and the Geology of the Surrounding Country. 121 



much more rapidly than if the whole were of uniform char- 

 acter. Thus it must have been that the fall over the sand- 

 stone, (Nc^ 2,) receded much more rapidly while there was a 

 considerable thickness of shale below, than when it approach- 

 ed the level of the water. This would happen after the falls 

 had retreated about three miles, or nearly to the whirlpool. 

 At this point the recession would go on very slowly for a long 

 period, for this hard mass, being at the level of the water, 

 would effectually suspend the undermining process. Even at 

 the present time the mass may be seen stretching into the 

 river from either side beyond the other rocks, and at the point 

 where it crosses, producing a fall of eight or ten feet within 

 a few rods. 



After this long and almost stationary period at the whirl- 

 pool, the recession would again go on more rapidly ; soft ma- 

 terials being presented at the river level to be excavated by 

 the force of the falling water, which would thus undermine 

 the harder mass above. 



When the cascade had receded to near its present position, 

 another pause similar to that at the whirlpool would occur, 

 from the approach of the higher layers of sandstone, (No. 4.) 

 and the hard limestone, (No. 6,) to the surface of the water. 

 There are various proofs of this halting, both in the form of 

 the chasm below the present fall, and from the fact that this 

 lower limestone still remains in place ; for it is seen that 

 having passed a few feet beneath the water at the cascade, 

 it supports large fragments of the upper limestone fallen from 

 above. 



The conclusion then, seems inevitable, that the river has 

 been the great agent in excavating its own chaimel, from near 

 the escarpment between Lewiston and Queenston, to the 

 present position of the cataract ; that the recession has been 

 aided by the character of the rocks, presenting alternate hard 

 and soft strata ; — and that the descent was overcome, not by 

 one perpendicular fall, but by several, produced by the suc- 

 cessive harder layers. In support of this latter assertion, a 

 single analogous case will furnish stronger evidence than a 

 long argument. 



16 



