Nechako River Map-Area

Tr eS

Frangois Lake

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uk

Volcanic Bay,
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Strand line of Middle Jurassic unit

Strand line of chert pebble
Conglomeratenunita sss ae

‘GSC

FIGURE 4. Suggested position of Middle Jurassic strand lines within
the Nechako River map-area.

hills and mountains were established. Valleys were generally broad and the relief
on the whole not great. In the low areas basaltic to andesitic flows began to
accumulate, interbedded with thick layers of breccia and tuff. In freshwater lakes,
\or mud and tuff beds formed, in which were preserved leaves and shells. By Eocene
v time much of the volcanic material was rhyolitic and trachytic composition al-
though andesite was common. Still later (Oligocene time) rhyolitic flows greatly
predominated.
During this time, at least by late Oligocene time, the area was deformed
again and the youngest rocks were folded into broad open folds.

Miocene Time

ag

AUS Beginning in late Oligocene or early Miocene time basaltic and andesitic

aN Qe plateau lavas were extruded and floored many of the valleys or built accumula-
ys

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