Dr. Mac Culloch on the Lignites. 223 



completely removed. In Italy, trees have been found entangled 

 in perfect lavas, having burnt out only in those superficial parts 

 where there was access of air ; and, in the Isle of Bourbon, the 

 trunks of palms have thus also been observed wrapped in lava, so 

 that the stony matter had penetrated the fissures formed in them 

 by shrinking, and assumed the shapes of these. 



It is thus also not difficult to conjecture why, in certain circum- 

 stances, the lignites of trap should preserve their character in a 

 considerable degree of perfection, retaining a great proportion of 

 the original structure and chemical nature of the vegetable ; while, 

 in other cases, they should have been entirely converted into coal. 

 In the lignites of Meissner, the woody kinds are actually changed 

 into coal where they are in contact with basalt. But this part of 

 the chemical nature of the lignites will be examined immediately, 

 when some direct experiments, explanatory of this circumstance, 

 will be related. It is sufficient now, barely to say, that the de- 

 gree of pressure under which they must have existed, may have 

 been sometimes such as to prevent the entire dissipation of the 

 volatile matters contained in them, and that the degree of heat 

 and of pressure, having been present in proportions inferior to 

 those which were required for the fusion of the mass into shape- 

 less coal, the vegetable structure has been preserved, exactly as it 

 would have been in charcoal, under similar circumstances ; while 

 the form has perhaps also, in many cases, remained more entire, 

 in consequence of the protection afforded by unfused fragments 

 of strata, or by the earthy original matters entangled together 

 with it in the trap. 



If these remarks on the association of the lignites with the trap 

 are just, it must now be obvious that this circumstance presents 

 no valid objection to the igneous origin of trap. But that it does 

 not prove coal to have originated in the action of fire on vegetable 

 matter, is a separate question, which will be examined when the 

 chemical nature of the lignites is considered. In the mean time 

 it will not be uninteresting to inquire under what circumstances 

 the trap rocks can have entangled the remains of trees or other 

 vegetable matters. 



R 2 



