ON THE DESTRUCTION OF ROCKS. 235 



action of mechanical powers of more acknowledged 

 and obvious force. But it must be remembered that 

 whether the process of destruction be slow or rapid,, 

 and though it may, to our limited views, often appear 

 contemptible in its effects, it is a process that never 

 ceases. However limited these actions may have been 

 as to the past, their unintermitting continuance, 

 through a duration to which we can assign no liinits ? 

 must produce effects which we should vainly attempt to 

 measure by the small portion of that time which is 

 bounded by our own experience. Yet it will be seen, 

 that even within the short records of history, the 

 changes which Nature thus effects, are no less exten- 

 sive than remarkable. 



If the mere solvent power of water on the earths is 

 the most feeble of these agents, its action is still 

 unquestionable, and must not be overlooked. That it 

 does dissolve silica and lime both, has already been 

 shown; and thus it may often loosen the bonds by 

 which the more insoluble substances are united, so as 

 to produce a greater effect of destruction than would 

 result merely from its solvent power. It is so easy 

 to trace its action on limestones, that instances of 

 this nature need not be adduced. The surfaces of 

 quartz rock which are exposed to rain, are often 

 polished as if by a lapidary's wheel, and the peculiar 

 roundness of the angles, here evinces the cause. The 

 effect, however, in such cases as this, may fairly be 

 taken as nothing ; since, as far as direct solution is 

 here concerned, scarcely eternity itself could be 

 imagined capable of dissolving a mountain of this 

 refractory material. But the looser aggregated rocks 

 of this nature, or the common sandstones, give every 

 where abundant proofs of its influence, in the corro- 

 sion they suffer on long exposure, even where most 



