210 THE ILLINOIS GLACIAL LOBE. 



deposited. The depth of the gravel deposits on the outer face of the Shel- 

 by ville moraine is but a few feet, seldom so much as 15 feet, and the 

 gravelly belt, including the knolls as well as plane-surfaced tracts, has a 

 width of scarcely more than 2 miles. The gravel has been carried but a 

 few miles south of the limits of the moraine, there being only sand from 

 the vicinity of Greenup southward in the terrace remnants found along the 

 valley. These terrace remnants stand 20 to 40 feet below the border 

 uplands and have apparently been built up at least from the level of the 

 stream, 25 feet or more. The moderate transportation of gravel seems to 

 indicate that the discharge was not vigorous and that drainage conditions 

 were rather imperfect, except on the slope of the moraine. 



Passing westward to the Kaskaskia Valley, which leaves the Shelby- 

 ville drift at the city of Shelbyville, one hnds that the valley below the 

 border of the moraine contains scarcely any deposits coarser than sand in 

 the terraces built up during the Shelbyville or later stages. Light deposits 

 of gravel were found on small tributaries at the points where they leave the 

 Shelbyville drift sheet, but these are only a few feet in depth and are not, 

 as ;i rule, continued down to the river valley. "Within the limits of the 

 moraine immediately above Shelbyville there is a terrace standing about 25 

 feet above the river which contains gravel and cobble. In places the gravel 

 and cobble are found to rest upon till and to have a depth of but 8 or 10 

 feet. In other places the gravel apparently extends to the underlying shale, 

 which, as shown by the bridge piers east of Shelbyville, sets in at 15 or 20 

 feet below low water. It is not entirely clear that this gravel and cobble 

 was formed as an outwash from the ice sheet at the Shelbyville stage. On 

 the contrary, it seems quite as probable that it is a residue resulting from 

 the cutting down of the valley since the Shelbyville stage. In the process 

 of cutting down, the coarse material would become concentrated while the 

 hue material would lie transported dowu the valley. In harmony with 

 this view it is found that the surface of the terrace is somewhat below the 

 level of the Shelbyville drift sheet and occupies a valley cut in that and the 

 older drift sheet. The evidence from this valley, therefore, indicates a 

 feeble outwash from the ice sheet at the Shelbyville stage. 



The next valley of importance leading away from the Shelby ville drift 

 sheet is that of the Sangamon River. Along this valley from the edo-e of 



