Part 14

The Temple of Serapis at Puzzuoli, near Naples, is perhaps, of all the structures raised by the hands of man, the one which affords most instruction to a geologist. It has not only undergone a wonderful succession of changes in past time, but is still undergoing changes of condition. This edifice was exhumed in 1750 from the eastern shore of the Bay of Baiæ, consisting partly of strata containing marine shells with fragments of pottery and sculpture, and partly of volcanic matter of sub-aerial origin. Various theories were proposed in the last century to explain the perforations and attached animals observed on the middle zone of the three erect marble columns until recently standing; Goethe, among the rest, suggesting that a lagoon had once existed in the vestibule of the temple, filled during a temporary incursion of the sea with salt water, and that marine mollusca and annelids flourished for years in this lagoon at twelve feet or more above the sea-level.

This hypothesis was advanced at a time when almost any amount of fluctuation in the level of the sea was thought more probable than the slightest alteration in the level of the solid land. In 1807 the architect Niccolini observed that the pavement of the temple was dry, except when a violent south wind was blowing; whereas, on revisiting the temple fifteen years later, he found the pavement covered by salt water twice every day at high tide. From measurements made from 1822 to 1838, and thence to 1845, he inferred that the sea was gaining annually upon the floor of the temple at the rate of about one-third of an inch during the first period, and about three-fourths of an inch during the second. Mr. Smith of Jordan Hill, from his visits in 1819 and 1845, found an average rise of about an inch annually, which was in accordance with visits made by Mr. Babbage in 1828, and Professor James Forbes in 1826 and 1843. In 1852 Signor Scaecchi, at the request of Sir Charles Lyell, compared the depth of water on the pavement with its level taken by him in 1839, and found that it had gained only 4½ inches in thirteen years, and was not so deep as when MM. Niccolini and Smith measured it in 1845; from which he inferred that after 1845 the downward movement of the land had ceased, and before 1852 had been converted into an upward movement.

Arago and others maintained that the surface on which the temple stands has been depressed, has _remained under the sea, and has again been elevated_. Russager, however, contends that there is nothing in the vicinity of the temple, or in the temple itself, to justify this bold hypothesis. Every thing leads to the belief that the temple has remained unchanged in the position in which it was originally built; but that the sea rose, surrounded it to a height of at least twelve feet, and again retired; but the elevated position of the sea continued sufficiently long to admit of the animals boring the pillars. This view can even be proved historically; for Niccolini, in a memoir published in 1840, gives the heights of the level of the sea in the Bay of Naples for a period of 1900 years, and has with much acuteness proved his assertions historically. The correctness of Russager’s opinion, he states, can be demonstrated and reduced to figures by means of the dates collected by Niccolini.--See _Jameson’s Journal_, No. 58.

At the present time the floor is always covered with sea-water. On the whole, there is little doubt that the ground has sunk upwards of two feet during the last half-century. This gradual subsidence confirms in a remarkable manner Mr. Babbage’s conclusions--drawn from the calcareous incrustations formed by the hot springs on the walls of the building and from the ancient lines of the water-level at the base of the three columns--that the original subsidence was not sudden, but slow and by successive movements.

Sir Charles Lyell (who, in his _Principles of Geology_, has given a detailed account of the several upfillings of the temple) considers that when the mosaic pavement was re-constructed, the floor of the building must have stood about twelve feet above the level of 1838 (or about 11½ feet above the level of the sea), and that it had sunk about nineteen feet below that level before it was elevated by the eruption of Monte Nuovo.

We regret to add, that the columns of the temple are no longer in the position in which they served so many years as a species of self-registering hydrometer: the materials have been newly arranged, and thus has been torn as it were from history a page which can never be replaced.

THE GROTTO DEL CANE.

This “Dog Grotto” has been so much cited for its stratum of carbonic-acid gas covering the floor, that all geological travellers who visit Naples feel an interest in seeing the wonder.

