284 AUSTIN fF. ROGERS: 
orthoclase is intergrown with albite with characteristic twin lamellae 
appearing around the border or in the interior, thus forming micro- 
perthite, which is a characteristic feature of the rocks of this locality. 
An occasional Carlsbad twin occurs. The quartz is full of very minute 
inclusions. ‘The amphibole is a dark-colored one with the following 
axial colors: a, brown, D, deep greenish-blue, €, deep bluish-green. 
The extinction angle on (110)" is about 25°. The elongation is 
parallel to slower ray. It has the 124° cleavage of amphibole. 
Doubtless it is a soda amphibole, perhaps nearer hastingsite than any 
described mineral. Several small zircon crystals were discovered 
in the fragments of the crushed rock. Biotite was also noticed in 
some of the rock. 
GRANITE-PORPHYRY, MICRO-GRANITE, ETC. 
About half of the number of rock varieties collected are included 
under this heading. They grade from coarse granites with porphy- 
ritic tendency to fine-grained micro-granites, and are usually reddish 
or reddish-gray in color. 
These fine grained micro-granites weather into rather angular 
bowlders. 
The rocks are aggregates of quartz and orthoclase (often micro- 
perthite) with accessory amphibole, biotite, magnetite and apatite: 
The amphibole is sometimes riebeckite, sometimes one resembling 
that of the country rock. A rather peculiar intergrowth of quartz 
and orthoclase was noticed in one rock (No. 3). It may be described 
as an orthoclase mosaic in quartz. The quartz areas have uniform 
extinction over quite large areas, while the orthoclase areas only have 
uniform extinction over small areas. Thus it is neither a micropeg- 
matitic nor micropoikilitic growth. One of the micro-granites occurs 
on the top of Mt. Walsh, the highest point of the Headquarters group. 
It is but a few feet thick and a little way down the slope the contact 
between it and the coarse granite may be seen. 
APLITE VEINS 
Perhaps the most interesting rocks of the region are the narrow 
dikes that cut the coarse granite, the country rock. About seven or 
t Determined on cleavage flakes. 
