Subsurface Methods as Applied in Geophysics 



1059 



Allowing 9,500 feet for the radius, the igneous core should be encountered 

 at 7,500 feet below the surface. 



The Gulf Rainey A-1 entered igneous rock at 2,996 feet, and drilling 

 ceased at 3,607 feet while still in igneous material described as a "perido- 

 tite" in the upper part and a "lampophyre" in the lower part. Subsequent 

 deeper wells have indicated that the igneous material encountered by 

 the drill may be sills or slivers and that the actual igneous core has not 



Ground Survey 



flown 1300 above ground 



miles 

 Contour interval = 100 gammas 



Figure 558. Portion of air-borne-magnetometer survey in Greer County, Oklahoma. 

 Results of a ground survey in same area also shown. (After Balsley. Repro- 

 duced permission U. S. Geol. Survey.) 



as yet been reached. Better agreement between magnetic data and sub- 

 surface conditions would be achieved if the presence of a large igneous 

 core at depth were confirmed. The igneous activity in this region appar- 

 ently occurred during Tuscaloosa time and extended over southern Arkan- 

 sas and central Mississippi.^^ 



Mangum, Oklahoma — The results of an air-borne magnetic survey are 



pp. 14 



Spraragen, L,, Magnetometer Survey of the Jackson Area: Oil and Gas Jour., vol. 30, no. 26, 

 ., 15, 83, Jan. 1932. 



