RESEARCHES UPON" THE CHEMICAL PROPERTIES OF GASES. 



225 



VII. ORIGIN OF NATURAL GAS AND PETROLEUM. 



Soon after the early discoveries of oil and gas in Pennsylvania, the geologists 

 proposed a hypothesis to account for the origin of these remarkable substances. 



Remains of the marine vegetation of the Devonian inland sea, as they were grad- 

 ually buried under the later accumulations of sediment and exposed to gentle heat 

 from below, underwent a slow process of destructive distillation. In this way, all 

 the varieties of petroleum and natural gas were produced. This view, adopted from 

 a purely geological standpoint, seemed so plausible that for a long period no other 

 was thought of. Mr. J. F. Carll, of the Second Geological Survey of Pennsylvania, 

 has discussed the hypothesis very exhaustively in his various official reports. If 

 this view is correct, oil and gas are probably stored products, and are not being con- 

 tinuously generated at the present time. 



Opposed to this view is the more strictly chemical hypothesis of Mendeleeff, who, 

 in 1876, expressed his belief that petroleum and gas are of igneous origin. 



On account of the high value assigned by astronomers for the mean density of 

 the earth as compared with that of the surface rocks, it follows that the heavy metals 

 are mainly accumulated at great depths where a temperature of fusion may be as- 

 sumed. Many of these metals combine readily with carbon to form carbides. Iron, 

 in form of a carbide, when exposed to steam at high temperatures, is rapidly oxidized, 

 the hydrogen of the water then combining with the carbon set free and producing 

 hydrocarbons. 



Citing experiments of Cloez, who produced mixtures of hydrocarbon oils by 

 the action of hydrocTiloric acid upon ferromanganese, Mendeleeif concluded that such 

 reactions have occurred at great depths below the earth's surface by the contact of 

 steam with incandescent metallic carbides. 



" During the upheaval of mountain ranges, crevices would be formed at the 

 peaks with openings upward, and at the foot of the mountains with openings down- 

 ward. Thus there was opportunity for the water to penetrate to great depths and for 

 the hydrocarbons to escape. The situation of naphtha at the foot of mountain chains 

 is the chief argument in my hypothesis " (Mendeleeff, Principles of Chemistry, 

 Yol. I, p. 365). 



According to this view, oil and gas are being continuously generated, for there is 

 no reason to suppose that the masses of metallic carbides in the earth's interior are 

 exhausted ; such, in fact, seems to be Mendeleeff 's view. 



