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X. — An Investigation into the Structure of the Torbanehill Mineral, and of 

 various kinds of Coal. By John Hughes 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 I 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. 3 a 



