748 THE ILLINOIS GLACIAL LOBE. 



MADISON COUNTY. 

 GENERAL STATEMENT. 



Madison Count}' borders the portion of the Mississippi River between 

 Alton and East St. Louis and extends a short distance northwest of the 

 former city. It has an area of 740 square miles^ with Edwardsville as the 

 county seat. The eastern part of the county drains southward through 

 Silver Creek, a tributary of the Kaskaskia. The northwestern jjortion is 

 drained southwestward to the Mississippi through Cahokia Creek and Wood 

 River. The drainage is generally sufficiently well developed to carry off 

 the surplus rainfall rapidly, but there are small tracts in the eastern part 

 of the county where drainage lines are not well developed, and the white 

 clay which covers that region will not absorb the rainfall. The western 

 half of the county is covered with a uorous loess which absorbs water 

 rapidly. 



The southeastern part of the county is traversed in a southwestward 

 course by a belt of drift ridges and knolls, which rise in places to a height 

 of 50 or 75 feet above the bordering plain. A few knolls occur in the 

 northeastern part of the county, which reach heights of 30 to 50 feet. In 

 the western part of the county the surface is generally plane, though a 

 knoll about 4 miles northwest of Edwardsville has a height of 30 or 40 feet, 

 and knolls 10 to 15 feet in height are not rare. 



The drift of this county, like that of Macoupin County, which joins it 

 on the north, consists largely of a compact till. This till has been noted 

 along the bluffs of the Mississippi as well as farther east, and the entire 

 county appears to have been heavily glaciated. Strise have been found in 

 several places in and north of Alton, within 1 or 2 miles of the Mississippi 

 River. The average thickness of drift in fifteen borings which reach the 

 rock is found to be 40 feet. As this does not include borings which have 

 been made in preglacial valleys, the average for the county probably is 

 somewhat greater than 40 feet. 



Wells are often obtained at depths of 20 to 25 feet without entering 

 a blue till, and they very seldom need to be carried into the rock. Wells 

 furnishing 20 barrels per day may usually be obtained from the drift, both 

 at shallow and greater depths. Wells are often sunk below the first water 

 vein in order to guard against contamination, for the porous loess of the 



