No. 1.] SPENCER — SURFACE GEOLOGY. 235 



(at least during a portion of its history) across the southwestern 

 counties of the Province of Ontario, and entfring the Erie basin 

 somewhere between Vienna and Port vStanley ; as well as a 

 former outlet of Ltike Erie into Lake Ontario, have been dis- 

 cussed somewhat fully in my paper published in the Transac- 

 tions of the American Philo.<*ophical Society, already referred to. 

 In order to keep nearer to the present subject of study, I will 

 confine my remarks on the " Origin of the Lakes," to that of 

 Lake Ontario, for the other hikes give corresponding testimony. 



Dr. Newberry prophesied that an outlet for Lake Erie into 

 Lake Ontario would be discovered near the Welland canal. Thia- 

 outlet in an unexpected position I have discovered, and in a 

 position which explains more perfectly the cause of the topography 

 of Lake Ontario than any that could have been discovered forty 

 miles to the eastward. 



When was the advent of such a drainage system for this con- 

 tinent ? Some of our Au»erican friends, who have advocated the 

 sub-aerial and fluviatile origin of the lakes, have placed it back to 

 the Devonian A"e. About the commencement we know nothing:. 

 Ft would be safer to place it after the Palaaozoic time, for probably ^ 

 some portions of the Province of Ontario were covered with 

 carboniferous deposits, as well as Michigan and Ohio, which havd 

 subsequently been removed by denudation. 



Excavation of Lake Basins. Having seen the course of the 

 Preglacial drainage, let us ask how the broad lake troughs could 

 be excavated. Let us look at liake Ontario. 



The river coming down the Dundas valley flowed originally 

 near the out-crop of the Niagara limestones, elevated by geological 

 causes long ago. The direction of the stream was parallel to its 

 trend. On the one side were the soft Cambro-Silurian shales, 

 geographically higher, geologically lower ; on the other (southern) 

 side, the Niagara limestones, beneath which were the soft Me- 

 dina shales until these were worn away in part. As the shaly 

 rocks were removed and the limestones were undermined, the 

 Niagara escarpment was produced. How far these lime- 

 >itones have receded towards the present face and summit of the 

 slope, is a question yet to be decided. As the waters sunk to a 

 lower level a second escarpment was produced (the one noticed 

 at Port Dalhousie, at the present lake level). Afterwards the 

 Hudson River shale« (with some hard rocks) were pierced whilst 

 yet there were capping Medina shales, forming the surface of 

 the country between the river and the limestone escarpment. 



