94 
Rex T. Prider. 
Complex near Pretoria, are of the opinion that the original purity of the sedi- 
ment IS essential for the formation of ^-ery coarse grained types of quartzites. 
The purity of the very coarse quartzites described above supports this theory. 
That these rocks were deformed in an almost plastic state is seen in the 
minor drag folding which they exhibit ^'ocks from these dragfolded areas 
show no more cataclasis than in the less disturbed parts. 
It IS impossible to recognise any chronological succession in the quartzites 
as practically all sedimentary features have been obscured by recrystallisation. 
(d) The Fabric of the quartzites and its relation to the geological structure . — 
Fabric analyses have been made of several qiiartzites, but in the absence of a 
set of geographically oriented specimens, no conclusions can be drawn from 
these analyses. They are quoted here to show that the quartzites have a 
well-marked girdle fabric (he., are S-tectonites) and also because one of these 
rocks (figure 5A) exhibits a rare type of orientation (type “ b ” of quartz 
orientation, hairbairn, 193/, p. 70) — the optic axes are concentrated in a 
direction normal to the bedding planes {%.€., a prominent maximum lies in 
the direction of the “ c ” fabric axis). This maximum is somewhat elongated 
and spreads out into the typical girdle. 
The other analysis (figure 5B) is a more normal type. In it there is a 
well developed ac ” girdle with two prominent maxima, equally arranged 
on both sides of the “ ab ” plane. This is a common type of fabric noted 
by Phillips (1937) in the Moine Schists of Scotland. 
The analyses made, although insufficient to warrant any conclusions, 
serve to indicate that a fabric study of these rocks would probably yield much 
infoimation regarding the tectonics of this region. One feature brought out 
is that the b fabric axis in the tw'o analysed specimens coincides with the 
lineations on the bedding surfaces (see figure 2). Although no further fabric 
analyses have been made, as no universal stage ecpiipment is available in 
Western Australia (the analyses of the two unoriented specimens described 
above -were made in the laboratory of the Department of Mineralogy and 
Petrology at Cambridge under the direction of Dr. F. 0. Phillips), a re-examina- 
tion has been made of certain parts of the area with a view' to determining the 
direction and jjitch of these b ” lineations which, on the evidence of the 
two fabric analyses described above, are coincident with the “ b ” fabric 
axis (ne., the tectonic “ strike ” or tectonic axis, sec Phillips, 1937, p. 587). 
These readings are indicated in figure 1, and show that there has been 
considerable cross folding on the main N.W. trending structure on axes 
trending N.N.E. 
Although this structural study of the Jimperding quartzites is far from 
complete, sufficient has been done to indicate the desirability of continuing 
the work when universal stage equipment is available. 
(2) The Calc-Silicate Rocks. 
A rather interesting group of lime silicate rocks occurs in narrow kuiticular 
seams at a constant horizon in the lower quartzites. The rocks lie just below 
the hornblende schist band and are of rather sporadic occurrence. They are 
characterised by the presence of grossularite, diopside, pale green amphibole, 
epidote, and sphene. 
The first sign of the presence in the quartzite of lime-magnesia impurities 
is seen in the development of a pale greenish actinolite along with a little 
epidote in some felspathic quartzites (e.g., specimen 1250*). Such rocks are 
* Numbers are the catalogue numbers in the collection of the Department of Geology, University 
of Western Australia. 
