# Great Neapolitan Earthquake of 1857/Part II. Ch. II

CHAPTER II.
PERMANENT CHANGES OF LEVEL ACCOMPANYING EARTHQUAKE—THE THEORIES OF SERAPIS.
So much interest attaches to precise observations, as to permanent change of level of the land, occurring at the same time with earthquakes; and this object having been urged upon my attention, by my friend Sir Charles Lyell, before I left England; I therefore gave the question of whether any such change had attended this earthquake very careful investigation, and I may say, have examined, as to it, the whole coast at various points, from north of Pozzuoli to Pæstum. I found the almost universal opinion at Naples was, that an elevation of some inches around the whole bay, varying at different points, had taken place, and the circumstantiality, with which intelligent persons residing upon the shore, pointed to apparent proofs of their impression, demanded much caution. Professors Capocci and Scacchi, with Signor Guiscardi, doubted the existence of any change of level, but could give no facts either way. All the evidence presented to me, was based upon references to assumed changes of tidal level.
The English lady at St. Lucia, before referred to, pointed ​to a sloping quay bench (Fig. 116) opposite her windows. She had always remarked, that, at high water, the tide covered to the point $c$, or an inch or two above it, prior to
the 16th December; but since that, the high-water level had been permanently about five inches beneath the arris of the quay at $e$, giving a difference in level of from nine to twelve inches. To test this I examined the water level daily at the hour nearly of highest tide, and for four days found the highest tide-mark as at $b$; but on the next occasion of observation it was not only at $c$, but some inches above it. The difference was simply due to the off or on shore wind.
It would be tedious to record several other observations round the bay of like character.
On visiting the Temple of Serapis, at Pozzuoli, where the notoriety it had already acquired on this point, and the daily attention given to it, presented the best chance of decisive indication, no evidence whatever could be found of change of level. The "gardien " of the place, however, on being questioned as to whether he had observed any change of level, at once directed our attention to the base of one of the worm-eaten columns, and stoutly affirmed that the level of the ​water which was then standing at $a$ (Fig. 117), had, directly after the shock of December, fallen to $b$, equivalent to a rise of the temple of 7 inches, but that, since that time, the water had gradually returned to its former level, i. e. the land had sunk again.
He denied that the difference could be due to variability in the sea level. The utmost limits of disturbance by wind or tide within the sheltered valley of the ruins being, according to his stated experience, far within 7 inches.
I could not find, that any man of science in Naples, had ascertained what these limits of aqueous disturbance were, and on my return to the city (from the interior), I took the occasion of a severe gale of wind in shore—the "Garbino," from the S.W.—and at the presumed time of high water, to visit the temple again, in company with Signor Guiscardi, when I found the water rather above the level of the sill of the entrance iron gate, and fully 22 inches above the level of the 5th February, and it had been nearly 3 inches higher about two hours previously.
It is obvious, therefore, that any deduction whatsoever as to levels, whether of elevation or of depression, based upon the tidal level of the Mediterranean on this coast, cannot be depended upon, within the limits of 18 inches or 2 feet at the very least; and several of the speculations as to minute oscillations of level of the Temple of Serapis so based must henceforward be received with doubt.
Impressed with this fact, in which I found that Professor Capocci and Signor Guiscardi coincided with me, and with the extreme value to physical science, of possessing, in this instable region, some definite and unimpeachable standard of level, I addressed a formal letter, upon my return to Naples ​from the interior, to the government of his Majesty, the late king, suggesting the importance, of having an accurate line of levelling run through to Naples, from the sill of the front door of St. Peter's, at Rome, which may be presumed at present as the best, if not an invariable datum point, and the difference of level marked upon bench marks at and around Naples. (See Appendix No. 4.) The work could be performed with ease and little cost by the officers of the "Ponte e Strade," going along the high road between the capitals. I regret to say, however, that it was intimated to me, at the Ministry of the Interior, that this despotic government objected to entertain suggestions from foreigners, even as to matters of science; and the work, which could then have been accomplished with facility, in connection with certain railway surveys in progress, remains, and is likely to remain unperformed.
While the limits of error as to levels deduced from the sea, affect all minute questions of rise and fall of Serapis, they do not touch the great change of level, as evidenced by the celebrated columns; but they appear to me sufficient to destroy the force of the conclusions of Niccolini and others, as to oscillatory changes of level of small extent.
