550 THE ICE AGE IN NORTH AMERICA. 



other coming from the north from a small water shed bounded 

 by the escarpment at Queenston. As the gorge both above 

 and below the Whirlpool is for some distance not more than 

 one-half the average width, it is probable that through these 

 spaces these small streams had worn in preglacial times 

 narrow gorges leading to the Whirlpool which had only to be 

 cleared of their glacial debris and somewhat enlarged by the 

 present stream when the cataract had receded to that point. 

 This would account both for the narrowness and the shallow- 

 ness of the gorge at these places. Whereas the water at the 

 Whirlpool is 150 feet deep and still more than that for two 

 miles below the Falls, it is only 35 feet deep in the Whirlpool 

 Rapids. Furthermore, at Fosters Flats, one mile below the 

 Whirlpool there is a projecting shelf extending into the gorge 

 from the western side nearly half its width, but into its upper 

 end on the side next to the main cliff there is the head of an 

 old narrow gorge opening up stream. This can hardly be 

 anything else than a remnant of the gorge supposed to have 

 been formed by a small northerly stream which found an 

 outlet through the Whirlpool. 



We are bound to state, however, that Dr. Spencer main- 

 tains that the St. Davids outlet was not worn down to the 

 level of the present Whirlpool, and so is only a remnant of 

 erosion in some preceding era. But it is to be observed that 

 Dr. Spencer's borings to determine the depth of the glacial 

 filling in the St. Davids gorge, were considerably one side of 

 the center, while the measurement nearest the. center was 

 abandoned before penetrating the rock below. The great 

 age of the gorge would imply a fully formed V-shape for it, 

 which would make the depth of the glacial filling to be small 

 near the sides. There is, therefore, no valid reason to doubt 

 that the St. Davids preglacial outlet was complete from the 

 Whirlpool at a depth equal to that of the present Niagara 

 gorge. 



In view of all these considerations it seems evident that a 



