82 THE ILLINOIS GLACIAL LOBE. 



General observations. — The following observations concerning the belts in 

 Stephenson and Ogle counties are made by Hershey, in the paper above 



cited: 



(1) They are not confined to any level, but cross ridges of any height, in several 

 cases 150 feet or more above the present bottom of adjoining valleys. However, they 

 are best developed at lower levels and the most prominent knolls and ridges stand in 

 the center of valleys. 



(2) They will not bend from a direct course upon encountering a low ridge, but 

 are readily compelled to change direction upon meeting one of the high ridges, which 

 constitute the remains of the peneplain. 



(3) When in a narrow valley there is usually but a single ridge and only few 

 secondary belts, but in such a wide basin as that of the Pecatonica River and Yellow 

 Creek, there are a number of parallel ridges. 1 



The system of eskers of northwestern Illinois indicate that the drain- 

 age from the ice sheet was somewhat vigorous, though the combined bulk 

 of the gravelly material contained in them is but a small portion of the 

 drift of that region. It is probable that they were formed during the gen- 

 eral recession of a nearly stagnant sheet of ice. The trend of the main 

 ridges is about in line with the supposed direction of the ice movement, 

 which is usually nearly at light angles with the ice margin. Some of the 

 ridges, especially the Cedarville belt and the Hazelhurst esker, curve toward 

 the boundary in the western portions, changing from a westward to a north- 

 westward course. Whether the ice movement was characterized by a cor- 

 responding curve can scarcely be determined, though it seems a not 

 improbable movement. 



TRANSPORTED ROCK LEDGES. 



In northwestern Illinois there are several remarkable instances of 

 transportation of limestone ledges which have been discovered by Her- 

 shey, 2 the most of which are indicated on PI. XII. These ledges in some 

 instances occupy an area of several acres. They have been moved west- 

 ward from the crest of rock ridges without completely destroying their 

 stratification. In most cases they have been deposited at levels lower than 

 the ridges from which they are derived and rest upon glacial deposits on 

 the slopes or bottom of neighboring valleys, but in some instances such 

 ledges have been transported to points as high as their original position. It 



'Am. Geologist, Vol. XIX, 1897, pp. 197-209, 237-253. -Loc. cit., pp. 245 253. 



