94 On Spore-cases in Coals. 



mulation, and that they are more likely to have been abundant in 

 shales and cannel coals, deposited in ponds or in shallow waters in 

 the vicinity of Lycopodiaceous forests, than in the swampy or peaty 

 deposits which constitute the ordinary coals. It is to be observed, 

 however, that the conspicuous appearance which these bodies, and 

 also the strips and fragments of epidermal tissue, which resemble 

 them in texture, present in slices of coal, may incline an observer, 

 not having large experience in the examination of coals, to overrate 

 their importance, and this I think has been done by most micro- 

 scopists, especially those who have confined their attention to slices 

 prepared by the lapidary. One must also bear in mind the danger 

 arising from mistaking concretionary accumulations of bituminous 

 matter for sporangia. In sections of the bituminous shales accom- 

 panying the Devonian coal above mentioned, there are many rounded 

 yellow spots, which on examination prove to be the spaces in the 

 epidermis of Psilophyton through which the vessels passing to 

 the leaves were emitted. To these considerations I would add the 

 following, condensed from my paper above referred to, in which 

 the whole question of the origin of coal is fully discussed.* 



(1.) The mineral charcoal or " mother coal" is obviously woody 

 tissue and fibres of bark ; the structure of the varieties of which and 

 the plants to which it probably belongs, I have discussed in the paper 

 above mentioned. 



(2.) The coarser layers of coal show under the microscope a 

 confused mass of fragments of vegetable matter belonging to various 

 descriptions of plants, and including, but not usually largely, spo- 

 rangites. 



(3.) The more brilliant layers of the coal are seen, when sepa- 

 rated by thin laminae of clay, to have on their surfaces the markings 

 of Sigillarise and other trees, of which they evidently represent 

 flattened specimens, or rather the bark of such specimens. Under 

 the microscope, when their structures are preserved, these layers 

 show cortical tissues more abundantly than any others. 



(4.) Some thin layers of coal consist mainly of flattened layers 

 of leaves of Cordaites or Pychnophyllum. 



(5.) The Stigmaria underclays and the stumps of Sigillaria in 

 the coal roofs equally testify to the accumulation of coal by the 

 growth of successive forests, more especially of Sigillariae. There is 

 on the other hand no necessary connection of sporangite beds with 

 Stigmarian soils. Such beds are more likely to be accumulated 

 in water, and consequently to constitute bituminous shales and 

 cannels. 



(6.) Lepidodendron and its allies, to which the spore-cases in 

 question appear to belong, are evidently much less important to coal 

 accumulation than Sigillaria, which cannot be affirmed to have pro- 



* See also ' Acadian Geology,' 2nd edit., pp. 138, 461, 493. 



