Wherever the excavated rock is not hard or solid enough to bear the superincumbent weight, the galleries of a mine must necessarily be supported by timbering or walling. Timbering is most used, frequently in the form represented in the annexed woodcut; and when we consider how miles upon miles of galleries are thus supported, we can easily imagine that whole forests must be engulfed in our mines. It has been calculated that for the total quantity of timber in use for mining purposes in Cornwall, it would require no less than 140 square miles of forest of Norwegian pine, averaging a growth of 120 years. The expense thus incurred is enormous; the cost for timber, duty free, in Cornish and Devon mines, amounted in 1836 to 94,138l. and is probably still larger at the present time. For timbering, no tree is more esteemed than the larch or the Norwegian pine, on account of its great durability in the wet; but whatever wood may be employed, it is necessary to peel off the bark, experience having shown that unless this is done the wood rots much more easily, as the fibres of the rind attract a far greater quantity of moisture than the smooth surface of the splint. Like the potato and the grape, subterranean timbering is exposed to the attacks of a fungus, producing what is called dry-rot. The parasite germinates in the sap which remains in the wood, or at least derives its nourishment from it. Its vegetation is at first scarcely perceptible; but soon its white fibres multiply, and form at length small sponges on the surface. The decomposition of the wood now advances with rapid strides, and terminates at last in the total destruction of the ligneous fibres. Not satisfied with depriving the roof of its support, the dry-rot likewise produces a vitiation of the air, so that wherever timbering is employed, it is reckoned among the great enemies of the mine and of the miner. Many remedies have been recommended, among which kyanizing, or saturating the wood with a solution of corrosive sublimate, is one of the most efficacious, though unfortunately too expensive to be of universal use. Mushrooms of various kinds likewise flourish upon the moist surface of the spars, and various insects collect near this parasitic vegetation.

The timbering of a mine also affords very convenient lurking-places to the numerous rats which are met with underground, where they contrive to live upon the crumbs or offal of the miners’ meals, or upon candle-ends and remains of wicks. Not seldom the timbering of a gallery, weakened by rot, gives way under the pressure of the roof, which falls in with a tremendous crash, and sometimes buries the unfortunate miner under its ruins. Another disadvantage attending timbering is its liability to catch fire, and thus, wherever the cost is not found too great, the chief galleries of a mine are now usually constructed of stone. Sometimes the two sides of a gallery are lined with vertical walls, and its roof is supported by an ogival vault or an arch. If the sides of the mine are solid, a simple arch is sufficient to sustain the roof; and at other times the whole surface of a gallery is formed of a single elliptic vault, the great axis of which is vertical, and the bottom is surmounted by a wooden plank, under which the waters run off.

The miner is generally in a state of perpetual warfare with the water, which threatens to inundate the scene of his labours; and as in a leaky ship the pumps must be kept continually working to prevent the vessel from sinking, so here also perpetual efforts are necessary to keep off the encroachments of this never-tiring foe. When a mine is situated above the level of a valley or of the neighbouring sea, its drainage may be effected in a comparatively easy manner by means of sloping galleries, dry-levels or adits, which in many cases serve also for the transport of the ore or coal. In some mines these drainage levels are executed on a truly gigantic scale. Thus the Great Cornish Adit, which extends through the large mining district of Gwennap, begins in the valley above Carnon, and receives the branch adits of fifty mines in the parish of Gwennap, forming excavations and ramifications which have an aggregate extent of between thirty and forty miles, and which are in some places 400 feet below the surface of the ground. The longest branch is from Cardrew mine, and is five and a half miles in length. This great adit opens into the sea at Restronget Creek, and empties its waters into Falmouth Harbour.