This cavern was known to Pliny. It is continually exhaling from its sides and floor volumes of steam mixed with carbonic-acid gas; but the latter, from its greater specific gravity, accumulates at the bottom, and flows over the step of the door. The upper part of the cave, therefore, is free from the gas, while the floor is completely covered by it. Addison, on his visit, made some interesting experiments. He found that a pistol could not be fired at the bottom; and that on laying a train of gunpowder and igniting it on the outside of the cavern, the carbonic-acid gas “could not intercept the train of fire when it once began flashing, nor hinder it from running to the very end.” He found that a viper was nine minutes in dying on the first trial, and ten minutes on the second; this increased vitality being, in his opinion, attributable to the stock of air which it had inhaled after the first trial. Dr. Daubeny found that phosphorus would continue lighted at about two feet above the bottom; that a sulphur-match went out in a few minutes above it, and a wax-taper at a still higher level. The keeper of the cavern has a dog, upon which he shows the effects of the gas, which, however, are quite as well, if not better, seen in a torch, a lighted candle, or a pistol.

“Unfortunately,” says Professor Silliman, “like some other grottoes, the enchantment of the ‘Dog Grotto’ disappears on a near view.” It is a little hole dug artificially in the side of a hill facing Lake Agnano: it is scarcely high enough for a person to stand upright in, and the aperture is closed by a door. Into this narrow cell a poor little dog is very unwillingly dragged and placed in a depression of the floor, where he is soon narcotised by the carbonic acid. The earth is warm to the hand, and the gas given out is very constant.

THE WATERS OF THE GLOBE GRADUALLY DECREASING.

This was maintained by M. Bory Saint Vincent, because the vast deserts of sand, mixed up with the salt and remains of marine animals, of which the surface of the globe is partly composed, were formerly inland seas, which have insensibly become dry. The Caspian, the Dead Sea, the Lake Baikal, &c. will become dry in their turn also, when their beds will be sandy deserts. The inland seas, whether they have only one outlet, as the Mediterranean, the Red Sea, the Baltic, &c., or whether they have several, as the Gulf of Mexico, the seas of O’Kotsk, of Japan, China, &c., will at some future time cease to communicate with the great basins of the ocean; they will become inland seas, true Caspians, and in due time will become likewise dry. On all sides the waters of rivers are seen to carry forward in their course the soil of the continent. Alluvial lands, deltas, banks of sand, form themselves near the coasts, and in the directions of the currents; madreporic animals lay the foundations of new lands; and while the straits become closed, while the depths of the sea fill up, the level of the sea, which it would seem natural should become higher, is sensibly lower. There is, therefore, an actual diminution of liquid matter.

THE SALT LAKE OF UTAH.

Lieutenant Gunnison, who has surveyed the great basin of the Salt Lake, states the water to be about one-third salt, which it yields on boiling. Its density is considerably greater than that of the Red Sea. One can hardly get the whole body below the surface: in a sitting position the head and shoulders will remain above the water, such is the strength of the brine; and on coming to the shore the body is covered with an incrustation of salt in fine crystals. During summer the lake throws on shore abundance of salt, while in winter it throws up Glauber salt plentifully. “The reason of this,” says Lieutenant Gunnison, “is left for the scientific to judge, and also what becomes of the enormous amount of fresh water poured into it by three or four large rivers,--Jordan, Bear, and Weber,--as there is no visible effect.”

FORCE OF RUNNING WATER.

It has been proved by experiment that the rapidity at the bottom of a stream is every where less than in any other part of it, and is greatest at the surface. Also, that in the middle of the stream the particles at the top move swifter than those at the sides. This slowness of the lowest and side currents is produced by friction; and when the rapidity is sufficiently great, the soil composing the sides and bottom gives way. If the water flows at the rate of three inches per second, it will tear up fine clay; six inches per second, fine sand; twelve inches per second, fine gravel; and three feet per second, stones the size of an egg.--_Sir Charles Lyell._

THE ARTESIAN WELL OF GRENELLE AT PARIS.

