222 Dr. Mac Culloch on the Lignites. 



among earthy substances differing from the including rock, and 

 consisting of portions of those strata which have, perhaps, by their 

 fusion, produced the principal mass, or which have been entangled 

 in it during its state of fluidity. The unaltered or slightly modi- 

 fied state of those substances suffice to prove, that in the par- 

 ticular place in question, the heat has not been sufficient to effect 

 the fusion and ultimate change of the original strata into crystal- 

 line trap, so as to produce those final consequences which might 

 be expected to have resulted from its having been entangled in a 

 fluid mass. 



Even, however, if lignite should be found surrounded by a 

 crystalline trap, or a basalt, it does not by any means follow that 

 the rock has not been in a state of fusion, or at least softness, 

 sufficient to enable its parts to assume a crystalline character. In 

 the siliceous schist which lies beneath basalt, the character of the 

 rock is sufficient to prove that it has been, in a softened state, 

 a state capable of producing that difference which is found to exist 

 between it and the original substance from which it was derived. 

 Yet, in such cases, shells are often found entangled in the mass ; 

 and though sometimes deformed by pressure, as the lignites them- 

 selves are, still retaining their integrity, and a considerable por- 

 tion of their original characters. Neither is the bituminous mat- 

 ter which is contained in strata of this nature, dissipated in such 

 cases, since both the limestones and the shales found in these 

 situations are often highly bituminous. Charcoal also, it is well 

 known, is indestructible by heat, when protected from the access 

 of air : and though altered in its chemical character by the loss 

 of its hydrogen, in some such cases, it still retains its form. It is 

 therefore perfectly conceivable, that, where charcoal could retain 

 its form, and bitumen exist, the lignites might remain surrounded 

 by a mass of fluid trap till it had cooled, in all the situations in 

 which it has been found among these rocks ; as coal also unques- 

 tionably does, where the ordinary coal strata are found in similar 

 circumstances. 



Whether this particular case has or has not occurred in trap, it 

 is known to have happened with lava, so that the difficulty is 



