MAGNETIC RESURVEY OF OKLAHOMA CITY FIELD 5 
for both surveys and is thought to be in an undisturbed state, as no 
well is closer to it than 34 mile. Between the base and a point two 
miles farther east, also in an undisturbed condition, there is a marked 
accordance of anomaly, a difference of plus 34 gammas being measured 
in the first survey and a difference of plus 31 gammas in the second 
survey. The stations south and west of the base point, though they 
do not coincide, either in position or value, do roughly correspond. 
It appears, then, that in the undisturbed area on the south there is 
a pronounced accordance of anomaly value which gives a reasonable 
check on the comparative accuracy of the two surveys. 
The most pronounced discordance between the two surveys ap- 
pears one mile north of the base station. In the original survey this 
point falls on a gradual northward decline of anomaly which con- 
tinues uninterrupted for 5 miles. In the more recent work, there is a 
sharp decline of intensity in the first mile, followed by an almost 
equally sharp rise in the succeeding mile. Though every effort was 
made to keep pronounced effects of extraneous material from the 
survey, it is thought that this discrepancy represents such effects. 
When the instrument gave readings off the field of view, it was moved 
until large effects appeared vitiated. 
The changed aspect of the vertical component map may be at- 
tributed to one or all of several factors. No attempt is made to evalu- 
ate the relative importance of these. They are: (1) the recent survey 
was more compactly observed and for that reason the intensity 
changes may appear more accentuated than in the original su-vey; 
(2) the physical development produces major changes in the mag- 
netic field; (3) the actual extension of Oklahoma City proper, both 
laterally and vertically, has produced immeasurable changes in the 
magnetic field; and (4) secular variation causes slight differences. 
The results from one resurvey of this type can not be considered 
conclusive. It is reasonable to expect, however, that similar attempts 
in other areas will produce similar results. The results of the present 
survey tend to show that, with care in the selection of observation 
points, the general picture of an area will show little difference before 
and after the development of production; that, if the original mag- 
netic structure had any considerable relief, it will retain not only 
the same approximate closure, but also closure in the same direction. 
The early magnetic work in existing fields can thus be expected to 
have shown a rough approximation to the pre-development state. 
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