Geological Gleanings. 189 



called. All yield a fused and mamillated coke, varying in amount 

 from 65 to 70 per cent. Sp. gr. = 1.27-1.32. Commonly mixed 

 with thin layers of strongly soiling "mineral charcoal" or fibrous 

 anthracite. Mean composition (ash and moisture excluded) : Car- 

 bon 87.9, Hydrogen 5.1, Oxygen (with Nitrogen) 7.0. 



4. Cannel Coals. — These coals, at least in normal specimens, 

 do not fuse or " cake " in the fire. They give off a large amount 

 of volatile matter, frequently more than half their -weight ; hence 

 their popular name of " gas coals." They soil very slightly, or 

 not at all. The coke obtained from them is sometimes fritted, 

 and partially agglutinated, but never fused into globular, mamil- 

 lated masses, like that obtained from the caking coals. It varies 

 in amount from 30 to 60, or, in typical specimens, from 55 to 58 

 per cent. Mean composition (normal cannel) : Carbon 80-85, 

 Hydrogen 5.5, Oxygen (with Nitrogen) 9-12.3. 



5. Lignites or Brown Coals. — These coals of Tertiary age, differ 

 greatly from one another in external aspect. Some of the so- 

 called jets— passing into the cannel coals — are black, lustrous, 

 and non-soiling ; whilst other varieties are brown, and of a ligni- 

 form or stratified structure ; or, otherwise, earthy and loosely co- 

 herent. All, however, are partially soluble in caustic potash, 

 communicating to it a dark brown colour. The coke— usually of 

 a dull charcoal-like aspect, or in sharp-edged fragments retaining 

 their original form — varies from 25 to 50 per cent. Its separate 

 fragments are rarely agglutinated, except in the case of certain 

 varieties (as the lignites of Cuba, and those from the fresh-water 

 deposits of the Basse Alpes in France) which contain asphaltum. 

 All the typical varieties of lignite, as pointed out by Cordier, con- 

 tinue to burn for some time, in the manner of "braise" or ignited 

 wood, after the cessation of the flame occasioned by the combus- 

 tion of their more volatile constituents ; whereas with ordinary 

 coal, ignition ceases on the flame going out. The mean compo- 

 sition of lignite may be represented by — Carbon 65-75 ; Hydro- 

 gen 5, Oxygen (with Nitrogen) 20-30. 



All the different kinds of coal, enumerated above, contain a 

 variable amount of moisture, and of inorganic matter or •' ash." 

 The moisture rarely exceeds 3 or 4 per cent., although in some 

 samples of coal it is as high as 6 or 7, and even reaches 15 or 20 

 per cent, in certain lignites. The amount of ash is also necessa- 

 rily a variable element. In good coals it is under 5, frequently 

 indeed, under 2 per cent. On the other hand, it sometimes ex- 



