25(i 
C. K. 8. Davis 
rocks show signs ol:' crushing, Tlio plagioclaso probably rccrystallised under 
the stress, and later, smaller stresses jirodnced the fauiting now visible. In 
])egmatite and ajilile dykes, which crystallise at a lower temperature than 
the jiarent gi'anite, ori.ginal plagioclase was comparatively free from iiotash- 
felspar, and little .sericite has since formed. 
C. Acid Intrusives. 
1. Pegmatite mid Aplite, 
Tlieso two typos avo often associated, and in such instances the pegmatite 
occupies the border and apiite irregular ])atches in the centre of the 
intiu.sioii. C,oais(* ('rystals scatter(‘d nt^ar the edge of an apiite dyke are 
seen in section to be resoi’]K‘d. Emmons (1940, pp. 5-0) points out that the 
outstanding diffenmce between pegmatite and apiite is textural: if the volatile' 
constituents escape from a li(|uid wliidi is crystallising as a pegmatite, the 
residuum will solidify as a tine-grained ai)lite. 
rile pegmatites consist of plagioclase, microcline, microperthite or 
giajihic intergi'outh ot (luail/ and microcliiu*, together Avith fpiartz and 
small ])ooks of muscovite. The grain size of the pegmatite is up to 10 cm., 
but that of the aplites is only 0.3 mm. 
The plagioclase in lioth typ(‘s ot roi-k, as mentioned preA’iously, has 
been remarkably little sericitised. Microcline is usually subordinate to 
plagioclase. (jjuartz, though fairly common, is not as abundant as it is in 
the granite. Out' ajilite contained a few rods of muscovite and a few laths 
of tourmaline (pleochroic scheme X = deep blue, Z ^ colourless) but no 
dark minerals. 
2. Quorfz 
As described in the section on their held characters, (piartz masses may 
be from an inch to o^au’ 20 chains Avide. In spite of this tremendous difference 
in their size, all such masses appear to be of similar character. 
The central ] arts consist mainly of hue-grained massi\-e white puartz. 
In thin section, th(‘y are made up of irregular interlocking grains of (piartz 
of A-ery uneven texture (in one section the grain size varied from 0.03 mm. 
to 0.5 mm. and in another from 0.2 mm. to 1 mm.) Fndulose eN'tinction is 
very common, and is t'sp(*cially notic(‘able in the larger grains. 
Some of the (piartz from near tht' cmitre of tlu* “blow’’ is friable and 
“sugary ’ and contains numerous small tlakes of sericite. This sericite 
content iiH'reases towards the edge of the mass, but nowhere has much 
sericite recrystallised to muscovite. On the w(\st sale of the Mountain Quarry, 
sericitic and (piartzose bands are int(*rleave(l. In otinw iilai'es imar the edge 
of its out('rop, 1h(‘ (piartz “blow” is made up of a stockAvork of tiny ()iiartz 
veins (about 1 cm. wide) in a mi('ac(’Ous matrix. This is especially clear on 
weathered surfaces. “Shalv bands” noted in Aveathered rock near tin* edge 
of the “blow” consist entirely of an aggregate of small flakes of sericite. 
The granite is generally Aveatiiered aAvay for some 50 yards from the 
edge of tlu' (piartz outcrops. Where granite does outi'ro]) in the immediate 
vicinity of the larger quartz masses, it contains stockAvorks of (piartz, flanked 
by crushed and silicified granite containing bands rich in sericite. Most of 
the thinner quartz veins are surrounded by flaky, dark, weathered rock. 
bericite and subordinate green biotite haA e been introduced in cracks 
through the original felspars in apparently massiA’e granite threaded by 
