HYDROGRAPHY IN EARLY WISCONSIN EPOCH 



37 



Grand, Cheyenne, and White rivers, filling up their valleys in that order 

 for 100 miles or more. Of course this produced as many glacial lakes 

 at first; at least, so in the first and third cases. The Cheyenne had 

 formed a deeper and wider valley, and had perhaps so encroached in its 

 southern divide that it found a low col by which it seems to have 

 drained promptly into White river ; at least there is not so clear evidence 

 of a barrier there, nor of lacustrine action. This may have been due 

 partly to the divide being mostly Fort Pierre clay, with little hard ma- 

 terial in it. 



In the valley of Grand river, however, a large temporary lake was 

 formed, which has been called lake Arikaree * This is attested by a 



Figure Z.—Hydrographic Conditions in South Dakota in early Wisconsin Epoch. 



shoreline lying on the north slope of Fox ridge,f by the distribution of 

 northern boulders over its bed, and more clearly by traces of an old 

 channel 400 feet higher than the present Missouri and east of it in 

 northern Potter county.! By this means it drained by way of the Little 

 Cheyenne into the Cheyenne. We may suppose that there was another 

 outlet, which, cutting more rapidly, became the present Missouri at that 

 point. 



In the valley of White river another lake was formed north of the 

 high divide of which the Bijou hills are a remnant. The evidence also 



* Bulletin 1, South Dakota Geological Survey, p. 140. 



flbid., p. 119. 



| Figured, Bulletin no. 144, U, S, Geological Survey, pi. xi. 



