or three species, of corals, and of brachiopodous | serves for this purpose, when armies march that mollusca. XII. The Cumbrian System.-A like extensive series of deposites, obviously of sedimentary origin, but in which no organic remains have been discovered. THE PRIMARY STRATA. XIII. The Mica-schist.-Composed of mica and quartz, interlaminated so as to present the appearance of stratification, but containing no organic remains. XIV. The Gneiss.- Formed of the component parts of granite; mica, quartz, and feldspar, finegrained and laminated, so as to present the appearance of having been produced by the abrasion of granite, and then deposited in water. Both the gneiss and mica-schist are conceived to have been altered by heat, subsequently to their deposition. way; becoming then an impregnable retreat to the people that live thereabout. Nothing can be more beautiful than this cavern, when lighted up with torches: for there are thousands of square pillars, in large level walks, about twenty feet high; and all wrought with much neatness and regularity. In this vast grotto there is very little rubbish; which shows both the goodness of the stone and the carefulness of the workmen. To add to its beauty, there also are in various parts of it, little pools of water, for the conveni ence of the men and cattle. It is remarkable also, that no droppings are seen to fall from the roof, nor are the walks any way wet under foot, except in cases of great rains, where the water THE PLUTONIC, OR UNSTRATIFIED PRIMARY ROCKS. XV. The Granite and Trappean Rocks. -Com-gets in by the air-shafts. The salt-mines in Poprising granite, syenite, greenstone, hornblende, diallage, serpentine, &c.; together with basalt, porphyry, clinkstone, claystone, and the trap rocks, the whole being alike destitute of stratification and of organic remains. The relative thickness of each of these several deposites has been estimated as under, but the statement must be regarded as a mere approximation, and the probability is that, with reference to the lower beds, the thickness is much greater than is here mentioned. Tertiary system Weald Oolite and Lias Saliferous Carboniferous Old Red Sandstone Silurian Cambrian Cumbrian, at least 2,000 feet. 1,000 1,100 2,500 2,000 10,000 10,000 7,500 20,000 10,000 land are still more spacious than these. Some of the catacombs, both in Egypt and Italy, are said to be very extensive. But no part of the world has a greater number of artificial caverns than Spain, which were made to serve as retreats to the Christians against the fury of the Moors, when the latter conquered that country. However, an account of the works of art does not properly belong to a natural history. It will be enough to observe, that though caverns be found in every country, far the greatest part of them have been fashioned by the hand of nature only. Their size is found beyond the power of man to have effected, and their forms but ill-adapted to the conveniences of a human habitation. In some places, indeed, we find mankind still make use of them as houses; particularly in those countries Primary unascertained, but far exceeding that where the climate is very severe;1 but in genof any of the superposed deposites. CHAP. VII. OF CAVES AND SUBTERRANEOUS PASSAGES THAT SINK, eral they are deserted by every race of meaner animals, except the bat: these nocturnal solitary creatures are usually the only inhabitants; and these only in such whose descent is sloping, or, at least, not directly perpendicular. There is scarcely a country in the world without its natural caverns; and many new ones are discovered every day. Of those in England, Oakey-hole, the Devil's-hole, and Penpark-hole, have been often described. The former, which lies on the south side of Mendip-hills, within a mile of the town of Wells, is much resorted to by travellers. To conceive a just idea of this, we must imagine a precipice of more than a hundred yards high, on the side of a mountain which shelves away a mile above it. In this is an opening not very large, into which you enter, going along upon a rocky uneven pavement, sometimes ascending, and sometimes descending. The roof of it, as you advance, grows higher; and in some places is fifty feet from the floor. In some places, however, it is so low that a man must stoop to pass. It extends itself, in length, about two hun In surveying the subterranean wonders of the globe, besides those fissures that descend perpendicularly, we frequently find others that descend but a little way, and then spread themselves often to a great extent below the surface. Many of these caverns, it must be confessed, may be the production of art and human industry; retreats made to protect the oppressed, or shelter the spoiler. The famous labyrinth of Candia, for instance, is supposed to be entirely the work of art. Mr. Tournefort assures us, that it bears the impression of human industry, and that great pains have been bestowed upon its formation. The stone-quarry of Maestricht is evidently made by labour carts enter at its mouth, and load with-dred yards and from every part of the roof and in, then return, and discharge their freight into boats that lie on the brink of the river Maese. This quarry is so large, that forty thousand people may take shelter in it and it in general : the floor, there are formed sparry concretions of various figures, that by strong imaginations have 1 Phil. Trans. vol. ii, p. 368. 