General Geology

strata are underlain conformably by a thick series of volcanic rocks the base
of which was not seen, or at least not recognized. These volcanic rocks may
be Middle Jurassic in age or may be in part of Lower Jurassic age and
belong to the Takla group. In this report, however, because there is no definite
evidence that they are Lower Jurassic, they have been included with the
Hazelton group.

In Smithers map-area to the north, the Hazelton group contains strata
of Upper Jurassic or Lower Cretaceous age as well as some continental strata
that are correlative with the Kootenai and Blairmore formations of Alberta
(Armstrong, 1944a). These Cretaceous continental beds do not extend
southward into Whitesail Lake area but terminate at its northern boundary.
The Lower Cretaceous beds occurring on Swing Peak and Laventie Mountain
are marine strata and are not correlative with the Hazelton group but with
the Haida formation of the Queen Charlotte Islands.

Lithology

In Whitesail Lake map-area the Hazelton group consists of at least
11,500 feet of interbedded volcanic and sedimentary rocks. This assemblage
may in places be roughly divided into a lower, mainly volcanic division;
a middle, mainly marine sedimentary division; and an upper, dominantly
volcanic division. Boundaries between these divisions are arbitrary and cannot
be followed across the area as a whole. For this reason the group was mapped
as a single unit. The three divisions vary in thickness and composition along
strike, so that a section in one locality may bear no resemblance to a section
in another. The two volcanic divisions are similar in general character and
are not always separable. The lower division is characterized by a larger
proportion of massive green and purple andesite, generally duller colours, and
contains a larger proportion of sedimentary material than the upper volcanic
division. The base of the lower division was not observed but the thickness
of this division is probably not less than 3,000 feet.

Lying above the lower volcanic division on Chikamin Range, along
Tahtsa River, and on Troitsa Peak is a succession of sedimentary rocks, with
minor interbedded tuffs and flows, which yield marine fossils of Middle
Jurassic age. The section on Chikamin Range exposes about 2,500 feet of
tuffaceous greywacke, black argillite, grey-green tuff, impure limestone, thin-
bedded chert, and minor andesitic flows. At the east end of Nadina Lake
a section of similar rocks yielding similar fossils is also about 2,500 feet thick.
Fossils of the same age were found along Tahtsa River, on Tweedsmuir
Peak, Michel Peak, and on Nadedikus Mountain.

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