1883] The Geology of Central Australia. 1121 
the micas. This normal rock passes on one hand into metamor 
phic granulite which has two varieties, one a fine-grained white 
rock containing a preponderance of quartz ; the other reddish and 
coarse grained, in which the orthoclase predominates. This 
again passes into a true metamorphic muscovite-granite. This is 
a light white-gray rock moderately fine in structure, and is very 
different in appearance to the granite forming the central axis. 
On the other hand the normal gneiss may become (a) hornblendic, 
in which case it generally loses some quartz; (6) garnetiferous, 
containing crystals of almandite; (c) epidotic, containing epidote 
(pistacite). The last variety passes into unakite, a very beautiful 
rock consisting of dazzling white quartz, reddish orthoclase and 
yellowish-green epidote; and this again into pure epidosite by 
losing its feldspar. All these rocks alternate with each other, are 
much folded, incline generally at a steep angle, and strike north- 
east. I consider them to be of Archean age; or the slates 
and schists which form the Flinders range, and are probably 
Cambrian or Lower Silurian, strike north-west and are uncon- 
formable to the Peake and Mt. Margaret ranges, formations which 
belong undoubtedly to the same horizon as the Musgrave Range 
rocks. 
The central granite is more recent than the Archæan gneisses, 
as it faults them and in places has partially re-metamorphosed 
them. 
The dolerite rocks are probably more recent than the granite, 
and are as follows : 
%. Dolerite——Consists of augite, labradorite, magnetite, olivine and sometimes 
chlorite. Biotite is often present as an accessory mineral. In structure it varies 
from a granular crystalline to a jet-black aphanitic variety. 
D: Norite.A coarse dark reddish-gray rock, consisting of foliated pyroxene and 
labradorite. 
c Augite-Andesite.—A nearly black, fine, granular rock consisting of andesite and 
augite. The latter is often in distinct though small crystals, giving the rock a 
Porphyritic structure. 
The main dykes follow the strike of the metamorphic rocks, 
but innumerable cross dykes are given off which run in every 
direction. What the exact chronological place is for the grapes 
and these rocks it is as yet, in the present state of Australian 
geology, impossible to say. About sixty miles south o 
Musgrave range there is another range exactly similar in every 
Particular, which is known as the Everard. The MacDonald 
