As a geologist the name of Agassiz will always be associated with what
is known in scientific parlance as “The Glacial Theory of Drift.” This
was first advanced by him, and by him was it triumphantly sustained. The
history of the growth and development of this important thought in his
mind, is worthy of attention—both because of its intrinsic interest and
importance and because it is an exhibition of the methods of research,
scientific insight and powers of generalization characteristic of Agassiz.
It is given here substantially as he gave it at the Anderson School at
Penikese. This theory proposes to account for the huge boulders that are
so profusely scattered over the surface of the continent north of the
40th parallel of latitude—and for all the gravel beds that are found
in the same localities, by assuming that during a comparatively recent
geological period the continents were covered with ice many thousand
feet in thickness, moving from the poles toward the equator—as glaciers
move down the Alps and other mountain regions, and doing the same kind
of work on a larger scale. This daring conception was received at first
by scientific men almost with contempt and derision—but is now generally
accepted.
Glaciers are accumulations of ice, descending by gravity combined with
other forces and conditions, down mountain slopes, along valleys, from
snow-covered elevations. They are streams or rivers of ice varying in
depth from a few hundred to thousands of feet. They are fed by the snows
and frozen mist of regions above the limits of perpetual snow. They
stretch far below the limit of perpetual snow, because their masses are
too thick to be melted by the heat of the summer.
Some of them reach down to the very orchards and the grain fields and
the blooming gardens of the valley; remaining all summer long within a
few hundred feet of the homes and cultivated fields of the inhabitants.
They bear upon their bosom vast streams of stones and rocks that have
fallen from the mountain slopes or have been torn from their places by
the movement of the glaciers. These they carry to their termination
and deposit in the valleys. These accumulations of stones, often many
square miles in extent and hundreds of feet in thickness, are called
moraines. Glaciers are not confined to mountain lands. Their domain is
rather in the polar regions, where vast masses of ice accumulate and move
forward by the same laws and in obedience to the same forces that govern
the formation and movement of mountain glaciers. They produce similar
effects, only upon a far grander scale.
The summer of 1836 Agassiz passed at the foot of the Alps with his old
friend Charpentier, who was familiar with the geology of Switzerland
and had devoted a great deal of his time to the study of the glaciers.
Charpentier had been told by the shepherds of the Alps that the glaciers
had brought down the rocks that were scattered through the valleys. The
scientists had previously believed them to have been transported by
water. Venetz, a Swiss civil engineer, told him that the peasants were
right, and the scientists wrong. “Upon this hint we acted,” said Agassiz,
“and together we went to ascertain the facts.” Many of the leading
geologists of the time believed with Werner, of Freiburg, Saxony, that
the loose unstratified material upon the surface of the earth should be
referred to the Noachian deluge as a sufficient explanation. From this
belief these phenomena were called Diluvium, or drift. Others, with
Hutton and Playfair, of Edinburgh, maintained that all rocks were derived
in one way or another by the agency of heat. That great master, Leopold
von Buch, soon showed that both were right, in part. “Von Buch,” said
Agassiz, “was a wonderful man—one of the great original investigators—a
man of indomitable perseverance. He traveled all over Europe on foot,
to study its geology. I have known him to go from Berlin to Stockholm
for the sake of comparing a single fossil with one there—or to start to
St. Petersburg with only an extra pair of socks in his pocket.” Yet he
was a German nobleman, and was welcome at the Emperor’s court—though
an exceedingly modest and humble man. Geology owes its present form to
Leopold von Buch, and to no one else. He was a pupil of Werner, but had
discarded Werner’s errors. In his travels in Scandinavia he laid the
foundation of geology as now known and understood. He had noticed the
loose boulders all over the sides of the mountains, and in the valleys
of Switzerland, to the Jura. He explained them by assuming that formerly
there were large lakes high up in the Alps, that had broken their
barriers and rushed down the mountains, carrying every thing with them
and sweeping the materials over an extensive territory. This opinion was
received as final, and the matter rested. Agassiz upon investigation,
began to doubt, and soon satisfied himself that the boulders were in
positions in which they could not have been placed by water. Charpentier
and Venetz, from the hint of the Alpine shepherds, had concluded that all
the phenomena were produced by the Alpine glaciers. Agassiz agreed with
them only so far as the range of Switzerland was concerned. But there
were boulders outside of Switzerland, beyond its valleys and mountains,
that were of such materials as were not found in the Alps. Germany was
covered with them clear up to the shores of the Baltic. Agassiz had
observed them in France, and was told that boulders of the same kind
were abundant in Scandinavia. “Then,” said Agassiz, “_it dawned upon me
that there might once have been glaciers in countries where they are not
now found, and they might have extended much farther than any we know of
now_.”
