If we were left in this matter to mere conjecture, we might offer the following hypothesis as a fair and reasonable solution. We might suppose that since the days of the Roman Empire, there have been _two successive movements_ of the Earth’s Crust in the neighborhood of Naples; first, a movement of subsidence, by which the ancient temples and roads were submerged to a considerable depth beneath the sea; afterward, a movement of upheaval, by which the marine strata were lifted up. If this second movement were exactly equal to the first, it is plain that the ancient roads and buildings would have been just restored to their former level. But let us suppose that the amount of upheaval was something less than the amount of previous subsidence, and we should have these roads and buildings still submerged, as they are in point of fact, in a few feet of water. By such an hypothesis, therefore, the two classes of phenomena might be brought into perfect harmony. But we are not obliged to take refuge in hypothesis: for it is now distinctly proved by a very curious kind of evidence, that the Crust of the Earth in and about the bay of Baiæ, has been successively depressed and upraised since the third century of the Christian era; nay more, that the subsidence in the first case was greater than the subsequent upheaval. Near Pozzuoli, on the level tract of land which, as we have said, intervenes between the sea and the lofty range of inland cliffs, are to be seen at the present day the ruins of a splendid Roman edifice, usually called the temple of Jupiter Serapis, though, according to some writers, it was not a temple at all, but a public establishment for baths. These ruins first attracted attention about the middle of the last century. Three magnificent marble columns were still standing erect, with their lower parts buried in the stratified deposits already described, and their upper portions, which projected above the surface of the land, partly concealed by bushes. When the soil was removed the original plan of the building could be distinctly traced. “It was of a quadrangular form, seventy feet in diameter, and the roof had been supported by forty-six noble columns, twenty-four of granite and the rest of marble.” Many of the pillars have been shattered in the course of time, and lie strewn in fragments on the pavements. The three which are still standing erect, are upward of forty feet in height, each carved out of a solid block of marble; and, what is chiefly to our purpose, they exhibit, curiously inscribed on their surface, memorials of the physical changes in which they have borne a part.