Otte striking and discriminating mark in these rocks is, that in the primitive class not a vestige of organic re mains is to be found, and very few in the secondary rocks, whereas the strata which compose the coal-fields abound with innumerable impressions and forms, both of animals and vegetables : The whole arrangement of the strata of the coal-fields exhibits a structure and form most dis tinctly differing from the other classes of rocks, and, therefore, has been with much propriety termed by the celebrated \Verner, The Independent Coal Formation.
The strata or rocks which accompany coal are chicfly as follows: 1. Sandstone of various hardness and colour, viz. shades of white, grey, and light red.
2. Slate-Clay.
3. Bituminous shale.
4. Indurated argillaceous earth or fire-clay.
5. Argillaceous ironstone.
6. Greenstone.
Although the independent coal-formation occupies a great area of Britain, as before mentioned, its continuity is frequently interrupted by mountain ranges and rock formations of very considerable extent, where no coal is to be found ; and even in those districts where there are valuable fields of coal found, the beds of coal do not in general extend over a great district of country, without being interrupted by what is commonly termed troubles, or more properly dikes and slips ; hence the difficulties which occur in working coals, and the caution requisite in searching a district for them.
The beds which compose the first and second class of rocks generally lie in a situation forming a great angle with the horizon, being in many cases nearly vertical, whereas the strata composing the coal-formation are commonly found forming a small angle of elevation with the horizon, although there are instances of their being absolutely vertical.
In some coal fields there is only found one bed of coal, and in others a very great number, varying in thickness from an inch to many feet ; it must, however, be remark ed, that those beds of coal which are very thick, have generally thin beds of stone running through them in a horizontal position, forming a number of snbordinate beds of coal, lying very close to one another, having, however, the appearance of one thick bed of coal.
In order to exhibit in a clear and distinct view, the various strata connected with beds of coal, the thickness of the coals, and alternations of the strata betwixt them, the following sections are examples, taken from the chief coalfields in England and Scotland.
of the strata ; these strata, so named, are, however, not Whin, out ere sandstones of the hardest kind. This mis of the name Whin, (or Greenstone) has led mineralogists to wrong conclusions as to the coal forma tion of that district.
The preceding section contains sixteen beds of coal, of various thickness, amounting to thirty feet two inches, many of which are unworkable. The quality is of the rich caking kind, such as the Newcastle coals in general are ; they are soft in their texture, break into very small pieces, and abound much with inflammable air.
In the sections which have been formerly made of the Newcastle coal-field, the term Whin is applied to many The preceding section contains thirteen beds of coal, of various thickness, amounting to 69 feet 3 inches. The first foul coals constitute a thickness of 35 feet ; these are wrought as one bed, under the name of the ten yard coal ; they are of open burning quality, break into large quadrangular pieces, abound with inflammable air, and are very liable to spontaneous ignition.
Indurated and fire clay predominate in the stratifica tion ; but the precise systematic names are not easily ap plied from the descriptions received. The names given to the coal strata in Staffordshire are very uncommon, and altogether local. These provincial terms are so va rious, that they present a great difficulty in comparing the strata of one district with another.
In the preceding section there are 24 beds of coal, of various thickness, amounting to 59 leer 4 inches, but man% of them Are unworkable; all or them are of open burning quality, and break into large quadrangular The above is a very interesting section of a coal field, which according to Werner belongs to the est Floetz troll formation. The striking peculiarities are, 1st, The great body of greenstone of the common crystalized texture, known in Scotland by the name of blue whinstone, found at the surface, and lying above the common coal strata, which are comparatively soft and have little coherence.