PLEISTOCENE HISTORY OF MISSISSIPPI VALLEY 625 
Valley, and Lake Chicago, in the Michigan Basin, through the IIli- 
nois Valley. At times Lake Chicago carried the drainage of glacial 
lakes in the Huron and Erie basins. As these lakes were settling 
basins, their outlets carried very little sediment, and the volume 
of water being large, they cut deeply into deposits that had been 
oAnamosa. 
Cedar Rapids | 
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e’Wew London 
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4 
Fic 2.—Map showing shiftings of course of Mississippi River 
built up by the waters flowing directly from the ice sheet, and 
developed a low gradient, lower than is consistent with the present 
Minnesota, St. Croix, and Illinois rivers, or even with the Mis- 
sissippi River. At the junction of the Minnesota and the Missis- 
sippi it cut to a level 30-40 feet below the present streams, and 
there is now backwater of that depth in the lower end of the Min- 
nesota Valley, caused by the aggrading effect of the Mississippi 
River. The conditions are similar at the mouth of the St. Croix 
