AND OTHER VARIETIES OF COAL. 123 



be produced by woody fibres. These characters of the Tor- 

 banehill coal are such as belong to the coke of the Methill 

 and Capledrae cannel coals. 1 feel satisfied that there are no 

 essential differences between them, and that they are not 

 distinguishable from each other by their microscopical cha- 

 racters. 



Ash. — Neither in this coal, nor any other, is there a trace 

 of vegetable structure in the ash, except where a very rare 

 silicification has taken place. Care must be taken, however, 

 that the mistake of confounding coke and the popular term 

 ashes with the scientific word ash be not repeated. The ashes 

 of coal (using the popular phrase) always contain vegetable 

 structures unconsumed ; but from the ash of coal, as spoken 

 of by scientific men, all the organic matters have been driven 

 off by careful combustion, and nothing but earthy matter 

 remains. 



It is important to distinguish the appearances first de- 

 scribed, which are general in the bed of coal, with some of 

 those last noticed, as only occurring occasionally in it. What- 

 ever explanation of the structure and mode of formation of 

 the bed may be adopted, it must be based on the appearances 

 which are delineated in Plate VII., figs. 1 to 4, rather than upon 

 those which are rare, selected from a number of specimens, 

 and shown in some of the other figures. It is always desira- 

 ble that the chemical composition of any body examined mi- 

 croscopically be taken into account ; because where the micro- 

 scope alone will not enable us to decide at once as to the 

 nature of an object, the microscopical and chemical charac- 

 ters, taken together, will often do so. This is precisely such 

 a case ; for the conclusions which, I think, are to be drawn 

 from the structure of this bed of coal, are in a most important 

 manner corroborated and strengthened by the evidence of its 

 nature which chemistry supplies. 



Were we to arrange and classify the known coals chemi- 

 cally and histologically, it would be found that anthracite 

 would take its position at one end of the scale and Torbane- 

 hill cannel coal at the other. Anthracite is almost pure car- 

 bon ; Torbanehill contains less fixed carbon than any other 

 coal. Anthracite is very difficult to ignite, and gives out 

 scarcely any gas ; Torbanehill coal burns like a candle, and 

 yields 3,000 cubic feet of gas per ton more than any other 

 known coal ; its gas being also of greatly superior illuminating 

 power to any other. Below the Torbanehill come the Wigan, 

 Capledrae, and Lesmahago coals. In lightness in colour of 

 the streak, Torbanehill stands highest, then come Methill, 

 Rochsoles, and Capledrae, 



