OLIVINE-BEARING QUARTZ-MONZONITE FROM KIANDRA. 261 
From Mr. Andrews’s description it is evident that the 
field relations of the rock are by no means clear, and, as a 
matter of fact, thespecimens available comprise both quartz- 
monzonite and other types which we have designated 
monzonite-porphyry, all of which are quite plainly closely 
related, judging from their mineralogical features. Mr. 
Andrews mentions an association, at one spot, of the norite 
with a small granite boss, but as no specimens of the latter 
appear to have been collected it is impossible to say whether 
this association has any genetic significance. 
Petrographical Descriptions. 
The quartz-monzonite is a phanerocrystalline rock of 
medium, fairly even, grainsize, and resembles a diorite in 
appearance. 
A Rosiwal measurement of a thin section gave the follow- 
ing approximate mineral constitution in volume percentages: 
Piagioclase ... .. 40°1 Hornblende AEs ea ees 
Orthoclase ... cng ie ® Biotite ... me O'S 
Quartz oy ae Bi Magnetite . LEU Beg 
Augite ae bee SNS) Olivine ... Vesela 
Clino-hypersthene (?)  5°5 Apatite less than ‘1 
These figures are nothing more than rough approxima- 
tions, but they will serve to give some idea of the quanti- 
tative relationships of the constituent minerals. 
Plagioclase is in well formed thick prisms and tables, 
averaging about °7 mm. in length, clear and fresh, showing 
albite twinning and marked chemical zoning. Measure- 
ments indicate quite a considerable range in the composition 
of the different zones, from labradorite (Absz;Ane3) at the 
centre to oligoclase or even albite at the periphery. Slight 
oscillation of composition is noticed. 
The orthoclase, which is untwinned and generally clouded 
by decomposition, envelopes the ends of the plagioclase 
