1897.1 NATURE AND ORIGIN OF PETROLEUM. 103 



ON THE NATURE AND ORIGIN OF PETROLEUM., 



BY S, F. PECKHAM. 



{Read Fehruary 5, 1S97.) 



Concerning the nature and origin of petroleum, I think we may- 

 say, after forty years of study and discussion, that we have not yet 

 learned its alphabet with certainty. As petroleum is one of the 

 forms of bitumen, in the line from natural gas to asphaltum, I do 

 not think it has an origin independently of the other forms, and I 

 shall therefore discuss the origin of bitumens together, as including 

 petroleum. 



Since I indulged my '' Retrospect," ^ two years ago last summer, 

 two works have appeared which notably discuss the origin of bitu- 

 mens, and I have in the course of my investigation of asphaltums 

 and California petroleum, during the same period, noted a number 

 of facts that bear upon the solution of this problem. In closing 

 the ''Retrospect" that I wrote while in southern California, and 

 which was in part a reply to criticisms made by our friend. Prof. 

 Orton, I remarked that I did not consider it necessary to represent 

 in terms of Fahrenheit's thermometer the temperature at which any 

 given specimen of petroleum was produced nor to produce the coke 

 that resulted from the distillation. On reading over the paper since 

 it appeared in print, I have feared that perhaps it had impressed 

 some readers as dogmatic or as begging the question. It is some- 

 times difficult to express deep convictions with enthusiasm and not 

 at the same time appear dogmatic. The Devonian shales, where 

 they outcrop at Erie, Pa., have not apparently been subjected to 

 alteration ] yet, a number of wells drilled into them, have yielded 

 an oil somewhat dense and of a bright green color. I believe that 

 that oil was a product of distillation at a low temperature and under 

 comparatively little pressure, the heat required being generated 

 spontaneously within the shales. In Ventura county, southern 

 California, metamorphism, that has resulted from sOme sort of 

 action that has generated heat, has left masses of originally highly 

 bituminous shale not only void of volatile matter but void of 

 carbon as well. The expulsion of carbon is complete. The tem- 

 perature must have been adequate, be the source of heat whatever 



^ Am. Jour. Science (3), xlviii, 389 ; Nov., 1894. 



