20 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



Electric Peak may be seen in the distance to the right, and presents 

 two main summits, the eastern one being higher and sharper than the 

 western. The strata of this mountain are wholly Cretaceous, and dip 

 also to the north at gentle angles. Between Mount Holmes and Electric 

 Peak we have a pretty good view of the great eastern wall of the range, 

 deeply cut at irregular intervals by four great valleys or canons which 

 drain to the east into Gardiner Eiver. In the steep walls of each of 

 these canons we have fine sections of the strata composing the wall. In 

 the first massive spur to the north of Mount Holmes the Silurian strata 

 have been disturbed by intrusions of immense masses of hornblendic 

 trachyte, which appear between the limestone strata where the latter are 

 horizontal, and also in the higb point to the left, where they have been 

 pushed up through the strata. 



Next to this ridge on the north is the valley of Indian Creek; beyond 

 this is a steep, almost vertical wall, in which some interesting features 

 appear. At the base is a massive ledge of Silurian limestone, which 

 weathers in vertical lines, as seen in the drawing. Lying on the upper 

 surface of the limestones is a mass of hornblendic trachyte (see Plate 

 XIII), which has been intruded between the limestones and the overlyiug 

 strata, arching the latter in a manner similar to the hornblendic tra- 

 chytes of southwestern Colorado and southeastern Utah. The Carbon- 

 iferous strata form the upper part of the wall. 



Beyond the next valley is a very broad, massive spur, formed almost 

 entirely of Carboniferous strata. The dip is uniformly to the north, as 

 may be seen by reference to the drawing. The valley between this spur 

 and Electric Peak is very broad, and the crest of the range, along which 

 all the spurs unite, is pushed far back to the west by the strong drainage 

 of this valley. To the east of Electric Peak we have Sepulchre Mouut- 

 ain, the western face of which is seen. Beyond, through the saddle 

 which connects these two peaks, the crests of the Yellowstone Eauge 

 may be seen. 



Such geologic details as I have collected in my brief visits to the 

 East Gallatin Eange will be presented in the order in which they were 

 observed. 



While encamped at the springs during our first visit, Mr. Gannett de- 

 termined to visit Electric Peak for topographical purposes, and I con- 

 cluded to keep him company, and make such observations of the geology 

 as my limited time would allow. 



On the morning of the 12th of September we left the springs at sun- 

 rise, and, not being acquainted with the shorter route to the west ot 

 Sepulchre Mountain, set out by the way of the wagon road and Cache 

 Creek. Having ascended the open valley of Cache Creek for about a 

 mile, we turned to the right up a very steep, grass-covered spur, that 

 leads up to the ridge which connects Cinnabar Mountain with Electric 

 Peak. On our left was the steep wall that surrounds the head of Cache 

 Creek, and above us, to the south, the rugged clifis of Electric Peak. 

 The Cretaceous strata, which at the base of Cinnabar Mountain are so 

 crumpled and broken, are here but slightly disturbed, and rise with a 

 gentle slope to the south. On the opposite side of Cache Creek the 

 northern spur of Sepulchre Mountain presents a steep, partially forest- 

 covered wall; in this a series of heavily bedded volcanic conglomerates 

 appear. 



We found the flatter parts of the northern slope of Electric Peak to 

 be covered with, snow to such a depth as to make progress in places 

 quite difficult. We were able, however, to take our animals to within 

 a few hundred feet of the summit. The strata are wholly Cretaceous, 



