Niagara Falls 



1907 a dark wedge projects obliquely downward and toward the 

 Gilbert left, interrupting the body of white. In the sketch its position is 



occupied by a sweeping curve, less angular than the other lines 

 representing the turn of the water. Making proper allowance 

 for the fact that the water was unusually low in the summer of 

 1895, I think it quite possible that these features of the two 

 pictures represent the same local and peculiar configuration of 

 the rock of the crest, and the suggestion they give is that there 

 has been no change whatever in the crest line of that portion of 

 the American Fall since 1827. 



The matter can be approached in another way. The distance 

 through which the Horseshoe Fall has retreated since it parted 

 from the American Fall is about 2,500 feet. Allowing five feet 

 per annum as the rate of recession, the parting took place about 

 five hundred years ago. The condition of the American Fall at 

 the time of separation may be inferred in a general way from an 

 examination of the eastern part of the Horseshoe Fall at the 

 present time (PI. X). From Goat Island to a point about 500 

 feet westward the water is shallow, corresponding in average 

 depth to that of the American Fall. Beyond that point it is 

 comparatively deep. In the region of deep water the recession 

 of the cataract is rapid, and the portion with shallow water is 

 being left behind. At the base of that part of the fall where 

 the water is shallow the descending stream does not plunge into 

 the pool, but strikes a talus of rock fragments. These fragments 

 are in part visible, and their existence is elsewhere inferred from 

 the forms given to the spray by the reaction. It seems to me 

 legitimate to infer that the American Fall at the time of its aban- 

 donment by the Horseshoe was not so advanced in position as 

 to plunge into standing water, but had already retreated far 

 enough to have acquired a talus above the level of the pool. At 

 the present time the profile of the American Fall where its volume 

 of water is greatest is approximately as shown in fig. 8. The 

 edge of the main river is at S, 220 feet horizontally from the 



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