400 
GEOLOGY OF THE FOURTH DISTRICT. 
This point of meeting between the surface of the river below the fall and the top of the 
thick-beddecl limestone, will be about one hundred feet lower than the top of the present 
cascade; and as there will be forty feet of rapids in the thin-bedded limestone within a short 
space, as there now is, it follows that there will be added to the descent of the river beyond 
the rapids, one hundred feet more than at present, as the surface of the limestone has dipped 
to that amount. The whole fall in the river at that lime, from Lake Erie to the point of 
junction between the limestone and water below the rapids ( li , o), will be about one hundred 
and sixty feet. The distance between this point and the oullet of Lake Erie is occupied by 
nearly uniform soft layers; and after a partial wearing down of the limestone forming the 
rapids, the descent will be equally distributed over the whole extent of sixteen miles, giving 
a uniform declivity of about ten feet in the mile, or one-third less than the present declivity in 
the bed of the river from the Falls to Lewiston. From the nature of the bed of the river for 
sixteen miles below Lake Erie, it may be doubted whether this rapid descent along the whole 
distance would be continued ; for the stream, having no heavy blocks of rock to remove, would 
keep its channel clear with a far less declivity; and should this prove the case here, we 
might still have a fall of a few feet, at the outlet of Lake Erie, over the limestone succeeding 
the salt group. 
Whether such a fall would occur, depends on the solution of the problem regarding the 
required declivity in the bed of the river below Lake Erie. AVhichever way it may occur, it 
will make no material difference in the great result, which will be either a continuous rapid 
stream from Lake Erie to Lewiston, or a rapid stream with a low fall at the outlet of Erie. 
If present causes continue to operate as now, such will be the consummation of the grand 
cataract of Niagara. 
It is unnecessary here to follow on this recession gradually from the outlet of Lake Erie to 
the final drainage of a portion of its waters. The views which have been entertained of 
the sudden drainage of this or any of the upper lakes, and a deluging of the country on the 
north and east are no longer considered as tenable by any one; and even if Lake Erie could 
be drained suddenly, it would cause no deluge of any importance. If the whole lake were 
at once placed upon Lake Ontario, it would only elevate its surface by about one hundred 
and fifty feet, so that its extent would not exceed the limits of the ancient lake ridge, and the 
outlet would still be the valley of the St. Lawrence. 
Thus far the country supplying water to the upper lakes has been but little changed by the 
hand of cultivation ; the primeval forests still clothe the surface, and evaporation, to a great 
extent, is prevented. This cannot always remain so ; the advancing settlements will yet 
penetrate even to the wilderness bordering Lake Superior, and the opening of the surface to 
the influence of the sun’s rays will greatly diminish the supply of water flowing into its 
tributaries. These causes will sensibly diminish the quantity passing down the natural out¬ 
let ; and the mighty Niagara is destined to be, at certain seasons, but a diminutive represen¬ 
tative of its former grandeur. 