2 Ibid. been likened to men, lions, and organs. At the | woodlands, we at length came to a little hill, on farthest part of this cavern rises a stream of wa- the side of which yawned a most horrid cavern, ter, well-stored with fish, large enough to turn that with its gloom at first struck us with terror, a mill, and which discharges itself near the en- and almost repressed curiosity. Recovering the trance. first surprise, however, we entered boldly; and had not proceeded above twenty paces, when the supposed statue of the giant presented itself to our view. We quickly perceived, that what the ignorant natives had been terrified at as a giant was nothing more than a sparry concretion, form Penpark-hole, in Gloucestershire, is almost as remarkable as the former. Captain Sturmy descended into this by a rope, twenty-five fathoms perpendicular, and at the bottom found a very large vault in the shape of a horseshoe. The floors consisted of a kind of white stone enamel-ed by the water dropping from the roof of the led with lead ore, and the pendant rocks were glazed with spar. Walking forward on this stony pavement, for some time, he came to a great river, twenty fathoms broad, and eight fathoms deep; and having been informed that it ebbed and flowed with the sea, he remained in this gloomy abode for five hours to make an exact observation. He did not find, however, any alteration whatsoever in its appearance. But his curiosity was ill-requited; for it cost this unfortunate gentleman his life; immediately after his return he was seized with an unusual and violent headach, which threw him into a fever, of which he died soon after.3 But of all the subterranean caverns now known, the grotto of Antiparos is the most remarkable, as well for its extent as for the beauty of its sparry incrustations. This celebrated cavern was first discovered by one Magni, an Italian traveller, about a hundred years ago, at Antiparos, an inconsiderable island of the Archipelago. The account he gives of it is long and inflated, but on the whole amusing. "Having been informed," says he, "by the natives of Paros, that in the little island of Antiparos, which lies about two miles from the former, of a gigantic statue that was to be seen at the mouth of a cavern in that place, it was resolved that we (the French consul and himself) should pay it a visit. In pursuance of this resolution, after we had landed on the island, and walked about four miles through the midst of beautiful plains and sloping 3 The caverns which are so frequently found in mountains, particularly in limestone formations, have been formed by the action of water,-by earthquakes, by the sudden sinking of portions of the soil, or by subterranean fires. They either consist of a range of galleries, or of one or more grottoes, lying behind or above each other. The depth of some caverns exceeds 1,000 feet; and some-such as the Nicojack cave in the territory of the Cherokees-extend severa! miles in length. Among the most remarkable caverns not enumerated in the present chapter are those of Alcantara near Lisbon; those of Castleton and Pool in England, and of Fingal or Staffa in Scotland; that of Sturth in Ireland; of Ombos in Egypt; Del Cane and Puzzuolo near Naples; the caverns of Mount Pilate in Switzerland; that of the Sorcerers in the Cevennes; of Saussenberg near Basle; the cavern of the Dragons in Darmstadt; and the great Mammoth cave of Kentucky.-ED. cave, and by degrees hardening into a figure that their fears had formed into a monster. Incited by this extraordinary appearance, we were induced to proceed still farther, in quest of new adventures in this subterranean abode. As we proceeded, new wonders offered themselves: the spars, formed into trees and shrubs, presented a kind of petrified grove; some white, some green; and all receding in due perspective. They struck us with the more amazement, as we knew them to be mere productions of nature, who, hitherto in solitude, had, in her playful moments, dressed the scene, as if for her own amusement. "But we had as yet seen but a few of the wonders of the place; and were introduced only into the portico of this amazing temple. In one corner of this half-illumined recess there appeared an opening of about three feet wide, which seemed to lead to a place totally dark, and that, one of the natives assured us, contained nothing more than a reservoir of water. Upon this we tried, by throwing down some stones, which rumbling along the sides of the descent for some time, the sound seemed at last quashed in a bed of water. In order, however, to be more certain, we sent in a Levantine mariner, who, by the promise of a good reward, with a flambeaux in his hand, ventured into this narrow aperture. After continuing within it for about a quarter of an hour, he returned, carrying some beautiful pieces of white spar in his hand, which art could neither imitate nor equal. Upon being informed by him that the place was full of these beautiful incrustations, I ventured in once more with him for about fifty paces, anxiously and cautiously descending by a steep and dangerous way. Finding, however, that we came to a precipice which led into a spacious amphitheatre, if I may so call it, still deeper than any other part, we returned, and being provided with a ladder, flambeaux, and other things to expedite our descent, our whole company, man by man, ventured into the same opening, and, descending one after another, we at last saw ourselves altogether in the most magnificent part of the cavern. "Our candles being now all lighted up, and the whole place completely illuminated, never could the eye be presented with a more glitter4 Kircher Mund. sub. 112. I have translated a ing, or a more magnificent scene. The roof all part of