308 WARREN UPHAM, ESQ., M.A., F.G.S.A., ON 
in the Mississippi river basin, probably of Albertan age, 
stretches south at least to southern Iowa, where it is overlain 
by interglacial beds, inclosing peat, well displayed in sections 
at Afton, Iowa. The Aftonian interglacial stage, especially 
notable for its extensive buried forest bed, containing trunks 
of hardy northern coniferous trees, has been ascertained to 
be earlier than the Kansan readvance of glaciation. It is 
therefore probably equivalent with the Saskatchewan stage 
of Canada, which name it should then displace according to 
the rule of priority. 
2, KANSAN STAGE.—Farthest extent of the ice-sheet in the 
Missouri and Mississippi river basins, and in northern New 
Jersey. The Saxonian stage of maximum glaciation in 
Europe. 
Area of the North American ice-sheet, with its develop- 
ment on the arctic archipelago, about 4,000,000 square 
miles; of the European ice-sheet, with its tracts now occupied 
by the White, Baltic, North, and Irish Seas, about 2,000,000 
square miles. 
Thickness of the ice in northern New England and in 
central British Columbia, about one mile; on the Laurentide 
highlands, probably two miles; in Greenland, as now, 
probably one mile or more, with its surface 8,000 to 10,000 
feet above the sea; in portions of Scotland and Sweden, 
and over the basin of the Baltic Sea, half a mile to a mile. 
3, HELVETIAN STAGE.—Recession of the ice-sheet from its 
Kansan boundary northward about 500 miles to Barnesyille, 
Minnesota, in the Red River valley; 250 miles or more in 
Illinois, according to Leverett, but probably lttle between 
the Scioto River, in Ohio, and the Atlantic coast, the 
maximum retreat of that portion being 25 miles or more in 
New Jersey. Deposition of the Buchanan gravels and 
sands, as named by Calvin in Iowa, during the retreat of the 
Kansan icefields ; and time of the Yarmouth weathered zone 
and erosion, noted by Leverett in Iowa and Illinois. A cool 
temperate climate and coniferous forests up to the receding 
ice border in the upper Mississippi region. Much erosion of 
the early drift. 
The greater part of the drift area in Russia permanently 
relinquished by the much diminished ice-sheet, which also 
retreated considerably on all its sides. 
During this stage the two continents probably retained 
mainly a large part of their preglacial altitude. The glacial 
recession may have been caused by the astronomic cycle 
