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Israel C. (Israel Cook) Russell.

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which are deposited beneath the ice during its advance, and form what
are frequently termed ground moraines. This material is widely spread
over formerly glaciated regions, and is now generally designated by the
Scottish name till, and is less frequently spoken of as boulder day.
The term boulder clay, however, has been given a somewhat different
meaning by a few authors.

The characteristics of till are its compactness, due to the pressure
to which it was subjected beneath the ice, and the worn and striated
condition of many of the pebbles and boulders scattered irregularly
through it. As till was not exposed to the atmosphere during its de-
position, and, on account of its compactness, is impervious to surface
waters, the material of which it is composed is in an unweathered
condition and frequently of a bluish color, owing to the fact that the
iron contained in it has not been oxidized. Its unweathered condition
is in marked contrast to the surface moraines of many glaciers and to
ancient glacial deposits which have been long exposed to the atmosphere.

Drumlins. The abandoned paths of great glaciers are sometimes
marked by smooth, oval hills that are lenticular in horizontal sections
and have their longer axes parallel to the movement of the ice which
formerly covered them. These peculiar and easily recognized emi-
nences are, in the case of certain typical examples, about 500 feet in
least diameter, with a length of from 1500 to 2000 feet, and a maxi-
mum height of from 50 to 150 feet. They exhibit many variations in
size and shape, however, some being nearly circular, mammillary hills,
and others lenticular hills, in which the longer axis is two or three
times as great as the shorter axis. In some instances they form narrow
ridges several miles in length. The beautiful curves formed by their
crests when seen from the side, is illustrated by the outline of a typi-
cal example near Groton, Mass., here presented. They occur at all
elevations from sea level, and even below that horizon, to 1500 feet or
more above tide, and are found on uneven, rocky ground as well as on
smooth plains. They are composed of compact till which is frequently
laminated, and seldom exhibit evidences of stratification or other water
action. Boulders and large angular stones occur within their mass, and
scattered over their surfaces. These peculiar hills, for which the Irish



INTRODUCTION. 25

term drumlin is now generally adopted, have been studied especially
near Boston, and occur also in many other parts of New England.
They are abundant in the upper portion of the Hudson River valley,
in central New York, and have been reported from Michigan and Wis-
consin. In general they are situated well within the terminal moraine
which marks the southern limit of the last ice invasion of northeastern
North America. Many drumlins in the Connecticut and Hudson val-




FIG. 2. DRUMLIN NEAR GROTON, MASS. AFTER FRYE.

leys, and other similar regions, are partially or wholly buried beneath
Champlain clays, which were deposited during a time of land depres-
sion immediately after the last recession of the ice. Thus far, drumlins
have not been observed in connection with existing glaciers. This is
due, perhaps, to the fact that they are not known to originate beneath
glaciers of the alpine type, and also because they seem to be a phase
of the behavior of the somewhat central portions of large ice sheets, and
are only open to view when the ice has withdrawn.

The characteristic whaleback shape of drumlins, the compactness
and frequent lamination of the till composing them, as well as other
facts in connection with their composition and distribution, have led to
the generally adopted conclusion that they were formed beneath moving
ice sheets. Various hypotheses have been proposed to explain their
origin, but thus far opinion is divided in reference to the precise man-
ner of their formation. 1

Without attempting to present a review of the various hypotheses that
have been advanced in reference to the origin of drumlins, I venture to
suggest that the effect of debris on the flow of ice enclosing it may fur-
nish the desired explanation.

The presence of debris, i.e. boulders, stones, sand, dirt, etc., in glacial
ice, increases its resistance to motion, as will be more fully discussed in

1 A discussion of the origin of drumlins, by Warren Upham, containing references to pre-
vious papers on the same subject, may be found in the Proceedings of the Boston Society of
Natural History, vol. 26, 1892, pp. 2-17.



