Intrusive bodics of rhyolite varying in size from dylze s

3 to 10 fect wide to stocks % mile in diameter are found throughout
the map-area cutting the older rocks and members of the andesite
division, but in no place cutting the Tertiary lavas. The two
largest stocks are exposed on Silver Island and Tsitsutl Mountain
and dykes are especially abundant near Taltapin Mountain. These
rhyolite intrusives are dense, porphyritic, white and buff rocks,
They contain phenocrysts of colourless quartz and white feldspar
from one-cighth to one-quarter inch in diameter, in a dense
feldspathic base.

Both the andesite and rhyolite divisions are younger
than the granitic rocks found outcronping in the same localitics.
They directly overlie the granitic rocks, contain fragments of
them, and the intrusive mombers of the rhyolite division cut the
granitic rocks,

Tertiary Lavas

Tertiary lavas occur as large areas south of Babine Lake ,
and to a lesser extent north of the lake. Thesc rocks are chiofly
green, red, brown, and black, dacitic, andesitic, and besalccaes
amygdaloidal, and vesicular lava flows, which are in places as
much as 2,000 feet thick. Chalcedonic quartz, cream-coloured

saleite, pectolite, prehnite, and zeolites fill the amyedules,

Interbedded with these vesicular flow rocks arc breceuias.
and columar basalts. The breccias are of tyro distinct types: (1)
an andesitic flow breccia in which angular fragments of a browm
y matrix; and (2) an acid
onts of andesite, chert,

vesicular andesite arc embedded in a clas
flow breccia composed of smal py .tavnibdlfsos ae
quartz, jasper, feldspar, anc cranite in a glassy ¢
Along the north shore of Babine Lake, west of Sixtcoenmilo
several outcrops of colwmar basalt occur in which six=sidod colums
are well developed, Tho mountain at the cast end of Babine Lake is

a few scattered vugs containins prehnite and zcolitos,

These rocks are placed in the Tertiary because in the

southern part of tho Fort Frascr mapsarca they unconformably overlic

BES)

Upper Bocene sediments,” and are overlain in places by glacial drift

1 Preliminary Roport on the West Half of the Fort Fraser Map-Area,
B.C., Paper 37-13, 1937, Geol. Surv., Dept. of Minos and
Resources, pp. 14 and 16.