Spencer — Another Episode in the History of Niagara. 443 



although this floor is now from 35 to 50 feet above the level 

 of Lake Ontario ; with the remains of a terrace considerably 

 higher. The rugged features of the upper part of the flats 

 indicate a transition stage. Had the descent of the river been 

 increased to the maximum at this time, the excavating power 

 of the Falls should have cut its channel deeply in the rock 

 beneath the floor, of which Foster's flats is a remnant. The 

 correctness of this conclusion is shown by the deeper (see sec- 

 tion, fig. 2) and wider channel above this section. The great 

 power of excavation during the full height of the Falls is also 

 illustrated just below the present cataract, where the thick bed 

 of hard Medina sandstone, the same as at Foster's flats, has 

 been more than penetrated by the impact of the water, 

 although this hard bed is far beneath the surface of the river. 

 The upper end of the flats (see F, fig. 1) marks the closing of 

 the episodes of the first inferior descent of the river. 



The excavation of the deep basin between the head of 

 Foster's flats (see fig. 2) and the whirlpool shows the amount of 

 work performed by the Falls during the next episode, when 

 the descent of the full volume of the river was increased from 

 200 to 420 feet ; but of the increased descent probably quite 

 170 feet* was situated in the lower part of the gorge and its 

 extension to the retreating shore line of Lake Ontario, when 

 the channel below the end of the gorge was excavated to a 

 depth of a hundred feet below the present surface of the lake. 

 It was the Medina sandstone, now exposed, which gave rise to 

 a distinct cascade, before mentioned, occurring two and a 

 half miles below the front of the main falls. This lower cata- 

 ract, with an interrupted history, has not yet completed its 

 work, although it has cut the modern secondary canon through 

 Foster's flats, having a width reduced to only 380 feetf with 

 vertical walls from 40 to 50 feet high. Here the river is esti- 

 mated at 35 feet deep, although it greatly increases in depth 

 below the flats. This portion of the river is still characterized 

 by heavy rapids. 



While the main cataract was descending over Niagara lime- 

 stone, just above Foster's flats, and the lower or Gilbert Falls 

 cascading nearer the mouth of the gorge (see section, fig. 2), 

 there seems to have been an intermediate fall from the 

 harder beds of the Clifton rocks; but as these do not give 

 rise to a separate cataract to-day, there does not appear any 

 reason to suppose that the intermediate cascade continued 



* The lloor of Foster's flats was 130 feet above the lake level as established 

 when the Niagara River descended 420 feet, with the estimated depth of water in 

 this portion of the canon reaching- 40 feet above it, or the descent of the lower 

 fall and rapids amounted to 170 feet. 



f Surveyed by au engineer for Mr. George Holley. 



