Niagara Falls 



1901 fall is narrow, the gorge will broaden as fast as the apex recedes, 



Hitchcock as explained above; and therefore it is reasonable to use the rate 

 of recession of the fall as equivalent to the average of elongation 

 of the gorge. Here and there the gorge may widen or contract, 

 according to variations in the volume of the water, its velocity, 

 the width of the channels, the thickness of the limestones and 

 other rocks, their comparative hardness, etc. It is not our pur- 

 pose to present allowances for these varied conditions, as the 

 approximate estimate derived from the rate of recession will indi- 

 cate how the calculations should be made. 



Estimates of Age in Years. 



Let us assume the present rate of recession to be four feet 

 annually. This is less than what has been observed, but some 

 think that the time for the wearing action must have been greater, 

 and the omission of the half foot may be nearer the true figure. 

 There is a greater thickness of limestone at the Johnson ridge 

 than elsewhere, in the first section of the gorge, from the falls to 

 near the railroad bridges, and possibly more time would be 

 required for its erosion. But it seems as if this excess of thick- 

 ness was removed in pre-glacial times, because the flat produced 

 by the ancient bed of the river, before the erosion of the rock 

 had been effected, slopes uniformly, without regard to the 

 presence of the ridge. Hence this excess of rock has not 

 materially affected the rate of erosion here. The total length 

 of this first section of the gorge is 1 1 ,750 feet. This measure- 

 ment was made in 1875, and the gorge must now be over 100 

 feet longer, making the entire length 1 1 ,850 feet. Divide this 

 by four, the number of feet the cataract recedes annually, and 

 the quotient is 2,962; i. e., the beginning of the great cataract 

 dates back to 1 062 B. C, 300 years before the time of Romulus, 

 or to the reign of King David at Jerusalem. 



The next section is that of the whirlpool rapids, 3,900 feet. 

 If the water of Niagara came from Lake Erie alone, under 



640 