A similar great drain is Nent Force Level, in the north of England, which drains the numerous mines in Alston Moor. It consists of a stupendous aqueduct nine feet broad, and in some places from sixteen to twenty feet high. For more than three miles it passes under the course of the river Nent, to Nentsbury engine-shaft, and is navigated underground by long narrow boats. At the distance of a mile in the interior, daylight is seen at its mouth like a star, and this star is continually enlarging upon you until you find yourself in open daylight. The ramifications of the Great Adit Levels of the mines of Freiberg in Saxony have a total length of seventy-two miles; but the most stupendous works of this description are those in the district of Clausthal and Zellerfeld, in the Hartz, where, as the mining operations have been carried on deeper and deeper, adits have been successively driven below adits. Four of these levels date from times previous to the seventeenth century; but, as they were found insufficient, the famous Georg Stollen was added to their number in 1777. This gigantic tunnel, which, piercing the hard rock, required twenty-three years for its completion, is above five miles long, and passes 900 feet below the church of Clausthal. It serves the double purpose of a draining gallery and of a navigable canal. The water is always kept at a height of from fifty to sixty inches; and the boats, which carry about five tons, are propelled by means of a chain attached to the vault, along which the boatmen drag or push them forward. In this economical manner about 20,000 tons of ore are annually brought to daylight. The boats are made and repaired in a subterranean wharf, which, though far from being one of the largest, may probably boast of being the deepest.

Until 1851 the Georg Stollen answered all the purposes for which it was constructed, but at the end of that period the increased depth and extension of the mines rendered necessary the addition of a new great adit level, which has been named the ‘Ernst August Stollen,’ in honour of the late king of Hanover. In spite of its vast dimensions, this magnificent work, which is six and three-quarter miles long, about ten feet high, and six and a half broad, required only thirteen years for its completion, and may justly be considered as one of the triumphs of modern engineering. The excavation was begun simultaneously at ten different points, and such was the admirable precision of the plans that all the junctions of the different sections of the gallery fitted accurately into each other.

Below the Ernst August Gallery (437 yards), the form of the country allows no deeper adit level to be driven; but to provide for the increasing vertical extension of the workings, a new underground gallery, without any opening to the surface, and at a depth of 262 yards below the former, is already in contemplation. The water is to be raised to the Ernst August Level by a special hydraulic machine placed in a vertical shaft, which will serve at the same time for raising the ore and for the passage of the miners. The expense is calculated at about 60,000l. but will be amply repaid by the new field of mineral wealth which it will open. Thus in the Hartz one magnificent work is but the precursor of another.

When a mine is so situated that drainage galleries cannot be established, engines must be employed for pumping up the waters. Thus, in Cornwall, where most of the copper mines open almost at the sea level, an enormous influx of water can be kept in check only by an equally enormous steam-power. In the United and Consolidated Mines between Truro and Redruth, seven steam-pumps, working with the united strength of 2,000 horses, are kept constantly in motion, and raise above 2,500,000 gallons of water in twenty-four hours.

In 1837 the whole quantity of water pumped out of the earth by sixty Cornish engines attained the amazing aggregate of close upon thirty-seven millions of tons; but since then mining has been carried on more extensively and deeper, and consequently additional steam-power has become necessary to keep pace with the increasing waters.

‘Even to the eye of an observer who is practised in machinery^[38] of great magnitude, the first sight and the subsequent examination of such engines is very gratifying. To watch the labour of a giant would be interesting; but to see the giant not only labouring at ease amidst his enormous work but at the same time at the command of a child, who should be able to stop him at any moment—this would be doubly interesting. Such is the case with the great Cornish engines, for even the largest of them may be stopped by a child of ten or twelve years of age. Another peculiar feature, too, of these engines is this, that they work with a quietness—or absence of clash and clatter—which is in the inverse ratio of their magnitude. The water makes a great rush in the pumps, but the engine itself is calm and comparatively noiseless—like a great mountain reposing in calm greatness while a perpetual spring brawls at its feet.’

In the coal-fields of the North equally gigantic efforts must be made to keep down the water.

