er. joux.]) STRUCTURAL RELATIONS—GROS VENTRE MOUNTAINS. 209 
the abrupt south slope of the northern fold. South of Gros Ventre Peak 
the site of the greater fold is concealed by Tertiary deposits, which 
reach high up on the mountain flank at this point and thence incline off 
gently into the Hoback-Green River Basin. 
~ Both the principal folds closely correspond in contour, and which is 
retained in a marked degree in the present configuration of the great 
ridges. It consists of long gentle slopes on the north, with abrupt flex- 
ure on the south, which latter was apparently, in places, accompanied 
by the rupture and complete severance of the sedimentary strata. Of 
the latter manifestations, such as were observed will be described farther 
on. Both termini of the range are masked by late geological deposits, 
and hence it is not clear what relation the Gros Ventre uplift holds to 
that of the Wind River Mountains on the one hand and the Teton Range 
on the other. An interesting and inaportant coincidence in this connec- 
tion is the existence of strongly marked, broad, deep gaps at either ex- 
tremity of the range in the vicinity of the junction of the three great up- 
lifts. The upper course of the Green, after it bends south, on leaving 
its mountain gorge, crosses the present uplitt, which has declined suffi- 
ciently to carry the Carboniferous to the level of the river, where it is 
seen in alow fold with comparatively gentle inclinations of the compo- 
nent strata on either flank. From this it appears that the uplift was 
much less emphasized in the region approaching the west flank of the 
Wind River Mountains than was the case at the opposite extremity, 
where the metamorphic nucleus has a much more abrupt termination on 
the borders of Jackson’s Basin, fronting the Téton Range. But here our 
resources fail; the interval separating the two ranges is oceupied by a 
deep valley filled with late Tertiary sediments, which are pierced at only 
two points by insular remnants of the older sedimentary rocks that enter 
so largely into the composition of the mountain folds. Yet the evidence, 
meager and incomplete as it is, points to a more intimate relation of the 
present uplift with those of the Téton and Wyoming ranges than with ~ 
that of the Wind River Mountains, though the whole may be said to be 
tied together by the transverse elevation of the Gros Ventre Mountains. 
The southern flank of the Gros Ventre Range, in the extreme north- 
west, was not approached nearer than Station XII, 8 or 10 miles to the 
eastward. It is known, however, that the Archean ridge of the south 
fold, on whose loftiest peak Station XII was located, extends through 
to a point opposite the Lower Gros Ventre Buttes in Jackson’s Basin. 
It carries in its western part a mantle of Paleozoic strata of variable thick- 
ness, through which the Archean nucleal rocks here and there protrude 
and at one point, 5 miles northwest of Station XII, rising into a sym- 
metrical cone overlooking Jackson’s Basin, on which was made Station 
XLIV of the Téton division the previous season. To the south of this 
ridge the surface falls in broken ridges, in which are discernible appar- 
ently the full Paleozoic series steeply inclining off the south flank into 
the Snake Valley. A little to the east high benches sweep up trom the 
terraces bordering the Snake into the broken hills at the north end of 
the Hoback Cafion ridge, in which, as has been already noticed, north- 
erly dipping Tertiary deposits occur, the higher mountainous belt beyond 
being made up of Carboniferous and the Jura-Trias. The latter belong 
to the Hoback Caiion ridge of the Wyoming Range, under which head 
they have been noticed in preceding pages. 
The ridge which culminates in Station XII corresponds to the crest 
of the south fold, of which about 3 miles linear extent is made up of 
the metamorphics, with remnants of the Lower Silurian quartzite still 
capping high points. The latter show dull buff and rusty exposures, the 
14 
