472 REPORT UNITED STATES GEOLOCICAL SURVEY 



merited volcanic accumulations out of which these mountains have been 

 sculptured. The summit of this peak rises a thousand feet above the 

 pass, and on all sides its slopes are steep, on the east precipitous. The 

 above-mentioned sombre volcanic breccia enters largely into the forma- 

 tion of the basis of the mountain, reaching more than half-way to the 

 summit. Then succeeds several hundred feet thickness of partially ex- 

 posed breccias, the steep slope covered with debris up to the shoulder, 

 from which rises the huge angular block that crowns the summit of the 

 mountain. The basis of this block is formed of drab breccia and inco- 

 herent or partially consolidated volcanic sands. A thickness of 20 feet 

 of conglomerate forms the plinth. The latter ledge presents great 

 variety in its components, bowlders and pebbles smoothly rounded, of 

 various shades of pink, drab, and red trachytes, porphyritic trachytes, 

 basalt, &c, which have a more or less distinct bedded appearance (in 

 the mass this is even conspicuously displayed) interlammated with lami- 

 nated soft sands which are very irregularly distributed through the 

 mass, though having every appearance of aqueous deposition, and a 

 general horizontal arrangement in more or less heavy beds. Seams or 

 laminae of calcite were observed in this bed. The uppermost deposit 

 shows a thickness of above 50 feet of a brecciated mass, consisting of 

 angular fragments of various kinds of volcanic rocks held in a fine, soft 

 drab-gray paste. These masses, by weather action, are wrought into 

 many curious shapes, rent and fissured and pinnacled, with cornices and 

 ashy, sandy taluses, which give to the mural exposures, seen at a dis- 

 tance, the sombre and light-gray banded aj)pearance which render their 

 recognition so certain wherever they appear. 



Notwithstanding the smoky state of the atmosphere, the view from 

 this high station was of unusual interest. The opposite side of the pass 

 is walled by far grander escarpments of the fragmental volcanics which 

 have intimate connection with a mountain ridge extending many miles 

 to the eastward, where it merges into that portion of this great volcanic 

 highland belt to which Captain Jones applied the name Sierra Shoshone. 

 This east-west ridge, itself of titanic proportions, forms the water-divide 

 between the sources of Buffalo Fork and the northern affluents of Wind 

 Eiver, and throughout it presents the same stupendous mountain wall. 

 The main Wind Eiver heads in the angle formed by this ridge and the 

 northern extension of the Wind Eiver Eange on its southwest. The 

 latter ridge is capped for a few miles by the volcanic breccias, a long, 

 spur-like ridge putting out from the peak of Station L, which was located 

 on the above-described mountain on the southwest side of the pass. 

 But a little to the east, or southeast, the main crest of this ridge is 

 formed of heavy deposits of dark, sombre, basalt-like lava, which stretches 

 for many miles along the level, wooded crest, presenting a low mural 

 break facing Wind Eiver Valley. In the midst of this ridge, about five 

 miles southeastward of Station L, the surface swells up into a low flat 

 dome, composed of dark and red scoriaceous lava, which forms slides of 

 deep red debris in the mountain side. It may be that this dome, on 

 which Station LI was made, marks the site of a gigantic crater from 

 which issued the volcanic effusions that make up the bulk of the mount- 

 ain crest. I am indebted to my young friend Stephen Kiibel, assistant 

 topographer, for the following details in relation to the disposition of the 

 volcanic pfoduets in the vicinity of Station LI, as derived from his ob- 

 servations and specimens brought to camp. The highest part of the 

 summit shows a cap of black, more or less scoriaceous lava, underlying 

 which occur red and yellow scoriaceous lavas, the latter apparently 

 .forming an intermediate belt between the black and the red, as appears 



