62 
of iron in a glassy groundmass. Corroded phenocrysts of 
olivine are plentiful. 
Metamor'pJtic Rocks. — The gneisses of the Musgrave 
Ranges, derived both from the alteration of sedimentary and 
igneous rocks, with few exceptions, skirt the chain on either 
side ; they also form the intermediate flanks of folds produced 
by the intrusion of the eruptives. They do not extend to the 
same altitude as the igneous rocks, and, as is the case in the 
Mann Ranges, they appear more extensive on the eastern 
than on the western limits of the range. 
A natural section along the course of Whittell's Creek 
presented a variety of schists within small range of country. 
The section showed a gradation from a compact gneiss through 
a series of beds, as follows : — Quartzite, quartz schist (lami- 
nated), schists of various kinds (mica, chlorite, epidote, and 
garnetiferous, with numerous perfect dodecahedral crvstals 
of garnet in a dark quartzitic, schistose matrix) ; thence 
quartzite, jointed regularly in two directions at right angles. 
The strike varies from almost due north and south to east and 
west ; the latter is. however, the general strike of the beds of 
this section. East of Mount Woodward the gneisses are in 
parts compact, in parts fissile. They are jointed vertically in 
direction north, few degrees east, and at right angles to this 
plane. The planes of foliation dip south. North of here it 
is distinctly granitic in character, and separated into more or 
less horizontal (lenticular) layers by planes of division ; these 
layers thickening appreciably as the depth increases (Bank- 
formigc A hsonderung). At the contact with a diorite dyke it 
has assumed a remarkable, closely foliated character ; the 
folia, produced by a very dark coloured biotite and stringlets 
of quartz running parallel with the direction of intrusion. 
The gorge cut by the Opparinna Creek affords another 
section within the gneisses that skirt the watercourse in the 
form of scarped, shattered walls. They show signs 
of earth - movement and folding, and are replaced 
in parts by smaller bands of chloritic and sericite schists, 
often traversed by small seams of epidote at the zone of con- 
tact with diorite dykes. At Opparinna Spring the country 
consists of a compact, dark bluish-black gneiss, vertically 
jointed in directions W., 20° N., and N., 10° E. (less per- 
fectly), and in planes dipping S. 5°. Along the last-men- 
tioned plane the rock parts readily into layers about twelve 
inches thick. North of the spring the metamorphic series 
changes to a compact brown gneiss, weathering massive 
granitic, and showing a regular cubic jointing. The texture, in 
parts, approaches the "graphic" intergrowth of some granites, 
the quartz occurring as rounded and elongated inclusions 
