iat

bance concomitant with the intrusion of the upper Jurassic
batholiths of the Coast ranges.

The subsequent erosional shaping of the uplifted mountain
ranges of the upper Jurassic caused valleys to form parallel to
the folds, that is, with a general north 30 degrees west direction;
and it was in these valleys, after their subsidence and invasion
by the sea, that the Cretaceous sediments were accumulated.
Erosion has now laid bare once more portions of the upper Jura-
sic land-surface where Cretaceous sediments rest on pre-Cretace-
ous rocks, and it is evident that the outlines of the basins of
Cretaceous rocks are controlled largely by the topographic
depressions of upper Jurassic time.

The general strike of the folds in the Cretaceous synclines
is not, however, parallel to the outlines of the basins. A parallel-
ism of internal strike and general outline holds near the margins
of the synclines, where they rest on the older rocks, but the main
folding inside the synclines is in a direction only a few degrees
west of north, at an angle of 20 to 30 degrees with the direction
of the earlier folds. It is thus clear that the orogenic forces
causing the second mountain building period recorded in the
rocks, acted in a more nearly due easterly direction than did
the first forces. The evidence of the dyke filled fissures in re-
gard to the divergence in direction of these two stresses will be
later mentioned. This second mountain building period may
be correlated with the Laramide revolution, as it uplifted rocks of
Upper Cretaceous age. A third period of folding affected the
island after the Masset formation had consolidated. The date
of eruption of the Masset rocks has been placed in the Pliocene,
so that this folding probably took place in the late Pliocene.

The direction of the stresses causing this folding has not been
thoroughly worked out, but many of the folds seen run more
nearly east and west than those in the pre-Tertiary rocks, and
these stresses may well have acted from a southwest or southerly
direction.

Faulting. A considerable amount of faulting accompanied

1Compare the east-west axes of Tertiary folding in southern California. Arnold, R.,
U.S. Geol. Surv., Bull. 321, 1907, Plate 1.
Arnold, R. and Anderson, R. M. U.S. Geol. Surv., Bull. 322, 1907, Plates 1 and 7.