216 Dr. Mac Culloch on the Lignites 



by which it approximates to coal ; containing more or less bitumen 

 intermixed with the peculiar compound that constitutes the lig- 

 neous matter of wood which has partially passed from the vege- 

 table state to that of peat. In these cases also it appears that 

 the several kinds are found at different depths ; those most deeply 

 situated being at the same time the most highly bituminized. The 

 strata at Bovey, just quoted, offer examples of this nature, if they 

 are really examples ; and, at this place, different strata are found 

 separated by the loose matter which fill this valley ; the more 

 perfect lignites occupying the lowest positions. 



It is plain that this and similar cases present examples of sub- 

 merged forests, which, no less from the nature and depth of the 

 alluvia under which they lie, than from their having undergone 

 that change to bituminization which does not occur in the sub- 

 merged wood of peat-bogs, are probably of a much higher anti- 

 quity than any of those deposites with which we are acquainted ; 

 or, at least, older than any of those peat- bogs which now occupy 

 the immediate surface. It is here, undoubtedly, assumed, that 

 antiquity alone, or time, superadded to the causes which convert 

 wood into peat, is sufficient to convert it into the same bituminous 

 compound that forms lignite ; but it is possible that, independently 

 of this, certain chemical agencies, of which the nature is not known 

 to us, may have aided in the operation. 



The succession of strata at Bovey, or in other situations where 

 similar phenomena occur, might lead to the opinion that succes- 

 sive forests had grown and been submerged in these particular 

 spots ; and, if it be true that time alone is the agent which in 

 these places tends to render the lignites perfect, this conjecture 

 would receive confirmation from the more perfectly-bituminized 

 nature of the deeper strata. But respecting this, it is impossible 

 to come to any decision ; as successive strata of wood and alluvial 

 matter might have been deposited by the transportation of both from 

 a distant point ; while, if something more than time alone is re- 

 quired for the perfection of lignite, these cases might have pro- 

 duced an effect on the deeper strata from which the more supers 

 ficial have been comparatively exempted. 



