350 
THE PREGLACIAL DRAINAGE. OF THE BASIN OF THE GREAT 
LAKES. 
The Great Lakes have been so closely connected 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 through 
a preglacial valley now occupied by the Mohawk river, 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 
Little 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. 
Spencer 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 first, 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 announced that the preglacial outlet 
was down the St. Lawrence (97, 100). Later he worked out the system of 
