WELLS OP JO DAVIESS COUNTY, ILLINOIS. 565 



Mississippi will average about 20 feet, but the average for the county will 

 probably not exceed 10 feet. Along the Mississippi Valley on the west 

 borders of the county there is a filling of sand and gravel about 150 feet 

 in depth, as shown by wells on the Iowa side at Dubuque and Sabula. The 

 tributaries of the Mississippi in this county have been silted up to a level 

 corresponding with the filling in the Mississippi Valley. The material in 

 these tributaries is usually a rather compact clay. 



Wells in the valley of the Mississippi obtain water at depths of 20 to 

 40 feet without entering the rock. In the tributaries of the Mississippi a 

 few wells obtain water from the clay deposits, but as a rule the residents 

 depend upon either springs from the limestone bluffs or wells sunk into the 

 rock. The wells on the uplands in the unglaciated part, and to some extent 

 in the glaciated part, obtain their water from limestone at depths ranging 

 from 40 feet to 150 feet or more. Usually a good supply may be obtained 

 at less than 100 feet. In the glaciated portions of the county the drift is 

 generally too thin to afford strong wells. There is, however, just north of 

 Stockton a preglacial valley filled to a depth of at least 140 feet, which 

 furnishes strong wells, some of which overflow. Throughout the county the 

 water is of excellent quality, although very hard. The expense of sinking- 

 wells to rock being heavy, many of the residents resort to cisterns for a 

 water supply. Impounded water is also used quite extensively to supply 

 the stock on farms. 



INDIVIDUAL WELLS. 



The city water supply at Galena, the county seat, is obtained from an 

 artesian well sunk to a depth of 1,200 feet and obtaining its supply from the 

 Potsdam sandstone. It has a head 85 feet above the surface and a capacity 

 estimated at 166 gallons per minute. An analysis made by the State Board 

 of Health appears in the Seventeenth Annual Report of this Survey. 1 Wells 

 are obtained in the vicinity of Galena from the limestone at depths of 60 

 to 200 feet. 



At East Dubuque the town well is artesian and has a depth of 940 feet. 

 The water is obtained from Potsdam sandstone and has a head nearly 100 

 feet above the surface and a capacity estimated at 420 gallons per minute. 

 Aside from the artesian well there are a few shallow wells obtaining their 

 supply from the gravel and sand of the Mississippi Valley. 



'Part II, pp. 820 and 827. 



