154 THE ILLINOIS GLACIAL LOBE. 



both in the northwest corner and in the southern end of the State, were 

 almost entirety covered by loess, though possibly some of the highest knobs 

 and ridges escaped. 



In northern Illinois, where the Iowan drift sheet is exposed to view 

 outside the limits of the Wisconsin, the loess-like silts are irregularly dis- 

 tributed. The Pecatonica lobe and the districts to the east, in Winnebago, 

 Boone, western McHenry, and northern Dekalb counties, have scarcely 

 any typical loess, and the silt deposits seldom exceed a depth of 1 or 2 feet. 

 It is not certain that these deposits are of similar origin and date to the silt 

 deposits on the west border of the Iowan drift. In passing southward from 

 the Pecatonica lobe loess-like silts overlap the Iowan drift to a distance of 

 several miles. In northern Lee County Illinois, they extend some miles east 

 of Rock River. Upon approaching the Green River Basin sandy deposits 

 appear which effectually conceal any silts which may have been deposited 

 farther south. However, the belt of drift thought to be of Iowan age that 

 is situated on the south border of the Green River Basin is not sand covered. 

 This has a much thinner deposit of silt than the Illinoian sheet to the south, 

 and much of its surface seems never to have been coated with silt. 



Attention has been called to the existence of a tract nearly free from 

 loess in southwestern Carroll and northwestern Whiteside counties, Illinois, 

 which may find its explanation in ice occupancy of the territory up to a 

 date so late that the loess was barred out. There are quite extensive loess- 

 covered tracts within this area, notably one which follows the Mississippi 

 Valley. This belt of loess seems to be a continuation of the extensive belt 

 which follows the west side of the Driftless Area throughout almost its entire 

 length, and is perhaps somewhat later than the loess deposits made on uplands 

 below the Driftless Area. Aside from this main belt along the Mississippi 

 River there is a heavy loess deposit in northern Whiteside County, which 

 is probably as old as the loess on the districts to the east. Loess is also 

 found on much of the narrow uplands lying between Rock and Green rivers 

 from Spring Hill southwestward to the junction of these streams. In addi- 

 tion to the loess which is deposited in sheets there is in this region a loess 

 capping the paha ridges. In some cases the paha are coated to a depth of 

 15 feet or more, while bordering plain tracts are nearly free from loess. In 

 other cases the loess appears to be nearly as heavy on the plain tracts as 

 on the paha. The distribution in the Iowan area is so irregular and patchy 