M. Peligot has ascertained that the Water of the Artesian Well of Grenelle contains not the least trace of air. Subterranean waters ought therefore to be _aerated_ before being used as aliment. Accordingly, at Grenelle, has been constructed a tower, from the top of which the water descends in innumerable threads, so as to present as much surface as possible to the air.

The boring of this Well by the Messrs. Mulot occupied seven years, one month, twenty-six days, to the depth of 1794½ English feet, or 194½ feet below the depth at which M. Elie de Beaumont foretold that water would be found. The sound, or borer, weighed 20,000 lb., and was treble the height of that of the dome of the Hôpital des Invalides at Paris. In May 1837, when the bore had reached 1246 feet 8 inches, the great chisel and 262 feet of rods fell to the bottom; and although these weighed five tons, M. Mulot tapped a screw on the head of the rods, and thus, connecting another length to them, after fifteen months’ labour, drew up the chisel. On another occasion, this chisel having been raised with great force, sank at one stroke 85 feet 3 inches into the chalk!

The depth of the Grenelle Well is nearly four times the height of Strasburg Cathedral; more than six times the height of the Hôpital des Invalides at Paris; more than four times the height of St. Peter’s at Rome; nearly four times and a half the height of St. Paul’s, and nine times the height of the Monument, London. Lastly, suppose all the above edifices to be piled one upon each other, from the base-line of the Well of Grenelle, and they would but reach within 11½ feet of its surface.

MM. Elie de Beaumont and Arago never for a moment doubted the final success of the work; their confidence being based on analogy, and on a complete acquaintance with the geological structure of the Paris basin, which is identical with that of the London basin beneath the London clay.

In the duchy of Luxembourg is a well the depth of which surpasses all others of the kind. It is upwards of 1000 feet more than that of Grenelle near Paris.

HOW THE GULF-STREAM REGULATES THE TEMPERATURE OF LONDON.

Great Britain is almost exactly under the same latitude as Labrador, a region of ice and snow. Apparently, the chief cause of the remarkable difference between the two climates arises from the action of the great oceanic Gulf-Stream, whereby this country is kept constantly encircled with waters warmed by a West-Indian sun.

Were it not for this unceasing current from tropical seas, London, instead of its present moderate average winter temperature of 6° above the freezing-point, might for many months annually be ice-bound by a settled cold of 10° to 30° below that point, and have its pleasant summer months replaced by a season so short as not to allow corn to ripen, or only an alpine vegetation to flourish.

Nor are we without evidence afforded by animal life of a greater cold having prevailed in this country at a late geological period. One case in particular occurs within eighty miles of London, at the village of Chillesford, near Woodbridge, where, in a bed of clayey sand of an age but little (geologically speaking) anterior to the London gravel, Mr. Prestwich has found a group of fossil shells in greater part identical with species now living in the seas of Greenland and of similar latitudes, and which must evidently, from their perfect condition and natural position, have existed in the place where they are now met with.--_Lectures on the Geology of Clapham, &c. by Joseph Prestwich, A.R.S., F.G.S._

SOLVENT ACTION OF COMMON SALT AT HIGH TEMPERATURES.

Forchhammer, after a long series of experiments, has come to the conclusion that Common Salt at high temperatures, such as prevailed at earlier periods of the earth’s history, acted as a general solvent, similarly to water at common temperatures. The amount of common salt in the earth would suffice to cover its whole surface with a crust ten feet in thickness.

FREEZING CAVERN IN RUSSIA.

