880 



GEOLOGY 



Fig. 584. The beginning of the Great Lakes. The ice still occupied the 

 larger parts of the present lake basins. (U. S. Geol. Surv.) 



Fig. 585. A later stage in the development of Lakes Chicago and Mumnce. 

 The ice has retreated, and the outlet of Lake Maumee has been shifted. 

 (U. S. Geol. Surv.) 



