Whitesail Lake Map-Area

Only in the northeast corner of the map-area is the possible base of
the group exposed and there it consists of a chert pebble conglomerate that
Tipper (1955) believed to be the base of the Middle Jurassic. This conglom-
erate bed, which Tipper followed down the western edge of Nechako River
map-area, is believed to be a shoreline deposit and to represent an uncon-
formity separating the Takla group rocks of Upper Triassic and Lower
Jurassic age from Hazelton group strata of Middle Jurassic and later age.
As stated previously, this break was used also in the Whitesail Lake area
to separate the Hazelton and Takla groups along the eastern boundary.
However, farther west in the map-area no similar conglomerate was observed
and it may be that, in the deeper part of the basin, sedimentation was con-
tinuous and no break occurred. There would therefore be no definite horizon
on which to separate the two groups and some Lower Jurassic rocks may
possibly be included with the Hazelton group. This is the situation near the
west end of the Whitesail Range and Troitsa Lake where the Hazelton group
as mapped may include some Lower Jurassic volcanic rocks, and also in
other areas where no definite break has been determined between Lower and
Middle Jurassic. Though Tipper pointed to a logical stratigraphic horizon that
may be used as the base of the Hazelton group, at least in Nechako and part
of Whitesail Lake areas, it is restricted in the sense that it is of a local nature
and as yet is not applicable to the group as a whole. Future work may prove
the presence of this unconformity in other areas of these rocks, thus widening
its application. It would seem then that where the age of strata can be
determined the base of the Hazelton group should coincide with the base
of the Middle Jurassic, and that no Middle Jurassic strata should be included
with the Takla group.

Distribution

In Whitesail Lake map-area rocks attributed to the Hazelton group are
by far the most common. The principal belt of these rocks lies adjacent to
the eastern contact of the main body of the Coast Intrusions, and traverses
the area in a northwesterly direction. These rocks constitute the strata on
Pattullo, Chikamin, Whitesail, Sibola, and Tahtsa ranges and those unnamed
ranges along Nanika and Morice Lakes. Most of them are of Middle J urassic
age, as indicated by fossil evidence. The possibility that some Takla group
volcanic rocks of Lower Jurassic age have been mapped with the Hazelton
group around the north end of Troitsa Lake, on Kasalka Range, and along
Tahtsa River near Huckleberry Mountain has been mentioned previously.
On the western slope of Troitsa Peak, fossils of lowest Middle Jurassic age
were collected from sedimentary strata interbedded with rhyolite flows. These

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