108 
C’liAKKE AND WILLIAMS. Gfoloflll of IhuUnff Ilaufje. 
in tlu‘ f^iirissic, nml ulnnit [ incli in Hk’ massive variety. Carlsbad 
twins are al)imdaiit. The {-ivstal shape is widl developed, but 
the edji'es oft(*n {*xlii))it a peculiar niblded outline, as if the crystal 
had uiidero'one partial resor]>tioii. The cross-liatchinj? is clearly 
defined, the lamellae being sjiindle-shaped. Tlu* inclusions comprise 
snbidiomor])hic to allotriomorphie crystals of oligoelase largely 
altered to scaly white mica and kaolin, rounded blebs of (piartz 
and partly chloritised biotite. The turbidity of the oligoelase is 
in niai'kod contrast to the comparatively fresh condition of the 
microcline. 
Tlie ground-mass is of coarse l)iit variable grainsize and of 
the usual granitoid texture. Patches of a micropegmatitic inter- 
growth of (piartz and ])lagioclase feldspar are not uncommon. The 
oligoelase is largely altered to small flakes of colorless mica and 
kaolin. The microcline of the ground-mass is of a later generation 
than the phenocrysts, and like the latter, is comparatively fresh. 
Hiotite occurs as rather ragged crystals and aggregates, in part 
cidoritised. I\lany of the biotite crystals contain inclusions, prob- 
ably of zircon, surrounded by pleochroic haloes. The quartz does 
not call for comment. 
The strongly gneissic varieties consist of alternate bands or 
lenses of biotite-ricli and feldspar-rich rock. The longest axeo 
of the microcline phenocrysts, and the cleavage planes of the 
biotite are parallel to the direction of the gneissic banding. 
Tlie development of both the porphyritic texture and the 
gneissic banding is extremely variable — one or both may be absent, 
(ienerally the more strongly gneissic varieties are the more con- 
spicuously por])hyritic. The trend of the banding in the Roleystone 
Area is a])proximately north and south. 
Field-work has shown that the varieties merge gradually into 
one ajiother; no definite boundaries caii be drawn between them. 
Nor does microscopic examination of the entire range of gneissic 
and por})hyritic varieties show any persistent differences by which 
the granites could be divided into two or more types. It seems 
therefore that the granites are a petrological unit showing wide 
variations from jdace to place in the development of porphyritic 
and gneissic textures. 
'2. F'uie-gra'wed biofific segregaUons . — Small exposures of these 
are fairly common in the Roleystone Area. They are dark green, 
fine grained and megascopically of thoroughly basic appearance. 
Under the microscope they are seen to consist of a fine even- 
grained aggregate of biotite and quartz with microcline and 
plagioclase. 
