184 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
serpentine are developed. These rocks are usually well banded. 
One of the striking types is composed of layers of brown garnet and 
white quartz, alternating with fine-grained bands of quartz, epidote, 
and other silicate minerals in which large crystals of brown garnet 
are locally embedded. Garnet also occurs in veins cutting the rocks, 
indicating a second recrvstallization of that mineral. A single speci- 
men of the banded rock examined under the microscope proved to be 
an uneven-grained, banded rock. The contemporaneous constituents 
of recrvstallization include slightly brownish garnets, quartz, epidote. 
zoisite, tremolite, calcite, orthoclase, and plagioclase (oligoclase and 
andesine), in places showing Carlsbad twinning. Apatite and titan- 
ite arc presenl as accessories and sericite and chlorite as secondary 
minerals derived from the feldspars. At the west end of the Gold 
Mountain ridge bands and lenses of brown garnet rock up to 30 feet 
in thickness are interbedded with white and canary-yellow marble. 
Crystals of garnet also occur in the numerous interstices of the 
weathered surface. 
These metamorphosed sedimentary rocks are similar to those 
of Slate Ridge, which grade into less metamorphosed facies, probably 
of Lower Cambrian age 
IGNEOUS ROCKS. 
Quartz-monzonite porphyry. — r rhc granite, particularly* near Old 
Camp, contains inclusions up to 1 foot in diameter of a fine-grained, 
medium-gray igneous rock, formed of biotite and white feldspar, in 
which are rather sparse phenocrysts of pink orthoclase reaching a 
maximum length of one-half inch, smoky quartz grains one-fourth 
inch in diameter, and smaller biotite plates. Under the microscope 
the groundmass is seen to be hypidiomorphic granular and to consist 
of grains of orthoclase and partial crystals of plagioclase (oligoclase) 
and biotite, with a little quartz. Magnetite, titanite, zircon, and 
apatite are abundant accessory minerals. The phenocrysts are ortho- 
clase, much of it zonally grown, quartz, biotite, and more rarely 
plagioclase. Similar inclusions occur in a number of the post- 
Jurassic granular rocks in other portions of the area, but beyond the 
fact that the quartz-monzonite porphyry is older than the granite, 
its age is unknown. 
Post-Jurassic granite. — The central portion of the Gold Mountain 
riclge is a mass of granite which prior to the formation of Oriental 
Wash was probably connected with the granite batholith at the west 
end of Slate Ridge. The smaller area of granite 8 miles west of Gold 
Mountain was also perhaps at one time connected with the Slate 
Ridge batholith. Dikes and apophyses extend from the main mass 
into the Cambrian rocks. 
