STATEMENT OF THE STRUCTURAL THEORY 557 



able to "anticlinal theory/^ in order to explain definitely the relations 

 which accumulations of oil and gas hold to geology within certain limita- 

 tions^ even where no definite anticline or syncline exists. The structural 

 theory, as understood by the writer of this paper, is as follows : 



Through some means, by organic or inorganic agency or agencies, the 

 petroleum and gas have come into or been generated in the porous forma- 

 tions in which they are found. The deposits may have originated through 

 the decomposition of plant or animal remains on an ancient sea-bottom, 

 as the adherents of the organic theory claim ; or, they may be the product 

 of chemical action deep in the earth, as the adherents of the inorganic 

 theory claim ; or, certain petroleum deposits may be of organic and certain 

 other deposits of inorganic origin. Whichever theory is true, the oil, gas, 

 and water in the formations (assumed to have been approximately hori- 

 zontal at the time the substances entered them) were at first widely dif- 

 fused in the porous formations or contiguous strata. Theylxave re- 

 mained in their diffused condition to the present time in many parts of 

 the world, where only small quantities of oil and gas, too slight for profit- 

 able development, have been found, and where the dip of the rocks is 

 very slight. 



T\Tiere the beds have been folded, however, as in the greater part of the 

 Appalachian region and in most oil fields throughout the world, the oil, 

 gas, and salt water have been enabled to separate out according to their 

 relative specific gravities. This separation and concentration may have 

 been assisted by rock pressure, diastrophism, hydraulic pressure, seepage, 

 capillarity, molecular attraction, internal heat, and other causes; but 

 whatever causes prevailed for the movement of the oil, gas, and water, 

 the law of gravitation, being ever operative, must be considered of most 

 importance in determining their arrangement; hence the accumulation 

 was in the order of the densities of the substances. 



The structural theory agrees with the anticlinal theorv, of which it is 

 an outgrowth, in acknowledging that on a stated anticlinal, monoclinal, 

 or quaquayersal structure gas lies nearest the top, oil lower down, and 

 still lower is the salt water, when present. Whether the pools occur at 

 the top of the anticlines, lower on their slopes, or in the synclines, is deter- 

 mined by factors of secondary importance. 



'• History OF THE STRUCTURAL Classification 



What is known as the "stnictural theory" or structural classification is 

 a natural =0'Utg^rowth of the "anticlinal theory.'' The structural classi- 

 fication was first proposed by the present writer in a paper before the 



