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varying from AbzsAngs to AbsoAnso, colourless augite, magnetite,
and a little biotite and titanite. Secondary minerals are abun-
dant, chiefly chlorite and calcite, with sericite, magnetite,
limonite, hematite, and perhaps serpentine and epidote. The
labradorite is typically developed in equant crystals, more
rarely tabular or lath shaped. The texture varies, either dense,
porphyritic, intersertal, or occasionally ophitic being found.
Phenocrysts of both labradorite and augite occur. Alteration
is considerable, the mafic minerals usually being replaced by
chlorite and calcite, in varying degrees up to completion, but the
feldspars are often little changed. When amygdules occur, they
are filled with chlorite, calcite, and quartz.

Augite Andesite.

The augite andesites are rocks similar to the basalts, and
clearly related to them, differing only in having andesine instead
of labradorite feldspar. In colour, textures, mode of occurrence,
etc., they resemble the basalts.

Pyroclastic Rocks.

The bulk of the Yakoun volcanics on Graham island are
bedded tuffs and agglomerates, clearly pyroclastic in their
origin, and in large part accumulated under water. The lower
beds of the formation are well stratified, rather fine-grained
tuffs, weathering rather readily, but for the most part coarse,
indurated, tough agglomerates prevail, in massive beds showing
little or no stratification.

Basalt Tuffs. These tuffs vary in the hand specimen from
light grey, porous rocks, to dark brownish and greenish varieties,
usually very hard and dense, and clearly showing their clastic
nature on the weathered surface.

Under the microscope angular fragments of basalt or augite
andesite, as well as individual pieces of labradorite, augite,
biotite, etc., are visible. The matrix is of finer fragments, ap-
parently very fine volcanic material. Alteration varies greatly,
and some specimens are almost wholly replaced by chlorite and
calcite.