CHAPTER HI—STRUCTURAL GEOLOGY.
REGIONAL.

The major structural element of the Cariboo series in the Barkerville region is a
broad, open anticlinorium whose axis trends about north 55 degrees west from Mounts
Pinkerton and Amador to Mount Nelson.. On the north-eastern side of the axis the
beds dip generally north-easterly and on the south-western side generally south-westerly.
Farther to the east and to the west the Slide Mountain series and the Quesnel! River
group are involved in this regional anticlinal structure. The Cariboo schists are not
only complexly folded and drag-folded but, in addition, are cut by large northerly and
north-easterly trending normal faults, some strike-faults, and are traversed by region-
ally developed north-north-easterly striking fractures or joints.

The Stanley area lies across the axis of the regional anticlinorium.

DETAILED.

The accompanying geological map does not show the distribution of any rock
members, and for that reason the representation of folding cannot be complete. To
substitute for this deficiency, structural lines have been drawn which are an interpre-
tation, incomplete and possibly imperfect, of the available information. They are lines,
based on numerous strike and dip observations, which are generalizations and which
are intended to illustrate the attitude of the bedrock formations. They should not
be interpreted as indicating the outcrop pattern of a particular bed, for they are
drawn without regard to topography. Minor drag-folding, either observed as such
or interpreted from strike and dip observations, is represented by S- and Z-shaped
structural lines.

Knowledge of the fold structures is incomplete because of the complete absence of
determinations of the tops or bottoms of beds. No observations of cross-bedding or
grain-size variations were possible, and attitude determinations based solely on flow
cleavage-bedding relationships, unless supported by other evidence, may not be com-
pletely reliable in an area where there may be unsymmetrical folding and where there
is more than one period of deformation.

The observations on which the structural lines are based are measurements of
strike and dip of the bedding of the bedrock formations. For the most part, cleavage
is parallel to the bedding or is only a few degrees divergent from it. The exceptions
are at places near the axes of drag-folds, where the cleavage is parallel to the axial
plane of the fold and cuts across the bedding (see Plate III A). On the limbs of such
folds, cleavage and bedding are closely parallel. In some outcrops where cleavage is
observed and bedding is indistinct or indeterminate, the attitude recorded is that
of the cleavage. Its use is based on the assumption that the bedding is essentially
parallel to it.

The folds indicated by the structural trend lines are folds largely representing a
second period of deformation. The primary flow cleavage has been folded, and the
inter-layer movement accompanying the bending has taken place along cleavage planes
which may be developed as prominently as, or more prominently than, bedding. Besides
the actually observed large-scale folding of primary cleavage, the second deformation
has produced in some places flow cleavage which is parallel to the axial planes of the
younger folds and which cuts across the earlier better-developed cleavage.

The second deformation folds are gentle open structures, and their representation
by structural lines on the map masks the older structures. These older structures,
Which were accompanied by the regional development of cleavage, are rarely seen.
They are thought to be tight, overturned, and to have been accompanied by the for-
mation of tight small drag-folds, such as may be seen in the hydraulic pits on the
Slough Creek benches and near the summit of Burns Mountain.

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