but a starting-point
from which to estimate the age of the high-level gravels in which
palæolithic implements were found; for, if we accept the ordinary theory,
we must add to this the time required for the river to lower its bed from
eighty to a hundred feet, and to carry out to the sea the contents of
its wide trough. But, as already shown, the Glacial period was, even in
the north of France, a time of great precipitation and of a considerable
degree of cold, when ice formed to a much greater extent than now upon
the surface of the Somme. The direct evidence of this consists in the
boulders mingled with the high-level gravel which are of such size as to
require floating ice for their transportation.
In addition to the natural increase in the eroding power of the Somme
brought about by the increase in its volume, on account of the greater
precipitation in the Glacial age, there would also be, as Prestwich has
well shown, a great increase in rate through the action of ground-ice,
which plays a very important part in the river erosion of arctic
countries, and in all probability did so during the Glacial period in the
valley of the Somme.
"When the water is reduced to and below 32° Fahr., although the rapid
motion may prevent freezing on the surface for a time, any pointed
surfaces at the bottom of the river, such as stones and boulders, will
determine (as is the case with a saturated saline solution) a sort of
crystallisation, needles of ice being formed, which gradually extend from
stone to stone and envelop the bodies with which they are in contact. By
this means the whole surface of a gravelly river-bed may become coated
with ice, which, on a change of temperature, or of atmospheric pressure,
or on acquiring certain dimensions and buoyancy, rises to the surface,
bringing with it the loose materials to which it adhered. Colonel Jackson
remarks, in speaking of this bottom-ice, that 'it frequently happens that
these pieces, in rising from the bottom, bring up with them sand and
stones, which are thus transported by the current.... When the thaw sets
in the ice, becoming rotten, lets fall the gravel and stones in places
far distant from those whence they came.'
"Again, Baron Wrangell remarks that, 'in all the more rapid and rocky
streams of this district [northern Siberia] the formation of ice takes
place in two different manners; a thin crust spreads itself along the
banks and over the smaller bays where the current is least rapid; but the
greater part is formed in the bed of the river, in the hollows among the
stones, where the weeds give it the appearance of a greenish mud. As soon
as a piece of ice of this kind attains a certain size, it is detached
from the ground and raised to the surface by the greater specific gravity
of the water; these masses, containing a quantity of gravel and weeds,
unite and consolidate, and in a few hours the river becomes passable
in sledges instead of in boats.' Similar observations have been made
in America; but instances need not be multiplied, as it is a common
phenomenon in all arctic countries, and is not uncommon on a small scale
even in our latitudes.
"The two causes combined--torrential river-floods and rafts of
ground-ice, together with the rapid wear of the river cliffs by
frost--constituted elements of destruction and erosion of which our
present rivers can give a very inadequate conception; and the excavations
of the valleys must have proceeded with a rapidity with which the present
rate of erosion cannot be compared; and estimates of time founded on
this, like those before mentioned on surface denudation, are therefore
not to be relied upon."[EQ]
[Footnote EQ: Prestwich's Geology, vol. ii, pp. 471, 472.]
Speaking a little later of taking the present rates of river erosion as a
standard to estimate the chronology of the Glacial period, the same high
authority remarks: "It no more affords a true and sufficient guide than
it would be to take the tottering paces and weakened force of an old man
as the measure of what that individual was, and what he could do, in his
robust and active youth. It may be right to take the effects at present
produced by a given power as the known quantity, a, but it is equally
indispensable, in all calculations relative to the degree of those
forces in past times, to take notice of the unknown quantity, x, although
this, in the absence of actual experience, which cannot be had, can only
be estimated by the results and by a knowledge of the contemporaneous
physical conditions. It may be a complicated equation, but it is not to
be avoided.[ER]
[Footnote ER: Prestwich's Geology, vol. ii, pp. 520, 521.]
"In this country and in the north of France broad valleys have been
excavated to the depth of from about eighty to a hundred and fifty feet
in glacial and post-glacial times. Difficult as it is by our present
experience to conceive this to have been effected in a comparatively
short geological term, it is equally, and to my mind more, difficult to
suppose that man could have existed eighty thousand years or more, and
that existing forms of our fauna and flora should have survived during
two hundred and forty thousand years without modification or change."[ES]
[Footnote ES: Ibid., p. 533.]
The discussion of the age of the high-level river gravels of the Somme
and other streams in northwestern Europe is not complete, however,
without considering another possibility as to the mode of their
deposition. The conclusion to which Mr. Alfred Tylor arrived, after a
prolonged and careful study of the subject, was that the main valleys of
the Somme and other streams in northern France and southern England were
preglacial in their origin, and that the accumulations of gravel at high
levels along their margin were due to enormous floods which characterised
the closing portion of the great ice age, which he denominated the
pluvial period.[ET] The credibility of floods large enough to accomplish
the results manifest in the valley of the Somme is supported by reference
to a flood which occurred on the Mulleer River, in India, in 1856, when
a stream, which is usually insignificant, was so swollen by a rainfall
of a single day that it rose high enough to sweep away an iron bridge the
bottoms of whose girders were sixty-five feet above high-water mark. One
iron girder weighing eighty tons was carried two miles down the river,
and nearly buried in sand. The significance of these facts is enhanced
by observing also that for fifteen miles above the bridge the fall of
the river only averaged ten feet per mile. Floods to this extent are
not uncommon in India. During the Glacial period spring freshets, must
have been greatly increased by the melting of a large amount of snow and
ice which had accumulated during the winter, and also by the formation
of ice-gorges near the mouths of many of the streams. It is probable,
also, that the accumulation of ice across the northern part of the German
Ocean may have permanently flooded the streams entering that body of
water; for it is by no means improbable that there was a land connection
between England and France across the Straits of Dover until after the
climax of the Glacial period. In support of his theory, Mr. Tylor points
to the fact "that the gravel in the valley of the Somme at Amiens is
partly derived from _débris_ brought down by the river Somme and by the
two rivers the Celle and the Arve, and partly consists of material from
the adjoining higher grounds washed in by land floods," and that the
"Quaternary gravels of the Somme are not separated into two divisions by
an escarpment of chalk parallel to the river," but "thin out gradually as
they slope from the high land down to the Somme."
Mr. Tylor's reasoning seems especially cogent to one who stands on the
ground where he can observe the size of the valley and the diminutive
proportions of the present stream. Even if we do not grant all that is
claimed by Mr. Tylor, it is difficult to resist the main force of his
argument, and to avoid the conclusion that the valley of the Somme is
largely the work of preglacial erosion, and has been, at any rate, only
in slight degree deepened and enlarged during post-Tertiary time.
[Footnote ET: Proceedings of the Geological Society, London, November 8,
1867, pp. 103-126: Quarterly Journal of the Geological Society, February
1, 1869, pp. 57-100.]
Summary.
In briefly summarising our conclusions concerning the question of man's
antiquity as affected by his known relations to the Glacial period, it is
important, first, to remark upon the changes of opinion which have taken
place with respect to geological time within the past generation. Under
the sway of Sir Charles Lyell's uniformitarian ideas, geologists felt
themselves at liberty to regard geological time as practically unlimited,
and did not hesitate to refer the origin of life upon the globe back to
a period of 500,000,000 years. In the first edition of his Origin of
Species Charles Darwin estimated that the time required for the erosion
of the Wealden deposits in England was 306,662,400 years, which he spoke
of as "a mere trifle" of that at command for establishing his theory of
the origin of species through natural selection. In his second edition,
however, he confesses that his original statement concerning the length
of geological time was rash; while in later editions he quietly omitted
it.
Meanwhile astronomers and physicists have been gradually setting limits
to geological time until they have now reached conclusions strikingly
in contrast with those held by the mass of English geologists forty
years ago. Mr. George H. Darwin, Professor of Mathematics at Cambridge
University, has from a series of intricate calculations shown that
between fifty and one hundred million years ago the earth was revolving
from six to eight times faster than now, and that the moon then almost
touched the earth, and revolved about it once every three or four hours.
From this proximity of the moon to the earth, it would result that if the
oceans had been then in existence the tides would have been two hundred
times as great as now, creating a wave six hundred feet in height,
which would sweep around the world every four hours. Such a condition
of things would evidently be incompatible with geological life, and
geology must limit itself to a period which is inside of 100,000,000
years. Sir William Thomson and Professor Tait, of Great Britain, and
Professor Newcomb, of the United States Naval Observatory, approaching
the question from another point of view, seem to demonstrate that the
radiation of heat from the sun is diminishing at a rate such that ten
or twelve million years ago it must have been so hot upon the earth's
surface as to vaporise all the water, and thus render impossible the
beginning of geological life until later than that period. Indeed, they
seem to prove by rigorous mathematical calculations that the total amount
of heat originally possessed by the nebula out of which the sun has been
condensed would only be sufficient to keep up the present amount of
radiation for 18,000,000 years.
