422 



EXPLORATION GEOPHYSICS 



the regional correction to be applied at a field survey station is found in 

 the same way as the latitude and longitude correction in magnetic survey 

 work; namely, at a given rate per mile, for the required number of miles. 

 The above procedure was successfully applied at the Wellington Field 

 in Colorado. This field was selected for an experimental gravity study in 

 1940, as it was a typical mountain fold, situated on the west flank of the 

 Denver Basin. It is an anticline about 5 miles long, with a closure of some 

 800 feet as shown by contours on the Muddy Sand (Figure 251). This 



R 69W v%, - 



»^_,„. ^^ 



Fig. 252. — Observed gravity, contoured at 0.1 mg. interval, and regional correction for N-S and 

 E-W profiles, Wellington Field, Larimer County, Colorado. (After J. H. Wilson, Geophysics, Vol. 

 6, No. 3, July, 1941.) 



horizon is at a depth of approximately 4250 feet on the top of the structure. 

 The field is cut by a fault running in a northwest-southeast direction. 



The results of the gravimeter survey of the Wellington Field are given 

 in Figure 252, in which gravity values relative to a base station have been 

 contoured in 0.1 milligal units. The gravity stations have been corrected 



