622 THE ILLINOIS GLACIAL LOBE. 



MERCER COUNTY. 

 GENERAL STATEMENT. 



Mercer County borders the Mississippi River immediately south of 

 Rock Island County and has an area of 555 square miles, with Aledo as the 

 county seat. It is drained by Edwards River and Pope Creek, each stream 

 having- a westward course entirely across the county. On the immediate 

 borders of the Mississippi the uplands are but 675 to 725 feet above tide, 

 but there is a gradual rise eastward across the county to an altitude of over 

 800 feet. Very few data concerning the wells have been obtained, the 

 writer having made but a single trip across the county. The drift appears 

 to be much thicker in the northern and eastern portions than in the southern 

 and western portions. In the latter district wells on the uplands often enter 

 rock at 50 feet or less, while in the former, if we may judge by wells in the 

 adjacent portions of Rock Island and Henry counties, the drift has a thick- 

 ness of about 150 feet. It is probable that the filling along the valley of 

 the Mississippi in the western part of this county is at least 150 feet, for the 

 river there is following the line of a deeply filled preglacial valley. 



INDIVIDUAL WELLS. 



The public water supply of the city of Aledo is obtained from a well 

 3,115 feet in depth, which probably is exceeded in depth by but one other 

 well within the limits of the State, a prospect boring- for salt water at 

 St. Johns which at last report (March, 1899) had reached a depth of over 

 3,600 feet. The Aledo well terminates in the Potsdam sandstone and has 

 a head 75 feet below the surface, or about 665 feet above tide. The well 

 is cased only 240 feet from top and 100 feet at 1,705 to 1,805 feet. Water 

 was struck at several levels, two strong- veins being found near the base of 

 the drift at 41 and 60 feet from the surface, and others in the Galena and 

 St. Peter and lower strata. The water was not markedly saline until a 

 depth of 2,620 feet had been reached. The temperature is 68° F. The 

 private wells in Aledo and vicinity are obtained at a depth of only 20 feet. 



At Keithsburg, in the Mississippi Valley, the public water supply is 

 obtained from wells driven to a depth of 20 or 30 feet in the valley gravel. 



A well on a terrace of Edwards River, in sec. 11, T. 14, R. 5 W., 

 entered a bed of peat at a depth of 44 feet, specimens of which were coh 



