COAL, in mineralogy, a most impor tant genus of mineral inflammables, in which is included the carbonaceous and carbono.bituminous fossils. In the excel lent dictionary by Messrs. A. and C. Ai kin, this genus is divided into the families of brown coal, black coal, and mineral carbon. The first, or brown coal, is im perfectly bituminous, of a brown colour and vegetable texture : of this there are four species. The second, or black coal, is perfectly bituminous, of a black co lour, and contains three species, of which one is the slate coal, which is soft and ea sily frangible: specific gravity 1,2 to 1.24 : it contains from 57 to 64 of carbon, and from 33 to 43 of bitumen, being a mix ture of maltha and asphalt, and from 3 to 6 of earth and oxide of iron. Most of our common coals belong to this species, and from the different phenomena which they exhibit during combustion, a great num ber of varieties are known in the market. The canal coal is of this family. See AM DELITES. The third sort, or mineral car bon, is destitute of bitumen, and consists of charcoal, with various proportions of earth and iron. There are three species, of which one is plumbago, or black lead.
See BLACK-LEAD.
Coal, of all the substances which natu ralists have arranged in the class of in flammables, is by far the most service able to mankind. Nature has dealt it to us with an unsparing hand, and has pro vided mines of this mineral which seem to defy the power of man to exhaust. England and France, where the different branches of manufacture are carried to a greater extent and perfection than in the other countries of Europe, are, at the same time, the most abundantly provid ed with mines of coal, as if nature was de termined to second the exertions of an industrious people by giving them the best possible assistance. Coal is always found in masses, sometimes in a heap, most frequently in beds ; but rarely in veins. The beds are disposed within the eartl, with different degrees of inclina tion, and in almost every possible direc tion. These beds of coal are supposed by most naturalists to be a deposit form ed by the waters of the ocean, which once covered our continent. They are never found single, but generally dispos ed in strata one above another. The beds of coal are separated by layers of stone, which are nearly of the same na-' ture in all coal mines. Those which form the side and the top of a stratum of coal are a sort of friable slate, containing more or less of bitumen, while the bot tom is generally more compacted, and mixed with micaceous sand. It is remark able that this slaty kind of stone, which so generally accompanies the coal, should frequently contain the impressions of plants, and particularly ferns, some of which are met with in the finest state of preservation.
In Scotland, the mines of Carron, of Edinburgh, and of Glasgow, are chiefly distinguished for their produce. There are three beds of coal at Carron, the first of which is about 40 fathoms below the surface, the second 50, and the third 55.
Only two beds are worked at Edinburgh, and one of them is remarkable for its situ ation, the of the mine being hardly forty fathoms from the sea, and only three fathoms above high water mark. The mines of Glasgow stretch from the north-east to the south-west, and occupy a considerable space of ground. Here are several beds of coal, placed on each other, and continued nearly from the surface of the ground to the depth of three hundred feet ; but of these beds there are only two or three that are worth the trouble of work ing.
The principal mines of this useful mi neral in England are those of Newcastle and Whitehaven. The town of Newcas tle absolutely stands on beds of coals, which extend to a considerable distance round the place. There are seven' or eight beds of this mineral,. one above the other, and all inclined in a south-east di rection; the lowest is a hundred fathoms from the surface of the earth. But the mines near Whitehaven will afford the best idea of these wonderful places. We learn that these coal mines are perhaps the most extraordinary of any in the known world. The principal entrance for men and horses is by an opening at the bottom of a hill, through a long pas sage hewn in the rock, which, by a steep descent, leads down to the lowest vein of coal. The greatest part of this descent is through spacious galleries, which con tinually intersect each other ; all the coal being cut away, except large pillars, which, in deep parts of the mine, are three yards high, and twelve square at the base. The mines are sunk to the depth of a hundred and thirty fathoms, and are extended under the sea to places, where, above them, the water is of suffi cient depth for ships of large burthen. These are the deepest coal mines that have hitherto been wrought, and per haps the miners have not in any other part of the globe penetrated to so great a depth below the surface of the sea; the very deep mines in Hungary, Peru, and elsewhere, being situated in mountain ous countries, where the surface of the earth is elevated to a great height above the level of the ocean. There are here three strata of coal, which lie at a consi derable distance one above another ; the communication between each is preserv ed by pits. The vein is not always regu larly continued in the same inclined plane, but is sometimes interrupted by hard rocks, and in those places the earth seems to hate sunk downwards from the sur face, while the part adjoining hath retain ed its ancient situation. These breaks the miners call dykes, and when they meet with one of them, they first ob serve whether the direction of the strata is higher or lower than in the part where they have been working. If, to employ their own terms, it is cast down, they sink a pit to it with little trouble ; but should it, on the contrary, be cast up to any considerable height, they are fre quently obliged to carry a long level through the rock, with much expense and difficulty, till they again arrive at the vein of coal.