Professor Harkness on Mineral Charcoal. 77 



of another prevailing genus, viz., calamites, the nature of 

 the tissue of which we are still in ignorance. Lindley and 

 Hutton, in the Fossil Flora, observe, when describing calamites 

 nodosus (plate 15, 16), " This belongs to a large and well- 

 known class of fossils of which the stems are more abundant 

 in the beds of the carboniferous formation of the North of 

 England than any others. They are often found in close 

 alliance with the coal itself, especially when thin layers of 

 mineral charcoal are discovered upon it:" a circumstance 

 supporting the conclusion of the relation of mineral charcoal 

 to calamites, and when it is considered that the specimen of 

 calamodendron from Wigan, containing the same form of 

 structure, is marked by nodi, one of the characteristic features 

 of the calamites, the conclusion that this substance has been 

 derived from such plants, is, to some extent, borne out, leading 

 to the inference that calamites were gymnospermous plants 

 having some affinity to the modern conifera in their internal 

 structure ; which probably may have consisted of a narrow 

 woody cylinder, marked with discs, enveloped in a great mass 

 of simple cellular matter. 



With respect to the mineral charcoal which is found in 

 coaly deposits of an age posterior to the carboniferous forma- 

 tion, this also partakes of a gymnospermous character. Among 

 the oolitic coal of Virginia, North America, mineral charcoal 

 of this nature occurs ; but, according to Mr Darker, this be- 

 longs rather to cycadia than conifera. That which is met 

 with in the lignite of Bovey Tracy is decidedly coniferous, 

 and the mode in which the circular areoloe arrange them- 

 selves, as seen in longitudinal section, shows an intimate rela- 

 tion to some of the modern conifera. In these three varieties 

 of coal we have three forms of fibrous mineral charcoal, which 

 are, to a considerable extent, related to each other, and which 

 have been derived from representatives of the same tribe of 

 plants, viz., gymnosperms, and the mode in which these are 

 met with at once points out that the partial drifting of vege- 

 table matter was the cause of the occurrence of mineral char- 

 coal. 



