Pbof. Rogers on the Probable Origin of Petroleum. 359 



In the districts south-east of the oil-producing tract these vola- 

 tile matters were not only set loose from the coal by the chemically 

 decomposing function of the compressed hot steam, but were dislodged 

 from the strata altogether by its well-known carrying agency; and 

 thence resulted the hard, compact, flinty anthracite, or the semi-an- 

 thracite or semi-bituminous coals, as the discharge was complete or less 

 or more imperfect ; while in the regions north-west of the inland fron- 

 tier of the Appalachian coal-field, where every feature in the geology 

 manifests a maximum of subterranean igneous force, this steaming 

 agency was less ; wherefore the coal there retains more nearly its 

 original full proportion of the volatile matters, and the including rocks 

 show a commensurately less amount of the native oil and gas. 



The contrast here sketched as to the impregnation and non-impreg- 

 nation of the rocks of the respective regions with the petroleum and 

 cai'buretted hydrogen gas, is not to be understood as absolute ; for the 

 gas or " fire damp " does exist to some extent in the anthracite coal- 

 measures, but with no traces of the petroleum ; whUe, on the other hand, 

 some gas and a little oil do imbue the strata of the western coal-fields 

 where the volatile matter in the coal attains its maximum. In the one 

 case the expulsion of the hydi-o-carbons was not entire, in the other the 

 decomposition of the coal had proceeded a certain length. 



Professor William Thomson exhibited his "Portable Atmospheric 

 Electrometer." 



Mr. Hunt reproduced some of the Cinephantic Colour Experiments 

 on an enlarged scale. 



The Shotts Iron Company exhibited a sample of their Bathgate Gas 

 Coal, with some of the Oils, Candles, &c., manufactured from the coal. 