The late Dr. Croll, feeling the force of these astronomical conclusions,
thought it possible to add sufficiently to the sun's heat to extend its
rule backwards approximately 100,000,000 years by the supposition of a
collision with it of another moving body of near its own size. Professor
Young and others have thought that possibly the heat of the sun might
have been kept up by the aid of the impact of asteroids and meteorites
for a period of 30,000,000 years. Mr. Wallace obtains similar figures by
estimating the time required for the deposition of the stratified rocks
open to examination upon the land surface of the globe. As a result of
his estimates, it would appear that 28,000,000 years is all the time
required for the formation of the geological strata. From all this it is
evident that geologists are much more restricted in their speculations
involving time than they thought themselves to be a half-century ago.
Taking as our standard the medium results attained by Wallace, we shall
find it profitable to see how this time can be portioned out to the
geological periods, that we may ascertain how much approximately can be
left for the Glacial epoch.
On all hands it is agreed that the geological periods decrease in length
as they approach the present time. According to Dana's estimates,[EU]
the "ratio for the Palæozoic, Mesozoic, and Cenozoic periods would be
12:3:1"--that is, Cenozoic time is but one sixteenth of the whole.
This embraces the whole of the Tertiary period, during which placental
mammals have been in existence, together with the post-Tertiary or
Glacial period, extending down to the present time; that is, the time
since the beginning of the Tertiary period and the existence of the
higher animals is considerably less than two million years, even upon Mr.
Wallace's basis of calculation. But if we should be compelled to accept
the calculations of Sir William Thomson, Professor Tait, and Professor
Newcomb, the Cenozoic period would be reduced to considerably less than
one million years. It is difficult to tell how much of Cenozoic time is
to be assigned to the Glacial period, since there is, in fact, no sharply
drawn line between the two periods. The climax of the Glacial period
represented a condition of things slowly attained by the changes of level
which took place during the latter part of the Tertiary epoch.
[Footnote EU: See revised edition of his Geology, p. 586.]
In order to estimate the degree of credibility with which we may at
the outset regard the theory of Mr. Prestwich and others, that all the
phenomena of the Glacial period can be brought within the limits of
thirty or forty thousand years, it is important to fix our minds upon
the significance of the large numbers with which we are accustomed to
multiply and divide geological quantities.[EV]
[Footnote EV: See Croll's Climate and Time, chap. xx.]
Few people realise either the rapidity with which geological changes
are now proceeding or the small amount of change which might produce a
Glacial period, and fewer still have an adequate conception of how long a
period a million years is, and how much present geological agencies would
accomplish in that time. At the present rate at which erosive agencies
are now acting upon the Alps, their dimensions would be reduced one half
in a million years. At the present rate of the recession of the Falls of
St. Anthony, the whole gorge from St. Louis to Minneapolis would have
been produced in a million years. A river lowering its bed a foot in a
thousand years would produce a cañon a thousand feet deep in a million
years.
If we suppose the Glacial period to have been brought about by an
elevation of land in northern America and northern Europe, proceeding at
the rate of three feet a century, which is that now taking place in some
portions of Scandinavia, this would amount to three thousand feet in one
hundred thousand years, and that is probably all, and even more than all,
which is needed. One hundred thousand years, therefore, or even less,
might easily include both the slow coming on of the Glacial period and
its rapid close. Prestwich estimates that the ice now floating away from
Greenland as icebergs is sufficient if accumulating on a land-surface
to extend the borders of a continental glacier about four hundred and
fifty feet a year, or one mile in twelve years, one hundred miles in
twelve hundred years, and seven hundred miles (about the limit of glacial
transportation in America) in less than ten thousand years.
After making all reasonable allowances, therefore, Prestwich's conclusion
that twenty-five thousand years is ample time to allow to the reign
of the ice of the Glacial period cannot be regarded as by any means
incredible or, on _a priori_ grounds, improbable.
APPENDIX.
THE TERTIARY MAN.
By Professor Henry W. Haynes.
"It must not be imagined that it is in any way proved that the
Palæolithic man was the first human being that existed. We must be
prepared to wait, however, for further and better authenticated
discoveries before carrying his existence back in time further than
the Pleistocene or post-Tertiary period."[EW] This was the position
assumed more than twelve years ago by the eminent English geologist
and archæologist, Dr. John Evans, and it was still maintained in his
address before the Anthropological Section of the British Association on
September 18, 1890. I believe that the study of all the evidence in favor
of the existence of the Tertiary man that has been brought forward down
to the present time will leave the question in precisely the same state
of uncertainty.
[Footnote EW: _A Few Words on Tertiary Man_, Trans, of Hertfordshire Nat.
Hist. Soc, vol. i, p. 150.]
"In order to establish the existence of man at such a remote period the
proofs must be convincing. It must be shown, first, that the objects
found are of human workmanship; secondly, that they are really found as
stated; and, thirdly, the age of the beds in which they are found must be
clearly ascertained and determined."[EX] These tests I propose to apply
to the evidence for the Tertiary man recently brought forward in Europe,
and then to consider the significance of certain discoveries on the
Pacific coast of our own continent.
[Footnote EX: Ibid., p. 148.]
Tertiary deposits in Europe are alleged to have supplied three sorts of
evidence of this fact: _First_, the bones of man himself; _second_, bones
of animals showing incisions or fractures supposed to have been produced
by human agency; _third_, chipped flints believed to exhibit marks of
design in their production.
A very complete survey of the question of the antiquity of man was
published in 1883 by M. Gabriel de Mortillet, one of its most eminent
investigators, under the title of Le Préhistorique. In that work he
subjected to a most rigid examination all the evidence for Tertiary man,
coming under either of these three heads, that had been brought forward
up to that date.
The instances of the discovery of human bones in Europe were two--at
Colle del Vento, in Savona, and Castenedolo, near Brescia, both in Italy.
At the former site, in a Pliocene marine deposit abounding in fossil
oysters and containing some _scattered_ bones of fossil mammals, a human
skeleton was found _with the bones lying in their natural connection_.
Mortillet, however, and many others regard this as an instance of a
subsequent interment rather than as proof that the man lived in Pliocene
times.[EY] At Castenedolo, in a similar marine Pliocene formation, on
three different occasions human skeletons have been discovered, but
in different strata. One investigator has accounted for these as the
result of a shipwreck in the Pliocene period. This bold hypothesis not
only requires that man should have been sufficiently advanced at that
very remote period to have navigated the sea, but it calls for two
shipwrecks, at different times, at the same point. It has, however, since
been abandoned by its author in favor of the presumption of subsequent
interments, as in the previous instance.[EZ]
[Footnote EY: This is also the opinion of Hamy, _Précis de Paléontologie
Humaine_, p. 67. Professor Le Conte, _Elements of Geology_ (third
edition, 1891), p. 609, is wrong in attributing the opposite conclusion
to Hamy, on the evidence of "flint implements found in this locality."]
[Footnote EZ: Bullettino di Paletnologia Italiana, tome xv, p. 109
(August 18, 1889).]
Animal bones showing cuts or breaks supposed to be the work of man have
been found in seventeen different localities in Europe. They can all,
however, be accounted for as the result of natural movements or pressure
of the soil acting in connection with sharp substances, like fractured
flints, or else as having been made by the teeth of sharks, whose fossil
remains are found in great abundance in the same formation.
All the discoveries of flints supposed to show traces of intentional
chipping are pronounced to be unsatisfactory, with the exception of
those found in three localities--Thenay (near Tours) and Puy-Courny
(near Aurillac), in France, and Otta, in the valley of the Tagus, in
Portugal. As European archæologists at the present time are substantially
in accord with Mortillet in restricting the discussion to these three
places, I will follow their example. But although Mortillet believes
that flints found at all these localities exhibit marks of intelligent
action, he will not admit that they are the work of man. He attributes
them to an intelligent ancestor of man, whom he calls by the name
of anthropopithecus, or the precursor of man. Of this creature he
distinguishes three different species, named respectively after the
discoverers of the flints in the three localities just mentioned. The
precursor, however, has found up to this time only a very limited
acceptance among men of science, although a few believe in him on purely
theoretical grounds. The discussion generally turns upon the question
whether these flints were chipped intentionally or are the result of
natural causes; and also upon the determination of the geological age of
the formations in which they are found.
[Illustration: Fig. 108.--Flint flakes collected by Abbé Bourgeois from
Miocene strata at Thenay (after Gaudry). Natural size.]
I visited Thenay, the most celebrated of these three localities, in 1877,
and had the advantage of studying the question there under the guidance
of the late Abbé Bourgeois, the discoverer of the flints, and one of the
most prominent advocates of the Tertiary man. This was the year before
he died, and he showed me at the time his complete collection, and gave
me several of the objects he had discovered. Geologists are agreed in
assigning the deposits in which they occur to the lower Miocene or middle
Tertiary period, which restricts the discussion to the character of the
flints themselves. The accompanying woodcut[FA] gives some indication
of their appearance, although it is misleading, because the long figure
resembling a flint knife is intended to represent a solid nucleus. None
of these objects, however, ought to be called "flints flakes," as very
few, if any, flakes showing the "bulb of percussion," always seen upon
them, have been discovered in the Tertiary deposits at Thenay,[FB]
although I have found them there myself _upon the surface_. The three
other figures would be classed by archæologists as "piercers," as
Bourgeois has himself designated them, and are also solid objects. Many
of the Thenay flints exhibit a "crackled" appearance, due to the action
of heat. On this account Mortillet maintains that they were splintered
by fire, and not formed by percussion, the usual method by which flint
implements were fabricated in the stone age. The Thenay objects are
all of very small dimensions, and are so absolutely unlike the large,
rudely-chipped axes of the Chellean type, found in so many different
parts of the world, and generally accepted as the implement used by
Palæolithic man, that the question naturally suggests itself, What could
have been the purpose for which these little implements were employed? No
better answer has been suggested than the ludicrous one that they were
used by the hairy anthropopithecus to rid himself of the vermin with
which he was infested.
