120 
Rex T. Prider. 
accessory epidote, magnetite, and sphene. The amphibole is idioblastic 
(figure 14A), in prismatic forms up to 2 mm. in length, usually clustered 
together, these groups being separated by finer granoblastic tpiartz-plagioclase 
aggregates. 
Some of the hornblende has a poikiloblastic structure carrying rounded 
inclusions of cpiartz, magnetite, and, more rarely, plagioclase. It is a much 
deeper coloured variety than that developed in the hornblende schists inter- 
bedded with the quartzites, and has pleochroism : — X yellow-green ; Y dark 
olive gret‘ii ; Z deeji bluish green ; and absorption X < Y Z, ^ = 1-675. 
Roth (piartz and plagioclase are xenoblastic. Two varieties of the latter 
are present in ajqH’oximately ecpial amoLint (1) a completely saussuritised 
variety, and (2) a clear rarely twinned variety often showing slight zoning. 
It is an oligoclase-andesine near Ab 7 Au 3 . 
Fig. U. 
Amphibolite xenoliths in the Lower Granite Gneiss. 
A. Medium grained amphibolite (15444). Con- 
stituents are: hornblende, turbid plagioclase, quartz, magnetite 
with rims of sphene. 
B. Coarser amphibolite (15441), showing poikiloblastic in- 
clusions of quartz and magnetite in hornblende. 
C'. ‘ ‘ lIornl)lendite ’ ' — Hare jioikiloblastic inclusions of quartz 
in the hornblende. 
Magnetite is the most abundant accessory and is invariably rimmed 
with splume indicating its origin from ilmenite. Epidote and apatite are 
rarer af*cessories. 
In coarser grained varieties (e.g., 15441), the felspar is completely re- 
placed by a fine granular sericite-opidote aggregate, and the larger, more 
abundant hornblende plates show' a well developed poikiloblastic structure 
(figure 14R) with inclusions of quartz and magnetite, the latter often with 
a narrow rim of yellow’ highly birefringent epidote. 
Hornblendites.'' 
With a decrcas(‘ of the quartz-felspar content the C|uartz-plagioclase 
amphibolites pass into almost pure hornblende rocks in wliich the only other 
constituent is an occasional small grain of quartz. 15436 is an example — 
ill hand speudmen it is made up of a granular aggregate of hornblende (figure 
14C), noticeably lighter in colour than in the above types. Under the 
