62

No Jurassic strata have been recognized in Tetsa River and Liard
River Valleys. Hither they have thinned out in that direction or are
included in basal shales of the Garbutt formation.

Age

Very little is known of the age of the Fernie group in northeastern
British Columbia, as few fossils of diagnostic value have been collected.
The fossiliferous strata on Pink Mountain, recorded by Hage, and the basal
beds of the Fernie on Black Bear Creek are of Lower Jurassic age.

LATE JURASSIC OR EARLY CRETACEOUS
CASSIAR BATHOLITH

The description of the Cassiar batholith is included at this point
because of its generally inferred late Jurassic or early Lower Cretaceous
age, and not because of any direct contact with the Fernie or Bullhead
groups. Indeed, neither diastrophism nor intrusion, but a gradational
sequence, marked the passage from the Fernie to the Bullhead in the
Foothills of the Rocky Mountains in the eastern system of the Cordilleran
region. The Cassiar batholith outcrops in a very different part of north-
eastern British Columbia, in the Cassiar Mountains of the Interior system
of the Cordilleran region.

The Cassiar batholith has recently been described by Hedley and
Holland (1941). It underlies a large area in the Cassiar Mountains, west
of the Rocky Mountain Trench, that is, west of the valley of Kechika
River and Sifton Pass.

“The rock is all quartz-bearing and light in colour, with a small amount
of dark-coloured minerals, chiefly biotite. The dominant type is granite,
but there is also granodiorite and some quartz diorite. Perhaps the com-
monest rock type is a pink granite or porphyritic granite, of rather coarse
grain, which, when prominently porphyritic, contains orthoclase pheno-
crysts up to 2 inches in length. Another type, probably a border phase,
is a medium to fine-grained, grey, speckled mica-granite. A third type,
One occurring in the southern part, is a grey to white porphyry, quartz-
bearing and with little or no pink orthoclase.”

Hedley and Holland note a roof pendant between the head of Mosquito
Creek and the mouth of Three Forks Creek, ‘‘and at least one other was
seen several miles to the northwest’’. They describe outlying bodies of
diorite and quartz diorite near the head of Wheaton Creek and rare dykes of
porphyry, andesite porphyry, diorite, and lamprophyre at several local-
ities. They note also the abundance of pegmatite in the southern part of the
region. With all of this detail they furnish little information concerning
what formations are intruded, and offer little or no evidence on the age of
the intrusion.

Farther south, in the Aiken Lake map-area, Roots (1948) is able to
prove that the similar intrusions of the Omineca batholith are of Upper
Jurassic or early Lower Cretaceous age (See also Armstrong, 1945).