[Footnote FA: From Le Conte, _op. cit._, p. 608. The figures are copied
from Gaudry, who borrowed them from the article by Bourgeois, _Congrès
Internat. de Bruxelles_, 1872, p. 89, pl. ii; and from his _La Question
de l'Homme Tertiare_. Revue des Questions Scientifiques, 1877, p. 15.]
[Footnote FB: Le Préhistorique, p. 91.]
But, leaving aside the question of their purpose, let us consider
the evidence presented by the flints themselves. Do they exhibit the
unmistakable traces of intentional chipping produced by a series of
slight blows or thrusts, delivered in regular succession and in the
same direction, with the result of forming a distinctly marked edge?
And does the appearance of the action of fire upon their surface imply
the intervention of intelligence? To both questions M. Adrien Arcelin,
the well-known geologist of Mâcon, has given very sufficient replies in
the negative. He has discovered numerous objects of precisely similar
appearance in Eocene deposits in the neighborhood of Mâcon.[FC] But,
instead of pushing man back on this account so much further into the
past, he accounts for the marks of chipping to be seen on many of these
objects as the result of the accidental shocks of one stone against
another in the countless overturnings and movements to which the
strata have been subjected during the long ages of geological time. He
gives photographs of some of these objects, which are to me entirely
convincing, and describes how he has surprised Nature in the very act of
fabricating them in an abandoned quarry worked in an Eocene deposit. He
thinks the "crackled" surfaces can be readily explained as the result
of atmospheric action, or of hot springs charged with silex. Numerous
examples of similar changes in the surface of flint, that have been
noticed by himself and others in different localities, are instanced.
Even if some have been caused by fire, this does not necessarily imply
the intervention of man to have produced it. Similar discoveries have
also been made by M. d'Ault de Mesnil, at Thenay, in Eocene deposits,[FD]
and by M. Paul Cabanne, in the Gironde.[FE] My own opinion, based
upon the experience of many years spent in the study of flints broken
naturally as well as artificially, and upon a careful examination of
Bourgeois's collections, is that the so-called Thenay flints are the
result of natural causes.
[Footnote FC: Matériaux pour l'Histoire Prim, et Nat. de l'Homme, tome
xix, p. 193.]
[Footnote FD: Matériaux, ibid., p. 246.]
[Footnote FE: Id., tome xxii, p. 205.]
The second locality where flints alleged to display marks of human action
have been found is the vicinity of Aurillac, in the Auvergne, especially
on the flanks of a hill called Puy-Courny. They occur in a conglomerate
of the upper Miocene period, and are consequently much later than the
Thenay flints. In this conglomerate, in 1869, M. Tardy discovered a
worked flint flake which has every appearance of being artificial.[FF]
Mortillet, however, says that it was found in the upper surface of the
deposit, where there may easily have been a mingling with the Quaternary
formation; and it certainly resembles worked flakes, which are not
uncommon in the Quaternary. The geological determination of the find may
consequently be regarded as uncertain.
[Footnote FF: See Matériaux, tome vi, p. 94. S. Reinach, however,
_Description Raison. du Musée de Saint-Germain-en-Laye_, i, p. 107, n. 8,
calls it "gravure inexacte."]
The flints discovered at Puy-Courny by M. Barnes are of small dimensions,
and have all been produced by percussion. Many of them are said to
bear some resemblance to pointed flakes of artificial origin, and
one has been figured, probably selected for its excellence.[FG] It is
by no means convincing to me, and I am not at all surprised that so
many archæologists question the artificial character of these objects,
which exhibit a great variety of forms. Upon this point Rames does
not profess to be qualified to pronounce judgment, limiting himself
solely to the geological questions. He argues, however, that the fact
that all the objects supposed to be artificial are made of the best
qualities of flint, of which implements are ordinarily made, although
fragments of inferior quality are abundant in the same formation,
implies the intervention of man's judgment in making the selection.
But M. Boule shows that this is merely the result of the erosion of an
ancient river, which operated only upon the upper beds, in which alone
the better qualities of flint are to be found; and Rames has accepted
this explanation.[FH] The flints of Puy-Courny seem to fall within the
same category as those of Thenay. They are the product of denudation,
have travelled long distances, and have been subjected to the action of
powerful agents. These causes are sufficient to account for the shocks of
which they show the traces, and to explain the production of splinters
arising therefrom.
[Footnote FG: Matériaux, tome xviii, p. 400.]
[Footnote FH: Revue d'Anthropologie (third series), tome iv, p. 217.]
The last locality in which flints claimed to have been manufactured by
the Tertiary man are supposed to have been discovered is the so-called
desert of Otta, in the valley of the Tagus, not far from Lisbon.
The formation there is a lacustrine deposit of great thickness, belonging
to the upper Miocene, and abounding in flint. Here, during the course of
twenty years, M. Ribeiro discovered, but mostly upon the surface, a large
number of flakes of flint and quartzite. After much debate in regard to
them, ninety-five of them were finally sent by him to Paris, in 1878, and
placed in the archæological department of the great exposition. There
they were to be submitted to the judgment of the assembled prehistoric
archæologists of all nationalities, many of whom, including the writer,
availed themselves of the opportunity of carefully studying them. The
judgment of Mortillet is that twenty-two specimens exhibited unmistakable
traces of intentional chipping, in which opinion I entirely concur.
Only nine, however, were represented as coming from the Miocene, some
of which showed on their surface an incrustation of grit, which was
claimed as proof of their origin. But the opinion was freely expressed
that, even if they really came from the Miocene deposits, they might
have penetrated into them from the surface, through cracks, and thus
have become so incrusted. It was accordingly resolved to hold the next
international congress of prehistoric archæologists at Lisbon, in 1880,
mainly for the purpose of settling this question, if possible, by an
investigation conducted upon the spot. In the course of a visit made at
that time to Otta, several artificial specimens were found on the surface
by different searchers, but Professor Bellucci, of Perugia, was fortunate
enough to discover a flint flake _in situ_, still so closely imbedded
in the deposit that it required to be detached by a hammer. There is no
question that this object was actually found in a Miocene deposit, but
unfortunately it belongs to the doubtful category of external flakes,
which, although they exhibit the "bulb of percussion," have no other
sure indication that they are the work of man.[FI] As such bulbs can
be produced by natural causes, some stronger proof than this of the
existence of Tertiary man is demanded.
[Footnote FI: It has been figured by Bellucci, _Archivio per
l'Anthropologia e la Etnologia di Firenze_, tome xi, p. 12, tav. iv, fig.
2. To me it possesses no value as evidence.]
These are all the localities in Europe claimed by Mortillet to have
furnished such evidence, but he thinks a strong confirmation of it
is afforded by certain discoveries made in the auriferous gravels of
California. I will not occupy space here in repeating arguments I have
brought forward elsewhere to show the utter insufficiency of this
evidence to prove the existence of man on the Pacific coast of our
continent during the Pliocene period,[FJ] They may all be summed up in
the words of Le Conte: "The doubts in regard to this extreme antiquity
of man are of three kinds, viz.: 1. Doubts as to the Pliocene age of the
gravels--they may be early Quaternary. 2. Doubts as to the authenticity
of the finds--no scientist having seen any of them in situ. 3. Doubts
as to the undisturbed conditions of the gravels, for auriferous gravels
are especially liable to disturbance. The character of the implements
said to have been found gives peculiar emphasis to this last doubt, _for
they are not Paleolithic_, but Neolithic."[FK] The question has been
raised whether this archæological objection is applicable to the stone
mortars, numerous examples of which have been found in the gravels, some
of them quite recently.[FL] If the evidence brought forward by Professor
Whitney and others were limited to these mortars, it might very well
be claimed that they are neither Palæolithic nor Neolithic; that the
smoothness of their surface is owing to their having been hollowed out of
pebbles that have been polished and worn by natural forces. But Professor
Whitney has cited numberless instances of "spear-heads," "arrow-heads,"
"discoidal stones," "stone beads," and "a hatchet" that have been found
under precisely similar conditions as the mortars. So Mr. Becker has
recently produced an affidavit of a certain Mr. Neale that in a tunnel
run into the gravel in 1877 "between two hundred and three hundred feet
beyond the edge of the solid lava, he saw several spear-heads nearly
one foot in length."[FM] Now it cannot be questioned that such objects
as these clearly belong to the Neolithic period, which does not imply
that all the objects used at that time were polished, but that together
with chipped implements "polished stone implements were also used."[FN]
No archæologist will believe that, while Palæolithic man has not yet
been discovered in the Tertiary deposits of western Europe, the works of
Neolithic man have been found in similar deposits in western America.
