GG THE CARBONIFEROUS. 



with facts as to the occurrence of spores and spore-cases as partial 

 ingredients in coal. Its conclusions are as follows : — 



" It is not improbable that sporangites, or bodies resembling them, 

 may be found in most coals ; but the facts above stated indicate that 

 their occurrence is accidental rather than essential to coal accumula- 

 tion, 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 microscopists, 

 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 accompanying 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, con- 

 densed 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, 

 sporangites. 



" (3.) The more brilliant layers of the coal are seen, when separated 

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

 Sigillarice and other trees, of which they evidently represent flattened 

 specimens, or rather the bark of such specimens. Under the micro- 

 scope, 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 

 * See also Acadian Geology, 2d edit., pp. 13S, 401,493. 



