Besides this argument of the gradation from a continent of land to a bare rock, we have another from the consideration of those rocks themselves, so far as these could not be formed by nature in their present state, but must have been portions of a greater mass. How, for example, could a perpendicular mountain, such as St. Kilda, have been produced in the ocean? Of whatever materials we shall suppose it formed, we never shall find means for the production of such a mass in its present insulated state. Let us take examples of this kind near our coast, and of known rocks. Staffa and Ailsa, on the west coast, and the Bass, upon the east, are mountains of either whin-stone or granite, similar to many such mountains within the land; and they are perpendicular around, except perhaps on one part. It is demonstrable that such basaltic rock as contains zeolite and calcareous spar, as most of our whin-stones do, could not have been the eruption of a volcano, consequently those rocks must have been masses protruded in a fluid state, under an immense cover of earth at the time of their production; and they could not have risen immediately out of the sea, with all their various minerals, their veins and cutters, their faces and their angles. In like manner, the east coast of Caithness is a perpendicular cliff of sand-stone, lying in a horizontal position, and thus forming a flat country above the shore. But along this coast there are small islands, pillars, and peninsulas, of the same strata, corresponding perfectly with that which forms the greater mass. Now, shall we suppose those strata of sand-stone to have been formed in their place, and to have reached no farther eastward into the sea?--It is unsupposable. Or, shall we conceive that the sea, which has made such depredations in land composed of much more solid materials, had spared this, and had not wasted much more than that now pointed out by the ruins which remain?--Impossible; we must suppose that there had once existed much land where nothing now is found but sea. But, if we are to suppose much to have been wasted, where shall we stop in this process of restoring continents? That is the question now to be discussed.