Prof. Rogers on the Probable Origin of Petroleum. 357 



ceous strata, except where these are fissured, as they are apt to he on 

 the anticUnal flexures, serves to hold down the elastic or volatile pro- 

 ducts, as evinced by their often sudden and copious effusion when the 

 mud-rocks are perforated, and the more porous grits are entered by the 

 boring tool. Recent experience, however, has shown that the gas and 

 petroleum are lodged plentifully in the more superficial strata of the 

 coal-measures, throughout a wide area bordering the Alleghany River, 

 large quantities being evolved from borings from 100 to 200 feet in 

 depth ; whereas the wells affording the steadiest supplies of richest 

 brine are usually between 500 and 1,000 feet deep. The most success- 

 ful holes hitherto sunk, especially in quest of the oil, do not exceed 200 

 feet of depth, while many of the borings begin to bring it up copiously 

 before they are down 100 feet. The proportion of petroleum to water 

 procured from these borings varies, of course, with the locality, and 

 especially the strata penetrated ; but it is safe to say that it generally 

 amounts to 1-lOth part. The commercial value of this product will be 

 appreciated, when it is understood that many of the " borings" yield 

 as much as 500 gallons of the oil alone, per day, its present market 

 price being about 65 cents, or 2s. 8d. sterling, per gallon. With these 

 facts it is easy to account for the eagerness at present manifested by 

 the people of Western Pennsylvania to secure the best oil-producing 

 localities. Indeed, the " petroleum fever," though less widely diffused, 

 has recently reached almost as high a pitch as ever did the " gold fever" 

 in its intensest days. 



Advancing to the third subdivision of his subject — the origin of the 

 petroleum and gas — the author of the paper undertook to show that the 

 presence of these inflammable products in the strata is but one phase of . 

 a very widely diffused metamorphism, by subterranean heat, which aU 

 the palseozoic formations, the coal-measures included, have undergone. 

 First, he called attention to the fact, that the coal strata, especially the 

 beds of coal themselves, are, of all known sedimentary deposits, those 

 which disclose best the various degrees or shades of metamorphic action ; 

 the coal, from its superior susceptibility to permanent change of texture 

 and chemical decomposition, with extrication of its more volatile ingre- 

 dients under a moderate heat, being, indeed, a sort of very sensitive 

 natural register tJiermo'nieter, recording the different grades of tem- 

 perature to which the strata have been exposed. Many of the larger 

 coal basins of Europe display more or fewer of tlieso lesser shades of 

 metamorphism in their coal, the basin of Belgium, and the still grander 

 one of South Wales, showing them in regular gradations through a 

 wider scale from non-hydrogenous anthracites to the fat, inflammable, 

 so-called bituminous varieties ; but no coal tract upon the globe dis- 



