ORIGIN OF PETROLEUM AND NATURAL GAS 713 



torical review of tlieories that during the past fifty years chemists and 

 geologists have been actively endeavoring to solve the problem of origin 

 of these natural liquids and gases, but that to date most of the hypotheses 

 have proved to be merely speculations. He cites the work of Arnold, 

 Anderson, and Johnson on the McKittrick- Sunset oil region of California 

 as being exceptional in this country, in that they seem to have discovered 

 in that case the actual origin of the petroleum, the same being from dia- 

 tomaceous and foraminiferal material deposited in beds of marine shale. 



One is safe in assuming that the origin of petroleum in any one field 

 may be entirely different from that in some other portion of the globe; 

 but we do not take so much latitude in viewing the origin of other hydro- 

 carbon compounds — as, for instance, coal. It is a generally accepted fact 

 that coal is of plant origin the world over, yet it is also a complex com- 

 bination of varied chemical nature, having gone through various changes 

 in its transformation from lignite to anthracite. In the metamorphism 

 of coal it has thrown off its volatile hydro-carbon compounds to be dif- 

 fused through the adjacent rock strata until the percentage of fixed 

 carbon in the remaining material is at its maximum. But coal was de- 

 posited originally under special physiographic conditions, unquestionably 

 being the accumulated debris from plants that grew in swampy grounds, 

 and were buried in shallow water, where they were subject to more or 

 less immediate transformation and loss of volatile materials. But other 

 plant remains drifted out to deeper waters or into the sea, probably in a 

 colloidal state and interlocked with clay, so that they finally rested on the 

 floor of the water body as carbonaceous deposits. 



A. V. Bleininger and others have shown that a solution of water con- 

 taining the organic substances from the distillation of plants, such as 

 straw, will produce a colloid with clay so that it will remain in suspen- 

 sion ; but the clay will again be thrown down on contact with salt water. 

 This has unquestionably been an important factor in the deposition of 

 clay deposits around the margin of bodies of marine and brackish water — 

 as, for instance, the clays of the coastal plain deposits, which represent 

 the marginal sediments of formations not yet entirely raised above the 

 ocean floor. There is a deposit of natural tarlike coal in the San Juan 

 Basin near Seven Lakes, and also north of San Mateo, Kew Mexico, which 

 is colloidal in nature. If blunged with water, it will remain in suspen- 

 sion as a black fluid until the water is evaporated or until otherwise pre- 

 cipitated. This is cited as an instance in nature where carbonaceous 

 material is colloidal, not having had its nature changed by contact with 

 other compounds. Collodial matter from decaying leaves is a familiar 

 coloring agent in concentrated water pools, and unquestionably an enor- 



