126 
G. T. PRIOR. 
large plates of orthoclase and oligoclase, with interstitial quartz-mosaic (cataclastic 
structure) and flakes of biotite. The oligoclase is mostly idiomorphic, and shows both 
albite- and pericline-twinning. A little sphene and small rounded zircons are present 
as accessory minerals. The rock shows evidence of pressure in the strain-shadows in 
the quartz, as well as in slight bending of the twin lamelhc and fracture of the crystals 
of oligoclase. The dyke-rock (155), except for the large porphyritic red felspars, is 
similar to 129, and also shows parallel structure in the arrangement of the biotite-flakes, 
but the quartz-mosaic is of coarser grain. The large porphyritic orthoclases enclose 
rounded crystals of oligoclase. 
Other veins in the gray granite are of quartz-porphyry, and are doubtless 
apophyses of the granite (155), since they show similar large red porphyritic 
crystals of orthoclase and oligoclase. In specimen 168 these phenocrysts occur with 
large rounded quartz-crystals and small pleochroic (grass-green to yellow) hornblendes 
in a cryptocrystalline felsitic base. 
The rock-specimens collected from the scree-slopes in Granite Harbour include : — 
augen-gneiss ; epidosite ; granites with large red porphyritic felspars ; pegmatite ; 
very beautiful quartz-porphyries, showing large pink porphyritic felspars and rounded 
quartz in a fine-grained felsitic base ; diorites with large porphyritic hornblendes, some- 
what similar to the dyke-rock (715) from Cathedral Rocks described below; sandstones 
and dolerites (seep. 138), precisely similar to those of the Ferrar Glacier; and also 
gabbros, showing under the microscope large ophitic plates of colourless augite and 
green uralitic hornblende in a coarse-grained aggregate of plagioclastic felspars with 
much pleochroic (colourless to rose-red) sphene. 
The Southern Foothills.— The gray rock (569) from the Southern Foothills, which 
occurs in bands parallel to the joint-planes of the crystalline limestone (see p. 25), consists 
of a medium-grained allotriomorphic aggregate of oligoclase, orthoclase and quartz, 
with shreds of green to brown hornblende and biotite showing well-marked parallel 
structure. Grains of honey-yellow sphene are very abundant. 
The Snow Valley. — Of the granites from the Snow Valley between Cathedral 
Rocks and the Northern Foothills (p. 33), the porphyritic rock (563) from c 6 is the 
most noteworthy. It shows large porphyritic pink crystals of orthoclase, around which 
lines of small hornblende-crystals appear to flow. Under the microscope the ground- 
mass is seen to consist of allotriomorphic oligoclase and orthoclase and pleochroic 
(yellowish-brown to black) hornblende, with quartz in quite subordinate amount. 
The coarse-grained porphyritic granite (555) from the knoll e b shows fairly idiomorphic 
oligoclase and less sharply defined orthoclase embayed by quartz, which has been 
obviously the last mineral to consolidate ; hornblende and biotite are not in large 
amount : some sphene is present. A dark patch in this granite has the composition of 
a basic diorite or essexite somewhat like the rock of the “tongue” (715) described 
on the next page. It consists of a coarse-grained aggregate of plates of altered 
plagioclase, large ophitic reddish-brown hornblende and colourless diopside. 
