1870.] 



DAWSON — SPORE CASES IN COAL. 



377 



in the prostrate and erect trunks contained in the beds associated 

 with coal, must have been highly carbonaceous and extremely 

 enduring and impermeable to water. In short, if instead of 

 ''spore-cases," we read "epidermal tissues in general, including 

 spore-cases," all that Huxley has aflBrmed will be strictly and lit- 

 erally true, and in accordance with the chemical composition, mi 

 croscopical 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, 

 published in 1859. 



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

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

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

 charcoal; its fallen leaves (and fruits), with remains of herba- 

 ceous 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 suitableness of this kind of tissue for the produc- 

 tion of the purer compact coals. It is also probable that the 

 comparative impermeability of the bark to mineral infiltration, is 

 of no importance in this respect, enabling this material to remain 

 unaffected by causes which have filled those layers consisting of 

 herbaceous materials and decayed wood with pyrites and other 

 mineral substances." 





Fig. 4. 



Fig. 3. 





Fig. ].— Part of a slice of shale from Kettle Point, shewing two spore- 

 cases and remains of spores; 70 diameters. 



Fig. 2 and 3.— Spore-cases from the same as opaque objects x 70. 



Fig. 4.— Part of a sHce of Ohio coal, showing at one side a large spore- 

 case and numerous spores x 70. 