Peculiar difficulties seem to surround the evidence brought forward
in support of such an assumption. We are told by Professor Whitney
that a stone mortar was "found standing upright, and the pestle was
in it, in its proper place, just as it had been left by the owner."
He fails, however, to explain how this was brought about in a gravel
deposit supposed to have been laid down by great floods of water. So,
when Mr. Neale swears that he saw fifteen years ago in the same gravels
spear-heads a great deal larger than those known to archæologists, may
we not ask whether reliance can be placed on the memory of witnesses who
testify to impossibilities to justify conclusions that rest upon such
testimony? I think we shall have to wait for further and better evidence
than this before we are called upon to admit that the existence of the
Tertiary man upon our Pacific coast has been established.
[Footnote FJ: _The Prehistoric Archæology of North America_, Narrative
and Critical History of America, vol. i, pp. 850-356.]
[Footnote FK: Le Conte, _op. cit._, p. 614.]
[Footnote FL: Professor George Frederick Wright, _Prehistoric Man on the
Pacific Coast_, Atlantic Monthly, April, 1891, p. 512; _Table Mountain
Archæology_, Nation, May 21, 1891, p. 419.]
[Footnote FM: _Antiquities from under Tuolome Table Mountain in
California_, Bulletin of the Geological Society of America, vol. ii, p.
192.]
[Footnote FN: Le Conte, _op. cit._, p. 607.]
INDEX.
Aar Glacier, 11, 43, 132.
Abbeville, France, 251, 263.
Abbott, C. C, cited, 242, 245.
Adams, Charles Francis, cited, 297.
Adhémar, cited, 307, 310.
Africa, ancient glaciers of, 191.
Agassiz, Louis, cited, 9, 11, 43, 128, 241.
Ailsa Crag, 167, 168.
Akron. Ohio, 220, 221.
Alaska, 1, 22, 23 _et seq._, 47, 212, 283;
climate of, 291, 302.
Aletsch Glacier, 9, 211, 241.
Alleghany Valley, 206, 214;
terraces in, 229.
Alpine glaciers, existing, 9-11, 43 _et seq._;
size and number of, 9;
depth of, 11;
velocity of, 43 _et seq._;
ancient, 58-60, 131-136;
advance and retreat of, 116.
Alps, 1, 9-11, 43 _et seq._, 58 _et seq._, 91, 131 _et seq._, 211;
age of, 328.
Altaville, Cal, 296.
Amazon Valley, temperature of, 316.
Amherst, Ohio, glacial marks near, 52.
Amiens, France, implements from, 252, 263 _et seq._;
terraces at, 360.
Andes, 17, 330;
age of, 328.
Andover, Mass., 77 _et seq._, 345.
Andrews, cited, 345, 347, 354, 356.
Animals, extinct, associated with man in eastern America, 262;
in France, 263;
in England, 264 _et seq._;
in Wales, 272;
in Belgium, 277 _et seq._;
summary concerning, 281-293.
Animals, relics of, in loess, 188.
Antarctic Continent, existing glaciers of, 1, 18 _et seq._
Arcy, Belgium, grotto at, 279.
Arenig Mawr, Wales, 150, 151, 172.
Argillite implement, face and side view of, 247, 259.
Arnhem, Holland, moraine at, 181.
Asia, existing glaciers in, 14 _et seq._;
ancient glaciers of, 190.
Assiniboine River, 228.
Astronomical theories of the Glacial period, 303 _et seq._
Atlantic Ocean, 314.
Aurillac, supposed flint-chips near, 367, 370.
Australia, ancient glaciers of, 126, 192.
Austria, existing glaciers of, 9.
Auvergne, 136.
Babbitt, Miss F. E., cited, 253, 254, 255.
Bakewell on age of Niagara gorge, 337.
Baldwin, C. C, 251.
Baldwin, P., 25.
Ball, cited, 310, 317.
Baltic Sea, 129.
Barnsley, England, 155.
Bates, cited, 204.
Bear, 270, 287, 290.
Bear, grizzly, 270, 288.
Beaver, 289.
Beaver Creek, Pa., 205, 230, 232.
Becker, cited, 296, 300, 349.
Bedford, England, 265.
Beech Flats, Ohio, terrace at, 217.
Belgium, human relics in glacial terraces in, 264;
caverns of, 274.
Bell, cited, 109, 117;
on unity of the Glacial period, 110.
Bellevue, Pa., glacial terrace on the Ohio at, 217.
Bellucci, cited, 372.
Ben Nevis, 240.
Bernese Oberland, 9, 59, 131, 132.
Big Stone Lake, 208, 226.
Birmingham. England, 150.
Bishop, cited. 306.
Bison, 262, 270, 271, 278, 289.
Black Forest, the, 136.
Black River, Ohio, 343.
Black Sea, 238.
Blanc, Mont, 1, 9-11, 132, 211.
Blandford, cited, 312.
Boone County, Ky., glacial deposits in, 212.
Boston, scratched stone from till of, 54;
drumlins in the vicinity of, 75.
Boston Society of Natural History, 296.
Boulder-clay. (See Till.)
Boulders, disintegrated, 57, 71.
Boulders, distribution of, in New-England, 57, 60, 61, 69 _et seq._;
in Switzerland, 58 _et seq._, 133.
Boulders, transportation of, in Pennsylvania, 57, 61, 85;
in New Hampshire, 60, 71;
in Kentucky, 63, 97;
in Ohio, 64, 72;
in Rhode Island, 67;
in Massachusetts, 69 _et seq._;
in Connecticut, 71, 72;
in New Jersey, 83;
in Illinois, 97.
Bourgeois, Abbé, cited, 367.
Bridgenorth, England, 150.
Bridlington, England, 156, 158.
Bristol Channel, 138, 178.
British Columbia, 1, 23, 121 _et seq._, 194, 198.
British Isles, ancient glaciers of, 136-181;
preglacial level of land in, 139-141;
preglacial climate in 141, 142;
great glacial centres--
Wales, 143;
Ireland, 143;
Galloway, 144;
Lake District, 144;
Pennine Chain, 144;
confluent glaciers--
Irish Sea Glacier, 145-153;
Solway Glacier, 153-158;
East Anglian Glacier, 158;
Isle of Man, 164-167;
the so-called Great Submergence, 167-180;
dispersion of erratics of Shap granite, 180, 181;
drainage of, 238;
caverns of, 267;
climate of, 314.
Brixham Cave, 267 _et seq._
Bromsgrove, England, 150.
Brooklyn, N. Y., 66, 67.
Brown, on glaciers of Greenland, 40, 41.
Brown's Valley, 226.
Bruce, skull of, 276.
Buried forests in America, 107 _et seq._
Buried outlets and channels, 199-210;
of Lake Erie, 201, 333;
of Lake Huron, 202;
of Lake Ontario, 202;
of Lake Superior, 203;
of Lake Michigan, 203;
in southwestern Ohio, 203;
near Cincinnati, 203;
near Louisville, Ky., 205;
in the Tuscarawas Valley, 205;
in the valley of the Beaver, 205;
of oil Creek, 205;
in the valley of the Alleghany, 206;
of Chautauqua Lake, 207;
near Minneapolis, 208.
Burton, England, 164.
Busk, cited, 267.
Buttermere, England, 153, 168.
Cache Valley, Utah, 233.
Cae Gwyn Cave, 148, 271 _et seq._, 280.
Caithness, Scotland, 180.
Calaveras skull, 295, 300.
California, 21, 124, 281, 287, 294, 358, 372.
Cambridgeshire, England, 158.
Canada, 94, 95.
Canstadt, man of, 279.
Canton, Ohio, 232.
Cape St. Roque, 31 3.
Caribbean Sea, 318.
Caribou, 262.
Carll, cited, 205, 207.
Carpathian Mountains, 136, 328.
Carpenter, F. R., cited, 321, 322.
Cascade Range, 21.
Caspian Sea, 238.
Cattaraugus Creek, N. Y., 220.
Caucasus Mountains, 15;
age of, 328.
Cave-bear, 269-271, 278, 280;
hyena, 269, 270, 278;
lion, 269-271, 278.
Caverns, British, 267-274;
on the Continent, 274-281.
Cefn Cave, 148, 271.
Cenis, Mont, 135.
Centres of glacial dispersion, 304 _et seq._, 323 _et seq._, 328;
in America, 113, 121;
in Europe, 129 _et seq._;
in the British Isles, 142 _et seq._
Cevennes, 136.
Chamberlin, T. C, terminal moraine of second Glacial epoch, 93,
98 _et seq._;
on driftless area, 102, 103;
cited, 110, 218, 229, 307;
on Cincinnati ice-dam, 218.
Chamois, 289, 290.
Chamouni, 132.