The evidence of elevation, of the whole building since its original construction appears to me irrefragable; but not so that upon which the supposition of its subsidence first, after its erection, and previous to its elevation are based. The argument for subsidence, rests upon the improbability that the level of the floor of the building was originally designed and constructed, below that of the mean tide of the Mediterranean. Now it appears to me that the probability runs just the other way. Archæologists appear to ​have settled, that the so-called Temple of Serapis was not a temple at all, but a public bath, a conclusion that forces itself upon the mind of any untheoretical observer of the general architectural structure of the place. If a bath, nothing is so probable, as that its level should have been fixed with reference to the sea, such that sea-water would run in, or command the baths, in a place where there appears to have been no fresh water except that of the thermal spring. The possible objection to this, that there would then be no drainage for the waste water of the baths is met by the fact, that the dry and porous subsoil, consisting of 12 to 20 feet of tufa, lapilli, and scoriæ, would soak away any amount of water, if simply discharged into a pit sunk in it, below the level of the baths, a method of drainage actnally practised from a remote age to the present day. A considerable district of Paris at present discharges the whole of its sewage into such a "puit d'absorption."
The land at the existing level of the terrace called La Starza, upon which the temple was built, is in rapid and constant process of marine degradation at present; so much so, that unless artificial means be soon taken to prevent its inroads, the sea will in another half-century probably, have swept away the whole temple (so called).
It therefore was probably very much more inland when first constructed, and was probably built either in some natural depression, of 10 or 12 feet below the sea level, or in one excavated to that depth, by a race whose burrowing tendencies are revealed by many of their buildings, in all directions around. If much inland, there was doubtless a sufficient mass, though of porous material, between it and the sea, to be water-tight; but if, as more and more of this ​became removed, the sea-water percolated the bank universally, at the seaward side, it could no longer be kept out from the building, and the place would have been abandoned as untenable.
The water of the sea would then stand permanently at a level with the highest line of testaceous perforations of the limestone columns, say about 20 feet above the level of the present floor, assuming that the general level of La Starza was then about 8 feet under what it now is, and that the floor was originally founded 12 feet below the level.
The channels or ducts that had before brought the seawater to the baths would also bring the young testacea, and preserve sufficient change for their healthy existence. If, subsequently, the land bearing the so-called temple upon it, were gradually elevated about 8 feet, resting at about its present level, we have sufficient to account for the phenomena observed, without having recourse to, several successive depressions and elevations.
Elevations are common, and obviously part of the established cosmos of the earth's surface, but depressions, due to subterraneous forces, appear exceptional and rare, and especially doubtful, close to volcanic vents. Land-slips and aqueous erosion, marine and of every other sort, appear the established agents for depression of surface, acting in antagonism to the former. Indeed, proofs seem wanting, of any such thing as recurrent oscillation of level, of any known tract of land within the historic period, traceable in both directions of movement, to subterraneous agency.
To the view here advanced as offering the simplest and most probable solution of the Serapis problem, it may be ​objected, that the adjoining ruins of the Temples of Neptune, and of the Nymphs, are some feet under water, and that the arches of the so-called Mole of Pozzuoli, are covered above the level of the springings. The levels of these two latter temples will not accord either with the presumed depression or elevation of Serapis, and may hence be made to argue as much against, as for the oscillatory view; and as to the arches and general structure, of the so-called mole now deeply immersed, I am satisfied that it never was built for a sea mole at all, and that the whole of the arches were originally built on dry land, and for other purposes. It would be a work of no small difficulty, to construct these piers and arches in the open sea-way, where their remains now stand, with all the aids that modern engineering afford: and without the diving-bell we may safely affirm that they never could have been built in open sea-water. They, further, are of dimensions and construction, that no Roman or any other architect would have adopted for a marine mole.
How, then, came they immersed as they are? It appears to me that they, and the incoherent tufaceous land, that sustains them and these temples, are now, and have long been, in gradual process of insensible land-slip downward and seaward, by the continual removal by tidal action of the loose material, from the foot of the submarine talus, which the soundings prove, to be outside them, in the roadstead, hence unequal subsidence, but always greatest where nearest the sea-shore. And this view is strongly corroborated by the fact, that all the standing columns at Serapis lean some inches out of plumb to seaward, and that the whole floor of the place is waved and uneven, and with a general ​out-of-level slope to seaward also, as though the whole mass stood upon a base of loose soft material that was gradually settling and going seaward from the effects of sublittoral erosion. This seems also to be the solution, of the instances of the Roman roads, under water between Pozzuoli and Baiæ, and the Lucrine Lake.
Moreover, if Serapis had been ever depressed to the extent required, then this so called marine mole must have been equally so; but it is quite obvious to an engineering eye that were the arches, upon the piers as now standing, depressed but a few feet more, so as to receive the full stroke of the waves in storms, or the entire impulse of the moving superficial column of the sea, they would have been overthrown long ago. They only stand because they never yet were wholly under water.
The general importance of questions of permanent elevation or depression, and their intimate 'connection with earthquake phenomena, will, I trust, be deemed sufficient ground for this digression, upon the much-discussed Temple of Serapis.