26 GLACIERS OF NORTH AMERICA.

advance. Debris included in ice may be said to stiffen it and to decrease
its plasticity ; or, in other words, increase its resistance to forces tending
to shear it. With this principle in mind, we are led to conclude that if a
mass of debris is included in a glacier, motion in the debris-charged mass
will be retarded, and the adjacent clear ice will flow around it. When the
debris reaches a certain proportion, varying with conditions, motion will
cease, and if the rate of flow of the clear ice does not increase, the debris-
charged mass will remain stagnant. If the debris is most abundant about
a central nucleus, and becomes less and less abundant in all directions
from the nucleus, the flow of the ice will be least in the center, or if the
debris is there sufficiently abundant, will remain stagnant, while motion
in adjacent portions will increase in a definite ratio until the normal flow
of clear ice under given conditions is reached. If a nucleus of debris, as
above postulated, is situated in the central part of a glacier, with clear ice
beneath, it may behave like a boulder and be carried bodily forward ; but
if situated at the bottom it will retain its position, and the clear ice will
flow over it. If the ice flowing past the stagnant mass has earth and
stones scattered through it, the debris reaching the nucleus will be
retarded and the clear ice flow on. The nucleus of debris would thus
receive additions and be compacted and moulded by the clear ice, or ice
but moderately charged with foreign matter, flowing past it. A shape
presenting least resistance to the flowing ice would thus be acquired,
and the longer axis of the stagnant mass would be parallel with the
direction of glacial flow. Under this conception: of the growth of
drumlins^ the fact that they frequently, and possibly normally, contain
debris that has been derived from lower levels presents no difficulty,
since ice under pressure behaves as a viscous fluid, and will flow in
the direction of least resistance. If the resistance at the sides of a
stagnant nucleus was greater than over its summit, the approaching ice
would rise and flow over the obstruction, carrying with it the debris
contained within its mass. The varying forms of drumlins, the fact that
they sometimes cover a nucleus of rock-in-place, their laminated structure,
remarkable compactness, and general flowing outlines, all seem to harmo-
nize with the view of their origin here suggested.

Certain drumlins of what may be termed the New York type, i.e. those
that are greatly elongated, are not symmetric, but their ends in the direc-
tion from which the ice came which moulded them into shape are moder-
ately broader and more blunt than the opposite extremities. These elon-
gated hills may be said to have the shape of half a cigar cut lengthwise,



INTRODUCTION. 27

the larger end of the cigar pointing in the direction from which the ice
came, which formerly covered the region where they occur. The sides
of these hills, as is common with all elliptical or elongated drumlins, are
more precipitous than the terminal slopes. On the larger or proximal
ends, of several cigar-shaped drumlins observed by the writer in Wash-
ington county, New York, there is a noticeable increase in the number
of boulders scattered over the surface, while at their tapering or distal
extremities, fine debris greatly predominates, and is noticeable beyond,
where the slope of the hills is lost. In these examples, coarse debris
seems to have been deposited on the enlarged proximal ends, while
the sides and distal portion suffered erosion, which removed the larger
stones.

Under the hypothesis here proposed, drumlins are considered to have
grown by the accumulation of debris about a central nucleus either of
solid rock or of ice charged with stones to such a degree as to increase
its resistance above the shearing forces brought to bear upon it; the added
material being derived from the ice which flowed past it. The location
of a drumlin would be determined by the presence of debris sufficiently
abundant to cause stagnation in the ice containing it, which would vary
with the rate at which the ice moved. When the ice contained but little
debris it might all be carried forward ; when the debris was in excess, it
might be left in a general sheet, without special form. The most favor-
able conditions would be when certain threads, so to speak, of the ice
current were lightly charged with debris, which on account of changes
in the contour of the land over which the ice flowed, or variations in
velocity due to other causes, would become sufficiently abundant at cer-
tain localities to check the flow of the debris-charged ice and cause it to
become stagnant. The ice current would then add fresh debris to the
stagnant nucleus, and a drumlin representing the excess of deposition
over erosion would result.

The hypothesis outlined above has not been subjected to severe tests,
and is introduced here in the hope that it will stimulate the student to
make observations in the field, which will either sustain it or lead to its
modification or rejection. In the study of the origin of topographic
forms, many trial hypotheses have to be introduced and their value
tested, in order to arrive at a true explanation. The above may be
considered an example of such a working hypothesis. It is the duty
of the compiler to take his reader as far as present knowledge seems
to warrant, and to point the way into the unexplored country beyond.



