Ch. 4] GEOPHYSICAL AIDS TO GEOLOGIC MAPPING 83 



without knowledge of subsurface geology, subsurface geological fea- 

 tures such as faults, buried channels, and basins filled with uncon- 

 solidated materials. Many famous structures are in danger because of 

 these oversights. Some of the errors could have been prevented by 

 the employment of competent geologists when the selection was made, 

 but they might have been unable to detect hidden features which 

 could be brought to light by geophysical methods. 



The properties of soils as components of structures and foundations 

 require more convenient and precise methods of determination. Con- 

 sultants in the field of soil mechanics are casting about for devices 

 which they may use for testing soils and their properties. It is diffi- 

 cult to prescribe one formula to meet all these needs. This is es- 

 pecially true because prevailing concepts in soil mechanics generally 

 omit the geological point of view, the concept of active processes which 

 affect the soil constantly throughout its life. 



The foregoing examples illustrate the need for research and de- 

 velopment in the field of applied sedimentation. In all these problems 

 it is clear that an application of the existing techniques of geophysics 

 will bring early assistance to bear. Already there are competent re- 

 sources of personnel and facilities if the way is made clear for their 

 utilization. The difficulty is to find sponsoring agencies who will co- 

 ordinate these efforts. This is a new borderline science which it 

 seems important to develop. It is hoped that these remarks may be 

 brought to the attention of those in position to chart future courses 

 of action. 



GEOPHYSICAL AIDS TO GEOLOGIC MAPPING 



One of the functions of the U. S. Geological Survey and of state 

 geological surveys is to map the geology and the mineral resources 

 of our country. In this function the surveys have for many years 

 carried out a comprehensive program of geologic and topographic map- 

 ping. The locations where these surveys have been completed are 

 those where the needs were greatest. At first, immediate develop- 

 ments followed closely upon the completion of adequate maps. This 

 function has been extended to subsurface mapping where underground 

 workings have been opened by mining operations and by the drilling of 

 wells for oil, gas, and water. 



We have come to a phase in the development of our country's 

 mineral resources where these methods of geologic mapping greatly 

 restrict the nation's development. It is now time to think of ways 

 of large-scale mapping of subsurface geology, without competing with 



