CHAPTER XVII.
SUBTERRANEAN HEAT—ITS POWERS ILLUSTRATED BY UNDULATIONS OF THE EARTH’S CRUST.
Gentle movements of the Earth’s Crust within historic times—Roman roads and temples submerged in the bay of Baiæ—Temple of Jupiter Serapis—Singular condition of its columns—Proof of subsidence and subsequent upheaval—Indications of a second subsidence now actually taking place—Gradual upheaval of the coast of Sweden—Summary of the evidence adduced to establish this fact—Subsidence of the Earth’s Crust on the west coast of Greenland—Recapitulation.
So far we have spoken of the disturbance of the Earth’s Crust in modern times by sudden and violent convulsions. But there are many phenomena with which the Geologist is familiar, that cannot be fairly accounted for unless by supposing that the surface of the Earth was often elevated and depressed in ancient times, without any sudden shock, by a slow and almost insensible movement. And, accordingly, gentle undulations of this kind enter largely into that general theory of Geology which we have been attempting to draw out and illustrate. It may be asked, therefore, if we are able to support this part of our system by examples of similar phenomena occurring within the period of history. In reply, we shall endeavor to set forth, as briefly as we can, some of the evidence which has recently come to light on this subject, and which seems to us not less conclusive than it is interesting and unexpected.
In the bay of Baiæ, to the west of Naples, two ancient Roman roads may be distinctly traced, at the present day, for a considerable distance, permanently submerged beneath the waters. There are, also, in the same neighborhood, the ruins of the temple of Neptune and of the temple of the Nymphs, both likewise submerged. “The columns of the former edifice stand erect in five feet of water, the upper portions just rising to the surface;[100] the pedestals are supposed to be buried in the mud below.” Again, on the opposite side of Naples, near Sorrento, “a road with fragments of Roman buildings, is covered to some depth by the sea;”[101] and in the island of Capri, at the opening of the bay of Naples, one of the palaces of Tiberius is also under water. Here, therefore, it is clear that the Crust of the Earth has subsided over a very considerable area; since what is now the bed of the sea, was in the days of the Romans dry land, traversed by roads, and dotted over with buildings. That the subsidence was slow and gradual may be inferred, partly from the absence of any record or tradition of a sudden convulsion producing such a change, and partly, too, from the unshaken and undisturbed condition of the monuments themselves.
But while this conclusion falls in most happily with our present argument, it would seem on further examination to bring with it a very serious difficulty. For, while those ancient monuments testify that the Crust of the Earth in this locality has subsided, the structure of the sea-coast, interpreted according to Geological principles, would indicate, on the contrary, that the Crust of the Earth has been upheaved. Close to the sea, at the present day, on the bay of Baiæ, there is a low, level tract of fertile land, and at a little distance inland, a lofty range of precipitous cliffs, eighty feet high, parallel to the line of the coast. This fertile tract, lying between the sea-beach and the perpendicular cliffs, is about twenty feet above the sea level, and is composed of regularly stratified deposits abounding in marine shells of recent species, together with works of human art, such as tiles, squares of mosaic pavement, fragments of bricks, and sculptured ornaments. Upon these facts a Geologist would pronounce without hesitation:—First, that at some period since the district around Naples was first inhabited by man, the waters of the sea washed the base of the perpendicular cliffs; secondly, that the strata in which we now find the recent marine shells, and the remains of man’s workmanship, were formed during that period by the process of deposition at the bottom of the sea; and thirdly, that at some subsequent time, by an upheaval of the Earth’s Crust, these strata were lifted up so as to form a pretty considerable area of dry land, fit for agriculture and the arts of life.
Does it not seem, therefore, that we have here a direct contradiction between the evidence of ancient Roman buildings and the inferences of modern Geology? Doubtless, they both agree in the main point about which we are concerned just now, that the Crust of the Earth has been moved in recent times on the shores of the bay of Naples; but according to the testimony of the Roman temples, now covered by water, this movement has been one of subsidence, while, according to the inferences of Geological theory, it has been one of upheaval. This apparent contradiction seems to call for some elucidation.
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.