THERMAL METHODS 



975 



A similar example was presented by Dartonf showing that the tem- 

 perature gradients in eastern South Dakota increase as the depth to the 

 granite or quartzite decreases. 



The Salt Creek anticline| provides an excellent example of a local 

 variation in which the isogeothermal surfaces are related to the structure. 



Fig. 597. — Salt Creek Dome, Natrona County, Wyoming. 

 (C. E. Van Orstrand, loc. cit.) 



In Figure 597 the closed broken lines represent elevations on the "Second 

 Wall Creek Oil Sand." Faults are represented by broken lines intersecting 

 the structural contours. The dots represent well locations, and the accom- 

 panying numbers represent the depth at which a temperature of 80° F. was 



t N. H. Darton, "Geothermal Data of the United States," U. S. Geol. Survey Bull. 701 (1920), 

 p. 80. 



t C. E. Van Orstrand, "Correlation of isogeothermal surfaces," Trans. Soc. of Petrol. Geophys., 

 Vol. II, March, 1932. 



