st. joux.|}) | GREEN RIVER VALLEY—GROS VENTRE RANGE alee 
mouth of Lead Creek. Ascending the valley of Green River from this 
point the east side of the stream is closely bordered for several miles 
by a low, outlying ridge at the western base of the Wind River Mount- 
ains, which is composed of gently-inclined Jura-Trias deposits. About 
11 miles north of the butte a low arch of Carboniferous limestone rises 
a few feet above the river-level, the strata gently inclining north and 
south at an angle not to exceed 10°, with which the superimposed Meso- 
zoic formations conform, as displayed in the exposures on both sides of 
the valley. The axis of this arch lies a little north of east of Gros Ventre 
Peak ridge, and in its physical character it offers little by which it may 
be distinguished from the low arch immediately south of the eastern ter- 
minus of the above-named ridge, as mentioned above. In case of their 
identity the trend of the Gros Ventre Peak, or north fold of the range, 
curves round from a southeasterly course, which it has hitherto held, to 
an easterly direction on approaching the Wind River uplift. The before- 
mentioned outlying ridge on the western foot of the latter range bears 
the record of dynamical disturbances that transpired in both zones of 
mountain elevation. 
The north flank of the Gros Ventre Range was not approached nearer 
than the outlying and probably geologically parallel low ridges that lie 
within the Gros Ventre Basin. But from the latter and more distant 
mountain peaks situated in the northern part of the Wind River Range 
and in the Mount Leidy highlands, to the northeast and north, respect- 
ively, a general knowledge of its geological structure was acquired. 
From the points of view above designated the great north fold of the 
range more or less closely corresponds to the prominent mountain crest 
that constitutes the eastern half of the northern barrier. ‘To the west 
the tributary drainage of the Gros Ventre River has eroded the north 
flank of the fold forming the culminating mountain ridge that makes a 
slight north deflection from the eastern portion of the ridge with which 
its topographical relations are most intimate. This ridge throughout 
ranges in actual elevation between 10,000 and 12,000 feet, bearing a grand 
chain of architectural peaks sculptured out of the uplifted sedimentaries. 
As has been already stated, the north flank of the range presents a 
comparatively gradual and remarkably uniform declivity descending 
into the basin area of the Gros Ventre. Its component geological for- 
mations embrace the entire sedimentary series of the region, from the 
Silurian to the Jura-Trias, inclusive. In the eastern half only the Pale- 
ozoic formations, chiefly the Carboniferous, remain along the main mount- 
ain crest, while to the west, in the before-mentioned north deflection of 
this topographic crest, the Triassic “red beds” hold a prominent place 
on the flank of the monoclinal ridge. But what is regarded as the west- 
erly continuation of the geological ridge or north fold, which was exces- 
sively eroded by the sources of the previously-mentioned south affluent 
of the Gros Ventre, which rises 5 or 6 miles to the northeast of Station 
XII, exists as a mere remnant, on the southwest flank of which low out- 
liers of nearly vertical strata were seen from Station XLIV at the west 
end of the range the previous season. The erosion of the Little Gros 
Ventre, which heads in this quarter, has stripped the sedimentaries from 
the axis of the fold, revealing the quartzite and possibly also a belt of 
the metamorphic nucleus of undetermined extent along the course of its 
caiion. The mountain ridge lying between Gros Ventre River and Little 
Gros Ventre Creek, and which constitutes the extreme northwest extrem- 
ity of the range, exhibits the lower limestone and middle reddish-tinted 
sandstone members of the Carboniferous in long lines of monoclinal 
