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ing scarcity of wood as fuel rendered some other substitute necessary; and, from its compact form and powerful heat, no known substance could for one moment be brought into competition with coal. The smoke nuisance was therefore submitted to; and despite of every obstacle, the "obnoxious" mineral was soon in the ascendant. At the beginning of the sixteenth century, it seems to have been getting into use in the Lowlands of Scotland, where we find Boethius taking notice of a "black stone" found in Fife and the Lothians, the heat of which was sufficiently intense to fuse the most refractory metals. Since the time of Charles I. it has become almost the only description of fuel used in London, and in most other towns and districts throughout the kingdom-peat or turf being but occasionally employed, and that solely in remote localities. It is within the current century, however, that the great demand has been made upon our coal-fields; since the application of the steam-engine to the purposes of the mine, the factory, the railway, and river; since the introduction of gas, the extension of our foundries, and the general advancement of those economical processes which distinguish the present from every other period of our country's history. According to the most recent estimates, not less than thirty millions of tons of coal are raised from the different mines in the British islands, of which between three and four millions are exported.

The coal worked in Britain may be said to be exclusively obtained from the great coal formation, where it alternates with strata of sandstone, bituminous shale, bands of ironstone, fireclay, and impure limestone. Attempts have been made to work the thin beds found in more recent formations, but in every case without success. The principal districts, or "fields," as they are called, are those of Northumberland and Durham, Lancashire, Stafford, South Wales, and the Lowlands of Scotland-the latter extending from Fife to Ayrshire at an average breadth of about thirty miles. In these fields there may be as many as ten, twenty, or even forty seams or strata of coal, varying from a foot to thirty feet in thickness; but of these, in general, not more than five or six can be worked with profit. The mineral so obtained is of different varieties and qualities; so pure, as to leave after combustion the smallest per centage of ash; or so foul, as to be burned with difficulty. The principal varieties are-caking coal, a highly bituminous sort, like that of Newcastle, which emits much smoke and gas, and cakes together during combustion; cubic, which is also bituminous, but breaks into larger cubical masses, and does not cake while burning; splint, a hard slaty variety, which is still less bituminous, and does not cake, but burns with great heat, and leaves little ash; cannel, a compact shining variety, also bituminous, burns with a clear flame, does not cake, and leaves a whitish ash, principally used, where it can be obtained, for the manufacture of gas. All these varieties are

less or more bituminous; but there is another variety, known by the name of anthracite, or "blind coal," which is non-bituminous. This anthracite has a glistening and semi-metallic aspect, does not soil the fingers when rubbed, and burns without smoke. It is, in fact, a natural coke, or charcoal, the original coal having been deprived of its bituminous products by heat or other causes. It is found in small patches in several coal-fields in contact with the igneous rocks, which have evidently produced the change, but abundantly in South Wales, where it occupies a considerable area. It is used exclusively in the reduction of the metallic ores, for which it has been employed only since the introduction of the hot-blast method.

Besides the supply obtained in Britain, there are coal-fields less or more extensive in France, Spain, Belgium, and Germany; in India, China, the East India islands, Australia, and New Zealand; in Nova Scotia, and the states of North America; in the Isthmus of Panama, Chili, and Peru; and even in some of the islands of the Pacific and Arctic Oceans. Of these fields, the North American are by far the most extensive and important, presenting areas of bituminous and anthracite coal greater than the whole extent of our own island. That of Pennsylvania, Virginia, and Ohio, for example, extends continuously from north-east to south-west for a distance of 720 miles, its greatest breadth being 180 miles; its area thus amounting to 129,600 square miles. That situated in Illinois, Indiana, and Kentucky, embraces an area of 14,000 square miles; while several, many times larger than the largest coal-field in Britain, are found in Michigan and other parts of the union. Many of the coal-fields in the world are yet untouched; it being only after the wood of a new country has been used up, and civilisation made some progress, that man betakes himself to the difficult and often dangerous task of extracting mineral fuel. All the coal-fields now mentioned belong to the same great formation; but there are other patches of a more recent date which are occasionally worked, as the lignite, or brown coal of Germany, and of Bovey Hayfield, near Exeter. This, however, is a very different material in comparison, and is only had recourse to where the lower formation is absent, or at such a depth as to preclude its easy working. Taking, therefore, an estimate of the whole amount of coal known to exist, there need be no dread of the supply being exhausted for thousands of years to come; for though the fields of one country should be exhausted, the fields of another lie patent to the same com mercial influence which imports tea from China, cutlery and cloth from Britain, and cotton from America.