This famous Cavern, at Ithetz Kaya-Zastchita, in the Steppes of the Kirghis, is employed by the inhabitants as a cellar. It has the very remarkable property of being so intensely cold during the hottest summers as to be then filled with ice, which disappearing with cold weather, is entirely gone in winter, when all the country is clad in snow. The roof is hung with ever-dripping solid icicles, and the floor may be called a stalagmite of ice and frozen earth. “If,” says Sir R. Murchison, “as we were assured, _the cold is greatest when the external air is hottest and driest_, that the fall of rain and a moist atmosphere produce some diminution of the cold in the cave, and that upon the setting-in of winter the ice disappears entirely,--then indeed the problem is very curious.” The peasants assert that in winter they could sleep in the cave without their sheepskins.

INTERIOR TEMPERATURE OF THE EARTH: CENTRAL HEAT.

By the observed temperature of mines, and that at the bottom of artesian wells, it has been established that the rate at which such temperature increases as we descend varies considerably in different localities, where the depths are comparatively small; but where the depths are great, we find a much nearer approximation to a common rate of increase, which, as determined by the best observation in the deepest mines, shafts, and artesian wells in Western Europe, is very nearly 1° F. _for an increase in depth of fifty feet_.--_W. Hopkins, M.A., F.R.S._

Humboldt states that, according to tolerably coincident experiments in artesian wells, it has been shown that the heat increases on an average about 1° for every 54·5 feet. If this increase can be reduced to arithmetical relations, it will follow that a stratum of granite would be in a state of fusion at a depth of nearly twenty-one geographical miles, or between four and five times the elevation of the highest summit of the Himalaya.

The following is the opinion of Professor Silliman:

That the whole interior portion of the earth, or at least a great part of it, is an ocean of melted rock, agitated by violent winds, though I dare not affirm it, is still rendered highly probable by the phenomena of volcanoes. The facts connected with their eruption have been ascertained and placed beyond a doubt. How, then, are they to be accounted for? The theory prevalent some years since, that they are caused by the combustion of immense coal-beds, is puerile and now entirely abandoned. All the coal in the world could not afford fuel enough for one of the tremendous eruptions of Vesuvius.

This observed increase of temperature in descending beneath the earth’s surface suggested the notion of a central incandescent nucleus still remaining in a state of fluidity from its elevated temperature. Hence the theory that the whole mass of the earth was formerly a molten fluid mass, the exterior portion of which, to some unknown depth, has assumed its present solidity by the radiation of heat into surrounding space, and its consequent refrigeration.

The mathematical solution of this problem of Central Heat, assuming such heat to exist, tells us that though the central portion of the earth may consist of a mass of molten matter, the temperature of its surface is not thereby increased by more than the small fraction of a degree. Poisson has calculated that it would require _a thousand millions of centuries_ to reduce this fraction to a degree by half its present amount, supposing always the external conditions to remain unaltered. In such cases, the superficial temperature of the earth may, in fact, be considered to have approximated so near to its ultimate limit that it can be subject to no further sensible change.

DISAPPEARANCE OF VOLCANIC ISLANDS.

Many of the Volcanic Islands thrown up above the sea-level soon disappear, because the lavas and conglomerates of which they are formed spread over flatter surfaces, through the weight of the incumbent fluid; and the constant levelling process goes on below the sea by the action of tides and currents. Such islands as have effectually resisted this action are found to possess a solid framework of lava, supporting or defending the loose fragmentary materials.

Among the most celebrated of these phenomena in our times may be mentioned the Isle of Sabrina, which rose off the coast of St. Michael’s in 1811, attained a circumference of one mile and a height of 300 feet, and disappeared in less than eight months; in the following year there were eighty fathoms of water in its place. In July 1831 appeared Graham’s Island off the coast of Sicily, which attained a mile in circumference and 150 or 160 feet in height; its formation much resembled that of Sabrina.

The line of ancient subterranean fire which we trace on the Mediterranean coasts has had a strange attestation in Graham’s Island, which is also described as a volcano suddenly bursting forth in the mid sea between Sicily and Africa; burning for several weeks, and throwing up an isle, or crater-cone of scoriæ and ashes, which had scarcely been named before it was again lost by subsidence beneath the sea, leaving only a shoal-bank to attest this strange submarine breach in the earth’s crust, which thus mingled fire and water in one common action.

