THE FLORA OF THE COAL FOKMATION. 463 



coals like cannel-coals, winch have been formed wholly under sub- 

 aqueous conditions, the mineral charcoal is deficient.* 



A consideration of the decay of vegetable matter in modern swamps 

 and forests sliovvs that all kinds of tissues are not, under ordinary cir- 

 cumstances, susceptible of the sort of carbonization which we find in 

 tlie mineral charcoal. Succulent and lax parenchymatous tissues 

 decay too rapidly and completely. The bark of trees very long resists 

 decay, and, where any deposition is proceeding, is likely to be im- 

 bedded unchanged. It is the woody structure, and especially the 

 harder and more durable wood, that, becoming carbonized and split- 

 ting along the medullary rays and lines of growtli, affords such frag- 

 ments as those which we find scattered over the surfaces of the coal.-j- 

 These facts would lead us to infer that mineral charcoal represents 

 the woody debris of trees subjected to subaerial decay, and that the 

 bark of tliese trees sliould appear as compact coal along with such 

 woody or herbaceous matters as might be imbedded or submerged 

 before decay had time to take place. 



My method of preparing the mineral charcoal for examination was 

 an improvement on the "nitric-acid" process of previous observers, 

 and the results gave very perfect examples of the disc-bearing tissue 

 restricted in the modern world to conifers and cycads, but which 

 existed also in the Sigillarice of the Coal period. With this were 

 scalariform vessels, like those of ferns and club mosses, and several 

 other kinds of woody tissue. On careful comparison, it was found 

 that all these tissues might be refei'red to the following genera of 

 plants common in the Coal measures: tSigillaria^ including St/'gmaria, 

 Calamites, Dadoxylon, and other conifers, Lepidodendron, Ulodoi- 

 dron^ ferns, and possibly some other less known plants. Another 

 form of tissue observed was a large spiral vessel, possibly belonging 

 to some endogenous plant. The perfect state of preservation of these 

 tissues may be inferred from the following figures, selected from 

 those prepared for my paper (Fig. 175). 



I shall first notice in detail the structures preserved in the layers 

 of shining compact coal, and afterwards those found in the mineral 

 charcoal. 



I. The compact coal, constituting a far larger proportion of the 

 mass than the "mineral charcoal," consists either of lustrous con- 

 choidal dierry or pitch coal, — of less lustrous slate coal, with flat 



* American Journal of Science. See also Goeppert, " Abhandlung uber Stein- 

 kohlen; " also a paper by tiie author, " On Fossils from Nova Scotia," C^unrt. Journ. 

 lieol. Soc. 18iG. 



t See paper of 184G, previously cited. 



