416 



THE ILLINOIS GLACIAL LOBE. 



a bearing S. 44° W. Associated with these are striae of feebler develop- 

 ment, which vary in direction fully 10 degrees to the east and west of the 

 heavy scorings, thus ranging from S. 34° to S. 54° W. An escarpment of 

 the dipping layers which rises about 6 feet above the remainder of the 

 quarry is glaciated not only on the upper surface and nearly vertical front, 

 but also beneath one of the lower layers, its dipping under surface being 

 smoothly polished for about 18 inches back from the front of the ledge. A 



rface in bed of Chii 



go drainage caual. [Drawing from a photograph taken by Chicag 

 Commission.] 



photograph of this ledge has been furnished by the Chicago Academy of 

 Sciences (see PL. XVI). 



A glaciated surface exposed near Lemont in the excavation of the 

 Chicago drainage canal is represented in fig. 2, which has been drawn from 

 a photograph taken by the Chicago Drainage Commission. The furrows 

 are remarkably direct for a- distance of several rods, and the planing is 

 exceptionally smooth. 



In the vicinity of Lemont the bed of the Chicago Outlet is extensively 

 channeled by nearly parallel grooves several inches in width and depth and 



