Subsurface Logging Methods 



401 



but they are both higher than the limit Rum above which beds should be 

 classified as impervious. For intermediate values of the resistivity, and 

 because of the limited dimensions of the pad, a departure between the 



^ __ __ insulated Cable — ^ 



g \iSt 



M2 



Mi^^Electrodes 



■Steel Springs "^ — 



V/ 



Figure 178. Micrologging apparatus. 



microresistivity curves is sometimes observed on impervious beds; but, 

 in that case, the departure is negative; i.e. the longer spacing gives the 

 smaller value of the apparent resistivity, so that there can be no con- 

 fusion in the interpretation. 



These different features of the interpretation will be discussed in 

 more detail in a later section. 



