Читать книгу The Subterranean World - G. Hartwig - Страница 12

Table of Contents

Carbonic-acid Springs—Grotto del Cane—The Valley of Death in Java—Exaggerated Descriptions—Carburetted Hydrogen Springs—The Holy Fires of Baku—Description of the Temple—Mud Volcanoes—The Macaluba in Sicily—Crimean Mud Volcanoes—Volcanic Origin of Mud Volcanoes.

The numerous gas springs which in many countries are evolved from an unknown depth, afford us a convincing proof that the remarkable chemical transformations of which we find so many traces in the past history of our planet are still perpetually taking place in many of the mysterious crevices and hollows of the earth-rind. In Auvergne, the Vivarrais, the Eifel, and along the whole basaltic range from the Rhine to the Riesengebirge in Silesia, carbonic acid gas is exhaled in incredible quantities from the vast laboratories of the subterranean world.

Professor Bischoff found that a single gas spring near Burgbrohl daily produced 5,650 cubic feet of carbonic acid, a quantity amounting in the course of a year to no less than 262,000 pounds in weight; and, according to Bromeis, the great Artesian spring at Nauheim evolves every minute 71 cubic feet of carbonic acid, equal to a weight of 5,000,000 pounds annually. If from these two instances we judge of the produce of the many carbonic acid gas springs of Germany, and if we farther extend our view to the rest of the world, in many parts of which carbonic acid probably escapes in still greater quantities, we can form some idea of the geological importance of these springs, which also exercise no small influence upon the organic world. For the incalculable masses of carbonic acid which are thus constantly pouring from subterranean vents into the atmospheric ocean are again absorbed by millions of plants. They feed the forests and the fields; and thus these chemical changes, which are incessantly but imperceptibly modifying the earth-rind, ultimately tend to the advantage of man.

As a light dipped in carbonic acid gas is immediately extinguished, and every animal inhaling it is liable to instant suffocation, these properties are sometimes made use of for cruel experiments, for which, among others, the insignificant Grotto del Cane, in the kingdom of Naples—a cave or hole in the side of a mountain near the Lake Agnano—has become notorious. Some miserable dogs are thrust into the stratum of fixed air which covers the bottom of the hole, and are alternately almost choked and resuscitated to satisfy the idle curiosity of tourists. Their violent efforts to escape, when about to be plunged into the poisonous vapour, prove the horrible cruelty of the practice.

The carbonic-acid springs in the glen of the Brohl, a small rivulet flowing into the Rhine, near Andernach, are turned to a better purpose, for the manufacture of white lead.

The famous ‘Valley of Death,’ or Poison Valley, in the Island of Java, is nothing more than a funnel-shaped hollow, measuring about 100 feet in diameter at the top, and with a bare space in its centre fifteen feet broad and long, which is frequently covered with a stratum of carbonic acid gas. The sides of the hollow, and even the bottom, with the exception of the above-mentioned naked spot, are everywhere clothed with shrubbery, or even with forest trees.

The dead bodies of stags, tigers, wild boars, and birds are said to have been frequently found in the hollow; but Dr. Junghuhn, the author of a classical work on Java, saw in 1838 but one human corpse lying on its back in the centre of the bare spot. It was still there in 1840, and but slightly decomposed. In 1845 it had been removed, most likely by some compassionate wanderers desirous of giving it a decent burial, for not the slightest trace of the skeleton remained. During the years 1838, 1840, and 1845 Junghuhn visited the Valley of Death no less than thirteen times. When he last saw it, the bodies of six wild hogs were lying at the bottom, all more or less in a state of putrefaction. The crows that were feasting upon their remains proved that a descent might be effected without danger, for, on seeing them hopping about on the naked soil, even the Javanese entered the circle without hesitation. Not a single trace of carbonic acid was to be perceived, not even when the bold naturalist stretched himself out upon the ground and drew his breath in the crevices and rents with which it is furrowed. Probably the gas never rises more than three feet above the level of the soil, as at this height a luxuriant vegetation begins.

This simple description of an accurate observer forms a strange contrast to the gross exaggeration of other travellers, whose accounts, copied in many hand-books, have puffed up a phenomenon hardly superior to that of the Grotto del Cane into something like an eighth wonder of the world. Loudon, who in July 1830 visited the Pakamaran (as the natives call the pit), swells its dimensions to a vast crater about half a mile in circumference, thickly strewn with skeletons of men, tigers, game, and birds of all kinds; and another recent traveller goes so far as to give it an extent of twenty miles.

Next to carbonic acid, but of far less general occurrence, carburetted hydrogen, which gives rise to the wonderful phenomenon of fiery springs, is the gas most frequently evolved by volcanic spiracles.

