310 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



foreign membership of about 3,000 — a number greater than that of 

 any other geological society in the world. The association issues a 

 monthly bulletin containing about 150 pages in each number, and in 

 addition it has issued 12 special volumes. The reports of the Fed- 

 eral and State Geological Surveys dealing especially with petroleum 

 geology are numerous and constitute a major portion of the literature 

 on the subject. 



An important factor in the development and progress of petroleum 

 geology has been the mounting store of geologic data supplied by 

 wells that have constantly increased both in number and depth. The 

 number of wells that have been drilled for oil and gas in the United 

 States exceeds 900,000. The world's deepest well, completed this year 

 in the southern San Joaquin Valley, Calif., reached a depth of 15,004 

 feet. This well is nearly 9,000 feet deeper than the mine workings 

 (slightly more than 6,150 feet) of the Quincy Mining Co., Hancock, 

 Mich., and is about 6,500 feet greater than the 8,530-foot workings 

 of one of the Crown Mines on the Rand. The producing zone of this 

 deep California well is from 13,092 to 13,175 feet, but a more recently 

 completed well of the Fobs Oil Co., in Terrebonne Parish, La., is pro- 

 ducing from a slightly greater depth — namely, 13,254 to 13,266 feet. 



CONTRIBUTIONS OF PETROLEUM GEOLOGY TO GENERAL 

 SCIENCE OF GEOLOGY 



Petroleum geology, because of its wide field of opportunity for the 

 investigation of geologic conditions on the surface and also geologic 

 conditions to the depths penetrated by wells — 15,004 feet — and to the 

 depths reached by geophysical methods — more than 30,000 feet — 

 has made notable contributions to the general science of geology. 

 Some of the more important contributions will be mentioned briefly. 



Anticlines, as already noted, were first sought as favorable struc- 

 tural features on which to locate drilling sites for oil; but, with 

 further drilling and the consequently increased knowledge of the oc- 

 currence of petroleum, it was learned that oil occurs not only on sim- 

 ple anticlines but also on many other types of structural features 

 which include terraces, anticlinal noses, faults, unconformities, salt 

 domes, lenticular sands, and buried hills. 



Buried hills and the superposition of surface anticlines over them 

 were brought to the attention of geologists by Sidney Powers (13) 

 following the discovery of granite hills underneath the Eldorado line 

 of folding in Kansas and of hills of Ordovician rocks underneath the 

 Pennsylvanian sand production at Healdton, Okla. 



Our knowledge of the geology of the salt domes in Louisiana and 

 Texas has been revolutionized in the last quarter of a century. Now 

 the domes are generally regarded as intrusive plugs of salt that moved 



