10 W, 2: JENNY. 
the local anomalies, lie at depths ranging from 2,000 to 15,000 feet 
and that the magnetic effect is felt within a horizontal distance from 
the edge of a “‘structure”’ of only about twice its depth. Therefore it 
is reasonable to assume that, within a distance of 20-50 miles, only 
one station is occupied, as a rule, on a particular ‘“‘structure”’ and there 
is little use in combining the measurements of the different stations, 
unless broad structural features are suspected. 
Contrary to the opinion of some magneticians,'? the writer holds 
that at such large distances between stations, much more detailed 
information may be obtained by studying the horizontal intensity 
than by studying the vertical intensity, and thinks that this results 
clearly from a study of the horizontal intensities in Figure 1, especially . 
if it be realized that the anomalies are 3-dimensional. 
The best information is of course obtained by a combination of the 
horizontal and the vertical intensities of a magnetic vector in space. 
The Coast and Geodetic Survey has measured the declination and 
the horizontal and vertical intensities at the occupied stations. If 
the normal declination and the horizontal and vertical intensity be 
figured for each station and these normal values are deducted*# 
from the actually measured values, the local deviation of the declina- 
tion and the local vertical and south-north horizontal component of 
the total local magnetic vector are obtained as the difference. From 
the deviation of the declination may be easily figured also the local 
west-east component of the total local magnetic vector. 
The average absolute accuracy of the components of these local 
magnetic vectors empirically lies at +40 gammas, the average ac- 
curacy relative to neighboring stations at + 20 gammas. 
The local magnetic vectors have been plotted at their respective 
stations on the maps of the principal oil-producing states, in the 
shape of vector triangles. The two dashed lines represent the hori- 
zontal and the vertical vectors; the hypotenuse is the total vector. 
If the vector triangle be turned through go° around the horizontal 
vector, which is of course the dashed line beginning at the station 
point, the direction in space of the total vector may easily be visual- 
ized and the direction marked by a pin, if the map is mounted on 
cardboard. 
1A. Nippoldt, op. cit. 
2G. B. Somers, op. cit. 
® A, Nippoldt, op. cit. 
‘L. A. Bauer, “Chief Results of a Preliminary Analysis of the Earth’s Magnetic 
Field for 1922,” Terr. Mag., Vol. 28 (1923), pp. 1-28. 
338 
