472 J. W. Spencer — Duration of Niagara Falls. 



11. End of the Falls. 



As has already been noted, the falls was in danger of being 

 ended by the turning of the waters into the Mississippi, when 

 the cut through the Johnson ridge was effected. With the 

 present rate of calculated terrestrial uplift in the Niagara dis- 

 trict, and the rate of recession of the falls continued, or even 

 doubled, before the cataract shall have reached the Devonian 

 escarpment at Buffalo, that limestone barrier shall have been 

 raised so high as to turn the waters of the upper lakes into the 

 Mississippi drainage by way of Chicago. (An elevation of 60 

 feet at the outlet of Lake Erie would bring the rocky floor of 

 the channel as high as the Chicago divide, and an eleva- 

 tion of 70 feet would completely divert the drainage. This 

 would require 5,000 or 6,000 years at the estimated rate of ter- 

 restrial elevation. It would be a repetition of the phenomena 

 of the turning of the drainage of the upper lakes from the 

 Ottawa valley, into the Erie basin. 



12. Conclusions. 



The computation of the age of the Niagara river, — based 

 upon the measured rate of recession daring 48 years; upon 

 the changing descent of the river from 200 to 420 feet and 

 back to 320 feet ;• and upon the variable discharge of water 

 from that of the Erie basin only, daring three-fourths of the 

 life of the river, to afterwards that of all the upper lakes, — 

 leads to the conclusion that the Niagara Falls are 31,000 years 

 old and the river of 32,000 years duration ; also that the 

 Huron drainage turned from the Ottawa river into Lake Erie 

 less than 8,000 years ago. Lastly, if the rate of terrestrial 

 deformation continues as it appears to have done, then in 

 about 5,000 years the life of Niagara Falls will cease, by the 

 turning of the waters into the Mississippi. These computa- 

 tions are confirmed by the rate and amount of differential ele- 

 vation recorded in the deserted beaches. It is further roughly 

 estimated that the lake epoch commenced 50,000 or 60,000 

 years ago, and there was open water long before the birth of 

 Niagara in even the Ontario basin, and that under no circum- 

 stances could there have been any obstruction to the Ontario 

 basin, if even then, later than the end of the Iroquois episode 

 which has been found to have ended 14,000 years ago. 



