308 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



Texas, ranking first in production — 510,318,000 barrels of oil in 

 1937 — has 868 geologists; California, standing second — 238,521,000 

 barrels of oil in 1937 — has 314 geologists ; Oklahoma, standing third — 

 228,839,000 barrels of oil in 1937— has 430 geologists; Louisiana, stand- 

 ing fourth— 90,924,000 barrels of oil in 1937— has 124 geologists; 

 Kansas, standing fifth— 70,761,000 barrels of oil in 1937— has 134 

 geologists. In these five States there is 1 geologist for every 600,000 

 barrels of oil produced in 1937. 



METHODS EMPLOYED BY THE PETROLEUM GEOLOGISTS 



The oil geologist, in the application of his science to the recovery of 

 petroleum, has a wide field of opportunity before him and he makes 

 use of facts and conclusions from many phases of geology, including 

 structure, stratigraphy, paleontology, sedimentary petrology, sedi- 

 mentation, geomorphology, and metamorphism. In his search for, 

 and his location of, oil deposits he has from time to time abandoned or 

 modified old methods and has adopted new methods of exploration. 

 The available time will not permit the presentation of a full list of 

 these methods ; it will permit no more than brief mention of some ma- 

 jor developments during the present century. Important develop- 

 ments during the early years of the century were the adoption of the 

 structure contour to portray the structural features of prospective or 

 producing oil and gas areas and also the application of the plane table 

 and alidade as instruments for determining accurately the altitudes 

 of the "key beds" that were contoured. 



Airplane photography, first employed during the World War, was 

 utilized about 1920 by the oil geologist. Subsequently its utilization 

 by governmental agencies and by oil and other companies has in- 

 creased rapidly, and at present about half the area of the United 

 States has been covered by aerial photographs. To the geologist 

 such photographs record a wealth of essential details of geologic 

 features that are not obtainable by any other method of mapping. 

 As the years pass, he relies more and more on such pictures and 

 employs fewer and fewer plane table maps. 



Surface structural mapping reached its peak application between 

 1920 and 1925, and it has thus for many years occupied a place of 

 decreasing importance in the search for new oil fields. This decline 

 is attributable to the gradual decrease in number of favorable struc- 

 tural features that can be recognized by surface geologic mapping. 



Core drilling for the determination of structure was introduced in 

 the United States in 1919 and was employed on an extensive scale 

 for many years in portions of the midcontinent region. 



The microscopic examination of well cuttings was begun on a large 

 scale in 1917 and since that time it has reached a place of fundamental 

 importance. To it the oil geologist now gives about half of his effort. 



