Dr. Mac Culloch on the Lignites. 221 



nature will hereafter be adduced to shew that this result cannot 

 be produced by the action of fire alone. 



In other cases, where the lignites of this division are found in 

 the same connexion, they are not contained in beds of tufa, but 

 in veins or chasms in the solid rock. The specimen, already re- 

 ferred to in Mull, is a remarkable example of this nature, as well 

 for the erect position of the specimen, as for the magnitude of the 

 fragment. In these cases, also, it has been carelessly said, that 

 the lignite was contained in the solid trap ; but in all the instances 

 which I have observed, it has occurred in a tufaceous conglomerate 

 which filled the remainder of the vein, or cavity, in which it was 

 found. And thus, I have little doubt, it will be found to have 

 occurred in all parallel cases ; in which, either from superficial 

 observation, or from the tendency by which every one is influenced 

 to overlook circumstances which disagree with a favourite hypo- 

 thesis, this important circumstance has been neglected. Under 

 whatever state of things such conglomerated or tufaceous cavities 

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

 tufaceous beds, from a degree of heat capable of fusing them, and, 

 in the same manner, the accompanying lignites have escaped total 

 destruction, if indeed destruction be a necessary consequence of 

 that state of things. 



The last position, in which I have observed lignite in the trap- 

 rocks, appears rather more difficult to explain on the hypothesis 

 of their igneous origin ; but, when strictly examined, it does not 

 seem by any means inexplicable. 



In these cases, the substance in question appears absolutely im- 

 bedded in the solid rock ; and it must certainly be admitted, that, 

 were this truly the case, it would present a considerable difficulty 

 to the theory which supposes all the crystalline traps to have been 

 consolidated slowly from a state of igneous fluidity. But when 

 strictly examined, in all the instances of this nature which I have 

 witnessed, it will be found that the substances in the immediate 

 vicinity of the specimens are not crystalline, are neither green- 

 stone nor basalt. In general, some fragment or stratum of shale 

 will be found to surround the specimen, or else it is entangled 



Vol. XX, R * 



