Geology and Petrology of Part of Toodyay District, W.A. 113 
petrologically, being composed of partly chloritised biotite, quartz, and oligo- 
clase with accessory magnetite, apatite, and sphene. One specimen, however, 
shows a development of a deeply-coloured hornblende. 
The boundaries of the xenoliths are sharp and there is no transitional 
hybrid zone. The structure is fine, even granular, schistose (figure 12). The 
plagioclase carries minute rodlike inclusions of recrystallised muscovite. It 
is rarely twinned but its refractive index, approximately equal to that of 
Canada balsam, indicates that it is an oligoclase. 
Biotite-quartz-plagioclase graiiulite xenoliths in granite gneiss. 
A. No. 1220. Edge of xenolitli. The left hand edge of the 
field is occupied by the coarse granite gneiss, the right hand por- 
tion by the biotite-quartz-]3lagioclase granulite. 
B. No. 1221. Variety with deep greenish hornblende. 
The biotite is a greenish-brown variety, altered along cleavages to chlorite. 
The deep green hornblende present in one of these rocks tends to occur in 
small clots, often enclosing magnetite. 
Accessories are apatite, magnetite, epidote, and sphene. 
These rocks represent psammitic types of sediments, which with the 
admixture of a little calcareous material have at times developed hornblende 
and epidote ; they cannot be matched with any of the metasedimentary 
rocks in the Jimperding Series. 
(iv) Eulysitic rocks (meta-banded ironstones). — Banded quartz-magnetite- 
grimerite rocks with affinities to the eulysites have been noted vas enclosures 
in the Upper Gneiss in t-wo places : (a) At 26 chains E., 40 chains N. of datum. 
This occurrence is in the form of a band, several chains wide, which can be 
traced for about 30 chains in a south-easterly direction. (6) At 92 chains W., 
140 chains N. of datum. This occurrence is also a band in the gneiss, about 
1 chain wide and can be traced for about 30 chains in a north-easterly direction. 
Both of these bands lie close to the bottom of the Upper Gneiss and are 
probably both part of the same horizon. The rocks from both occurrences 
are essentially the same, being magnetic banded rocks composed of varying 
