113

From the foregoing description of the faults that occur
there, it is apparent that Skidegate inlet is an area of marked
fracturing mostly east-west in direction, and with considerable
downthrows to the north. For this reason the inlet forms, in
general, a geological boundary between the pre-Cretaceous
rocks of the southern islands of the Queen Charlotte group and
the Cretaceous and Tertiary rocks of Graham island. The
division is not complete, for small areas of Cretaceous rocks are
found on the northern end of Moresby island, and rocks of the
Vancouver group are the surface formations over portions of
Graham island.

Jointing. There is no apparent regularity in the directions
of jointing affecting the rocks. They are broken by planes in
great number and at all azimuths, and on account of the limited
size of the exposures major jointing cannot be distinguished
from minor breaks. A significant clue to the directions of
major jointing is obtained, however, from the directions of the
many dykes cutting the rocks. It may fairly be supposed that
these dykes occupy fissures extending to great depths, which
may be considered the major joints of the region. Of the many
hundred dyke-filled fissures only a few have been recorded, but
in these few there is a coincidence of direction that is deemed
worthy of remark. This coincidence consists of a marked
grouping of strikes about four principal directions, so that, in
virtually every instance, a dyke may be referred to one of these
four directions. The relations are shown in Figure 10, and it is
evident that there are two sets nearly at right angles, the result-
ants of one set striking north 24 degrees west and north 76 degrees
east, and of the other set, north 53 degrees west and north 45
degrees east. In explanation of these relations it is suggested
that each set represents strike and dip joints nearly at right
angles, and that the two sets are caused by the two periods of
severe orogenic movement which affected the region before the
intrusion of the dykes. It is true that the direction of the two
resultants of the strikes of the dykes are not parallel to the
general strike of pre-Cretaceous and post-Cretaceous folds; but
it is significant that the resultants are separated by the same
angular distance, 30 degrees, that separates the general di-