Niagara Falls 



1895 three such cascades over the same series of rocks may be seen 

 pcncer along the Genesee River near Rochester. Under this condition 



the upper cascade receded by itself past Foster's terrace, a dis- 

 tance of 3,000 feet. Thus closed the first stage of the second 

 episode. After passing Foster's flats the chasm shows the effects 

 of a greatly increased force, for the gorge is again widened with 

 the terrace below washed away. As no change in the total 

 height occurred about this time, the magnitude of the erosion 

 indicates an increased discharge, which was produced by the 

 turning of the waters of the Huron basin and adding them to the 

 Niagara drainage. The effects of the greatly increased volume 

 of the water were to widen the chasm and cut away part of 

 Foster's platform, but leaving enough to tell the history. The 

 upper falls were not joined by the more rapidly retreating lower 

 cascades until after the whirlpool was passed, for the evidence 

 of the upper water-level is left in the deposits of river gravels at 

 an elevation of 190 feet on the northern side of the whirlpool 

 ravine, which would not have been the case if the river were at 

 a lower level after cascading over one united falls. Just above 

 the whirlpool, the chasm becomes narrow, and here I close the 

 second stage of this episode of three cascades. The length of 

 this section of the gorge from (C to D fig. 24) is 7,000 feet. 

 By considering the proportional amount of work accomplished 

 during the elongation of the chasm, the deepening of the gorge 

 left at the close of the first episode, and its extension 12 miles 

 lakeward (the mean depth of shales removed from eight miles 

 was 180 feet, and from four miles, 60 feet), and applying the 

 laws of erosion, I have found that the first stage required 6,000 

 years and the second 4,000 years; or the duration of the second 

 episode was 1 0,000 years. 



Third Episode. — The narrowest portion of the gorge extends 

 from the whirlpool for a distance of 4,000 feet as is shown in 

 figure 25 and on the map in fig. 17. The various sections .(figs. 

 22, 23, 25, 26, 27) should be compared. 



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