80 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
II. A rather light-gray rock, containing occasional small feldspar phenocrysts 
and many small lath-shaped prisms of pyroxene, which indicate direction of flow, 
in a very finely granular groundmass. In thin section the larger feldspars are seen 
to be orthoclase, microcline, and microperthite, with a larger amount of a zoned 
plagioclase, which corresponds to oligoclase-albite. The phenocrysts of pyroxene 
usually have good crystal outline and are not uncommonly twinned; micropegmatitic 
intergrowth with hornblende and with feldspar is sometimes seen. Hornblende is not 
plentiful and is usually surrounded by a zone of pyroxene and magnetite, indicating 
resorption. A few foils of biotite are present. Irregular grains of magnetite are 
common. Apatite and titanite occur sparingly in sharp crystals. Small grains 
of sodalite and patches of analcite are inclosed in fresh feldspar phenocrysts. The 
groundmass is very fine grained, but shows a distinct trachytic texture. The 
minute feldspar laths are too turbid for identification, but are probably orthoclase. 
Microlites of pyroxene and tiny grains of magnetite are plentiful. This specimen 
is from the Anaconda tunnel. The rock appearing above on the surface was desig¬ 
nated on the earlier map as syenite-porphyry. 
III. A finely granular rock of rather dark-gray color, containing plentiful 
phenocrysts and irregular grains of pyroxene and noticeable yellow crystals of 
sphene. Under the microscope it is found to be composed mainly of large and 
small crystals of feldspar, often of diamond-shaped outline. These crystals are as 
calcic as oligoclase in the interior, and are bordered by a zone of orthoclase. Pyrox¬ 
ene is fairly plentiful, both in sharp crystals and irregular grains. It is light green, 
noticeably pleochroic, and has an extinction angle corresponding to aegirine-augite. 
Hornblende is not uncommon, but is usually surrounded by resorption rims. Anal¬ 
cite occurs in partially decomposed masses, sometimes giving a suggestion of crys¬ 
talline outline. Nosean is fresher, in crystals of square outline. Apatite, mag¬ 
netite and noticeable titanite are the accessories. The groundmass is decidedly 
subordinate. Microlites of feldspars, some of which seem to be albite, and tiny 
grains of sodalite, pyroxene, and magnetite are the chief constituents. This 
specimen represents much of the mass occurring on the south slope of Battle 
Mountain, in the vicinity of the Portland mine. 
IV. A rather dark-gray rock, containing small phenocrystic grains of feldspar, 
pyroxene, and a little hornblende in a predominant fine-grained groundmass. 
Microscopic examination reveals abundant feldspar, usually in individuals of imper¬ 
fect crystallographic form. Many of the larger phenocrysts are orthoclase, often 
intergrown with a finely striated oligoclase-albite. Some sodic plagioclase has both 
albite and pericline twinning resembling microcline; outer zones of orthoclase are 
commonly present. The pyroxene corresponds to aegirine-augite in composition, 
but possesses the augite outline. Hornblende, which is not plentiful, occurs never¬ 
theless in individuals of good size. It has suffered some resorption. Nosean is 
rather prominent in turbid crystals of good size. Analcite is also common, but is 
somewhat decomposed into other zeolites, probably stilbite and natrolite. Sodalite 
is not readily distingu'shed, occurring as minute crystals in the somewhat turbid 
groundmass. Apatite, magnetite, and titanite are prominent accessory constit¬ 
uents. The groundmass, though not as abundant as the hand specimen indicates, 
is prominent notwithstanding. It is composed chiefly of laths of orthoclase, with 
small grains of pyroxene, sodalite, and magnetite, and has the trachytic texture. 
