B?. JOHN.] MESOZOIC DEPOSITS—GROS VENTRE RANGE. 213 
side of the easterly continuation of this ridge fronting the basin is also 
plated by the uplifted sedimentaries, while looking up the cation, the 
Archean is conspicuously displayed, making up the greater height of 
the mountain walls in the sides of the amphitheater. The latter mount- 
ain ridge sweeps round to the north where it merges into the main north 
ridge of the range 8 miles to the northwest of Gros Ventre Peak. 
The former described axial ridge that forms the west wall of the amphi- 
theater has a much more involved relationship in consequence of its 
median position between the two principal topographical ridges of the 
range in the region of the sources of Gros Ventre and Hoback tributa- 
ries “and forming what may be termed a third mountain ridge with spurs 
connecting both with the south and north ridges, with the ‘former in the 
vicinity of Station XII, northeast, and with the latter at a point about 
11 miles northwest of Gr os Ventre Peak. 
These connecting spurs are but remnants left by erosion of the broad 
summit of the principal north fold, which indeed still retains much of 
its distinctive features in the elevated mountain plateau into which the 
central topographic ridge expands a few miles to the northwest in the 
direction of Station XLVI (1877) with which it forms a circuitous but 
almost uninterrupted chain of mountain tables from the point northeast | 
of Station XII, where this ridge veers round from the axial line of the 
fold easterly and then northwesterly, finally forming the northern bar- 
rier towards the northwest extremity of the range 
In the outlying slopes in the vicinity of the cascade nmmigtakable and 
most interesting exhibitions of Mesozoic strata are encountered, the first 
of these rocks observed on this side of the range east of Hoback Caiion 
ridge. Drab and bluish indurated arenaceous clays, associated with 
buff sandstone, containing obscure vegetable remains, outcrop in the 
divide west of the cascade, dipping northeastward toward the mountain 
at an angle of 20° to 45°. There are indications of a fold in these depos- 
its with more gentle inclination on the southerly flank. These deposits . 
bear a strong resemblance to Laramie horizons occurring in the Wyo- 
ming Mountains. Their exposure is also here accompanied by the brown- 
drab soil and numerous spring sources that are the concomitants of the 
outcrop of certain Laramie deposits in the latter region; and further, 
the presence of ferruginous-stained impressions of plants in some of the 
sandstone layers furnish additional evidence of their probable strati- 
graphical identity with those deposits. On the stream below the de- 
bouchure limited exposures of dark colored limestone were seen which 
recall similar layers that were found in lower member of the Laramie 
west of the Hoback Canon ridge. Next the mountain occurs a set of 
beds resembling the Jura-Trias conformably superimposed on the south- 
erly dipping Carboniferous. At the base of the Jura occurs a heavy 
bed of buff Magnesian limestone abounding with calcite. The‘red beds,” 
however, seem to be attenuated as compared with their thickness in 
the Wyoming Mountains. These deposits at this locality reach well up 
on the foot of the mountain, where they are much obscured by accumu- 
lations of rock débris. 
Outlying the Jura-Trias belt, in the extremely broken slopes rising 
into the high bench on the southeast side of the stream, perhaps a 
couple of miles below the cascade, an interesting oyster-bed exposure 
occurs within the limits of the previously mentioned outlying fold. 
The bed shows a thickness of about 2 feet, closely packed with fossil 
Ostrea, included in a thin-bedded grayish buff sandstone which inclines 
northward at an an gle of 50°, more or less, at the point examined. The 
exact stratigr aphical relations of this bed to the before-mentioned Lara- 
