698 THE ILLINOIS GLACIAL LOBE. 



than 200 feet, The elevation of the northern portion is greater than the 

 southern, but not so much as the difference in the thickness of drift, being 

 perhaps 50 or 75 feet greater. 



In the northern half, where the drift is thick, the structure is similar to 

 that of Iroquois County, which borders it on the north; there being a soft 

 blue till about 100 feet in thickness along the moraines, and of somewhat 

 less depth on the narrow plains between them. Beneath this till there is 

 frequently a black muck or soil, under which a harder till sheet sets in. In 

 places the lower portion of the drift is sand or gravel instead of hard till. 

 In the southern part of the county, where the drift is comparatively thin, it 

 consists of soft till similar to the surface portion in the district to the north. 

 The older sheets of drift are apparently present only in thin deposits. 



Many flowing wells have been obtained in the valley of Middle Fork, 

 near Potomac. J. M. Crayton, in a letter addressed to the Director, February 

 3, 1897, reported that within a square mile in the vicinity of Potomac there 

 are over 200 flowing wells, varying in depth from 65 to 140 feet, each 

 throwing a continuous and never-failing 2-inch stream of palatable water. 

 The water is obtained from beds of sand below blue till, and there are 

 three or more water-bearing beds, separated by thin beds of till or clay. 

 The wells situated on low tracts between morainic ridges in this county 

 have generally a strong hydrostatic pressure, with head but a few feet below 

 the surface. The absorbing area is, in all probability, on the neighboring 

 moraine. The sheets of drift are usually so arranged that water absorbed 

 by a moraine may readily pass northward beneath the neighboring till plain. 

 In the southern portion of the county there is also some rise in the wells, 

 especially if made on slopes north of the moraines. The wells there are, 

 however, shallower than in the northern portion of the county, and condi- 

 tions are, on the whole, less favorable for obtaining flowing wells. 



INDIVIDUAL WELLS 



The public water supply of Hoopeston is from a well 350 feet in 

 depth, which enters rock only 50 feet. The upper 30 feet of the drift is 

 clay and sand, the remainder principally gravel. The well is only 8 inches 

 in diameter, vet in 1895 it had an estimated capacity of 2,000,000 gallons 

 a day. The head is about 20 feet below the surface. The water is mod- 

 erately hard, and has a small amount of sulphate of sodium and a still 

 smaller amount of sulphate of magnesium, but is very palatable. The 



