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











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II 11 





race, a distance 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 helow 

 washed away. As no change 

 in the total height occurred 

 about this time, the magni- 

 tude 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 in- 

 creased volume of the water 

 were to widen the chasm 

 and cut away part of Fos- 

 ter's platform, but leaving 

 enough to tell the history. 

 The upper falls were not 

 joined by the more rapidly re- 

 treating 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 cas- 

 cades. The length of this 

 section of the gorge (from 

 C to D fig. 8) is 7,000 feet. 

 By considering the propor- 

 tional amount of work ac- 

 complished during the elon- 

 gation of the chasm, the 

 deepening of the gorge left 



