(173) 
X.— An Investigation into the Structure of the Torbanehill Mineral, and of 
various kinds of Coal. By Joun Hucurs Bennett, M.D., F.R.S.E., Professor 
of the Institutes of Medicine in the University of Edinburgh. (With Two 
Plates.) 
(Read 6th February 1854.) 
The investigation of which I am now about to give an account, was under- 
taken with the view of determining whether the structure of the Torbanehill 
mineral was similar to or unlike that of coal. I was aware that the subject 
would be brought before a court of law, and that many scientific persons of great 
eminence had already spent much time in the inquiry. With the understanding, 
therefore, that my evidence, should it be required, was to be limited to the struc- 
ture of coal and of the mineral in question, I gave directions to Mr Bryson, the 
optician, of this city, to make thin sections of attested specimens of various coals 
and of the mineral, conceiving that a careful examination of them would easily 
determine the point. It was soon apparent, however, that a far more extended 
series of researches was necessary than [| at first anticipated; but as it was also 
evident, from the marked structural differences which were observed in the sec- 
tions, that the investigation would not be destitute of positive results, I determined 
on pursuing it to a conclusion. 
The plan adopted was, in the first instance, to make myself familiar with the 
structure of the ordinary household coals used in this city, of which those called 
the Zetland and the Dalkeith or Buccleuch coals may be considered as the types. 
I then examined the structure of the Wallsend, Newcastle, and various other 
kinds of household coal, in every case observing, with magnifying powers of va- 
rious diameters, thin sections made horizontally and longitudinally with the 
line of stratification. I next examined similarly made thin sections of the Tor- 
banehill mineral, and was struck with the remarkable dissimilarity which existed 
between them. I now had numerous sections prepared of various cannel coals, 
and having previously determined the appearances presented by true coal and by 
the mineral, I was readily enabled to distinguish the various shades of differences 
between them. I saw that although the cannel coals, and especially one of 
them, the Brown Methil, approached in structural character to that of the Tor- 
banehill mineral, it could still be distinguished from it by a practised eye; and 
that although gradations existed between these different substances, there was 
at least one element which served readily to characterize all the different kinds 
of coal I had hitherto examined, and which was not present in the mineral. I 
VOL. XXI. PART I. BA 
