242 G. F. WRIGHT ABANDONED BEACHES ABOUT LAKE MICHIGAN 



the ice had receded be^'ond Mackinac, when it would pour through the 

 straits to Lake Michigan, though there may be some doubt as to when 

 the outlet through the ]\loliawk Valley to the east was so opened as to 

 take off a part of this lower accumulation. The opening through the 

 Mohawk Basin and Xiagaia gorge at last would bring the water down to 

 its present ley el. 



•■0»A , <:%T'~^n . . 



Figure 2. — Stages of glacial Lakes in the Erie-Ontario Basin 



Boundary of lakes Maumee and Whittlesej' and the Imlay outlet into Lake 



Michigan 

 Boundary of Lake Warren, with its Ubly and Saginaw outlets into Lake 



Michigan 



Compiled and drawn by Miss Lonie Shedd. Fort Wayne, outlet into the Wabash River 

 of Lake Maumee. about 200 feet above Lake Erie, as glacier ice-front receded. Imlay. 

 outlet of Lake Maumee through Grand River down to level of Lake Ayhittlesey. about 

 150 feet above Lake Erie. Ublj% outlet of Lake Whittlesey through Grand River down 

 to level of Lake Warren, about 100 feet above Lake Erie. Saginaw Bay, outlet of Lake 

 Warren through Grand River to about 70 feet above Lake Erie. 



That this influx of water from the Lake Erie Basin would be sufficient 

 to raise Lake Chicago to a 40-foot level is easily belieyed when we con- 

 sider the size and depth of the outlet at Fort Wayne and the extent of 

 the glacial lakes which occupied the Erie-Ontario Basin. The old outlet, 

 now occupied by the major portion of the city of Fort Wayne, is nearly 

 2 miles wide and 20 feet in depth, such a channel having been necessary 

 to carry off the surplus watev from tlie melting ice to tlie northward. 

 When the opening into Lake Chicago tlirough the Grand River valley 

 occurred, all this surplus water, as well as that ponded up to the 200- 



