WELLS OF STEPHENSON COUNTY, ILLIN3IS. 567 



although they are all situated within 5 miles of the glacial boundary, and 

 some of them within 2 miles. 



STEPHENSON COUNTY. 

 GENERAL STATEMENT. 



Stephenson County is situated immediately east of Jo Daviess County, 

 on the north border of the State, with Freeport as its county seat, and has 

 an area of 560 square miles. It is drained chiefly by Pecatonica River, 

 which traverses its northern and eastern portions. With the exception of 

 a few square miles in the northwest corner, this county is covered with 

 glacial drift. The thickness of the drift is insufficient to conceal the main 

 preglacial valleys, and extensive upland tracts have rock within a few feet 

 of the surface. The average of the well sections reaching rock so far as 

 collected are as follows: Forty-eight wells on uplands and slopes, 31 feet; 

 12 wells along preglacial valleys, 130 feet. Of these, 17 wells are in 

 Freeport and vicinity, and average 50 feet. 1 The drift, as already noted, 

 is frequently aggregated in small knolls and ridges having a gravelly con- 

 stitution. At such places it has exceptional thickness. Aside from the 

 preglacial valleys and the knolls and ridges just referred to, the drift is 

 usually too thin to be depended upon as a supply for wells. 



Most wells in this county, as in Jo Daviess County, obtain water from 

 the Galena limestone at depths ranging from 30 or 40 feet up to about 

 200 feet. Their average depth is somewhat less than in Jo Daviess 

 County. In the preglacial valleys and in some of the drift knolls and 

 ridges strong wells are obtained at convenient depths — 25 to 50 feet. 



The highest portions of the county are very thinly coated with drift, 

 rock usiially being entered at 15 to 20 feet or less. A few instances, how- 

 ever, are reported in which the drift has a thickness of 80 feet or more. 

 The lowlands are generally covered to a sufficient depth to afford an ade- 

 quate supply of water without entering the rock; but there are small areas 

 within the lowland districts in which rock is very near the surface. These 

 contrasts in the thickness of drift, both on highland and lowland tracts, are 

 set forth in the table of wells given below. 



1 Many of the well records "were collected by Mr. Oscar Hershey during or prior to liis connec- 

 tion with this Survey. 



