364 POPULAR SCIENCE MONTHLY. 



consider to have been formed rapidly while the ice was retreating 

 from its Iowan stage, with no important general readvance di- 

 viding the Iowan from the Wisconsin or moraine-forming stage. 



Not only are the Kansan and Iowan stages of culmination of 

 the ice sheets closely alike for North America and Europe, but 

 also the land depression of the Champlain epoch in both these 

 widely separated great areas brought marine submergence of 

 coastal tracts, and caused rapid disappearance of the ice sheets, 

 with the formation of their drumlins and marginal moraines. 

 These two continents were included in the portion of the earth's 

 crust which twice experienced far-extended epeirogenic move- 

 ments, first of high uplift, bringing the cold climate and snow 

 and ice accumulation of the Glacial period, and afterward of de- 

 pression somewhat lower than now, whereby the vast ice fields 

 were melted away. 



The accompanying maps * show the area of the North Amer- 

 ican and European ice sheets in their maximum extension, and at 

 definite times in their recession, as known by their areas of drift 

 and belts of marginal moraines, and by the beaches of glacial 

 lakes formed between the present watersheds and the northwardly 

 retreating ice border. These maps give the boundaries of the 

 Kansan, Iowan, and Wisconsin formations, adopting these names, 

 according to the law of priority, for both continents, and add for 

 the northeastern United States and Canada the subsequent War- 

 ren, Toronto, Iroquois, and St. Lawrence stages in the glacial re- 

 treat. 



The culmination of the great epeirogenic uplift, which had 

 been in progress through the preceding Lafayette period, raised 

 the glaciated areas, both in North America and Europe, to so high 

 altitudes that they received snow throughout the year, and be- 

 came deeply ice- enveloped. Submerged valleys and fiords show 

 that this elevation was one thousand to four thousand feet above 

 the present height. The accumulation of the ice sheets, due to 

 snowfall upon their entire areas, was attended by fluctuations of 

 their gradually extending boundaries, giving the Scanian and 

 Norfolkian stages in Europe, and an early glacial recession and 

 readvance in the region of the Moose and Albany Rivers, south- 

 west of James Bay. 



During the Kansan stage the ice sheet attained its farthest ex- 

 tent in the Missouri and Mississippi River basins and in northern 

 New Jersey, this being probably at the same time with the Saxo- 

 nian stage, as later named by Geikie, of maximum glaciation in 

 Europe. 



In the Aftonian stage the ice sheet receded from its Kansan 



* From Greenland Icefields, chapter xiv, but on an enlarged scale. 



