126 BULLETIN UNITED STATES GEOLOGICxiL SURVEY. [Voir. 



are a number of silicified trunks in situ, most of wliicli occur in a stra- 

 tum of sandstone that lies directly upon the eroded surface of a series 

 of mica-schists that belong to the metamorphie range north of the Yel- 

 lowstone Eiver. This is at an elevation of 6,000 feet. 



On the south side of the third caiion, opposite the mouth of Hell Eoar- 

 ing Creek, is a massive promontory composed of conglomerates, in which 

 are very numerous intercalated beds of sandstones and shales. In the 

 steeper faces of this promontory, many fine trunks are exposed. In 1872, 

 Dr. Peale obtained some very perfect specimens of fossil leaves from 

 these beds, on the Elk Creek side, which were determined by Professor 

 Lesquereus to be of Eocene types. The waUs of the caiion in the vicin- 

 ity of Hell Eoaring Creek are formed of the same series of rocks, which 

 occur also at a number of points on the river between Elk Creek and the 

 lower falls. 



In the valley of the East Fork, the sedimentary formations of the Vol- 

 canic Tertiary reach their maximum developement. Here they rest upon 

 the unevenly eroded surfaces of the palaeozoic and granite rocks, and form 

 a great part of the mountain ranges that enclose the valley. They are 

 horizontal and apparently conformable throughout the entire thickness 

 of 5,500 feet. The greater part of this immense group of strata is filled 

 with the sihcified remains of a multitude of forests. 



The section given in the accompanying plate occurs in the north face of 

 Amethyst Mountain, opposite the vaUey of Soda Butte Creek, and in- 

 cludes upwards of 2,000 feet of strata. The bed of the river is at an eleva- 

 tion of 6,700 feet above the sea, and the summit of Amethyst Mountain, 

 9,400. On the north side of the valley, near the mouth of Soda Butte 

 Creek, there are between 300 and 400 feet of Carboniferous strata exposed 

 along the base of the mountain slope. On the south side, occasional 

 ledges of limestone appear above the detrital deposits. Thin sheets of 

 basalt cover the flat part of the valley, which is here less than a mile in 

 width. 



The north face of Amethyst Mountain does not present as abrupt a 

 profile as that given in the section, the middle part only being so pre- 

 cipitous. At the base and top there are comparatively gentle slopes; 

 nevertheless, the actual stratigraphical conditions are truthfully repre- 

 sented. 



As we ride up the trail that meanders the smooth river-bottom, we 

 have but to turn our attention to the cliffs on the right hand to discover 

 a multitude of the bleached trunks of the ancient forests. In the steeper 

 middle portion of the mountain face, rows of upright trunks stand out 

 on the ledges like the columns of a ruined temple. On the more gentle 

 slopes farther down, but where it is still too steep to support vegetation, 

 'save a few pines, the petrified trunks faMy cover the surface, and Avere 

 at first supposed by us to be the shattered remains of a recent forest. 



In ascending one of the steep spurs that project from the main wall, 

 the strata were found to consist, toward the base, of shales and fine- 



I 