In sinking to the coal at Dalton-le-Dale, eight or nine miles from Durham, the borers penetrated the vast bed of sand beneath the magnesian limestone, which appears to contain the chief subterranean water-stores of the district. In this case their outburst was truly terrific, amounting, on June 1, 1840, to the enormous quantity of 3,285 gallons every minute. To oppose this formidable enemy the spirited proprietors of the mine at once proceeded to erect the necessary steam-power for pumping off 3,000 or 4,000 gallons a minute; but, the waters still increasing, it became necessary to meet them with a double and treble force, so that finally the floods had to be kept down by steam engines of an aggregate power equivalent to 1,584 horses and setting twenty-seven sets of pumps in motion.

Sometimes the influx of water into a coal mine is so enormous that no human contrivance can oppose it, and man is obliged to give up the conflict in despair. During the progress of the attempted winning of a pit at Haswell in the county of Durham, the engine power erected pumped out the water to the amount of 26,700 tons per day; but still the floods came in, and at last won the victory.

From the same cause many collieries have been closed, of late years, on the banks of the Tyne, and among these the famous Wallsend Colliery, which has given its name to the best kinds of coal.

The drowning of a coal mine not seldom occurs from the irruption of water accumulated in old wastes or ancient workings occupying a higher level in the vicinity. The growing pressure of such a body of water upon the beds or barriers below becomes enormous; and then the water, testing every weak point of the body opposed to its escape, at length unexpectedly rushes into the space which it finds open before it. All the works below are completely filled, and the mines are for a time rendered useless, or, it may be, for ever abandoned. This was the cause, in 1815, of the celebrated accident at Heaton, near Newcastle-on-Tyne, in which ninety lives were lost. The water flowed from two adjoining old collieries which had been abandoned seventy years before. A barrier of six feet withstood a pressure of thirty fathoms of water. But an irruption was aided at last by a natural fissure of the rock, and the catastrophe followed before any adequate protection could be interposed.

About thirty years later a tremendous calamity of the like kind, after an outlay of 100,000l., totally ruined the Baghilt coal mines, in Wales. The water came from adjoining mines, which had been long abandoned.

If correct plans and descriptions of all the ancient workings had been preserved, these accidents, which happen frequently, might easily be prevented, as an exact knowledge of the localities would enable the owners to leave sufficiently strong barriers in parts where they are now often most inadequate. Such is the importance of accurate mining records that thousands of pounds would be freely given at this moment by many owners for a knowledge of old works of which no plan exists and which no memory can now recall. Fortunately, the legislature has now taken steps to introduce a system of registration such as has already existed long ago in Prussia, Austria, and Belgium, and which, at least, will answer the purpose of obtaining greater security for the future.

Sometimes an enormous fall of rain, descending on the neighbouring country, finds its way into the mines through fissures in the ground or by breaking through galleries, and causes irreparable mischief; sometimes even a whole river bursts into the works and ruins them for ever. Thus, in 1856, the South Tamar Consols, in Devonshire, was flooded by the giving way of the bed of the Tamar, under which the workings were carried.

Even the Sea has been known to take fatal vengeance for the undermining of her domain.

Workington Colliery extended to the distance of 1,500 yards under the Irish Channel, and the workings, being driven considerably to the rise, were brought at length within fifteen fathoms of the bottom of the sea. The pillars of coal which supported the overlying strata were hardly strong enough to support the roof, but the imprudence of a manager eager to produce a larger quantity of coal weakened even this insufficient support by working it partly away. Heavy falls of the roof, accompanied by discharges of salt water, gave repeated warnings of the impending catastrophe, which took place on July 30, 1837. So violent was the irruption that many persons at a distance of hundreds of yards observed the whirlpool commotion of the sea as it rushed into the gulf beneath. Some few workmen near the shaft had time to escape, but thirty-six men and boys and as many horses were destroyed by the waters, which in a few hours entirely filled the excavations, the extension of which had tasked the labour of years.

