230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1942 



be expressed in one word and that word was "downward." He went 

 on to explain that he did not mean that we were going into a decline, 

 but that the thought and the effort of the petroleum geologist were 

 more and more being concentrated below the surface and in the realms 

 of subsurface sedimentation, subsurface stratigraphy, and subsurface 

 paleontology. This entire subsurface development stems directly 

 from the place microscopic methods have taken as a technique of pe- 

 troleum geology. A person working with subsurface geology began 

 with the terms of the well drillers — "hard rock," "soft rock," "mud," 

 "slate," and the like. Gradually he was able to change those to terms 

 with a more geological sound — limestone, sandstone, and shale, and, 

 as a further refinement, added such general textural and qualifying 

 terms as crystalline, dense, lithographic, porous, sandy, dolomitic, 

 calcareous, and argillaceous. Now, we find him beginning to examine 

 microscopically the individual mineral grains and to reduce their 

 primary characteristics to the simplest possible terms; we find him 

 concerned deeply with slight changes in f acies ; and we find he is be- 

 ginning to look into the possibilities of distinguishing the variations 

 of single minerals as a guide to the sedimentary environments of dep- 

 osition. Some think it is deplorable, but it is nevertheless true in 

 petroleum geology, that the microscope has pretty well supplanted 

 the plane table and stadia rod as the leading method of obtaining 

 geologic data. 



Geophysical methods have become so well established in the oil- 

 finding teclinique as to have long since passed beyond the trend stage. 

 Moreover, it is not the purpose of this discussion to go into other than 

 the strictly geological aspects of petroleum exploration, leaving to 

 others the telling of the brilliant contribution geophysics is making 

 to the oil industry. 



The chief function of geophysics in petroleum exploration is to 

 obtain structural data in advance of drilling. Geophysical data, in 

 order to be effective, require geological interpretation and so far this 

 has been successful only in the search for structural accumulations. 

 The time will certainly come, however, when the geologist will be 

 able to interpret geophysical data in terms of sedimentation and stra- 

 tigraphy and then the entire field of stratigraphic type oil pools will 

 be opened to geophysical methods. Since geophysical data are all be- 

 low the surface of the ground, when they are added to the steady 

 stream of subsurface well data, they further tend to push our 

 thinking deeper and deeper. Even now the commercially accurate 

 mapping of geologic conditions 5, 10, or even more thousands of feet 

 underground is a daily routine in many areas. 



As the exploratory effort becomes deeper, it becomes more complex, 

 and it also increases rapidly in cost. There is a tendency, therefore, 

 in some quarters to go back to a reinterpretation of surface and sub- 



