1428 ROBERT H. MILLER 
cline, therefore, represented by the profile curve HK, is a sine curve 
having a period equal to O’D and a half-amplitude of 1,600 feet. This 
curve is represented by curve GEF in the figure. As the point G has been 
dragged below its original level F, it is evident that the fault is down- 
thrown on the left. As the earth movements which caused the anticline 
evidently caused motion of the beds from left to right, friction and in- 
ertia must have caused the horizontal dimensions to be foreshortened to 
an extent varying inversely with the distance from the fault, so that the 
fault is nearer the axis of the anticline than is indicated by this theoretical 
analysis, and the left limb of the fold is somewhat steeper. 
Though this discussion has been devoted solely to the distribution 
of gravity in the Los Angeles basin, where the density conditions are 
exceptional, an accurate interpretation can be made of the data acquired 
from measuring any of the other properties of materials which are utilized 
in geophysics in any region, provided that the data which have been 
obtained are complete. 
DISCUSSION 
Frank A. Moss, Los Angeles, California (written discussion received, 
March 12, 1931): The author of the preceding paper offers an interesting ex- 
planation for gradient profiles in which the points of maximum gradient are 
too close together to be caused by density differences in beds extending across 
a fold. In a loosely consolidated bed of sand, folding reasonably could be ex- 
pected to cause an increase of density as postulated, but it is questionable 
whether there would be a decrease in density due to tension. However, there 
still would be gravity ‘‘highs”’ over the crest of the fold and over the flanking 
synclines. 
Other possibilities to be considered in the example given are (1) that the 
gravity “highs” on either side of the fold could be caused by heavy beds trun- 
cated and covered by alluvium and (2) that a combination of lenses of heavy 
and light materials might distort the effect of inherent changes in density 
sufficiently to produce the results observed. 
These theoretical considerations do not apply to folds in the western side 
of the San Joaquin Valley, where the beds involved in the folding are fairly 
well indurated and would be sheared rather than appreciably compressed. Ob- 
served variations in gravity can be related satisfactorily to panges ie lle changes 
in density of the underlying materials. 
Donatp C. Barton, Houston, Texas (written discussion): Geologically, 
it seems to me that we must examine more closely the reasoning leading to the 
assumptions that a soft, poorly consolidated California sediment will act as if it 
were a rigid body. Without more definite corroboratory data, I would be un- 
willing to postulate the compression-rarefaction assumed by Mr. Miller. 
Geophysically, I can not reach Mr. Miller’s conclusions. Mathematically, 
it commonly is possible to obtain a considerable series of tentative structural 
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