The heroic devotion of a miner has invested with a more than ordinary interest the inundation of the mine of Beaujonc, near Liège, which took place on February 28, 1812. One hundred and twenty-seven persons were in the pit when the waters burst in from some old workings. Thirty-five had time to make their escape through the shaft; twenty-two were drowned in their eagerness to reach it; the majority, severed from the upper world by an impassable gulf, remained behind. Hubert Goffin, the overman, could have ascended in the tub; but, though the father of six children, his sense of duty would not allow him to desert his post, and he resolved to save all his men or to perish with them. As the rising waters forced the prisoners to seek a higher level, the boys burst out weeping and the boldest began to despair; but Goffin revived their courage by reminding them that their friends without would make every effort to save them. As one day after another passed, the prisoners suffered all the horrors of hunger, which some of them endeavoured to appease by devouring the candles they had brought with them. Others went to the water in the hopes of finding the body of some drowned comrade. Two of the pitmen quarrelled, and were on the point of coming to blows. ‘Let them fight,’ said the others; ‘if one of them is killed we will eat him’—a declaration which at once put an end to the dispute. To satisfy their thirst they had nothing but the foul water of the pit. Some made vows to all the saints, others complained in their delirium that they had to wait for their meals. In the midst of these scenes of horror, Goffin alone retained his courage, and, exhorting, consoling, encouraging, and reproving on all sides, appeared as the guardian angel of his despairing comrades.

Meanwhile every effort was being made from without to bring them succour. Although as soon as the accident took place the pumps were incessantly at work, the water had risen to a height of 14 metres in the shaft on the following morning, and as it was still rising there was reason to fear that the captives, blocked up in a constantly narrowing space, would soon be suffocated. It was resolved to strike a gallery from the neighbouring pit of Mamouster to Beaujonc, a distance of 175 metres. Unfortunately, only two men could hew at a time, but such was the ardour with which the work was prosecuted that on the morning of March 4 a shout of triumph announced that the longed-for communication was effected, and that the prisoners were alive. Crawling through the narrow passage, they were wrapped up in woollen blankets and strengthened with soup and wine before being hoisted to the surface. Goffin and his son, a lad of twelve, were the last to leave the pit; as a brave sea captain, after some great catastrophe, never thinks of his own safety till he has satisfied himself of that of his men. With the exception of those who were drowned immediately after the accident took place, all were saved. The joy of some families, the despair of others, may be imagined when the final count was made. As a reward for Goffin’s admirable conduct, he was decorated with the cross of the Legion of Honour and received a pension of 600 francs. Nine years later he was killed by an explosion of fire-damp, and thus the hostile elements with which he had so long waged a successful war triumphed over him at last.

The sudden irruption of an immense body of water into a mine naturally causes a compression of the air in those galleries which are cut off from all communication with the shaft. This pressure, which may rise to three or four atmospheres—or, in other words, may be three or four times greater than that of the external air—not only produces symptoms of suffocation and cerebral congestion in the unfortunate miners who are exposed to it, but, forcing its way through fissures in the roof or violently rupturing it, sometimes produces the effect of an explosion of gunpowder, throwing the earth to a distance, and even overturning houses. One of the most interesting of the accidents of this kind on record occurred in 1833, in an extensive Scotch colliery, into which the waters of the river Garnock had broken through a cavity in its bed. As the stream poured into the mine the opening gradually enlarged, until at length the whole body of the river plunged into the excavations beneath. The river was affected by the tides, and this engulfment took place at low water; but as the tide rose the sea entered with prodigious force, until the whole workings, extending for many miles, were completely filled. No sooner, however, had this taken place, than the pressure of the water in the pits became so great that the confined air, which had been forced back into the high workings, burst through the surface of the earth in a thousand places, and many acres of ground were seen to bubble up like the boiling of a cauldron. Great quantities of sand and water were also thrown up, like showers of rain, during a period of five hours, and an extensive tract of land was laid waste.

