104 The American Gcohxjist. August, 1895. 
linquislied b}^ the luueh diminished ice-sheet, whieh also re- 
treated considerably on all its sides. 
During this stage the two continents probably retained 
mainly a large part of their preglacial altitude. The gla- 
cial recession may have been caused by the astronomic cy- 
cle which brought our winters of the northern hemisphere in 
perihelion between 25,000 and 15,000 years ago.* 
4. lowAN STAGE. Renewed ice accumulation, covering the 
Aftonian forest beds, and extending again into Iowa, to a dis- 
tance of 350 miles or more from its most northern indentation 
by the Aftonian retreat, and re-advancing about 150 miles in 
Illinois, while its boundary eastward from Ohio probably re- 
mained with little change. 
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. 
//. The Champlain Epoch. 
5. Champlain subsidence ; Neudeckian stage. Depres- 
sion of the ice-burdened areas mostly somewhat below their 
present hights, as shown by fossiliferous marine beds overly- 
ing 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 southwest of Hudson 
and James bays, and similar or less altitudes on the coasts of 
British Columbia, the British Isles, Germany, Scandinavia, 
and Spitzbergen. 
Glacial recession from the lowan boundaries was rapid un- 
der the temperate (and in summers warm or hot) climate be- 
longing to the more southern parts of the drift-bearing areas 
when reduced from their great preglacial elevation to their 
present hight or lower. The finer portion of the englacial 
drift, swept down from the ice-fields by the abundant waters 
of their melting and of rains, was spread on the lower lands 
and along valleys in front of the departing ice as the loess of 
the Missouri, the Mississippi, and the Rhine. Marine beds 
reaching to a maximum hight of about 375 feet at Neudeck, 
in western Prussia, give the name of this stage. 
6. Wisconsin stage. Moderate re-elevation of the land, in 
the northern United States and Canada advancing as a perma- 
*Am. Geologist, vol. xv, pjx 201, 255, and 293, March, April, and 
May, 1895. 
