210 ILLINOIS ACADEMY OF SCIENCE 



LATERAL EROSION IN THE UPPER ILLINOIS 

 VALLEY BY THE CHICAGO OUTLET 



ABSTRACT 



Gilbert H. Cady, University of Illinois 



The effect of the lateral erosion of the great stream known 

 as the Chicago Outlet upon the upper Illinois Valley has been 

 to truncate the normal cusps and indentations and to straighten 

 the valley wall. The effect upon the lateral (tributary) val- 

 leys has been varied. Some valleys have been dismembered, 

 as at Starved Rock, and others have suffered incision so that 

 they have been cut in two. Where Illinois Valley crosses 

 the LaSalle anticline the unusual resistance of the St. Peter 

 sandstone, presumably due to the folding, has resulted in a 

 conspicuous narrowing of the valley. In general there is a 

 definite relation between the character of the country rock and 

 the width of the valley. 



THE NEW RICHMOND SANDSTONE OF NORTH- 

 ERN ILLINOIS 



ABSTRACT 



Gilbert H. Cady, University of Illinois 



The New Richmond sandstone is the oldest known forma- 

 tion outcropping in Illinois. This sandstone is a member of 

 the Prairie du Chien group (lower magnesian limestone.) As 

 an aquifer it has an importance in certain parts of the state 

 comparable to that of the St. Peter sandstone. Its distribu- 

 tion can be better indicated and its character better described 

 han formerly because of recent drilling near LaSalle and be- 

 cause of the recent discovery near Franklin Grove of the only 

 known outcrop in the state. 



