


































82. ROCK RUINS. 
are not shattered like brittle glass under a trip-hammer, and 
swept away. =- 
We must, however, even before this exhibition of power, 
remember that water is not the only instrument which is 
carving out the softer shales. Wherever these are uncov- | 
ered, as in the “Cave of the Winds,” they are cased in ice 
during the winter. Experience has taught us all how the 
frost loosens the bricks of the side-walks, throws down mas- 
sive stone-walls, and bursts our water-pipes. All these 
effects are not due to any miraculous power possessed by 
frost, but to the fact that water when freezing expands and 
forces room for its increasing volume. In the crevices of 
the shale it acts quietly but with resistless force between the | 
layers, like millions of minute wedges lifting and loosening 
the edges of the rock-beds, which are thus rendered an easy 
prey to the waves, if they do not fall of themselves in the 
early spring. Goat Island recedes almost as fast as the cata- 
ract itself, and yet frost alone is the workman that under- 
mines its rocky face. 
The future of the cataract may be read in the stru 
ure of the rocks, as well as its past. Professor Hall, who 
has studied it more carefully than any other geologist, pre 
dicts that Niagara is slowly but surely destroying i 3 
Thousands of years hence and the cataract will have eaten 
its way back until the solid limestone layers, which are 2 
on its verge, will be at its base (i, k). Here it will prot 
bly remain for a long time almost stationary. The low 
portion being as hard as the upper, will not be eaten 4 
into caves and hollows as at present, but, being less expos! 
will give way even more slowly than the upper limest | 
These last, however, notwithstanding their hardness, ` 
be gradually worn down, as the hard layers (2) are a 
whirlpool (c), or the limestones on the bed of the $ 
above the present fall (8’) to the ascending level © 
river bed, as at d in the wood-cut. The softer laye 
greenish marl, marked 9, will have been already lev 
Sy slic 