Kircher's description, rather than Tourne-hung with solid icicles, transparent as glass, yet fort's, as the latter was written to support an hypo thesis. solid as marble. The eye could scarcely reach the lofty and noble ceiling; the sides were regu ous passages under the earth, and by long degrees hollowing the beds in which they flowed, the ground above them has slipt down closer to their surface, leaving the upper layers of the earth or stone still suspended: the ground that sinks upon the face of the waters forming the floor of the cavern; the ground or rock, that keeps suspended, forming the roof: and indeed there are but few of these caverns found without water, either within them, or near enough to point out their formation. larly formed with spars; and the whole presented | been owing to waters. These finding subterranethe idea of a magnificent theatre, illuminated with an immense profusion of lights. The floor consisted of solid marble; and in several places magnificent columns, thrones, altars, and other objects appeared, as if nature had designed to mock the curiosities of art. Our voices, upon speaking or singing, were redoubled to an astonishing loudness, and upon the firing of a gun, the noise and reverberations were almost deafening. In the midst of this grand amphitheatre rose a concretion of about fifteen feet high, that in some measure resembled an altar; from which, taking the hint, we caused mass to be celebrated there. The beautiful columns that shot up round the altar, appeared like candlesticks; and many other natural objects represented the customary ornaments of this sacrament. "Below even this spacious grotto there seemed another cavern; down which I ventured with my former mariner, and descended about fifty paces by means of a rope. I at last arrived at a small spot of level ground, where the bottom appeared different from that of the amphitheatre, being composed of a soft clay yielding to the pressure, and in which I thrust a stick to about six feet deep. In this, however, as above, numIbers of the most beautiful crystals were formed, one of which particularly resembled a table. Upon our egress from this amazing cavern, we perceived a Greek inscription upon a rock at the mouth, but so obliterated by time that we could not read it. It seemed to import that one Antipater, in the time of Alexander, had come thither, but whether he had penetrated into the depths of the cavern, he does not think fit to inform us." Such is the account of this beautiful scene as communicated in a letter to Kircher. We have another, and a more copious description of it by Tournefort, which is in every body's hands; but I have given the above, both because it was communicated by the first discoverer, and because it is a simple narrative of facts, without any reasoning upon them. According to Tournefort's account, indeed, we might conclude from the rapid growth of the spars in this grotto that it must every year be growing narrower, and that it must in time be choked up with them entirely; but no such thing has happened hitherto, and the grotto at this day continues as spacious as we ever knew it. This is not a place for an inquiry into the seeming vegetation of those stony substances, with which this and almost every cavern are incrusted; it is enough to observe, in general, that they are formed by an accumulation of that little gritty matter which is carried thither by the waters, and which in time acquires the hardness of marble. What in this place more imports us to know, is, how these amazing hollows in the earth came to be formed. And I think, in the three instances above-mentioned, it is pretty evident, that their excavation has CHAP. VIII. OF MINES, DAMPS, AND MINERAL VAPOURS. THE caverns which we have been describing, generally carry us but a very little way below the surface of the earth. Two hundred feet, at the utmost, is as much as the lowest of them is found to sink. The perpendicular fissures run much deeper; but few persons have been bold enough to venture down to their deepest recesses; and some few who have tried, have been able to bring back no tidings of the place, for unfortunately they left their lives below. The excavations of art have conducted us much farther into the bowels of the globe. Some mines in Hungary are known to be a thousand yards perpendicular downwards; and I have been informed, by good authority, of a coal-mine in the north of England, a hundred yards deeper still. It is beside our present purpose to inquire into the peculiar construction and contrivance of these, which more properly belongs to the history of fossils. It will be sufficient to observe in this place, that as we descend into the mines, the various layers of earth are seen as we have already described them; and in some of these are always found the metals or minerals for which the mine has been dug. Thus frequently gold is found dispersed and mixed with clay and gravel; sometimes it is mingled with other metallic bodies, stones, or bitumens;3 and sometimes united with that most obstinate of all substances, platina, from which scarce any art can separate it. Silver is sometimes found quite 1 The following is a list of some of the deepest mines at present wrought. Kit's pühl copper-mine in the Tyrol moun tains 2 Ulloa, vol. ii. p. 470. 