84 Dr Colquhoun on the Argillaceous Ore of Iron. 



also are perpendicular to the general stratum. Besides these, 

 there are sometimes found, though very rarely, crystalline in- 

 crustations of gypsum, or calcareous spar. Isolated masses 

 of stoney matter which is sometimes siliceous, but oftener ar- 

 gillaceous, are frequently met with in the coal strata. All 

 these stoney intermixtures ate distributed with so much irre- 

 gularity, that it is very often impossible for the ironsmelter to 

 say with precision, what may be the average quantity or qua- 

 lity of the earthy matter contained in any given mass of his 

 coal. For the same reason, it is quite an uncertain test of the 

 precise effects which any particular coal will produce in the 

 furnace, to examine the nature and amount of the earthy mat- 

 ter, which is obtained by incinerating a small fragment of it. 

 The portion examined may, according to circumstances, con- 

 tain a large excess, or exhibit a great deficiency of earthy con- 

 stituent, when compared with the average composition of the 

 coal <;omposing the stratum. 



There are only two kinds of coal in this country which can 

 be considered to be of general interest to the ironsmelter. 

 These are the splint coal and the cherry coal, or, as it 

 may be properly enough termed, the bituminous free coal. 

 The blind coal, an imperfect kind of anthracite, is indeed 

 used with great advantage in most of the smelting establish- 

 ments in the south of Wales, but compared with the others 

 already mentioned, both that and the cannel and caking 

 coals are of rare occurrence. 



Cherry coal, on account of the remarkable brilliancy of its 

 lustre and the evenness of its fracture, surpasses in beauty all 

 the other varieties of coal. Its colour is intense black. Its 

 fracture in the direction of the stratum is slaty, and from this 

 cause, when in masses, it generally affects a tabular form : in 

 other directions, the fracture is either even or flatly conchoi- 

 dal. It is extremely friable, and when broken has a peculiar 

 tendency to separate into rectangular-shaped fragments. The 

 lustre of its fractured surface is strongly splendent. The 

 purer specimens, in the smoothness and glossy aspect of their 

 fracture, in their intense black colour and brilliant lustre, have 

 a considerable general resemblance to some of the most beau- 

 tiful specimens of native asphaltum. 



