THE GLACIAL. LAKES 



Lake Chicago 



As Lake Maumcc increased In size Lake Chicago also in- 

 creased and was building its liigliest beach, the Glenwood, a 

 few miles south of Chicago. Lake Chicago never had tiie 

 varied history of the other lakes. Its several beaches are paral- 

 lel to the present beach and are so near Lake Michigan that 

 in places they actually have been undercut and destroyed by 

 the present lake. The outlet was through Des Plaines River 

 to the Illinois and the Mississippi — the "Chicago Outlet," now 

 utilized by the Chicago Ship and Drainage Canal. 



Lake Arkona 



The next important step in the development of the lakes 

 in the Erie basin was the rather sudden withdrawal of the ice 

 from the Thumb region of Michigan. All the lake waters to 

 the eastward fell to the level of Lake Saginaw, which had ex- 

 panded northeastward in a broad strait around the northern 

 end of the Thumb, and merged with it to form the larger lake 

 known as Arkona — the first lake to fill a part of the Lake 

 Huron basin. (Figure 7.) Lake Arkona endured for a long 

 time, as is shown by the height and strength of its beaches and 

 the size of the river deltas which were built into it and were 

 not wholly destroyed by powerful later events. That the lake 

 was large and deep and that the ice front stood far to the 

 north and east, is also shown by the strong gravelly beaches 

 which must have been made by waves that had a long 

 "fetch" on shore. The beaches show that Arkona, the largest 

 lake to occupy the Erie basin, was nearly three times as large 

 as Lake Erie. It extended northward as far as Gladwin, Michi- 

 gan, and eastward forty to fifty miles east of Buffalo, New 

 York, and received from the east the waters of the long nar- 

 row ice border drainage covering the Finger Lakes region. It 

 was the first lake to make definite beaches in Ontario, along 

 the southern edge of the Ontario nunatak around which 

 the ice had separated into two independent lobes — one in the 



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