260 
C. E. S. Davis. 
heated at some period after its consolidation, minute traces of impurities, 
of which iron oxide is the commonest, would separate, resulting in o'rey- 
nnd brown-clouding, lie contends (p. 537) that: — 
“it seems necessary to i)rove that (any igneous rock with clouded 
fe]s[)ars) . . . can never have been subjected to regional- or contact- 
thermal metamorphism before the clouding can be regarded either as 
an original teahna' ot the felspar or as a deuteric effect that arose 
at a late stage in the consolidation period.” 
In the (rosnells area, there are no later inti’usioris to etfect contact 
nu'tamorphism and, as has just been shown, no regional metamori>hLsm can 
have taken i)lace. (bonding, Ihen, was producml either at a primary or at a 
deut(n*ic stage. He('rystallise<l epidiorites from Gosnells contain unclouded 
f'els])ar, and f(*ls]')ai’s in (losru'lls epidiorites are far less clonded than those 
from basic dykes farther north. In the Low(*r Cluttering, Miles (1938, p. 31) 
notes that clouding was especially marked in the unaltered <lolerites. It 
appears that clomling is best developed in the rocks which Imve undeigone 
least deuteric alteration, and is therefort' an original feature of tin* felspars. 
The h‘ast recryslallised dolerite from (iosnells contains abundant iiralite 
as irregular fibrous aggregates or irregular plates with the tollowing optical 
])roperlies: pleochroism X = vei'v pale green, V — ]:ale greem, Z = pale 
brown; extinction Z /\ c ^ 22° and ( — ) 2V large. Along edges adjacent 
to fels[)ar^ part of the uralite ha.s recrystallised to blue-green hornblende 
(]»leochroi<' scheme X = pale green, Y “ grass-green, Z = l)lne-green, Z /\c 
— 23°). There are occasional crystals of euhedral primary brown horn- 
blende (X — light yidlow-iirown, V = dee]) grtnai, Z = deep green-])rown) . 
The plagioclase is generally fresh with a, slight brownish smoky colora- 
tion, and has a maximum extinction angle of 32° in sections cut normal to 
the alhite twin lamellae, indicating a composition of about Ah,.. Tn some 
rocks, however, plagioclase has been entirely replaced by an aggregate 
of turbid, colourless epidole, and o])id()te has elsewhere gatbertnl into a mass 
of clearer laths and granules. Other constituents of llu‘ ro('k are hmco.xene 
(with a small (-ore of ilmenite)» laths of apatite and a little interstitial micro- 
pegmatite. The opliitic ti'xture of doleriti'S has l)een well preserved. 
A similar dyke from the Ilu'kley Hrook Reservoir (Quarry, one mile 
north of the area, has been analysc'd ((3arke and AXilliams, l!)2(i, p. 173). 
It contains more hlue-gn‘en hornhleiuh', and a little brown hornblende in 
the central i)arts. Some of the felspar has lieen converted into a Tnass of 
epidote, but other crystals are brown and smoky. 
In some rocks, the felspar is always refdaced i)y a turbid niass of 
epidote and the ophitic texture lost. Hornblende in this type of rock (a 
lighter blue-green variety) forms cryslals with very irregulai borders. 
Quart/ and microjiegmalite tuv common, and, in certain segregations, 
dominant. The felspar of the micropegmatite is extensively sericitisf'd. 
Nodules and veins of ei>idote are scattered through the dykes exposed 
in 1he (marries in the (iosnells area. The dolerite surrounding a nodule, 
sphcrulitic in structure, was totally recrystallised to a non-porphyritic 
medium-grained (grain si/e 2 mm.) ophitic intergrowth of clear albite 
felsi)ar and pale green hornblende. The albit(‘ contains a few ])ale green 
inclusions and both albite and hornblende are v(u-y similar in this rock and 
in a fresh porphyritic epidiorite (4. below) from fartlmr south. The pleo- 
chroic scheme of the hornblende is X = pale yellow; \ — Z = pale green, 
and its refractive index ^ is 1.641, compared with 1.657 in primary brown 
hor-nblende from the Bickley Brook Reservoir Quarry. 
