118 THE ILLINOIS GLACIAL LOBE. 



stream action in this part of the Mississippi Basin just before the first ice 

 invasion. 



The character of the deposits beneath the till in the valleys of south- 

 western Indiana has not received attention, for that region has been given 

 only a hasty reconnaissance. The Wabash Valley is filled to considerable 

 depth with sand and fine gravel, but this may be in large part derived from 

 the Wisconsin glacial drainage. Its rock floor stands 75 to 100 feet below 

 the present stream at the points where tested hj borings. The tributaries 

 show a correspondingly low rock floor, but their filling in the district outside 

 the Wisconsin drift is not so coarse as that along the Wabash. 



