356 PEAT. 



containing less hydrogen, and therefore verging nearer 

 to plumbago, the nearest substance to metallic carbon 

 that we know. Nature herself almost gives us this 

 series, including plumbago, from one original substance, 

 under the presence of trap: as I long ago showed that 

 this last must be an oxyde of carbon, from the facts 

 which attend its production from cast iron. And it 

 must now be plain, that the varieties in this series de- 

 pend on the varying proportions of hydrogen and car- 

 bon, just as in that from naphtha to asphaltum ; render- 

 ing the chemical theory of the constitution of coal, no 

 less than of these substances, perfectly consistent and 

 simple. The other differences between the two sets 

 are chiefly of a mechanical nature, belonging to the 

 mineral, not the chemical characters ; and if x especially, 

 asphaltum differs from the nearest coal, it is because it 

 has been produced from a liquid bitumen; having thus 

 a relation to coal, similar to that which the aqueous 

 bistre has to ordinary peat. In what manner Nature 

 has produced these varieties, it is not so easy to con- 

 jecture, though the basis is plain ; yet, it is certain that 

 a resinous plant, such as a fir for example, would pro- 

 duce a fatter coal than an oak, because the resin itself 

 is converted into bitumen. 



On the geological connexions of Peat, Lignite, 8$ Coal. 



Using the term in its mineral sense, lignite presents 

 no difficulty ; being derived from submerged wood or 

 forest peat. I have shown that all the deposits of this 

 substance are of a far higher antiquity than any peat; 

 and thus the degrees of bituminization are accounted 

 for, even up to brown coal and jet, though there may 

 be other causes also, still unknown to us. And if there 

 are lignites produced from any other kind of peat, I 

 am not aware that they have yet been discovered. 



