7 8 
ALASKA GEOLOGY 
mit. The beds are almost horizontal in this section, and the thickness, 
from the top of the lower beds, was estimated at about 1,200 feet. 
The rocks of the Stepovak Series have been folded and 
faulted. Plate vm shows the broad domal uplift which is 
magnificently exposed on the eastern wall of Chichagof 
Valley. From Chichagof Peak, in which the beds are prac¬ 
tically horizontal, and beneath which, as will be shown 
below, is an extensive laccolithic intrusion, the strata dip 
away on all sides, with gradually increasing inclination, 
reaching 45 0 at East Point, which is about five miles from 
the peak. This doming up of the strata was accompanied 
by minor faulting and by the formation of fissures or lines 
of weakness, roughly radial to the dome, into which the 
igneous rock made its way in the form of dikes. 
The attitude of the rocks has controlled the development 
of the drainage in very marked manner. The streams fol¬ 
low the strike of the beds, working down along the soft shale 
horizons; the southward facing sides of the valleys have 
gentle dip slopes; the northward facing sides are steep, 
often precipitous, scarps formed by the harder sandstones. 
As far as West Point the dome structure controls the 
attitude of the beds. Beyond this point, and west of a 
line running a little west of north from it, there is an 
abrupt change of the strike through an angle of 90°, so 
that the beds strike nearly parallel to the shore of West 
Cove and dip northeast at angles never exceeding 30°. It 
appeared in the field that this abrupt change of strike 
could only be due to a north-south fault of considerable ex¬ 
tent, but the character of the exposures in the course of 
this probable fault was unfavorable to its direct observa¬ 
tion. In traversing the ridges from the head of West 
Cove to Chichagof Valley, the strike of the rocks was 
found to be persistently about northwest, and the streams 
to follow the strike closely in direction. But the dip 
changes from northeast to southwest after passing the 
