93

medium to coarse-grained, and disintegrates readily. It is
characterized by a large percentage of well rounded, milky
quartz grains with a few dense black rock fragments.

Under the microscope its composition .is seen to be quartz
and white chert, with a good deal of decomposed plagioclase,
and fragments of the argillites of the Maude formation and the
Yakoun volcanics cemented by chlorite and argillaceous matter
stained with limonite.

Feldspathic Arkoses. The arkoses are green, fine to medium
grained, fairly hard rocks, and make up a large part of the for-
mation.

In thin section the minerals are seen to be: quartz, in angular
to sub-rounded grains, generally less than 40 per cent of the
fragments; almost as much plagioclase as quartz, usually fresh,
and quite angular, ranging from oligoclase to labradorite;
chlorite and calcite in grains, augite, biotite, and decomposed
rounded fragments of the Yakoun basalts. Chlorite and calcite
form the cement. Glauconite may be present, but could not be
distinguished from chlorite. Pyrite is sparingly found, probably
as an impregnation. The textures are usually fine, grains aver-
aging from 0-15 mm. to 0-25 mm., and the rocks are on the whole
moderately well sorted.

Quartz Sandstones. Some of the finer, more massive sand-
stones are largely composed of quartz fragments.

Under the microscope, besides quartz, appreciable amounts
of plagioclase, biotite, augite, chlorite, etc., are seen to be present.
The cement is usually calcite, with a small amount of argillace-
ous matter and chlorite. These rocks are more even grained
and better sorted than are the arkoses.

Tufaceous Sandstones and Breccias. In the lower part
of the formation beds composed almost exclusively of fragments
of the Yakoun volcanics are found. They are poorly sorted,
and the fragments are often very angular, usually less than an
inch in size, and embedded in varying proportions of a tufaceous
matrix.

As seen in thin section, these rocks are not so compact as
the agglomerates from which they were formed, and there is
more calcite, limonite, and chlorite present. Fragments of

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