NIAGARA FALLS. 
399 
of all residents at this place, that the American fall is becoming more curved in its outline, 
whereas formerly it was nearly in a straight line. The successive descent of large masses 
of limestone, and the still continued overhanging of the table rock, prove very conclusively 
the unremitting action of water and air upon the shale below. 
In the absence of established landmarks, we are compelled to leave the rate of recession 
unsettled for the present. The accompanying trigonometrical map of the falls will furnish 
the means of doing this, by the monuments which have been established, and which may 
be considered as permanent points of reference for the future. 
Leaving out of view the time or rate of recession, we have sufficient data to establish with 
certainty the future changes which will supervene, allowing the recession to go on as it is now 
doing. The lower half of the rock at the cascade, or about eighty feet, is of soft shale, the 
limestone above being of equal thickness ; higher still is about sixty feet of thin-bedded 
limestone, forming the rapids. These different rocks are represented in the section as 7, 8 
and 8', respectively. Now these beds dip to the south at the rate of about twenty-five feet 
in the mile, and the declivity of the bed of the river is about fifteen feet in the mile from 
the falls to Lewiston. It follows, therefore, that as the falls recede, there will be a less 
amount of shale above water, owing to the dip; and to this must be added the amount of 
declivity in the river bed, both together making forty feet. So that when the fall has receded 
one mile, the surface of the water will stand at k, of section page 386, or a point in the shale 
half way between the present surface of the water and the bottom of the limestone. Going 
on at this rate for another mile would take away from the fall forty feet more of the shale, so 
that the surface of the river would then stand at p, or the base of the limestone. 
The cataract would then have a solid wall of limestone to wear down, the river beneath 
protecting, in a great measure, the undermining action upon the shale. During this time, and 
at the end of the first mile, the falls would have arrived at the present site of the commence¬ 
ment of the rapids, and thus about sixty feet more of limestone would be added to the height; 
unless from its thin-bedded character it continued to recede faster, and thus remain a rapid. 
In this case, there would be a fall of one hundred and forty feet at the end of the first mile 
(i, k ); and one of one hundred feet (o, p ) at the end of the second mile. 
At this period, then, we are to contemplate the cataract of Niagara as having receded two 
miles, the shale having disappeared beneath the river, and the cascade presenting a solid wall 
of limestone one hundred feet high, and a rapid of forty or fifty feet (o, m) beyond. The 
recession will then go on very gradually; and so soon as masses from this cliff have fallen 
down to fill up the river bed, as they inevitably will in a great measure, then the base will be 
protected so effectually that little influence will be exerted by the force of the water. Even¬ 
tually, however, the cliff will be broken down, and huge fragments piled up below, until the 
cataract will be nearly lost amid them. This state of things will continue for a long time, 
the height gradually diminishing, till the river has cut its way back for two miles further, 
when there will be no thick-bedded limestone above water, and the higher beds will form a 
rapid as before. 
