148 C. A. HETLAND 
ness of 400 feet underlain by salt. The resistance of the gypsum is 
high, and that of the shales is low. Where the effect of the salt has 
been picked up, its resistance seems to be fairly tow, such as shown 
in well No. 48, which is somewhat contrary to the experience obtained 
on salt domes. AJL resistivity traverses shown in Figure 31 have a simi- 
lar appearance as far as the very high resistance surface layers are con- 
faddaty Corp #2 
appa ren (6 




Resistivit. YY 
Single Probe 
Method 

Water Sand 
Fic. 32.—Results of electrical vertical drilling using single-probe method (IIa) and 
corresponding well log at Berthoud dome, Colorado. (Measurements made by Keen, 
Bishop, and Johnson.) 
cerned. Then they all show a pronounced “low,” corresponding with 
the influence of the red beds and shales close to the surface. After that, 
all curves go up again, depending on the amount of gypsum present 
in the section. Thus, while the curves of Nos. 45 and 46 are practically 
flat, they are steeper in 49, 44, 43, and steepest in 48. Just what takes 
place in No. 48 is not very well known on account of lack of knowledge 
of the well log; but it seems that the formations present at that local- 
ity, probably gypsum, are very poor conductors. A striking similarity 
478 
