CHAPTER III 

 THE LIFE OF GLACIAL LAKE CHICAGO AND ITS SUCCESSORS 



I. General Statement 



In subsequent chapters the Ice Age is discussed and its different stages, 

 both glacial and interglacial, are considered. In the present chapter only the 

 life of Lake Chicago, and its immediate successors, is discussed, the inter- 

 glacial stages, as well as the postglacial territory lying beyond Chicago, being 

 reserved for succeeding chapters. The discussion is taken up chronologically 

 in order that the evolution and migration of the biota may be clearly shown. 

 Comparisons are made with recent lake areas in New York State, as they 

 plainly illustrate a part of the history of the formation of old Wilmette Bay. 



II. Waning of the Wisconsin Ice Sheet and Formation 

 of Ponded Waters 



As the ice receded in the Mississippi Valley, several bodies of water were 

 formed at the ends of three lobes known respectively as the Erie lobe, the 

 Michigan lobe, and the Superior lobe. These lakes were bounded on one side 

 by the ice and on the other sides by high portions of the land surface, usually 

 moraines. These bodies of water, known as lakes Maumee, Chicago, and 

 Duluth, drained into the Mississippi river via the Wabash, Desplaines, and 

 St. Croix rivers. There is believed to have been, also, a lake (Lake Jean 

 Nicolet) southwest of Green Bay which drained thru the Wisconsin River. 

 By these water routes the biota advanced northward and reoccupied the 

 glaciated territory (Plate XXXI). Of these water bodies only one, 

 Lake Chicago, is considered in detail in this chapter. 



III. Glacial Lake Chicago 



The body of water formed at the extremity of the Michigan lobe has been 

 given the name of Lake Chicago by Mr. Leverett. 1 This lake stood at various 

 levels which are marked by more or less well-developed beaches. These 

 beaches indicate well defined stages, several of which embraced the entire Great 

 Lakes system. 2 



1 Pleistocene Features, pp. 6i-65, 1897. 



2 The physical history of the formation of the Great Lakes has been well described by 

 Alden, Leverett, Goldthwait, and Taylor (see Bibliography). 



