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Fine conglomerates!, containing an abundance of fragments from 2
to 10 mm. in mean diameter, are, however, abundant, and are a distinctive
feature of all parts of the Ingenika group exposed in the map-area. As
much as 60 per cent of the volume of the rock of these conglomerates may
be composed of rounded fragments of granule or pebble size. The granules
are almost exclusively of three types; single quartz grains, single grains
or aggregates of grains of feldspar, and fine-grained quartzite composed of
an aggregate of quartz grains with very minor muscovite and feldspar.
The proportions of these constituents vary widely from bed to bed; but
in general the granules of individual quartz grains are more abundant
than those of feldspar and quartzite together. About half the feldspar in
the granules is twinned oligoclase or andesine. Other feldspar grains
include microcline, perthite, and an untwinned alkali plagioclase. Almost
all the feldspar grains are relatively unaltered. Most of the quartzite
pebbles are of uniform, erystalloblastic texture, with an average grain size
about 0-2 millimetre. A few quartzite pebbles contain parallel-oriented
muscovite flakes, and grains of cloudy feldspar partly altered to sericite.

Most of the pebbles are well rounded, and well sorted in any one bed.
An excellent shape orientation persists, with elongated and lenticular
pebbles lying parallel with the bedding. Recrystallization has been slight
to moderate, and has developed fine, sutured, interlocking contacts between
the pebbles and matrix. In a few instances it has undoubtedly been
effective in promoting a lenticular, oriented shape of some of the quartz
pebbles. However, the presence of broken pebbles with partly rounded,
partly jagged outlines, and the general lack of crystalloblastic contacts of
the feldspar granules, suggest that the amount of recrystallization has been
slight, and that most of the grains have their original detrital form.

The matrix of the conglomerates ranges from relatively pure quartzite
to quartz-sericite schist, in every respect similar to the non-conglomeratic
quartzites and schists.

The elliptical and cigar-shaped, very fine-grained, black bodies
embedded in schistose quartzite north of Mount Melvin are seen in thin
section to be composed of minute grains and flakes of black opaque material,
so abundant that the other minerals in the rock cannot be identified.
Accompanying the black matter are a few rounded blebs up to 0:01 mm.
in diameter of orange-brown material, apparently aggregates of minute,
variously oriented crystals, for the blebs remain illuminated in all positions
under crossed polarized light. Both the black flakes and the orange-brown
material are thought to be carbonaceous matter, probably derived from
organic material in the original sediment. The black ‘pebbles’ themselves,
however, are very hard, and probably contain much siliceous material.

Quartzites

Probably more than half the Ingenika group rocks may be classed as
quartzites, in that they are metamorphosed sedimentary beds whose chief
detrital constituent is quartz of sand size. The quartzites range from
granular rocks composed of coarser granules in a distinctly finer grained

1JIn this report the classification of detrital sediments recommended by Pettijohn is followed.
Conglomerate is defined as a clastic rock containing an appreciable (10 per cent or more of the
rock volume) number of rounded fragments greater than 2 millimetres in diameter (Pettijohn, 1949,
p. 195).