Geology and Petrology of Part of Toodyay District, W.A. 119 
TABLE 3. 
Analyses of cordierite-anthophylUte rocks and related types from Toodyay, W.A. {quoted 
from Prider, 1940, 
p, 377). 
1 . 
2 . 
3. 
4. 
SiO., 
30-91 
30-83 
33-20 
49-73 
21-36 
20-47 
19-75 
12-70 
FegOg 
/19-971 
9-23 
3-36 
4-56 
FeO 
\ / 
11-28 
13-23 
12-27 
MgO 
23-57 
16-10 
21-57 
16 -.59 
CaO 
Tr. 
Tr. 
Nil 
Tr. 
NagO 
Nil 
0-36 
0-24 
0-40 
K^O 
Nil 
5-18 
0-22 
0-54 
HgO+ ... 
2-58 
4-87 
8-43 
2-77 
H^O- ... 
0-90 
0-42 
0-10 
0-12 
TiOa 
1-66 
0-70 
0-06 
0-21 
P 2 O 5 
Tr. 
nd. 
nd. 
Tr. 
MnO 
0-16 
0-07 
0-14 
Nil 
Cr^Oa ... 
0-17 
Nil 
Nil 
Nil 
101-28 
99-51 
100-30 
99-89 
1. Olivine-spinel-anthophyllite-hypersthene rock, Toodyay, W.A. 
2. Biotite-clinochlore-magnetite-corundum rock, Toodyay, W.A. 
3. Corundum-spinel-anthophyllite-cordierite-clinochlore rock, Toodyay, W.A. 
4. Biotite-cordierite-anthophyllite rock, Toodyay, W.A. 
(iv) The Amphibolite Xenoliths. — Amphibolites, varying from almost 
pure hornblende rocks to quartz-plagioclase amphibolites in which the 
felsic minerals are in excess of hornblende, are the most abundant xenolithic 
types in the lower gneisses. They are found in lenticular masses, measuring 
up to 10 chains long x 3 chains wide, and in thinner bands which may be 
traced for greater distances. The elongation and lamination in the amphibo- 
lites are parallel to the strike of the enclosing gneiss. The occasional pre- 
sence of narrow sill-like veinlets from the granite gneiss at the edges of the 
amphibolite masses indicates the intrusive character of the gneiss. There 
has, in some instances, been a considerable hybridisation of the granite 
gneiss, which has been changed from its normal character into a more basic 
hornblende granite gneiss. 
These amphibolites comprise a number of types which are illustrated 
by the following description of typical members : — 
Quartz-plagioclase amphibolites. 
These vary from medium-grained dark coloured rocks with a visible 
lamination (15438) . to types with a more granular structure in which no 
lamination is visible (e.g., 15444). 
The former are darker and more granular than the hornblende schists 
described earlier in this paper. The non-foliated granular type of amphibolite 
is the most common, and No. 15444 will be described as typical of this group. 
In hand-specimen it is a dark coloured granular rock with only a slight trace 
of parallelism of the hornblende which is the dominant constituent. It is 
a dark green variety in well shaped prisms 1 mm. in length, the interspaces 
between these prisms being occupied by light coloured fine granular felsic 
material. 
Under the microscope the structure is granoblastic, and the rock is made 
up of brown-green hornblende (65 per cent), saussuritised plagioclase (15 
per cent), clear oligoclase-andesine (10 per cent), cpiartz (10 per cent), with 
