75 
X. SyenitE Porpuyry,* Yardea, Gawler Ranges. 
This rock, which has been a good deal altered, is composed of 
a felsitic ground-mass of a brown color, in which occur porphyri- 
tic crystals of felspar, greatly altered and clouded. This felspar 
polarises in low tints, and much resembles soda-orthoclase. 
Augite is present as a porphyritic constituent, the crystals of 
which have been much altered, with separation of brown iron- 
oxide, especially along the cleavage cracks. There is a blue 
mineral, with high refractive index and quite unaltered, present 
in the ground-mass in tiny granules, which I have not been able 
to determine (corundum ?). Agatite is present as an accessory. 
The felspars show secondary growth very well. The rock has a 
sp. gr. of 2°63, is very hard and compact, and tends to break 
with a splintery and rather conchoidal fracture; it may be an 
anorthoclase syenite porphyry. 
XJ. Biotire Granite (from an erratic boulder), Hallett’s 
Cove, S.A. 
This rock is a coarse-grained granite. The hand specimen is a 
small one and rather weathered. It consists of felspar, ortho- 
clase, with a little plagioclase, cracked, clouded, and altered ; 
quartz in plenty, containing liquid cavities ; biotite, a good deal 
altered and darkened. The texture is coarse and the structure 
typically granitic. 
XII. Coarse MuscovirE Granite (Pegmatite), Mount Gawler, 
near Port Lincoln, S.A. 
This is a much decomposed rock of a very coarse texture. 
The felspar has nearly all passed to kaolin, the plates of musco- 
vite are turning silvery-white, and losing their transparency and 
elasticity. The quartz is abundant and, of course, unaltered 
As this rock was so decomposed and presented no particular 
features of interest, no section was cut, but the foregoing notes 
were made from an examination of the rock specimen itself. It 
is an exceedingly acidic rock. 
XIII. Brorire Granite (red), Murray Bridge, S.A. 
This granite, which is coarse-grained, consists of orthoclase and 
mcrocline, the latter showing microperthitic structure; plagio- 
clase well-twinned in lamelle ; quartz in large grains, which ap- 
pear smoky in the hand specimen and in the section are seen to 
be full of beautiful liquid cavities with moving bubbles. Biotite 
is present in fair amount. Apatite occurs as an accessory con- 
* Vide ‘‘ Report on the Geological Character of Country passed over 
from Port Augusta to Eucla,” H. Y. L. Brown, Adelaide, 1885. No quartz 
at all observable in my sections.—J.C M. 
