On Spore-cases in Coals. 97 



general, including spore-cases," all that Huxley has affirmed will be 

 strictly and literally true, and in accordance with the chemical com- 

 position, microscopical characters, and mode of occurrence of coal. It 

 will also be in accordance with the following statement, which I 

 may be pardoned for quoting from my paper " On the Structures 

 in Coal," pubhshed in 1859 :— 



" A single trunk of Sigillaria, in an erect forest, presents an 

 epitome of a coal-seam. Its roots represent the Stigmaria under- 

 clay ; its bark the compact coal ; its woody axis, the mineral char- 

 coal ; its fallen leaves (and fruits), with remains of herbaceous plants 

 growing in its shade, mixed with a little earthy matter, the layers of 

 coarse coal. The condition of the durable outer bark of erect trees 

 concurs with the chemical theory of coal, in showing the especial 

 suitableness of this kind of tissue for the production of the purer 

 compact coals. It is also probable that the comparative impermeability 

 of the bark to mineral infiltration, is of importance in this respect, 

 enabling this material to remain unafiected by causes which have 

 filled those layers, consisting of herbaceous materials and decayed 

 wood, with pyrites and other mineral substances." — American 

 Journal of Science, No. 4, Vol. I. 



