OUR PETROLEUM SUPPLY MISER 311 



upward from bedded salt of probable late Jurassic or early Creta- 

 ceous age. The salt is believed to have moved upward as much as 

 30,000 feet in the coastal portions of Louisiana and Texas. Formerly 

 the salt masses were believed to have been formed as a result of vol- 

 canic activity, gas uplift, or the crystallization of the salt along zones 

 of weakness in the rock strata. 



The Gulf Coastal Plain may be cited as an example of an area 

 whose tectonic map has undergone great transformation as the result 

 of oil exploration. To the tectonic map of the Gulf Coastal Plain such 

 structural trends as the Mexia fault zone, the buried course of the 

 Ouachita belt of Paleozoic rocks, and the Gulf Coast geosyncline, have 

 been added. 



From the determination of the effect of regional structural defor- 

 mation and the attendant metamorphism on deposits of petroleum 

 and coal in the eastern United States, David White drew, in 1915, a 

 "deadline" beyond which oil may not be expected in the Appalachian 

 and Ouachita regions (22). This oil "deadline," or extinction zone, 

 lies between the 60- and 65-isocarbs, lines connecting points where 

 the coals have 60 to 65 percent of fixed carbon. 



Also the composition of the hydrocarbon gases in the northern 

 Appalachian region bears a close relation to the structure and the 

 degree of metamorphism of the associated strata. This has been 

 pointed out recently by S. H. Hamilton (7), Charles K. Fettke (5), 

 Paul H. Price and A. J. W. Headlee (14). 



From the measurements of the temperatures of deep wells by Van 

 Orstrand (21) and others in the United States it has been shown that 

 relatively high temperatures are generally associated with faults, 

 salt domes, sand lenses, and anticlines of both large and small closure. 

 It appears that both the local and regional variations of earth tem- 

 peratures of the sedimentary strata thus penetrated by wells are re- 

 lated to thermal conductivity and to the depth to the underlying 

 crystalline basement. Differential uplift on either a large or a small 

 scale would tend to elevate the isotherms irregularly. 



Stratigraphy, of a refined character, has received impetus in conse- 

 quence of the requirements of the oil industry for exact information 

 concerning the thickness and character of the rock strata of prospec- 

 tive oil regions and of areas under development. This type of infor- 

 mation is required for an interpretation of geologic history and for 

 the preparation of precise structure maps. The geologic history has 

 a bearing on the origin and migration of oil and the structure maps 

 may reveal favorable places for its accumulation. 



Time will permit mention of only three interesting types of strati- 

 graphic work. One of these is to be found in western Kansas where 

 petroleum geologists have matched the intervals between bentonite 

 beds in the Niobrara chalk in a way suggestive of the matching of 



