The Contact Between the Gkanitic Rocks and the Cardcp Series 
AT Armadale. 39 
minute idieblastip prisms to O.Oo mm. in length scattered sparsely, Avith 
random orientation, throughout the rock. It is strongly pleochroic, 
oj brownish green, e colourless, and the refractive indices e = 1.621, 
oj ^ 1.649, ai»pear to indicate a membei of the dravite-schorl group. 
(b) The white dates: these rocks are made u]) almost (.mtirely of fine 
fibrous serieite with a much smaller amount of [>ale broAvnish flaky biotite 
and minute clear grains of (piartz. Minute idioblastic tourmaline prisms, 
similar to those in the black slates are distributed sparsely throughout the 
rocks (all of the slaty rocks examined contained this tourmaline none of 
which is detrital). Narrow darker coloured bands (up to 1 inch Avide) 
occur in the Avhite slates in places and these consist predominantly of pale 
broAvnish biotite with serieite in minor amount. The grain in these narroAV 
bands is considerably coarser but this is largely an original feature and is 
not clue in the main to recrystallisation as the quartz grains of such bands 
are markedly larger than in the Avhite slate. The minute tourmaline prisms 
appear to be more abundant in these bands. 
In some i)]aces near the Avestern Avail oC the slate quarry, close to the 
albite-epidiorite, the Avhite slate has a slightly knott<‘d structure, the “knots’’ 
usually being small rectangular shaped j)latc's (up to 4mm. x 4mm. x 1mm.) 
which consist of kaolin Avith small <iuartz grains distributed uniformly 
through(Uit. Th<*se porphyroblasts a|)|)ear from their shape to b(‘ andalusites 
but careful search has not disclos(>d any relicts of this mineral. Their true 
character must thenTore remain unknoAvn but they ajipear to be the result 
of contact nufamorphism of the slate by the nearby basic intrusion. 
Joint jdanes in the Avhite slates near the south-Avest corner of the slate 
quarry are coated Avith ])ale yelloAV earthy jarosite. 
Other than the o('casioiial thin dark bands and rare examples of the 
knotted slate, this group of Avhite slates appears to be rather uniform in 
character. An analysis of a specimen from the AA^est side of the slate quarry 
yielded the result shoAvn in table II. 
Table IT. 
'SiO., 
1. 
65-22 
2. 
61 -63 
3. 
58*38 
4. 
50-10 
5. 
50-00 
ai.,6, 
16-71 
16-33 
15-47 
25-12 
24-14 
FcoO, 
1-93 
4-10 
4-03 
5-12 
2-79 
FeO 
3-23 
2-71 
2-46 
1-52 
4-67 
MgO 
2-87 
2-92 
2*45 
3-93 
4-16 
•CaO 
005 
0-50 
3-12 
0-35 
0-07 
Na„0 
0-76 
-26 
1*31 
0-05 
MO 
K.,0 
H'0| 
5-98 
5-54 
3-25 
6-93 
8-63 
2- 12 
3-24 
3-68 
6-82* 
3-06 
H.O— 
016 
0-31 
1-34 
. . 
0-24 
TiO., 
0-35 
0-68 
0-65 
0-50 
0-50 
€0., 
0-05 
0-41 
2-64 
0-07 
P.,0, 
0-08 
0-16 
0-17 
. . 
0-11 
MnO 
0-03 
0-09 
Tr. 
. . 
0-04 
BaO 
0-1 1 
O-OB 
0-05 
015 
FeS., 
Nil 
O-OI 
. . . 
Cr.,0., 
0-01 
. . . 
0-01 
V.,0.. 
0-03 
... 
004 
SO, 
0-11 
« « « 
0-65 
. . . 
0-15 
Ora])liite 
0-05 
Nil 
O-Slt 
0-07 
NaCl 
Nil 
((Others) 
... 
0-06 
... 
99-85 
99-98 
100-46 
100-44 
100-00 
Analyst : C. R. Le Alesurier. 
* [gnition loss on material dried 
at IIO^C. 
t Organic 
material. 
