ELECTRIC PEAK AND SEPULCHRE MOUNTAIN. 91 



tral portion of the stock is located on the northeastern spur of the mountain, 

 where it is surrounded by sandstones. It is well exposed through a vertical 

 distance of a thousand feet. A large apophysis extends up the crest of this 

 spur, forming dark-colored pinnacles, shown on the right-hand side of the 

 panorama. The southwestern end of the stock is exposed in the southern 

 wall of the amphitheater (left side of the panorama). It is a high wedge 

 of crystalline rock, reaching to within a few hundred feet of the top of the 

 cliff. The crest of the southeastern spur, from an altitude of 10,000 feet 

 to the summit of the peak, is serrated by numerous narrow gulches and 

 rocky points, caused by the unequal weathering of dikes and of upturned 

 intrusive sheets. The nearly vertical dikes are frequent between the 

 wedge of crystalline rock and the fault to the west. They become fewer 

 toward the summit of the peak and do not occur farther northwest. They 

 extend across the southeastern spur, appearing on its southern slope in walls 

 rising above the black shales. They do not occur at the eastern base of 

 the spur. Where dikes and upturned intrusive sheets are parallel it is 

 difficult to distinguish them from one another. The sheets, however, usually 

 exhibit signs of- crushing and displacement. The dikes are more numerous 

 and thicker nearer the area of metamorphism. They are not more than a 

 mile and a half long, and radiate from a center on the northeastern spur, 

 which is about the location of the stock. They range through 45° from 

 south to southwest. 



Sepulchre Mountain, east of the great fault, located near the line of 

 Reese Creek, consists of andesitic tuff-breccia. With this mass of breccia, 

 which also forms the low ridge south of the mountain, is associated a set 

 of dikes and broad intrusive bodies that have broken up through the breccia. 

 The breccia is 3,000 feet thick, and rests upon Cretaceous and older strata 

 exposed along the northern and eastern bases of the mountain. It is well 

 exposed in bold escarpments on the northern side of the mountain, the 

 southern and southwestern sides being smooth, glaciated slopes with few 

 outcrops. The contrast between the northern and southern sides of the 

 mountain is shown in PL XV, the view having been photographed from the 

 northwestern spur, looking southeast. 



The breccias are but crudely bedded ; in places not bedded at all. With 

 them are a few massive lava streams. The whole mass is distinctly volcanic. 

 The dikes in the western part trend mostly in a north and northeasterly 

 direction, radiating from the vicinity of Cache Lake. A few trend east. 



