30 
Kex T. Pkider. 
from the older rocks) is exposed over the g-reater jiart of the north-west 
and south-west walls of tlie quarry. It is clearly intrushe into the hybrid 
gneiss (b above) which, in i)laces, occurs in the form of large irregularly 
oriented angular blocks suspended in the aplogranite which truncates the 
banding of the gneiss. The aplogranite is therefore definitely a later in- 
trusion and I'cpresents the second period of granite intrusion. 
(d) Dolerite. A [)ost-aplogranite dolerite dyke is present near the 
north-eastern edge of the main (piarry and is younger than all the above 
mentioned rocks which it cuts indiscriminately. 
The exposiu’cs in this Koads Board quaiTV therefore give us consider- 
able information regarding the ago relations within the eastern group of 
gneisses of the Aimadale aiX'a. The sequence is: — 
Younger. (4) Dolerite dykes. 
(3) Massive aplogranit(’s. 
(2) Hybrid augen gneisses. 
Older. (1) Biotite-ei^idote-hornblende bornfelses and (juartz xeiio- 
liths in the hybrid gneiss. 
The field relations of the eastern group of gneisses to the western group 
are unknown. The eastern group shows the highest degree of hybridisation in 
the north-eastern part of the area but continue to be hybridised to some 
extent even at the south-eastm’u corner. 
A number of well defined quartz veins which all have the same strike 
of approximately 305° and dips of 85° to 90° to the north-east are seen to 
cut through both the hybrid gneisses and the fine banded granitic gneisses. 
Two of these quartz veins (one of them some three or four feet wide) were 
traced right to the contact of the gneiss and tlie Cardup sediments but cai'e- 
ful search sliows that they do not extend ]»eyond the contact and they appear 
to be of inv-Canlup age, probably representing an ultra-acid differentiate 
from tlie aplogranite magma. If this he the ease the position of the Cardup 
Series in the Pre-Cambrian siicc(‘ssiou is lixed as younger than the granite- 
but older than the (luartz dolerite intrusions, which are considered by all 
observers to have taken place during late Pre-Cambrian times and which 
represent the youngest ro('ks in the Western Australian Pre-Cambrian shield. 
(Clarke, 1930; Forman, 1937.) 
Quartz veins striking almost due north also occur but are not so well 
developed as those which strike north-west. The main imunber of the north 
striking group forms a lu’omitient quartz blow on the north side of the 
Bedfordale Road near the southern lioimdary of the ai-ea ( Idate 1). The 
^‘blow” is lenticular and a])pears to be surrounded by granitic gneiss. There 
are some small miueworkiiigs on this blow in the form of a shallow incline 
shaft ami an adit — observations made on the white quaifz from the surface 
and the softer more micaceous rock below are described in the section on 
petrology. The surface (juartz in jilaces shows the presence of irregular' 
strings of line grained dark coloured roek, not uidike slate in appearance. 
Extending north from this (luartz blow along the same strike there is a band 
where no outcrops are to be found but wlim'e occasional small l)oulders of 
the dark coloured tine grained slaty rock are noticeable. There is no doubt 
that this band of slaty roek extends north to at least as far as the centre 
of the mai'tped area (Plate 1), Further consideration of the origin of this 
rock is given in the petrology section of this paper. 
