74 
secting at about 120°. Some of this mineral has undergone 
chloritic change. Plagioclase polysynthetically twinned and 
altered ; epzdote in fair grains as an alteration product ; secondary 
colorless awgite, sparingly ; secondary quartz, which is very clear 
and contains liquid enclosures; and apatite which is rather 
abundant in grains. Some sphene is also present as an accessory. 
It has a sp. gr. of 3:03. 
The whole rock has been a good deal crushed and indicates a 
tendency to become schistose. . 
VIII. Aucen Gneiss, Florence River “Ruby” Field, Central 
Australia. 
This gneiss is composed of a good deal of biotite, which is very 
pleochroic ; plagioclastic felspar, beautifully twinned and clear, 
the twin lamelle show intense strain and bending, and in fact 
the whole rock has been much strained and shorn; quartz, 
forming a mosaic with felspar ; mzcrocline containing apatite (?) 
as needle-like inclusions; garnets of a clear pink color, surrounded 
by bzotite and some greenish alteration products; epidote(?) with 
high polarisation colors. The garnets are isotropic. Some of the 
felspar contain some ramifying masses of calcite as a secondary 
infilling. A little rutile is present as an accessory constituent. 
The rock has a sp. gr. of 2°75 and has a perfectly gneissose 
structure. Zirconsin small crystals are present, as is often the 
case in these rocks. It is an augen-gneiss with garnet. 
IX. GARNETIFEROUS GNEISs, from same locality as No. VIII. 
The minerals present are as follows:—Plagioclase felspar, 
showing splendid lamellar twinning ; one piece shows both the 
albite and pericline types combined; it is fairly clear. Ortho- 
clase felspar is present ; quartz in plenty, also as an inclusion in 
the garnets present ; biotite in plenty; garnets of a beautiful pink 
color are abundant in the slide and hand specimen, they are 
irregularly cracked across and are full of cavities and inclusions, 
are quite isotropic and show no anomalous optical characters. 
Rutile is present as an accessory mineral ; crystals of light yellow 
and of a dark red are present, both as simple prismatic forms and 
as geniculate twins. The geniculation angle of one of the latter 
was found to be 114° 30’ (this angle is given by Rosenbusch as 
114° 25’). In some cases the rutile occurs as an inclusion in 
biotite, while in one case it occurs in garnet. Apatite occurs, 
both as fairly large prisms in felspar and as long needle-like 
forms ; zircon is moderately abundant as an accessory in small 
colorless crystals with dark borders, due to the high index of 
refraction. 
The whole rock is typically metamorphic, has a sp. gr. of 2°83 
and is rather coarse-grained. 
