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.

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.

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.

We must not omit to state, before leaving the subject, that it is now ascertained, by a series of accurate observations, that the Crust of the Earth in this interesting locality is once again slowly and gradually subsiding. At the beginning of the century the platform of the temple stood at about the level of the sea; it is now more than a foot below it. Nay, this second subsidence appears to have begun even before the present century. “In the year 1813,” writes a modern traveller, “I resided for four months in the Capuchin convent of Pozzuoli, which is situated between the road from Naples and the sea, at the entrance of the town of Pozzuoli. In the Capuchin convents the oldest friar is called ‘il molto reverende,’ and the one who then enjoyed the title in this convent was ninety-three years old. He informed me that, when he was a young man, the road from Naples passed on the seaward side of the convent; but that, from the gradual sinking of the soil, the road was obliged to be altered to its present course. While I was staying at the convent, the refectory as well as the entrance gate, were from six inches to a foot under water whenever strong westerly winds prevailed, so as to cause the waters of the Mediterranean to rise. Thirty years previously, my old informant stated, such an occurrence never took place. In fact, it is not probable that the builder of the convent would have placed the ground-floor so low as to expose to inundation as it now is.”102

On the shores of the Baltic Sea we find another illustration of our theory upon a more extended scale. About a century and a half ago the Swedish naturalist, Celsius, expressed a belief that a remarkable change of level was taking place along the eastern coast of Scandinavia; and he ascribed the change to a subsidence of the waters of the Baltic Sea. This opinion was received at first with no small amount of incredulity; but the arguments of Celsius were plausible and attractive enough to excite a controversy, and the controversy once aroused was not easily set at rest. Accordingly, since his time the facts upon which he relied have been more strictly examined, difficulties have been started and investigated, many new facts, at first unknown or unnoticed, have been brought to light, and the whole question has been rigorously discussed by scientific men. It would be tedious to go through the history of the discussion, or to develop at any length the arguments which in the end have proved successful, involving as they do a multitude of minute observations and nice measurements, made at a great variety of different places with hard-sounding names. But the general result may be readily stated and as readily understood.

It appears that numerous sunken reefs, well known to navigators, have, within the last two centuries, become visible above water; that many ancient ports have become inland towns; that many small islands have become united to one another and to the mainland by grassy plains; that rocky points which in former times just peeped above the water, and afforded refuge only to a solitary sea-bird, are now grown into little islets; and that several of the old fishing grounds are now deserted for their shallowness, nay, in some cases, altogether dried up. From these facts the inference is plain; either the solid Crust of the Earth has been uplifted, or the waters of the sea have subsided. Now it is certain there has been no subsidence of the sea; for such a subsidence, as we before observed, if it took place at all, should have been general; whereas there are many points on the shores of the Baltic, especially along the coasts of Denmark and Prussia, where it can be proved that no change of level has taken place for centuries. And therefore the phenomena above described we must attribute to an upheaval of the Earth’s Crust.103

Such is the kind of reasoning with which this inquiry has been pursued; and it may now be set down as a received and established fact, that a slow and gradual process of upheaval is going on, at the present day, on the shores of the Baltic Sea, at the rate of from two to four feet in a century; and this is over an area of unknown breadth, and not less than 1000 miles in length. Evidence of a similar kind has lately been adduced to prove that the west coast of Greenland is just now gradually subsiding for a space of more than 600 miles from north to south. “Ancient buildings on low, rocky islands, and on the shore of the mainland, have been gradually submerged, and experience has taught the aboriginal Greenlander never to build his hut near the water’s edge. In one case the Moravian settlers have been obliged more than once to move the poles upon which their large boats were set, and the old poles still remain beneath the water as silent witnesses of the change.”104

It should seem, therefore, that the Crust of the Earth is not that fixed and immovable mass of unyielding rock which it is often supposed to be. Whatever the gigantic power is which lies shut up within it, and which seems, clearly enough, to be developed in some way or another—perhaps in many ways at once—from internal heat, that power exercises a mighty influence from age to age on the outward form of our planet. Like the wind, indeed, it bloweth where it listeth, and we cannot tell whence it cometh or whither it goeth; but we can hear the sound thereof, and witness its effects when it breaks out now in this quarter of the world, and now in that, bursting open the massive rocks, and furiously vomiting forth whole mountains of smouldering ashes and molten mineral; or again, when, failing to find a vent, it shakes the foundations of the hills, and shivers into fragments the most enduring works of man—castles, temples, palaces,—filling every heart with terror and dismay; or, in fine, when it gently upheaves the bottom of the ocean, or by withdrawing the strain, allows the Crust of the Earth to subside, with a movement so gradual and insensible as to escape the notice of the multitudes who are toiling in the busy cities on its Surface. That phenomena of this kind have been going on in all past ages, is now universally assumed in the speculations of Geology: that they are going on in the present age, we have here endeavored to prove by the evidence of facts. If we have succeeded according to our expectations, the reader will be prepared to admit that, on this point at least, it is not the Geologist who may fairly be charged with having recourse to the inventions of his fancy, but rather those who, assuming as a first principle that Geology is false, perseveringly shut their eyes to the physical changes that are going on around them.

PART II.
THE ANTIQUITY OF THE EARTH CONSIDERED IN RELATION TO THE HISTORY OF GENESIS.