Charpentier, 9, 59.
Chasseron, 58, 132.
Chautauqua Lake, buried outlet of, 207.
Chenango River, 220.
Cheshire, England, 149,153,178,180.
Cheyenne River, 228.
Chicago, Ill., 346.
Chimpanzee, skull of, 276.
Chur, 133.
Cincinnati, buried channels near, 203 _et seq._;
glacial dam at, 212 _et seq._;
terraces at, 231.
Clarksburg, W. Va., 216.
Claymont, Del., 258 _et seq._;
view of implement found near, 259.
Claypole, cited, 200, 219, 221.
Climate of Glacial period, 291.
Clwyd, vale of, 147 _et seq._. 271 _et seq._
Clyde, the, 144.
Collett, cited, 107.
Colorado, 123, 124.
Columbia deposit, 245, 254 _et seq._
Columbiana County, Ohio, 232.
Comstock, cited, 307.
Conewango Creek, 232;
ancient depth of, 206.
Connecticut, 71, 72, 74, 91.
Conyers, cited, 265.
Cook on subsidence in New Jersey, 196.
Cope, cited, 288.
Cordilleran Glacier, 121 _et seq._
Corswall, England, 312.
Cows, 268.
Cresson, cited, 251, 258 _et seq._
Crevasses. (See Fissures.)
Croll, cited, 304, 307 _et seq._, 332, 362.
Cro-Magnon, rock shelter of, 281.
Cromer, England, 160.
Crosby, on composition of till, 81 _et seq._
Cross Fell escarpment, 153, 180.
Culoz, 132.
Cumberland, England, 146, 153, 168, 173.
Gumming, quoted, 166.
Gushing, H., 26
Cuyahoga River, 220, 221;
buried channel of, 200.
Dana, Professor J. D., on depth of ice, 91;
on driftless area, 102;
cited, 320, 363.
Danube, ancient glaciers of the, 129, 134, 188.
Darent, valley of, 265.
Darrtown, Ohio, 107.
Darwin, Charles, cited, 17, 126, 170, 241, 361.
Darwin, George G., cited, 361.
Darwin, Mrs. M. J., mortar owned by, 297.
Date of Glacial period, chapter on, 332-364.
Davidson Glacier, 23.
Davis on drumlins, 75.
Dawkins, cited, 238, 267, 269, 291.
Dawson, G. M., cited, 121;
on ice-movements, 97;
on oscillation of land-level, 125, 126.
Dawson, Sir William, on the fiord of the Saguenay, 197;
cited, 285.
Dee, the river, 149.
Deeley, quoted, 164.
Delaware River, 232, 242 _et seq._, 254, 258;
section across the, 245.
Delta terrace at Trenton, N. J., 242 _et seq._;
at Beaver, Pa., 230.
De Ranee, cited, 272.
Derbyshire, England, 270.
Desor on age of Niagara gorge, 337.
Diore, glaciers of the, 135.
Disintegration, amount of, near glacial margin, 117, 118.
Diss, England, 266.
Dnieper, the, 185, 188.
Don, the, 185, 188.
Dora Baltea, 134.
Dover, N. H., section of kame near, 77.
Dover, Straits of, 238.
Drave, glaciers in the, 134.
Drainage systems in the Glacial period, 335, 339, 340, 343, 344;
chapter on, 193-241.
Drayson, cited, 317.
Driftless area in the Mississippi Valley, 101, 102.
Drumlins, description of, 73 _et seq._;
view of, 73;
occurrence of, in Massachusetts, 73;
in New Hampshire, 74;
in Connecticut, 74;
in New York, 74, 94;
in the British Isles, 74, 137, 167.
Dunbar, Scotland, 312.
Dupont, cited, 279.
Du Quoin, Ill., 98, 119.
D'Urville, 20.
Düsseldorf, 275.
Eagle, Wis., view of kettle-moraine near, 99.
East Anglian Glacier, 158-164.
Eccentricity of the earth's orbit, 308.
Eden Valley, 180.
Eggischorn, 211, 241.
Eguisheim, skull found at, 279.
Elephant, 265, 280, 282, 283, 292.
Elevation, preglacial, 112, 194, 198;
the cause of the Glacial period, 113, 320-331;
about the Great Lakes, 224;
in the latitude of New York, 261.
Elyria, Ohio, 342.
Engis skull, view of, 274.
England. (See British Isles.)
Enville, England, 150.
Erosion, preglacial, 193 _et seq._
Erosion in river valleys, 198, 329, 332.
Erzgebirge, 136, 181.
Europe, existing glaciers in, 9, _et seq._, 43 _et seq._;
ancient glaciers of, 129-190;
former elevation of, 238;
ice-dams in, 360.
Evans, cited, 263, 267, 354, 365.
Falconer, cited, 263.
Falls of St Anthony, 200.
Faudel, cited, 279.
Fiesch, Switzerland, 131, 211.
Filey Brigs;, Eng., 155.
Finchley, Eng., 158, 159.
Finger Lakes, 94.
Finsteraarhorn, 9.
Fiords, 194 _et seq._;
of Greenland, 212.
Fissures in glacial ice, 3, 48, 49.
Flamborough, 140, 156, 157, 176.
Florida, 314.
Flower, cited 263.
Forbes, 9, 38, 43, 44, 48.
Forel, M., cited, 116.
Fort Snelling, Mississippi gorge at, 208, 340 _et seq._
Fort Wayne, Incl., 220, 224.
Foshay, cited, 119.
Fox, 270, 289, 290.
Fraipont, cited, 275 _et seq._
France, existing glaciers of, 19;
ancient glaciers of, 136;
glacial gravels of, 262 _et seq._
Frankley Hill, England, 150.
Franklin, Pa., 230, 232.
Franz-Josef Land, 14.
Frederickshaab Glacier, 91, 212.
Frere, cited, 266.
Frickthal, 133.
Frondeg, Wales, 149, 178.
Gabb, cited, 318.
Galloway, ancient glaciers of, 144, 145, 154, 157, 167, 168, 173.
Garda, Lake, moraine in front of, 135.
Garonne, the, 136, 188.
Gaudry, cited, 263.
Geikie, Archibald, cited, 272, 312.
Geikie, James, on kames, 76;
on loess, 187, 188;
cited, 291 _et seq._, 307, 353.
Genesee River, 220.
Geological time, 361 _et seq._
Georgian Bay, 339.
German Ocean, 129.
Germantown, Ohio, 107, 108.
Germany, North, moraine in, 181, 183;
glacial lakes in, 238;
Quaternary animals in, 279.
Gietroz Glacier, 211.
Gilbert, cited, 233 _et seq._, 350 _et seq._;
on age of Niagara gorge, 339.
Glacial dispersion. (See Centres of Glacial Dispersion.)
Glacial boundary in New England, 67;
in New Jersey, 83;
in Pennsylvania, 84 _et seq._;
in New York, 84;
in Ohio, 95, 100, 106;
in Kentucky, 96;
in Indiana, 96;
in Illinois, 96, 100;
in Kansas, Nebraska, Missouri, Montana, South Dakota, 96;
in Minnesota, 101;
in British Isles, 137, 148, 150, 151, 155, 167;
in Holland, 181;
in Germany, 181, 183;
in Russia, 181, 189.
Glacial erosion, 118, 119, 182.
Glacial ice, depth of, in Pennsylvania, 90 _et seq._;
in Connecticut, 91;
in New York. 91;
in Greenland, 91;
in the Alps, 91, 131, 133, 182;
in Germany, 182;
in Norway, 182;
amount of, 330.
Glacial lakes in Germany, 283.
Glacial motion, limit of, 2;
chapter on, 43-50;
plastic theory of, 48.
Glacial outlets of the Great Lakes, 220-222.
Glacial periods, cause of, 113;
chapter on, 302-331;
date of, chapter on, 332-364.
Glacial periods, supposed succession of, 106 _et seq._, 311, 324-326,
332;
criticisms of the theory, 116 _et seq._
Glacial striæ. (See Rock-Scoring.)
Glacial terraces, 229-238;
in Pennsylvania, 87 _et seq._, 215, 217, 229, 230;
in New York, 88; at Beech Flats, Ohio, 217;
at Granville, Ohio, 227;
on the Minnesota River, 228;
around Great Salt Lake, 233 _et seq._;
on Delaware River, 243 _et seq._;
in Europe, 238-241;
in Ohio, 249 _et seq._;
human relics in, 241-267;
on Delaware River, 245;
of the Mississippi River, 254;
in France, 263 _et seq._, 360;
in England, 264 _et seq._;
in Belgium, 264;
in Spain, 264;
in Portugal, 264;
in Italy, 264;
in Greece, 264.
Glacial theory, crucial tests of, 62, 65, 257, 302 _et seq._
Glaciation, signs of past, chapter on, 51 _et seq._
Glacier Bay, 24;
map of, 25.
Glacier, denned, 2;
formation of, 3;
characterised by veins and fissures, 3;
advance and retreat of, 116;
velocity of, in the Alps, 43 _et seq._;
in Greenland, 36, 46-48;
in Alaska, 47.
