294 THE ILLINOIS GLACIAL LOBE. 



the farm of James Powell, in sec. 7, near the crest of the ridge, and the 

 section is as follows: 



Section of James Powell's boring near Lily Lake, Illinois. 



Feet- 

 Pebbly soil 1 



Brownish-yellow pebbly clay 15 



Grayish-bine pebbly clay 180 



Black mucky soil 2 



Greenish clay 3 



Hard pebbly clay of brownish-blue color 40 



Sand .' 2 



Hard clay 8 



Limestone 200 



Total depth 450 



The thickness of the yellow till in the above well section is greater than 

 the average, though instances were found in which the till presented a yel- 

 lowish color to a depth of 35 feet from the surface. The average depth of 

 the yellow till is about 10 feet. Several sections of wells along this ridge 

 are presented below in the discussion of the wells of Illinois. The till is 

 thought by some well drillers to be slightly more stony in the ridges than 

 on plane tracts in McHenry and Kane counties, but the difference is not 

 very marked. Surface bowlders are common over the entire length of the 

 ridge, and in a few places are very numerous. They are especially abun- 

 dant in the vicinity of the McHenry-Kane county line and also near East 

 Burlington. Bowlders are composed mainly of granitic and other rocks of 

 Canadian derivation, limestones and local rocks being rarely found at the 

 surface. In the till, however, limestone rocks are a conspicuous ingredient, 

 and also in the kames or gravelly knolls. 



■ CHARACTER OF OUTWASH. 



Along the outer or western border of this ridge from the State line 

 southward to Hampshire there is a nearly continuous gravel plain formed 

 apparently as an outwash from the ice sheet. It extends out usually a mile 

 or more from the foot of the moraine, and leads westward down the Kish- 

 waukee Valley to Rock River. From Hampshire southward the plain out- 

 side Marengo Ridge is nearly free from coarse outwash and carries only 

 slight deposits of silt and sand. 



The gravel plains usually have a capping of loamy clay 2 to 6 feet or 

 more in depth, which gives them great fertility. Beneath this clay are beds 

 of sand and gravel which show considerable variety in coarseness in vertical 



