252 REPORT UNINED STATES GEOLOGICAL SURVEY. 
rising on the mountain flank; but immediately bordering the valley on 
the north side, to which the present examinations were confined, it 
has been much eroded and heavily loaded with morainal deposits which 
reach high up on the mountain foot in the debouchure. In the opposite 
side, however, this horizon is well displayed together with its relations 
to subjacent formations. About opposite the narrows a sudden flexure 
or up-bending in the lower limestone formations takes place, where the 
strata are tilted at a high angle, the tension accompanying their abrupt 
displacement manifesting its intensity by the rupture and faulting of 
certain beds, while the continuity of other and less refractory strata was 
unaffected. As seen from the summit of the ridge, looking down along 
the mountain flank to the north, a slight undulation in the declining 
strata was the only evidence of the continuation in that direction of the 
flexure which forms so marked a feature in the cafton-walls. Above the 
flexure the strata resume their former moderate inclination thence to the 
summit of the ridge. This highland region abounds in excellent pastur- 
age, and along the streams considerable tracts of mountain meadow are 
met with. The rugged slopes are well stocked with evergreen forests 
up to a line nearly corresponding to the altitude 11,000 feet above the sea. 
After leaving the mountains Wind River flows through a broad fertile 
valley, in the midst of which Camp Brown and the Shoshone Indian 
Agency are located. The altitude at the debouchure of North Fork is 
about 6,730 feet, the stream descending to 5,700 feet at the military post, 
in a distance of about twelve miles. The north side of this valley is 
bounded by the outlying uplands which break down in grassy declivities, 
in which the geological formations are in the main concealed from view 
by the loose soil. Here and there, however, over comparatively limited 
areas, the component strata crop out, and with care a detail section might 
possibly be made connecting the basin deposits with those more clearly 
shown along the foot of the mountains. Two or three miles below Camp 
Brown, and perhaps twelve or fourteen miles distant from the mountain 
foot, there appears an anticlinal fold with indications of a sharp synclinal 
on the west flank, which has brought up a series of variegated arena- 
ceous and clayey deposits which, lithologically, bear striking resemblance 
to lower horizons occurring in the Jura of this region. On the west 
slope of this anticlinal the occurrence of drab fragmentary limestones, 
red and drab clays, and soft buff and grayish sandstones are certainly 
more in concordance with the stratigraphy of the Jura than with that of 
the Cretaceous members met with farther north, as described in fore- 
going pages. At the locality examined the axis of the sharp synclinal 
fold is occupied by an apparently heavy deposit of reddish and drab 
clays with associated sandstones, to the west of which obscure exposures 
of drab clays and soft arenaceous deposits, inclining eastwardly, seem 
to merge into the dark drab Colorado shales that appear in their proper 
stratigraphical order in the upland bench rising up against the foot of 
the mountains. The broad, shallow depression through which the Sage 
Creek drainage seeks Little Wind River marks the axis of the anticlinal 
fold, in the crest of which is located the bitumen spring which was described 
by Dr. Endlich in the Report of the United States Geological Survey for the 
season 1877. The flow of water is feeble, bubbling up in several hardly 
discernable vents, around which the bitumen is deposited, forming sheets 
whose consistency in the margin of the overflow becomes the hardness 
of an asphalt pavement. The spring is slightly raised above the general 
level of the plain, averaging perhaps 50 yards in diameter, and is par- 
tially overgrown with tall grass. Birds and small Indians, frequenting 
the place for water and sport, not infrequently become entangled and 
Se 
