77 
The rock in structure and texture is almost identical with No. 
XV.(A), but it is crushed and has a metamorphic appearance. 
Apatite is present as an accessory constituent, as also are 
ilmenite, sphene, and zircon, though sparingly. The felspars ap- 
pear to have been crushed. The sp. gr. was found to be 2°62. 
XVI. BiotTitE GRANITE, Port Victor, S.A. 
This rock is a coarse-grained grey granite, compact and hard. 
It consists of the following minerals :—Quartz, very conspicuous 
in good-sized masses both in the hand specimen and the slide. It 
has a curious blue color and opalescent appearance, and, in section 
under the }” objective, shows some liquid enclosures, though they 
are not nearly so large or so abundant as in the quartz of No. 
XIII. The felspar is mostly orthoclase, sometimes well-zoned ; 
but plagioclase is also present, as shown by lamellar twinning. 
The predominant mica is biotite, but a little muscovite is also 
present. Zzrcons in small crystals occur as accessories in some 
of the biotites, while the hand specimen shows some small spots 
and grains of pyrites. The liquid cavities in the quartz contain 
moving bubbles in some places. The rock is altogether a typical 
granite, the most curious feature of which is the “blue” quartz 
resembling that of the Norwegian “‘ Rumburgite.” Some of the 
felspars show good secondary growth. 
XVII. Oxpsipian “ Bomss” (2), Stuart’s Creek, Lake Eyre, S.A. 
These two specimens are types of the “bombs” which occur 
in so many parts of Central Australia. They appear to have 
been slightly water-worn. Their origin is, as yet, quite unknown. 
They consist of a brownish volcanic glass, which in section gives 
no trace of devitrification—a perfect natural glass in fact. From 
determinations upon some nine specimens in my possession, the 
mean specific gravity is about 2°44. The glass fuses before the 
blowpipe without intumescence and in the closed tube it atfords 
no water. When sliced through, it shows a compact interior, 
with merely one or two steam holes or cavities not much larger 
than pin-points. I add no more at present, as I hope to investi- 
gate them more fully in the future. 
XVIII. GarnetiFEROUs GNeIss, Block 10 Mine, 315-ft. level, 
Broken Hill, N.S.W. 
This rock rather approaches a schist in its character. It is 
tough and compact, and has a sp. gr. of 2-71. It contains quartz 
in plenty. A good deal of orthoclase and biotite are also present. 
Garnets—both pink and green—form a fair amount of the rock ; 
they are quite isotropic between crossed nicols. Jwscovite and 
altered mica are present with the biotite. There is an accessory 