Besides the danger of being crushed to death by a fall of rock, or immured in a living tomb by an obstruction of the shaft or an irruption of water, the miner has another, and often still more formidable, enemy to encounter in the noxious gases frequently evolved in coal-pits. Thus in all well-regulated mines the greatest attention is paid to ventilation, so that no part of the workings may be left without a proper supply of air. In ordinary cases the natural currents, which set in different directions through the shafts and galleries, may sufficiently purify the atmosphere; but in the coal mines which are peculiarly subject to the evolution of foul gases, artificial or mechanical means must be resorted to for driving away the hurtful vapours as quickly as they form. To establish a proper air current, the usual method is to keep a large fire continually burning at the bottom of one of the two shafts of the pit, or of one of the two compartments of the single shaft, and the difference of temperature thus caused between the column of air of the upcast shaft and the downcast becomes the motive power which impels or drags the air current in obedience to it.^[39] Yet this meets but half the difficulty; for the air current, which naturally tends to the shortest passage, must be forced to do its duty in every corner of the pit, and not suffered to escape through the upcast shaft before it has performed the longest circuit. For this purpose a great number of mechanical contrivances are adopted, in the shape of ‘stoppings,’ of brick, or wood, or stone, all so placed as to divert

and drive the air current into the several galleries of the pit, and to make it perform every kind of complex movement, from turning back upon its own right or left to turning over in a somersault upon itself. The most curious and admirably simple contrivance is that of splitting the air by means of a wooden erection, which meets and cuts the current in two, and sends one part on the one hand and another on the other hand. In fact, what is commonly practised in minutely irrigating a meadow is also effected in thoroughly airing a mine. We may form some idea of the underground travels which the air is thus obliged to perform, by being forced along from split to split, when we hear that at Hetton Colliery the ventilating current in the total equals no less than 196,000 cubic feet of air per minute circulating through the mine at a velocity of 18 feet 3 inches per second.

The foul gases or damps evolved in mines are either heavy or light. The most remarkable of the former is the choke-damp, or black-damp, the name given by the miners to carbonic acid gas. From its great specific gravity (1·527), this gas rests on the floor of the mine and gradually accumulates, having no tendency to escape beyond a slow mixture which takes place with atmospheric air; while the light fire-damp, or carburetted hydrogen, which, though not immediately fatal when breathed, explodes on the slightest contact with flame, tends to rise to the surface. The quantity of fire-damp which is poured out into the workings of some mines is very considerable, and constantly varying. Some seams of coal are much more full of it than others, and in working these, which are technically called fiery seams, it is not uncommon for a jet of inflammable air to issue out at every hole made for the reception of the gunpowder before blasting.

In the celebrated Wallsend Colliery, in an attempt made to work the Bensham Seam (an attempt which ended in a fearful accident), Mr. Buddle said, in evidence before a committee of the House of Commons:—‘I simply drilled a hole into the solid coal, stuck a tin pipe into the aperture, surrounded it with clay, and lighted it. I had immediately a gas light. The quantity evolved from the coal was such that in every one of those places I had nothing to do but to apply a candle, and then could set a thousand pipes on fire. The whole face of the working was a gas-pipe from every pore of coal.’

The force with which the gas escapes on some occasions from clefts or joints is so great as to prove much previous compression. These sudden outbursts are locally termed blowers. Their issues and effects are surprising. In one minute they have been known to foul the air to a distance of 300 yards, and their noise is described as like that of rushing waters, or the roar of a blast furnace. They are not merely dangerous from their inflammable vapours, but also from the pieces of coal which their tension not seldom forces from the roof, and whose fall maims or kills the unfortunate workmen beneath.

The fire-damp is very liable to accumulate in old workings, or goaves, which thus, unless completely isolated by stone and mortar, become a highly dangerous neighbourhood to the other parts of the mine. The immense quantity of gas evolved from a goaf of about five acres in Wallsend old pit affords a striking example of the danger of all such accumulations. A four-inch metallic pipe was conducted from the bottom of the pit to the surface of the ground and a few feet above it, when, a light being applied, a hissing streamer of flame flashed forth and burned night and day. The amount of gas thus drawn off from the mine was at first computed at about 15,000 hogsheads in twenty-four hours. Long did the little pipe continue to pour out in streaming flame thousands upon thousands of hogsheads of escaping fire-damp. The total issue might have illuminated a little town.

