92 
Quartz in smaller, blackish, segregations throughout the 
mass. Mica black, not infrequently as lenticular aggregates 
having their long axes indistinctly parallel, and surrounded 
by a border of pink secondary mineral. The rock has suf- 
fered from the effects of mountain building forces. 
Microscopically. — Rock with a holocrystalline ground- 
mass, in which the larger crystals of felspar are embedded. 
In parts the quartz (appearing normal in plain light) 
when viewed in plane polarised light, proves to be microscopi- 
cally separated into numerous contiguous particles; micro- 
graphic intergrowths with the felspar common ; generally 
speaking it is allotriomorphic, crowded with inclusions, and its 
fissures stained by oxide of iron, subsequently precipitated. 
The potash felspar is clouded and crowded with minute 
inclusions, which are frequently arranged in parallel bands, 
and some, on decomposition, locally stain the enclosing mine- 
ral. The felspar crystals are corroded and surrounded by a 
border of secondary mineral fibres, radially arranged : the 
cleavage ciacks are filled with secondary mineral, polarising 
with high colours. "Strain shadows" traverse the quartz and 
felspar crystals on rotating the stage with crossed nicols. 
The mica, a rather decomposed dark green biotite in ir- 
regular aggregates of crystals, is almost invariably surrounded 
by a broad band of closely set, pink garnets, which are 
minute (averaging '005 millimetres in diameter). The indi- 
vidual grains appear rather to have been separately develop- 
ed than to be crushed parts of larger garnets. Optical ano- 
malies are general among them. 
Magnetite is scarce ; the rock also contains patches of an 
earthy form of iron oxide. Epidote as a scantily develojDcd 
accessory (secondary), in small though conspicuous (on ac- 
count of the high refractive index) aggregates with no definite 
geometrical boundaries. 
Granite. 
Locality. — Mount Sir Henry, Ayers Ranges. 
Macroscojjically. — A moderately coarse-textured, holo- 
crystalline rock, considerably decomposed : the quartz and 
felspar appear brown from iron pigment ; the black-looking 
mica in fairly large, irregular aggregates. 
Mici'oscopically. — Texture typically hypidiomorphic 
granular, the rock being composed essentially of quartz, fel- 
spar species, and biotite. The normal order of crystallisation 
from the rock magma has generally pievailed, although the 
mica occurs in parts interstitial to the felspar. A micro- 
graphic intergrowth between quartz and felspar on a very 
minute scale is apparent, and the former contains numerous 
unindividualised inclusions in parallel bands. 
