742 THE ILLINOIS GLACIAL LOBE. 



knolls they are often sunk to depths of 40 feet or more without encounter- 

 ing blue till. 



A well on a drift ridge in the east part of the county in sec. 17, T. 10, 

 R. 1 W., reached a depth of 97 feet without entering rock and was mainly 

 through a hard clay of yellowish brown color. Beds of dry sand and cob- 

 blestone were also penetrated. A well on a neighboring section (sec. 20) 

 obtained water in cobble below brown till at a depth of 40 to 47 feet. 



MACOUPIN COUNTY. 

 GENERAL STATEMFNT. 



Macoupin County is situated southwest of the center of the State, 

 immediately south of Sangamon and west of Montgomery County. It has 

 an area of 864 square miles, with Carlinville as the county seat. The 

 county is traversed nearly centrally from east to west by Macoupin Creek, 

 which is the only stream of importance found within its limits. The south- 

 east part is drained southward through Silver, Cahokia, and Piasa creeks 

 and "Wood River. The northwest, portion of the county drains westward 

 through Apple Creek. Narrow strips of imperfectly drained land occur 

 along the divide between Macoupin Creek and streams flowing southward, 

 but the greater portion of the county is well drained. It has a thin deposit 

 of silt somewhat less porous than typical loess, yet it absorbs the excess of 

 rainfall more rapidly than the white clay districts to the east. 



The drift surface is generally plane, though occasional knolls 20 to 30 

 or even 50 feet in height occur. The largest ones noted are about 5 miles 

 easl of Carlinville, on the borders of Macoupin Creek. The thickness 

 of the drift is apparently less on the water partings in the north and south 

 parts of the county than near Macoupin Creek in the central portion. It is 

 probable as noted above that this stream follows approximately the line of 

 a preglacial valley. 



The wells are usually found at depths of 25 to 50 feet, many of them 

 obtaining their supply above blue till, but others in sand and gravel beneath 

 it. The wells and natural exposures indicate that a sheet of hard blue till 

 is generally present in this county as in Montgomery County, setting in at 

 about 20 feet and extending to the rock. 



