« AnteriorContinuar »
the earth, and light a quickly blazing fire over it, when the desired coolness is produced. On the contrary, the more the warmth and dryness of the external air are diminished, as in winter, the less will be its capability to promote evaporation in the cavern, the warmth contained in the air will no longer be absorbed, and the ice which has been produced must melt. The cooling in these caverns, however, so as to sink below the freezing point, can only occur where there is a certain relation, which but rarely subsists, between the openings and the evaporating surface of the interior. If the opening is too large, too much warm air is introduced, and the temperature of the interior is thereby much more increased than it can be diminished by evaporation. If it is too small, the vapours cannot withdraw themselves fast enough, and the evaporation is lessened, because the surrounding air is saturated with moisture. The ice-caverns, therefore, are comparatively rare; but, in addition to those named, there is a cave at Vesoul, in France, where a stream flowing through it is frozen over in summer, and clear of ice in winter. Sir Roderick Murchison, in the course of his geological surveys in Russia, met with a freezing cavern near the imperial salt-works at Iletski, to the south of the Ural mountains, situated at the southern base of a hillock of gypsum, one of a series of natural hollows used by the peasantry for cellars or stores. The cave in question is however the only one in the district which possesses the singular property of being partially filled with ice in summer, and of being destitute of it in winter. Standing on the heated ground and under a broiling sun, I shall never forget," he remarks, “my astonishment when the woman to whom the cavern belonged unlocked a frail door, and a volume of air so piercingly keen struck the legs and feet, that we were glad to rush into a cold bath in front of us to equalise the effect." Three or four feet within the door, and on a level with the village street, beer and quash were half frozen. A little further the narrow chasm opened into a vault fifteen feet high, ten paces long, and from seven to eight feet wide, which seemed to send off irregular fissures into the body of the hillock. The whole of the roof and sides were hung with solid undripping icicles, and the floor was covered with hard snow, ice, or frozen earth. During the winter all these phenomena disappear; and when the external air is very cold, and all the country is frozen up, the temperature of the cave is such, that the Russians state they could sleep in it without their sheep-skins.
There is another circumstance of high interest disclosed by the interior of many caverns, the occurrence of extinct animals of the ancient earth; on which account these receptacles have obtained the name of zoolithes or bone caverns. These sites are observed in almost every country of Europe and America, but the fact was not much known till the late Dr. Buckland published the result of his investigations. He made it the subject of his peculiar study, and with great felicity, illustrated the light which it throws upon the ancient condition of the earth, and the changes which the surface has undergone. His researches into the condition of a cave discovered in 1821 at Kirkdale in Yorkshire are highly valuable, and deserve a notice here. Its mouth had long been choked up with rubbish, and overgrown with grass and bushes, but was accidentally found by some workmen. The cave is situated on the older portion of the oolite formation (in the coral rag and Oxford clay) on the declivity of a valley. It extends as an irregular narrow passage 250 feet into the hill. There are a few expansions, but scarcely high enough to allow a man to stand upright. The sides and floor were found covered with a deposit of stalagmite, beneath which there was a bed of from two to three feet of fine sandy and micaceous loam, the lower portion of which in particular contained an innumerable quantity of bones, with which the floor was completely strewn. The greatest part of them were very well preserved, and still retained a great portion of their natural gluten, in consequence of the peculiar nature of their investiture. The animals
to which they belonged were the hyæna, bear, tiger, and lion, elephant, rhinoceros, hippopotamus, horse, ox, deer of three species, water-rat, and mouse, belonging wholly to extinct species, and the
same with those with which we are acquainted in the steppes of Asia. The most plentiful of all were the remains of the hyæna, and from the amount which he saw, Buckland estimated the number of the individuals interred here to be between two and three hundred. The animal must have been one half larger than the living species, in its structure resembling the hyæna of the Cape. The bears, which were less abundant, belonged to the
large cavern species, which, according to Cuvier, was of the size of a large white horse and about eighteen feet in length. The elephants were the Siberian mammoth. Of the stags the largest was of the size of the moose deer. Of the ox two species were distinguished, and its bones were most frequent next to those of the hyæna. bones lay irregularly strewed one with another, but those of the largest animals were in the most remote and narrowest corners, into which they never could have penetrated while living. The teeth, and the hard marrowless bones of the extremities, as well as those of the fore and hind feet, were uninjured: these were so numerous that they must have belonged to a much greater number of individuals than could be estimated as belonging to the other bones. Many of the bones bore marks which exactly corresponded with the form of the incisor teeth of the hyæna, and the broken horns of the stag were evidently marked by gnawing. These facts warranted the conclusion, that the hyenas must have lived for a long time in this cave, and have dragged the bones of the larger animals, particularly the oxen, into this den, as their prey. The supposition was confirmed in the most striking manner by a variety of other facts. Dr. Buckland found that bones which he caused to be gnawed by living hyænas had exactly the same appearance as those found in the cavern, and the teeth and harder bones were thrown aside by them. He even found in great abundance excrements of the hyæna, which offered the closest resemblance to those of the living animal. From the facts described, it appears that the Kirkdale cave was for a long series of years a den inhabited by hyænas, who dragged into its recesses the other animal bodies whose remains are there commingled with their own,- some great catastrophe causing an inundation in this region which destroyed the whole race.
