44 Structure of a peculiar Combustible Mineral, 
present communication with a most pleasing and perfect accordance of 
observation and opinion. 
" The following are the principal results : — 
"I. A very thin section of the Torbanehill mineral, when viewed by- 
transmitted light, has a pale-yellow colour, is semi-transparent, and, with 
the exception of very slight variations in the depth of the colour, probably 
dependent on the varying thickness of the section, it appears to be a 
uniform homogeneous mass. Tlie same appearance is constantly presented 
notwithstanding that the sections are taken in various directions. While 
this is the usual appearance of what may be termed the average specimens, 
viz., of portions taken from the centre of the block (or seam), yet, in 
sections taken from near the outside, or lower portion of the seam, I find 
a quantity of small opaque particles (evidently earthy matter) in the form 
of a fine powder, scattered through the yellow-coloured medium forming 
the mineral. In such specimens the transparent yellow substance forms 
irregular rounded granules, and the opaque powder is either sparingly 
diffused over, or forms an outline or partition, more or less perfect, around 
the exterior of the yellow granules. These granules vary much in size, 
being as small as l-4000th of an inch, and of every intermediate size 
from that up to l-200th of an inch in diameter. 
^* In sections taken from the outside, as above described, I have observed 
occasional patches of opaque material of every irregular form, and which 
I could not liken to any other substance, unless I spoke of them simply 
as specks of dirt. In the same sections I have also found stalks of plants 
and fragments of wood. These opaque patches and vegetable fragments 
are always distinctly isolated ; that is, they do not in any way resemble 
or form part of the substance of the mineral, otherwise than by being 
involved or contained in it, and their presence, therefore, can only be 
considered accidental. 
" II. When reduced to a fine powder, and examined under water, all 
the particles of the mineral have a clear, and generally a sharp outline, 
are of an irregularly rounded form, and may be described as of a uniform 
granular appearance. About 7-lOths of the granules are very translucent, 
and of a light amber or yellow colour. About 2-lOths of the particles 
(also translucent) partake more of a flat, angular shape, and are quite 
colourless, probably consisting of siliceous matter. The remainder of the 
powder consists of dark semi-opaque particles. 
" In specimens of powder taken from an outside portion of the mineral, 
there is observed a larger proportion of the semi-opaque particles, together 
with the occasional appearance of vegetable stalks, rough fibrous frag- 
ments, and delicate fibrils of microscopic plants. With these special 
exceptions, the powder gives no trace whatever of organic structure. 
" III. The ash of the mineral, when examined under water, presents a 
considerable quantity of the colourless particles already described, lying at 
the bottom of the fluid, white a filmy particle of transparent particles floats 
on the surface. No trace whatever of organic structure is here observed. 
*' Polarised light does not in any way affect the appearances of the 
mineral. 
I have, in consequence of these investigations, a firm conviction of the 
non-identity of the Torbanehill mineral with coal, setting aside those 
differences which may be found to exist under mineralogical, geological, or 
chemical investigation. I cannot conceive how the evidence of Amorphisin 
in the one case, and of intimate vegetable composition and of regular 
structure in the other, can be explained away, or any other view than 
that of non-identity of physical structure. In coal we find a well- 
characterized organization, or regular arrangement of its component parts 
