Geology and Topography of Western New York. 97 



In order to understand the origin, and to account rationally for 

 the present location of this cataract, let us go back to the time 

 when the process of elevation was going on, and the highest parts 

 of this limestone ridge had just appeared above the surface at low 

 water. It then became a partial barrier across the ancient gulf, 

 and cut off the free communication between its southwestern ex- 

 tremity (now Lake Erie) and the northeastern section. Across 

 the lowest points of the reef, a strong current would be thereby 

 produced, alternately flowing in opposite directions, during the 

 ebb and flow of the tide. As the reef became more elevated, the 

 currents would gradually become more and more confined to those 

 passes where the fewest obstructions existed. In process of time, 

 some one of these gaining the ascendency, the whole force of the 

 conflicting currents would be concentrated at one point. The 

 .power of the waves and influx of the tide, operating from below, 

 would be applied to the best possible advantage, in tearing up 

 those strata which most impeded their course ; while the current, 

 combined with the receding tide, would carry ofl" the fragments. 

 In this manner the valley of the Niagara was doubtless formed; 

 and circumstances, which will be detailed further on, render it 

 highly probable, that the ledges above the cataract, which form 

 the rapids, had the same origin. 



That such a strait did exist, after Lake Erie became fresh, and 

 before the deep gorge below the falls was excavated, is certain. 

 The ancient banks may be traced on both sides of the gorge ; 

 and that portion of the ancient bed, from the brink of the preci- 

 pice up to the level of the river above the rapids, contains a fresh 

 water deposit, embracing shells of species identical with those 

 now inhabiting the waters of Lake Erie.* This deposit consists 

 principally of gravel, containing fragments and boulders of primi- 

 tive rocks, but chiefly made up of water-worn fragments of 

 the limestone itself At some places, at the depth of from two 



* The Unios appear to be a thick-shelled species, and consist of water-worn 

 fragments. I have not met with a single whole valve, although recently I had a 

 good opportunity for examination, where an excavation for a mill-race was in pro- 

 gress ; and likewise on Goal Island, where the bank had been undermined and 

 caved off. They are exceedingly friable, and will scarcely bear handling. Some 

 of the small univalves, however, as Melania, Planorbis, Paludina, &c., and one 

 minute bivalve, which I take to be a Cyclas, are not only abundant, but well pre- 

 served, and probably inhabited the locality. The Unios may have been brought 

 down by the river current. 



YoL. XXXY.— No. L 13 



