122 
Rex T. Prider. 
(/) Hybridisation of the granite g^ieiss. 
There is a considerable development of quartz-oligoclase-hornblende 
gneisses in the Lower Gneiss as a result of hybridisation of the granite by 
basic inclusions. These types are well developed 80 chains N., 300 chains 
of datum, where the lower gneiss is seen to transgress the bedding of the 
hornblende schists and metasediments. The gneisses are of variable com- 
position averaging : — 
Hornblende 
Oligoclase 
Quartz 
Chloritised biotite 
30 to 35 per cent (by volume). 
45 to 50 per cent. 
15 per cent. 
5 to 10 per cent. 
Microcline is rare and the accessories are : magnetite, sphene, epidote, and 
^patite. The plagioclase is usually much saussuritised but when determinable 
s an oligoclase (Ab^An^). The hornblende is a slightly deeper coloured variety 
han in the associated schists, and the biotite is the characteristic greenish 
Pig. 15. 
Granite gneiss — amphibolite hybrids. 
A. 15640. Showing clotted aggregates of hornblende (often 
with poikiloblastie structure). The other constituents are turbid 
plagioclase and clear quartz. 
B. 15397. Hornblende granite gneiss. Constituents are 
deeply coloured hornblende, somewhat fibrous pale greenish 
ainphibole, oligoclase, quartz, idioblastic sphene (with central ore 
inclusions) and apatite. 
chloritised variety, with sagenitic rutile inclusions. The hornblendes are 
often clustered together (fig. 15A) and may have a poikiloblastie structure. 
In specimen 10420, lenticular remnants of schistose plagioclase amphibolite 
are present in a hornblende-granite gneiss. 
A hornblende-granite gneiss (15397) from the vicinity of a coarse amphi- 
bolite enclosure has been analysed (Table 4, No. 2) and will be described in some 
detail. It is an even granular rock -with a gneissic structure and it contains 
several sill-like quartz-felspar layers. 
