82 Dr. Thomson on the Composition of [Aug. 



Glasgow. I am far from certain that they include all the varie- 

 ties of coal known in Great Britain, though, in all likelihood, at 

 least the most important . of these varieties are found in this 

 neighbourhood, which constitutes one of the richest coal dis- 

 tricts in the island. The species of coal which I have examined 

 are distinguished here by the following names : 



1. Caking coal. 



2. Splint coal, or lightburn hard coal. 



3. Cherry coal, or soft coal. 



4. Cannel coal. 



Besides these four species, I am aware of the existence of 

 another, which is found in Wales under the name of Welsh culm, 

 and in Ireland under the name of Kilkenny coal. This species 

 does not burn with rlame, and leaves about 95 per cent, of 

 charcoal. Want of specimens prevented me from subjecting 

 this species to experiment. I think it not unlikely that the coal 

 which exists in veins in the isle of Skye constitutes likewise a 

 different species. The wan* of specimens prevented me from 

 examining it ; but, as far as I recollect, it possesses many of 

 the qualities of vegetable charcoal. 



1 . Caking Coal. 



The beds of coal in this neighbourhood, which are techni- 

 cally distinguished by the name of the Glasgow seams, are six 

 in number. The sixth, or lowest of these beds, consists of 

 caking coal. It is a thin bed, little more than two feet in thick- 

 ness. On that account, it is nowhere wrought at present; but 

 the same species of coal exists in many other places. Thus it is 

 found at Bannockburn, in Stirlingshire, and in various parts of 

 the coal district in Fife. The coal in the neighbourhood of New- 

 castle, which is carried to London and to all the south of 

 England and the north of Scotland, belongs to this species. As 

 the Newcastle variety is the most important, both on account of 

 its quantity and the uses to which it is applied, I employed it in 

 my experiments. It was from picked specimens of Newcastle 

 coal that the following description was drawn up : 



Colour, velvet-black ; in some places (from the fracture) 

 greyish-black. 



Lustre, shining ; resinous. 



Principal fracture straight slaty ; cross fracture partly small- 

 grained uneven, when the lustre is only glistening ; partly small 

 conchoidal, when the lustre is shining. It is not uncommon to 

 observe the cross fracture having exactly the appearance of 

 wood charcoal. 



It is soft, and very easily frangible. The fragments have more 

 or less of a cubical shape. 



Brittle. Soils the fingers. 



Specific gravity, 1*269. 



