COAL is an inflammable substance, of a very black colour, somewhat shining, opaque, soft, dry, and light in comparison with any of the strata in which it is found. It occurs in beds varying in thickness from an inch to many fathoms.
It is used for fuel, and is found widely scattered over the globe. The most valuable and extensive beds of coal which have been found and wrought, arc in Great Britain.
This mineral is never found in the primitive nor tran sition rocks, but in a third class of rocks very regularly stratified, the most common of which arc, 1st, sandstone, 2d, slate clay ; 3d, indurated or fire clay ; 4th, argillace ous iron stone ; 5th, limestone ; and 6th, greenstone. Of the two first there are very many varieties, both in re spect of colour and hardness. In the coal, and in all its accompanying strata, distinct organic remains are found belonging to the animal and vegetable kingdom : the greenstone, however, is an exception, as it is questioned whether any organic remains have ever been found in that rock. In the sand stones, the forms of large trees, and jointed reeds, (arundo,) are found abundant, but im pressions of shells are very rare. In the slate clay, the forms of large trees are seldom seen, but innumerable impressions of leaves, ferns, and moss plants, (crypto gamia,) are found in the area of a few feet ; and it is remarkable that where the forms of shell fish are found in this kind of strata, they are never of the same sub stance as the matrix, but arc always of argillaceous iron stone embedded in the slate clay. In the fire clay, a branched tree of singular appearance is most frequently found. The iron stone abounds with forms and impres sions of plants, but more frequently with the forms of shell fish of the class Mytelus. The upper part of the coals have frequently the distinct impressions of large trees, and the lime stone is in many instances a congeries of marine animals. In the sand stone, where forms of trees are found, the bark or exterior part is of coal only, which is very thin, of a bright shining black colour, and cubical.
From the very regular stratification of this field of the mineral kingdom, the vast beds of inflammable matter it contains, the great abundance of organic remains found in it, and as none of the primitive or secondary rocks are connected with the strata, it has therefore very properly been denominated by the celebrated and great minera logist Wearer, the independent coal formation.
Coals, with their various accompanying and parallel strata, are found lying in every inclination to the horizon.
Some of teem "le N ertacal, others neatly horizontal, but octet abbOhltek so to any considerable extent. The most .omition dip or declination is from 1 in 5, to I in 20. A bed of coal. as to its form or shape, considered in the abstract, is generally somewhat semicircular or semi iiiptical and is the segment of a flat bason. There are some instances where the bason shape is complete, the slips and dislocations of the strata which occur, de •anise the general form ; still, however, each segment vidently partakes of the bason form. In some few in stances the form is quite the reverse, as if the coal bed was formed by being revolved round a cone. The verti cal coals do not partake of this bason shape, which might be easily inferred from their peculiar situation.
We are inclined to conclude from practical observa tion, that the forms of coal fields depend upon the shape of the primitive or secondary rocks, upon which they certainly rest. Coals, we believe, and as far as our in vestigation goes, arc never found in veins in the moun tain rocks, similar to those in which metals occur.
The coal formation is found chiefly in the northern hemisphere, and abounds in the countries lying nearly in the same latitudes with Great Britain. Coal is found in Siberia, Canada, Newfoundland, and Cape Breton ; also in France, Germany, and Sweden. It is likewise said to be found in the northern parts of China. In the southern hemisphere, it is stated to be very abundant in New Hol land, but we have no distinct accounts of coal in the con tinent of Africa.