DRIFT SHEETS OF NORTHWESTERN ILLINOIS 



269 



4. The gorge of the Mississippi River below Cordova seems refer- 

 able in time to the invasion of the Green River lobe, and the gorge 

 of the Kishwaukee River and the youthful gorge of the Rock River, 

 extending from just below the debouchure of the Kishwaukee to 

 Byron, is referable to the invasion of the Belvidere lobe. The rest 



Fig. 2. — Glacial map of northwestern Illinois, showing the drift sheets and out- 

 wash deposits outside of the Bloomington moraine and the Marengo Ridge. The 

 broken boundary lines indicate indefiniteness. Scale, i" = approximately 30 miles. 



of the Rock River Valley, below Byron, is Illinoian and post- 

 Illinoian in development. 



A more complete account of the evidence for these conclusions 

 will be pubHshed in a report by the lUinois Geological Survey, but 

 it was deemed of sufficient scientific interest to give the main lines 

 of evidence and interpretations in the present paper. 



ACKNOWLEDGMENTS 



The writer was greatly favored and helped by field conferences, 

 one at the close of each of the first two seasons, by the late Professor 

 R. D. Salisbury, of the University of Chicago, and F. W. DeWolf, 

 Chief of the Illinois Geological Survey. Grateful acknowledg- 



