77 
the surface of which lie boulder-shaped tors that of^en rest 
in perilous positions. 
Diorite and pegniatite dykes occur in fair number, the 
former more frequently than the latter. 
Metamorphic Rocks. — The gneiss occurring in this 
locality is, without exception, granitic and largely "meta- 
pyrigen." The best exposures that came under notice are 
those occurring south-east of Artootinna soakage well. At 
this spot the planes of foliation, greatly contorted and folded, 
strike easterly, and the rock is vertically jointed in direction 
north and south. The foliation is made conspicuous by 
planes of dark-coloured biotite, the mica in the original in- 
trusive mass being in parts poorly developed or absent. 
Vei7is, etc. — Veins of barren quartz within the bedrock 
are not wanting. To the east of the ranges, further, small 
pegmatitic veins exist within the gneiss, containing irregular 
secretions of magnetite. 
Ayees Ranges. 
General Bemarks. — The group of hills, situated for the 
most part in the southern limits of the Northern Territory 
and partly in South Australia proper, and generally known 
as Ayers Ranges, is hardly deserving of such a geographical 
term. In appearance the hills are similar, though smaller 
and more disconnected than the previously mentioned groups 
of elevation. Mr. Ernest Giles, describing these ''ranges," 
which he discovered in 1872, from the summit of Mount Sir 
Henry, stated* that "the mount and all others connected 
with it rose simply like islands out of a vast ocean of scrub," 
and that the mount "consisted of enormous blocks and boul- 
ders of red stone, so riven and fissured that no water could 
lodge for an instant upon it." 
The hills are of fair altitude ; yet they appear compara- 
tively low. This is because the red sands from which they 
rise cover their flanks to a considerable height. The highest 
point, Mount Cavenagh,t stands 2,200 feet above sea level, 
but only 300 feet above the adjoining sands. They may be 
divided into three groups : firstly, that comprising Mounts 
Cavenagh, Barrow, and Reynolds, all of which are portions 
of the same outcrop and in proximity to one another : second- 
ly. Mount Sir Henry, situated about three miles south of the 
former ; and lastly, a prominent southern ridge that extends 
into South Australia proper. All these prominences have 
been determined by igneous intrusions, the first two sets con- 
sisting of granite, the last of an extensive belt of diorite dykes. 
* Geogr. Travels in Centr. Austr., 1872-1874, I., page 78. 
t Mount Cavenagh of Giles was re-n«ined Mount Burton by 
Carnithers' party. 
