624 



REPORT — 1891, 



polished and cut into ornaments in a lathe. Yields niineral oil by distillation. 

 Much used in gas-makinp: ; not lit for coliing. 



Torbanite, Torbanehill 7nineral, Boghead cannel-coal, or Boghead coal, is a kind 

 of dark brown cannel-coal, good for making gas and oil (paraffin, &c.), and gives 

 a light, spongy coke. It consists of minute light brown granules of hydrocarbon, 

 with some earthy matter and portions of the tissues of coal-plants. 



As a scheme for the general classification of the coals the following table may 

 be useful : — 



Torbanite, cannel-coal, \ Vegetable matter 

 parrot-coal . . .J much altered. 

 1 Tasmanite, Better-bed 1 ci t 



L coal,.<L-c. . . .} Spore-coals. 



r Caking and coking coal, 1 Laminae of charcoal 

 \ cherry coal, splint I (mother - coal) 

 [ coal, and other coals . J and hydrocarbon. 



f 1 . Charcoal deposited abundantly at first. 

 \ 2. Hydrocarbon partially lost by change. 



Highly Bitu- 

 minous . . 



Gas coals 



J 



Common Bitu- 

 minous . . 



Semi - bitumi- 

 nous . . . 



Anthracitic 

 Anthracite . . 

 Coke . . . . 



Household coals 



f Free - burning 

 I steam coals 

 f Nearly smokeless 

 ] steam coal 



Smokeless coal 



f 1. Natural . 

 I 2. Artificial 



!■ Hydrocarbon nearly all lost by change. 



■{ 



•1 

 •J 



AU the hydrocarbon lost by heat under pres- 

 sure. 



Hydrocarbon lost by heat without pressure. 



8. Constituents of the Coal-measures and of Coal. — Sandstone, shale, coal, and 

 clay, in successive repetitions, constitute (as we all know) the main materials of the 

 ' Coal-measures ' {' measures ' being an old mining term for strata). Each of these 

 suhstances well deserves the close investigation they have received from numerous 

 observers. We need not take the sandstone in hand now ; it will be enough to 

 say that tlie quartz-grains have been derived from the quartz of the same granite 

 rocks which gave the little mica-flalies to mix with much of the sandstone, and the 

 kaolin to form the basis of the shales and clays in the same great Carboniferous 

 formation. 



Shales and Ironstone. — The shales are varied ; some are almost purely argilla- 

 ceous ; others contain carbonaceous matter in different proportions, even becoming 

 quite black and bituminous. The lighter coloured shales often have plant-remains, 

 especially ferns, scattered through them, and even whole stems and branches of 

 Lepidodendron and Sigillaria, squeezed flat, and reaching long distances. The 

 darker shales also have plant-remains, but less perfect, and very often shells and 

 other fossils, including relics of fish and numbers of small bivalved crustaceans ; 

 with regard to the last, the fishes, when alive, fed on the Cypridffi and such like, 

 and in turn these little Ostracoda ate the dead fishes when they could. 



Here and there are more or less continuous layers oi ironstone, or more frequently 

 groups of nodules parallel with the planes of bedding, and containing either parts 

 of plants, more rarely small limidoids or other crustaceans, or even spiders, scor- 

 pions, insects, or relics of fishes and amphibia. In some cases the shales are of 

 marine origin, judging from the character of the shells imbedded in them ; but 

 usually the evidence from the fossils is of a negative character. The shells that 

 were formerly thought to be mussel-shells, like freshwater Unios, are now known 

 to belong to a different family ; and, not being quite the same as any known sea- 

 shell, they may have been estuarine. 



The nodular and the flat masses of clay-ironstones in the shales have been due 

 to the formation of carbonic acid in the water and mud by the decomposition of 

 vegetable matter and the removal of some oxygen from the peroxide of iron pre- 

 sent there, and by the carbonic acid thereupon forming carbonate of iron. This 

 then segregated around some organic object in the mud, and, mingled with clay, 

 gave rise to nodules or larger masses of argillaceous ironstone.' In consolidating, 



' De la Beche, Memoirt Geol. Survey, vol. i., pp. 186, 186. 



