84 beers. GEOPHYSICAL PROBLEMS [Ch. 4 



the functions in this realm normally exerted by commercial operating 

 companies. To expand the mapping function it is inevitable that 

 resort be made to geophysical methods. The seismograph has dem- 

 onstrated well its ability to portray the attitude and depth of key 

 horizons in sedimentary provinces. If structure and stratigraphy are 

 concealed beneath a cover of overburden, alluvium, or valley fill, there 

 is no better method of unveiling subsurface conditions than by the use 

 of geophysics. Its cost is insignificant compared with that of drilling 

 an adequate number of holes in a virgin territory. The distribution of 

 data yields a much better density than other methods permit. The 

 prevailing lack of appreciation of geophysical methods may be at- 

 tributed in part to lack of understanding of the method, but also to 

 lack of facilities and trained personnel in the United States. Since it 

 is the proper function of the geological surveys to develop new methods 

 of exploration and survey, it is hoped that this area of investigation 

 may be developed in the near future. Already we have valuable ex- 

 amples of the contribution made to the nation's resources by the air- 

 borne-magnetometer maps which the U. S. Geological Survey has pro- 

 duced in the Lake Superior region, in the magnetite, lead, and zinc 

 deposits of New York, in the central portion of the state of Pennsyl- 

 vania, and elsewhere. These reconnaissance maps will be of value for 

 many years to those who follow with ground surveys of greater detail. 



DEVELOPMENT OF ORE DEPOSITS 



Since the mining industry has not developed geophysical methods 

 for exploration to a high degree, it is conceivable that a beginning 

 might be made in the development of existing ore deposits. There 

 are many problems in the extension of working properties to which 

 geophysics would make substantial contributions. These would employ 

 the conventional instruments and techniques of the principal kinds 

 discussed herein. Close correlation by the geophysicist and the min- 

 ing geologist is likely to develop profitable areas of application through 

 the extension of known ore deposits. None of the principal geophysical 

 techniques has been exhausted in this connection. It seems likely that 

 valuable advances could be made in this field at relatively small costs. 



DEVELOPMENT OF PETROLEUM PRODUCTION 



In sharp contrast to the mining industry, the petroleum industry 

 has expanded large numbers of geophysical techniques to the benefit 

 of producing properties everywhere. The industry is quick to take 



