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CHAPTER V

HISTORICAL GEOLOGY
GENERAL STATEMENT

Not enough is known at present to write an unqualified account of the
geological history of northeastern British Columbia. It seems worth while,
however, to treat the subject briefly and make the best of the evidence now
available. The account given should be considered merely as a working
hypothesis, subject to revision as new evidence is acquired. It is hoped
that the attempt will stimulate interest in the geology of this part of British
Columbia, will draw attention to some of the more outstanding features of
the geology, will show how the local history is related to the history of the
western interior of Canada, as a whole, and that it will focus attention on
some of the unsolved problems of the geology of northeastern British
Columbia.

AN OLD, PROTEROZOIC(?) BASEMENT

The most important feature of the lower part of the geological column
in northeastern British Columbia, as described by Williams, and by Laudon
and Chronic (See Chapter III), is the angular unconformity between two
rock groups of pre-Silurian age, that is, between the quartzites, argillites,
and slates of Toad River, below, and the Macdougal conglomerates and
sandstones of Muncho Lake, above. After deposition, probably in Pro-
terozoic time, in an old geosynclinal basin, the beds of the older group were
deeply buried, metamorphosed to argillites, intruded by basic dykes,
uplifted to form ancient mountains, and deeply eroded. The occurrence of
igneous rock on the site of the Rocky Mountains is most unusual. It may
be recalled, however, that diorite sills and basaltic flows have been found
in the Proterozoic, Purcell group, far to the south in the Clark Range of
the Rocky Mountains. The flows, of course, appeared during the geo-
synclinal phase, and the intrusions, either then or in some early phase of
the succeeding orogeny.

The original sands and muds, now metamorphosed as the older and
lower part of the Misinchinka schists in the western part of the mountains,
along Peace River, may have accumulated in seas of Proterozoic age and
in some old geosyncline, the limits of which are unknown.

PALAOZOIC SEAS

The Cambrian history ot the region is, as yet, obscure. Sands and
gravels of the Macdougal group were laid down on the old Proterozoic(?)
basement, in a sea possibly of Cambrian age. This and other Cambrian
seas may have spread over a wide area, even to the west of the present
Trench where beds of Cambrian age have been definitely recognized (Roots,
1948).