ON THE FORMATION OF COAL 



[1870] 



The lumps of coal in a coal-scuttle very often 

 have a roughly cubical form. If one of them be 

 picked out and examined with a little care, it wiU 

 be found that its six sides are not exactly alike. 

 Two opposite sides are comparatively smooth and 

 shining, while the other four are much rougher, 

 and are marked by lines which run parallel with 

 the smooth sides. The coal readily splits along 

 these lines, and the split surfaces thus formed 

 are parallel with the smooth faces. In other 

 words, there is a sort of rough and incomplete 

 stratification in the lump of coal, as if it were a 

 book, the leaves of which had stuck together very 

 closely. 



Sometimes the faces along which the coal splits 

 are not smooth, but exhibit a thin layer of dull, 

 charred-looking substance, which is known a3 

 " mineral charcoal" 



