EARTH RESISTIVITIES 53 
5 feet in error. The curve as a whole is very poorly diagnostic and is 
not satisfactory. It is given to show what can and does occur in some 
determinations. The writer is inclined to believe that because of the 
fairly low resistivity of the limestone alone, and perhaps because of the 
nature of the contact with the shale, whatever it is, the total resistiv- 
ity is low. 
A second example of low resistivity rock over high is given in 
curve KX/, Graph No. 13. The log of the hole drilled by a clay auger 
beneath the place of set-up is: 
Feet 
Gravelly soil and clay o-10 
Diaspore and burley clay 10-60 
Plastic clay and rotten rock 60-95 
“Cotton rock” (Jefferson City dolomite) 95—— 
The transition in this case from “plastic clay and rotten rock”’ 
to dolomite is sharp and clear. The electrical prediction of dolomite 
at 96 feet was very satisfactory. 
Perhaps the upper contact of the dolomite was nonconductive or 
the resistivity of the dolomite high so that the influence of the clay 
on the total resistivity was not marked. The writer is not able to 
explain adequately the difference between the transitions on the two 
curves. 
Station K XJ was located over a diaspore pit 1.5 miles southeast 
of Swiss, Gasconade County, Missouri. 
The stations shown on Graph No. 12 were located one mile north- 
west of Elsberry, Missouri. 
EQUI-RESISTIVE FORMATIONS 
A complete series of 2 formational resistivity curves will include 
those of 2 rocks of similar resistivity. Such is shown in curve 75 on 
Graph No. 13, at which location 56 feet of Joachim dolomite overlies 
the St. Peter sandstone. Since both rocks have high resistivity no 
marked break in the curve would be expected and there is none. A 
small irregularity occurs at 60 feet and may represent the discon- 
formable contact, or, being so slight, may simply be caused by a 
variation in the rock. At any rate it is too small to be used as a mark 
separating formations in interpreting an unknown curve. 
The location was half a mile west of Corinth Church, near Foley, 
Missouri. 
RESISTIVITIES ACROSS FAULT 
In the next study measurements were made across an upturned 
series of rocks and an included fault occurring in Lincoln County, 
575 
