206 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
the composition of an acidic quartz monzonite, containing a little 
biotite altered to chlorite. The accessory minerals are the same as 
those of the quart/ monzonite. Some of the aplite is blotched by 
globular aggregates of coarser hornblende from 1 inch to -± inches in 
diameter. These aggregates are formed by the segregation of horn- 
blende from the surrounding rock and are rimmed by halos of almost 
pure feldspar in individuals from one-half to 1 inch Avide. The 
aplite is probably but a later differentiation product of the monzonitia 
magma. 
Scattered throughout the monzonite are segregations of hornblende 
from 2 to 3 inches in diameter. These represent a threefold enrich- 
ment in hornblende by magmatic differentiation. 
The monzonite i- cut by and grades into thin dikes of coarser 
grained rock, locally having the same composition a- the monzonite, 
but usually of more acidic constitution. The individuals of thesd 
pegmatite dikes reach a maximum diameter of 2 inches. Some of 
the dikes have basic borders composed of almost pure hornblende, 
with a median band of feldspar. While the boundary planes are 
rather distinctj individual crystals extend from the 1 monzonite into 
the basic bands and from these into the acidic center. The more 
acidic portion of this pegmatite -hows under the microscope the 
composition <>!' a soda syenite, containing orthoclase, anorthoclasej 
augite, hornblende, biotite. quartz, titanite, magnetite, apatite, and 
zircon, lite augite probably contains a little of the segirite molecule. 
Other forms of the pegmatite are composed of quartz, pinkish-gray 
feldspar, and hornblende, named in the order of abundance and the 
reverse order of solidification. Some limonite pseudomorphs after 
pyrite occur in the pegmatite, but the original character of the 
pyrite was not determined beyond doubt. In other pegmatites par- 
tial crystals of ferromagnesian minerals are inclosed in a coarse 
crystalline aggregate of feldspar. Microscopic examination showed 
that orthoclase and microperthite are so predominant over plagio* 
clase in this rock that it has the composition and texture of a syenite 
porphyry. The ferromagnesian minerals include augite, olivine, 
brown hornblende, and biotite. Apatite occurs in unusually large 
crystals and magnetite in grain.-. Miarolitic openings occur in this 
pegmatite and crystals of the constituent minerals protrude into 
them. The pegmatite therefore consolidated under less pressure 
than the monzonite, which lacks such cavities, or its composition was 
more favorable to their production. The pegmatite is evidently 
but a late intrusion of the monzonite-magma residuum. Not only 
is the pegmatite more acidic than the quartz monzonite, but it has 
undergone an enrichment in soda, linking the quartz monzonite to the 
soda syenite next to be described. 
The batholith sends thin dikes into the Pogonip limestone. At the 
