THE BLOOMINGTON MORAINIC SYSTEM. 269 



Bureau, Marshall, and Peoria counties, there being some farms on which 

 they are a serious hindrance to the cultivation of the. soil. But much of 

 the moraine in these counties is silt or sand covered to a depth of several 

 feet, so that bowlders, if present, are concealed. In the portion of the 

 morainic system between the Illinois River and Bloomington scarcely any 

 surface bowlders were noted, though there the surface silts are several 

 feet in depth. From Bloomington eastward there is generally a sufficient 

 number ot bowlders at surface or at slight depth in the soil to meet 

 demands for some time to come in supplying foundations for buildings 

 In places they were so numerous that farmers have collected them in piles 

 m the fields. Such is the case in the northern tier of townships of Vermil- 

 ion County, both along the crest of the north ridge and on its inner slope 

 The bowlders range in size from 8 or 10 feet in diameter downward the 

 ordinary size being 2 to 4 feet. Granite bowlders predominate over other 

 classes of rock along nearly the entire belt, and a few limestones were 

 noted. Greenstones and quartzites are also common. The bowlders are 

 in some cases much rounded by exfoliation, a feature which seems more 

 conspicuous than in bowlders on the Shelbyville sheet. Numerous com- 

 parisons were made of bowlders embedded in the till with those found at 

 the surface, and in almost every instance it was found that local or semi- 

 local rocks are much more abundant in the till than among the surface 

 bowlders. A much larger proportion of striated stones is also found in the 

 till than at the surface ; indeed, the surface bowlders are seldom striated. 

 These are features which, as already noted, are generally characteristic of 

 the till of the entire region under discussion in each of the several sheets 

 represented. Occasionally very large limestone blocks are found at the 

 surface or but slightly embedded in the drift. One block found a short 

 distance northwest of RossviUe, in Vermilion County, furnished several 

 wagon loads of excellent building stone, and when first discovered was 

 thought to be a ledge in situ, but subsequently proved to be a bowlder 

 embedded in the till. In that vicinity the drift is about 200 feet in depth 

 and is underlain by the Coal Measures. The nearest known outcrop of 

 limestone is about 30 miles to the north. 



Numerous well sections collected along the line of this morainic system 

 are presented in the discussion of the wells in the latter part of this report, 

 and these will serve to illustrate the variations in structure which this 

 morainic system presents. 



