398 
GEOLOGY OF THE FOURTH DISTRICT. 
are the surrounding surfaces, both in the rapids and on either bank of the river. The deposit 
is of greatest thickness towards the fall, and thins entirely out at its southeastern extremity. 
In some places the lowest part of this deposit is of clay, which has been subsequently covered 
by gravel and sand, containing the freshwater shells. This proves the first condition to have 
been that of a quiet lake, while subsequently a current, transporting pebbles and sand, passed 
over the same bed, leaving the coarse deposit. 
There is another indentation on the eastern bank of the Niagara, below the Whirlpool. 
This has been cited as a case where the small stream coming in, is insufficient to account for 
such an excavation.* It occurs at the junction of Bloody run and the river, and bears the 
strongest evidence of having been produced by the common agents, frost and water. The 
wearing action of the stream alone is probably insufficient to produce this short ravine, which 
extends a few rods back from the margin of the river bank ; but when we take into considera¬ 
tion the fact, that the water penetrates all the fissures of the rock, and then, during fall and 
winter, expands by freezing, we shall find means of explaining the mode of operation. At the 
falls, the recession is by the undermining and breaking down of the upper masses ; the action 
of frost is not to be taken into consideration, as the water, probably, never freezes in the fissures 
behind the fall. Now I consider it as an established fact, that small streams, which freeze 
during Winter, will excavate their beds more rapidly in proportion than large bodies of water 
which never freeze. It appears to me that the indentation at Bloody run is not greater than 
might be expected to have taken place while the main channel receded to its present position. 
Whatever facts and arguments may be advanced to prove the existence of phenomena indi¬ 
cating the former action of the sea in excavating the Niagara channel, and whatever objections 
may be advanced for or against other theories, I am fully convinced, from the facts presented, 
that the existence of the falls and the Niagara river, in their present position, is of very recent 
date geologically. 
We come now to consider the future recession of Niagara falls, and its consequences. 
This is a subject on which many speculations have been hazarded, but no one appears to 
have undertaken the calculation with a full knowledge of the geology of the district, or to have 
taken into account the many disturbing influences. At the present time, the cliff over which 
the water is precipitated, is nearly equally divided between thick-bedded limestone and soft 
disintegrating shale. It is by the action of the spray from the falling water upon the shale, 
undermining and leaving the limestone unsupported, which falls down by its own weight, 
that the falls recede from their present position. Now if we believe the statements of those 
who have resided at the falls, the recession has been about fifty yards within the last forty 
years; but from all the data I have been able to obtain, this appears to be much too great an 
estimate ; indeed, it is extremely questionable if the fall has receded as many feet within that 
time. The central portion of the Horseshoe fall recedes more rapidly than any other part, 
for here the greatest force of the river is exerted. We know, likewise, from the testimony 
* Am. Journal of Science, Vol. XXXV. No. 1. 
