1420 ROBERT H. MILLER 
of geophysics is examined by men who hold such erroneous ideas the 
result is confusion, and geophysical methods are hindered in getting the 
endorsement they merit. 
It has generally been assumed that the distribution of gravity meas- 
ured by the torsion balance depends on the configuration of denser or 
lighter rocks below the surface of the ground; in other words, it depends on 
the distribution of subterranean mass caused by the inherent density of 
the contorted beds, and as no inherent density differences are detectable 
within moderate depths in many places in California, this has been taken 
as prima facie evidence that the torsion balance was not adaptable to 
California conditions. When it was shown that all California oil fields 
do affect the distribution of gravity in their vicinity, the effect was at- 
tributed to slight inherent density changes, and the method of deter- 
mining densities from core samples was questioned. Simple reasoning 
will show that the distribution of gravity in many oil fields in California 
has little if anything to do with the inherent density of the beds below 
the surface. 
Figure 1 represents a cross section of an oil field in the Los Angeles 
basin. AA’ is the observed gradient profile curve. The maximum or- 
dinates, b and 8’, are 1,600 feet apart. BB’ is the calculated gradient 
profile curve where a heavier bed of the same cross section just reaches 
the level surface of the ground at the crest of the fold, the ordinates of 
the profile curve being proportional to the difference in density of the 
heavier bed and the surface fill. This profile curve does not reach its 
maxima within the limits of the sketch. If this heavier bed had occupied 
a lower position in the series, or a higher position, and had been subse- 
quently eroded to a level surface, the maxima on the profile curve would 
be still farther apart. Therefore, as the first case considered does not 
produce a distribution of gravity comparable with that observed in the 
field, no heavier bed in any position, nor any combination of lighter or 
heavier beds, nor increasingly lighter or heavier beds, can produce results 
in any way comparable with those observed. Hence it is proved that the 
observed distribution of density represented by the profile curve AA’ 
does not depend on the inherent density change of the subsurface forma- 
tions. Also, as all the oil fields in the Los Angeles basin cause a similar 
distribution of gravity, the proof may be extended to include them. 
It seems probable that the causes which underlie the distribution 
of gravity over many structures in California must generally be sought 
in the compaction and rarefaction of the beds caused by folding. The 
forces of earth movement which give rise to structures generally remain 
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