63 
(quartz de corrosion) in the felspar."^ The optically-continu- 
ous character of the quartz and felspar can readily be detected 
in hand specimens by suitably reflecting the light from a 
freshly fractured surface. The planes of loliation of the 
true gneiss strike W., 20*^ S., and dip northerly 11°, 
South of Opparinna Spring the gneissic quartzites t com- 
posing the ranges are thrown into a great overthrust fold 
which can be observed on the eastern face of the gorge cut 
by Moffat Creek, by following up the exposure of two pro- 
minent parallel layers of the rock. These, on the south, dip 
at a low angle of about 30°, and on the north the same bands 
are seen dipping in the same direction at a high angle, with 
an inward curve at the top. The crest of the fold has been 
removed by denudation ; yet the outline of the original con- 
tortion of the beds, upon reconstruction, was evidently as 
represented in the figure. Within the fold exists a zone of 
extensive dioritic intrusion, while the country is severely frac- 
tured. 
Fig. 2. — An Overthrust Fold in Beds of Gneissic Quartzite. 
Moffat Creek, South of Opparinna Spring, Musgrave 
Ranges. 
A similar feature, though on a smaller scale, was en- 
countered in Jacky's Pass. Beds of gneiss are in this case 
bent to a considerable degree ; a diorite intrusion within the 
fold accompanied the earth-movement. 
Several island-like masses of gneiss rise above the sands 
to the west and south-west of the group of hills termed the 
Kelly Hills. One of such occurs close to a native soakage 
* Lacroix has described a somewhat similar type of g:neiiss 
from Southern India. — Record Geol. Survey, India, xxiv., page 
157 (1891). 
t No doubt equivalent to the "granitoid quartzites" of this 
locality mentioned by R. W. Murray. Extracts Journals of Ex- 
plorations, by R. T. Maurice (by authority: 1904, page 29). 
