Ch. 4] EXPLORATION GEOPHYSICS 77 



basins; hydroelectric developments; reservoir and dam construction 

 projects, irrigation projects, land usage surveys. 



References to Literature 



At the ejid of this chapter is a list of references which the reader 

 may consult for further information on the foregoing subjects. There 

 is a wealth of knowledge in the texts and periodical literature cited 

 in these references, much of which is in suitable form for immediate 

 utilization by engineers and scientists who are approaching problems 

 in sedimentation without previous experience in the field. 



EXPLORATION GEOPHYSICS (For Petroleum and Minerals) 



The United States petroleum industry spent approximately $500,- 

 000,000 during 1948 in search of new deposits of oil and gas. At 

 least one quarter of this amount was spent in scientific methods of 

 exploration employing geology and geophysics. Most of the latter 

 sum was spent on exploration geophysics through the activities of 

 approximately six hundred field parties in the United States alone. 

 It may be inferred, correctly, that the expenditure of sums of this 

 order implies the existence of a high degree of scientific and technical 

 competence. It is true that the expenditures provide a return in new 

 discoveries of oil and gas equal in value to many times the exploration 

 costs. The success of the petroleum industry during the past twenty- 

 five years is ample testimony to the philosophy of multiple working 

 hypotheses. Although most of the money is spent on exploration geo- 

 physics, the strategy of long-range campaigns embraces every imagi- 

 nable point of view in petroleum geology. 



The consequence of this great effort has been the development of 

 an extremely high degree of scientific and technical skill in the pur- 

 suit of new discoveries. The success of an exploration program, when 

 distributed over a sufficiently broad base, is now taken for granted. 

 There is a direct relation between the amount of oil discovered and 

 the funds applied to the task. It is true that the unit cost of discovery 

 is constantly rising, but the law of diminishing returns is not yet too 

 seriously felt. Exploration by scientific means is still profitable on a 

 large scale. 



The technical basis of petroleum exploration geophysics can be 

 expressed briefly. Through many years of trial and error the industry 

 has found that many physical properties of rocks are systematically 

 distributed with reference to oil and gas. Four or five of these prop- 

 erties are significant enough to warrant serious prospecting techniques. 



