64 THE ILLINOIS GLACIAL LOBE. 



penetrated 40 feet of nearly pebbleless brown clay, beneath which there is 

 a black muck 5 or 6 feet in depth which rests upon a red clay, apparently 

 a residuary product from the decay of limestone. 



East of Bay Creek, in T. 6 S., R. 2 W., wells along the outer drift 

 ridge frequently reach a depth of 50 feet, and occasionally 80 feet, without 

 entering rock. From descriptions of the material, it is probable that ordinary 

 till is penetrated, but no exposures were found. The loess in that locality 

 is about 20 feet in depth. 



From Pike County the drift border passes to the east side of the 

 Illinois. A typical till constitutes the greater part of the drift exposed in 

 ravines along that side of the river in Scott, Greene, and Jersey counties. 

 The loess on the river bluff is usually 20 or 30 feet in depth, but within 8 

 or 10 miles east of the river it decreases to 10 feet or less. The drift forms 

 a deposit probably 50 feet in average depth at the east border of the Illinois 

 Valley, but immediately west of the Illinois, in southern Pike and in Calhoun 

 County, there is scarcely a trace of drift. 



There are several knolls and ridges of drift a few miles back from the 

 drift border in Greene and Jersey counties, but no accurate well sections or 

 other exposures of their structure were obtained. The descriptions given 

 by residents, however, indicate that they are composed largely of clay. 



In Madison County typical till is found along the east bluff of the 

 Mississippi throughout the entire width of the county, as well as at points 

 farther east. At the immediate border of the valley there is a deposit of 

 loess 30 to 50 feet in depth, but within 10 miles back from the bluff the 

 thickness decreases to 10 feet or less. The till is usually 25 to 50 feet in 

 depth, and where thickest is of a blue color near the bottom. 



Opposite Madison County, in St. Louis County, Missouri, north from 

 the city of St. Louis, deposits of waterworn material of glacial derivation 

 underlie the loess for a few miles back from the bluff of the river. These 

 deposits contain a few bowlders, 1 to 2 feet in diameter, as well as cobble and 

 gravel. The rock constituents appear to be different from those of the drift in 

 Madison County, Illinois, there being present considerable material appar- 

 ently- brought down from the exposures of the sandstone and limestone of 

 Silurian age on the borders of the Mississippi in Calhoun County, Illinois, 

 and Lincoln County, Missouri. The presence of this material suggests 

 water rather than ice transpi »rtation, and it remains an open question whether 



