“5

Roddacker Creek; argillite, greywacke, tuff,

chert ecoveseseverereveveaeoeseeoveereaeoeeaseeeeeeeee ee 1,200
Kwanika Creek; argillite, greywacke,. tuff seceecressee 1,500
The Upper Triassic rocks exposed on the north shore of

Pinchi Lake represent a different part of the section than those found
elsewhere. Hence the maximum thickness of the Upper Triassic series

_is probably well over 2,000 feet.

The fol lowing Upper Triassic fossils were identified by
F. §. MeLearn of the Geological Survey: Monotis subcircularis Gabb,
from the limestone on the north shore of Painchi Take, and Halobia,
from argillite outcropping along Halobia Creek.

Jurassic

The Jurassic rocks exposed along the Pinchi Lake mercury

belt consist chiefly of tufts, with some sedimentary rocks and lavas.
A medium-grained, green, andesitic tuff extends from the east end of
Pinchi Lake 80 miles northward to east of Indata Lake. it consists of
angular fragments of andesite, basalt, volcanic glass, pyroxene,
amphibole, pink and white. feldspar, chlorite, and quartz. Fragments
of volcanic rocks normally ‘make up more than half of the total frag-
ments. In places the tuff grades into an andesitic breccia, in which
the larger fragments range from g to 1 inch in diameter and include

a few of limestone and chert. Wherever observed this tuff and breccia
occur in beds 10 feet or more thick. Also widespread along the mercury
belt are dense, grey to black, basaltic tufiis. Approximately 1,000
feet of them outcrop at the southeast sidé of Pinchi Lake, where they
occur in-massive beds 5 to 20 feet thick alternating with fissile beds
3 to 8 inches thick. Similar basaltic tuffs in bed$ 1 inch to 1 foot
thick were observed at the east end of Tezzeron Lake, northeast of
Kazchek Lake, east of Kloch Lake, and along Takatoot Creek. A few
bands of red, ande sitic tuffs occur interbedded with the grey and black,

_ basaltic, and green, . -andesitic tuffs. Red, green, grey, Abel black,

porphyritic and non-porphyritic andesites and basalts are interbedded
with the tuffs and in places predominate. In the POneEvnt SS types
the phenocrysts are feldspar, pyroxene, and amphibole. In places the
lavas are amygdaloidal and are brecciated. Rear

Near the Pinchi Lake sawmill at least 100 feet of con-
glomerate and tuffaceous sandstone were observed interbedded with tuff
and lava. .The conglomerate consists chiefly of grey chert pebbles up
to 14 inches in diameter in a tuffaceous matrix. Pebbles of argillite,
andesite, and basalt were. also noted. Interbedded with the lavas. on
the hill north of the Pinchi Lake mercury mine are lenses of grey
limestone 10 to 30 feet wide and 100 to 400 feet long.

The Jurassic rocks are poorly exposed throughout most of

-the area and it was not possible to ascertain the complete succession.
The best section .is exposed on the south side of. Pinchi Lake, near the

east end, and has a maximun thickness of at least 2h 000 feet. It con-
sists of about 1, 000, feet of basaltic tuffs overlain, by 1,000 feet of
interbedded lavas and tuffs, the lavas vale bps in’ proportion toward
the top of the seption.

moses collected from the sandstone outcropping south
of the road at the Pinchi Lake sawmill were reported on by F. EH. VeLearn
as follows: ‘Trigonia (clavellatae group), Astarte?, Nerinea sp. Age:
Jurassic. SMOG) AR