Glaciers, ancient, in North America, 66-128;
in Central and Northern Europe, 58-60, 131-136;
in the British Isles, 136-181;
in Northern Europe, 181-190;
in Australia, 126, 192;
in Asia, 190, 191;
in Africa. 191, 192.
Glaciers, existing, in the Alps, 9 _et seq._, 43 _et seq._;
in Scandinavia, 12;
in Spitzbergen, Nova Zembla, and Franz-Josef Land, 12;
in Iceland, 14;
in Asia, 14 _et seq._;
in Oceanica, 16;
in South America, 17;
in Antarctic Continent, 18 _et seq._;
in North America, 20 _et seq._;
in Greenland, 32 _et seq._, 46, 48, 364.
Glen Roy, parallel roads of, 239.
Glutton, 293.
Goat, 268.
Goffstown, N. H., 73.
Grafton, W. Va., 214.
Grand Haven, Mich., 346.
Granville, Ohio, terrace at, 227, 343.
Grape Creek, Col., view of moraines of, 123.
Great Bend, Pa., depth of river-channel at, 206.
Great Lakes, depth of, 115; formation of, 199 _et seq._;
glacial outlets of, 220-222;
elevation about, 224.
Great Salt Lake, Utah, 233 _et seq._, 350.
Greece, human relics in glacial terraces of, 264.
Greenland, existing glaciers of, 1, 32 _et seq._, 46, 48,364;
map of, 33;
climate of, 302.
Gross Glockner, 9, 134.
Ground ice, 357.
Gulf of Mexico, 313, 318.
Gulf Stream, 13, 311, 313, 317 _et seq._
Guyot, 9, 58, 133.
Haas, 16.
Hall, on the age of Niagara, 336.
Hare, 289.
Harrison, quoted, 167.
Harte, Bret, cited, 296.
Hartz Mountains, 136, 181.
Hayes, 36.
Haynes on Tertiary Man, 365-374.
Heald Moor, England, 147.
Hebrides, the, 136.
Heim, 9.
Helland, 14, 46-48.
Hennepin, cited, 340.
Heme Bay, England, 265.
Herschel, cited, 310.
Hertfordshire, England, 158.
Hicks, Dr. II., cited, 272.
Hicks, L. E., cited, 343.
Himalayas, 1,45, 292, 330;
age of, 328.
Hingham, Mass., section of kame near, 79.
Hippopotamus, 263, 265, 271, 280, 284, 285, 290, 292.
Hitchcock, C. II., discovery of boulders on Mount Washington, 60;
on drumlins, 73;
cited, 309, 313.
Hitchcock, E., on kames, 77.
Holland, terminal moraine in, 181.
Holderness, 157.
Hooker, cited, 191.
Horse, 188, 263, 268-270, 272, 278, 280, 288, 289.
Horseheads, N. Y., 220.
Horseshoe Fall, 337 _et seq._
Hottentot skull, 276.
Hoxney, England, 266.
Hudson River, preglacial channel of, 194 _et seq._
Hugi, 9, 43.
Hungary, Quaternary animals in, 279.
Huxley, cited, 276, 278.
Hyena, 271, 272, 282, 291, 292.
Ibex, 289.
Icebergs, 18, 20;
formation of, 28.
Ice, characteristics of, 2, 48 _et seq._, 302 _et seq._;
transporting power of moving, 5.
Ice-dams, 211-228;
in the Alps, 211;
in the Himalayas, 211;
in Greenland, 212;
in Alaska, 212;
at Cincinnati, 213 _et seq._;
across the Mohawk, 92, 220, 334, 335;
in the Red River of the North, 225;
in Europe, 360.
Iceland, existing glaciers of, 1, 14.
Ice-pillars, 6, 27.
Ice-sheet, retreat of, 333 _et seq._
Idaho, 122; lava-beds of, 297.
Illicilliwaet Glacier, 23.
Illinois, 96-98, 100, 119, 121, 345 _et seq._
Indiana, 96, 98, 107, 119, 121.
Indian Ridge, 80.
Iowa, 98, 101.
Ireland, ancient glaciers of, 143.
Irish elk, 270, 278, 288.
Irish Sea Glacier, 137, 145-153, 164, 271.
Irthing, valley of the, 153.
Isère, glaciers of the, 132.
Isle of Man, 164-167.
Isle of Wight, 266.
Italy, existing glaciers of, 9;
ancient glaciers of, 185;
human relics in glacial terraces of, 264;
supposed Tertiary man in, 366.
Ivrea, 134.
Jackson, cited, 357.
Jackson's Lake, 123.
Jakobshavn Glacier, velocity of, 46, 47;
depth of, 91;
ice-dams of, 212.
James, cited, 204.
James River, Dak., 228.
James River, Va., 257.
Jamieson, cited, 330.
Jensen, 91.
Judge's Cave, 72.
Jura Mountains, ancient glaciers of, 58-60, 132.
Kames, formation of, 7, 76, 77;
of Muir Glacier, 29, 30;
in Massachusetts, 77 _et seq._;
in New Hampshire, 80;
map of, in Maine, 81;
in Pennsylvania, 87.
Kanawha River, 216.
Kane, 36-38.
Kansas, 96.
Kelly's Island, view of grooves on, 103, 105.
Kendall, chapter by. 137-181;
cited, 273.
Kent, England, 265.
Kent's Hole, 267 _et seq._, 352 _et seq._
Kentucky, 63, 96, 97, 212;
view of boulder in, 63.
Kentucky River, 214.
Kettle-holes, formation of, 7, 68;
of Muir Glacier, 29, 30;
in New England, 66 _et seq._, 344, 345;
in Pennsylvania, 86;
sedimentation of, 333, 344 _et seq._
Kettle-moraine in Wisconsin, 100.
King, 21, 351;
implement discovered by, 297.
Knox County, Ohio, 232.
Kurtz, Nam pa image discovered by, 297.
Lake Agassiz, 126, 223, 225;
continuance of, 347 _et seq._
Lake Bonneville, 233 _et seq._, 299, 350 _et seq._
Lake Constance, 60, 133.
Lake Erie, origin of, 200 _et seq._;
ridges around, 222;
preglacial outlet of, 200, 333.
Lake Geneva during the Glacial period, 131, 132.
Lake Huron, preglacial outlet of, 202;
ridges around, 224.
Lake Itasca, 254.
Lake Lahontan, 233, 234.
Lake Michigan, age of, 345 _et seq._
Lake Nipissing, 339.
Lake Ontario, origin of, 201 _et seq._
Lake Traverse, 208, 226.
Lake District, England, the, 144.
Lake dwellings in Switzerland, 281.
Lake ridges, 222 _et seq._
Lakes, sedimentation of, 333, 344 _et seq._
Lamplugh, glacial observations of, 140, 196.
Lancashire, 153, 178, 180.
Lancaster, Ohio, 232.
Lang, cited, 116.
Lark, England, valley of the, 266.
Lateral moraines, 5.
Laurentide Glacier, 113 _et seq._, 121, 321.
Lava on the Pacific coast of North America, 294, 298, 300, 306, 321.
Lawrence, Mass., 80.
Lawrenceburg, Ind., 231, 232.
Le Conte, cited, 286, 322 _et seq._, 330, 372.
Leicestershire, England, 158.
Lehigh River, 243.
Lemming, 289.
Lenticular hills, 73.
Leopard, 282.
Lesley, cited, 215.
Lesse, Belgium, valley of the, 279.
Leverett, cited, 101, 218.
Lewis, on transported boulders, 57, 61;
work of, in Pennsylvania, 84, 119;
in Great Britain, 137;
cited, 254 _et seq._, 273.
Lickey Hills, 151.
Licking River, 214.
Liége, Belgium, 274.
Lincolnshire, England, 158.
Lindenkohl on old channel of the Hudson, 195 _et seq._
Lion, 282, 293.
Little Beaver Creek, 231, 232.
Little Falls, Minn., 225, 232, 252, 254.
Little Falls, N. Y., buried channel near, 202.
Livingston, Mont., 122.
Llangollen, vale of, 151.
Loess in the Mississippi Valley, 98, 119, 120;
in Europe, 186 _et seq._
Lohest, cited, 275 _et seq._
Lombardy, 134.
London, 158, 159, 178;
glacial terrace in, 264.
Long Island, 66, 67.
Louisville, Ky., buried channel near, 205.
Loveland, Ohio, 232, 250.
Lubbock, cited, 267.
Lucerne, 133.
Lyell, on Richmond train of boulders, 70;
cited, 239, 263, 267, 274, 276, 285, 355, 361;
on the age of Niagara, 336.
Lyons, 132.
Maack, cited, 318.
Macclesfield, England, 273.
MacEnery, cited, 267.
Machairodus, 270, 282.
Mackintosh, quoted, 149, 150, 173.
Mâcon, France, 369.
McTarnahan, mortar discovered, by 297.
Madison boulder, 71.
Madisonville, Ohio, 232, 250, 254.
Magdalena Bay, 13.
Mahoning River, 220.
