Phe Geology and Physiography of the W’ongong-C^ardxh^ Area 
(i) ^‘Black"' Slate. — This is a black to dark-grey coloured rock, in which 
<ilose bedding planes are well developed and marked by alternating light and 
dark bands. 
Barite occurs on the joint j)lanes of the black slate in the Brickworks 
Quarry. 
In thin section: — Minute sericite plates and microcrystalline (luartz form 
the ground mass which is banded with graphitic material. Light brown-green 
idioblastic tourmaline prisms are scattered Avith random orientation through- 
out the rock. 
(ii) ‘GP/ufc’’ Shite. — This variety of slate has a white to light grey 
colour. The light grey type is compact and hard and corresponds to the 
slate interbedded with the sandstones. Such slate shows a greater develop- 
ment of microcrystalline tiuartzj under the microscope, than do the lighter 
types. 
In thin section the white slate is seen to consist of minute sericite Hakes 
and a smaller amount of microcrystalline quartz, Avhich may be intei*mixed 
with or may form lentieles in the sericitic groundmass. Later veinlets of 
strained quartz cut the bedding. 
In the Cardup quarry, pale green chlorite is developed in the “white-' 
slate near the contact Avith an epidiorite dyke. 
The small tourmaline prisms are distributed sparsely throughout all the 
-slates, and do not decrease in quantity, even half a mile west of the Cardup 
Series-granite gneiss contact at Cardup. This supports Frider’s suggestion 
(1941, p. 41) that the tourmaline Avas deri\pd from the crystallisation of the 
original constituents of the argillaceous sediments rather than from material 
introduced by an intrusive granite. 
C. Basic Intrusives of Post-Cardap Age. 
The folloAving types are recognised : — 
1. IJralitised quartz dolerite. 
2. Bioiitic epidiorite. 
3. Porpht/ritie chlorite-albite epidiorite. 
1. Uralitised quartz dolerite . — As at Armadale, most of the dykes are 
■of this dominant type. 
A typical specimen is dark grey-green in colour, with tine to medium 
grain. The texture is o])hitic to subophitic and is obscured by the formation 
■of uralite and epidote. 
Uralitic amphibole is the dominant mineral. IHagioclase occurs, almost 
entirely replaced by granular epidote and zoisite. 
The mesostasis is clear (piartz, often in micrograi)hic and rarely grano- 
phyric intergroAvth with the et)idotised felspar. The <iuarlz encloses apatite 
pris'.us. Brownish hornblende, biotite and chlorite may be associated Avith the 
uralite. Leucoxene is abundant as large skeletal plates replacing ilmenite. 
Some leucoxene has also recrystallised to granular sphene. 
The uralite is often developed in large oiystals Avith good cleavage and 
simple twinning. The colour is rather variable in intensity, a typical pleo- 
chroism is X = very pale yellow-green ; Y = pale olive-green ; Z = pale 
greenish-blue ; X<Y<Z,'Z/\^e = 20^ (-) 2V is large. 