The explosion of inflammable gas is the most fearful enemy the collier has to encounter. Three or four cubic inches of carburetted hydrogen, when ignited, produce a detonation like that of a pistol-shot; half a cubic foot, enclosed in a bottle and set fire to, shivers the bottle into fragments; hence we may judge how terrific the effects must be when a blower pours forth its thousands of cubic feet into the galleries of a mine, and the careless approach of a light lets loose the demons of destruction. The explosion of a large subterranean powder magazine would not be more terrific. Often without a moment’s warning the unfortunate pitman is scorched and shrivelled to a blackened mass, or is literally shattered to pieces against the rugged sides of the mine.

It may easily be imagined that many efforts have been made, and many contrivances suggested, to disarm the fire-damp of its terrors; but Sir Humphry Davy’s safety-lamp was the first invention which successfully coped with it. The power of the safety-lamp lies in the non-communication of explosions through small apertures, and the discovery of this natural law, as well as its practical application, is one of the greatest exploits of Sir Humphry Davy. A cylinder an inch and a half in diameter and seven inches long, formed of wire gauze, with 784 apertures to the square inch, surrounds the light of the lamp. When the miner, armed with this apparatus, enters an atmosphere tainted with fire-damp, a light blue flame fills the cylinder; but, as if chained by some magic power, it is unable to transgress its bounds; and as in our Zoological Gardens we quietly view the beasts of the forest behind their iron grating, so the miner looks calmly upon his powerless foe.

Unfortunately, the negligence or the obstinate and blind perversity of the miner too often renders even this splendid invention ineffectual.

The safety-lamp requires to be kept in perfect order, and unless certain precautions are taken while using it, it loses its protecting power. Thus, although perfectly secure when at rest, it seems certain that the rapid motion communicated by the swing of the arm during a hurried transit through the mine has in many cases produced an explosion. Blowing out the lamp is likewise attended with danger, as the flame is then easily driven through the gauze, and, like a tiger escaping from his den, may spread terror and havoc around; but the chief cause of accidents consists in the small quantity of light diffused by the safety-lamp, and the consequent dislike acquired by the miners to its use.

Though in all well-regulated coal-pits one or several workmen are exclusively employed in keeping the lamps in the most perfect order, though they are handed to the miners burning and well closed, and fines are imposed upon any attempt to remove the gauze, yet the best regulations cannot possibly exclude the chance of accident resulting from the almost inconceivable carelessness of men whose daily tasks lead them into imminent danger. Thus it is a melancholy but unquestionable fact that the number of accidents from fire-damp since the introduction of the Davy lamp has been many more in a given number of years than before that invention. This has, no doubt, partly arisen from the larger number of persons employed on the whole; but it is to be feared that it has chiefly happened from dangerous portions of a mine being taken into work which without the Davy could not have been attempted, and partly also from the extreme carelessness of the workmen in removing the wire gauze.^[40]

Unfortunately, the fatal effects of this rashness are not confined to the foolhardy miner who thus casts away the shield that preserves him from danger, but generally extend to many of his innocent comrades. In the year 1856 an explosion which took place in the Cymmer coal-pit killed 110 persons, and in the year 1857 170 workmen in the Lundshill colliery were swept from life to death with the rapidity of lightning. In the year 1858 the fire-damp levied a contribution of 215 victims in the coal-pits of England, while in 1859 it was satisfied with 95. But in 1860, as if to make up for this deficiency, it raged with double violence; for, after having already claimed a tribute of 80 lives, the dreadful explosion which took place in the Risca Colliery on December 1 destroyed no less than 142 men and boys. The fire-damp explosion which occurred at the Oaks Colliery in 1866 swept away the unprecedented number of 361 victims, and in the same year 91 workmen perished from the same cause at Talk-o’-th’-Hill Colliery.

