COMPOSITE MOEAINIC BELT OF NORTHERN ILLINOIS. 293 



entering rock. In the portion north from Hampshire the thickness is prob- 

 ably not much greater than the relief of the ridge, for rock is encountered 

 at a depth of 50 feet or less in much of the border district on the west. The 

 drift referable to the invasion which formed this ridge has probably a thick- 

 ness about equal to the relief of the ridge, which, as stated above, is usually 

 100 to 150 feet or more. 



STRUCTURE OF THE DRIFT. 



The ridge is composed mainly of blue till. Sand and gravel beds are 

 not sufficiently extensive to afford a general water supply. Even weak 

 wells are difficult to obtain in some parts of the ridg*e. Many wells must 

 be sunk 100, 125, or even 150 feet to obtain an adequate water supply. In 

 not a few instances the water supply appears to be obtained at about the 

 level of the base of the ridge and the junction between the Wisconsin and 

 older drift sheets. 



A few gravelly knolls were noted along the outer border of the ridge 

 west of Marengo, and at occasional points between there and Hampshire. 

 None of these rise more than 10 feet above the general level. A few gravel 

 knolls were noted near East Burlington, in sees. 23, 24, 25, and 26, T. 41, 

 R. 6 E., and low gravel ridges occur along the tributaries of the South 

 Kishwaukee in Ts. 40 and 41, R. 6 E. Excavations in these knolls usually 

 show a preponderance of sand and gravel over till, though the latter is often 

 present in considerable amount. The beds have no apparent uniformity in 

 direction or degree of dip. They are often curved and disturbed as if 

 affected by movements of the ice sheet over them. 



The presence of a buried soil was noted in several well borings of 

 which records were obtained. In the city of Marengo, on the borders 

 of Kishwaukee Valley, it is found at a depth of 30 to 60 feet, the variation 

 in distance being due to difference in elevation of the wells. In sec, 11, 

 T. 43, R. 5 E., a well on the outer slope of the moraine struck a. buried soil 

 at 70 feet. The soil was underlain by a soft whitish clay of slight depth, 

 beneath which gravel, yielding water, was found. In the cases just noted 

 the soil seems referable to the Peorian interglacial stage. A buried soil 

 was noted in one of the deep borings in T. 40, R. 7 E., which reached the 

 bottom of the drift. This soil, as noted on a preceding page, seems to be 

 at a level low enough to be referred to the Sangamon. The boring is on 



