76 Professor Harkness on Mineral Charcoal. 



this exhibits, not only when viewed under ordinary circum- 

 stances, but likewise when submitted to microscopical exami- 

 nation, a more highly organized structure than that which 

 exists in the granular kind. A longitudinal section of the 

 fibrous variety shows that the walls of the cells, instead of 

 being simple, are marked by numerous hollow spaces which 

 have commonly an elliptical form, the major axis of the 

 ellipsis being across the cells. The spaces are closely ap- 

 proximated one to another, and they present a form of tissue 

 which is allied to the discigerous tissue of conifera, and the 

 fibrous mineral charcoal appears to have been derived from 

 the woody portion of plants which had some affinity to this 

 tribe of gymnosperms. 



On comparing this fibrous tissue with that of a fossil ob- 

 tained from the coal mines at Ince Hall, near Wigan, which 

 I procured last summer when visiting this neighbourhood along 

 with Mr Binney, I find that the structure of both these is 

 such as to support the conclusion that the fibrous mineral 

 charcoal has been derived from plants of a similar character 

 with the fossil referred to. This fossil, which seems to belong 

 to the Calamodendron of Brongniart is, in part, converted into 

 iron-pyrites, and in part into mineral charcoal. It possesses 

 the markings of nodi, such as prevail in calamites, and these 

 are about half an inch separate from each other. But as the 

 specimen is devoid of the external portion, its affinity to the 

 ordinary plants of the carboniferous formation cannot be 

 distinctly made out. There is sufficient evidence to show that 

 this plant has, however, been the fertile source of the fibrous 

 mineral charcoal. From the structure of this variety of mi- 

 neral charcoal, and from the nature of the vegetation from 

 which it appears to have been principally derived, it would 

 seem that forms someAvhat allied to conifera were the tribe 

 of plants supplying this substance. 



As mineral charcoal occurs abundantly in some varieties of 

 coal, it must have been derived from plants which prevailed 

 to a considerable extent during the coal epoch ; and since 

 neither Sigillaria, the most prevalent form, nor Lepedodendron 

 afford the discigerous structure which manifests itself in mi- 

 neral charcoal, this woody matter may have formed portions 



