126 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [FoZ.V. 
are a number of silicified trunks in situ, most of which occur in a stra- 
tum of sandstone that lies directly upon the eroded surface of a series 
of mica-schists that belong to the metamorpkic range north of the Yel- 
lowstone River. This is at an elevation of 6,000 feet. 
On the south side of the third canon, opposite the mouth of Hell Roar- 
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 
Lesquereux to be of Eocene types. The walls of the canon in the vicin- 
ity of Hell Roaring 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 Pork, 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 silicified remains of a multitude of forests. 
The section given in the accompanying plate occurs iu the north face of 
Amethyst Mountain, opposite the valley 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 
Greek, 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 fiat 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 fairly cover the surface, and were 
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- 
