176

commonly fresh black hornblende and brown biotite. In hand specimens
most of these rocks look like normal granites. Microscopic examination
shows that few or none of the common varieties of this rock contain
sufficient potash feldspar to be classed as true granites, although most of
them lie close to the granite-granodiorite boundary. All have the composi-
tion of adamellite or quartz monzonite.

QUARTZ

B Vou

GRANITE
i

oT ‘,
*T \

|

p, l GRANODIORITE
|
|

e as °
ADAMELLITE 7. a MONZOTONALITE \
eT e

ees

Figure 10. Modes of thirty-nine specimens of the Hogen batholith and three
typical dyke rocks.

Generally somewhat darker in colour, less quartzose, and more variable
in texture and composition than the granite-like rocks are the normal
granodiorites, which differ from the adamellites by reason of their lower
potash feldspar content and correspondingly greater proportion of grey
plagioclase. Most of these rocks have a mineral composition equivalent
to an orthoclase-bearing quartz diorite, or monzotonalite.