Niagara Falls 



1903 channel at St. David's, where it approaches and cuts the escarp- 

 Upham ment; nor does it show evidence of much greater age there, as 



geologists count time, than along any other part, even near the 

 present cataract. Professor G. F. Wright has proved, instead, 

 that the oldest part of the gorge, at and near the escarpment, 

 can have endured the inevitable weathering of its cliffs no longer 

 than 10,000 years, and that indeed its age, which is also the 

 entire age of the Niagara river and falls, may be a considerably 

 shorter period. 



It seems very clear to my mind that the gorge erosion above 

 the whirlpool was much aided by the preglacial St. David's 

 stream for the distance of one mile occupied by the great rapids. 

 Here the major part of the depth and width of the gorge had 

 probably been already eroded before the Ice age, being then filled 

 with drift, which the postglacial river easily removed as soon as 

 its gorge toward Lewiston was sufficiently deepened. No powerful 

 falls have there cut a deep channel, and the river consequently has 

 a restricted and very rapid course. Above the old St. David's 

 ravine, however, a massive waterfall has operated along the latest 

 distance of nearly two miles of the gorge, giving to the river 

 there its great depth. 



The action of a high waterfall, with great volume of water, 

 precipitated over a hard rock stratum, of which large blocks give 

 way and fall because they are gradually undermined, as in the 

 Horseshoe falls, is well compared by McGee to the deep wear- 

 ing of potholes. The fallen blocks are moved under the powerful 

 impact of the high cataract and wear a deep channel, attaining 

 near the foot of the present falls the depth of almost 200 feet 

 under the river level. Such cataract action of deep channel 

 wearing may be supposed also to have produced the great depth 

 of the Niagara river at the mouth of the gorge; but I think that 

 this is better attributed to the usual process of stream cutting at 

 the time of depressed level of this part of Lake Ontario, which 

 is otherwise known by its lower inclined beaches extending here 

 under the lake. 



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