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be observed. The chief impurities, where present, are muscovite (sericite)
and chlorite. A distinctive series of beds of remarkably pure white quart-
zite, with a maximum total stratigraphic thickness of about 1,500 feet, is
exposed on Ingenika Cone, in a belt leading north from Mount Isola to
Barrier Peak, and on the ridge east of Pelly Creek. This series consists
almost entirely of milky white, fine-grained, crystalline quartzite, in which
the only impurities visible in hand specimens are scanty, minute grains of
mica or metallic sulphides, and in which many beds show no impurities.
The quartzite is fairly well bedded, with the bedding planes outlined chiefly
by differences in texture; and in places partings of chloritic slate from a
fraction of an inch to 2 inches thick occur at intervals of 50 to 200 feet.
South of Ravenal Peak, a pale buff quartzite exhibits good crossbedding.
The stratigraphically higher beds in this area are also characterized
by abundant quartzites, but include a greater proportion of conglomerate,
quartzitic grit, chloritic schist, phyllite, slate, and limestone. A bed of
conglomerate consisting of rounded, slightly elongated quartzite pebbles
up to 3 inches in diameter in a mixed micaceous quartz-sericite phyllite
matrix, is exposed near Flood Creek, south of Ingenika River at the
eastern border of the map-area. Beds of fine conglomerate containing
quartzite and quartz-feldspar pebbles less than 4 inch long in a sericite-
chlorite phyllitic matrix, are widespread in the eastern part of Russel
Range. North of Pelly Lake, a 60-foot bed of light grey, crystalline lime-
stone contains many rounded to subangular fragments of detrital quartz.

PETROGRAPHIC DESCRIPTION AND CHEMICAL COMPOSITION
General Statement

The Ingenika group strata represent a varied assemblage of coarse-
and fine-grained clastic material, and chemical precipitates. All the rocks
have suffered some degree of regional metamorphism, but, with the exception
of those included in the Wolverine complex, the grade of metamorphism
has been low, and original differences in chemical and mechanical composi-
tion of the beds have been largely preserved. The minerals comprising
these rocks include detrital minerals, stable under low-grade metamorphism,
and metamorphic minerals produced by alteration of sedimentary rocks of
normal composition. The original sedimentary textures are, in most places,
recognizable; they have been obliterated by superimposed metamorphic
textures to only a minor degree.

The following is a description of the principal rock types of the
Ingenika group, as viewed mainly in thin section under the microscope.

Conglomerate

Coarse conglomerates are relatively scarce in the Ingenika group of
Aiken Lake map-area, and are restricted to a few individual beds, such as
those exposed south of Ingenika River near Flood Creek and in the Russel
Range east of Ed Bird Creek, where rounded fragments of quartzite up
to 3 inches in diameter occur in a schistose quartzitic matrix.

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