350 



THE PREGLACIAL DRAINAGE OF THE BASIN OF THE GREAT 



LAKES. 



The Great Lakes have been so closely coiuiected with the glacial history 

 of the Mississippi basin, their origin is so closely connected with the pre- 

 glacial Mississippi basin that it seems well to add a chapter to present 

 briefly what is known about their preglacial history. 



Newberry was one of the earliest writers to state the theory now so 

 universally believed, that the antecedent of the Great Lakes was a great 

 river system. According to him the first suggestion of the notion was 

 given by deep borings in the valley of the Cuyahoga at Cleveland, which is 

 a deep valley filled with drift (79). As early as 1882, in a summary of his 

 work, Newberry mentioned, among other points, that he believed that "an 

 extensive system of drainage lines which once traversed the continent, had 

 been subsequently filled up and obliterated by the drift of the ice period." 

 .(79.) 



Newberry thought the outlet of the lakes through Ontario was throxigli 

 a preglacial valley now occupied by the Mohawk riv;er, and so mapped 

 it in 1878. Spencer took exception to this idea, saying, "The Mohawk course 

 will not answer, as the geological survey of Pennsylvania has shown that at 

 I^ittle Falls, Herkimer county, the Mohawk flows over metamorphic rocks." 

 (79.) Lesley added that this rock divide was 900 feet above the floor of 

 Lake Ontario. 



Silencer began the study of the connection between Lake Erie and Lake 

 Ontario before 1880, and in 1881 announced that he had found that the 

 connection was through the Dundas Valley (94), and Newberry at once 

 declared that he himself had prophesied the location of the connection where 

 Spencer found it. Spencer thought that the outlet of the preglacial valley 

 occupied by Lake Ontario could not be the St. Lawrence river, because the 

 bed of the St. Lawrence river is of solid rock (94), nor the Mohawk, be- 

 cause of the rock divide at Little Falls. The channels through northern 

 New York were unimportant and would not answer. The Seneca basin 

 and the Susquehanna seemed available at flrst. for the deepest part of Lake 

 Ontario is north of Seneca Lake, but too much subsidence would be required 

 (94). After studying the beaches about Lake Ontario and noticing that 

 they were tilted to the west, Spencer nun(uuu'ed that the preglacial outlet 

 was ddwn (lie SI. L.nwrcnce (97, 100). L:it(M' he woi'kcd out the system of 



