312 THE ILLINOIS GLACIAL LOBE. 



In Kendall Comity it has a known range from 100 feet to fully 200 feet. 

 In Lasalle County the well records show a range from about' 100 up to 

 285 feet. In Livingston County the range is still greater, the distance to 

 rock varying from 100 to 360 feet. Along the line of Kankakee and 

 Iroquois counties it decreases from about 160 feet at the west to only 60 

 feet at Ste. Anne, but wells between Ste. Anne and the State line penetrate 

 80 to 150 feet of drift. 



The greater part of the drift appears to be referable to the Wisconsin 

 drift sheets. The older sheets are seldom entered at less than 100 feet 

 along the crest of the moraine, and in some wells a fresh-looking drift 

 (Wisconsin) is reported to extend to a depth of 160 feet. The drift refer- 

 able to the invasion which formed the Marseilles moraine probably about 

 equals in thickness the measure of the relief of the moraine, which, as 

 noted above, is 50 to 125 feet. 



STRUCTURE OF THE DRIFT. 



The Marseilles moraine consists mainly of a sheet of blue till which 

 contains only a moderate amount of coarse rock materials. A few low 

 gravelly knolls occur in some of the recesses on the outer border of the 

 moraine in Kane, Kendall, and northern Lasalle counties. The sharp 

 knolls south of Hersher, and the prominent group of knolls known as Mount 

 Langum, near Ste. Anne, are composed largely of gravelly material. 

 These constitute the chief instances of the occurrence of gravelly knolls 

 along the entire length of the belt. There are often small pockets or thin 

 beds of sand and gravel inclosed in the sheet of till, which afford a supply 

 of water for the shallow wells. These seldom afford a sufficient amount of 

 water for dairying or stock raising, the supply for these purposes being 

 obtained either from the older sheets of drift or from the underlying rock. 



This moraine carries very few surface bowlders, there being scarcely 

 enough to supply the needs of the residents for foundations of buildings 

 and construction of bridge culverts. In one locality, however, east of 

 Yorkville, the moraine is crossed by a bowlder belt which apparently 

 pertains to a later advance of the ice, since the bowlder belt does not follow 

 the moraine but passes southward across the inner-border plain, as indicated 

 later (pp. 325-326). 



