BOWLDER BELTS. 325 



An extensive sand-covered tract south of the Kankakee, in western Indiana 

 and the east border of Illinois, is discussed below. 



The portion of the till plain north of the head of the Illinois shows 

 usually a perceptible descent away from the Minooka Ridge, accompanied 

 by a corresponding decrease in the thickness of the drift, On the borders 

 of the ridge the drift is 100 feet or more in average depth, while at the east 

 border of the till plain next to the Valparaiso system it is in places but 20 

 to 30 feet in depth. The drift appears to be mainly soft till, referable to 

 the Wisconsin sheets. In places it is gravelly or sandy at base. 



The portion of the till plain north of the Kankakee in general rises 

 slightly toward the north. The drift is apparently only 30 to 40 feet in 

 averag-e depth. In places rock ridg-es which cany scarcely any drift rise 

 slightly above the general level of the plain. Such ridges may be seen near 

 Manteno. The drift is apparently nearly all Wisconsin. A few instances 

 of the penetration of a buried . soil in wells were reported from the north- 

 east part of Kankakee County. This soil is within a few feet of the bottom 

 of the glacial drift. The drift north of the Kankakee contains much sand 

 and gravel, but there is usually a capping of till a few feet in depth. The 

 well sections of Will and Kankakee counties, presented in the latter part of 

 this report, will set forth the variations in the structure and the thickness of 

 the drift. 



SECTION II. BOWLDER BELTS. 



The Marseilles moraine and also the Minooka Ridge, as already indi- 

 cated, carry a very few bowlders on the surface. Bowlders are also com- 

 paratively rare on the inner or eastern slope of these ridges and on the till 

 plain between the Kankakee River and the Valparaiso moraine. There is, 

 however, a strip on the borders of the sand area along the south side of the 

 Kankakee in Kankakee and Will counties, and in places within the sand 

 area, where bowlders abound. This belt may connect on the southeast 

 with the Iroquois moraine, though the connection is rather obscure because 

 of sand accumulations. It appears to find a continuation northwestward in 

 Grundy County along the borders of Mazon Creek, from the vicinity 

 of Gardner to the mouth of the stream near Morris. From Morris a belt 

 of bowlders extends northward 3 or 4 miles, beyond which, for about 6 

 miles, they are comparatively rare. Near Plattville a narrow belt sets in, 



