406 THE ICE AGE IN NORTH AMERICA. 



the northern half of the lake area, while the region at the south 

 was almost at rest; and finally, during the recent epoch, after 

 the whole basin of Lake Agassiz was passed by this wave like 

 permanent uplift, it has been elevating the basin of Hudson 

 Bay, where the movement appears to be still in progress. 

 Pleistocene oscillations of the land in many other parts of 

 the world have been independent of glaciation, or these have 

 been combined with movements due to the accumulation of 

 ice-sheets and to their removal; but the uplifting of the basins 

 of Lake Agassiz and Hudson Bay is apparently attributable 

 wholly to the departure of the ice-sheet. 



The entire duration of Lake Agassiz, estimated from the 

 amount of its wave action in erosion and in the accumulation 

 of beach gravel and sand, appears to have been only about 

 1,000 years; and the time of its existence and of the end of the 

 ice age is thought, from the rate of recession of the Falls of 

 St. Anthony, cutting the post-glacial gorge of the Mississippi 

 River from Fort Snelling to Minneapolis, to have been some- 

 where between 6,000 and 10,000 years ago. 



