115

quiet, uniform, apparently widespread conditions, and at
moderate depths, in lower Jurassic time, or perhaps it began in
upper Triassic time. In this epoch the Maude formation was
accumulated. If the classification of the conglomerates of
Pillar bay and that vicinity as basal Maude is correct, then the
lowermost Jurassic (upper Triassic) was a time of littoral sedi-
mentation on a large scale, and these shallow, turbulent water
conditions gave way to the quiescent ones outlined above.

Towards the close of the lower Jurassic epoch, an uplift
caused slightly coarser sediment to be deposited and about the
same time explosive volcanic action began. This volcanic epoch,
which began gradually, continued with great violence through
middle Jurassic time, and gave rise to the Yakoun formation.
The region now occupied by Graham island was then the scene
of violent volcanic activity and vast amounts of basaltic ejecta
were accumulated, at first under marine conditions, and later
probably on the land platform built up by the eruptions. Lava
flows were apparently not a large feature of the eruptions.
The length of this stage of vulcanism is unknown as the volcanics
are everywhere removed or truncated by the surface of pre-
Cretaceous erosion. That there was a considerable covering
over the formations now exposed at the surface is evident from
the fact that they are intruded by batholithic rocks, requiring
at least several hundred feet of cover.

After their accumulation and consolidation the lower and
middle Jurassic rocks were folded to a considerable degree, and
intruded by masses of igneous rocks in the form of batholiths
and probably laccoliths. As the gap in the time scale repres-
ented by the unconformity at the top of the middle and lower
Jurassic rocks extends to the base of the Upper Cretaceous,
there is obviously no means of fixing the date of this intrusive
epoch exactly; but it’ may be correlated with the intrusion of
the Coast Range batholith, generally supposed to be upper
Jurassic in age.

The late Jurassic folding and uplift raised the region, so
that the rocks of the Maude and Yakoun formations, together
termed the Vancouver group, formed a range of mountains with
axes striking about north 30 degrees west. These mountains