OLIVINE-BEARING QUARTZ-MONZONITE FROM KIANDRA. 269 
In this rock the groundmass forms much less than ten 
per cent. of the whole, but ina slide from another specimen 
very Similar in outward appearauce, it actually exceeds in 
volume the plagioclase of the first generation, so that the 
rock looks markedly porphyritic, with large phenocrysts of 
pyroxene and smaller ones of plagioclase set in a fine-grained 
Matrix in which pyroxene and magnetite granules and 
microlites play a conspicuous part, as well as quartz, ortho- 
clase, plagioclase and apatite. In this particular rock 
there is practically no hornblende, and biotite is much less. 
important than in either of the rocks already described. 
Probably this rock is best called a monzonite-porphyry, 
and the same name may perhaps be applied to the second 
type, intermediate in texture between this and the quartz- 
monzonite, although in this case the groundmass is very 
subordinate and the plagioclase crystals of the first genera- 
tion are generally in contact with each other. 
Chemical Composition of the Rocks. 
Complete chemical analyses were made by one of us. 
(W.A.G.) of the quartz-monzonite and of the monzonite- 
porphyry last described, with the results tabulated in 
columns I and II below :— 
i JUG ITI. IV. ve 
SiO, 57-18 57°08 7°80 56°91 54-90 
Al,O, 14°13 13°62 16°43 15°54 17°44 
He,O, upp AG, eal) 1-62 Vea) 9-64 
FeO 5°85 (7H || o6 oil 4°98 
MgO 7°00 8:07 4°14 5:71 Se 
CaO 7°64 7°54 C20 5:80 6:96 
Na,O 2°36 2-50 Dias) 2°45 3°50 
K,0O 2°30 2°50 eo) 2°74 Se Silt 
H,O+ 0:45 Clg 0:31 2°29 ) 
H,O- 0:07 0:05 Oia eo 
CoO., abs. abs. abs. - j 
EX). U-60 0:65 0:70 Oo Oat 
ZrO, abs. abs. Ad. 
B40 Ot O22 0-19 0-21 0-51 
