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Pyrite is frequently found impregnating the tuffs.

Basali Agglomeraties. These are coarsely fragmental types,
well exposed along the government road and on the shore east
of Skidegate village. They are purplish and greenish, massive
rocks, consisting of angular fragments of effusive types, basalt,
amygdaloids, and porphyries, in a dense tufaceous matrix.
The fragments sometimes attain a diameter of 5 feet, though
this is not common.

These pyroclastic rocks are clearly related to the primary
types occurring interbedded with them, and were derived from
the same magmas by explosion instead of extrusion or injection.

BATHOLITHIC ROCKS.

Kano Quariz Dvortite.

Under this head are classified a number of rocks of plutonic
habit which appear to make up the bulk of the batholithic rocks
of southwestern Graham island. They are in general light
grey, speckled, whitish weathering, and medium even grained.

In thin section the rock is seen to be composed largely of
andesine and quartz, with subordinate amounts of hornblende,
perhaps orthoclase, and magnetite and titanite. Secondary
minerals are biotite, chlorite, calcite, magnetite, epidote, and
hematite.

In some varieties the andesine is present in two generations
of crystals. The first average 1-5 to 2 mm. diameter, and are
mostly equant (some of them tabular) and euhedral. In size
and shape they partake of the nature of phenocrysts. The
composition of this andesine is about Ab;; Ang; as determined
by index of refraction, optical character, the statistical method,
and by measurements on Carlsbad twins and albite twinning.
In addition to these twins, pericline twinning has been observed.
In several instances the polysynthetic twinning after the albite
and pericline laws is so complete and minute that the mineral
was at first mistaken for microcline. However, the indices of
refraction (about those of quartz) and the optical character
negative this. Zonal structure has been noted. The centres