562 Reports and Proceedings — 



formation; in Soutli "Wales also, as already stated, the anthracite and the other 

 coals are all of one age. The squeezing, faulting, and inversions in the former field 

 are accompanied by an alteration of the highly bituminous coals into dry coals and 

 anthracite. 



An interesting historical sketch of the use of anthracite, and some systematic 

 remarks on its distribution in South Wales, were given by J. P. Bevan, F.G.S., in 

 the "Geologist," vol. ii. 1859, pp. 75-80. 



The anthracite of Pennsylvania is traceable from the inner folds of the mountain 

 chain, where the strata have become more and more crystalline, and contain 

 graphite as well as this non- bituminous coal, westward into Ohio, where the same 

 beds consist of ordinary coal. In the eastern part of the Alleghanies the coal has 

 only 6 to 14 per cent, of volatile matter, further west 16 to 22 per cent., 30 to 35 

 per cent., and in Ohio 40 to 50 per cent. (Prestwich). This coal-field before compres- 

 sion was probably 900 miles long by more than 200 broad in some places (Lyell). 



The depression of strata by accumulated sediment above them may raise their 

 temperature by the rise of the isogeotherms (surfaces of equal subterranean tempera- 

 ture), and they may reach a relatively high temperature. "Mere descent to a 

 great depth, however, will not necessarily result in any marked lithological change, 

 as has been shown in the cases of the Nova-Scotian and South-Welsh coal-fields, 

 where sandstones, shales, clays, and coal-seams can be proved to have been once 

 depressed 14,000 to 17,000 feet below the sea-level, under an overlying mass of 

 rock, and yet to have sustained no more serious alteration than the partial conversion 

 of the coal into anthracite. They must have been kept for a long period exposed 

 to a temperature of at least 212° Fahr. Such a temperature would have been 

 sufficient to set some degree of internal change in progress had any appreciable 

 quantity of water been present, whence the absence of alteration may perhaps be 

 explicable on the supposition that those rocks were comparatively dry." ^ 



Coal in contact with granite is changed into anthracite or graphite ; when in 

 contact with volcanic and trappean rocks, • it may become coke (columnar or other- 

 wise) or mere soot. 



Steam coal is very compact, burns with little smoke, and contains so Kttle 

 bituminous matter that it is not liable to spontaneous combustion, whether pyrites 

 be present or not. It is an intermediate land of coal, having more hydrocarbon 

 than any anthracite has. 



Ordinary coal, common coal, household coal, pit coal, hlack coal, coal proper, 

 bituminous stone coal ; of this there are several sorts : — 



1. Caking coal, coking coal, bituminous coal (not really bituminous, but containing 

 the constituents of bitumen — 7 to 9 per cent, of hydrogen, with carbon and oxygen, 

 or 4 to 6 per cent, of hydrogen and 6 to 8 per cent, of oxygen). When heated, it 

 undergoes a kind of fusion and ' cakes ' together, one piece adhering to another by 

 the soft bituminous matter into which it is mainly changed. Such coals are used 

 for coking, coke being more or less impure carbon left after the hydrocarbons have 

 been driven ofi". 



2. Cherry coal, or soft coal, is thinly laminated, soft, velvety, short-fractured, 

 friable. 



3. Splint coal (breaking off in long 'boards,' and into fragments with angular 

 ends called 'splints' — Mushet), bone coal, hard coal, free-burning coal, dry coal 

 (passing into shah/, slaty, and stony coal). This is less bituminous than some of the 

 foregoing; burns free and open (that is, without swelling and caking), with a long 

 smoky flame ; with less than 6 to 8 per cent, oxygen and 4 to 6 per cent^ hydrogen ; 

 it is also called dry coal. The hard coal comes out in long blocks ; the cherry coal 

 in short pieces. 



Reedy coal has alternate layers of splint coal and bright coal (Mushet). 



Cannel coal, or parrot coal, is compact, and varies from lustrous to a dull earthy 

 aspect ; breaks irregularly, but with a conchoidal (shell-like) fracture ; can be 

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

 Much used in gas-making ; not fit for coking. 



Torbanite, Torhanehdl mineral. Boghead cannel-coal, or Boghead coal, is a kind of 

 dark brown cannel-coal, good for making gas and oil (parrafin, etc.), 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. 



1 Geikie, "Textbook," etc., 2nd edit., 1885, p. 273. 



