J. W.Spencer — Duration of Niagara Falls. 469 



of the infant river, — and adding the duration of the four epi- 

 sodes, which have been calculated at 31,000 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 com- 

 pensated for possible over-estimates in degrees of hardness, 

 and fairly represented the age of the falls, which is very near 

 that of Ly ell's conjecture. There is considerable cumulative 

 evidence adduced from the history of the lakes to strengthen 

 confidence in the methods pursued in this investigation. Let 

 us see. 



9. Confirmation of the Age of the Falls by the Phenomena 

 of Terrestrial Movements. 



In the deformatory elevation of the Niagara district, the 

 Johnson ridge was raised 24 feet above the Chicago divide, 

 between the Michigan and Mississippi waters, and did cause a 

 rise of the waters in the lakes to the point of overflowing, but 

 the ridge was incised by the retreating falls in time to prevent 

 the change of the lake drainage. By the simplest case of 

 division we have seen that Johnson's ridge was completely cut 

 through only about 1,500 years ago. Allowing two or three 

 feet of water to have been on the Chicago divide (covered 

 with silt) and as much more for error, we find that the differ- 

 ential elevation of the Niagara district becomes a local abso- 

 lute uplift of about 1*25 feet a century. The equivalent rate 

 of elevation northeast of Lake Huron is 2 feet and at the out- 

 let of Lake Ontario 2*5 feet a century. This average is that 

 of episodes of activity and repose during 1.500 years. Apply- 

 ing the time ratio to the amounts of deformation we shall 

 obtain the results given below in a form for comparison. 



The rise of the Algonquin beach of the Huron basin, be- 

 tween the present outlet of the lake and the former outlet at 

 Lake Nipissing, amounts to 660 feet,* about 560f of which 



* Elevation south of and adjacent to Lake Nipissing determined by Mr. F. B. 

 Taylor. 



f The waters of both Lundy aud Algonquin lakes were lowered about 1 00 feet 

 before the beginning of the Niagara river; this being apparent and local, pro- 

 duced by a pre-Iroquois uplift of about half a foot per mile, thus raising the 

 northeastern extensions of the beaches. 



