272 
Brendan P. Thomson. 
Aiuilysis 1. indicates that the Cardup xeiiolith is rich in iron and potash 
like the Armadale hornfels, and is likewise the result of the action of potassie 
solutions on original basic material. A feature of the analysis is the hio-h 
alumina content. " ^ 
This hybridisation (which is essentially a granitisation process involving 
the addition of KgO, AloOjj and SiOo to the original basic xenolith), was 
effected during an early period of granite intrusion (Prider, 1941). 
2. Tlornblende-'^cJnst .rcnoUt/is. — These are not widely distributed like 
the hornfelses. Tliey occur as angular blocks, up to five' feet long, which 
appear to be ])art of a larger mass which is cut by narrow veins of 
aplogranite. They are best developed on the south side of the Wongong 
gorge, bid have also been found in gneiss a quarter of a mile south-east of the 
Brick Works Quarry and on the south side of Cardup Brook. 
The hornblemle-schists are black, medium to even-grained and lia\X‘ a 
schistose structure which may not be aiiparent in the hand specimen, but 
is obvious in larger masses. When felspar is present a gneissose structure 
may develop. 
The rock is composed mainly of subhedral hornblende crystals, for 
which — 
X = light yellow-brown; Y = dark brown-gTeen ; Z = dark blue- 
gi’een; X <_ Y < Z and Z /\e=18°. 
A small amount of biotite occurs either as plates or decussate clots. 
The biotite has X = yellow; Y = Z = dai’k brown and ( — ) 2V small. 
Quai’tz forms small clear angular inclusions in the hoiaiblende. Saussuritised 
plagioclase is found as subhedral crystals in the slightly hybridised types. 
Accessoi-ies are pyrite and magnetite and rare prisms of apatite and epidote. 
The relation between these two main types of X('nolith is not visible 
in the field. The biotite-hornblende hornfels xenoliths represent hybridised 
rocks, probably of original gabbroic comj)osition. The hornl)lendo-schist 
xenoliths appear to represent amphibolite Avhich has escaped intense hybridisa- 
tion. 
3. Hybrid Gneiss. — This rock is identical with the Armadale type. The 
foliation is well-marked by biotitic clots and streaks. Light-cotouve<l bands 
contain pale mierocline phenocrysts, greenish saussuritised felspar and quartz. 
The more porphyritic types have augen of mierocline which are de\-e}oiied 
with vitreous quartz in a black biotitic ground-mass. 
The dark bands are similar to the associated biotitic xenoliths and are 
composed of decussate clots of biotite containing euhedral apatite, sphene, 
and accessory magnetite and pyrite. Euhedral zircons up to 0.4 mm. long, 
occur rarely. 
The leucocratic bands contain plagioclase (albite-oligoclase) as subhedral 
crystals which are invariably saussuritised and often sericitised. Occasionally, 
clear irregular areas of oligoclase occur in the cloudy iilagioclase. The 
twin lamellae are continuous in the clear and <*loudy areas, but the extinction 
angles of the lamellae differ. This may be a replacement structure. 
Mierocline forms large clear crystals, often with a microiierthitic struc 
ture. ^‘Phantom Twinning^’ is present in the central ])arts of some crystals, 
indicating that some orthoclase is present, partlv inverted to mierocline 
(Ailing 1923, pp. 283-305.) 
