The Contact Between the Granitic Rocks and the Cardup Series 
AT Armadale. 29 
noted elsewhere in the vicinity of the Darlino- Scarp are developed. This 
small area is therefore perhaps the most suitable place to commence a de- 
tailed study of the petrology and structure of the Scar]). 
11. GEOLOGY. 
(1) The fiehl dlstribaiion nnd age relationH of the rocks. 
The eastern half of the area (Plate 1) is occupied by granitic gneisses 
in which there a])pear to be two distinct grou]>s: 
(i) The tine banded granitic gneisses forming the western edge of the 
granitic rocks. These form a band apj)roximately 8 chains wide Avhich 
trends 350'^ parallel to the contact of the granitic rocks and the Cardu]) sedi- 
ments. The foliation in those gneisses strikes ])ara]]e! to the gneiss-sediment 
contact and dips at 50° to 00° towards the east. These gneisses apjiear to 
be uniform and granitic in character throughout the whole band and no- 
where were they found to carry .xenolithic inclusions as do tlie hybrid 
gneisses farther to the east. Contortion of the gneissi(' l)anding is visible 
in places and in other })laces tin* banding may ])e almost invisible, the rocks 
there being indistinguishable from massive granites. 
(ii) The hybrid gneisses which occupy all the area to the east of (i). 
These gneisses have a general strike of 25° and dip at angles of 40° to 60° 
to the east. They are l)est exposed in the Roads Board (piarry in the north- 
eastern corner of the area. 
The rocks in this (piarry and their titdd relations will be described in 
some detail as it is clear here that there have been two distinct periods of 
granite intrusion, the twidence for which periods of granite intrusion in the 
Pre-Cambrian history of Westei'n Australia has been accumulating during 
recent years (Miles, 1038, p. 36; Prider, 1938, p. 101, and 1939", p. 93; 
Ellis, 1939, p. 91 ). 
The rocks developed and their ti(‘]d relations as seen in this quarry are 
(a) Dark coloured biotite-epidote-hornblende hornfelses. These rocks 
are well developed on the southern wall of the quarry where they ap])ear 
to form a flat lying band in a more granitic gneiss (b) which is crowded 
with xenoliths of this dark green hornfels. On the westtum Avail of the 
quarry, just inside the entranct' the biotite-epidote-hornblende hoiTifels 
occurs as niunerous xenoliths U]) to 12 inches diameter accompanied by 
xenoliths of coarsely granular quartz ( ‘F quartzite) in a hybridised gneiss 
(b) (plate 2, fig. 1). This dark coloured hornfels (together with the (piartz 
xenoliths) is clearly the oldest rock exposed in the quarry. 
(b) Mesocratic hybrid augen gneisses. These form the base in Avhich 
the xenoliths (described above) occur. They are well banded coarsely granu- 
lar rocks, often exhibiting augim structures and are composed of quartz 
and felspar with thin lenticular dark coloured bands, Avhich under the micro- 
scope arc seen to Ix^ remnants of the biotite-e]')idote-hornblende hornfels 
and they appear to have resulted from the intrusion of granitic material 
into the hiotitf^-t'pidote-hornblende rocks (see under ]>etroIogy) — this rock 
thus represents the first period of granite intrusion (or granitisation). The 
best exiiosuivs of this rock are to be seen on both faces of the (juarry just 
inside the eiilrance. 
(e) A])]ograiiite. This rock, a leucocratic medium grained massive to 
A’eiw slightly gneissic granite with little or no forro-magnesian constituents 
(with the exception of occasional biotite-epidoto-hoiTd)l(mds clots ])icked up 
