108 
Rex T. Prider. 
The Upper Gneiss is constant in conaposition and structure throughout. 
In places the crushing has been so complete as to obliterate the augen 
structure and fine banded gneisses have resulted. Such rocks have elongated 
narrow lenticles rich in fine granulated microcline, alternating with long 
sill-like streaks of unstrained c^uartz, in which the cpiartz extinguishes as a unit. 
The foliation in both bands conforms to that in the associated meta- 
sediments. In the case of the upper gneiss, the gneiss-quartzite contact is 
often a narrow crush zone, varying from a few inches to a few yards in v idth. 
The rocks of this zone are (juartz-sericite schists, in which the cpiartz appears 
in elongated lenticles up to 1-| inches x } inch x J inch with prominent cross 
fractures (tension joints) — these lenticles are elongated in the plane of 
foliation, but more elongated parallel to the strike than to the dip. 
In both gneisses there is often an irregular folding and contortion of 
the flow layers rich in biotite, due to folding movements which were taking 
2 >lace contemporaneously with the flowage. 
That the gneisses are of igneous origin cannot l>e doubted in the evidence 
presented by mimerous xenolithic bodies of variable composition— some 
metasediments, others metabasic igneous. These will be described presently. 
In places at the bottom of the Upper (hieiss (notably in Poison Creek), the 
gneiss is discordant to the bedding in the (piartzite and small offshoots 
traverse the bedding of the ({uartzite. 
We will consider firstly the Uppei' Gi’anitic Gneiss and its associated 
xenoliths. 
(a) The Tapper Granitic Gneiss. 
The niaiji characteristics may be summarised thus : — 
(1) Augen gneissic structure is characteristic throughout. 
(2) Ptygmatic folding is occasionally developed. 
(3) With the exception of occasional small basic xenoliths, narrow 
lenticles of plagioclase amphibolite and irregular small biotite 
granulite xenoliths, the composition is fairly constant throughout. 
(4) Microcline is the dominant felspar. 
(5) Myrmekitic structures are developed in most types. 
(6) Biotite is im-ariably chloritised and contains sagenitic rutile in- 
clusions. 
(7) Narrow veins of pegmatite and aplite are numerous. 
(8) Garnet and the ^•a^ious aluminium silicates characteristic of meta- 
sediments are completely absent. 
The main type of the Upper Gneiss is a microcline granite gneiss, but 
other minor types are occasionally noticed. The varieties of Upper Gneiss- 
are : — 
(i) Biotiteanicrucline granite gneiss. — These are medium-grained rocks 
vlth augen gneissic structure. The augen are of microcline up 
to 1 cm. X O’O cm., in an even-grained ground of cpiartz, felspar, 
and biotite, the latter in sub-parallel alignment. The cpiartz is 
in elongated ellipsoidal grains (5 mm. x 3 mm. x 1 mm.) showing 
greatest elongation parallel to the strike and lesser parallel to the dip. 
Under the microscope the minerals observed were quartz, micro- 
cline, oligoclase, and biotite vith accessory magnetite, apatite, 
muscovite, zircon, epidote, rutile, and myrmekite. 
Microcline is most abundant, occurring in xenoblastic plate‘S, usually, 
but not always showing peripheral granulation (Plate III, C). This 
