THE GEOLOGY OF CENTRAL AUSTRALIA. 
91 
hills are traversed by large quartz reefs while others of exactly the 
same formation have not been invaded by quartz, in which respect also 
the hills resemble the Lawn Hills. 
East of Central Mt. Stuart the road crosses some low hills called 
the Stirling Hills. The rock outcropping on these hills is thinly inter- 
laminated, coarser and finer red sandstone (dipping very gently north), 
which appears to be of glacial origin. In the valley north of these hills 
there are basalts, andesites and rhyolites, tentatively assigned to the 
Nullagine. Further north at Barrow Creek faulting again brings the 
Arunta Complex to the surface, and north of a narrow east-west horst 
of Aruntan rocks there is a large intrusion of porphyritic dark granite. 
This is followed further north by more formations of volcanic nature, 
a mass of rocks of Mosquito Creek formation on Neutral Downs, and 
another mass of Mosquito Creek rock further west at the Anningie tin- 
field. 
Several other ranges further north consist of quartzites and schists 
probably of Mosquito Creek age, but no rocks of a Cambrian limestone 
facies were seen along the Northern Road, south of Wauchope Creek. 
The Cambrian sedimentary rocks are probably much more extensive 
in the Eastern half of Central Australia than in the western half. In 
the eastern half they extended with interruptions from the Plenty 
River to Lawn Hill. In the Western half the volcanic rocks of andesitic 
and trachytic nature are very widespread, and though they are at 
present regarded as Nullagine they may be Lower Cambrian. They are 
said to dominate over most of the country between Teatree and the 
Granites. The writer has not personally been beyond Anningie from 
the Alice Springs end, nor beyond Tanami from the Darwin end. 
The volcanics in the Anningie area north-west of Teatree show a 
strong tendency to laterisation and kaolinisation with subsequent dissec- 
tion of the laterites. This appears to be the result of a wet climate 
in the Pliocene or thereabout. 
The only extensively developed rock series later than the Cambrian 
in Central Australia is the Ordovician Larapintine System consisting 
of gently folded to flat calcareous sandstones, shales and marls. They 
contain no dykes or intrusions whatever, according to experience up to 
the present. 
There are small pockets of late Tertiary rocks in many places, 
and large areas capped often to a depth of up to 600 ft. with wind-blown 
sand. The valleys now filled with these quaternary sand deposits were 
probably carved in the moister Pliocene period. 
III. MINERAL DEPOSITS IN CENTRAL AUSTRALIA. 
Central Australia is not rich in economic minerals, at least not the 
easily accessible parts. 
