The Geology and Physiography of the \''’ongong-Cardup Area. 271 
lY. PETROGRAPTIY. 
A. Aployranites, Gneisses and Associated Basic XenolitJis, 
Tho basic xenolitlis include hybridised varieties of the biotite-horn- 
blende hornfels found at Armadale (Pridcr, 1941) and hornblende schist 
xenoliths. 
1. Biotite-hornhlende Koryifelses. — Xenoliths of these rocks are common 
in the hybrid g-neiss. They form rounded masses up to four feet long. 
In the granitic phases of the gneiss the xenoliths form narrow sheets 
intercalated * ‘ lit-par-lit ’ with line-grained granite. 
The rocks are dark grey to black in colour, and generally have a fine 
even-grained hornt'elsic texture. 
In thin section, clots of decussate greeTiish biotite are associated 
with saussuritised plagioclase. Subhedral hornblende may be present 
with synantectic reaction rims of biotite or chlorite. Quartz is rare as small 
clear interstitial areas. Apatite prisms and euhedral sphene, as crystals 
up to 1 mm. long, are chai-acteristic accessories together -with pyrite and 
magnetite and more rarely, pink euhedral zircon up to (Ko mm. long. 
The felspar crystals are crowded Avilh epidote grains and small 
clinozoisite prisms. Lamellar tAvinning is common and extinction angles 
indicate all)ite-()Iigoclase. 
Biotite varies from a brownish variety with X = pale yellow to colour* 
less ; Y = Z = yellow-brown ; X < Y = Z, to a greenisli chloritised variety 
with X = pale green-yellow ; Y = Z = yellow-brown ; X<Y = Z. 
The hornblende has the pleochroic scheme : — 
X = light brown-green ; Y = dark green ; Z = dark bluish- 
green ; X <■ Y 5' 2 ; Z/\c ^ 17°. 
The xenoliths are distinguished from the hybrid gneiss by the absence 
of microcline. Apparently, all the potash which was introduced during 
granitisation, reacted with the hornblende of the xenolith to form biotite 
instead of crystallizing as microcline. 
Table T. 
Analysis of Biotitic. Xenolith 
ir Matrrial. 
1. 
2. 
3. 
SiO, 
41-95 
40-09 
69-52 
A1 (). 
17-70 
14-01 
13-22 
Fe ().. 
3-12 
9-05 
4-99 
FeO 
11-32 
14-42 
3-29 
MgO 
6-08 
4-34 
0-58 
CaO 
3 -OS 
9-89 
2-84 
Na 0 
3-03 
0 - 49 
3-45 
K 0 
9-38 
3-78 
2-95 
HO 
1-41 
1-97 
0-50 
H.,0— 
0-12 
0-07 
Nil. 
CO. 
0-08 
0-03 
TiO, 
1-39 
2-79 
0-99 
p,o-, 
0-95 
1-24 
o-io 
YnO 
0-14 
0-38 
0-15 
BaO 
Nil. 
0-53 
FeS. 
0-77 
0-07 
Fe S, 
0-02 
Nil. 
V 
0-03 
0-04 
99-94 
100*39 
99-92 
1. Fine-grained biotitic hornfels xenolith, Cardup (Analyst, B. P. Thomson). 
2. Hornblende-epidoto-biotito-hornfels xenolith, Hoads Hoard Quarry, 
Armadale (Prider, 1941, p. 39). 
3. Hybrid Gneiss, Hoads Board Quarry, Armadale (Prider, 1941, p. 39). 
