Niagara Falls 



1895 Tonawanda basin south of Johnson's ridge, whose rocky floor, 

 pencer generally speaking, is about 80-90 feet lower than that on the 



ridge (see fig. 24) ; yet the canon just north of the ridge is only 

 250 feet wider than through that barrier. The drift filling the 

 basin offered but little resistance to the recession of the falls and 

 accordingly the rate of retreat has been comparatively rapid along 

 this section of the river, which is 6,000 feet long. Consequently 

 its age is about 1 ,500 years. Thus the duration of the fourth 

 epoch has been 3,000 years. 



Age of the Falls. — Allowing 1,000 years for the duration of 

 the river before the advent of the falls, — for that its commence- 

 ment was not characterized by a cascade is shown by the terraces 

 on the edge of the escarpment and at the deserted mouth of the 

 infant river, — and adding the duration of the four episodes, 

 which have been calculated at 3 1 ,000 years, the age of Niagara 

 River would be 32,000 years; and the date that the Huron 

 drainage turned from the Ottawa valley to the Niagara was 

 7,800 years ago. In order to reduce the errors in reading the 

 means of erosive effects, the component stages have been taken 

 to as great a degree of accuracy as practicable. In the changes 

 of level, the error would suggest itself to me as on the side of 

 shortening the time ; and there is no evidence that a much greater 

 rate of recession than now has occurred other than that already 

 made use of; also I have used the maximum discharge of Lake 

 Erie. Consequently I am led to conclude that the present study 

 has set forth the history and has compensated for possible over- 

 estimates in degrees of hardness, and fairly represented the age 

 of the falls, which is very near that of Lyell's conjecture. There 

 is considerable cumulative evidence adduced from the history of 

 the lakes to strengthen confidence in the methods pursued in this 

 investigation. 



598 



