46 
Rex T. Prider. 
Table TV. — continued. 
1 . 
2 . 
3. 
4. 
Norms. 
Q 
Or 
Ab 
An 
di 
hy 
1-86 
3-48 
4-14 
2-78 
1-11 
1-78 
11-00 
14-15 
15-74 
29-19 
27-52 
25-18 
23-86 
24-88 
22-15 
23-07 
18-60 
20-12 
mt 
cm 
il 
ap 
py 
Tralitised 
4-18 
0-22 
2-28 
0-34 
5-34 
2-43 
0-34 
0*45 
4-58 
3-80 
0-34 
0-22 
Board 
quarry, Armadale. 
(Prider, 1938, p. 95.) 
(Clarke 
qiiart'/.-dolerite (20464), near Roads 
Fralitiped quartz doierite, Toodyay, Western Australia. 
Epidiorite (uralilised (piartz doierite), Bickley, Western Australia. 
and Williams, 1926, \). 173). 
Quartz doierite (average of 6 analyses), Wdun Sill, Northern England. 
(Holmes and Harwood, 1928, p. 530.) 
These rocks are therefore best described as eomj.detely uralitised qnartz- 
dolerites. An analysis of the typical specimen described above is given in 
Table W. wlu're it is compared with other nralitised qnartz-dolerites from 
Western Australia and with the average composition of the Whin Sill. 
It will be seen that the analyses of the throe Western Australian (luartz 
dolerites are very simihuy So far as i>s knoAvn, these roeks all belong to 
the same period and are all intrusive into the granitic rocks of the Darling- 
Range. In comparison with the normal fiuart/ dolerites (as exemplified 
by the Whin Sill roeks), they are somewhat richer in iron, lime and mag- 
nesia and coiTospondingly slightly poorer in silica and soda. 
(iii) Mlcroporpliyritic epidiorite. 
The occurrence of this rock as a narrow intimsion into the chloritc- 
albite epidiorite has been noted above. The rock is greenish and extremely 
fine grained and has a mici'oporphyritic texture with equidimensional pheno- 
crysts of uralite (? after pyroxene) u\) to Vo mm. diameter (often aggre- 
gated to form glomerophenocrysts), and tiny plagioclase laths to Yz mm. 
long, in a fine grained ground of plagioclase, epidote, /oisite, uralite and 
pale brown i.sh hiotite. The fibrous uralite of the ],)henocrysts is very pale 
in colour with similar pleochroism to that in the (piartz dolerites, and it 
shows i>alc,hy alteration to hiotite. No original i)yrox(uie is visible. This 
type appeal's to be closely i-elated to llie quartz dolerites, of which it is a 
fine grained p(>r[)hyritic re|>rescntative. 
(iv ) Biotite epidioriten. 
This ty|)e of rock has lu'en noted in two places only- — as a nai’row dyke 
(four feet wide) intrusive into the hybridised gneiss in the Roads Board 
quarry ami as a. narrow dyke (10 inches wide) intrusive into the slates in the 
Slate (piarry. The occurrence in the Roads T3oard quarry appears to be 
an offshoot I'rom the larger nralitised quartz doierite to the south-east 
(descril)ed above) but this is by no means certain. It is definitely intrusive 
into the liyl)i‘id gneiss, for it truncates the banding sharply and cannot be 
one of the basic xunioliths (which it resembles minoralogically). 
Tt is a due even grained gia^enish rock showing little, if any, sign of 
schistose structure. ruder the microsco]ie it is seen to consist of a fine 
allot riomorphic granular aggregate of brownish-green biotite, plagioclase, 
epidote (and zoisite) and pale green amphibole with accessory leucoxene 
(after small ilimmite grains) and (piartz in small angular grains. 
