356 The Philosophical Society of Glasgow. 



tains which emit, along with their waters, a very sensible quantity of 

 the rock-oil, in a sufficiency admitting of its being collected by skim- 

 ming or sopping up with cloths, are usually termed " oil springs ;" 

 nevertheless, nearly all of the far more numerous class commonly 

 called " burning springs," from their evolving the gaseous carburetted 

 hydrogen, reveal appreciable traces of the petroleum in the form of a 

 thin oily scum. Indeed, all the phenomena naturally and artificially 

 presented, prove abundantly that both classes of the hydro-carbon com- 

 pounds, the liquid and the gaseous, exist almost universally diffused in 

 the coal strata throughout the district above specified. But these 

 inflammable products are by no means evenly distributed. The geolo- 

 gical conditions connected with their greater or less copiousness — the 

 second main topic of the paper — are therefore next to be noticed. 

 Superficially, the gas- and oil-emitting springs, within the coal-field, are 

 chiefly found upon the antichnal flexures of the strata, and those ex- 

 ternal to the coal formation, in proximity to the outcrops of the black 

 bituminous slate subjacent to that formation, in localities where the 

 gas-evolving slate lies at the moderate depth of a few hundred feet 

 below the soil. 



The petroleum, or oil, appears to be in its greatest abundance in that 

 part of the coal-field of Western Pennsylvania which is limited by the 

 Alleghany Eiver on the east, and which embraces its western and 

 north-western tributaries north of the Clarion Eiver; but the district 

 promising a profitable product in it, extends to Mercer and Butler 

 counties, Pennsylvania, and even into some of the eastern counties of the 

 State of Ohio. Perhaps the tract where it is most accessible and 

 abundant is the valley of Oil Creek, so named from the existence there 

 of several natural oil springs. French Creek also exhibits indications of 

 the material in various places, while symptoms of it appear on the 

 Brokenstraw and various other upper feeders of the Alleghany, as far 

 as the Oil Creek or the Olean Creek of New York. 



Stratigraphically, the gas and the petroleum seem chiefly to accom- 

 pany the briny waters copiously diffused in the pores of the loosely 

 aggregated sandstones, but not imbuing as abundantly the more water- 

 tight shales and slates. A long experience has taught the sinkers of the 

 Artesian wells this contrast, so that it is now a matter of common noto- 

 riety throughout Western Pennsylvania and Western Virginia, Eastern 

 Ohio and Eastern Kentucky — the districts where the strata are perfor- 

 ated by these borings — that the inflammable products gush up only upon 

 the chisel's penetrating certain beds, especially certain thick pale sand- 

 stones of open texture, most abundant near the bottom of the lower 

 coal-measures. It would seem that the imperviousness of the argilla- 