2764 feet. 2230 2170 1650 1600 1520 1414 1380 ED. 3 Ulloa, ibid 4 pure, sometimes mixed with other substances | in the bowels of the earth by nature. Sulphurs and minerals. Copper is found in beds mixed and irons are intimately blended together, and with various substances, marbles, sulphurs, and want only the mixture of water or air to excite pyrites. Tin, the ore of which is heavier than their heat; and this, when once raised, is comthat of any other metal, is generally found mixed municated to all bodies that lie within the sphere with every kind of matter: lead is also equally of their operation. Those beautiful minerals common; and iron, we well know, can be ex- called marcasites and pyrites, are often of this tracted from all the substances upon earth. composition; and wherever they are found, either by imbibing the moisture of the air, or having been by any means combined with water, they render the mine considerably hot.8 The variety of substances which are thus found in the bowels of the earth, in their native state, have a very different appearance from what they are afterwards taught to assume by human industry. The richest metals are very often less glittering and splendid than the most useless marcasites; and the basest ores are generally the most beautiful to the eye. This variety of substances, which compose the internal parts of our globe, is productive of equal varieties, both above and below its surface. The combination of the different minerals with each other, the heats which arise from their mixture, the vapours they diffuse, the fires which they generate, or the colds which they sometimes produce, are all either noxious or salutary to man; so that in this great elaboratory of nature, a thousand benefits and calamities are forging, of which we are wholly unconscious; and it is happy for us that we are so. The want of fresh air also, at these depths, is, as we have said, another reason for their being found much hotter. Indeed, without the assistance of art, the bottom of most mines would, from this cause, be insupportable. To remedy this inconvenience, the miners are often obliged to sink, at some convenient distance from the mouth of the pit where they are at work, another pit, which joins the former below, and which, in Derbyshire, is called an air-shaft. Through this the air circulates; and thus the workmen are enabled to breathe freely at the bottom of the place; which becomes, as Mr. Boyle affirms, very commodious for respiration, and also very temperate as to heat and cold. Mr. Locke, however, who has left us an account of the Mendip mines, seems to present a different picture. "The descent into these is exceedingly difficult and dangerous; for they are not sunk like wells, perpendicularly, but as the crannies of the rocks happen to run. The constant method is to swing down by a rope placed under the arms, and clamber along by applying both feet and hands to the sides of the narrow passage. The air is conveyed into them *This difference in the air was supposed by through a little passage that runs along the sides Boyle to proceed from magazines of fire that lay from the top, where they set up some turfs, on nearer the centre, and that diffused their heat the lee-side of the hole, to catch and force it to the adjacent regions. But we now know that down. These turfs being removed to the windy it may be ascribed to more obvious causes. In side, or laid over the mouth of the hole, the some mines, the composition of the earth all miners below want breath, and faint; and if around is of such a nature, that upon the admis- sweet-smelling flowers chance to be placed there, sion of water or air, it frequently becomes hot, they immediately lose their fragrancy, and stink and often bursts out into eruptions. Besides like carrion." An air so very putrefying can this, as the external air cannot readily reach the never be very commodious for respiration. bottom, or be renewed there, an observable heat is perceived below, without the necessity of recurring to the central heat for an explanation. Upon our descent into mines of considerable depth, the cold seems to increase from the mouth as we descend; but after passing very low down, we begin by degrees to come into a warmer air, which sensibly grows hotter as we go deeper, till at last, the labourers can scarcely bear any covering as they continue working. Hence, therefore, there are two principal causes of the warmth at the bottom of mines: the heat of the substances of which the sides are composed; and the want of renovation in the air below. Any sulphureous substance, mixed with iron, produces a very great heat, by the admission of water. If, for instance, a quantity of sulphur be mixed with a proportionable share of iron filings, and both kneaded together into a soft paste, with water, they will soon grow hot, and at last produce a flame. This experiment, produced by art, is very commonly effected with 4 Macquer's Chymistry, vol. i. p. 316. 5 Hill's Fossils, p. 628. 6 Boyle, vol. iii. p. 232. 7 See Supplementary Note A, p. 89. Indeed, if we examine the complexion of most miners, we shall be very well able to form a judgment of the unwholesomeness of the place where they are confined. Their pale and sallow looks show how much the air is damaged by passing through those deep and winding ways, that are rendered humid by damps, or warmed with noxious exhalations. But although every mine is unwholesome, all are not equally so. Coal-mines are generally less noxious than those of tin; tin than those of copper; but none are so dreadfully destructive as those of quicksilver. At the mines near the village of Idra, nothing can adequately describe the deplorable infirmities of such as fill the hospital there; emaciated and crippled, every limb contracted 8 Kircher Mund. Subt. vol. ii. p. 216, or convulsed, and some in a manner transpiring he happened to be