Similar zoolithic caverns occur in the following places in our own country: - 1. Kent's Cavern, in the limestone of North Devon, about a mile from Torquay. It is said to be nearly six hundred feet long, varying in width from two to seventy feet, and in height from one to six yards. The bones of extinct species of animals are found buried in a mass of mud, covered over with a crust of stalagmitic formation. From certain appear
ances in this cavern, it seems to have been in former times the habitation of man, perhaps the bandit's home. 2. Cave near the village of Hutton in the Mendip Hills. This
is a series of cavernous chambers found by the labourers in working for ochre, which occurs in fissures of the mountain limestone. In the first chamber, about twenty feet square and four high, a large stalactite depends from the roof in the centre, and beneath a stalagmite rises from the floor, nearly touching it. The bones from this cavern are those of the elephant, horse, ox, deer, bear, and hog. 3. Cave at Balleye, near Wirksworth. Bones and molar teeth of the elephant were discovered here in a cavity of mountain limestone by the lead miners, mentioned in the following record of a workman: "In sinking for lead at Baulee, within two miles of Wirksworth, A. D. 1663, they came to an open place as large as a church, and found a skeleton reclining against the side, so large that his brain-pan would have held two strike of corn, and so big that they could not get it up without breaking it. My grandfather having a share in the said mine, they sent him a tooth, weighing four pounds three ounces. - George Mower." Some of these remains are still preserved. 4. Dream Cave, near Wirksworth. This was likewise discovered by the miners in pursuing a vein of lead. After sinking about sixty feet through solid mountain limestone, they came to a large cavern filled with argillaceous earth and stony fragments. Here were found the remains of a rhinoceros, in a high state of preservation. They belonged apparently to the same individual, and formed probably an entire skeleton, though several parts were wanting, having been separated from the rest through the subsidence of the mass in which they were imbedded into an underlying hollow, owing to the workmen disturbing the site. Bones of deer and fragments of horns were found in the same spot, all of which are now deposited in the Oxford Museum. 5. Cave on Derdham Down, near Clifton; a fissure which contained fragments of stone and stalagmite, with bones incrusted with stalactitic matter, among which was a fossil joint of the horse. 6. Caves at Oreston, near Plymouth. Several caverns were discovered in removing materials for the construction of the Breakwater from a hill of transition limestone. They contained bones belonging to a species of rhinoceros, the tiger, hyæna, horse, ox, wolf, and deer. 7. Cave of Crawley Rocks, near Swansea. This cavity was accidentally intersected in working a quarry. It has now been entirely cut away. Various parts of the elephant, rhinoceros, hyæna, ox, and stag were found in it. 8. Caves of Paviland. Two cavities occur in a lofty cliff of limestone facing the sea on the coast of Glamorganshire, which the waves reach in considerable storms. The remains of an immense number of animals of extinct species have been found in them.
