Niagara Falls 



1841 ridges, and terraces, found at different heights above the present 

 y lakes. These ridges and terraces are partly due to the denuda- 



tion and re-arrangement of the materials of the drift itself, which 

 had previously been deposited on the platform, the sloping face 

 of the escarpments, and in the basins of the great lakes. 



As soon as the table-land between Lakes Erie and Ontario 

 emerged and was laid dry, the river Niagara came into existence, 

 the basin of Lake Ontario still continuing to form part of the sea. 

 From that moment there was a cascade at Queenston of moder- 

 ate height, which fell directly into the sea. The uppermost lime- 

 stone and subjacent slate (8 and 7, fig. 4, p. 37) being exposed, 

 the cataract commenced its retrograde course, while the lower 

 beds in the escarpment (from 6 to 1 ) were still protected from 

 waste by remaining submerged. A second fall would in due 

 time be caused by the continued rise of the land and the exposure 

 of the hard beds (6 and 4) , constituting what is called the Clin- 

 ton group, together with the soft and easily undermined red shale 

 (3), on which they repose. Finally, a third cascade would in 

 all likelihood be produced by the rise of another hard mass, the 

 quartzose sandstone (2, fig. 4) resting on very destructible red 

 shale ( 1 ) . Three falls, one above the other, very similar in their 

 geological and geographical position to those actually seen on 

 the river Genesee at Rochester, would thus be formed. The 

 recession of the uppermost must have been gradually retarded 

 by the thickening of the incumbent limestone (No. 8, fig. 4), in 

 proportion as the Falls sawed their way southwards. By this 

 means the second cataract, which would not suffer the same 

 retardation, might overtake it, and the two united would then 

 be retarded by the large quantity of rock to be removed, until 

 the lowest fall would come up to them, and then the whole 

 would be united into one. 



The principal events enumerated in the above retrospect, com- 

 prising the submergence and re-emergence of the Canadian lake 

 district and valley of the St. Lawrence, the deposition of fresh- 

 water strata, and the gradual erosion of a ravine seven miles long, 



558 



