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Langara Quartz Diorite.

The Langara quartz diorite is a grey, fine, even-grained,
plutonic rock.

In thin section the essential minerals are seen to be andesine
and quartz, with subordinate biotite and perhaps orthoclase and
secondary kaolin and chlorite. The andesine has the composi-
tion Abss Anss, and is in euhedral to subhedral grains, showing
Carlsbad, albite, and pericline twins. Zonal development has
been noted. The mineral is usually fresh. Quartz is clear,
forming equant irregular grains, containing strings of micro-
scopic cavities. The biotite is characteristically changed to
chlorite.

Some varieties of the rock possess an almost phenocrystic
development of the andesine.

As only a small area of this quartz diorite was studied, it is
impossible to say how well the above description fits the rock as
a whole. The specimens from Langara island have a distinct
resemblance to the Kano quartz diorites. The compo-
sition and habit of the feldspars are virtually identical, but in-
stead of hornblende, the chief mafic mineral is biotite, which
appears primary. The hornblende of the Kano quartz diorites
alters to biotite, so the Langara biotite may represent a late
magmatic change.

Diabase.

This is a dark, greenish grey, medium-grained rock, usually
altered in appearance. In thin section it is seen to be composed
of labradorite, Abs Anjo, and a colourless augite, with accessory
magnetite. Secondary minerals are usually present, and chlo-
rite, calcite, and kaolin are greatly developed in the more altered
varieties. The texture is ophitic, and augite crystals up to
3 mm. with a rectangular tendency poicilitically enclose short
prismatic grains of labradorite, averaging about 0-3mm. Augite
also forms smaller grains, interstitial to and wrapping around
the labradorite.

HAIDA FORMATION.

Coarse Quartzose Sandstone. This rock, a typical variety
occurring near the base of the formation, is light yellowish buff