In these dreadful catastrophes the most terrible agent of destruction is not always the burning and concussion of the actual blast of fire-damp, but the choke-damp which succeeds the explosion. For the carbon of the inflammable gas, uniting with the oxygenoxygen of the air, produces that deadly poison, carbonic acid gas, which, from the disturbed ventilation of the pit, soon spreads far and wide through the galleries; so that the poor colliers who are caught in an exploded pit have two chances of death against them—one from burning, and the other from suffocation. The effect of death by the one gas or the other is very distinctly seen in the countenances of the dead. The men killed by the fire-damp are marked with burns and scorching, and their features are more or less distorted or disfigured. On the other hand, where men have been suffocated by choke-damp, their features are placid and simply inanimate. The fragile and faulty separations (whether doors or stoppings of any kind) having been broken down, there is an end to a hope of safe retreat even for men totally unharmed by the flames, for at once the air takes the shortest course between the entrance and exit, and leaves the shattered parts unventilated. Whatever after-damp is then and there generated exerts its effects in full, and those who cannot rush to the shaft are suffocated. In the explosion at Risca it was declared by the surgeon to the pit that of those who were killed no less than seventy persons died from the effects of after-damp who had not been near the fire. In the great Haswell explosion, several years since, seventy-one deaths out of ninety-five were occasioned by choke-damp; and at the explosion in the Middle Dyffryn Pit in 1852 no less than seven-eighths of the deaths proceeded from this cause. Persons of great experience attribute at least seventy per cent. of the deaths in fiery mines to after-damp, while some advance them even to ninety per cent.

After relating so many frightful disasters, too frequently caused by imprudence and rashness, it is a more pleasing task to mention a few instances of warnings taken in time. At Walker Colliery on the Tyne, in the year 1846, a huge mass of coal weighing about eleven tons was forced from its bed, and a great discharge of gas succeeded. Two men who were furnished with Davy lamps were working where this discharge took place; one of them had his lamp covered with the falling coal, and the other had his extinguished. They groped their way to warn the other miners, and then all, extinguishing their lamps as they went, safely escaped to the bottom of the shaft, and were drawn up.

A few months after a second discharge from another part of the same colliery took place. A bore-hole having been made, a violent noise like the blowing off of steam was heard, and a heavy discharge of gas filled the air courses for a distance of 641 yards and over an area of 86,306 cubic feet. At 400 yards from the point of efflux a mining officer met the foul air, felt it blowing against him, saw the safety-lamp in his hand enlarge its flame, and drew down the wick. Still the gas continued to burn in his lamp for ten minutes, making the wires red hot, and then the light went out—a hint not lost on the owner, who quickly followed its example. At a distance of 641 yards from the efflux of the gas he met four men and boys whose lamps were rapidly reddening. At once they had the self-possession to immerse them in water, and thus escaped all danger of explosion.

The disastrous effects of the fire-damp are not confined to the loss of human life; they are also extremely injurious to the workings, tearing up galleries, shattering machinery, or even setting fire to the mine—an accident which may also be caused by spontaneous combustion^[41] or by the negligence of the workmen. These fires are often subdued by isolating the burning coal seam, by means of dams or clay walls, or by filling the mine with water; but not seldom they last for years, and assume dimensions which mock all human efforts to extinguish them.

At Brûlé, near St. Etienne, a coal mine has been on fire for ages. The soil on the surface is barren and calcined, and the dense sulphurous fumes, escaping from innumerable crevices, give the country a complete volcanic aspect.

In the carboniferous basins of Staffordshire and of Saarbrück and Silesia there are likewise coal mines which have been on fire for a long period. At Zwickau in Saxony the first accounts of one of these subterranean conflagrations date as far back as the fifteenth century, and the fire still burns on. The hot vapours which rise from the surface have since 1837 been put to an ingenious use. Conducted through pipes into conservatories, they ripen the choicest fruits of the south, and produce a tropical climate under a northern sky.

In a Staffordshire colliery which had been on fire for many years, and which was called by the inhabitants Burning Hill, it was noticed that the snow melted on reaching the ground, and that the grass in the meadows was always green. Some speculators conceived the idea of establishing a school of horticulture on the spot, and imported colonial plants at a heavy expense. These flourished for a time, but one day the subterranean fire went out, and as the heat it had imparted to the soil gradually diminished and departed, the exotic vegetation likewise drooped and died.