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Contact Gneiss. 
Tjocality. — Oppariniia, Musgrave Ranges. 
Macrofico'pically. — A closely foliated, fine-grained gnei.s:s, 
with prominent dark planes of mica (linear foliation), and 
narrow lenticles of quartz and felspar. The rock occurs in 
direct conta.^t with a diorite dyke, and its planes of foliation 
have the same strike as the walls of ilie dyke. 
Micro^coiJicalli/. — The distinct gneissic foliation remains 
prominent even under a high power objective; the mica in 
regular parallel stringlets. The fine state of crushing of the 
rock appears to be an ultimate stage of metamorphism. 
The quaitz occurs as excessively crushed particles that 
displav marked "shadowy extinction" when viewed under 
crossed nicols. It is comparatively fresh-looking, and free 
from interpositions except the minutest. 
The felspar, orthoclase, as small, irregular individuals, 
showing shearage on a microscopic scale, with few indi- 
vidualised inclusions. 
Microperthite is developed to a limited extent, and dis- 
plays a very delicate lamination under crossed nicols. 
The biotite is clear, strongly pleochroic, and appears in 
the form of elongated flakes. 
Schistose Quartz Rock (so-called '"'Quartz Blow"). 
Locality. — Mann Ranges, south-east of Mount Edwin. 
Macroscopically. — A fine-grained, white quartzose rock, 
schistose, with well-defined planes of brown secondary mica, 
in parts decomposed and brown. 
Microscopically. — Essentially composed of closely aggre- 
gated, allotriomorphic grains of quartz, the boundaries of 
which are usually sharp, and the grains in direct contact with 
one another. A fair amount of amorphous silica is present. 
The quartz is fresh, but contains numerous unindividualised 
fluid inclusions, with stationary and mobile gas bubbles, ii.su- 
ally arranged in faiily broad parallel bands, crossing in a 
continuous line several adjacent grains. It, therefore, ap- 
pears that the inclusions are to a certain extent not original, 
but have subsequently been produced by the metamorphism 
of the rock by igneous intrusion. Individualised inclusions 
occur in the form of elono-ated prisms of colourless apatite, 
with indistinct, rounded prism- terminals and transverse frac- 
turing. 
The decomposed mica flakes do not exhibit anv striking 
tendency to parallel orientation. Dark strain shadows cros- 
sing the quartz on rotation of stage between crossed nicols 
Sfive ample evidence of stress to which the rock has been sub- 
jected. 
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