the Prussian Coal-Mines. 187 



of the earth plays an important part in this process, if coal 

 strata reach to depths where a distinctly increased tempera- 

 ture prevails, is not to be doubted. Nay, it is known that the 

 evolution of marsh-gas goes on better in the warm season of 

 the year than in the cold, and that it is by these exhalations 

 under the tropics that the air is infected in such a terrible 

 manner. 



I was anxious to have opportunities of examining all exha- 

 lations of inflammable gases, siich as those of Baku on the Cas- 

 pian Sea, to ascertain if they also c(Jntain no vapours which 

 are absorbable by sulphurous acid, and no carbonic acid gas. 

 These, however, are pia desiderata. The examination of the 

 etei'nal fire of Baku, as it is called, would be of especial inte- 

 rest, as tliese evolutions of gas undoubtedly stand in connec- 

 tion with the springs of mineral-oil. If the mineral-oil, as has 

 been long supposed, be a product of subterranean distillation 

 from coal, the inflammable gases at Baku are most probably 

 the result of the same process. In this case, however, these 

 gases would contain the vapom-s which are condensed by sul- 

 phuric acid, and carbonic oxide gas. . Without anticipating the 

 result of such an investigation, I would remark, that many rea- 

 sons might be adduced against that h>^othesis, as I shall, on 

 another occasion, endeavour to prove from observations and 

 experiments. The assumption is, at least, extremely impro- 

 bable, that such subterranean processes of distillation are still 

 going on. It may be, then, that the central heat has, by vol- 

 canic action, reached the region of the secondary strata Avhere 

 there are very numerous organic remains. If a volcano were 

 to break out anywhere in such strata, or if lavas or whole hills 

 of melted matter were to rise through beds of coal, it cannot 

 for a moment be doubted, that the same products would make 

 their appearance as in our gas-works. 



These considerations lead us of themselves back to those 

 epochs, when Plutonic masses burst through all formations 

 from greywacke to the tertiary deposits, and came in contact 

 in all ways with organic remains. If the changes which com- 

 mon and brown coal have undergone in the vicinity of Plu- 

 tonic masses, and of which you have so fully treated in your 

 " Basall-Oebilde," are just so many proofs of the fiery liquid 



