80 
Metarnorphic Iiocks. — In traversing the outcrop from 
south to north a gradual alteration in the structure of the 
bedrock will be noticed, the rock grading from a quartz mica 
schist on the south, through a highly micaceous black biotite 
schist, to a finely foliated quartzitic gneiss, to a typical augen 
gneiss on the north. The strike of the beds varies (in zones 
of extreme pressure considerably), though the general direc- 
tion appears slightly south of west. The dip is doubtful, 
possibly northerly. The augen gneiss, compact and granitic, 
contains lenticular veinlets of quartz, which are often con- 
siderably distended as a result of lateral pressure during a 
state of semi-plasticity, and in addition are frequently found 
turned upon themselves or complex-folded. The schist can 
be distinguished from the gneiss in the field even at a dis- 
tance by contrasting its serrated lines of outcrop with the 
rounded, massive, boulder-like outcrops of the gneiss. On 
the north-east the rock consists of a rotten biotite schist, in 
which planes of mica have become so aggregated that the rock 
appears to be almost entirely built up of the pure mineral 
biotite. Even in hand specimens the curved and crinkled 
lamellae of the mica indicate how great a stress the beds have 
been subjected to. The planes of schistosity of the rock 
strike from 10 to 20^ south of east, and dip N. 32^. The beds 
are further jointed in directions E. 10° S., with a dip of 60° 
S., N. and S., with a dip of 85° W., and irregularly by a 
poor vertical plane. To the south this rock becomes less per- 
sistent, and has yielded more to weathering. A small de- 
velopment of chlorite schist occurs in contact with the augen 
gneiss, and a local production of hornblende epidote schist 
has taken place at the contact with certain diorite dykes. 
Skirting the north-western limits of the outcrop a finely crys- 
talline gneiss seems to point to a zone of crushing of an 
igneous rock. (See Appendix. Pages 94-5.) Outcrops of 
quartz schist, mica schist, and gneiss extend more or less con- 
tinuously westwards to Indulkana soakage well, at which 
spot the gneiss contains coarse vein-segregations of felspar 
with a development of tourmaline and titaniferous iron ore. 
Repeated searching for tin ore proved fruitless. 
Some miles south of the main outcrop low surface expo- 
sures of ferruginous clay slates and mud stones appear, the 
sharp, serrated edges of the same standing out conspicuously. 
In some parts the rock comes near to a phyllite, and is tra- 
versed by very many small quartz veins. 
Veins, etc. — The so-called ''quartz reefs" of the locality 
are of two kinds, namely, those forming portions of a true 
igneous (pegmatitic) dyke, and those formed subsequently by 
deposition froixi solution in fissures of the rock. The latter 
have a remarkably fresh, compact, crystalline appearance, 
