266 THE ILLINOIS GLACIAL LOBE. 



caps is Iowan or Illinoian has not been determined. Upon this determina- 

 tion must rest the age of the lower soil horizon. 



Buried soils are exceptionally well preserved along much of the course 

 of the Bloomington system east from the Illinois River, instances of their 

 occurrence in well sections being much more numerous than in districts to 

 the north, except limited areas in Bureau, Lasalle, Kane, and McHenry 

 counties. There is scarcely a township in which the junction of the Wis- 

 consin drift with older sheets may not be satisfactorily ascertained, either 

 through the presence of the buried soils or by a change in the till. 



STRUCTURE OF THE DRIFT. 



Throughout the entire length of the Bloomington system the great mass 

 of the drift composing its moraines, and also the plains between them and 

 on their inner borders, together with earlier sheets of the Wisconsin series, 

 consists of a soft blue till moderately stony and strikingly in contrast with 

 the harder till found beneath it. The till is very adhesive, so that when 

 excavated by a well auger it may be unrolled in great masses. The under- 

 lying harder till is far less adhesive. The surface portion of this till sheet 

 is oxidized to a depth of 6 to 10 feet and has a brownish color. There are 

 occasional developments of a pink-colored till. In places the pink color 

 extends to great depth, but usually the blue color sets in within a few feet 

 of the surface. The pink color is especially noticeable in the western and 

 northern part of the morainic system, from Peoria County northward. 

 Yellow till is also reported to occur in the midst of the blue till at many 

 points. It apparently marks the surface of earlier sheets of the Wisconsin 

 series. Its occurrence is known by well records only, no natural exposures 

 having- been found. Its degree of leaching and its state of oxidation are 

 not known. 



Associated with the till at various depths there are beds of sand and 

 gravel, often of considerable extent, which afford a supply of water for many 

 wells. It is not usual, however, to obtain strong wells within this drift 

 sheet. In every county hundreds of wells have been sunk to lower horizons 

 because of the inadequate supply found in this sheet of drift. 



There are very few gravel knolls in the moraines of this system, though 

 it is found that many knolls contain graved}' pockets in the till and these 

 have been utilized to some extent for road ballast. The amount of avail- 