Maine, 80; re-elevation of, 331.
Malaspina Glacier, map of, 31.
Mammoth, 188, 190, 263, 265, 269-272, 278, 280, 283-285, 287, 292, 293.
Man, relics of, in the Glacial period, chapter on, 242-301;
in glacial terraces of the United States, 242-262;
of Europe, 262-267;
in cave deposits of British Isles, 148, 267-274;
of the Continent, 274-281;
under lava-beds of the Pacific coast of North America, 294-301;
extinct animals associated with, 281-293.
Manitoba, 97.
Mankato, Minn., 229.
Marcilly, skull at, 279.
Marietta, Ohio, 231.
Marmot, 289, 293.
Marsh Creek Valley, Utah, 233.
Martigny, ancient glaciers near, 59, 60, 131, 211.
Massachusetts, 67 _et seq._, 73, 77 _et seq._, 81, 344, 345.
Mastodon, 262, 278, 285, 286.
Mattmark See, 211.
Maumee River, 220.
McGee, cited, 245, 254 _et seq._
Medial moraines, formation of, 6;
of Muir Glacier, 27;
in Ohio, 100.
Medlicott, cited, 312.
Medora, Ind., 232, 251, 254.
Menai Straits, 145.
Mentone, skeleton of, 281.
Mer de Glace, 11, 44.
Merjelen See, 211, 241.
Mersey, the, 140.
Meteorites, 305.
Metz, cited, 250.
Meuse, valley of, 274 _et seq._
Miami, the Great, 204, 220.
Miami, the Little, 231, 250.
Millersburg, Ohio, 232.
Mills, cited, 251.
Minneapolis, 232; buried outlet near, 208;
recession of falls at, 210, 340 _et seq._, 364.
Minnehaha, Falls of, 342.
Minnesota, 101, 107, 252 _et seq._;
lakes of, 344.
Minnesota River, a glacial outlet, 208, 225, 228, 342.
Miocene epoch, animals of the, 285.
Mississippi River, gorge of, at Fort Snelling, 208, 364;
terraces on, 229;
erosion by, 329;
glacial drainage of, 335, 340.
Missouri Coteau, 101, 126, 228.
Missouri, 96, 98, 119.
Moel Tryfaen, 145, 167 _et seq._, 178, 273.
Mohawk River, glacial drainage of, 92, 202, 335;
ice-dam across, 220, 334, 335.
Mohegan Bock, 71; view of, 72.
Monongahela River, 214 _et seq._
Montaigle, valley of the, 279.
Montana, 96.
Montreal, re-elevation of, 331.
Moose, 262.
Moraines, formation of, 6;
in Wisconsin, 98-100;
in Italy, 134, 135;
between Speeton and Flamborough, 156;
in Germany, 183.
Morecambe Bay, 146, 180.
Morgantown, W. Va., 215.
Morlot, cited, 354.
Mortillet, cited, 366, 369, 372.
Morvan, the, 136.
Moulins, formation of, 7.
Mount Shasta, 21.
Mount Washington, 61.
Mueller Glacier, 17.
Muir Glacier, 24 _et seq._. 47, 68, 212;
view of front of, 26.
Muir, John, 24.
Muskingum River, 220, 231.
Musk ox, 262, 280.
Musk sheep, 289, 290, 293.
Nampa image, 297 _et seq._
Nansen, 39, 41.
Naulette, jaw found at, 278, 279.
Neale, implements discovered by, 296, 373.
Neanderthal skull, 275 _et seq._
Nebraska, 96.
Nelson River, 349.
Neufchâtel, 133.
Nevada, 124; lakes of, 233.
Névé-field defined, 3.
Newark, Ohio, 232.
Newberry on the preglacial drainage of the Hudson, 195 _et seq._;
on the formation of the Great Lakes, 202 _et seq._;
cited, 320.
Newburg, N. Y., 286.
New Comerstown, implement from, 232, 250, 251 _et seq._, 254.
New England, 57, 60, 61, 91;
ancient glaciers in, 66-83.
New Hampshire, 69, 71, 74, 80.
New Harmony, Ind., 232.
New Jersey, 83.
New Lisbon, Ohio, 232.
New York, 74, 84, 88, 91, 92 _et seq._
New York Bay, 184, 197, 249.
New Zealand, 1, 126, 192, 330.
Niagara gorge, age of, 333 _et seq._;
section of strata along the, 336.
Nile River, 285.
Nordenskiöld, 32, 34.
Norfolk, England, 161.
North America, existing glaciers in, 20 _et seq._
North Sea, 238.
Norway, climate of, 314.
Nottingham, England, 164.
Nova Zembla, 14.
Oberlin, Ohio, 64, 344.
Oceanica, existing glaciers of, 16, 17.
Ohio River, glacial terrace, 217, 229.
Ohio, 64,72, 95, 98, 100, 103, 106,107-117, 119, 217, 249 _et seq._,
343, 344.
Oil Creek, 205, 232.
Olmo, skull at, 279.
Oregon, 21, 124.
Orme's Head, Little, 147.
Orton, cited, 72, 107.
Oscillations of land-level in America, 124 _et seq._
Oswestry. England, 173.
Ottawa River, 339.
Otter, 290.
Ouse, valley of the, 265.
Ox, 269, 270.
Pacific coast of America, 349.
Pacific Ocean, 318, 320.
Panama, Isthmus of, 113, 313, 314, 318.
Parsimony, law of, 117.
Pasterzen Glacier, 134.
Patagonia, 1.
Patton, 25.
Payer, 14, 39.
Peat-beds, 68, 125;
in Ohio, 107;
in Minnesota, 108;
in valley of the Somme, 355 _et seq._
Pembina River, 228.
Pengelly, cited, 267, 270.
Pennine Chain, glaciation of, 137, 144, 146, 147, 154, 177.
Pennsylvania, 57, 61, 84 _et seq._, 119, 217.
Perry County, Ohio, 232.
Perthes, Boucher de, 262 _et seq._
Philadelphia Academy of Sciences, 296.
Philadelphia, red gravel of, 254 _et seq._
Phillips, cited, 267.
Picardy, glacial gravels of, 262.
Pittsburg, Pa., submergence of, 214, 217, 230.
Plum Creek, Ohio, 344.
Po, valley of the, 135;
erosion by, 328.
Pocatello, Idaho, 236, 299.
Pocono Mountain, 61.
Poland, 181.
Polynesian skull, 276.
Pomp's Pond, section of kettle-hole near, 345.
Portageville, N. Y., 220.
Port Neuf River, Idaho, 236.
Portsmouth, Ohio, 231.
Portugal, human relics in glacial terraces of, 264;
supposed Tertiary man in, 367, 371 _et seq._
Post-glacial erosion, 332 _et seq._;
in Ohio, 343, 344;
in Illinois, 345 _et seq._
Potomac River, 256 _et seq._
Pot-holes in Lucerne, 133.
Pouchet, cited, 263.
Precession of equinoxes, 308.
Preglacial climate in England, 141, 142.
Preglacial levels in England, 139-142.
Prestwich, cited, 186, 189, 263 _et seq._, 284;
on date of Glacial period, 354, 357, 363, 364.
Provo shore-line, 237.
Putnam, cited, 250.
Puy-Courny, France, supposed Tertiary man at, 367, 370, 371.
Pyramid Lake, 350.
Pyrenees, glaciers of the, 11, 136;
Quaternary animals of, 280, 282;
age of, 328.
Quaternary animals of California, 281, 287;
in Germany, 279;
in Hungary, 279.
Quatrefages, cited, 276.
Queenston, Canada, 333 _et seq._
Rabbit, 289.
Raccoon Creek, 343;
view of glacial terrace near, 227.
Rames, cited, 370, 371.
Ramsay, cited, 311.
Rappahannock River, 257.
Rawhide Gulch, Cal., 296.
Recession, rate of, of Falls of Niagara, 333 _et seq._;
of Falls of St. Anthony, 340 _et seq._, 364;
of Black River, 342, 343.
Red deer, 263.
Red River of the North, 209, 228, 340;
ice-dam in, 225.
Regillout, 263.
Reid, Clement, quoted, 162.
Reid, H. F., 26, 47.
Reindeer, 188, 262, 263, 269, 270, 278, 280, 287, 290, 293.
Rhine, ancient glaciers of the, 129, 133.
Rhinoceros, 188, 263, 265, 271, 277, 278, 280, 284, 286, 287, 292;
woolly, 269, 270, 272, 280, 287.
Rhode Island, 67.
Rhône, ancient glaciers of, 58-60, 131,132, 185, 188;
map of, 58.
Richmond, Mass., train of boulders in, 70, 71.
Rink, Dr., 35.
Roanoke River, 257.
Rocky Mountains, 320, 322;
age of the, 328.
Rock-scorings, cause of, 51 _et seq._;
in New England, 69;
on islands of Lake Erie, 103, 104;
in Pennsylvania, 119;
in Ohio, 103, 119;
in Indiana, 119;
in Illinois, 119;
in Missouri, 119.
Roman remains, 356.
