THE NONMETALLIC MINERALS. 431 



exhaustive consideration of the occurrence of petroleum, natural gas, 

 and asphalt in Kentucky, 1 gives the following precise summary: 



1. Petroleum is derived from organic matter. 



2. Petroleum of the Pennsylvania type is derived from the organic matter of bitumi- 



nous shales, and is probably of vegetable origin. 



3. Petroleum of the Canadian type is derived from limestones, and is probably of 



animal origin. 



4. Petroleum has been produced at normal rock temperatures (in American fields), 



and is not a production of destructive distillation of bituminous shales. ' 



5. The stock of petroleum in the rocks is already practically complete. 



Hofer 2 regards petroleum as of animal origin only, and advances the 

 arguments given below in support of his theory: 



1. Oil is found in strata containing animal, but little or no plant remains. This is 



the case in the Carpathians, and in the limestone examined in Canada and the 

 United States by Sterry Hunt. 



2. The shales from which oil and paraffin were obtained in the Liassic oil shales of 



Swabia and of Steirdorf, in Styria, contained animal, but no vegetable remains. 

 Other shales, as, for instance, the copper shales of Mansfield, where the bitumen 

 amounts to 22 per cent, are rich in animal remains and practically free from 

 vegetable remains. 



3. Rocks which are rich in vegetable remains are generally not bituminous. 



4. Substances resembling petroleum are produced by the decomposition of animal 



remains. 3 



5. Fraas observed exudations of petroleum from a coral reef on the .shores of the 



Red Sea, where it could be only of animal origin. 



The relationship which exists between the solid or viscous bitumen 

 and the fluidal petroleum have not in all cases been satisfactorily 

 worked out, though Peckham has shown 4 that in California at least 

 there are almost infinite gradations from one extreme to the other. In 

 Ventura County, for instance, the petroleum is held, primarily, in strata 

 of shale, from which it issues as petroleum or maltha, accordingly as 

 the shales have been brought into contact with the atmosphere, the 

 asphaltum being produced by a still further exposure to the atmosphere 

 after the bitumen has reached the surface. This relationship between 

 the more fluidal and viscous varieties is shown in tig. 18, copied from 

 Professor Peckhaur s paper above referred to, and which represents a 

 section across a portion of Sulphur Mountain between the Hayward 

 Petroleum Company's tunnels in Wheeler Canyon, and the Big Spring 

 Plateau on the Ojai ranch. In this section it will be noted that the 

 mountain is formed of a synclinal fold of shale, the strata dipping 



'Report on the Occurrence of Petroleum, etc., in Western Kentucky. Geological 

 Survey of Kentucky, John R. Proctor, director, 1891. 

 2 As quoted by Redwood, I, p. 238. 



3 Dr. Engler, as quoted by Redwood, obtained by distillation of menhaden oil, 

 among other products, a substance remarkably like petroleum, and a lighting oil 

 indistinguishable from commercial kerosene. 



4 See Report of the Tenth Census, p. 68. 



