•36 
Rex T. Prtder 
Apatite is reniarkal)ly aRuudant and builds well shaped stout prisms 
which are idioblastic towards all the other constituents— it aiipears to ha^e 
been introduced durin- the process of granitisation to which these basic 
rocks liave been subjected. Magnetite and pyrite, scattered uniformly (1he 
latter very sparsely) throughout the rock are the only other accessoiies. 
An analysis made of this type yielded the result shown in Table I., 
column 1. 
Table I. 
SiO 
Al.,0, 
Fe,0, 
FeO 
IMgO 
CaO 
Na^O 
K..0 
H.,0+ 
HoO— 
COo 
TiOo 
P.,0, 
MnO 
BaO 
FeS., 
Fe^Sn 
Cr.,0;i 
v;o, 
so. 
1 . 
40-09 
14-01 
6-05 
14-42 
4-34 
9-89 
0 - 46 
3-78 
1 - 97 
0-07 
0- os 
2 - 70 
1 - 24 
0-38 
Nil 
0-77 
0-02 
Nil 
003 
Nil 
100-36 
2 . 
66-52 
13-22 
4-99 
3-29 
0-58 
2 - 84 
3 - 45 
2-95 
0-50 
Nil 
0 03 
0-66 
O-IO 
0-15 
0-53 
0-07 
Nil 
Nil 
0-04 
Nil 
99-92 
Analyst : 0. R. Le Mesurior. 
1. Ilornbloiulc-epidote-biotite honifels (19483), xenolithic in hybrid gneiss, 
Roads Board quarry, Armadale. 
:2. Hybrid gneiss (19482), rock enclosing the xenolitli from which analysis 1 
was made, Roads Board quarry, Armadale. 
Tho comi)osition of the basic xenoliths is peculiar, the most striking 
feature being the low silica and magnesia and the high ligiires for the iron 
oxides and ]>otash. F^’rom the texture of the rock it a]) pears to have been 
originally a medium grained basic igneous rock such as a gabhro although 
the PeO/MgO ratio is rather high. It must be borne iu mind, however, that 
this rock has suffered considerable change, the original pyroxene having 
gone over to biotite, involving a loss of silica, magnesia, and lime and an 
addition of potash and alumina — the chemi(*al evidence then supports the 
-suggestion that these rocks were originally basic igneous types. There has 
been a marked concentration and hxing of in these xenoliths. No 
rocks have been noted amongst the Cardup Series which (‘ould possibly be 
related in any way to the xenolithic masses in the hybrid gneisses. 
The hffhridised gneiss itself is a medium grained, well handed mesocratie 
rock. The dark hands which produce the gneissie appearance are composed 
largely of material similar to the basic xenoliths described above. Tnter- 
banded with this material are leucoeratic bands of pale tlesh coloured felspar 
closely associated with quartz and a pale greenish slightly epidotised fel- 
spar — in })laees the flesh coloured felspar is present as augen. 
