Subsurface Methods as Applied in Geophysics 



1043 



mended the use of more accurate exploration methods, which were given 

 credit for the location. 



Soon after the discovery of the Hobbs field, New Mexico, on a mag- 

 netic high, any person who could raise the necessary thousand dollars to 

 purchase a magnetometer became a magnetic "expert." Inadequate field 

 technique and poor interpretation resulted in the drilling of hundreds of 

 dry holes in structurally normal areas. Although several crews operated 

 periodically during the following decade, it was not until World War II 



UJ 



o 



LJ 



Z 



o 

 < 



K= 



K>0 



PARA- 

 MAGNETIC 



NON- 

 MAGNETIC 



DIA- 

 MAGNETIC 



Figure 547. Effect on vertical component of earth's magnetic field of paramagnetic, 

 nonmagnetic, and diamagnetic materials. Susceptibilities of paramagnetic and 

 diamagnetic materials assumed to be equal. 



that extensive magnetic programs were again included in the geophysical 

 efforts of many companies. Peters ^- reports about 165 crew-months of 

 ground magnetic activity during 1947 and about 17 crew-months of air- 

 borne-magnetometer work. 



Basic Principles 



Stated in simplest terms, magnetic prospecting consists in comparing 

 the intensity of the magnetic field between observation points that are 



•■^Peters, J. W., The Role of the Magnetometer in Petroleum Exploration: Mines Mag., vol. 39, 

 no. 7, pp. 11-15, 1949. 



