of the Guyet Formation conglomerate. Any errors accumulated
from analyzing nongeometrically deformed markers must be
added to those that Seymour and Boulter (1979) attributed to
the strain analysis.

Assuming a random initial distribution can only introduce
small percentage errors for any but low strains. Assuming non-
random distributions can only introduce larger possible errors
by misinterpretation of distribution patterns and the inherent
error in the final distribution.

Strain orientation and magnitude

The strain ellipsoids which were chosen to represent a conser-
vative strain estimate for each rock are marked in Table 17.
The axes of these strain ellipsoids are plotted on equal area nets
in Figure 66. The mean axes’ directions are also plotted.

The average long axes of the strain ellipsoid (X, maximum
extension direction) closely parallels the mean orientation of
the ductile fold axes of the Cariboo Terrane (Fig. 59, 66, 24).
The mean maximum compression direction (Z) is toward the
southwest. This agrees with the predominant eastward dip of
the cleavage and yields a Z direction approximately perpendic-
ular to the cleavage. This relationship is confirmed by hand

sample and thin section examination. The intermediate axis (Y)
lies in the cleavage plane.

The average deformation ellipsoid approximates plane strain
(Fig. 67) assuming there has been no volume change. Any
volume decrease, resulting from compaction of the rock, would
increase the field of constriction and include the average strain
ellipsoid and some of those in the apparent flattening field. The
distribution of strain forms is not related to rock type (Fig. 67)
and does not follow an obvious geographic pattern. Tobisch
et al. (1977) summarized average strain ellipsoids for some large
orogenic belts, and all but two of these fall within the apparent
field of flattening.

The elongation in the fold axis direction for the mean strain
ellipsoid is 42.5%, assuming no volume change during defor-
mation. The elongation is accompanied by a 28.8% shortening
perpendicular to the eastward-dipping cleavage and a 1.7%
shortening in the dip direction of the cleavage. Cloos (1947)
suggested that elongation of this sort in the Appalachian fold
belt could be attributed to arcing of the orogenic front. Any
arcing present for the Barkerville area is insufficient to account
for a 42% elongation parallel to the orogen. No other struc-
tures in the area take up the elongation by compression per-
pendicular to the orogen. The strain ellipsoid is thought to
record a component of shear that parallels the orogenic trend.