TORBANEHILL MINERAL AND OF VARIOUS KINDS OF COAL. I 77 



the Torbanehill mineral is pure, and unmixed with vegetable matter, it exhibits 

 the dull brown streak. In such places, the mineral is characterized, under the mi- 

 croscope, by its yellow masses and black basis ; the coal, by its rich brown fibrous 

 structure. (Plate I., fig. 12, and Plate II., fig. 2.) Occasionally sections at the 

 point of junction, prove that the scalariform tissue, like the substance of coal, is 

 very friable and easily broken down. This fact which was pointed out to me by 

 Mr Kirk, induced him to think that the amorphous basis might be composed of 

 such tissue disintegrated, a supposition negatived by the absence of all trace of 

 structure through the mineral generally. 



From what has been said it must be evident, that there is a wide distinction 

 between all kinds of household coal and the Torbanehill mineral, and the correct 

 discrimination between the fibrous, woody texture of the one, and the granular 

 bituminoid, and earthy substance of the latter, will enable us to understand the 

 more confused texture presented in certain cannel coals, which it has been con- 

 tended are identical in structure with the mineral. 



I have examined a large number of cannel coals, and in every case have been 

 enabled to recognise the fibrous structure of the longitudinal section, and the ap- 

 pearance of rings in the transverse sections, as they are seen in household coal. 

 They contain, however, a greater or less number of the bituminiod masses, identical 

 with those which constitute the principal substance of the Torbanehill mineral.* 

 (Plate I., figs. 4 to 9.) 



The Capeldrae and brown Methil coals are especially rich in these bitu- 

 minoid 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 nume- 

 rous 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. 

 (Plate I., figs, 8 and 9.) 



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 difference can be de- 

 tected 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 I have never been de- 

 ceived in doing so, although the attempt has often been made ; nor do I believe 



* In reference to this point, I have carefully examined transverse and longitudinal sections of 

 the following household and cannel coals, namely, — Buccleuch, or Dalkeith; Zetland; Newcastle; 

 Wallsend ; Jordan Hill ; Knightswood ; Arniston ; Sheepmount ; Drumfillan ; Cowdenhill ; Barton 

 Hill; Eastfield, Glasgow; Stonilaw, Glasgow; Gartnavel, Glasgow; Claycross ; Lesmahagow ; 

 Wemyss ; Lochgelly ; Capeldrae ; Wigan ; Civility Pit ; Huddersfield ; Bredisholm ; Black Methil ; 

 and Brown Methil. 



VOL. XXI. PART I. 3 B 