Near Pietra Mala, between Bologna and Florence, on a spot about twelve feet in diameter, several flames rise from the earth, the largest of which ascends to a height of five feet, and is seen burning at night with a pale yellow flame, while its minor satellites around are blue tipped with white. No doubt many a terrible legend is attached to this infernal spectacle. Near Barigazzo, between Modena and Pistoja, near the ruins of Velleji, and in many other parts of the volcanic region of the Apennines, similar flames gush out of the ground. The neat little town of Fredonia, in the State of New York, on the eastern shore of Lake Erie, is lighted by natural springs of carburetted hydrogen, which, being led into a gasometer, feed the seventy or eighty lamps of the town. The thrifty and practical Chinese, who have preceded us in so many useful discoveries, have for centuries made a like use of the many gaseous emanations in the provinces of Yunnan, Szutschuan, Kuangsi, and Schansi, by leading the inflammable air in pipes, wherever they want it for lighting or cooking.

But there is no place in the world more remarkable for its burning springs than Baku, on the western coast of the Caspian Sea, where the holy and eternal fires are worshipped by the pious Parsees as the special symbol of the Almighty.

Like most of the cloisters and convents of the Orient, which are exposed to the incursions of plundering hordes, Aleschga, the temple dedicated to the worship of fire, is a fortified square inclosing a large courtyard, and capable of being defended from the terraced roof. The outer wall forms at the same time the back of the cells, which front the yard. Over the entrance gate, which is situated to the north, rises a high bastion or tower, serving as an additional defence, from the summit, of which the visitor enjoys after sunset the fantastic view of the flames which, untarnished by smoke, rise on all sides from rents and crevices in the neighbouring steppe, and wave their bright summits to and fro like tongues of fire. In the centre of the court stands a square tower supported by four columns, and inclosing a basin-like excavation, three or four feet in diameter, into which the gas is conducted by a pipe from sources beyond the walls of the temple. Four chimneys at the four corners of the tower are fed in a similar manner. From the centre of the tower rises a trident, called Thirsul. The Parsees relate that the Devil once got possession of the earth, and reigned with despotic fury. But man in his distress prayed to the Almighty, and an angel came down and planted this identical trident in the earth as a token that the dominion of his Satanic Majesty had ceased. Round the court are twenty-two cells, like those of a Catholic convent. They are very small, and, with the exception of a ragged rug, wholly without furniture; but each of them is provided with a gas pipe, which can be opened or closed at pleasure, and furnishes light and warmth to the inmate. Near the temple a well has been dug fifty feet deep, in which the gas accumulates in larger quantities. Koch (‘Wanderungen im Oriente,’ 1843–4) tells us that he here enjoyed a sight more wonderful and surprising than any he had ever witnessed before. A carpet was spread over the mouth of the well to prevent the gas from escaping. After a few minutes, a priest seized a bundle of brushwood, in which a piece of burning paper had been stuck, and flung it into the well, after quickly removing the carpet. The strangers had previously been warned to keep at some distance, and the priest and his assistants likewise ran off as fast as they could. About half a minute after the fire-brand had been cast into the pit, a terrific explosion took place, and a vast column of fire, in the shape of an inverted cone (from the gas spreading out as soon as it emerges from the pit), ascended to the skies.

How long the fires of Baku may have been burning is unknown, but it is very probable that they did not exist before the Christian era. No Greek or Roman author mentions them, and it is not before the tenth century that Arab writers take notice of Baku and its wonders. When the Sassanides restored the religion of Zoroaster, the attention of these fire-worshipping princes was naturally directed to a place where fire gushes pure and unbidden from the earth. They raised a temple on the spot, and thousands of pilgrims wandered to the holy fires of Baku. But when the fanatical Arabs overthrew the Persian Empire, times of persecution and distress began for the Parsees; and still later they were almost entirely extirpated by the hordes of Tamerlane. During the last centuries fire-worshipping was again introduced by the Indians, who, after the Sefides had ascended the Persian throne, gradually settled in the Caspian provinces, and whose number must have been considerable, as travellers inform us that in the latter half of the seventeenth century 200 rich Indian merchants were residing in the town of Schemachi. But the anarchical times which followed the usurpation of Nadir Schah forced most of these Indians to leave their adopted country, and since then only solitary pilgrims have found their way to Baku. But the number even of these is constantly diminishing, although the Russians, to whom the sanctuary now belongs, allow them full freedom of access. When Koch was at Baku, he found there only five Indians from Mooltan, whither the majority would gladly have returned, had they but possessed the necessary means. Their squalid appearance and tattered raiment formed the strongest imaginable contrast to the splendour of the element they worshipped. Among them was a Fakir, who had made a vow constantly to remain in the same position absorbed in religious contemplation, and who for sixteen years had never moved from the spot.

