176 DR BENNETT ON THE STRUCTURE OF THE 



yellow matter, resembling bees- wax, with only a few irregular spots of the black 

 matter. In some sections, especially of the light-brown specimens, the rounded 

 masses, as they are ground thinner, may be seen, as it were, to melt into one 

 another (Plate I., fig. 11). In such sections, no difference whatever can be made 

 out, whether they be made in a longitudinal or in a horizontal direction. But in 

 certain sections, the yellow masses assume an elongated shape, so as to resemble 

 the appearance represented, Plate I., fig. 9. 



In some thin sections these rounded transparent bodies can be separated from 

 one another , and be distinctly seen to possess a radiated crystalline appearance, 

 strongly reminding one of the crystals of carbonate of lime which occur in urine. 

 (Plate II., fig. 1.) At certain angles, also, a few of them refract light, and be- 

 come strongly tinted with the orange ray when polarized, — a circumstance per- 

 haps dependent on the admixture of mineral matter. When a section of the 

 mineral, presenting both the substances described is held over the flame of a lamp, 

 the yellow matter evaporates in the form of thick smoke, leaving the black mat- 

 ter unaffected, with large holes or loculi in it. It must be clear from this expe- 

 riment that the yellow matter is some bituminous or resinous substance, easily 

 decomposed by the heat of a lamp, and that the black matter is an earthy mate- 

 rial, which resists the same amount of heat. We can have no doubt, therefore, 

 that an easily volatilized and highly inflammable matter has concreted in the 

 form of rounded masses, and constitutes the light-coloured portion of the mineral 

 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 ex- 

 amined. 



Some portion of the Torbanehill mineral, however, has a tendency to split up 

 into thin laminse, and presents smooth or irregular depressions, dependent on the 

 presence of Stigmaria or other fossil plants, which, in these places, come in con- 

 tact 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 occasionally the woody fibres and rings of coal. These 

 latter are most common where the mineral forms a junction with coal, and where 

 the one is more or less mingled, or alternates with the other. In these places the 

 great difference in structure between them is easily recognized both by the naked 

 eye, and by microscopic demonstration. 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 