It is clear from these facts, that anciently, as Dr. Buckland remarks, "extinct species of hyæna, tiger, bear, elephant, rhinoceros, and hippopotamus, no less than the wolves,
foxes, horses, oxen, deer, and other animals which are not distinguishable from existing species, had established themselves from one extremity of England to the other-from the caves of Yorkshire to those of Plymouth and Glamorganshire - whilst the diluvial gravel beds of Warwickshire, Oxford, and London, show that they were not wanting also in the more central parts of the country; and M. Cuvier has established, on evidence of a similar nature, the probability of their having been spread in equal abundance over the continent of Europe. But it by no means follows, from the certainty of the bones having been dragged by beasts of prey into the small cavern at Kirkdale, that those of similar animals must have been introduced in all other cases in the same manner; for, as all these animals were the antediluvian inhabitants of the countries in which the caves occur, it is possible that some may have retired into them to die; others have fallen into the fissures by accident, and there perished; and others have been washed in by the diluvial waters. By some one or more of these latter hypotheses, we may explain those cases in which the bones are few in number and not gnawed, the caverns large, and the fissures extending upwards to the surface; but where they bear marks of having been lacerated by beasts of prey, and where the cavern is small, and the number of bones and teeth so great and so disproportionate to each other as in the cave at Kirkdale, the only adequate explanation is, that they were collected by the agency of wild beasts." In Germany the zoolithic caverns are much more numerous and important than in England. There is a remarkable example on the north-east border of the Hartz Mountains, called Bauman's Höhle, after an unfortunate miner who, in the year 1670, ventured into it alone in search of ore; and, after having wandered three days and nights in its solitude and darkness, at length found his way out, but in such a state of exhaustion that he died almost immediately. It is a suite of natural chambers in a bed of transition limestone, the floor of which is composed of a thick crust of stalagmite, beneath which lies an accumulation of several feet of mud mixed with bones and pebbles. But the caves of Franconia are by far the richest and most beautiful of this class. They lie on the north-east extremity of the chain of the Jura between Nuremburg and Baireuth, in the valley of the Wiesent, a tributary stream of the valley of the Maine. The most important is the Cave of Gailenreuth, situated in a perpendicular rock, its mouth being upwards of three hundred feet
above the bed of the river, consisting of an aperture seven feet high and twelve broad. An open fissure in the rock extends from the cave to the table-land above, as shown in the illustration. The floor consists of stalagmite lying over a bed of slime which contains the animal remains. The cave has two chief chambers, the roof of which is abundantly hung with stalactites. From the first to the second chamber the visitor descends by a ladder, as represented in the section, which exhibits the breccia of bones, pebbles, and loam, and the artificial extension of the cavern by the removal of it.
Almost all the bones belong to the bear of the caverns, and are admirably preserved. Those of a species of cat, resembling the American jaguar, have also been discovered, and those of the hyæna; but the latter are of rare occurrence. In conformity with the habits of the bear, the remains of prey, dragged in, are almost entirely wanting. There are two neighbouring caverns of the same class; those of Zahnloch (teeth-hole) and Kühloch.
The latter is supposed to contain animal matter equal to at least 2500 individuals of the cavern bear; and allowing an annual mortality of 2, it follows that here we have the history of a thousand years; for probably these animals retired to the solitude of this spot upon the approach of death, as is the well-known
custom of many creatures. The bone caverns in our own
records of human
history - the rhinoceros, elephant, and hyena, now, and for ages past, exclusively confined to more southern latitudes.
There is another class of caverns remarkable for the development of irrespirable gas, which often renders the access to them dangerous. They are of two kinds; those in which the gas is produced by the surrounding rocks, and those in which it proceeds from the interior of the earth. The first class are principally caves of gypsum. The gypsum is not, however, the cause of the phenomenon, the component parts of which are not susceptible of any decomposition from the air. There is commonly fœtid limestone intimately mixed up with it, which forms connected wavy stripes, and even single beds of considerable thickness. This earthy limestone, which is penetrated with bitumen, and often very clayey in its composition, has the property of giving out all its carburetted hydrogen in the air; and in every case where caves exist in it, its presence, on account of its connection with gas, is offensive and much dreaded. In the limestone caves of the sandstone formations, on the contrary, there commonly prevails a very pure air, possibly because they are filled with mouldering animal remains. The development of irrespirable gases from the interior of the earth, which, penetrating through fissures, collect in caves, is a constant result of volcanic activity. The chemical processes continually going on in volcanic regions must produce the liberation of great quantities of gas, which are connected with the world above by these chimneys of the perpetual forge. Caverns of this nature occur therefore only in the neighbourhood of volcanoes, or at points where volcanic processes may be supposed to be going on beneath. The gases so developed are almost entirely the carbonic and sulphuric acids. Among the most important of the grottos which give out carbonic acid, there is the Grotto del Cane at Naples, in the neighbourhood of the Lago d'Agnano, near Pozzuoli. It was known to the ancients, and is mentioned by Pliny, who refers to it as one of a class of excavations called, in his time, "Charon's ditches." Its size is very unimportant; ten feet deep, four feet broad, and nine feet high. The carbonic acid collects itself on the soil in a bed of about six inches deep; and, on account of its specific gravity, does not mingle with the atmospheric air. Its actual height may be clearly ascertained by lighting some candles, which, when they reach its surface, are extinguished at once. Small animals falling