r42 The American Geologist. September, 1902 
to the .southern half of ^Minnesota, is therefore named the Af- 
tonian stage. 
During- this time, apparently, the Mississippi river in the 
vicinity of Minneapolis eroded a rock channel which is now 
mostly filled by the drift of the later glaciation, but is marked 
by a series of lakes, namely. Cedar lake, the Lake of the Isles, 
lakes Calhoun and Harriet, and others farther south. Prof. 
N. H. Winchell from his study of this interglacial channel of 
the Mississippi, has estimated the duration of the interglacial 
stage there as about 15,000 years.* It seems to be represented 
also in the history of the Quaternary lakes Bonneville and La 
Hontan, respectively described by Gilbert and Russell, as a pro- 
longed stage of desiccation of those lakes under a drier cli- 
mate, while their earlier and later flood stages are correlated 
with the Albertan and.Kansan stages of glaciation. Near the 
southern limit of the glacial drift, the Aftonian interval was 
doubtless much long'er than in jMinnesota. 
3. During the Kansan stage the ice-sheet attained its farth- 
est extent in the ^Missouri and Mississippi river basins, and in 
northern New Jersey. It is correlative with the Saxonian stage 
of maximum glaciation in Europe. The area of the North 
American ice-sheet, with its development on the Arctic arch- 
ipelago, was about 4,000,000 square miles ; and of the European 
ice-sheet, with its tracts now occupied by the White, Baltic, 
North, and Irish seas, about 2,000,000 square miles. 
4. In the Helvetian stage, named by Geikie from its re- 
cognition, in Switzerland and elsewhere in Europe, the ice- 
sheets receded far from their Saxonian and Kansan bounda- 
ries. The Buchanan gravels and sands, as named by Calvin in 
Iowa, were de]wsited during the retreat of the Kansan ice- 
fields ; and this time is also represented by the Yarmouth weath- 
ered zone and erosion of the Kansan drift, noted by Leverett 
in Iowa and Illinois. The greater part of the drift area in 
Russia was permanently relinquished during this stage by the 
much diminished ice-sheet, which also retreated considerably 
on all sides. 
5. The lozvan stage was marked by renewed accumulation 
of snow and ice. extending over a part of the country that had 
been laid bare by the preceding retreat. Before the farthest 
*Aw. Geologist, vol. X, pp. 69-80, with map and sections, Aug., 1892; and 
p. 302, Nov., 1892. 
