Dr. Mac Culloch on the Lignites. 229 



portion of both asphaltum and bistre. Thus it may be inferred, 

 as well as by a more operose and perfect analysis, that the lignites 

 hold an intermediate state between wood, or peat, and coal, or 

 bitumen ; and the degree in which they approach to perfect bitu- 

 minization may be appreciated in a manner sufficiently accurate 

 for general purposes, by the relative power of their volatile oils 

 in dissolving bistre or naphtha. 



This view of the mixed, or intermediate nature of the lignites, 

 is confirmed by Mr. Hatchett's experiments on the submerged 

 resinous matter found with the lignite of Bovey, which appears, 

 iLi a similar manner, to be either a compound or a mixture of 

 vegetable resin and asphaltum, and of which other specimens, 

 found in different places, have exhibited characters intermediate 

 between resin and amber. 



In a former essay on peat, published elsewhere, it was argued 

 that the process of bituminization was a result of the action of 

 water, not of fire or heat, and that time alone seemed requisite to 

 convert peat into bituminous lignite, and ultimately into jet, if 

 not finally into coal. Not to repeat this, I shall therefore here 

 content myself with shewing that the presence of bituminized 

 lignite, or even of coal, in the trap rocks, is no proof of the effect 

 of heat in bituminizing the vegetable fibre ; but that, in this case 

 also, the charge is probably alike owing to the action of water. 



It was shewn that in many of the cases in which bituminous 

 lignite was entangled in the rocks of the trap family, it was ac- 

 tually contained in earthy, tufaceous, or conglomerated matters, 

 which had undergone the action of water. It is easy to conceive 

 that in such cases it had been bituminized before the deposition 

 of the solid trap, having been buried in the earthy strata invaded 

 by it. While, therefore, this circumstance offers no argument 

 against the igneous origin of the trap rocks, neither does it prove 

 that the action of heat is required to convert vegetable matters 

 into bitumen. By direct experiment, indeed, the power of fire to 

 produce this consequence is disproved, as its effects on the ve- 

 getable fibre, whether under pressure or not, is to convert it into 

 bistre, and not into asphaltum or coal. Yet it must be admitted 