next the entrance, she so far quicksilver at every pore. There was one man, ventured down as to see where he lay. As she says Dr. Pope,10 who was not in the mines above approached the place, the sight of her husband half-a-year, and yet whose body was so impreg-inspired her with a desire to rescue him if possinated with this mineral, that putting a piece of brass money in his mouth, or rubbing it between his fingers, it immediately became as white as if it had been washed over with quicksilver. In this manner all the workmen are killed sooner or later; first becoming paralytic, and then dying consumptive: and all this they sustain for the trifling reward of sevenpence a-day. ble, from that dreadful situation; though a little reflection might have shown her it was then too late. But nothing could deter her; she ventured forward, and had scarce touched him with her hand, when the damp prevailed, and the misguided, but faithful creature, fell dead by his side. Thus, the vapours found beneath the surface of the earth are very various in their effects upon the constitution: and they are not less in their But these metallic mines are not so noxious from their own vapours, as from those of the substances with which the ores are usually unit-appearances. There are many kinds that seem 11 ingly are no way prejudicial to health, but in which the workmen breathe freely; and yet in these, if a lighted candle be introduced, they immediately take fire, and the whole cavern at once becomes one furnace of flame. In mines, therefore, subject to damps of this kind, they are obliged to have recourse to a very peculiar contrivance to supply sufficient light for their operations. This is by a great wheel, the circumference of which is beset with flints, which striking against steels placed for that purpose at the extremity, a stream of fire is produced, which affords light enough, and yet which does not set fire to the mineral vapour. Of this kind are the vapours of the mines about Bristol: on the contrary, in other mines, a single spark struck out from the collision of ed, such as arsenic, cinnabar, bitumen, or vitriol. From the fumes of these, variously combined, and kept enclosed, are produced those various damps, that put on so many dreadful forms, and are usually so fatal. Sometimes those noxious vapours are perceived by the delightful fragrance of their smell, somewhat resembling the peablossom in bloom, from whence one kind of damp has its name. The miners are not deceived, however, by its flattering appearances; but as they have thus timely notice of its coming, they avoid it while it continues, which is generally during the whole summer season. Another shows its approach by the burning of the candles, which seem to collect their flame into a globe of light, and thus gradually lessen, till they are quite extinguished. From this, also, the miners frequently escape; however, such as have the mis-flint and steel would set the whole shaft in a fortune to be caught in it, either swoon away, flame. In such, therefore, every precaution is and are suffocated, or slowly recover in excessive used to avoid a collision; the workmen making agonies. Here also is a third, called the fulmi- use of wooden instruments in digging; and benating damp, much more dangerous than eithering cautious, before they enter the mine, to take of the former, as it strikes down all before it like a flash of gunpowder, without giving any warning of its approach. But there is another, more dangerous than all the rest, which is found in those places where the vapour has been long confined, and has been, by some accident, set free. The air rushing out from thence, always goes upon deadly errands and scarce any escape to describe the symptoms of its operations. Some colliers in Scotland, working near an old mine that had been long closed up, happened, inadvertently, to open a hole into it, from the pit where they were then employed. By great good fortune, they at that time perceived their error, and instantly fled for their lives. The next day, however, they were resolved to renew their work in the same pit, and eight of them ventured down, without any great apprehensions; but they had scarcely got to the bottom of the stairs that led to the pit, but, coming within the vapour, they all instantly dropped down dead, as if they had been shot. Amongst these unfortunate poor men, there was one whose wife was informed that he was stifled in the mine: and, as out even the nails from their shoes. Whence this strange difference should arise, that the vapours of some mines catch fire with a spark, and others only with a flame, is a question that we must be content to leave in obscurity, till we know more of the nature both of mineral vapour and of fire. This only we may observe, that gunpowder will readily fire with a spark, but not with the flame of a candle; on the other hand, spirits of wine will flame with a candle, but not with a spark: but even here the cause of this difference as yet remains a secret.12 As, from this account of mines, it appears that | the internal parts of the globe are filled with va- | pours of various kinds, it is not surprising that they should, at different times, reach the surface, and there put on various appearances. In fact, much of the salubrity, and much of the unwholesomeness, of climates and soils, is to be ascribed to these vapours, which make their way from the bowels of the earth upwards, and refresh or taint the air with their exhalations. Salt mines, being naturally cold,13 send forth a degree of coldness 12 See Supplementary Note B, p. 90: |