714 J. II. GAKDNER THE MID-CONTINENT OIL FIELDS 



mous amount of h3^dro-carbon compounds have in this manner found 

 their way in the course of geologic time to areas of deposition. Imagine 

 what an enormous area was covered by the deposit of carbon -bearing ma- 

 terial that formed the famous Pittsburgh coal bed. Waters drained from 

 such a region at the time the plants were undergoing their first stage of 

 decomposition and mechanical destruction must have carried fine clay 

 and were probably black with the sediments of plant debris. 



The carbonaceous elements of the black shale beds have been subjected 

 to a long period of natural distillation in the buried sediments such as 

 characterize the Mid-Continent oil and gas fields. It is believed that 

 these shale beds have supplied the contributing material of the petroleum 

 and natural gas accumulations throughout this region, regardless of the 

 geological horizons in any particular district. Shale containing more or 

 less carbonaceous matter is common in all the formations from the Mis- 

 sissippian series up to the youngest oil-producing beds of the Cretaceous, 

 or even in the later Tertiary sediments of the Gulf coast. 



The Accumulation of Petroleum and Natural Gas in the Mid- 

 Continent Fields 



There are certain principles in the accumulation of oil and gas that 

 are alike applicable to all producing fields in the Mid-Continent region. 

 While it is recognized that here is one of the most perplexing subjects 

 with which the petroleum geologist has to deal and one that would be of 

 great practical value if clarified in its entirety, still there have been recent 

 contributions to the subject that are advanced steps of great importance. 

 There are two American authors in geology who have recently brought 

 forward ideas based on physics that are destined, in the writer's opinion, 

 to remain classic milestones along the highway of approach to a final 

 understanding of the subject. One is M. J. Munn, who has set forth 

 reasons why the old application of the anticlinal theory must be altered, 

 and has laid stress on the importance of hydraulic forces which accom- 

 pany moving bodies of water in the underground rocks; the other is 

 Chester W. Washburn e, who has discussed the effect of capillary move- 

 ments due to the difference in surface tension of water, gas, and petro- 

 leum. These principles have surely played important roles in accumula- 

 tion. 



Petroleum and gas were originally diffused through certain strata and 

 have later been gathered into "pools" of commercial size. In this con- 

 nection, the writer believes, the simple effect of early consolidation due 

 to pressure of overlying sediments has not received the attention due it. 



