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CHAPTER ‘VI.

STRUCTURAL GEOLOGY, HISTORICAL GEOLOGY,
AND CORRELATION.

STRUCTURAL GEOLOGY.

Folding. The structure of the Queen Charlotte series has
already been discussed in some detail in the description of those
rocks. A more general treatment of the structural features of
the district as a whole follows.

The pre-Cretaceous rocks are affected by a series of folds
with a general strike of north 30 degrees west, corresponding
with the trend of the islands south of Skidegate inlet. The
general structure of these rocks is not wholly evident, as the
Cretaceous and Tertiary covering obscures them, but there is
good evidence that they are disposed in a broad, major anticline,
with the above strike. The central part of this anticline is
occupied by the Maude argillites, which are flanked on both sides
by the overlying Yakoun volcanics. This general anticlinal
structure is complicated by many smaller folds, especially in the
less competent argillites of the Maude formation. These thin
bedded and relatively plastic rocks readily yielded to deforming
stresses, and were bent into close, often isoclinal folds. While
the information is meagre, it is the writer’s opinion that the fold-
ing on a major scale was not as intense as might be imagined
from a study of locally plicated areas of the argillites. These
fine-grained beds, although thin, are remarkably uniform over
wide areas, and, as already explained, allowed stresses to accu-
mulate to a certain point, when zones in the argillites were in-
tensely deformed, giving the close folding already described.
In these argillites the type of folding is that termed parallel.
In the massive, more competent volcanics, the strains caused
shear zones and faults, instead of folds. The orogenic move-
ments causing the upheaval and deformation of these rocks mani-
fested themselves as compressive stresses acting in a direction
north 60 degrees east, and may be correlated with the distur-