Coal being, in every instance, a true stratified rock, the modes of obtaining it are much the same in the different countries where it is sought after. In early times, our ancestors could avail themselves of little more than the mere outcrop—that is,

that portion of a seam which approaches the surface; and this was excavated just as a stratum of limestone or sandstone is quarried at the present day. By and by they sank to greater depths; but still entering in a slanting direction, after the dip or inclination of the strata, and not descending by shafts or perpendicular pits, as is now the practice. To rid their workings of water, they hewed long tunnels or subterranean drains from some low level, and carrying this forward to the seam of coal, effected a drainage to that depth. Where the coal seams lay on high ground, and where there was any deep glen or ravine in the neighbourhood, such drainage often allowed them to work at a considerable depth; but these day-levels (so called from their discharging their contents to the open day, in contradistinction to other levels within the mine) were, upon the whole, but imperfect and expensive affairs. In some instances, where pits were sunk, windmills were erected for the purpose of pumping the water; but no certain effect could be calculated upon from an agency so unstable as the wind. The invention of the steamengine soon set aside these rude and imperfect appliances; shafts, instead of slanting adits, are now everywhere sunk, and the water brought to the surface at once, no matter whether the depth be 30 or 300 fathoms. Of course the fittings of a coal mine depend, as do all other commercial speculations, upon the value of the material sought to be obtained. In some districts the shafts are of no great depth, the pumping engines small and rude, and the mineral brought to the surface simply by animal power; while in other localities the shafts are of enormous depth and finely executed, the engines of great magnitude and superior finish, and no animal power employed unless in the hewing of the coal. In Britain, a Newcastle colliery may be taken as the most perfect of its kind. Here the shafts vary from 150 to 300 fathoms in depth, are lined with casings of stone, wood, or iron, and are divided into various compartments for the accommodation of the pumping gear, and the ascending and descending corves which contain the coal-these compartments also subserving an important end in the ventilation of the mine. Having reached the stratum of coal, which generally lies at a considerable inclination, main drifts or excavations are made in different directions for drainage, transit, and ventilation; and then the minor workings branch off from these, care being taken to leave pillars or masses of the stratum for the support of the superincumbent material. The water that oozes from the workings finds its way to the lower level of the pit's bottom, from whence it is pumped up by a powerful engine; and the coal hewn out is brought from the various workings to the main drifts, whence it is dragged by ponies to the bottom of the shaft, and raised in corves or baskets to the surface.

Were the accumulation of water the only obstruction to the mining of coal, the difficulty could be easily surmounted. A

