The Geolohy and Physiography of the Lwvnswood Area. 
6T 
Text Fig. .*). 
Porphyi'itie 'lounger Granite with adamellite xenolitlis. Note 
the " jihenoeryHts of mieroeline v hieh have developed both in the 
xeiiolitliH (compare rapakivi ovoids) and in the granite itself. Note 
also the absence of any j>refeiTed orientation of the mieroeline “ pheno- 
crysts of the granite. 
colourle^^s glassy puartz abou] live nun. in dianieltn*, pale green oligoclase^ 
three to five mm. in diatnetei-, , [>ink microi-iine averagt* (liameter live mm> 
and black biotite and hornblende average grain size four mm. 
Jhe mieroeline ‘‘ pheuoeryst.s” are (mhedral with many poikiloblastie 
inclusions of felspar, puartz, biotite, iuid hornblende. Smaller euhedral 
mieroeline grains, sometimes vt-ry slightly kaolinised, oeeui’ in the ground- 
mass. Mieroperthite is fre{iuently developed in the mieroeline, Oligoclase 
forms euhedi'al grains which are eitiier extiamiely sanssuritised, tlu^ “saus- 
surite” be:ng mu(di coar.sei- than in the granitic gneisses, ay clear ami slightly 
zane.l with well developed lami'llar twinning. The saussui'itised {)Hgoelase 
thought to be a relie from the granitic gneiss. Coarse myrmekite struc- 
tures are common. Quartz occurs in clear very irregular grains, free from 
inclusions, and appears to hav(‘ crvsiallised last in interstic<'s between oaidier 
formed oligoclase, liiotite, hoiaihlende, and mieroeline. The biotite is a 
.strongly pleochroic brown variety with suhhedi'al form, usually occurring 
in aggregates with the otluu' ferromagnesian ininerals surrounding the eolour- 
le.ss fe’snar and puartz grains. Tt has (-) 2V very small, pleoehroism 
.strong Y and Z — dark brown, X light hi’own, absorption Y = Z, h ^ X, 
c;^ c X = 0°. There are pleochroic haloes aroumf purple zircon inclusions 
and other inclusions of apatite and epidote. The hornblende is a strongly 
])Ieochroic type X = yellow, Y — b = dark grey green, Z “ bluish green, 
absorption X <^Y<;Z,c^Z — 24°, optically uegatiA'e. Accessory minerals 
are titanite, magnetite, apatite and epidote. 
Order of crystallisation :—Afagnetife, titanite, apatite, hornblende, biotite, 
oligoclase, mieroeline, and quartz. The average composition is quartz 35 
