56 
J. R. H. McWhae. 
are larger than those in the Upper Quartzite hcing 0.3 to 0.5 mm. in 
diameter and lie between the grains of the quartz mosaic, while there 
are iDoikiloblastie inclusions of rutile, magnetite, sillimanite (?), fels23ar, 
and zircon in the ipiartz grains. 
(iii) Tb(‘ Infcdded Quartzites lithologically reseinl.de the Lower 
Quartzites, b(‘ing a felspathic variety free froTii oriented, poikiloblastic 
inclusions of idiol)la.stie chrome-iuuseovite in the quartz grains. The 
felspar is slightly kaolinised microeline \\ilh frequent microperthite w^hieh 
generally oeeur.s in xenoblasts up to one mm. in diameter in the quartz 
mosaic and may form tive to six per cent, of the rock. The inclusions 
in the (lunrtz grains are zircon, red-brown biotite and a green pyroxene, 
forming two to three per cent, of one lax-k (22742)*. 
Ontjin of the quart — The <iuartzit(>s a})]iear to have been derived 
l]'om reiuaj’kably pure (piartz sands which have recrvstallized in the 
sillimanite zone r('sulliug‘ in the obliteration of the clastic structure (23, pp. 
92 and 94). 
(b) Mica S chi. •it. 
The init'a schists occur in the western metasedimentary band and are 
light yellow-bi't)wn to grey brown, generally highly schistose, medium- 
gTained, micaceous rocks whi(4i are fre(]uently contorted. The characteristic 
features of tliese rocks are the constant jn'esence of bands and lenses of sil- 
linianite in very title aggregates of acicular crystals Avlnch are frequently 
alt(‘red to siwicite {26, p. 13) and the marked schistosity — the tjuartz grains 
having an index of (dongation of four to five. 
(i) The ^tiiseip ile-quartz-silliuuinite schist (22569) has the following 
miiun-als visible in hand specimen — gobhai plates of muscovite two to three 
nun. in length: colonrlcrs, strongly elongated ([uartz grains three to five mm. 
long; and bands up to two cm. wide ami more than 10 cm. long' containing 
an aggregate of line while acienUn- sillimanitf^ and .scricile. There arc rare 
inclusions of sericite ami minute silliniaiiite jirisms in the quartz and very 
corroded biotite is sometimes observed. The complete absence of uiidulose 
extinction in tlu' idongated quartz grains indicates that complete reerystal- 
lisatiou took place dui'ing metamorphism. 
The apju’oximate mineralogical composition is muscovite 40 per cent, 
quartz 30 per cent, sericite 30 per cent. Avith biotite, sillimanite and iron 
ores accessory. 
The serieite-sillimanite bands become most common in the south of the 
area in the vicinity of the Clackliue firi'-clay deposits, Avhich are highly 
kaolinised sillimanite-mica schists composed largely of white kaolin with up 
to 10 ptu' cent, of lenticular bands of very acicular sillimanite (26, ]i. 12). 
Quartz and kaolinised muscovite are visible in hand specimens. This sil- 
limanite f-lay lies close to the Younger Granite and seA'ernl ]3egmatite veins, 
genetically related to tills granite, occur in the west of the deposit. 
"Mr. IT. BoAvley ^‘picked up a loose crystal of kyanite a little to the 
north of the lirickpit” (26, p. 11), but no kyanite has been found in the 
present investigation. 
A lateritised form of the muscovite-quartz sillimanite schist (22568, 
22569, 22570) occurs in a band in the upper granitic gneiss about 10 chains 
*N’iimbrrs refer jo llio catalogue of the collection of the Department of Gcolosrv of 
the University of W’.A. 
