Page:Popular Science Monthly Volume 68.djvu/304

THE DEVELOPMENT OF THE GLACIAL HYPOTHESIS IN AMERICA^[1]

By Dr. GEORGE P. MERRILL,

U. S. NATIONAL MUSEUM

GEOLOGY is preeminently a science of observation and deduction. Certain phases of it are, nevertheless, dependent upon advances in other branches. As the science grows this mutual interdependence becomes more and more apparent, and it is perhaps now questionable if further advance, aside from a purely geographic extension of knowledge relative to the distribution of geologic groups, is possible without calling in the aid of physics and chemistry.

Among those phases of geology which have been most independent of the allied sciences, and in which the gradual development of the power to observe correctly and deduce accordingly can incidentally be readily studied, the phenomena of the drift stand prominent. They furnish, moreover, an excellent example of the growth of knowledge through cumulative evidence, since of all phenomena, those relating to the drift have, in America, been perhaps longest under observation. In that which follows, however, it has been my principal aim to trace the gradual progress of the glacial hypothesis in America. Beyond this my references are purely incidental.

Out of numerous observations relating to the phenomena of the drift and, incidentally, to glaciation, those which seem most worthy of consideration at the present time were by Benjamin De Witt and are to be found recorded in the second volume of the 'Transactions' of the Philadelphia Academy for 1793.

De Witt noted the occurrence, along the shores of Lake Superior, of boulders representing a large variety of rocks, sixty-four different types being collected. In the discussion of this occurrence, he remarks:

Now, it is almost impossible to believe that so great a variety of stones should be naturally formed in one place. . . . They must, therefore, have been conveyed there by some extraordinary means. I am inclined to believe that this may have been effected by some mighty convulsion of nature, such as an earthquake or eruption, and perhaps this vast lake may be considered as one of those great 'fountains of the deep' which were broken up when the earth was deluged with water, thereby producing that confusion and disorder in the composition of its surface which evidently seems to exist.

This, so far as I am aware, is the first attempt to account for the

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1. Adapted from a presidential address delivered December 13, 1905, before the Geological Society of Washington.