9 
TIME DIVISIONS OF THE ICE AGE, 399 
which brought our winters of the northern hemisphere in 
perihelion between 25,000 and 15,000 years ago,* 
4, IJowAN Stace.—Renewed ice accumulation, extending 
again from central Minnesota into Iowa, to a distance of 
300 miles or more from its most northern indentation by the 
Helvetian retreat, and readvancing about -150 miles in 
Illinois, while its boundary eastward from Ohio probably 
remained with little change. 
Previous to the farthest extension of this glaciation in 
Iowa, on the west side of the Wisconsin driftless area, the 
ice-lobe east of that area advanced from Illinois into the 
edge of south-eastern Iowa, giving an Illinoian stage of 
glaciation which somewhat antedated the maximum of the 
Iowan, though not probably by a wide difference of time. 
Between the retreat of the Illinoian ice-lobe and_ the 
deposition of the Iowan loess, Leverett notes interglacial 
deposits and a zone of weathering, the records of his 
Sangamon stage. 
Iowan time seems correlative with the Polandian stage of 
renewed growth of the European ice-sheet, probably 
advancing its boundaries in some portions hundreds of miles 
from the Helvetian retreat. 
Il. The Champlain Epoch. 
5, CHAMPLAIN SUBSIDENCE; NEUDECKIAN STAGE.—Depres- 
sion of the ice-burdened areas mostly somewhat below their 
present heights, as shown by fossiliferous marine beds 
overlying the glacial drift up to 300 feet above the sea in 
Maine, 560 feet at Montreal, 300 to 400 feet from south to 
north in the basin of Lake Champlain, 300 to 500 feet south- 
west of Hudson and James Bays, and similar or greater 
altitudes on the coasts of British Columbia, the British 
Isles (1,200 feet maximum), Germany, Scandinavia, and 
Spitzbergen. 
Glacial recession from the Iowan boundaries was rapid 
under the temperate (and in summers warm or hot) climate, 
belonging to the more southerm parts of the drift-bearing 
areas when reduced from their great preglacial elevation to 
their present height or lower. ‘lhe finer portion of the 
englacial drift, swept down from the icefields by the 
* American Geologist, vol. xv, pp. 201, 255, and 293, March, April, and 
May, 1895. 
