Whitesail Lake Map-Area

of rhyolite talus and were a distinctive feature of the country. Critical
exposures covered by the flooding include the basal conglomerate of the
group at the eastern end of Whitesail Lake, the bedded tuffs near Streatham,
and the fossil locality at Chief Louis Bay east of the map-area.

Distribution

This group occurs in relatively small patches in the eastern and north-
eastern part of the map-area, but was not encountered in the western half of
the area. The outcrops are concentrated mainly along and adjacent to the Ootsa
Lake drainage basin from as far west as the mouth of Whitesail Lake. They
underlie a large proportion of the ridge between Ootsa and Francois Lakes
and extend across Francois Lake a short distance northward. They are very
prevalent in Nechako River area to the east where they have been studied
in some detail by H. W. Tipper of the Geological Survey. In Whitesail Lake
map-area some of the largest and best exposed areas of these rocks are in the
vicinity of Ghitezli, Thletelban, Chief Louis, and Uduk Lakes lying east of the
Quanchus Range. Small areas of these rocks were found in the valley of
Tetachuck Lake.

Lithology

Sedimentary rocks are not common in the group but on the east side of
Whitesail Lake about 1 mile from the mouth are two relatively small outcrops
of a very coarse conglomerate composed of roundstones of Hazelton group
rocks in an arenaceous matrix. The stones, mostly greenish grey, range from
cobble size to well-rounded boulders as much as 3 feet in longest dimension.
The matrix is a coarse, grey-green sand.

Between 2 and 3 miles north of Wistaria landing is a band of con-
glomerate in which the pebbles consist of subangular to well-rounded frag-
ments of red andesite, vesicular basalt, and dense black basalt. To the north
the stones increase in size up to 6 inches in diameter.

Basalts are well represented towards the base of the group and some are
amygdaloidal. They are dark grey to black, and are commonly marked by the
development of very large labradorite phenocrysts up to 1 inch in length and
4 inch wide. The amygdaloidal varieties are less common than the massive
types. Amygdules are most commonly chalcedonic quartz. One flow on the
former shore of Ootsa Lake between Ootsa landing and Streatham contains
thousands of chalcedonic amygdules of pea size. Commonly these amygdules

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