a2

Origin. From its mode of occurrence and lithologic char-
acter it is inferred that the Kano quartz diorite must have
consolidated under batholithic conditions, in magma chambers,
where slow cooling and favourable conditions for a high degree
of crystallinity and medium sized granularity prevailed.

LANGARA QUARTZ DIORITE.

Disiribution. The rock forms somewhat over half of Langara
island, in its northern part, and is well exposed on the coast.

Lithology. The quartz diorite is a grey to dark-grey, fine to
medium even-grained rock, with a slight porphyritic structure
in some exposures. It is largely composed of plagioclase feldspar,
with small amounts of a black mineral, difficult to determine
in the field, but which the microscope shows to be biotite. At
the contact of the quartz diorite and conglomerate, dykes of the
former, lighter in colour and finer in grain than the usual rock,
cut the conglomerate.

Structure. The Langara quartz diorite is very clearly
intrusive into the conglomerates forming the lower member of
the sediments on the southern portion of Langara island. This
contact is very well exposed on the east coast, north of Egeria
bay. The quartz diorite penetrates irregularly between the
pebbles of the conglomerate, and encloses both pebbles and
fragments derived from it. Dykes, related to the quartz diorite,
but intruded after the consolidation of the main mass, cut both
the quartz diorite and the conglomerate.

Dawson considered this quartz diorite to be older than the
conglomerates, basing his statement on the fact that pebbles
“like those of the north end of North (Langara) island,’ are
found in the sediments. This evidence, based on a superficial
similarity noted in the field, he would, of course, have rejected,
had he observed the contact as described above.

Origin. No detailed observations have been made on the
Langara quartz diorite from which a statement in regard to its
origin may be made, other than that it is essentially similar in
its genesis to the Kano quartz diorite.

1 Dawson, G. M., Geol. Surv., Can., Ann. Rept., 1878-79, p. 84B.