THE TORBANEHILL MINERAL, ETC. 189 



neral formerly described. Whether this be chemically the 

 same as, or only allied to bitumen, resin, or amber, I leave to 

 be determined by chemists. But we may at least correctly 

 denominate it a Bituminoid substance, that is, one which 

 closely resembles, even should it turn out not to be identical 

 with bitumen. The matter in which this is imbedded seems 

 for the most part to be composed of clay, or earthy matter 

 which leaves a white ash, altogether destitute of structural 

 traces, and is equally amorphous in whatever direction the 

 section of the mineral is examined. 



Some portion of the Torbanehill mineral, however, has a 

 tendency to split up into thin laminae, and presents smooth or 

 irregular depressions, dependent on the presence oi Stigmaria 

 or other fossil plants, which, in these places, come in contact 

 with, or are imbedded in, the substance of the mineral. Thin 

 sections of such portions exhibit masses of a rich-brown colour, 

 composed of scalariform ducts in great numbers, and occasion- 

 ally the woody fibres and rings of coal. These latter are 

 most common where the mineral forms a junction with coal, 

 and whei'e the one is more or less mingled, or alternates with 

 the other. In these places the great difference in structure 

 between them is easily recognised both by the naked eye, and 

 by microscopic demonstrati(m. By the naked eye, the black 

 shining layers of coal are easily distinguished from the brown 

 dull appearance of the mineral, and wherever such coal exists, 

 the streak is dark and lustrous ; wherever the Torbanehill mi- 

 neral is pure, and unmixed with vegetable matter, it exhibits the 

 dull-brown streak. In such places, the mineral is characte- 

 rized, under the microscope, by its yellow masses and black 

 basis ; the coal, by its rich-brown fibrous structure. Occa- 

 sionally sections at the point of junction, prove that the scala- 

 riform tissue, like the substance of coal, is very friable and 

 easily broken down. This fact, which was pointed out to me 

 by Mr. Kirk, induced him to think that the amorphous basis 

 might be composed of such tissue disintegrated, a supposition 

 negatived by the absence of all trace of structure through 

 the mineral generally. 



From what has been said it must be evident, that there is a 

 wide distinction between all kinds of household coal and the 

 Torbanehill mineral ; and tlie correct discrimination between 

 the fibrous, woody texture of the one, and the granular bitu- 

 minoid, and earthy substance of the latter, will enable us to 

 understand the more confused texture presented in certain 

 cannel coals, which it has been contended are identical in 

 structure with the mineral. 



I have examined a large number of cannel coals, and in 



