THE CHAMPAIGN MORAINIC SYSTEM. 233 



loam 2 to 4 feet in thickness, and this has probably concealed many 

 bowlders which would otherwise have been exposed on the surface of the 

 till. The number of bowlders on the surface is less than on the plains 

 between this morainic system and the Cerro Grordo moraine. The sheet of 

 loam is apparently distinct in origin from the sheet of till which underlies 

 it, but no evidence was discovered that it was separated from it by a wide 

 time interval. This silt is distinct from the main loess deposit of western 

 and southern Illinois, since the latter preceded the Shelbyville moraine in 

 its date of deposition. The origin of surface silts of this class, like that of 

 the great loess deposits, is problematical. 



A buried soil is frequently found beneath the ridges of this morainic 

 system, but it appears to be at a lower horizon than the base of the drift 

 deposited in connection with these moraines. Its horizon is probably at 

 the junction of the Shelbyville drift sheet with the underlying older drift. 

 Professor Rolfe, of the Illinois State University, has collected records of 

 many wells in southern Champaign County, between Urbana and Tolono, 

 in which a buried soil is found at a depth of 60 to 100 feet. These records 

 have not as yet been published by him. When found beneath the plains 

 the depth to the soil is less than when beneath the drift ridges. On the 

 ridge in the vicinity of Tolono it is struck at about 100 feet and it is found 

 at nearly as great depth on the ridge near Urbana, while on intervening 

 plains the depth is but 60 to 75 feet. Instances of buried muck reported 

 from Vermilion County, Indiana, by F. H. Bradley 1 occur beneath the 

 gravel of the Wabash terraces. Wells were sunk through about 60 feet of 

 alluvial sand, and then encountered 6 to 10 feet of soft, sticky bluish mud 

 filled with leaves, twigs, and trunks of trees. In Fountain County, Indiana, 

 between the main morainic belt and the Inner Ridge, there is a plain in 

 which a black muck has been struck below the till at depths of 25 to 50 

 feet. Although the depth is much less than in Champaign County, Illinois, 

 the soil is thought to be at the same horizon, namely, the junction of the 

 Shelbyville drift sheet with the imderlying older drift. 



The detailed discussion of well sections which follows begins at the 

 west end of the morainic system in Piatt County and passes eastward, and 

 serves to illustrate variations in the structure from point to point. There 

 are, unfortunately, but few reliable records obtained. 



1 Geol. of Indiana, 1869, p. 140. 



