744 THE ILLINOIS GLACIAL LOBE. 



on tributaries of Cahokia Creek. Private wells are obtained usually at 

 16 to 20 feet. Coal shafts penetrate 90 to 110 feet of drift, mainly blue 

 till. The drift is much thinner northwest from Staunton than at this 

 villag-e, rock being exposed along - Cahokia Creek at a level only 25 feet 

 below the bordering uplands. At the villages of Gillespie and Dorchester 

 rock is entered at 25 to 40 feet, or at a higher elevation than the surface 

 of the ground in Staunton, the altitude of the railway station at Gillespie 

 being 60 feet and at Dorchester 45 feet above Staunton. 



GREENE COUNTY. 

 GENERAL STATEMENT. 



Greene County is situated on the east side of the Illinois River, a short - 

 distance above its mouth, and has an area of 544 square miles, with Carroll- 

 ton as the county seat. It is drained westward principally by Apple Creek 

 and Macoupin Creek, the former leading through the north-central and the 

 latter through the southern portion of the county. Each of these streams 

 flows in a trough-like depression, which probably was the line of a pre- 

 glacial stream. The divides on either side of these depressions rise 50 or 

 75 feet above the level of the drift surface on the borders of the creeks, and 

 they apparently have a thinner coating of drift than the trough- like depres- 

 sions. AVells, however, are seldom sufficiently deep to test the thickness of 

 the drift. The county is well drained by streams and has also a coating of 

 loess which absorbs the rainfall rapidly. 



There are a few drift knolls in the western half of the county, the 

 largest of which rise about 50 feet above bordering plane tracts. There 

 are not such well-defined ridges in this county as in Pike and Adams coun- 

 ties, but it is thought that these knolls in Greene County mark the continu- 

 ation of the belt of drift ridges noted in those counties. 



The drift of Greene County consists largely of blue till, as in counties 

 to the north and east. The few borings which have reached rock penetrate 

 about 50 feet of drift, and this is probably about the average for the county. 

 Preglacial A-allevs may perhaps materially increase the average. The wells 

 are usually obtained before entering blue till at a depth of but 15 or 20 

 feet. In the Illinois bottoms they are often sunk to a depth of 40 feet, 

 mainly through fine sand. 