Surely this was a moment of inspiration—the first glimpse of the light
which has since become clear and perfect day. So Agassiz conceived the
idea of studying the glaciers, and went to work. In prosecuting his
investigations he passed nine successive summer vacations upon the
surface of the glaciers of the Alps, devoting his entire time to this one
object. During one season he slept seventy-one consecutive nights upon
the ice, under the stars. He said, “I studied glaciers to see how they
were made; to see how they worked; what they did, and what effects they
produced upon the countries where found. I was soon familiar with the
condition of the surfaces under a glacier. I saw that they are smoothed,
polished, grooved, scratched—as though a gigantic file had moved across
them. I compared their effects with those produced by the action of
water on rocks, in rivers, on the sea shore, in all sorts of places and
conditions, and I found that wherever water was at work the surface of
rocks was acted upon in a manner entirely different from that of ice. Ice
acts like a plane; water wears into ruts. Pebbles by the motion of water
are smoothed and rounded, but never polished. The effects are produced by
pounding and not by rubbing. But when ice moves over a solid surface the
moving mass between would be rolled, rubbed and polished. Scratches will
be made, rectilinear in direction, if the mass moves continuously in one
direction. The pebbles are found not only polished, but also themselves
scratched. In this way I learned to discriminate between loose pebbles
formed by water and those formed by ice. I next noticed that erratic
boulders were found to be always associated with scratched materials,
and lay over the surface, scratched. The materials were not stratified,
as were river deposits, but piled pell mell together. Satisfied with the
correctness of my observations in southern Europe, I asked myself whether
any other country, England, for example, in which there was no suspicion
of glaciers ever having existed, would exhibit the same phenomena. In
1840 I went to England with this idea in view.
“It was said, ‘Agassiz has gone to England on a glacier hunt,’ and I
was laughed at all over Europe. There were at that time many harsh
discussions going on between scientific men and others, and much
heart-burning among the scientists themselves. But all geologists were
satisfied, and agreed that the drift materials were all produced by the
agency of water. Leopold von Buch, the veteran, was the leader in this
opinion. So by my assertion that the drift had never been touched by
water, I had offended the great master, and I was only a boy, and had
only my convictions. _But I knew from my own investigations that I was
right_, and I fought my way, not by argument or prevailing influence, but
by evidence. In 1838, two years before my trip to England, I requested
Dr. Buckland, of Oxford, to come over and see me in Switzerland, and
allow me to show him the evidence of my convictions. Buckland was
Professor of Geology in Oxford University, author of the Bridgewater
treatise on geology, and afterward Dean of Westminster. He accepted my
invitation and became satisfied that the holders of the old opinions had
not seen all the facts—that the water theory, in short, was erroneous.
I found in him the first friend ready to investigate and explore. So
when I went to England in 1840 I readily induced him to accompany me in
my journey. In company with him I traveled over most of that country
and Scotland. The morning on which we approached the castle of the Duke
of Argyle is one I never shall forget, for as we looked from the top
of the coach upon the valley in which the castle lay, reminding me so
strongly of some of the familiar landscapes of Switzerland, I said to Dr.
Buckland: ‘Here we shall find our first indications of glaciers;’ _and
we actually had to ride over glacial moraines_ to reach the castle. We
traveled over nearly the whole of Great Britain, and I made a geological
map of the island to which, I think, not much has since been added.
