Page 23 - muehlberger1954

-13-

Pelona. In 1939, Hill (pp. 1-118) de scribed the petrography of the

Pelona schist in detail. Wallace (1949, pp. 786-787) briefly described

the Pelona schist in his study of a part of the San Andreas rift.

The following discussion of the Pelona schist is limited to the

exposures of the Pelona schist in the Sierra Pelona, except where

otherwise stated. Along the southern margin of the range, the schist

is intruded by granitic rocks. Much of the contact between the schist

and granite is obscured or deeply buried by overlapping sedimentary

rocks of Tertiary age. Elsewhere the schist of the range is in fault

contact with granitic rocks or with Cenozoic sediments.

Slightly more than 7,400 feet of mica schists and actinolite-

chlorite schists; with rare beds of quartzite and layers of interbedded

quartzite and limestone, is exposed in Bouquet Canyon. Table 1

summarizes this sequence.

About 5, 000 feet of the exposed Pelona schist consists of

silvery-gray muscovite schist and chlorite-muscovite schist. The

layers in the schists, which may be in part original stratification,

range in thickness from a fraction of an inch to several inches, and

some probably are near-ly a foot thick. Porphyroblasts of quartz and

grayish sodic plagioclase are abundant, and are one to two millimeters

in maximum dimension. Laminae of biotite schist are commonly inter-

layered with muscovite schist.

An average mineral composition of the muscovite schists, as

computed from Hill's (1939, pp. 50-55) detailed petrographic data, is