Geology and Petrology of Part of Toodyay District, W.A. 89 
On all the bedding surfaces a well marked lineation (figure 2), due to 
elongation of mica flakes, is visible. This lineation is often accompanied by 
a corrugation of the surfaces of the Cjuartzite flags. Unfortunately the sig- 
nificance of this lineation as pointed out by Phillips (1937, p. 591) was not 
appreciated at the time when the original field survey (made j^rior to 1936) 
was being carried out, but certain significant localities within the area have 
since been re-examined and the direction and pitch of these lineations noted. 
The light that these observations have thrown on the geological structure will 
be given in a later section. 
Pig. 2. 
Quartzite outcrop in Gorge Creek, near Key Parni, Toodyay, show- 
ing well marked h-lineations. The clinometer indicates the strike 
and rocks dip towards the observer in the direction of the arrow. 
The hammer handle lies in the direction of the b-lineations which 
pitch to the left-hand side of the outcrop. The well-marked joint- 
ing of the quartzites is a noticeable feature. (Eeproduced from 
^‘Junior Geology by E. de C. Clarke and L. P. Hanrahan, by kind 
permission of "the University of Western Australia Textbooks 
Board.) 
The structure in all tlie specimens examined microscopically, is similar, 
viz., coarsely granoblastic consisting almost entirely of irregular interlocking 
grains of cpiartz. All signs of clastic structure have been completely obliterated 
by recrystallisation. In all the rocks examined there is slight undulatory ex- 
tinction, but no other signs of crushing in the cpiartz. A pale greenish chrome 
muscovite is the most common constituent other than rpiartz, and is present 
in all the specimens examined. Occasionally narrow seams up to 2 inches 
thick of this mica are interbedded with the quartzites. Felspar (mainly 
microcline with a little oligoclase) is a common constituent, but rarely exceeds 
5 per cent of the rock. Minor minerals present in varying amount, are mag- 
netite, apatite, rounded pink zircons, biotite, and rutile. These heavy ” 
minerals are occasionally concentrated into bands (figure 4B). 
In the earlier examination of these rocks from the Jimperding Area, it 
was thought possible to distinguish the various quartzite bands by means of 
the mmor constituents (Prider 1933, p. 7). Extension of the survey and an 
examination of a greater number of the lower quartzites has indicated that. 
