I NT ROD UCTION. 1 3 



non-caking coal, and anthracite ; the differences are made apparent by the 

 application of heat, when caking coal swells up considerably and liquefies and 

 forms coke, but the other kinds do not. The amount of carbon contained 

 in them increases constantly from caking coal to anthracite, while that 

 of the volatile hydrocarbons diminishes in the same direction, and this 

 change is generally coincident with decrease in the number of the trans- 

 parent yellow or red areas mentioned above. Coals may also be divided 

 according to their external character, colour, texture, a mode of divisiori 

 which shows no relation to the one previously mentioned, and in this way 

 we distinguish brown coal or lignite, anthracite, cannel coal and fibrous 

 coal (the fusain of the French, fossil wood -coal of older authors). 



Ordinary observation teaches us that external conditions have had 

 a great deal to do with causing these differences in the constitution of the 

 different kinds of coal. Every one knows how rapidly coal taken from the 

 mine changes in the air, how it falls to pieces even when it contains little 

 or no iron pyrites, and thus loses some of its value as fuel. Analogous pro- 

 cesses have gone on in the course of time in the seams themselves before 

 removal from the mine. Thus Goppert * cites many cases in which seams 

 of caking coal in.the neighbourhood of that which is being removed change 

 gradually into fritting coal and non-caking coal ; he states that the two latter 

 kinds almost everywhere take the place of caking coal at points where great 

 faults traverse the seam and displacements have occurred. Moreover, the 

 coal of seams of the most different character becomes anthracitic by contact 

 with intrusive porphyry, and this is often accompanied with the appearance 

 of columnar structure. Seams of caking coal also are locally converted into 

 coke by similar intrusions ; the eruptive rock may even occasionally change 

 the coal into graphite. Delesse 2 mentions a case of this kind described by 

 Boue from New Cumnock in Scotland, in which the direct passage of coal 

 into anthracite and graphite may be observed. A similar case occurs 

 according to Rink in Greenland, where coal is changed into coke, into 

 anthracite with a semi-metallic lustre, and even into graphite 3 . Hence it 

 would appear that caking coal, fritting coal, non-caking coal, anthracite, and 

 graphite are successive stages of development, through which any given 

 coal-seam may pass. If this is so, there is ground for surmising that some 

 layers of graphite, at least of the old formations, are the final condition of 

 a process of development, which our seams of coal may also in certain 

 circumstances eventually reach. 



If the seams exposed to these external influences throughout their 

 entire mass in essentially like manner always contained coals of thoroughly 

 similar character, we might in that case ascribe the differences which dis- 

 tinguish them from one another exclusively to the different effects of these 



Goppert (14). 2 Delesse (1). 3 Heer (3), vol. i, Introd. p. 4. 



