188 Prof. BiscLot" on (he Itiflammable Gases of 



condition of these erupted masses, it is just as certain and ne- 

 cessary a consequence, that at that time dry processes of dis- 

 tillation must have gone forward on a very large scale. In 

 those periods, therefore, inflammable gases, which were of the 

 same composition as our artificially-prepared coal-gas, were 

 evolved from the earth, and diffused through the atmosphere. 

 If these exhalations continued as the Plutonic masses became 

 hardened, and consequently became fissured, these gases would 

 penetrate through these fissures ; and they must then have 

 been decomposed in th& same manner as we artificially decom- 

 pose carburetted hydrogen, when we conduct it through a red 

 hot tube. The favourable circumstances for this occurxence 

 existed, more especially, when Plutonic masses covered coal- 

 strata. I have, in the course of my investigations, several 

 times decomposed inflammable pit-gas, during its passage 

 through a red-hot porcelain tube, and I was surprised by the 

 extremely beautiful metallic lustre of the coal deposited in the 

 tube. It bore a remarkable resemblance to graphite. The 

 thought naturally occurred, if many graphites, which occur in 

 veins and strings in granite, gneiss, porphyTy, &c., have not a 

 similar origin. 



Empyreumatic oils, the liquid products of dry distillation, 

 may partly be decomposed by the further action of the hot 

 plutonic masses, and partly distributed through the neighbour- 

 ing strata. It is a probable supposition, that many of the 

 mineral oils which at present flow sparingly, or proceed ais it 

 were from water, have an origin of this kind. That a portion 

 of these products of distillation even entered the Plutonic 

 masses themselves, seems to be proved by the bitumen found 

 by Knox in basaltic rocks. In this respect, it is particularly 

 worthy of observation, that the wacke of Ltmarsoall, on the 

 coast of Disco Island, which occurs associated with basaltic 

 tuffa and brown coal, contains no less than 19.4 per cent, of 

 bitumen. 



It cannot surprise us if we find bitumen also in the Plu- 

 tonic masses which have burst through the transition-rocks, 

 for the latter contain organic remains which would be decom- 

 posed l)y contact with the former. Some yeai's ago, wliile ig- 



