144 C. A. HEILAND 
shows two resistivity profiles with the corresponding drilling results. 
In interpreting the resistivity curves, reference should be made to 
the curves shown in Figure 16 for the case in which the resistivity of 
the lower layer is practically infinite. The two curves shown in Figure 
27 also illustrate the effect of a homogeneous and an inhomogeneous 
overburden. 
2 fcoweRresisTIWTY CURVE AND VALUE 
CF TAME RESISTIVITY 1M OHS 77/092 
SCALE: — 

Fic. 28.—Resistivity map of the Aricesti anticline. Work carried out in 1923 
(after Schlumberger). 
3. BY POTENTIAL AND PHASE MAPPING 
This method will probably find little application in oil structural 
work, although it can give valuable indications in determining the 
character of surface formations in suitable areas under a shallow 
cover. Figure 19 shows, as an example, the effect of a gabbro intrusion 
with two ore bodies on the contact zone upon the potential-drop and 
474 
