168 The American Geologist. March, 1902 
10,000 years ago, agreeing thus with the duration of the Post- 
glacial period estimated in America by Winchell, Wright, and 
others, including the present writer. The re-elevation of the 
area of lake Agassiz, to a vertical extent of 400 to 500 feet, 
took place, as I think, within a duration of no more than 
1,000 years, with departure of the ice-sheet from that lake 
area and its drainage as now to Hudson bay. The uplift there, 
in the center of North America, was thus at the average rate, - 
probably, of half a foot or more yearly, during several cen- 
turies.* In Scandinavia, and in the United States and Can- 
ada, the Glacial period was terminated alike by a great de- 
pression of the land from the high elevation to which it had 
been raised in preglacial time, and which continued doubtless 
through the greater part of the long Ice age. By this Cham- 
plain depression a temperate climate was restored on the 
boundary of the ice-sheets, which therefore receded by peri- 
’ pheral melting, probably with pauses or often short re-ad- 
vances where marginal moraines were formed. 
Under these temperate conditions, nearly the same fauna 
and flora followed close to the receding ice border as those 
which characterize the same regions today. Such climatic, 
faunal, and floral conditions, with the mainly rapid, but some- 
times wavering and interrupted, departure of the ice-sheet and 
re-elevation of the land from its Champlain subsidence, seem 
to me to require my explanation of the origin and history of 
the Toronto and Scarboro drift series,f instead of the view 
presented by Prof. A. P. Coleman.§ If epeirogenic move- 
ments of great preglacial elevation of a continent and ensuing 
depression, like those of Europe and America reviewed in this 
paper, have been respectively the causes of the oncoming and 
of the end of continental glaciation, it appears to me very 
highly improbable that such an interglacial stage as Coleman 
infers could have a place in the Glacial period. 
Nor is the difficulty of causation for distinct epochs of 
glaciation lessened, apparently, by the ingenious theories re- 
cently proposed by Chamberlin to account for the climatic 
changes of the Ice age.|| According to any available theory 
* The Glacial Lake Agassiz,’’ pp. 227-242. 
t AM. GEOLOGIST, vol, xxviii, pp. 306 316, Noy., 1901. 
§ AM. GEOLOGIST, vol, xxix, pp. 71-79. Feb., 1902. 
|| Journal of Geology, vol. v, pp. 653-688, Oct.-Nov., 1897; vol. vii, pp. 545- 
584. 667-685, 751-787, Sept.-Dec., 1899. 
