Popular Science Monthly/Volume 54/January 1899/Glacial Geology in America
|GLACIAL GEOLOGY IN AMERICA.|
By Prof. DANIEL S. MARTIN.
UNDER this title the vice-president of Section E (Geology) of the American Association—Prof. Herman L. Fairchild, of the University of Rochester, New York—gave an admirable résumé of the whole history, progress, and scope of the study of ice phenomena in North America, as the opening address before the section at the recent Boston meeting. Apart from the interest of the subject in itself considered, this address was a model of what such addresses should be. While strictly scientific, without the least attempt at rhetorical effect, it was at the same time so clear, so well arranged and so simple in language, that any intelligent auditor could enjoy it and grasp it, and carry away a distinct impression of the gradual development and present status of this great department of geological study. Professor Fairchild's choice of his subject was happy also in its fitness to the occasion, as covering almost exactly the half century of the life of the association, though going back indeed a few years further, into the period of the earlier society which developed into the association in 1848.
The great body of phenomena comprised under the term "drift," and the smoothed and scratched surfaces of rock, etc., had been by no means unnoticed by the early students of American geology, but they were attributed to violent and widespread water action, and were spoken of in general as "diluvial" formations. When the agency of ice began to be recognized, it was regarded as that of floating and stranding bergs; and this view for a long time contended with the theory of glacial action, even when the latter had been adopted and advocated by eminent students of the subject.
The first allusion to drifting ice as the agent of transportation of bowlders, etc., appears to have been made as early as 1825, by one Peter Dobson, of Connecticut, in a letter to Prof. Benjamin Silliman, of Yale College. Sir Roderick Murchison, who became the great champion of this view, credits Mr. Dobson's letter with giving him the first suggestion of it. Twelve years later, in 1837, T. A. Conrad made the earliest reference to land ice as the cause of our drift phenomena; he does this in very striking words when read in the light of the studies and determinations of later years, although of course imperfectly and vaguely.
Meanwhile, however, Agassiz and others had been working among the glaciers of the Alps, and their views as to a great period of former extension, in Europe and the British Isles, were finding some acceptance abroad. In this country, Prof. Edward Hitchcock, in his address as retiring president of the Association of American Geologists, in 1841, gave a broad and careful review of the drift phenomena in eastern North America, and referred to the work of Agassiz, Buckland, and Lyell with great interest, as having given him "a new geological sense" in observing these phenomena, and said, with prophetic foresight, "Henceforth, glacial action must form an important chapter in geology."
But the time was not ripe for the understanding and acceptance of the glacial theory as a later generation has come to know it. The studies of Agassiz and his confrères had been among glaciers upon mountain slopes, and hence, while many of the drift phenomena were strikingly accounted for, others were not and could not be. So it came to pass that, while Professor Hitchcock and others in this country were strongly impressed, they were not satisfied, and held for years an uncertain position. The glacial indications conformed in some aspects to the theory, but not in others; the striæ and groovings, instead of following valleys, all had a general trend to the southward, and the bowlders were carried across great depressions and deposited upon heights. How could these conditions be due to glaciers? Could ice flow uphill, or move long distances over level areas? These and other phenomena, such as the peculiar distribution of drift material, in "drumlin" ridges and the like, had no explanation. Hence, notwithstanding President Hitchcock's utterances above quoted, and his similar Postscript on the subject of drift and moraines, appended in the same year to his volume on the Geology of Massachusetts, we find him in 1843, when again addressing the Association of Geologists, adopting a modified tone, dwelling upon these points of difficulty, and seeking a compromise view, which he called "glacio-aqueous." The great influence also of Murchison and Lyell had been thrown into the scale in favor of the iceberg theory, and this fact doubtless had much to do with the slow development of true conceptions. Lyell visited America in 1842, and was present at the American Geologists' meeting, advocating the floating-ice doctrine, to which most of our observers already leaned; and so the views of Agassiz and the glacial school had to wait for a decade before they found general acceptance or even audience.
