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RESTRICTED LOWER AND MIDDLE TRIASSIC SEAS

Unless beds of Lower and Middle Triassic age west of the Trench have
been overlooked or were present and were removed by erosion before
Upper Triassic time, no Lower and Middle Triassic seas extended west-
ward into the Aiken Lake or adjoining areas, or occupied any part of
northern British Columbia west of the site of the Trench (Armstrong, 1946).
They were confined to the east, and may have extended in that direction
at least as far as the Pouce Coupé area. To the north, they did not inun-
date the site of the present La Biche and Liard Mountains.

Some seas! of this time may have extended far to the south or south-
east; others less so. The Lower Triassic Wasatchites sea may have con-
tinued south of the International Boundary; at least there was some direct
communication with the Wasatchites sea of Utah. The Beyrichites-Gymnoto-
ceras sea probably extended at least as far south as the central Canadian
Rockies, and perhaps to Nevada and California. The Nathorstites sea
has not yet been recorded south of Peace River Valley.

Although a few at least of the Lower and Middle Triassic seas had
direct connection with the Arctic Ocean, the path followed by these inun-
dations of the northwestern part of the continent is unknown. Unless
Triassic beds were removed in pre-Cretaceous time, this path lay west of
the site of Mackenzie River Valley and west and southwest of La Biche
and Liard Mountains. No Lower Triassic beds have yet been reported
from Alaska, and neither Lower nor Middle Triassic, as yet, from the Yukon.
Wasatchites occurs in the Arctic, but no evidence has yet been found of any
seaway between the Arctic and northeastern British Columbia. The
Beyrichites-Gymnotoceras sea may have been connected with the Arctic
Ocean across Alaska; if across the Yukon, no evidence of it has yet been
found. The Nathorstites sea may have extended across Yukon or Alaska,
or across both.

The sea floors of Lower and Middle Triassic time in northeastern
British Columbia were not disturbed by igneous activity. No flows,
tuffs, or agglomerates are interbedded with the sediments.

UPPER TRIASSIC MARINE EXPANSION

Unless their deposits were removed by uplift and erosion in pre-
Cretaceous time, the Upper Triassic seas did not extend as far to the north
as the earlier Triassic seas and perhaps not as far east; at least no record
of the Upper Triassic has been found in the Muskwa and Liard River
basins. However, some at least of the Upper Triassic seas extended far to
the west, beyond the site of the Trench, and spread widely over the north-
western part of the continent. Present information does not justify any
attempt to delineate the shores of these seas.

Late Karnian seas, of about T'ropites time, may have flooded extensive
areas far west of the Trench in Stikine River Valley, in the Yukon and
Alaska, and even in central, southern, and coastal British Columbia, but
may have had little expansion in the Arctic regions. Little is known of

1 It is not known whether the Triassic faunas of northeastern British Columbia record several,
separate inundations of the continental interior, one for each fauna, or whether the faunas succeeded

one another in one, continuous sea.