st. Jon.) TERTIARY CONGLOMERATE—GROS VENTRE RANGE. 205 
Although the immediate mountain border of the basin may be with 
equal propriety considered in connection with the description of the 
mountain areas for the sake of bringing together under one head all 
the data relating to the basin deposits, the observed occurrences in the 
border region are briefly reviewed in this place. In the narrow belt or 
saddle intervening between the Hoback Canon ridge and the southern 
foot of the Gros Ventre Mountains, a set of imperfectly exposed beds 
oceur, whose like was not elsewhere observed, unless they prove to be 
a recurrence of the Tertiary (?) conglomerate before mentioned, as oc- 
curring in the depression lying at the west foot of the Hoback Cation 
ridge, and thence extending north into the lower portion of Jackson’s 
Basin on the Snake. These deposits consist mainly of water-worn frag- 
ments of gray and bluish limestone, red and gray shaly sandstone, in- 
closed in a more or less calcareous arenaceous matrix, the exposures 
having a pale reddish color. The coarse materials vary from medium- 
sized bowlders to small pebbles. Their derivation may be traced to the 
neighboring mountains, the rect sandstones having been furnished by 
the Triassic deposits, the gray shaly sandstone pebbles are apparently 
identical with beds occurring in the Cretaceous or Laramie, and the 
limestone fragments may have come from either the Jura, Carbonifer. 
ous, or Quebec formations, all of which are in sitw near at hand. The 
more conglomeritic portions show a homogeneous mass with obscure 
lines of deposition, best seen in the partially bared slopes where the bed- 
ding usually may be readily made out. 
The latter deposits occupying the outlying slopes (9,000 to 10,000 feet 
altitude) at the foot of the mountain wall, a mile or so southeast of 
Station XII. The outcrop forms a belt several hundred yards in width, 
to the south of which and perhaps less than a mile distant, the south- 
westerly dipping Triassic red sandstones appear in the opposite side of 
the saddle, within the area of the Hoback Canon ridge. The conglom- 
erate dips at angles of 50° to 75° northward, or towards the Gros Ven- 
tre Mountains, in whose flank at this place the’ Paleozoic formations 
are much complicated and overtopped by the Archean in the crest of 
the mountain. To the southeast of the above locality, and still cling- 
ing high up on the mountain foot, the conglomeritic deposits appear in 
the grassy slopes of the much eroded divide which here separates 
Upper Hoback and Snake River drainage. It is here readily identified 
by its reddish color, though apparently less disturbed, indeed in places 
gently dipping away from the mountain and then gently rising, until it 
is lost to view a mile or so to the south. It was not recognized to the 
east of the stream descending from the divide to the Hoback, where its 
place appears to be occupied by the light drab and yellowish Yertiary 
sandstones and clays. In the divide it appears only in the ravines, tia 
slopes next the mountain being generally enveloped in morainal deposits 
brought from the immediately adjacent Archean and Paleozoic mount- 
ains, in the vicinity of Station XII, and which are piled in characteristic 
ridges, whose inequalities afford numerous receptacles for water, form- 
ing diminutive lakelets amidst the partially wooded and open herbaceous 
slopes. 
Hast of the divide beyond the limits of the mountain débris, the Ter- 
tiary deposits immediately appear in the sloping benches that make out 
into the basin to the south, a very broken region which, however, is 
traversed by beautiful terraced valleys of Hoback tributaries flowing 
out from the mountains to the north. The summits. of the Tertiary 
benches often present wide, flat surfaces, through which wind swale-like 
drainage depressions, aud covered with gneiss, quartzite, and limestone 