This, we may note in passing, Is but one marked instance out of many in the history of science, wherein the personal influence of eminent leaders has obstructed and retarded the advance of true knowledge. The whole recognition of the Cambrian system, as pre-Silurian and distinct, was suppressed and prevented for many years by Murchison's intense opposition to the views of Sedgwick. Similar facts might be cited in this country, did we care to mention names. Science can not claim, as is sometimes asserted, that it possesses or imparts any entire exemption from the influence of authority, and bestows complete independence from the tendency to "swear to the words of a master."
Of the New York geologists, Vanuxem alone, in his Geology of the Third District, 1842, inclined to the glacial theory; the others—Emmons, Mather, and Hall—advocated floating ice, the latter urging as a chief objection the absence of any great northern highlands from which glaciers could extend southward. Prof. Henry D. Rogers advocated De la Beche's view, of great catastrophic waves or débacles of water and ice, produced by sudden uplifts of the floor of a circumpolar ocean, and sweeping southward with tremendous power over the middle latitudes. These views were presented by him in 1844, at the Washington meeting of the geologists, and are to us a most curious illustration of the old "cataclysmic" phase of geological conceptions.
Two years later Agassiz came to America, and at once set about studying the ice evidences here, first in the White Mountains and then around the Great Lakes. At the first meeting of the American Association, in 1848, he presented his views as to the identity of our phenomena with those studied by himself, Desor, and Guyot abroad. His views were not very warmly received, however, and he did not attempt their public presentation again for some years, turning his attention more to the field of zoölogy. In 1850, in a work on Lake Superior, he refers somewhat sharply to the prejudice that seemed to prevail in relation to this subject.
From this time, however, the aqueous theories began to be less strongly presented; and a new generation of geologists was coming on, largely under the training of Guyot and Agassiz, and more open to their observed results. C. B. Adams, in 1850, presented a view nearly akin to that adopted by Dana a few years later, of an elevation of the high northern latitudes, resulting in a southward-moving glacial sheet, and a subsequent depression connected with its retreat, to account for the stratified deposits. Professor Dana accepted this doctrine in his presidential address before the association in 1855, adding the "Terrace period" of partial re-elevation. Prom this time he became the leader of the American glacialists, and his great Manual, issued in 1862, carried these views into all the colleges of the country.
In 1857 Prof. Edward Hitchcock published an important treatise on Surface Geology, particularly of the Connecticut Valley, in the Smithsonian Contributions to Knowledge. In this paper he noted the distinction, so important and now so familiar, between local striae and those with the general southward course of the "drift." Two years later his son, Prof. C. H. Hitchcock, extended this distinction widely over New England. In 1863 the report of progress of the Geological Survey of Canada gave an extended review of the surface geology, by Prof. Robert Bell, in which he fully adopted the glacial theory. Meantime, also, Professor Ramsay, in England, had abandoned the iceberg doctrine for that of glaciers.
In 1866 and 1867 important papers appeared by Charles Whittlesey, and one by Edward Hungerford; this last, read before the association, adopted the general views of Agassiz, with some important limitations now generally received. In the same year the revised edition of Dana's Manual gave yet fuller statement and wider diffusion to the generally accepted views as held to-day.
Professor Fairchild sums up this historical sketch as comprising four periods—viz., prior to 1841, undisputed reign of diluvial hypotheses; 1841 to 1848, suggestion and discussion of glacial hypotheses; 1849 to 1866, gradual acceptance of the latter view; from 1867 onward, development of glacial geology.
Erom this point, the address was occupied with consideration of the various aspects of the subject as studied and wrought out during the past twenty years by numerous observers. These are grouped under four main heads, each with various subdivisions—viz., (1) the ice sheet, as to its area, its thickness, its centers of dispersion, its migration of centers, etc.; (2) the ice period, as to its cause, its divisions, its duration, its distance in time; (3) the interpretation of special phenomena, such as moraines, drumlins, eskers, "kettles," and the like, valley drift, terraces, loess, etc.; and (4) existing glaciers, as discovered on our high mountains of the far West, and as studied in closer relation to the ancient phenomena in the great ice cap of Greenland and the immense glacier development in Alaska.
