212 



THE AMEEICAN MONTHLY 



[November, 



bably composed of the same sub- 

 stance as the bodies held to be spores 

 in the torbanite. There is no doubt 

 that in these observations first notice 

 is given of some forms of these essen- 

 tial constituents of coal which I des- 

 cribed in detail in the first division 

 in my book on the microscopical 

 structure of coal * * * * 



If we make a careful examination 

 under a low magnifying power of the 

 vertical fracture of a piece of com- 

 mon and normally developed carbon 

 coal, the first thing we observe is a 

 remarkable homogeneousness and re- 

 gularity in the structure of the sub- 

 stance in one and the same direction, 

 viz., the direction of the bed. Among 

 ICO pieces from various localities 

 there would not be found four or five 

 cases of differing structure. We ob- 

 tain the same result if we examine 

 any coal bed in the mines at a little 

 distance. We observe in the vertical 

 fracture symmetrical stripes, running 

 in the same direction, and belonging 

 in most cases to one and the same 

 substance. The thickness of these 

 stripes is found to be nearly uniform 

 in a piece of larger size, but very often 

 the substance is found gradually to 

 decrease in quantity in the bed. At 

 the distance of some metres the sub- 

 stance dwindles and ultimately disap- 

 pears. ****** 



If we examine with higher power 

 (200 to 300) these constituents of 

 coal, in any good and transparent 

 microscopic section of coal, we see 

 clearly a great uniformity and con- 

 stancy in the microscopical structure 

 of the various substances discernible 

 even with the naked eye. 



A. — The dark substance with con- 

 choidal fracture, and nonfilamentous 

 structure, making the principal con- 

 stituent of coal (over 30 per cent), 

 is composed of a net-work of very nu- 

 merous extremely delicate ramifica- 

 tions, the larger branches of which 

 are connected with larger and thicker 

 stems of more compact and semipel- 

 lucid substance running along the 

 direction of the bed. In a section of 



at least ^J-^ mm. thickness, the single 

 meshes and branchlets appear dis- 

 tinctly limited and composed of 

 nearly homogeneous substance. The 

 tint is a deep reddish-purple. The 

 spaces between the meshes are co- 

 lorless and filled with mineral sub- 

 stance more or less soluble in hydro- 

 chloric acid, and of low polari- 

 zing power. Some variety is obser- 

 vable in the structure of the larger 

 stems: they are composed either of 

 distinctly separated, irregular incras- 

 sated filaments, or of longitudinal bo- 

 dies with perforated and reticular 

 structure. 



The nodules inclosed in this con- 

 stituent of coal appear, when viewed 

 in a thin and polished section, to be 

 composed of semi-transparent, yel- 

 lowish, polarizing substance, either re- 

 gularly arranged round a centre or 

 forming bodies of dendritic and leaf- 

 like shape with radial structure. 

 Bodies of regular and globular shape 

 show the dark variable or revolving 

 cross of polarisation very regularly. 

 This substance, containing from 10 

 to 30 per cent of combustible matter, 

 is found constantly in some marked 

 varieties distinguished in color, re- 

 gular shape, size, and structure. 



B. — The dark substance with fila- 

 mentous structure appears in any mi- 

 croscopical section to be composed 

 of filaments, running exactly in the 

 direction of the coal bed. The fila- 

 ments connected with hair-like rami- 

 fications, and arise from larger stems 

 composed of the same substance. 

 The finest ramifications, attached 

 closely together in the typical sub- 

 stances, are found separated through 

 small spaces with interposed lamellae 

 of transparent mineral substance. In 

 a great many coal beds are found, 

 interspersed between the filaments, 

 numerous corpuscles of substances 

 belonging to other constituents of 

 coal either isolated or connected. 

 From the nature of the substance 

 these corpuscles cannot be constitu- 

 ents of the filamentous substance, 

 both because of their irregular occur- 



