Plates V, VI, VIIB and VIIIB) and in Figure 29. The fold
style varies directly with lithology and proximity to faults.
Lithologically, the different response of quartzite versus
pelite is the most obvious.

Quartzite forms open to tight folds on both outcrop
and regional scale. Commonly the folds are not continu-
ous because of forelimb fault disruption. Backlimbs and
hinge areas approximately maintain bedding thickness.
The forelimbs, where faulted, show dramatic thinning,
accompanied by recrystallization of the quartzite. The
recrystallization can leave the quartzite with the appear-
ance of a quartz vein. An example of which is the ‘‘quartz
comb’’ on Middle Ridge as mapped by Holland (1954).

Pelite is a common rock constituent of the area and
shows the most diversity of fold styles, ranging from
asymmetric open and tight to asymmetric-to-recumbent
tight and isoclinal. The black pelite unit of the Black
Stuart Group is locally isoclinally folded on the outcrop-

42

and hand-specimen-scale with the best examples of this
in the Tinsdale-Cunningham Creek and Black Stuart
Mountain areas (Fig. 30). Pelite of the Isaac Formation
folds in the same manner as the black pelite unit of the
Black Stuart Group. Impure quartzite, limestone and silty
pelite have fold styles intermediate between those of pure
quartzite and pelite.

Near faults the intensity of folding increases. Tight
and isoclinal folds are localized in the hanging and foot-
walls of thrust faults. Fold amplitudes increase and wave-
lengths decrease adjacent to high angle reverse faults of
the Roundtop-Middle Mountain area (Fig. 27).

Conical folds of Cariboo Group of the Roundtop
Mountain area were first described by Sutherland Brown
(1957, p. 48-49). It is suspected that they are common
in the area but are obscured by lack of outcrop. Because
of this obscurity, folds are projected into structural cross-
sections as though they were nearly cylindrical. The cross-

Figure 30. Isoclinal folds in the
black pelite unit of the Black Stuart
Group.

A) Refolded isocline on Tinsdale
Creek. Fold axes of isoclines paral-
lel the outcrop. (@SC 191025)

B) Ilsoclines near Black Stuart Moun-
tain. (GSC 191026)