not very considerably,) by which means it returns whenever the force is removed, and vibrates backward and forward, till it is reduced to rest. Were it required to remove the stone from its place, it might be most easily done, by cutting off a part from one side, or blowing it away by gunpowder; the stone would then lose its balance, would tumble from its pedestal, and might roll to a considerable distance. Now, what art is here supposed to perform, nature herself in time will probably effect. If the waste on one side of this great mass shall exceed that on the opposite in more than a certain proportion, and it is not likely that that proportion will be always maintained, the equilibrium of the Logan stone will be subverted, never to return. Thus we perceive how motion may be produced by the combined action of the decomposition and gravitation of large masses of rock. [Footnote 178: I do not presume so far as to say, that all rocking-stones are produced by natural means: I have not sufficient information to justify that assertion; but the great size of that at the Land's End, its elevated position, and the approaches toward something of the same kind which are to be seen in other parts of that shore, prove that it is no work of art. They who ascribe it to the Druids, do not consider the rapidity with which the Cornish granite wastes, nor think how improbable it is, that the conditions necessary to a rocking-stone, whether produced by nature or art, should have remained the same for sixteen or seventeen hundred years.] 356. Besides the gradual waste to which stones exposed to the atmosphere are necessarily subject, those of a great size appear to be liable to splitting, and dividing into large portions, no doubt from their weight. This may be observed in almost all stones that happen to be in such circumstances as we are now considering; and from this cause the subversion of their balance may be more sudden, and of greater amount, than could be expected from their gradual decay.