321 
In some sections it would appear that, as an accompani- 
grain, for the grain is not optically continuous throughout. 
b. these cracks the quartz may show higher polarization 
co 
Quartz is also present in the slides in allotrimorphic 
grains, or as a constituent of a graphic intergrowth with 
microcline. This intergrowth may develop around the large 
quartz or microcline crystals, and is obviously of later 
crystallization 
Microcline is present in ahida crystals, which 
Z 
sca on (010) sections has a maximum value of 6°-7° 
from the basal cleavage. Some sections show a very fine 
perthitic TE with plagioclase. The layers traverse 
the microcline, and are optically continuous; optically they 
have the properties sti albite. This is the typical microcline 
Limb ed structu 
oclase occurs in more or less tabular crystals of well- 
developed form, and shows the characteristic albite lamellae. 
Zon ning is characteristic. The refractive oaa ig => C 
Balsam, and most sections show R.I. a 
In zoned sections showing no ali. twinning the 
extinction from the (001) PO read as maxima : 
Outer zone : +9 
Intermediate zone  ... v 2i a 
Central zone 
This ser regrets ee a ae , from ‘Oligo (Ab, An,) to 
Andesine (Ab, 
uc ie in (010) in —— light show EE 
emergence of a bisectrix to be practically normal to 
cti ion This is ins obtuse hbri, and the iati 
Some sections of the loko pe the presence of a 
more acid plagioclase than the above. This has the pro- 
perties of oligoclase albite. It estt a later stage of 
crystallization, but is of minor developme 
Biotite.—This mineral is developed in m of flakes 
= d section showing m strong basal cleavage. The 
