HISTORY OF THE GLACIAL THEORY, AS TOLD BY AGASSIZ.
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.”