The burning springs gush out not only from the ground near the temple and in other parts of the peninsula of Abscheron, but even from the bottom of the neighbouring Caspian Sea; and as Sir Charles Lyell saw carburetted hydrogen rise in countless bubbles through the crystal waters above the falls of the Niagara, and shoot up in bright flames at the approach of a light, so Dr. Abich mentions a spot in the Gulf of Baku where the inflammable gas issues with such force, and in so great a quantity, from the bottom, which is there three fathoms deep, that a small boat is in danger of being overturned when coming too near it.

As gas springs most frequently occur in districts which have been the former seats of volcanic action, and as similar exhalations often arise from still active craters, they are supposed by many geologists to be the last remaining traces of an expiring volcanic energy. Bischoff considers the carbonic acid of the German gas springs to be developed by the decomposition of carbonate of lime by volcanic heat or heated water.

A phenomenon which is sometimes found connected with gas springs is that of the mud volcanoes, which may be described as cones of a ductile, unctuous clay, formed by the continued evolution of a sulphurous and inflammable gas, spurting up waves and lumps of liquid mud. These remarkable cauldrons are found in many parts of the world, in the Island of Milo, in Italy, in Iceland, in India, about 120 miles from the mouths of the Indus, on the coast of Arracan, in Birmah, in Java, Columbia, Nicaragua, and Trinidad, but probably nowhere on a grander scale than at either extremity of the chain of the Caucasus, towards the Caspian on the east and the Sea of Azof on the west, where in the peninsula of Taman, and on the opposite coast of the Crimea, near Kertsch, vast numbers of mud volcanoes are scattered, some of them 250 feet high. Their operations have apparently been going on for countless ages, and have covered a great extent of land with their products.

MUD VOLCANOES OF TRINIDAD.

The Macaluba, in Sicily, which owes its name to the Arabs, is the mud volcano most anciently known. It is mentioned by Plato in his ‘Phædon,’ and has been described by Strabo. It is situated five miles to the north of Girgenti, on a hill of a conical shape, truncated at the top, and 150 feet high. The summit is a plain half a mile round, and the whole surface is covered with thick mud. The depth of the mud, which is supposed to be immense, is unknown. There is not the slightest appearance of vegetation upon it. In the rainy season the mud is much softened; the surface is even, and there is a general ebullition over it, which is accompanied with a very sensible rumbling noise. In the dry season the mud acquires greater consistency, but its motion still goes on. The plain assumes a form somewhat convex; a number of little cones are thrown up, which rarely rise to the height of two feet. Each of them has a crater, where black mud is seen in constant agitation, and incessantly emitting bubbles of air. With these the mud insensibly rises, and as soon as the crater is full of it, it disgorges. The residue sinks, and the cone has a free crater, until a new emission takes place.

Such is the ordinary state of the Macaluba; but from time to time the hill becomes subject to alarming convulsions. Slight earthquake shocks are felt at the distance of two or three miles, accompanied with internal noises resembling thunder. These increase for several days, and are followed at last by a prodigious spout of mud, earth, and stones, which rises two or three hundred feet in the air.

Similar paroxysmal explosions have been observed in the Caucasian mud volcanoes. In February 1794, the Obu, in the peninsula of Taman, had an eruption accompanied with a dreadful noise, and an earthquake which radiated from the cone, and was felt as far as Ekaterinodor, at a distance of fifty-five leagues. At the beginning of the eruption flames were seen, which rose to a prodigious height, and lasted about half an hour. At the same time dense clouds of smoke escaped from the crater, and mud and stones were cast up to the height of 3,000 feet. Six streams of mud, the largest of which was half a mile long, flowed from the volcano, and their volume is said to have been equal to twenty-two millions of cubic feet.

Violent eruptive symptoms accompanied the formation of a new mud volcano in the vicinity of Baku on the Caspian. On November 27, 1827, flames blazed up to an extraordinary height for three hours, and continued for twenty hours more to rise about three feet above a crater from which mud was ejected. At another point in the same district, where flames issued, fragments of rock, of large size, were hurled up into the air and scattered around.

The phenomena exhibited by the Macaluba and other mud cauldrons are certainly very distinct from those of true volcanoes, since no scoriæ or lava or heated matters of any kind are sent forth, the mud being described as cold when emitted, although the gas, whose violent escape throws it up, is sometimes ignited. Hence geologists commonly regard these phenomena as entirely distinct from the volcanic, and ascribe their origin to chemical action going on at no great depth beneath the surface, among the constituents of certain stratified matters; while other scientific authorities declare them to be as much connected with internal igneous agency as any other eruptive phenomena. Their occurrence in districts not remote from the sites of vast volcanic disturbance, and their occasional violent paroxysms, certainly afford much support to this view, and show that it is probably the same power, in different degrees of energy, which casts up the mud of the Macaluba and pours forth the lava-streams of Cotopaxi.