Science, Geology and Physics 



Chronological Conspectus 



At its maximum the great Laurentide glacier covered the 18Q 5 

 whole area of the Great Lakes. By a correlation of the aban- ay °' 

 doned shore lines, moraines and outlets, and the gorges, recently 

 submerged shores and rivers of this region the following order 

 of events is made out for the post-glacial history of the Great 

 Lakes. They are set down in seven principal stages with 

 transitions or critical stages between. 



I. Glacial, ice-dammed lakes. Outlets at Fort Wayne, 

 Chicago and other places. Beaches correlated with moraines in 

 Ohio. Glacial lakes fall by stages as outlets change on with- 

 drawal of the glacier-dams. Land relatively high in the north 

 but slowly subsiding. 



First Transition: By withdrawal of glacier the Niagara river 

 is opened and the upper lakes become united. 



II. First Niagara lakes. First epoch of Niagara Falls begins 

 at Lewiston. For a short time glacial Lake Iroquois receives the 

 water from Niagara. Shore lines of lower levels 'of this glacial 

 lake washed over and obliterated by later marine invasion. 

 Gradual depression of land continues at north, finally opening 

 Nipissing outlet. 



Second Transition: First two-outlet climax. Marked by the 

 ALGONQUIN Beach. (Possible subdivision here for supposed 

 Trent river outlet.) Gradual northward depression continues. 

 First epoch of Niagara Falls closes at the Whirlpool. Epoch 

 of Erigan Fall begins. 



III. First Lake Algonquin. Outlet eastward over Nipissing 

 pass. 



Third Transition: Gradual northward depression continues. 

 Nipissing outlet brought down to sea level. Lakes become 

 marine. 



IV. Warren Gulf (rising stage). Marine waters fill the 

 three upper lakes, the Ontario, St. Lawrence and Winnipeg 

 basins. 



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