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VERYTHING we enjoy, as food or clothing - every substance we employ, for the purposes of life, whether useful or ornamental—is derived from the earth, or
the earth's productions. Be the products animal or vegetable, mineral or metallic, they are alike gifts from the same source; though, in respect of their origin and position, the latter may be more strictly regarded as the
“ treasures” of that solid or stony portion which is accessible to man. In this sense we intend to devote the present sileet to the more important minerals, describing their nature, origin, and uses, and presenting such particulars respecting their commercial history as may seem Interesting to the general reader.
For the more accurate comprehension of the subject, it may be necessary to premise that we speak of the crust of the earthmeaning thereby that superficial rind or portion accessible to human investigation in contradistinction to the interior masses, concerning the nature of which we can only form conjectures. In this crust the rocky substances are variously arranged: some are found in layers or strata—hence said to be stratified; others appear in vast irregular masses, presenting no trace of bed or layer, and are accordingly termed unstratified. The matter of the stratified has evidently been deposited from water, and from this view of their origin, they are generally known as aqueous
or sedimentary rocks; while the unstratified, presenting no appearance of deposit, but everywhere an irregular configuration, and, moreover, often breaking through and contorting the stratified, are considered of igneous or volcanic origin. Both sedimentary and igneous rocks present various mineralogical and chemical characters: thus, of the former, we have roofing-slate, sandstone, coal, limestone, &c.; of the latter, granite, basalt, and lava—all very distinct in composition and appearance. Besides differences in mineral composition, the sedimentary rocks contain different kinds of fossils—that is, the petrified remains of animals and plants; and such distinctions have rendered it necessary to arrange the rocks constituting the crust of our globe into various formations—meaning, by a formation any suite of rocks possess‘ing some peculiar mineral or fossil character. Thus we speak of the “coal formation,” meaning thereby not merely the beds or layers of coal, but the sandstones, shales, ironstones, and the like, which alternate with and accompany that mineral-seeing that the whole have been evidently deposited under similar conditions, and that the same kinds of plants and animals are found fossil within them. Deviating in some degree from the usual technical arrangements, we shall describe the various mineral treasures of the earth under such heads as appear best calculated to aid the comprehension of the ordinary inquirer.
BITUMINOUS SUBSTANCES. Bitumen—from a Greek word signifying the pitch-tree-may be regarded as embracing all those inflammable mineral substances which, like pitch, burn with flame in the open air. Naphtha, petroleum, and asphalte are familiar examples; but all substances impregnated with these bitumens are said to be bituminous. Hence under this head may be included coal in all its varieties, as well as bituminous slate, slaggy mineral pitch, and the asphaltes of commerce.
Coal, of which there are several distinct varieties, is one of the most important minerals with which man has yet become acquainted. By it he fuses the metals, produces steam which sets machinery in motion, prepares gas' for light, heats his apartments, cooks his food, and, in short, renders all the resources of naturé fit for civilised use. It is uncertain when coal first began to be used in Britain as fuel, but in all probability it was not earlier than the beginning of the twelfth century. In 1281, Newcastle is noticed as having some trade in that article; and a little later, we find it mentioned in the Chartulary of the Abbey of Dunfermline. In the reign of Edward I., its use in London was prohibited, in consequence of the supposed injurious influences of the smoke; and this prohibition we find renewed at several subsequent periods; but all to no purpose. The increas
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 pot 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
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 commercial 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