supply of fresh air, however, must be regularly and unceasingly maintained in every part of the workings; and not only so, but care must be taken to prevent the accumulation of two gases most destructive to human life; namely, carburetted hydrogen and carbonic gas-the fire-damp and choke-damp of the miners. For this purpose the various underground workings are so arranged and boarded off, that while one set receives the descending current, another carries it forward again to the pit bottom, where, by means of rarefaction, produced by a huge fire, it is carried up the shift to the atmosphere. By these means not only is fresh air supplied to the miners, but the deleterious gases are carried off, and the whole subterranean recesses rendered safe and healthy. The most ingenious of human inventions are, however, imperfect; and choke-damp and fire-damp will exude from the coal seam, and lurk in recesses, there either to suffocate the first comer, or to explode the instant that a lamp is brought in contact. To prevent these casualities as much as possible, various air-tight trap-doors and boardings are employed, and the miner is furnished with safety-lamps of various constructions, which, while they afford sufficient light, prevent the carburetted bydrogen from coming in contact with the flame within. These remarks apply in particular to the Newcastle coal-field, where, in consequence of such difficulties, coal-mining is conducted with greater care and skill than in any other district; but it must be remembered that there are many fields where fire-damp is unknown, and where the most ordinary ventilation is sufficient to prevent the accumulation of carbonic acid or any obnoxious effluvia. Indeed we know of an excellent coal-field which returns its thousands annually, and where no precaution either as to lamps or ventilation is necessary-all that is requisite being occasional wooden props to prevent falls of loose material from the roof of the compartment in which the miner may be working. In some of the largest Pennsylvanian mines even this precaution is unnecessary, the anthracite being of great thickness, and so exposed and level, that it is hewn out either in open quarry or in huge drifts, precisely after the fashion of our railway tunnels.

Important and varied as are the uses, and vast as must be the consumption, of this mineral in Britain, yet so abundant is it, that in many localities the best household coal never exceeds 7s. a ton, while in Edinburgh it averages about 12s.; and in London, to which it is all sea-borne, it ranges between 18s. and 22s. "Notwithstanding the cheapness of the produce of this kind," says Mr Ansted, "the value of the coal actually brought to the surface in Britain amounts annually to nearly ten millions of pounds sterling, and almost the whole of this is derived, although in unequal proportions, from the Newcastle, the South Welsh, the Staffordshire, and Scotch coal-fields. With regard to the first of these-the Newcastle coal-field-it is said that upwards of six millions of tons are there annually

raised up out of the bowels of the earth; that 60,000 persons are employed in the mining operations; that 1400 vessels are constantly engaged in conveying the coal (amounting to three millions of tons) required for the consumption of the metropolis alone; and that the capital employed in simply conducting this trade amounts to several millions of pounds sterling." From this single instance some idea may be formed of the magnitude of the entire trade in coal, which is doubtless one of the most important props of our country's commerce.

As to the origin of coal, no matter what the variety, there can be no doubt that it is essentially vegetable. Not only are fossil trunks, branches, leaves, and fruits found in the mass, but scarcely a portion of it, when submitted to the microscope, but shows the ducts and fibres of a true vegetable structure. We know, moreover, that vegetable matter, when subjected to moisture and pressure, and excluded from the action of the air, will in a short period pass into a bituminous or carbonaceous mass, which time and greater pressure and heat would by and by convert into true mineral coal. Peat, were it excluded from atmospheric influence, would soon pass into a species of coal: brown coal and lignite, in which the trunks and branches of the trees are still perceptible, are only varieties less perfect than the true coal; and even in the old coal-formation itself, various beds present various degrees of perfection, according as the vegetable mass seems to have been more quickly and perfectly removed from the action of the atmosphere. How the masses of vegetable matter were accumulated, is still a subject of speculation with geologists-some contending that the trees, grasses, ferns, &c. which compose it, must have grown and accumulated just as peat-mosses do at the present day, and that the land was then submerged, and the mass covered over by layers of sand and mud, which, hardening, formed strata of stone and shale; others reject this theory as untenable, and consider the whole strata (sandstone, shale, &c.) of the coal-measures to have been deposited in estuaries liable to periodic inundations, like those of the Niger and Ganges, but only on a more gigantic scale. According to this notion, which is more in accordance with the phenomena presented, coal is partly composed of vegetables which grew in situ in the form of jungle, and partly of masses drifted down from the interior by the waters of the river.

Jet-Amber.

Though the chief use of coal be doubtless that of producing heat, there are certain minor purposes to which some of the varieties are applied. Thus we have occasionally seen very pretty vases, and other ornaments, made from cannel coal when it is sufficiently compact and lustrous. It is easily turned, and takes a polish which is not readily tarnished; the only objection to it being its brittleness, and liability to be injured by fire.

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