It is impossible to go into a detailed review of the numerous points of interest covered in this discussion. Suffice it to say that one who heard or who reads it finds an admirably clear and condensed account of all the problems and phenomena that have been and that are now encountered in the study of glacial geology on this continent, and of their gradual interpretation and solution by the combined labors of many students. The progress of knowledge over this wide field, advancing step by step, amid conflicting views and perplexing conditions, is beautifully shown, and leaves a very striking impression on the mind, of the difficulties and the successes of scientific research. Nor is Professor Fairchild disposed to claim too much or assert too strongly. He recognizes that, with all that has been met and mastered, there are still questions unsolved, and laurels to be won by others.
Among the facts brought out, a few may be briefly alluded to. The early abandonment of Agassiz's original view of a vast extension of the polar snow caps, and the recognition of separate centers of continental glaciation, now distinctly determined as three in number—a western, a central, and an eastern—the former being the earliest, and the others following in succession; the recognition by the Western geologists of the twofold character of the Glacial epoch, as also determined in western Europe, but less markedly traceable in our Eastern States, though now generally admitted; in close relation to this the determination of the line of the great terminal moraine, traced by successive observers from the Atlantic seaboard to Minnesota, and the subsequent recognition of an older, eroded, and fragmentary morainal "fringe," marking the line of the earlier ice sheet, somewhat beyond the later. With regard to the actual distance of the last glacial retreat, as expressed in years, Professor Fairchild is both cautious and frank. He notes the general consensus of recent observers toward a much shorter period than was formerly supposed—from five to ten or perhaps fifteen thousand years. At the same time, there are many elements of uncertainty involved, and the problem is by no means settled. The Niagara gorge, so long looked upon as a possible chronometer, grows more complicated as it is further studied; the rate of erosion has evidently varied much with the volume of water carried by the river; and this, in turn, has varied with the changes of level, and consequently of drainage routes, in the basin of the Great Lakes. There have been times when only the Erie waters flowed through the Niagara outlet, the upper lake drainage passing eastward independently, until a gradual northern rise of the land, which is proved to be still going on, turned the entire drainage into the present St. Clair route from Lake Huron into Lake Erie, and so through Niagara.
This point leads us to digress for a moment from the address under consideration to allude to a very interesting department of study that is now growing into prominence—to wit, the restoration of pre-glacial geography and hydrography, and the genesis of our existing river and lake systems throughout the northern part of the country. The discussions and results in regard to Niagara and the Great Lakes are somewhat familiar, but the work on the rivers and smaller lakes is not so widely known. Professor Fairchild himself has done much in relation to the "central lakes" of New York State; and one very interesting paper of this kind on The Development of the Ohio River was read before the section by Prof. William G. Light, of Granville, Ohio, besides many papers by others on similar topics.
The work done within a few years upon the glaciers of Arctic America has proved peculiarly fruitful in results. Here, again, the whole subject is reviewed historically, and the name and work of each observer are impartially noted. Much of the difficulty encountered by the glacial theory arose, as we have seen, from the fact that only mountain glaciers had been studied, so that many of the phenomena produced by continental ice could not be explained. Professor Fairchild says, as to this aspect: "More has been learned of the structure, behavior, and work of our ancient ice sheets by the study of the Alaskan glaciers during the last ten years, and especially by the study of the Greenland ice cap during the last four years, than by all the study of the Alpine glaciers for the seventy years since they have been observed." Prominent among those who have worked in this field are the names of Professors Chamberlain and Salisbury in Greenland, and Professors H. F. Reid and I. C. Russell in Alaska; other important contributors are Prof. W. P. Blake, the pioneer geologist in Alaska, 1867; Dall and Baker, who discovered and named the Malaspina Glacier in 1874; and John Muir, 1878, for whom the Muir Glacier was named; Wright, Baldwin, Schwatka, Libbey, and others, and Barton and Tarr in Greenland.
Professor Russell, in 1891, recognized and named a type of glacier that was before unknown. In his studies on the Malaspina he found a condition that does not occur, so far as yet observed, anywhere else than on the northwest coast of America; this is where a number of mountain glaciers debouch upon a low, flat coast plain, and unite to form a great sluggishly moving sheet of ice. This particular development he called the Piedmont type.
In closing his address, Professor Fairchild remarks that the word "theory," as applied to the glacial origin of the drift and its phenomena, may and should now be abandoned. The subject has passed beyond the stage of theory, and is as well understood and as clearly established as the volcanic origin of the cone of Vesuvius or the sedimentary origin of stratified rocks.