28 GLACIERS OF NOETH AMERICA.

I trust this little excursion beyond generally accepted conclusions will
encourage the student to continue the investigation.

GLACIAL SEDIMENTS.

Deposits made by streams while yet confined by glacial ice, and for
some distance after escaping from its borders, may for convenience be
termed glacial sediments, in distinction from glacial deposits made
directly from the ice and classified as moraines, till, drumlms, etc.
These fluvio-glacial sediments are characterized by the worn and
rounded condition of the sand, pebbles, and boulders composing them,
and also by their more or less perfect stratification ; while glacial
deposits are, in the majority of instances, composed of unassorted,
angular debris. Glacial sediments are in reality stream deposits made
under peculiar conditions, determined by the presence of land ice. For
this reason, they are of greatest interest when studied in connection with
other glacial phenomena. The deposits here referred to are designated in
many geological books, some of them of recent date, as modified drift ;
the early supposition on which this term is based being that they consist
of glacial deposits that have been worked over and modified by streams.
The leading characteristics of some of the best-defined deposits made by
glacial streams are briefly described below.

Osars. In formerly glaciated regions there are, in certain instances,
long, gently curving, and sometimes tortuous ridges, trending with the
direction of former ice movement, and composed of water-worn sand
and gravel. When their internal structure is exposed, they exhibit
more or less well-defined cross-bedding or oblique stratification, pro-
duced by rapid water currents ; and on their surfaces large, angular
boulders are frequently to be observed. Ridges of this character, some-
times 50 to 150 feet or more in height, and perhaps scores of miles in
length, have been named osars, and are believed to have been formed
by streams flowing in channels beneath ice sheets. The large, angu-
lar stones resting on them are of the same origin as the similar boulders
on the surface of drumlins already referred to, and were deposited when
the ice in which the osars were formed was melted.

Kames. Other accumulations of water-worn sand and gravel, depos-
ited beneath glaciers or about their immediate margins, have irregular
shapes and form hills and knolls with undrained basins between. These



INTRODUCTION. 29

peculiar and frequently very picturesque topographic forms are known as
frames. They are believed to owe their origin to the drainage of glaciers,
and to have been formed by the deposition of gravel and sand in cavities
beneath the ice, or after being swept out from ice sheets by the streams
flowing from them and dropped in open channels in their margins.
These are the most common of topographic forms composed of glacial sedi-
ments, and, like osars, frequently have large, angular blocks of rock scat-
tered over their surfaces, and are sometimes completely coated with what
was at one time englacial or superglacial material. They differ from osars
in the fact that they form irregular hills with basins between, instead of
long, winding ridges ; and are distinguished from drumlins, since they are
composed of water-worn sand and gravel, instead of till, and differ in
their outlines. Their distinguishing characteristics are, especially, the
irregularity and frequent changes in the character of the layers of which
they are composed, their knob and basin topography, and the fact that in
general they trend at right angles to the direction of movement in the ice
sheet to which they owe their origin.

Sand and Gravel Plains. About the margins of regions formerly
covered by ice sheets and associated with osars and kames, there are
frequently broad plains composed of irregularly stratified sand and gravel.
These are the deposits made by overloaded glacial streams on emerging
from restricted channels in the ice and expanding and dividing into many
branches, and consequently dropping a large part of their loads, or flowing
into lakes where their sediments were deposited.

The formation of sand and gravel plains, both by subdividing streams
and in bodies of still water, may now be seen in progress about many
glaciers. Conspicuous examples occur at the extremities and along the
borders of several glaciers in Alaska. About Norris glacier in Taku inlet,
shown in Plate 11, there are large deposits of sand, forming a low,
gently sloping plain, across which the feeding stream divides into many
distributaries. Other deposits of this same general character will be
mentioned in advance in describing the Malaspina ice sheet.

