MICHIGAN ACADEMY OF SCIENCE. 21 



PREGLACIAL DRAINAGE. 



The courses of pregkuial drainage from the loAvlands are now con- 

 cealed beneath thick deposits of glacial material and can only be parti 

 ally outlined. There is as vet uncertainty whether the drainage was 

 chiefly to the Gulf of ir>t. Lawrence or to the Gulf of Mexico. The 

 high altitude which affected 'the eastern part of the United States, may 

 have given the region along the St. Lawrence below Lake Ontario 

 and also that along the Mohawk greater altitude than was presented 

 by the district between the Great Lakes region and the Gulf of Mexico, 

 thus favoring discharge of the Great Lakes region to the south. It 

 seems highly probable That in the remote past there was a divide on the 

 line of the present St. Lawrence below Lake Ontario, where the river now 

 flows among the Thousand Isles, and that from it drainage passed south- 

 westward to the central United States. But whether this divide had 

 been cut through h\ headwater erosion of the St. Lawrence and jiart of 

 the southwest flowing drainage had been changed to a northeast tlo wing- 

 system prior to the Ice Age is not known. The bed of Lake Ontario 

 reaches now the lowest altitude of any of the Great Lakes. Whether 

 the preglacial altitude was lower in this bn&in, or whether this lovr 

 altitude is due to greater sinking and greater ice erosion tliere during 

 the Ice Age than occurred in the neighboring basins of Huron and 

 Erie is not yet determined. In the former case it would seem pro')ab]e 

 that the Ontario basin had a discharge through some buried channel 

 among the Thousand Isles to the Gulf of St. Lawrence and took Avith it 

 the drainage from the Erie basin if not from the Huron and the Su- 

 Iterior and the northern jiart of the Michigan basin. 



The most ambitious effort to restore the preglacial drainage of the 

 Great Lakes region is that of J. W. Spencer, Avho some 20 years ago 

 presented a map and discussion of the ancient drainage of the Great 

 Lakes region in a British publication.^ It was based on a study, (1) 

 of the hydrography of the modern lake basins and submerged channels 

 on the coast, (2) results of well borings which have revealed the position 

 of buried valleys, and (3) the uplift which the Great Lakes region has 

 exjerienced as shown by tilting of old shore lines. He reached the 

 conclusion that the drainage was to the Gulf of St. Lawrence though 

 not fully along the present lines. From the Erie basin the discharge 

 to the Ontario basin was farther west than Niagara river so that ir 

 entered the extreme western end of the Ontario basin. He interpreted 

 the Lake Huron basin to have had a direct southeastward drainage 

 through Georgian Bay and past Lake Simcoe into the Ontario ba^-in near 

 Toronto. He outlined a drainage from the south part of the Lake Michi- 

 gan basin acreiss the southern peninsula of Michigan into Saginaw Bay 

 and Lake Huron. Tlie northern part of the Lake Michigan ba^in he 

 interpreted to have drained through the Straits of Mackinjic and east- 

 ward into Georgian Bay to join the old Huron drainage. S} encer's ma'js 

 and discussion do not include the Lake Superior basin. 'My own stuoies 

 of the distri( t nnith of Lake Su};erior have brought to light a dee]) buried 

 channel leading southward from the east end of the basin to the head 

 of Lake Huron some distance west of the present line of discharge 

 throush Ste. Marvs Kiver. 



^Quarterly Jour. Cieol. Soc'y of I.,ondon. Vol. XLVI, 1890. 



