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intrusions of McConnell Creek map-area to the west (Lord, 1948), and may
be related to them; somewhat similar intrusions in Fort St. James map-area
to the south are probably of Eocene or Oligocene age (Armstrong, 1949).

Diorite(?) Porphyry

Two dykes, 400 and 100 feet wide, respectively, of highly altered green
porphyry cut impure Ingenika group limestones on the lower slopes of the
mountain east of Pelly Creek, south of Zygadine Creek. The present
rock is a confused aggregate of chlorite, sericite, altered feldspar, and
carbonate. It originally consisted of phenocrysts of plagioclase feldspar
up to 5 mm. long ina fine-grained matrix that was probably of intermediate
to relatively basic composition. Clots of chlorite in this groundmass may
represent altered ferromagnesian phenocrysts. The rock contained as much
as 2 per cent ilmenite or titaniferous magnetite, in euhedral grains up to
2mm. in diameter, which is now largely altered to leucoxene. The original
rock may have had a composition close to that of a diorite.

The dykes are steeply dipping. The contact relations are obscured by
shearing. There has been no noticeable contact metamorphic effect on the
adjacent limestone, but some rocks in the immediate vicinity are unusually

rich in tourmaline.

: These large, isolated dykes are of interest chiefly because they are
the only igneous bodies known in the entire one-third of the map-area
north of Chase Mountain. No dykes quite comparable to these have been
found elsewhere in the map-area, with the possible exception of some
coarse, feldspar porphyry bodies close to the Hogem batholith, and the
small andesite dykes described cutting the granodiorite northeast of
Blackpine Lake.

LATE PALZOZOIC SEDIMENTARY AND VOLCANIC ROCKS

GENERAL STATEMENT

A thick assemblage of interbedded volcanic and sedimentary rocks
outcrops in a belt 6 to 10 miles wide stretching northwesterly across the
map-area from east of Uslika Lake to the headwaters of Lay Creek. This
belt includes two distinct mountain groups separated by about 20 miles
of relatively low country where outcrops are confined to isolated ridges and
stream canyons. The apparently conformable rock assemblage, grouped
into one map-unit, consists of andesitic and basaltic flows intercalated
with tuff, greywacke, limestone, sandstone, conglomerate, and chert.

LITHOLOGY AND STRATIGRAPHIC SECTIONS

ROCKS IN THE SOUTHERN MOUNTAIN GROUP

The southern mountain group composed of these rocks lies east of
Osilinka River, east and northeast of Uslika Lake, and west of Osilinka
River between Vega and Tenakihi Creeks. The succession in these
mountains consists of at least 11,000 feet of strata. The characteristic
rocks are fine- to very fine-grained, well-bedded, grey-green to green tuffs

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