LIGNITES. 327 



and structure justifying the name, either of coal or of 

 lignite, as it may happen, while there is an identity or 

 resemblance in the chemical characters of both. 



The last geological situation in which the lignites 

 occur, is among the traps ; while they have been in- 

 correctly examined and described, as the facts have 

 been also misapplied, to support an hypothesis re- 

 specting these rocks. These have been called bitu- 

 ininized wood, and basaltic coal ; but I have already 

 given reasons for preferring that of basaltic lignites. 

 They sometimes retain, in a considerable degree, the 

 chemical nature of vegetable matter, or peat ; giving 

 out, on distillation, the particular volatile products 

 by which the other lignites are distinguished, while, 

 at others, they are converted into perfect coal. It is 

 in the former case chiefly, that they retain the vege- 

 table form and structure ; but they do not always en- 

 tirely lose it, even when they have become coal. 

 They sometimes occur in insulated fragments, or as 

 portions of trees ; at others, they are accumulated in 

 a particular place, so as to form small irregular depo- 

 sits ; in which cases the vegetable form disappears, 

 or becomes very obscure. When these are of consi- 

 derable size, they often put on the rocky character 

 with the chemical nature of coal, and are sometimes 

 partially wrought for ceconomical uses. In one in- 

 stance, in Mall, the specimen of lignite is a large por- 

 tion of the trunk of a tree ; the % vegetable texture 

 being perfectly distinct, but the substance so tender 

 as to fall into powder under a very slight force, like 

 some of the specimens from Cologne. 



It is necessary to state accurately the connexion 

 between the trap rocks and the accompanying lignites, 

 because this has frequently been used as an argument 

 against the igneous origin of the former, on the one 

 hand, while, by another party, it has, under equal mis- 



