OEIGIN OF THE BASINS OP THE GREAT LAKES OF AMERICA. 523 



3] . Origin of the Basins of the Great Lakes of America. Ey J. W 

 Spencer, M.A., Ph.D., P.G.S. (Eead April 16, 1890.) 



Contents. 



1. Inh'oduction. 



2. Features of the Ontario Basin. 



3. „ „ Erie Basin. 

 1. ,, ,, Huron Basin. 



5. Features of Lake Michigan. 



6. Buried Valleys revealed by Borings. 



7. Glaciation of the Region. 



8. Former High Continental Elevation of North America. 



9. Deformation of Raised Shores and Beaches. 

 10. Conclusions from the Observations. 



1. Introduction. 



Even as recent as a decade ago very little was known as to the 

 origin of the Great Lakes of North America. "Whilst we find such 

 generalized statements as " most lakes are due to terrestrial crust- 

 movements," yet such crust-movements had not been tested in the 

 American lake-region. Again, from the time of early geological 

 investigations in America, statements are found that the basins were 

 the result of erosion; but the methods of erosion were not explained, 

 and this was the more necessary as most of the basins have rock- 

 bound outlets. Later, in some geological literature, the method of 

 excavation was hypotheticall}^ attributed to glaciers. Such was the 

 unsatisfactory condition of our knowledge of the problem when the 

 writer first commenced the study, in attempting to solve the origin 

 of the Dundas Valley, at the western end of Lake Ontario, more than 

 a dozen years ago. This investigation has developed results bearing 

 not only upon the origin of the lake-basins, but also upon the phy- 

 sical history of the lakes, and broader questions of the building and 

 sculpturing of the continent. 



The methods of investigation have been the studying — (1) of the 

 hydrography of the modern lake-basins and submerged channels upon 

 the coast of America ; (2) of the deep wells bored into, or through, 

 the Drift deposits, by which buried channels, and their relation to 

 or contrast with the modern valleys, have been discovered ; (3) of the 

 elevation of the continent ; (4) of the direction of the glaciation in the 

 lake-region ; and (5) of the now high-level beaches, in which are 

 recorded continental uplifts, together with the deformation of the 

 old surfaces, owing to unequal terrestrial movements or warpings of 

 the earth's crust*. The lakes which have been the basis of the more 

 careful investigation are Ontario, Erie, Huron, and Michigan, with 

 the respective altitudes of 247, 573, and, of the last two, 582 feet 

 above the sea (see the Map, p. 524). 



* In the field-work I here acknowledge the assistance of Professors D. F. H. 

 Wilkins, W. W. Clendenin, and W. J. Spillman. 



Q.J.G.S. No. 184. ,,\'{nr.i-j<^p 2q 



