Spencer — Another Episode in the History of Niagara. 445 



The JVeicly-dlscovered Episode — the Niagara Strand. 



The closing part of this last episode, and the next, during 

 which the Falls receded to a point above the Narrows (tig. 2) 

 of the Whirlpool Rapids has proved the most difficult of 

 explanation. The writer provisionally adopted* a hypothesis 

 by which the maximum height of the Falls was continued 

 throughout this section. But the recent investigation shows 

 that during this time the descent of the river was reduced 

 from 420 to 250 feet, before it was increased to the present 

 amount of 326 feet. Consequently, in the earlier writings 

 upon the history of the Falls, this important episode, and its 

 effect upon the Falls, were unknown. 



Below Foster's flats, the sloping sides of the gorge are cov- 

 ered with talus, while the section passing the flats is that of a 

 newly formed canon with vertical walls, except at the foot 

 (showing a transition stage). Opposite the lower end of the 

 flats, there is a delta deposit of river stones, some of which are 

 more or less subangular, forming a sort of terrace within the 

 canon, rising to a height of 70-75 feet. Its occurrence shows 

 first the excavation of the gorge, and then the rise of the 

 waters in it to the named height, so as to have allowed the 

 accumulation of the deposit. The evidence of this rise of the 

 river is further demonstrated by the occurrence of terraces 

 immediately below the end of the gorge, having a height of 

 50-55 feet, on which there is a beach-like gravel ridge at an 

 elevation of 70-75 feet above Lake Ontario. This terrace 

 with its surmounting ridge is here named the Niagara Strand. 

 The further sinking of the water is shown in the terraces at 

 about 35 feet, and at 5-10 feet. The rising of Lake Ontario 

 to a height of 75 feet would back the surface of the river to 

 not merely the whirlpool, but had the canon been excavated, 

 it would have extended the lake level to about the point of 

 the inclined railway (opposite the middle of Whirlpool Rapids). 

 This backing of the waters would naturally protect the floor 

 from erosion, and would explain the shallowness of the section 

 of the Whirlpool Rapids. The amount of work performed by 

 the Falls during this episode of reduced descent of the river is 

 represented by the excavation of the canon for a distance of 

 6,800 feet,f to a point just above the railway bridges, figure 2 

 (less that portion of the rock which had been removed from 

 the valley in preglacial times). The narrowness of the gorge 

 at the Whirlpool Rapids will be considered later. 



* See Duration of Niagara Falls, cited before. 



f Of this distance, 2500 feet is the portion of the section between the Medina 

 sandstone barrier at the outlet of the whirlpool and the foot of the rapids above, 

 while through the Narrows the length is 4300 feet. 



