78 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 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 persistent!}' about northwest, and the streams 

 to follow the strike closely in direction. But the dip 

 changes from northeast to southwest after passing the 



