3d. Shaken Coal.—By this trouble the texture of the coal is not only destroyed entirely, but the whole of the coal from roof to pavement is of no use whatever ; the roof and pavement generally keep their common parallelism, and no convulsion is to be observed in the adjoining strata. The shaken coal has the appearance of the rubbish of an old coal waste, being a heteroge neous mass of dusty coal, mixed with small cubical pieces of good coal. This shaken coal is so soft, that frequently it can he dug with a spade.
4. Foul Coal.—This denomination of trouble is ap plied to no specific kind of coal, every coal which is deteriorated in quality, or so mixed with heterogeneous matter as to be useless, or the greater part so, is de nominated foul coal.
5. Pyritaceous Coal, or the Brassy Coal of the miners. —This trouble arises from the coal being so mixed and cntwisted with pyrites as to be of no use as coal. It may be remarked, however, that the term pylitaceous coal is not applicable to those coals which have pyrites in them of a lenticular form, and which can with ease be separated from the coals, for these do not deteriorate the quality of the coal as they are picked out.
6. Sparry Coal.—This trouble arises from the coal having an increased number of fissures together, and filled with a hard white sparry substance, the sulphate of lime, so that the coal is rendered useless and very difficult to work.
7. Stoney Coal.—This trouble arises from the coal becoming very much mixed with stone in an irregular manner. These stones do not lie in regular beds ; and they are so intimately joined or connected with the coal, that they cannot be taken out without destroying and breaking to small pieces a great proportion of the coal to which they are attached ; on which account such stoney coals have frequently to be sent to market with the stone in them, which is greatly against their sale. Coals having regular bands of stone in them, and which are easily separated, do not come under the denomination of stoney coals.
8. Black Coal.—This is a trouble which rather af fects the appearance than the absolute quality of the coal ; it generally occurs suddenly, that is, while in one part of the coal-field the coals have the common bright fracture, a slip or hitch of very trifling magni tude will produce on the other side coals termed black coal. The appearance is dull, without the least lustre. It is equally compact in texture as the other coals of the field, and burns well. This trouble, however, greatly reduces the value of the coal at market, its ap pearance being so very much against it.
9. Sooty Coal.—This trouble renders the coal of a dead, sooty, friable appearance, and of no use, is never of great extent, nor does it appear to have arisen from any convulsion of the immediately adjoin ing strata, as the roof and pavement where it occurs keep their parallelism with each other. This trouble is, however, generally found when approaching some considerable dislocation of the strata, such as a slip or dike.
lo. Dike Coal, named also Burnt Coal, Dander Coal, or Humphed Coal, are all names applied to the same kind of trouble in the bed of coal. The particular names above mentioned are applied by the common workmen and miners, the name dander signifying .scoria. The appellation humphed is a provincial term, and only used amongst miners, signifying the same thing as burnt or dander coal. This kind of trouble is in general found to exist on both sides of dikes composed of greenstone, basalt, or prophyretic clay ; the trouble beginning at a distance from the dike on both sides, the coal at first by degrees losing its bright fracture and becoming black coal, then burnt or dander coal, which next the dike ap pears run into a tortuous mass, with irregular cellular cavities, and is more of the nature of a dull, black, stoney matter, than any thing connected with coal. Coal found in this kind of trouble has none of the qualities of glance coal, the blind coal of Scotland, or the stone coal of Wales ; for, although placed in a heap, they will not kindle though fire is applied, they will grow red hot, but instantly cool, as stones would do when heated and the fire withdrawn. Some pieces are found occasionally of the purest kind of glance coal, with a very bright metallic lustre, and so hard as to be with difficulty scratched with a knife ; such coal is divided by nu merous small veins of a white sparry substance. This kind of trouble, besides being found adjoining dikes of the above description, is found occupying considerable districts of a coal-field ; and though no change is ob served in either the roof or pavement, the coal is com pletely useless, and will not burn though fire is applied to it. It is, however, in general different in appear ance from the coal found adjoining dikes as before mentioned, in as much as more of the stratified tex ture remains, and is not run into a tortuous mass with irregular cavities. It has been asserted by some miners, that this change is occasioned by greenstone or basalt being near the coal, either above or below it. This we presume remains to be proved.