Abundant examples of the deposits referred to above occur in the
region occupied by morainal material in the northeastern part of North
America, and also for many miles southward from the southern limit
reached by the ice during what is generally termed the Second Glacial
epoch. Plains of sand and gravel, either formed in small lakes and having
horizontal surfaces, or laid down by bifurcating streams and having gently



30 GLACIERS OF NORTH AMERICA.

sloping surfaces, make up a very large portion, and perhaps the major
part, of glacial deposits over great areas in the region of the Laurentiaii
lakes. At times these plains are marked by depressions, frequently rudely
circular in outline, with steep banks of gravel and sand, and in such in-
stances have acquired the name of pitted plains. The pits dotting their
surfaces, and forming a marked characteristic of their topography, are
believed to have been formed by the melting of isolated ice bodies which
were surrounded or perhaps deeply buried by the gravel and sand during
the last retreat of the glaciers.

CHANGES IN TOPOGRAPHY PRODUCED BY GLACIERS.

Glaciers have a twofold and opposite effect upon the relief of the
regions they occupy. The abrasion produced by moving ice masses tends
to reduce and smooth out inequalities, cut away prominences, and, as a
minor feature, excavate rock basins. The deposits formed by glaciers, either
directly or through the agency of streams, in many cases fill up and level
off previously formed depressions, but in other instances, especially during
retreat, tend to accent the relief of the surface and produce inequalities.
The debris carried by ice streams and by ice sheets is left in confused
heaps when melting takes place, and produces well characterized topo-
graphic forms. Frequently these deposits cover immense regions, and
are striking in appearance, and vary abruptly in relief. The sediments of
glaciers, and particularly the fine debris washed from them by outflowing
water, fill inequalities, and on the whole, except in the case of osars and
similar accumulations, tend to subdue and make uniform previous
inequalities of the land.

About the margins of existing glaciers that are retreating, there are
barren areas in which the topographic forms peculiar to glacial action are
well displayed. In such instances one finds tumultuous piles of earth and
stones, now rising into knolls and steep-sided hills, and, again, sinking into
dales and sand plains with but little variation in the surface contours.
One of the most striking features in these fresh morainal deposits is the
presence of many depressions without surface outlets and very frequently
containing lakes. The drainage is markedly immature.

On old moraine-covered areas the ruggedness is commonly concealed
somewhat by vegetation, and many of the lakes that formerly existed in
the depressions are transformed into bogs and grassy meadows. Streams
originating in such areas cut channels for themselves and tend still



INTRODUCTION. 31

further to drain the land. As time goes on, a well-developed drainage
system is established. The lakes disappear, and the work of the streams
in reducing the country to base level, i.e. the level of standing water into
which they discharge, is carried forward much the same as in regions that
have not been affected by glacial action. This task is frequently greatly
delayed, on account of the climatic conditions and for the reason, also,
that glacial deposits, especially osars, kames, etc., composed of unconsoli-
dated gravel and sand, are sufficiently porous to absorb the rain water that
falls upon them and allow it to percolate slowly away, thus robbing it of
its power to erode. The most prominent relief of glaciated lands is fre-
quently such as is produced by open, porous deposits of the nature of
kames and osars. These retain their primitive form, while mountains of
indurated rock yield to the forces of the atmosphere and are sculptured
in various ways.

The most pronounced topographic evidences of the former presence of
an ice sheet are irregular moraines ; undrained basins ; numerous lakes ;
long, winding gravel ridges, or osars ; tumultous hills of gravel, or kames ;
lenticular hills of till with smooth surfaces, or drumlins ; broad and
frequently gently sloping gravel plains, sometimes with pitted surfaces ;
boulders, occasionally perched on hilltops and mountain sides ; faceted
and striated stones ; outcrops with smooth and rounded contours, and
polished and striated surfaces.

With this elementary discussion of the general characteristics of
glaciers and of the records they leave when climatic changes lead to their
disappearance, we will pass in the following chapters to an account of the
glaciers now in existence in North America.



CHAPTER II.

GENERAL DISTRIBUTION OF THE GLACIERS OP
NORTH AMERICA.

THE glaciers of North America are confined to the Cordilleran
mountain series and to the Greenland region.

