336 THE ICE AGE IN NORTH AMERICA. 



According to Professor Todd the preglacial Missouri 

 River entered the valley of the James near its upper portion, 

 reaching its present channel at Yankton. Having filled this 

 valley, the advancing ice from the northeast obstructed the 

 mouths of the Grand, Moreau, Cheyenne, and White river 

 and, forcing the drainage in front of the ice across the cols 

 between these streams, gave rise to the present tortuous 

 channel across the State of South Dakota. Lake Arikaree 

 was one of the temporary results of this advance. Its shore 

 lines being clearly traced at a height of 400 feet above the 

 the present Missouri. The bowlders near the Moreau River 

 and the deserted river bed mentioned on pages 146 and 147 

 are connected with the existence of this lake. 



Coming still farther southeast, we find that the Minnesota 

 River makes a sharp turn to the north at Mankato, and so is 

 favorably situated for having its drainage reversed while the 

 ice rested over the counties about its junction with the Mis- 

 sissippi near St. Paul. The facts are found to be according 

 to the programme. There is abundant evidence of a tempo- 

 rary lake, covering the territory of Blue Earth and Faribault 

 counties, which emptied through a channel known as Union 

 Slough, about eight miles long and from one-eighth to one- 

 fourth of a mile wide, with bluffs from twenty to thirty feet 

 in height, which connect Blue Earth River with the Eastern 

 Branch of the Des Moines in Kossuth County, Iowa. 



In this connection it is in place also to refer to the dramatic 

 history of Lake Bonneville during the Glacial Period, though 

 a fuller account will be necessary in future chapters (see 

 pages 615 and 703) . This body of water accumulating in the 

 basin of Great Salt Lake during the moist and cool climate of 

 that period attained a depth of 1,000 feet, covering an area 

 of 20,000 square miles. At this elevation there is a distinct 

 shore line traceable around the whole distance, broken into 

 occasionally by terminal moraines of the glaciers that came 

 down from the Wasatch mountains. Near the northeast 

 corner of the basin a dirt dam had been formed 375 feet high 