Floating islands are not very rare: in 1827, one was seen twenty leagues to the east of the Azores; it was three leagues in width, and covered with volcanic products, sugar-canes, straw, and pieces of wood.

PERPETUAL FIRE.

Not far from the Deliktash, on the side of a mountain in Lycia, is the Perpetual Fire described some forty years since by Captain Beaufort. It was found by Lieutenant Spratt and Professor Forbes, thirty years later, as brilliant as ever, and somewhat increased; for besides the large flame in the corner of the ruins described by Beaufort, there were small jets issuing from crevices in the side of the crater-like cavity five or six feet deep. At the bottom was a shallow pool of sulphureous and turbid water, regarded by the Turks as a sovereign remedy for all skin complaints. The soot deposited from the flames was held to be efficacious for sore eyelids, and valued as a dye for the eyebrows. This phenomenon is described by Pliny as the flame of the Lycian Chimera.

ARTESIAN FIRE-SPRINGS IN CHINA.

According to the statement of the missionary Imbert, the Fire-Springs, “Ho-tsing” of the Chinese, which are sunk to obtain a carburetted-hydrogen gas for salt-boiling, far exceed our artesian springs in depth. These springs are very commonly more than 2000 feet deep; and a spring of continued flow was found to be 3197 feet deep. This natural gas has been used in the Chinese province Tse-tschuan for several thousand years; and “portable gas” (in bamboo-canes) has for ages been used in the city of Khiung-tscheu. More recently, in the village of Fredonia, in the United States, such gas has been used both for cooking and for illumination.

VOLCANIC ACTION THE GREAT AGENT OF GEOLOGICAL CHANGE.

Mr. James Nasmyth observes, that “the floods of molten lava which volcanoes eject are nothing less than remaining portions of what was once the condition of the entire globe when in the igneous state of its early physical history,--no one knows how many years ago!

“When we behold the glow and feel the heat of molten lava, how vastly does it add to the interest of the sight when we consider that the heat we feel and the light we see are the residue of the once universal condition of our entire globe, on whose _cooled surface_ we _now_ live and have our being! But so it is; for if there be one great fact which geological research has established beyond all doubt, it is that we reside on the cooled surface of what was once a molten globe, and that all the phenomena which geology has brought to light can be most satisfactorily traced to the successive changes incidental to its gradual cooling and contraction.

“That the influx of the sea into the yet hot and molten interior of the globe may occasionally occur, and enhance and vary the violence of the phenomenon of volcanic action, there can be little doubt; but the action of water in such cases is only _secondary_. But for the pre-existing high temperature of the interior of the earth, the influx of water would produce no such discharges of molten lava as generally characterise volcanic eruptions. Molten lava is therefore a true vestige of the Natural History of the Creation.”

THE SNOW-CAPPED VOLCANO.

It is but rarely that the elastic forces at work within the interior of our globe have succeeded in breaking through the spiral domes which, resplendent in the brightness of eternal snow, crown the summits of the Cordilleras; and even where these subterranean forces have opened a permanent communication with the atmosphere, through circular craters or long fissures, they rarely send forth currents of lava, but merely eject ignited scoriæ, steam, sulphuretted hydrogen gas, and jets of carbonic acid.--_Humboldt’s Cosmos_, vol. i.

TRAVELS OF VOLCANIC DUST.

On the 2d of September 1845, a quantity of Volcanic Dust fell in the Orkney Islands, which was supposed to have originated in an eruption of Hecla, in Iceland. It was subsequently ascertained that an eruption of that volcano took place on the morning of the above day (September 2), so as to leave no doubt of the accuracy of the conclusion. The dust had thus travelled about 600 miles!

GREAT ERUPTIONS OF VESUVIUS.