Everywhere I found abundant evidence of glaciers, everywhere scratched
surfaces, covered with scratched boulders. Moraines piled up, and
elevations swept. _Then I did not hesitate to go beyond my facts, and
generalize_; and my generalization was this: As all mountain centers,
all high lands, constitute centers around which erratic boulders are
scattered, and as in that country, these mountain centers are now all
below the snow-line—that is, the line of perpetual snow—there must have
been a colder climate, _and glaciers must have existed upon mountains now
below the line of perpetual snow_. But this is true not only of England,
but also of other countries. All boulders come from their own mountain
centers, and similar phenomena are found in many parts of Europe, and on
the other continents. There are also still more telling facts. There are
spaces, now impassable, intervening between the drift boulders and their
origin, that must have been bridged over by ice. There are boulders in
Great Britain that must have come from Scandinavia across the North Sea.
Those which are spread over northern Germany also came from Scandinavia,
as is proven by the fossils they contain, and must therefore have crossed
the Baltic Sea. These and similar facts lead to a broader generalization.
_There was a time when the whole globe was very much colder than now,
when a great geological winter spread over the whole earth._ This period
I called the glacial period. It was anterior to our present state of
things, but subsequent to a period much warmer than now.” That the
age immediately preceding, which geology calls the Tertiary, was much
warmer, is proven by the fact that the remains of tropical animals are
scattered all over the American continent. Elephants, rhinoceroses,
tigers, camels, and many other tropical animals roamed over the northern
parts of the continent. They are all gone, and over their remains, and
covering the continent everywhere from Baffin’s Bay to Cape Horn, are the
erratic boulders and the drift. An examination of the drift phenomena of
North America led Agassiz to the conclusion that during this succeeding
geological winter our continent was covered by a sheet of ice many
thousands of feet—not less than a mile—in thickness.
Such is a brief account of the history of the inception and growth of
this now well known theory. From 1837 to 1840 no geologist was bold
enough to admit its truth; now no one is bold enough to deny it, except
in unimportant particulars. It has stood the test of years of violent
controversy. It stands now among the established facts of science. “In
some recent geological writings,” says Dr. Thomas Hill, “it is assumed
as a doctrine accepted from time immemorial, yet we all know that
forty-five years ago Agassiz was the only man who had ever peered into
the silent desert of that new thought.” Sir Roderick Murchison, the great
English geologist, once said of the glacial theory: “I have been for
twenty years opposing Agassiz’s views, and now I find that I have been
for twenty years opposing the truth.” The establishment of this theory
has a significance not thought of originally by its propounder. In one
of his lectures on Brazil he thus states the case: “If this doctrine
be true, you see at once how this intense cold must have modified the
surface of the globe, to the extent of excluding life from its surface—of
interrupting the normal course of the vital phenomena, and preparing the
surface of the earth for the new creation which now exists upon it. I
attach great importance in a philosophical point of view to the study
of this ice period; because, if demonstrated that such was once the
condition of our earth, it will follow that the doctrine of transmutation
of species, and of the descent of animals that live now, from those of
past days, is cut at the root by this winter, which put an end to all
living beings on the surface of the globe.”
* * * * *
Archbishop Usher, when crossing the Channel from Ireland to England,
was wrecked on some part of the coast of Wales. After having reached
the shore, he made the best of his way to the house of a clergyman, who
resided not far from the spot on which he was cast. Without communicating
his exalted station, the archbishop introduced himself as a brother
clergyman in distress, and stated the particulars of his misfortune. The
Cambrian divine, suspecting his unknown visitor to be an impostor, gave
him no very courteous reception, and said: “I dare say, you can’t tell
me how many commandments there are?” “There are eleven,” replied the
archbishop, very meekly. “Repeat the eleventh,” rejoined the other, “and
I will relieve your distress.” “Then _you_ will put the commandment in
practice,” answered the primate: “A new commandment I give unto you, that
you love one another.”