93 
Felsj3ar is of two species : orthoclase and a delicately 
twinned plagioclase. Decomposition has acted to a consider- 
able extent U2^on many of the constituents ; the felspar, being 
clouded when viewed by plain transmitted light, becomes 
brilliantly tinted in the dull portions under crossed nicols on 
account of the strong double refraction of the products of de- 
composition (kaolin). Orthoclase is somewhat subordinate to 
plagioclase ; the cleavage cracks and borders of both are lined 
with oxide of iron. 
The mica, a green biotite, occurs principally as aggre- 
gates of flakes, partially decayed ; the whole rock section, 
moreover, is speckled with minute particles of biotite. 
Magnetite is fairly plentiful, usually surrounded by a 
layer of secondary mineral. 
Apatite is present as stout, prismatic individuals, with 
prominent cross fracture. 
HORNBLENDIC GrANITE. 
Plate xviii. , fig. 2. 
Locality. — Glen Ferdinand, Musgrave Ranges. 
Macroscopi rally. — Rock granitic, normal ; composed of 
white felspar, colo\irless quartz, dark mica, and hornblende, 
as largish, cystalline secretions. 
Microscopically. — Texture hypidiomorphic granular ; the 
quartz and felspar uniformly distributed over the sections ; 
the mica and hornblende not so. A fine mosaic of microcline 
and quartz is characteristic. 
The felspar is represented both by orthoclase and micro- 
cline, the former being occasionally crowded with numerous 
very slender, crystalline needles of zircon. 
Mica (strongly pleochroic, brownish biotite), as irregu- 
lar, curved, and twisted lamellae, partially or wholly altered 
to a dark-green chlorite, more or less fibrous, and with a 
weak double refraction. Pink, fractured garnets of fair size 
are rather plentiful, usually, though not necessarily, in prox- 
imity to the mica and the altered chlorite. 
Magnetite is present as irregular particles. 
Granite. 
Locality. — Everard Ranges. 
Mac/'oscopically. — A coarsely crystalline, normal granite 
with prominent pink felspar (orthoclase) and dark-coloured 
mica. The rock is deeply "honeycombed" on its surface, this 
being a result of the ready decomposition and removal of the 
felspar. 
Microscopically. — Rock typically hypidiomorphic granu- 
lar, consisting of clear quartz, a clouded orthoclase, and a 
strongly pleochroic biotite. Micrographic intergrowths be- 
tween quartz and felspar are common. Magnetite scarce. 
