42 The Atfierican Geologist. July, 1893 
Hict of ice with earth, the ice itself beint, r visible only in those places 
where crevasses reveal it, or where deep gorges are worn by running 
streams. Travelling still farther south, the explorer would come upon 
large areas in which he would not be able to know whether the glacier 
underlay the superficial drift or not. If he were to stop on one of those 
wide areas, and make his latitude and longitude certain, by a series of 
astronomical observations, he might rind to his surprise, after a few 
years' residence, that his observatory and apparatus had been bodily 
carried, by an imperceptible motion, some rods to the south. If he 
were to penetrate the earth on which his foothold seems so steadfast, 
he might find, equally to his surprise, that he was still riding on the 
surface of a vast ice-sheet, the earth and soil of which may have fur- 
nished him annual crops of potatoes and barley. In other places in 
the same latitude he would find the ice laid bare over considerable 
areas, washed clean by the drainage incident to the dissolution of the 
glacier. The turbid streams would be vastly larger than those which 
occupy the same beds to-day. They would run with tenfold more 
violence. The drift-materials would be freed from the clayey portions, 
and be spread along their channels in curious and varying assortment. 
In some places the thickness of the whole sheet of drift would be 
brought under this washing and stratifying process. In others, the 
ice gently dies out, and lets it down on the rocky surface without any 
change from the condition in which it lay on the glacier.* 
Besides regarding the area of predominant ablation as much 
wider than seems to me probable, even during the glacial re- 
treat, this view, like that of Dana, attributes nearly all the 
drift deposition to the Champlain epoch or time of departure 
of the ice-sheet, in which the drift had been enclosed. On the 
contrary, it seems to me certain that much deposition of drift 
took place under the ice, probably even in larger aggregate 
amount than the portion which was englacial when the ice- 
sheet finally disappeared. But the latter, as I have elsewhere 
endeavored to show in the papers before cited, appears, ac- 
cording to my studies, to have been the source of a consider- 
able part of the till, and of nearly all the material forming the 
eskers, kames, and other modified drift : while the terminal 
moraines, if I understand the method of their formation, 
were chiefly amassed from previously englacial drift, and the 
drumlins, though subglacial accumulations, were made of ma- 
terial which had been englacial until peculiar conditions at- 
tending the departure of the ice caused it to be deposited in 
these remarkable subglacial hills. f 
*Popular Science Monthly, vol. iii, pp. 293, 294. 
"{""Conditions of Accumulation of Drumlins,'' Am. Geologist, vol. x, 
pp. 339-362, Dec, 1892. 
