288 Mr • Foster mi the Falls of the Niagara 



present after the transient denuding causes above spoken of had 

 ceased, or, in other words, when the existing streams first found 

 their way to the ocean ? The surface of the land was evidently 

 what is now denuded and every where scooped into a multitude 

 of valleys, the receptacles, of course, of the newly-formed rivers. 

 This being the case, is it not extremely probable that the de- 

 pressions into which the Niagara and other rapid streams first 

 fell, were originally valleys of denudation ? The existing Falls 

 upon these streams have no doubt contributed, in a considerable 

 degree, to deepen and prolong the gorges through which they 

 flow ; but that they began these excavations, is what I cannot 

 consider established. One has only to explore the vicinity of 

 Trenton Falls, of the Upper Falls of the Gennessee river at 

 Portage, and of Niagara itself, to perceive that all these in- 

 teresting scenes are surrounded by the evidences of extensive 

 denudation. The numerous beautiful cascades which distin- 

 guish the first-named scene, descend over a series of steps occu- 

 pying a trough somewhat similar to the one below Niagara, but 

 much deeper and shorter. The total descent here is 300 feet, 

 and the length of the ravine about half a mile, instead of seven. 

 There is a striking analogy between the structure of those upon 

 the west Canada Creek, and that of those upon the Gennessee 

 river, and there is this resemblance between them both and those 

 of Niagara, that they all consist of perfectly horizontal strata. 

 The Portage Falls of the Gennessee resemble the Falls of Nia- 

 gara, moreover, in the great length of the ravine, that of the 

 Gennessee being several miles long, and having also a depth, in 

 many places, of four or five hundred feet. 



Mr Fairholme seems to consider our numerous falls and ra- 

 pids as the result of what he states to be a characteristic feature 

 of this continent, — the arrangement of the surface in several 

 vast secondary planes, principally composed, as he conceives, of 

 calcareous rocks in horizontal stratification. This is a misap. 

 prehension, for it is well known to all who have examined the 

 physical features of the United Suites, that, in the greater num- 

 ber of our streams, particularly those entering the Atlantic, the 

 rapids are created by the passage of the waters through moult* 

 tain barriers, and in nearly all cases over rocks highly inclined. 

 This is so, where the Potomac finds a pass through the blue 



