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 saetere at low 
a tremity (now Lake Brie) 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 mor re 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 cur.ent, 
combined with the receding tide, would carry off 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, aftet Lake frie became fresh, ‘sist 
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 — 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 
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. — 
Vou. XXXV.—No. 2 13 
