240 THE ILLINOIS GLACIAL LOBE. 



Illinois, it decreases to 10 or 12 miles, and continues into Indiana with 

 about the same width. On this plain, as on the plains between the ridges 

 of the Champaign morainic system, the surface is generally much smoother 

 than on the ridges. There are occasional knolls, however, which reach a 

 height of 30 feet or more, and swells 5 to 10 feet in height are found in 

 nearly every township. 



The thickness of drift differs from that in the morainic ridges only by 

 the measure of the relief of the ridges. In the Indiana portion, and for . 

 some distance westward into Illinois, rock is often encountered at a depth 

 of 50 feet or less, but in Champaign County the drift thickness increases to 

 200 feet or more, for the thickness, as on the ridges, is much greater in the 

 western than in the eastern portion of the county. The thick drift continues 

 northwestward into Ford and McLean counties. 



There is beneath these plains a buried soil found at a depth of 75 to 

 100 feet or less in Champaign County, and at 25 to 50 feet in counties 

 farther east. This appears to be at the base of the Shelbyville drift sheet. 

 As yet no soil has been discovered between the Champaign and Shelbyville 

 sheets. The drift appears to be composed more largely of till beneath 

 these plains than in the moraines, but sufficient gravel and sand occur to 

 afford water for wells throughout most of the region. 



SECTIOX III. BLOOMINGTON MORAINIC SYSTEM. 



The system of moraines to which the name Bloomington is applied is 

 scarcely surpassed in strength of development or in complexity of features 

 by any other morainic system in the early Wisconsin series. It is one of 

 the most important in the series, not only because of its strength of develop- 

 ment but because it extends in places beyond the earlier moraines of the 

 series, and for a distance of about 120 miles constitutes the border of the 

 Wisconsin drift. It receives its name from the city of Bloomington, Illinois, 

 which stands on a prominent portion of its chief ridge. The name seems 

 especially pertinent since Bloomington is situated near the middle point of 

 this morainic loop, just as Shelbyville is situated near the middle point of 

 the Shelbyville loop. 



Where best developed there are two bulky ridges, constituting the 

 outer part of the system, and two smaller ridges constituting the inner part. 

 The four ridges are not continuously developed, however, since they inter- 



