PLEISTOCENE HISTORY OF LOWER WISCONSIN RIVER 679 



This hypothesis involves a damming of the Mississippi River 

 by the ice tongue at the mouth of the Wisconsin. Under this 

 condition the Mississippi must then have flowed between this ice 

 tongue and the northern wall of the Wisconsin Valley and thence 

 eastward to the Rock River or more probably the Lake Michigan 

 Basin. Such an eastward flowing river, if the bedrock divide 

 near Portage had about the present altitude of 600 feet," would have 



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Fig. 4. — View of the outwash material on the high terrace at Wauzeka showing 

 lenses of sand in the gravel. 



had a gradient of about 2.5 feet per mile, or a foot per mile greater 

 than that of the present Wisconsin River. This suggests that the 

 down-warping of the eastern part of the area, mentioned above, had 

 already taken place. It seems, in fact, quite probable that this 

 eastern part of the region was lower than it is at present, for post- 

 Champlainic uplift and warping in the Great Lakes area probably 

 raised the divide from some lower elevation to its present altitude. 

 Since such down-warping as first mentioned has been found in 



' W. C. Alden, op. cit., Plate II. 



