The Geology and Physiography op the Wongong-Cardup Area. 273 
4. Aplogranite. — This rock typo is tho same as the Armadale a})lo- 
granite. A typical aplogranito is a medium-grained leucoeratic rock, contain- 
ing albitic plagioclase, quailz and mierocline. The texture is allotriomorpliic 
granular. The plagioclase is albite-oligoclase, slightly clouded with kaolin and 
])artly S[)anglod with soricite (lakes. 
Mierocline is microperthitic and slightly kaolinised. 
Quartz forms clear allotriomorpliic crystals with undulose extinction. 
Blebs of (piartz are also common in the mierocline, with which they form 
myrmekitic structures. 
Rare chlorite wisps are. the only ferromagnesians present. 
A characteristic of the aplogranite is the domination of sericitisation over 
saussuritisation. Otherwise, the plagioclases in the aplogranite and the gneiss 
show no marked ditfereiiees : both are all)ite-oligoclase, although the abundance 
of epidote and clinozoisite in the plagioclase crystals of the gneiss suggests 
that in these the original felspar was more calcic. 
5. Pegmatite and Aplite. — No coarse-textured })egmatite dykes or veins 
were found, but the gneiss may be locally }>('gmatitic and contain mierocline 
crystals up to 2 inches long. Whetluw this pegmatitic phase is derived from 
the early granite magma that formed the hybjid gneisses or from the latter 
aplogranite magma, cannot at ]>resent be stated. 
Garnet-Muscovite yipUte. — A vein of this rock 13 inches wide occurs in 
the gneiss in the extreme east of the area near the Wongong Brook. 
The aplite is pale pink in colour and varies in grain from a fine-grained 
saccharoidal to a more pegmatitic phase with small mierocline ])henocrysts 
and muscovite plates up to 12 mm. aci’oss. 
The texture in thin section is allotriomorpliic. The minerals present are 
fresh albite, unstrained quartz allotriomorphs, perthitic mierocline, rare 
large muscovite flakes and garnets. 
The gaimets form small pale pink euhedra up to 0.5 mm. diam. Acces- 
sories are a little chlorite and epidote. 
Sonu'what similar garnet aplites occur at Jimperding (Prider, 1934, 
p. 10) and Malku]i (Cole and Gloe, 1940, p. .160), whei-e they are related 
to granite intrusions of post-gneiss age. 
The origin of this garnet-muscovite aplit<‘ is not certain, but Ix^ause of 
its remarkable freedom from alteration, it is most pi'obably a phase of the 
aplogranite. 
6. Relation between the Aplogranite and Hybrid Gneiss. — In the M on- 
gong-Cai’du]t Area no evidence was found of two tyiies of gneiss striking 
discordantly to each other, as do the fine-banded and hybri<l gneisses at Arma- 
dale (Prider, 1941). 
Prider considers that tluu'e are two periods of granile intrusion. 
(1) An early period that led to the foiauation of the hyl)rid gneiss. 
(2) A later i>eriod, represented by the aplogranite. In the Wongong- 
Cardup Area, tivo periods of granite intrusion are indicated by — 
(a) Angular xenoliths of gneiss in aplogranite, best ex]> 08 ed on the 
soiuh side of the Wongong Brook gorge. 
(b) The truncation of gneissic banding by masses of aplogranite. 
