208 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
The soda syenite is cut by dikes of compact greenish-gray aplitid 
rocks. Pink feldspar is associated with the gray feldspar and pyrox- 
ene and it alone forms some veins. The aplite under the microscope 
has a very uneven-grained allotriomorphic texture. The feldspar! 
include microperthite, orthoclase, and some anorthoclase. A little 
quartz is also present. While the rock- i- not rich in ferromagnesiaij 
minerals, there are many small grains and partial crystals of segiriteJ 
augite. This mineral shows the usual zonal structure, with deeper 
green hands on the border. Irregular grains of a light-yellow garnet 
are rather abundant. The accessories arc titanite and apatite] 
Fluorite occurs in small blebs, surrounded by a mesh of sericitd 
shreds, which were probably formed by the same gases that deposited 
the fluorite. Calcite is also present and its contacts with other min 
erals are so sharp that it was probably deposited in miarolitic open- 
ing-. The contact between the aplite and the syenite i- in some case*! 
sharp, in other- gradational. In one instance a dike of syeni'e 
porphyry is faulted by an aplitic dike, but there can be little doubt 
that the two are genetically related. Narrow pegmatitic dikes, the 
feldspar and pyroxene of which reach a diameter of 1 inch, occur. 
The lime-tone immediately adjoining the igneous mas- i- meta- 
morphosed to a coarse- or line-grained white marble, through which 
small plate- and veinlets of tremolite are scattered. 
The soda syenite intrudes Pennsylvanian limestone and has suffered 
practically the same deformation as the quartz monzonite, and it may 
well be. as indicated by the monzonite-pegmatite, a later variant of 
the same magna. 
Granite. — A considerable area of biotite granite occurs to the ea-t 
of the Emigrant Wash, 3 mile- south of the area surveyed. Dikes 
of muscovite granite, genetically related to the biotite granite, were 
observed cutting the Cambrian rock- 1 mile south of Tucki Moun- 
tain, and a few probably occur in the area surveyed. This granite 
i- probably of post-Jurassic age. 
Later quartz-monzonite j><>r;>h)/r)i. — Four miles south of Tin Moun- 
tain is an area of siliceous quartz-monzonite porphyry, probably in- 
trusive in the Pogonip lime-tone. This area was not -ecu by the 
writer, but specimens collected by Mr. R. II. Chapman closely resem- 
ble the white quartz-monzonite porphyry of the Silver Peak Rangej 
and. like it. this rock is probably genetically related to the intrusion 
of the post-Jurassic granitoid rocks. Under the microscope the 
phenocrysts of quartz, orthoclase, plagioclase, and biotite are -ecu 
to be embedded in the finely granular groundmass of microcline, 
plagioclase, quartz, and biotite. The accessory minerals are magnet- 
ite, titanite, and apatite. 
Diorite porphyry.— Dikes of diorite porphyry from -2 to 6 feet 
wide cait the quartz-monzonite batholith in the southwest comer of 
