October 25, 1895.] 



SCIENCE. 



531 



in regarding the Ice age as continuous, with 

 fluctuations but not complete departure of 

 the ice sheets, my view of the history of 

 the Glacial period, comprising the Glacial 

 epoch of ice accumulation and the Cham- 

 plain epoch of ice departure, may be con- 

 cisely presented in the following somewhat 

 tabular form. The order is that of the ad- 

 vancing sequence in time, opposite to the 

 downward stratigraphic order of the glacial, 

 fluvial, lacustrine and marine deposits. 



EPOCHS AND STAGES OF THE GLACIAL 

 PEEIOD. 



/. The Glacial Epoch. 



1. The ctTLMiNATioN OP THE Lafayette 

 EPEiROGENic UPLIFT, aflfecting both ]S"orth 

 America and Europe, raised the glaciated 

 areas to so high altitudes that they received 

 snow throughout the year and became 

 deepljr ice-enveloped. Valleys and fjords 

 show that this elevation was 1,000 to 4,000 

 feet above the present height. 



Rudely chipped stone implements and 

 human bones in the plateau gravels of 

 southern England, 90 feet and higher above 

 the Thames, and the similar traces of man 

 in high terraces of the Somme valley, at- 

 test his existence there before the maxi- 

 mum stages of the uplift and of the Ice 

 age. America appears also to have been 

 already peopled at the same early time. 



The accumulation of the ice sheets, due 

 to snowfall upon their entire areas, was at- 

 tended by fluctuations of their gradually 

 extending boundaries, giving the Scanian 

 and ISTorfolkian stages in Europe, and an 

 early glacial recession and re-advance in 

 the region of the Moose and Albany rivers, 

 southwest of James Bay. 



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 development on the Arctic archi- 

 pelago, abou.t 4,000,000 square miles ; of the 

 Greenland ice sheet, then somewhat more 

 extended than now, 700,000 square miles or 

 more, probably connected over Grinnell 

 land and Ellesmere land with the continental 

 ice sheet [the area of Greenland is approx- 

 imately 680,000 square miles, and of its pres- 

 ent ice sheet 575,000 square miles]; of the 

 European ice sheet, with its tracts now oc- 

 cupied 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 high- 

 lands, 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 basins of the Baltic sea, a half mile 

 to one mile. 



3. Helvetian or Aptonian stage. Ee- 

 cession of the ice sheet from its Kansan 

 boundary northward about 500 miles to 

 Barnesville, Minn., in the Red river valley; 

 250 miles or more in Illinois, according to 

 Leverett ; but probablj^ little between the 

 Scioto river, in Ohio, and the Atlantic coast, 

 the maximum retreat of that portion being 

 25 miles or more in New Jersey. A cool 

 temperate climate and coniferous forests up 

 to the receding ice border in the upper Mis- 

 sissippi 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 re- 

 treated considerably on all its sides. 



During this stage the two continents 

 probably retained mainly a large part of 

 their preglacial altitude. The glacial re- 

 cession majr have been caused by the astro- 

 nomic cycle which brought our winters of 

 the northern hemisphere in perihelion be- 

 tween 25,000 and 15,000 years ago. 



4. lowAN STAGE. Renewed ice accumu- 



