WELLS OF KOCK ISLAND COUNTY, ILLINOIS. 619 



tion it may be stated that the wells throughout the sand district of tin- 

 Green River Basin are reported to furnish a water that is less hard than 

 that obtained from the till. 



ROCK ISLAND COUNTY. 

 GENERAL STATEMENT. 



Rock Island County occupies a narrow strip bordering the Mississippi 

 River for a distance of about 50 miles, the city of Rock Island, its county 

 seat, being about midway of its western border. The area of the county 

 being but 440 square miles, its average width is less than 10 miles. Rock 

 River divides it into two nearly equal portions and forms the eastern border 

 for about 20 miles in the northern part of the county. Meredosia Slough 

 forms the northern border of the county. Between this slough and the vil- 

 lage of Hampton there is an island-like tract of upland standing about 150 

 feet above the Mississippi River, which at times of high water either in the 

 Mississippi or Rock River is completely encircled by streams. Between 

 this upland and the city of Moline a gravel-filled valley, called "Pleasant 

 Valley," leads across from Rock River to the Mississippi (see PI. XVIII). 

 Its elevation is but a few feet above the high-water stages of the streams. 

 Between this valley and Rock River is another island-like tract of upland 

 leading from the city of Rock Island eastward to Carbon Cliff, which stands 

 about 150 feet above the Mississippi and Rock rivers. South from Rock 

 River Valley is an upland tract rising gradually southward from an eleva- 

 tion of 150 feet above the river at the bluff to fully 250 feet at the Mercer 

 County line, or to slightly more than 800 feet above tide. 



The island-like upland tract northeast from Hampton has a denosit of 

 loess 30 or 40 feet in thickness, beneath which there is blue till extending 

 to the rock, which is usually entered at 100 feet or less. The upland 

 between the city of Rock Island and Carbon Cliff has about 40 feet of 

 loess near the Mississippi, but the thickness decreases eastward to scarcely 

 more than 25 feet at Carbon Cliff. Beneath this loess is a thin sheet of 

 glacial drift, rock usually being struck at 50 to 75 feet. The upland south 

 of Rock River has a loess capping about 25 to 40 feet in thickness on the 

 borders of the Rock and Mississippi rivers, which decreases southward to 15 

 feet or less at the Mercer County line. On the brow of the Rock and Mis- 

 sissippi River bluffs rock is usually entered in wells at 50 to 60 feet, but on 



