] 90 DR. BENNETT, ON THE STRUCTURE OF 



every case have been enabled to recognise the fibrous structure 

 of the longitudinal section, and the appearance of rings in the 

 transverse sections, as they are seen in household coal. They 

 contain, however, a greater or less number of the bituminoid 

 masses, identical vi^ith those wrhich constitute the principal 

 substance of the Torbanehill mineral. 



The Capeldrae and brown Methil coals are especially rich 

 in these bituminoid bodies, and in consequence have been 

 regarded as identical in structure with the mineral. In some 

 sections of the latter coal, they are almost as numerous as those 

 in the dark specimens of the Torbanehill mineral ; but a 

 careful examination will show that it also possesses the same 

 organic structure as coal, and may be at once distinguished by 

 its reddish fibres, when cut in one direction, and by the distinct 

 rings, though few in number, observed on a transverse section. 



I consider that this proof of structure in the brown Methil 

 coal, is decisive of the question as to the distinction between 

 coal and the Torbanehill mineral. Every one allows, that of 

 all the cannel coals, the brown Methil is the one which most 

 closely resembles it. It has also been reported that no differ- 

 ence can be detected between them by the aid of magnifying 

 glasses. To this I may reply, that I have always been able 

 to distinguish them at once ; that 1 have never been deceived 

 in doing so, although the attempt has often been made ; nor 

 do I believe that any histologist who has made himself ac- 

 quainted with the structure of coal on the one hand, and of 

 the Torbanehill mineral on the other, could easily confound 

 the two together. 



There are two other modes of examination which also indi- 

 cate the broad distinction in structure between coal and the 

 mineral. These are by reducing them to powder and to an ash. 



Tlie powder of household coal contains numerous short 

 black fibres, separated or aggregated together, mingled with 

 mineral particles and fragments of cells. That of the Tor- 

 banehill mineral is composed of transparent yellowish masses, 

 evidently the same as those seen in section, but more broken 

 up, and without any trace of an envelope, mingled with frag- 

 ments and the debris of the dark amorphous mineral matter. 

 Tliis mode of examination, though distinctive between the 

 household coals and the mineral, is not so much so, when the 

 brown Methil coal is chosen as the subject of comparison. 



An examination of the ash, however, is still more character- 

 istic. In the brown or blackish ashes of coals will be found, 

 1st, A greater or less number of mineral spicula, evidently 

 the skeletons of the woody fibre ; 2nd, Siliceous masses of 

 various irregular forms, obtained from the interstices of the 



