440 



EXPLORATION GEOPHYSICS 



Representative graphs of experimental values of the resistivities of 

 emulsions of oil and water as a function of the percentage of water 

 content are shown in Figure 263. Similar graphs for rocks impregnated 

 with various percentages of moisture are shown in Figure 264. 



Magnitudes of the Resistivities. — The electrical constants of rocks 

 may be obtained by laboratory measurements, using rock specimens, 



ou«TowAirr 



CRETACtOUS 



CAHtONIfBIOOS 



PRE ■ CAMBMAN 



^ r 



I DEVONIAN 



SILURIAN ~ 

 OROOVKIAN 



CARSOHinilOUS 



MC -CAialllAN 



AUimUH STONE ALLUVIUM 

 OUARTZni SHALE 



The heavy lines ind'cate the range of eHective resistivities for 

 tesb in which measurements were made in several subsections or 

 exploring wires^ tfie mean effective resistivities are indicated by 

 circles. Isolated circles indicate effective resistivities where only 

 one measurement was made 



The sequence In which the various types of materials are listed is 

 rot necessarily the time sequence in which these materials occur 



in the jeological structures, although the oldest materials are, in 

 general, -on the left 



The overburden is not indicated except in a few cases where ma- 

 terial thicknesses of alluvium are present 



"Limestone" as used in connection with Silurian and earlier 

 formations includes, in many cases, dolomites as well 



Fig. 365. — Correlation of effective resistivities witli geological periods and materials. (R. H. Card, 

 "Earth Resistivity and Geological Structure," Electrical Engineering, Nov. 1935, p. 1156.) 



