LIGNITES. 329 



chasms in the solid rock; as is the fact respecting the 

 specimen in Mull, remarkable for the erect position, 

 as for the magnitude of the fragment. If, in these 

 instances also, the lignite has been said to be con- 

 tained in the solid trap, this is another bad observa- 

 tion ; as the vein is always filled by a tufaceous con- 

 glomerate, wherever these cases have occurred to my- 

 self. And this, I doubt not, is the fact in all the re- 

 corded cases ; where, either from superficial examina- 

 tion, or ignorance, or from that tendency to overlook 

 circumstances which disagree with a favourite hypo- 

 thesis, this important circumstance has been neglected. 

 In whatever manner such tufaceous cavities have been 

 formed, it is evident that they have been exempt, like 

 tufaceous beds, from a degree of heat capable of fusirig 

 them ; and thus have the accompanying lignites es- 

 caped destruction ; if indeed destruction be that ne- 

 cessary consequence which has been supposed. Nor 

 is there any difficulty in seeing how a fused rock 

 should have entangled a portion of a conglomerate in 

 this very manner ; as such a vein also, formed at first 

 in an open cavity, might be sealed up by fresh erup- 

 tions of fused matter. 



In the last position in which I have found a lignite 

 in trap, it has appeared to be imbedded in the solid 

 rock ; which, were this truly the case, might present a 

 difficulty as to the theory of this family. But when 

 strictly examined, it will be found that the substances 

 in the immediate vicinity of the specimen are not cry- 

 stalline, but that some portion of shale surrounds it, 

 or that it lies among earthy fragments of those strata 

 which have, by their partial fusion, produced the 

 principal mass, as other portions have been entangled 

 in it during its state of fluidity. And the unaltered, 

 or slightly modified state of those substances, proves 

 that the heat has not been sufficient to effect the en- 



