140 THE GEOLOGICAL HISTORY OF PLANTS. 



exceptional fact to all coals, and placed this supposed 

 origin of coal in a light so brilliant and attractive that he 

 has been followed by many recent writers. The fact is, 

 as stated in " Acadian Geology," that trunks of SigillaricB 

 and similar trees constitute a great part of the denser 

 portion of the coal, and that the cortical tissues of these 

 rather than the wood remain as coal. But cortical or 

 epidermal tissues in general, whether those of spore-cases 

 or other parts of plants, are those which from their re- 

 sistance to water-soakage and to decay, and from their 

 highly carbonaceous character, are best suited to the pro- 

 duction of coal. In point of fact, spore-cases, though 

 often abundantly present, constitute only an infinitesimal 

 part of the matter of the great coal-beds. In an article 

 in " The American Journal of Science," which appeared 

 shortly after that above referred to, I endeavoured to cor- 

 rect this error, though apparently without effect in so far 

 as the majority of British geological writers are con- 

 cerned. From this article I have taken with little change 

 the following passages, as it is of importance in theoretical 

 geology that such mistakes, involving .as they do the 

 whole theory of coal accumulation, should not continue 

 to pass current. The early part of the paper is occupied 

 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 re- 

 sembling them, may be found in most coals; but it 

 is most likely that their occurrence is .accidental rather 

 than essential to coal accumulation, and that they are 

 more likely to have been abundant in shales and cannel 

 coals, deposited in ponds or in shallow waters in the vi- 

 cinity of lycopodiaceous forests, than in the swampy 

 or peaty deposits which constitute the ordinary coals. 

 It is to be observed, however, that the conspicuous ap- 

 pearance which these bodies, and also the strips and 

 fragments of epidermal tissue, which resemble them in 



