VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 4Qg 



alike, and it is all indiscriminately used for the same purposes; yet there is some 

 difference in the colour, form, and texture of the several veins. The exterior 

 parts, which lie nearest to the clay, have a greater mixture of earth, and are 

 generally of a dark brown, or chocolate colour ; some of them appear like a mass 

 of coal and earth mixed; others have a laminous texture, but the laminae run in 

 such oblique, waving, and undulating forms, that they bear a strong resemblance 

 to the roots of trees, like some specimens from Lough Neagh in Ireland, which 

 seem to be the same sort of fossil. 



There are other veins of this coal, which lie more in the centre of the strata, 

 and abound most in the lowest and thickest bed, the substance of which is more 

 compact and solid: these are as black and almost as heavy as pit coal; they do 

 not so easily divide into laminae, and seem to be more strongly impregnated with 

 bitumen : these are distinguished by the name of stone coals, and the fire of 

 them is more strong and lasting than that of other veins. But the most re- 

 markable and curious vein in these strata, is that which they call the wood coal, 

 or board coal, from the resemblance which the pieces have to the grain of deal 

 boards. It is sometimes of a chocolate colour, and sometimes of a shining black. 

 The former sort seems to be less impregnated with bitumen, is not so solid and 

 heavy as the latter, and has more the appearance of wood. It lies in straight 

 and even veins, and is frequently dug in pieces of 3 or 4 feet long, and with 

 proper care might be taken out of a much greater length. Other pieces of the 

 same kind are found lying on them in all directions, but without the least inter- 

 mixture of earth, or any other interstices, except some small crevices, by which 

 the pieces are divided from each other in all directions. When it is first dug, 

 and moist, the thin pieces will bend like horn, but when dry it loses its elasti- 

 city, and becomes short and crisp. At all times, it is easily to be separated into 

 very thin laminae or splinters, especially if it lie any time exposed to the heat of 

 the sun, which like the fire makes it crackle, separate, and fall to pieces. The 

 texture of this fossil consists of a number of laminae, or very thin plates, lying 

 over each other horizontally, in which small protuberances sometimes appear, 

 like the knots of trees; but on examination they are only mineral nuclei, which 

 occasion this interruption in the course of the laminae; and pieces of spar have 

 been sometimes found in the middle of this wood coal. 



Though the texture of this coal is laminated, yet it does not appear to have 

 any of those fibrous intersections observed in the grain of all wood. This coal 

 easily breaks transversely, and the separated parts, instead of being rugged and 

 uneven, are generally smooth and shining, in which even the course of the 

 laminae is hardly discernible. They dig its coal in an open pit, together with 

 the clay that is mixed with it; and though it lies very close and compact in its 

 original bed, yet it is so easily separated, that they can afford to sell it for half 



