1891.] 
235 
[Upham. 
bia, and Washington. In the Cordilleran region the high summits 
of the Coast range projected above the ice surface ; but the Rocky 
mountains were probably wholly covered in their northern portion 
and southward to the Peace river, where they rise only 6,000 feet 
above the sea or 3,500 feet above the adjoining country. Farther 
to the east the mountains of northern Labrador, about 6,000 feet 
high, the Catskills, but none of the Adirondacks, and the peak 
of Mt. Katahdin, but not that of Mt. Washington, were visible 
as islands of rock upon the ocean-like expanse of ice, like the nuna- 
taks of the Greenland ice-sheet. 1 This was at the culmination of 
the second Glacial epoch, giving us a view of the maximum ex- 
tent and thickness of its ice-sheet, the departure of which was 
attended with the deposition of our modified drift and the forma- 
tion of these lake basins. 
The climatic conditions producing so great accumulation of ice 
were followed by the temperate or warm climate of the Cham- 
plain epoch, when it was melted away under the alternate influences 
of the sun’s heat and of rains. During the time of increase and 
culmination of the ice-sheet, we must believe that the conduction 
of heat from the earth’s interior to its surface, though of small 
amount, was sufficient to maintain there the temperature of 32° 
F., at which ice is melted, so that a feeble subglacial drainage 
would take place, producing probably in its main avenues of dis- 
charge considerable streams or even large rivers. The summer 
melting of the surface of the ice-sheet during its growth and 
greatest extension doubtless also added to the subglacial drainage 
by streams falling through crevasses and moulins. But in the 
Champlain epoch, or time of disappearance of the ice-sheet, the 
superficial melting was rapid throughout the warm portion of each 
year, while the subglacial melting went on at a very slow rate 
through both winter and summer, the same as it had been during 
the entire epoch of glaciation. Owing to the rapidity of the 
Champlain melting on the ice surface, and to the amount of drift 
thus exposed and subjected to erosion and transportation, which 
will be more fully discussed in a later part of this paper, the sub- 
glacial stream-courses were inadequate for the Champlain drainage 
1 “Glaciation of mountains in New England and New York,” Appalachia, vol. v 
1889, pp. 291-312; also in Am. Geologist, vol. iv, Sept, and Oct., 1889. “Glacial 
Lakes in Canada,” Bulletin, Geological Society of America, vol. ii, for 1890. 
