178 DR BENNETT ON THE STRUCTURE OF THE 



that any histologist who has made himself acquainted with the structure of coal 

 on the one hand, and of the Torbanehill mineral on the other, could easily con- 

 found the two together. 



There are two other modes of examination which also indicate the broad dis- 

 tinction in structure between coal and the mineral. These are by reducing them 

 to powder and to an ash. 



The powder of household coal contains numerous short black fibres, separated 

 or aggregated together, mingled with mineral particles and fragments of cells. 

 That of the Torbanehill 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 fragments and the debris of the dark amorphous 

 mineral matter. This 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 characteristic. 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 ; 2d, Siliceous masses of various 

 irregular forms, obtained from the interstices of the organic substance ; 3d, Black 

 fibres, separated or in masses, evidently the woody fibre carbonized ; 4th, Flat 

 carbonaceous plates, presenting round apertures corresponding in size to the 

 woody cells which passed through them, and exhibiting at their margins sections 

 of larger circles, which doubtless bounded the large resin cells in the recent wood. 

 (Plate II., fig. 3). None of these appearances are visible in the ash of the Torbane- 

 hill mineral, when care is taken to exclude such portions of it as are free from the 

 stigmaria or other plants imbedded in it. Indeed I myself have never seen such 

 appearances in the ash, even when no such precaution has been taken. Dr George 

 Wilson gave me a considerable quantity of it, which everywhere exhibited 

 nothing but an amorphous material, such as might result from the incineration 

 of clay or other earthy non-organic substance. (Plate II., fig. 4). In all the 

 cannel coals, traces of these forms, though not so numerous or abundant, can be 

 seen. Mr Quekett has even applied this test to Welsh anthracite, in which 

 substance no rings or fibrous structure can be made out in sections, yet where he 

 says, the ash gives unmistakable evidence of the presence of woody tissue.* 



II. Such, then, are the facts which an investigation into the structure of coals 

 the one hand, and of the Torbanehill mineral on the other, has elicited. If the 

 account I have given of them be correct, it must be evident that the differences 



* Quarterly Journal of Microscopical Science, No. VI., p. 43. This number of the Journal for 

 January 1854, was not published until February, after the present paper was written. I was enabled 

 however, by the kindness of Mr Highley, the publisher, to peruse a proof of Mr Quekett's valuable 

 paper, before my own was read to the Society, and to interpolate the above passage. 



