6 3 8 



THE PLEISTOCENE PERIOD 



was freed of ice, and a lake (Lake Arkona) twice as large as Lake 

 Erie developed. An advance of the ice changed the lake and with 

 its changed outline it is known as Lake Whittlesey (Fig. 528.) 



Fig. 528. A later stage in the development of Lakes Chicago, Maumee, and 

 Saginaw. (Leverett and Taylor, U. S. Geol. Surv.) 



Fig. 529. Illustrating the relations of standing water to the ice in the Erie and 

 Ontario regions after the ice had retreated farther than represented in Fig. 528, 

 The numerous lobate arms of lakes south of the Ontario lobe of ice will be noted, 

 and also the fact that the discharge of Lake Warren was still to Lake Chicago. 

 (Taylor and Leverett, U. S. Geol. Surv.) 



With further retreat of the ice, the ponded waters of the region 

 assumed the form shown in Fig. 529. At first, this lake discharged 

 across Michigan into Lake Chicago, but later, when the Mohawk 



