48

is found in steep, bare cliffs, and is typically exposed in Delta
creek. It is also found forming the high steep hill west of the
Yakoun river, opposite Wilson creek.

Iithology. The Yakoun formation is formed largely of
pyroclastic rocks, and in great part of waterlain agglomerates
and tuffs. Effusive types also are found, and possibly sills and
dykes. Well rounded conglomerates of volcanic rock fragments
in a matrix of similar material are occasionally met with. The
formation is dominantly sub-silicic, augite andesites and basalts
being the usually occurring varieties both as effusive (or injected)
and pyroclastic types. The pyroclastics are virtually always
dark greenish or brownish types, and the primary volcanic
rocks are characteristically of a purple tint. All types are hard,
dense, considerably metamorphosed rocks, and are greatly
jointed and sheared (see Plate XIIA).

In the lower part of the formation very well bedded tuffs
and tufaceous sandstones occur, which, except for the fossils
they contain in abundance, might be correlated with the Haida
formation on account of the great lithologic similarity between
the two. This similarity led Dawson to map the middle Jurassic
rocks of Alliford bay as Cretaceous, and caused confusion in
regard to the exact age of the Cretaceous rocks of the Queen
Charlotte series, which was not cleared up until the investiga-
tion now reported on was completed.

Metamorphism. The Yakoun formation while greatly joint-
ed, and in some places sheared and faulted, is not extremely
metamorphosed. Recrystallization is virtually absent; augite
alters to chlorite and calcite, instead of to uralite, and much of
the feldspar is still quite fresh. Locally, narrow quartz veins
are common. As in the case of the Maude formation, the met-
amorphism may be best explained as the result of pressure during
mountain-building, aided by slight hydrothermal action.

Structure —Internal. Folding in the Yakoun volcanics is
apparently not so severe as in the case of the conformably under-
lying Maude argillites, because the more massive agglomerates
deformed by cracking and shearing, rather than by local, complex
folding. Jointing in every direction and minor faults are com-
mon in the volcanics. On account of the massiveness of the