TORSION-BALANCE RESULTS IN CALIFORNIA 1421 


B 
GRADIENTS CALCULATED- DENSITY 
CHANGE AT BEDDING SURFACE 

OBSERVED GRADIENTS 
SECTION Of FOLDED 
BEDDING SURFACE SCALE - VERTICAL HORIZONTAL 
Se LL ae 
° 1000 2000 3000 4000 
FEET 
os 10 20 
esTVv6S UNITS 
ROBERT H. MILLER, 
GEOLOGIST & ENGINEER, 
308 H W.HELLMAWN BLOG. 
LOS ANGELES,CAL. 
Fic. 1 
active through a long peried of time, and deposition and erosion occur 
contemporaneously in many places so that the formations at depth may 
be more folded than those at the surface. The effects of distance, how- 
ever, more than offset the greater degree of folding that may occur at 
depth, so that only the folding of the surface formations has an appre- 
ciable effect on the distribution of gravity at the surface. When a whole 
series of formations is folded, the series may be divided into members 
that react to folding in the manner of rigid bodies and those that flow 
plastically or slip on cleavage planes; otherwise the strain in the ma- 
terials would exceed all possible limits. It is not necessary to assume 
that sand beds exhibit the properties of rigid bodies and that under 
linear compression shales flow plastically, but it is a fact that surface 
sand formations, within 1,000 or 2,000 feet of the surface, when folded, 
assume a form that only rigid bodies would acquire under the circum- 
stances. If allowances are made for the effects of friction, this form may 
131 