Cordilleran Region. The Cordilleran series is, in fact, a family of
mountain systems in most of which there are several independent ranges
and multitudes of individual peaks. It is the longest mountain series in
the world, extending as it does from Cape Horn to the western extremity
of the Aleutian islands, a distance of over 7000 miles. In Central
America it is represented hy a single system, in Mexico it becomes divided,
and in the United States it is definitely separated into the Rocky mountains,
Sierra Nevada-Cascade, and Coast systems. In Canada the breadth of the
series increases northward, and four well-defined mountain systems are
recognized, viz. : the Rocky, Gold, Coast, and Vancouver. What is known
as the Coast range in Canada is not a continuation of the Cascade mount-
ains, as sometimes stated, but is distinct from them both topographically
and geologically. Vancouver system may sound strange to many readers,
but is an appropriate designation, proposed by the Geological Survey of
Canada, for the great system of uplifts beginning at the south in the
Olympic mountains, Washington, and extending northward through
Vancouver and Queen Charlotte islands, and attaining its greatest
development on the coast in southern Alaska, and finally terminating
at the west in the Aleutian islands. 1

In Canada and Alaska the mountains of the Cordilleran series near
the coast become more elevated than those of the interior and bend
abruptly westward in the central part of their course. The eastern
system in the same series is prolonged northward, and judging from the
meagre information at hand, decreases in height and ends indefinitely
before reaching the shores of the Arctic ocean.

1 A. R. C. Selwyn and G. M. Dawson, "Descriptive Sketch, Geological and Geographic,
of the Dominion of Canada," Montreal, 1884, p. 35.



DISTRIBUTION OF THE GLACIERS OF NORTH AMERICA. 33

Several of the great volcanic peaks of Mexico, which belong with the
Cordilleran series but are of secondary origin, attain an elevation of from
17,000 to over 18,000 feet, and reach the horizon of perpetual snow. In
some instances true glaciers of small size are said to exist about their
summits, but little if any reliable information is available concerning
them, however, and we are obliged to pass them by.

The southern limit of glaciers in the United States is in the High
Sierra, California, in about latitude 39. The ice bodies of that region
are small, but have many of the essential features of the most typical
ice streams of the alpine type. They are confined to sheltered amphi-
theatres about the highest peaks, and do not extend lower than about
13,000 or 12,000 feet above the sea. In most instances they are at
the northern base of sheltering precipices, and terminate before reaching
the upper limit of timber growth.

In northern California, and in Oregon and Washington, glaciers are
more numerous, of greater extent, and reach lower limits than in the
Sierra Nevada, but are still confined to the higher portions of the more
elevated peaks and do not extend to a lower horizon than about 6000
feet above the sea. In many instances they reach the upper limit of forest
growth. The best examples cluster about the summits of Mount Shasta,
Mount Rainier (Tacoma), Mount Baker, and other volcanic peaks of the
same region.

In the Rocky mountains, glaciers are foreshadowed at the south by
small snow bodies in Colorado, which certain travelers who have examined
them consider worthy of being numbered among glaciers. 1 Perennial
snow banks increase in number and in extent towards the north, and true
glaciers occur in Montana and adjacent portions of Canada.

Glaciers are numerous in the Cordilleran series in Canada and furnish
some of the most attractive features in the scenery of that wild and
picturesque land, but unfortunately only meagre information concerning
them is yet available. The best known examples appear in the Selkirk
mountains, one of the loftiest ranges in the Gold system, and in the
Coast mountains in the vicinity of the Stikine river. Further north, in
the same great mountain series, bodies of perennial ice become more and
more numerous, at the same time increasing in size, and reach their

1 F. H. Chapin, "The First Ascent of a Glacier in Colorado," Appalachia, vol. 5, 1887,
pp. 1-12.

An account of the occurrence of typical glaciers near McDonald lake, in northern
Montana, by L. W. Chaney, Jr., was published in Science, vol. 2, 1895, pp. 792-796.



34 GLACIERS OF NORTH AMERICA.

most magnificent development in southern Alaska. The most thoroughly
ice-covered region in the Cordilleran series is in the vicinity of Mounts
Fairweather, Logan, and St. Elias, and lies partially in Alaska and
partially in Canada. Westward from that stronghold of perennial
ice, as previously stated, the mountains decrease in elevation. The



Online LibraryIsrael C. (Israel Cook) RussellGlaciers of North America; a reading lesson for students of geography and geology → online text (page 4 of 24)