Rome, N. Y., 335.
Rosa, Mount, 9, 134, 211.
Ross, Sir J. C, 18, 19, 311.
Royston, England, 155.
Runaway Pond, 207.
Russell, I. C, exploration of Mount St. Elias by, 30, 212;
cited, 233, 350 _et seq._
Russia, glacial boundary in, 181, 189;
glacial drainage of, 238.
Saguenay, fiord of the, 197.
Salamanca, N. Y., buried channels near, 206.
Salisbury, cited, 183, 184.
Salt Lake City, 123.
Sandusky, Ohio, section of the lake ridges near, 223.
Sandusky River, 220.
Sanford, cited, 267.
Saskatchewan River, 228.
Saxony, 181.
Scandinavia, existing glaciers of, 2, 12;
ancient glaciers of, 129, 136, 157, 181-190;
re-elevation of, 331.
Scioto River, 231.
Scotland. (See British Isles.)
Seattle, section of till in, 55.
Second Glacial period, 106 _et seq._
Section, ideal, across river bed in drift region, 229.
Sedimentation of lakes, 333.
Seine, terraces of the, 186, 188, 264.
Seracs, 4, 5.
Settle, England, 270.
Severn, the, 149-151, 285.
Shaler, 67, 242.
Shap granite, 154, 157, 180.
Ship Rock, 71.
Shone, cited, 180.
Shoshone Falls, 299.
Shrewsbury, England, 150.
Shropshire, England, 149, 173.
Siberia, 190;
Quaternary animals in, 280, 282, 283, 290;
climate of, 302, 316.
Sierra Nevada Mountains, 21, 294, 301, 320, 322, 349, 352.
Skertchly, quoted, 159.
Skipton, 144, 146.
Skull, comparative study of, 276.
Slickenside, 53.
Smock on depth of glacial ice, 90.
Snake River Valley, 236 _et seq._, 298.
Snowdon, 145, 171.
Snowy vole, 289.
Soleure, 133.
Solferino, 135.
Solway Glacier, 153, 155, 180.
Somme, terraces of the, 186, 262 _et seq._, 285, 286, 355, 359 _et seq._
Sonora, Cal., 294 _et seq._
South America, existing glaciers of, 17;
ancient glaciers in, 126.
Southampton, England, 266.
South Dakota, 96, 98.
Spain, ancient glaciers of, 136;
human relics in glacial terraces of, 264;
Quaternary animals of, 280.
Speeton, 140, 155, 156.
Spencer, cited, 224.
Spencer, N. Y., 220.
Spitsbergen, 12.
Spy, man of, 275, 277.
St. Acheul, 263.
Stag, 289.
Stainmoor, England, 154, 157, 180.
Stalagmite, rate of accumulation of, 352 _et seq._
Stanislaus River, Cal., 294.
St. Anthony, Falls of, 340 _et seq._, 364.
Steamburg, N. Y., buried channel at, 206.
St. Elias, 30 _et seq._, 212.
St. Lawrence River, glacial drainage of, 335, 339.
St. Louis, Mo., 119, 364.
St. Paul, Minn., 228.
Stone on kames in Maine, 80.
Straits of Dover, 360.
Straits of Gibraltar, 292.
Striæ, direction of, in New Hampshire, 69;
in Lake Erie, 104;
presence of, in Pennsylvania, 85, 119;
in Ohio, Indiana, Illinois, and Missouri, 119;
in Stuttgart, 279.
Subglacial streams, 23, 29, 120.
Submerged channels on the coasts of America, 194-198.
Submergence theory, 60-63, 70.
Subsidence of the Isthmus of Panama, 113, 318;
in Mississippi Valley, 93, 113, 120, 121;
on east coast of North America, 255 _et seq._;
about the Great Lakes, 224, 339;
in Great Britain, 167-181.
Susquehanna River, glacial drainage of, 93, 232, 257.
Svartisen Glacier, 13.
Svenonius, Dr., 12.
Sweden, 81.
Switzerland, existing glaciers of, 9-11;
ancient glaciers of, 131-136;
lake-dwellings in, 281.
Table Mountain, Cal., 294 _et seq._, 300.
Table of changes during the Glacial epochs, 324, 325.
Tagus, valley of the, 367, 371 _et seq._
Tait, cited, 362.
Tardy, cited, 370.
Tasman Glacier, 16.
Teesdale, England, 155, 157.
Terminal moraines, formation of, 6;
in Pennsylvania, 61, 62, 85 _et seq._;
on the southern coast of New England, 66 _et seq._;
in Ohio, 106;
in Puget Sound, 122;
in Tyghee Pass, 122;
in Italy, 135.
Terminal moraines of the second Glacial epoch, 93, 100, 101, 106.
Terraces. (See Glacial Terraces.)
Tertiary animals, 286.
Tertiary man, 365-374.
Tertiary period, climate of, 113, 117, 182, 305, 307.
Teton Mountains, 123.
Texas, Pleistocene animals of, 288.
Thames, England, 138, 264, 285.
Thenay, France, supposed Tertiary man in, 367, 371;
view of flint-flakes collected at, 368.
Thompson, 50.
Thomson, cited, 362.
Till, description of, 53;
composition of, in Massachusetts, 81 _et seq._;
section of, in Ohio, 108;
depth of, in Germany, Scandinavia, and Russia, 182.
Tinière River, 354.
Titusville, Pa., 232.
Todd, on forest beds and old soils,110 _et seq._;
cited, 228.
Torquay, England, 267.
Trade-winds of the Atlantic, 314, 318.
Tremeirchon, Wales, 271.
Trenton, N. J., 87, 232, 242 _et seq._, 254, 257;
view of implement found at, 247.
Trenton gravel, section of the, 246.
Trent, valley of the, 163, 164.
Trimmer, quoted, 148.
Trimingham, England, 162.
Trogen, Switzerland, 60.
Trons, Switzerland, 60.
Tuolumne County, Cal., 294, 299.
Turin, 135.
Tuscarawas Valley, 220, 221, 232, 251;
buried channel in, 205.
Tylor, cited, 359 _et seq._
Tyndall, 44-46, 49.
Tynemouth, England, 155, 157.
Tyrol, 134, 135, 211.
Tyrrell, cited, 109.
Ulm, 134.
Upham, on drumlins, 73;
on two ice-movements, 97;
cited, 222, 253 _et seq._, 301, 318, 320 _et seq._, 330, 348;
on the Columbia gravel, 261;
on date of the Glacial period, 344.
Ural Mountains, 15, 280.
Utah, 123;
lakes of, 233.
Utica, N. Y., 220.
Utrecht, moraine near, 181.
Valais, the, 133.
Vegetable remains in glacial deposits, 117, 125;
in Ohio, 107, 117;
in Indiana, 107;
in Minnesota, 107, 109;
in Iowa, 108;
in British America, 109.
Veins in glacial ice, 3.
Vermont, Runaway Pond in, 207.
Vernagt Glacier, 211.
Vessel Rock, view of, 56.
Vezère, valley of, 281.
Victoria Cave, England, 270, 280.
Virginia City, 349.
Vivian, cited, 267.
Volga, the, 185.
Vosges Mountains, 136.
Wabash River, 220, 231, 232.
Wahsatch Mountains, 237.
Wales, ancient glaciers of, 143, 150 _et seq._;
caverns of, 271.
Wallace, cited, 331, 343, 362.
Walrus, 262, 285.
Warren, Pa., buried channel near, 206.
Warren River, 226.
Washington, 1, 21, 122.
Washington, D. C., gravel deposit of, 254.
Water, transporting power of running, 5, 51-53.
Waveney, England, valley of the, 266.
Wealden formation, 361.
Weasel, 290.
Wells, England, 270.
Western Reserve Historical Society, 104.
Weston, W. Va., 216.
West Virginia, 214 _et seq._;
glacial terrace in, 216.
Wey, valley of the, 265.
Whitby, England, 155.
White, cited, 215 _et seq._
White River, Ind., 232, 251.
White Sea, 181.
Whitney, 14, 21, 295, 349, 373.
Whittlesey, 100.
Wild-boar, 290.
Wild-cat, 290.
Winchell, Alexander, cited, 321, 330.
Winchell, N. H., cited, 107, 210, 252;
on the Falls of St. Anthony, 341 _et seq._
Wisconsin, 98, 99, 100, 101.
Woeikoff, cited, 316.
Wolf, 270, 290.
Wolverine, 289.
Wood, cited, 179.
Woodward, quoted, 160;
on age of Niagara, 337 _et seq._
Wookey Hole, England, 270.
Wrangell, cited, 357.
Wright, 373.
Yankton, 120.
Yellowstone Park, 122.
Yorkshire, 140, 154, 155, 157, 176, 270, 283, 286.
Yosemite Park, 21, 350.
Young, Rev. Mr., 24.
Young, Professor, cited, 362.
Younglove, 104.
Zermatt Glacier, view of, 2.
Zuyder Zee, 181.
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Transcriber Note
Figure captions were standardized. All figures were moved to avoid
splitting paragraphs. Any minor typos were corrected.
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