WELLS OF JERSEY COUNTY, ILLINOIS. 747 



valleys are liable to increase the average much beyond this amount. The 

 drift is sufficient to greatly obscure the preglacial valleys and ridges. 



Wells are ordinarily but 20 or 30 feet in depth, being obtained usually 

 before entering the blue till. On the bottoms of the Illinois and Mississippi 

 they are obtained at about 30 feet in sand and gravel. 



INDIVIDUAL WELLS. 



At Fieldon, in the western part of the county, rock is struck in wells 

 at about 25 or 30 feet, and the best wells are obtained from this source at 

 depths of 40 to 60 feet. 



At Otterville the wells are from 14 to 35 feet in depth, and usually 

 obtain water without entering rock. A section on Otter Creek bluff, near 

 this village, reported in the Geology of Illinois, is as follows: 



Section of bluff of Otter Greek, near Otterville, Illinois. 



Feet, 



Yellowish brown clay (mainly loess) 16 



Sand and gravel with bowlders _ 30 



Blue clay 15 



Total 61 



The writer found a similar section on a ravine southwest from Fieldon, 

 and there the blue clay at the base is a typical till. 



At Beatty's Mound, between Otterville and Jerseyville, a well reached 

 a depth of 65 feet without entering rock. The mound or drift knoll stands 

 about 40 feet above the bordering plain. Wells on the plain north of the 

 mound enter rock at about 30 feet. 



At Jerseyville the public water supply is obtained from a well 2,003 

 feet in depth, which obtains most of its supply from the St. Peter sand- 

 stone at 1,400 to 1,600 feet. The water rises within 100 feet of the sur- 

 face, or to 562 feet above tide, and the well will yield by pumping 200 

 gallons per minute from a 3-inch hole. An analysis of the water is pre- 

 sented in the Seventeenth Annual Report of this Survey (Part II, p. 827). 

 It contains about 86 grains of salt per gallon, but is considered a palatable 

 water. Rock is entered in that vicinity at about 20 feet, and wells are 

 obtained either near the base of the drift or the top of the rock. 



At Fidelity, in the eastern part of the county, wells are usually obtained 

 at about 25 feet near the base of the drift, but a few pass into the underlying 

 rock. In the eastern and southeastern parts of the county the drift is 20 to 

 35 feet in depth, and wells not infrequsntly enter the rock. 



