and the Geology of the Surrounding Country. 119 



through the bed, leaving waterwom materials along the sides, 

 monuments of the wearing action of the waves. In the 

 Niagara/chasm there are no pebbles, boulders, or gravel ; the 

 river occupies nearly the whole width at the bottom, allowing 

 a talus of angular fragments of the rocks fallen from above. 



The valley of the Genesee, from Rochester to Dansville, 

 affords a good example of a ravine excavated during the 

 emergence of land from beneath the sea ; but this valley is 

 broad, and partially filled with drift, the sides sloping gradu- 

 ally and for the most part covered with deep soil, partially 

 from decomposition and disintegration of the rocks beneath, 

 but principally from transported materials. 



The small amount of wearing accomplished by a stream 

 during the period of our observation might incline us to 

 doubt the possibility of any body of water having excavated 

 its channel backwards for a length of seven miles, and to a 

 depth of from three to five hundred feet. But if the period 

 of one life be sufficient to admit of observation proving the 

 smallest amount of recession^ then it is only requisite that we 

 should carry on the process for an indefinite period, to accom- 

 plish the utmost that we require ; or, that we extend back- 

 ward our imagination regarding time, in order to prove what 

 is already accomplished. Now it is attested, within the re- 

 corded observations of those residing in the vicinity of Niaga- 

 ra, that the falls have receded within their recollection. If 

 then it is proved that this ravine could not have been excava- 

 ted by the sea during the emergence of the land, we have 

 only this mode of operation left to account for its formation. 

 From analogous facts, we learn that it only requires an ele- 

 vation of the drift, filling up the old channel, to be greater 

 than that of the rocky strata, in order to turn the water in 

 that direction, and cause it to form a new channel. We 

 have only to suppose the ravine, from the whirlpool to St. 

 Davids, filled, as it now is, with drift, to such a height as to 

 prevent the water from flowing in that direction, and the con- 

 sequence would be, as I said before, that it would seek an 

 outlet at the lowest point along the terrace, which appears to 

 have been in the direction of Lewiston. Here the water 



