Geology and Petrology of Part of Toodyay District, W.A. 109 
granular microcline aggregate is comparatively coarse-grained and 
seems to be a protoclastic, rather than a cataclastic structure — 
this is supported by the absence of any cataclasis or marked strain 
in the associated quartz. Tlie microcline may carry small inclusions 
of quartz and plagioclase, and in the latter instance mynnekitic 
intergrowths of quartz with the plagioclase are usually present. 
Pig. 11. 
Fabric diagram of Upper granite gneiss. Plot of 
poles of optic axes of 200 quartz grains, showing the 
complete absence of any orientation in the quartz. 
The Cjuartz is in irregular shaped unstrained grains forming a con- 
stituent of the microcline mosaic and, as alloti’iomorphs, elongated 
parallel to the gneissic banding (Plate IT, A and B, and Plato 
III, D), in which case it often includes parallel aligned biotite 
flakes. The (juartz shows slight undulatory extinction but has 
not suffered any granulation and has been either : — 
(1) of post t(*ctonic crystallisation : or 
(2) original cruslied gj’ains, eoTnphdely recrystallised into elong- 
ated xenoblastic forms. 
A fabric analysis was made of a fine even-grained granitic gneiss, 
showing this marked elongation of unstrained ijuartz grains, but 
after the measurement of 200 grains no apparent concentration 
of the o])tic axes in any direction was noticeable (figure 11). 
Similai' results wert‘ obtained from se\-eral othei* granite gneiss(>s 
wliich wei'(‘ analysed. 
It is interesting to coinpaie this result with those obtained for several 
of the (juartzites (figure 5. A and B), which show sucli a well- 
marked fabric. It would be expected that the gneiss would 
possess a fabric similar to the (piartzites. The complete absence 
of any girdle in the diagram for the gneiss indicates that the quartz 
is of post tectonic crystallisation. This is verified by the observation, 
in somf' j*ocks, ofgj'aimlar jnicrocline mosaics included in the quartz. 
