WATERFALLS. 
379 
This mode of operation will explain the cause of recession in a great number of instances. 
Where, however, the water is in such quantity as to preserve a temperature above freezing, 
as in the outlets of some of the lakes, the recession is slower ; the chief agents in effecting the 
destruction of the rock being the wearing action of water, and the effects of air and moisture. 
It may be natural to suppose, that if these streams commenced their operation at the same 
period, and upon similar rocks, that they would have worn back the strata to the same distance. 
The fact, however, is, that the falls are at extremely unequal distances from the main valleys 
into which they flow. This may, in part at least, be accounted for from the circumstances of 
a different proportion of water and a greater or less height of fall, as well also as many other 
minor causes which may have operated to vary the amount of recession. Along the Seneca 
and Cayuga lakes there are many examples of falls over the same strata, at almost equal dis¬ 
tances from the lake. About one mile north of the Taghannuc falls, there is another fall of 
water over somewhat similar strata; but here are no indestructible layers near the summit to 
act as a table rock, and the whole elevation is worn down in a continuous slope, with some 
narrow projections formed by thin arenaceous strata. Had there been, near the top, a thick 
stratum, capable of sustaining the water, we might have had a fall similar to the one in the 
illustration. 
182 - 
