74 [August, 1S41. 



4. An octahedron with tolerably well-defined faces striated in 

 different directions on the adjoining sides, was exhibited, and the 

 circumstance of possessing- a large portion of earthy matter was 

 noticed, as belonging to many samples of coal which exhibit this 

 exterior aspect. 



The presence of several well marked crystalloid forms being 

 thus established, Prof. Johnson adverted to the argument which 

 such forms had been supposed to furnish against the vegetable 

 origin of coal, and stated that in the very samples under examina- 

 tion were seen the most incontrovertible evidences of the source 

 from which not only bituminous coal, but anthracite also had been 

 derived. In one and the same specimen of the latter, were seen 

 mineral charcoal, natural coke, and true anthracite, indicating as 

 well the vegetable origin of all, as the process of formation, by 

 which the last two had probably been derived from the interme- 

 diate state of bituminous coal. 



In accounting for the supposed impossibility of crystalline struc- 

 tures being formed out of organic matter, he observed that a dis- 

 tinction is to be drawn between organic elements and organized 

 substances, and that the former may often be so proportioned, 

 when derived by distillation, fermentation or other chemical re- 

 action from the latter, as to be capable of assuming definite figures. 

 The production of coal from vegetable bodies is supposed, on all 

 hands, to have resulted from a slow chemical decomposition of 

 the latter and the establishment of new orders of affinity between 

 the original constituent atoms. The carbon as well as the other 

 materials of vegetables was by this process reduced, at least in 

 part, to the condition of ultimate molecules, instead of being 

 merely mechanically divided into small particles. It would there- 

 fore be capable of obeying any law of movement which either its 

 own affinities or those of the earthy constituents which had en- 

 tered into the composition of the vegetables fiom which it had 

 been derived, might tend to impress. That it is the earthy con- 

 stituents which determine the forms assumed by coal, seems pro- 

 bable from the fact that the more earthy residuum of a particular 

 kind any coal contains, the more prone does it appear to be to 

 assume a crystalloid structure. 



Reference was made, in this connexion, to those cubic, rhombic 

 and columnar structures which ofien occur in both anthracite and 

 bituminous coal, and which not unfrequently exhibit to the eye, 

 especially after partial incineration, the clearest evidence of a ten- 

 dency among the earthy ingredients to regulate the arrangement 

 of forms throughout the whole mass. Prof. Johnson also stated 

 that the result of a considerable number of analyses of the ashes of 

 coal, appeared to favour the presumption that the two principal con- 

 stituents, silica and alumina, are in definite proportion to each other, 



