Formation of Cliffs or Steep Shores.
On the other hand, when the coast is high, the sea, which is thus prevented from throwing up any thing, exercises a destructive action upon it. Its waves, by sapping the foundation, cause the superincumbent portion of the face of the cliff, thus deprived of support, to be incessantly falling down in fragments. These fragments are tumbled about by the billows, until the softer and more divided parts disappear. The harder portions, from being rolled in contrary directions, assume the form of boulders and pebbles; and these, at length, accumulate in sufficient quantity to form a rampart, by which the bottom of the cliff is protected against farther depredations.
Such is the action of water upon the solid land; and we see, that it consists almost entirely in reducing it to lower levels, but not indefinitely. The fragments of the great mountain ridges are carried down into the valleys; their finer particles, together with those of the lower hills and plains, are borne to the sea; alluvial depositions extend the coasts at the expence of the high grounds. These are limited effects, to which vegetation in general puts a stop, and which, besides, presuppose the existence of mountains, valleys, and plains, in short, all the inequalities of the globe; and which, therefore, cannot have given rise to these inequalities. The formation of downs is a phenomenon still more limited, both in regard to height and horizontal extent; and has no relation whatever to that of those enormous masses into the origin of which it is the object of geology to inquire.[11]