ltf THE ILLINOIS GLACIAL LOBE. 



There is not even a well-developed system of ravines and tributaries on its 

 surface, but ravines partially developed often discharge their waters into 

 sink holes and have no surface indications of connection with other lines 

 of drainage. 



In the northwestern part of Illinois a few conspicuous outlying mounds 

 of Lockport (Niagara) limestone appear. Some of these are situated in the 

 drift-covered region and others in the Driftless Area. They rise 75 to 300 

 feet above border districts. The majority of these mounds rise above the 

 1,100-foot contour, and one of them, Charles Mound, as noted above, forms 

 the highest point in the State (1,257 feet). They vary in size from a fraction 

 of a mile to several square miles. In the latter case a chain of mounds 

 occurs, rather than a single mound or ridge. These mounds lie but a few 

 miles north and gast of continuous Niagara formations and were apparently 

 once joined with them, their separation, as long since stated by Worthen, 

 being due to denudation. 1 The greater part of the district among these 

 mounds has been denuded of the Hudson River or Maquoketa shales as 

 well as of the Lockport limestone, thus exposing the Galena limestone. 



East from the district just discussed is the broad drainage basin of 

 Rock River, which has no conspicuous ridges or remnants of higher strata 

 capping its present surface formations, though the latter are thoroughly 

 sculptured by drainage lines. 



Between the Rock River drainage line and Lake Michigan there is a 

 somewhat elevated belt of limestone, which extends curvinglyin a direction 

 cast of south into western Indiana. It is generally so heavily covered with 

 drift that its lesser features can only be conjectured. Borings indicate that 

 variations o( 100 feet or more in altitude occur within a distance of a few 

 rods. It was in all probability thoroughly sculptured by drainage lines. 

 The rock surface has its greatest altitude at the north, being 400 feet above 

 Lake Michigan at the Illinois-Wisconsin line, while in the vicinitv of the 

 Indiana line it rises only 100 to 200 feet above the lake. The Fox, 

 IVs Plaines, and Kankakee rivers now cross this limestone belt from the 

 low belt bordering Lake Michigan into the old Rock and Illinois drainage 

 basin, thus extending the latter at the expense of the former. 



In southern Indiana there is a comparatively elevated region along the 

 easl border of the Coal Measures formed largely by the Conglomerate 



1 Geology of Illinois. Vol. I. 1866, p. -1. 



