316 THE ILLINOIS GLACIAL LOBE. 



and shallow wells and even the cellar bottoms reach it. The drift appears 

 to be composed mainly of till and differs in no essential degree from that 

 found in the Marseilles moraine. The yellow or oxidized till at surface is 

 apparently somewhat thicker than on the moraine. At the smi'ace there 

 are extensive deposits of sand and silt occurring up to an altitude of nearly 

 650 feet, though most abundant at 575 feet or less, which in all probability 

 are referable to the lake that occupied the basin. These deposits in some 

 places reach considerable depth and are either accumulated in knolls and 

 ridges or spread evenly over the surface. In other places they are insuffi- 

 cient to conceal the surface bowlders. 



In the greater part of this district wells may be obtained at a depth of 

 25 feet or less. In some cases they are obtained at the base of the surface 

 sand; in others near the junction of the yellow and blue tills, there being 

 not infrequently thin beds of sand and gravel at that horizon; in still other 

 cases they enter the blue till. Several flowing wells have been obtained 

 from the drift. These are discussed in connection with other wells, in the 

 detailed discussion of wells given in Chapter XIV. 



