LAKE KANKAKEE. 333 



borders of the sand area, the trend is not so easily systematized. The ridges 

 there are arranged in groups or strips, among which there are extensive 

 plane tracts, often bowlder strewn, and having only a thin sand coating. 

 Some attempts to systematize these ridges and associated bowldery tracts 

 have been made both by Professor Chamberlin and Professor Purdue, but 

 without the satisfactory results which they had sought to obtain. 1 



THICKNESS OF THE SAND. 



The thickness of the sand varies, both because of aggregation in ridges 

 and because of irregularities of the surface over which it is spread. In 

 much of the region within the Tippecanoe drainage basin the sand is very 

 thin except in the ridges. This condition prevails also over southern Jasper 

 and Newton counties, Indiana, and in parts of Kankakee and Will counties, 

 Illinois. An extensive region on either side of the Kankakee from eastern 

 Iroquois and Kankakee counties, Illinois, eastward to Marshall and St. 

 Joseph counties, Indiana, is covered with sand to a depth of several feet 

 below the level of the base of the ridges. Throughout much of this region 

 wells are obtained without passing below the sand. Their depth is shallow, 

 being generally 10 feet or less on the flat tracts, and correspondingly deeper 

 on ridges. 



Averaging the available data the sand apparently amounts to a contin- 

 uous sheet not far from 10 feet in depth, over the 3,000 square miles which 

 it covers, or to 5.68 cubic miles. 



VARIATIONS IN COARSENESS. 



The sand presents but little variation in coarseness. It is usually 

 sufficiently coarse for individual grains to be readily discerned by the 

 naked eye and is seldom too coarse for plasterers' use. Coarse gravelly 

 material is found in a ridge near Rensselaer and in beaches on the border 

 of the Illinois in Grundy County, Illinois. There are also gravel plains on 

 the border of the Valparaiso and Maxinkuckee moraines in Laporte and St. 

 Joseph counties. With these exceptions it is rare to find in these deposits 

 a pebble as coarse as a buckshot. 



In the Iroquois Basin in Newton County, Indiana, and also in parts of 

 Iroquois County, Illinois, thin beds of silt about as fine as loess and much 



1 Professor Purdue contemplates further study of the region to determine whether it is possible 

 to bring order out of the present apparent lack of system. 



