ESTIMATING THE AGE OF NIAGARA FALLS. 147 



turned through Lake Nipissing down the valley of the Mattawa into 

 the Ottawa River, following nearly the line of Champlain's old trail 

 and of the present Canadian Pacific Railroad. The correctness of 

 this inference has been abundantly confirmed by subsequent inves- 

 tigations of Mr. F. B. Taylor and Dr. Robert Bell.* The occasion 

 of this diversion of the drainage of the Great Lakes from the Niagara 

 through the Ottawa Valley was the well-known northerly subsidence 

 of the land in Canada at the close of the Glacial period. When the 

 ice melted off from the lower part of the Ottawa Valley the land 

 stood five hundred feet lower than it does now, but the extent of this 

 subsidence diminished both to the south and the west, making it 

 diflicult to estimate just how great it was at the ISTipissing outlet. A 

 subsidence of one hundred feet at that point, however, would now 

 divert the waters into the Ottawa River. That it actuallv was so 



P \.^ Jfl 



Fi<). 2. — \'ie\v looking east across the gorge near the mouth, showing the railroads and the 

 outcrops of Clinton and Niagara limestones above the steam road. 



diverted is shown both by converging high-level shore lines at the 

 head of the Mattawa Valley and by the immense delta deposits at 

 its junction with the Ottawa, to which attention was first called in 

 my paper referred to above. 



* See article by Mr. Taylor on The Scoured Bowlders of the Mattawa Valley, in the 

 American Journal of Science, March, 1897, pp. 208-218. 



