The base of these lofty columns is, at present, slightly below the level of the sea. Their outer surface is smooth for about twelve feet above the pedestals; then, for the next nine feet the marble is everywhere bored by a well-known species of mussel, which it is certain can live only in the sea. Above this band of perforations the pillars again present a smooth surface, and continue smooth to the top. The first inference from these facts is, that the columns in question must have been at one time submerged to a height of twenty-one feet above the pedestals; otherwise they could not have been bored at that height by a species of animal that can only exist in sea-water. Since that time, therefore, the land at this spot must have been upraised twenty-one feet. Furthermore, the temple of Jupiter was certainly not built at the bottom of the sea, but upon dry land; therefore, after the temple had been built, the Crust of the Earth must have subsided at least twenty-one feet. Once more: as the floor of the temple is now somewhat below the level of the sea, and as it is not very likely it was at first so built, we may fairly infer that it is now lower than it originally stood; and consequently, that the total amount of upheaval has not been equal to the total amount of subsidence. Though we cannot fix the exact date at which the subsidence began, it was probably not earlier than the third century; for in the atrium of the temple is an inscription recording that it was adorned with precious marbles by the emperor Septimus Severus. It cannot be supposed for a moment that these changes were effected by a rise and fall in the level of the sea rather than by a movement of the Earth’s Crust. A permanent change in the level of the Mediterranean, in any given locality, would, of necessity, imply a change of level over its entire extent; and therefore, if the phenomena exhibited in the bay of Baiæ arose from such a cause, we should meet with phenomena of the same kind along the whole length of the Italian coast. Now, in point of fact, no such changes of level are elsewhere apparent; and consequently, they must be ascribed in the bay of Baiæ, not to an upward and downward movement of the sea, but to an upward and downward movement of the land.