THE PLEISTOCENE OR GLACIAL PERIOD. 



401 



Fig. 520. — Lake Erie and Lake Iroquois; a stage in the history of the eastern Great 

 Lakes, after the ice had retreated so as to open the Mohawk outlet. (Gilbert, 

 U. S. Geol. Surv.) 



Fig. 521. — The Great Lakes at the Algonquin-Iroquois stage. (After Taylor.) 



