st. JOHN.] GROS VENTRE PEAK—CARBONIFEROUS SANDSTONE. 215 
face of the east arm of this mountain ridge, forms long, steep talus slopes 
of loose débris, terminated above in a grand line of escarped ledges that 
rise up into the crest. Gros Ventre Peak i iS a conspicuous object. viewed 
from the south, having the appearance of a bulky quadrangular mass of 
sedimentary rocks lifted bodily to the height of nearly 11, 500 feet above 
_ sea-level. A low wedge of compressed pyramidal shape near the south- 
west angle of the mountain was selected for Station XIII, and which 
also served the purposes of a primary station for Mr. Wilson the previous 
seasane The west and south fronts break down abruptly from eleva- 
tions 2,000 to 3,000 feet above the basin benches at their foot. Near the 
angle, the heavy bedded light buff magnesian limestone, elsewhere pro- 
visionally identified with the Niagara, rises up steeply in the mountain 
foot, forming a sharp flexure with southwesterly inclination at a high. 
angle. These beds are succeeded by the thinner-bedded gray and red- 
dish-stained limestones of the Carboniferous, which curve over and at a 
higher elevation from the escarped monoclinal heights of the ridge. The 
crest of this mountain was found to consist of a narrow ridge; that to 
the east wrought out of sandstones into a jagged, almost ‘impassable, 
comb. On the north the descent is precipitous, broken by vast piles of 
angular débris, in 300 to 500 feet, reaching the limestone floor of an ex- 
tensive, glaciated mountain basin. On this side the Carboniferous strata 
everywhere slope off to the northeastward, at a comparatively moderate 
angle of inclination. In theupper portion of the basin the limestone 
plane is burdened with low piles and ridges of débris, probably of mo- 
rainal origin, and dotted with lakelets. The drainage flows east into the 
Green, and at the western end of the depression a south affluent of the 
Gros Ventre rises, flowing out to the northward across a wide belt of 
Jura: Trias. 
A section of nearly 1,000 feet vertical thickness of Carboniferous strata 
is exposed in the east arm of Gros Ventre Peak. The upper 500 
feet consists of a heavy deposit of buff-gray and reddish tinted, lami- 
nated sandstone, with obliquely laminated and quartzitic lay ers, and 
thin bands of deeper red color. The inferior half of the exposure is 
made up of numerous ledges of drab and gray limestones, the upper part 
containing layers stained chocolate-red, and containing characteristic 
Carboniferous fossils—Zaphrentis, crinoidal remains, Hemipronites cre- 
nistria, &c. The beds incline northward, at an angle not exceeding 10°, 
and generally not more than 5° to the horizon. As before stated, the 
sandstone forms a mere wall along the crest, which gradually declines 
to the east, where its appearance will be again referred to further on. 
To the north, in low southerly-facing declivities, defining that side of 
the mountain basin, the sandstone horizon reappears, where it is over- 
laid by several hundred feet thickness of drab limestones, sandstones, 
and shales, alternating. Beyond the latter, in similar abrupt terminat- 
ing benches, typical exposures of the Triassic ‘red beds” occur, occu- 
pying a wide belt sloping off the gently inclined north flank of the range 
into the basin area, drained by Gros Ventre River. The occurrences 
above noted bear a strong likeness to the stratigraphical sequence of 
the Carboniferous observed the previous season in the Téton Range and 
in the Snake River Mountains, to the west. Indeed, the resemblance is 
so marked that it may be regarded as conclusive evidence of the iden- 
tity of the strata of these horizons in the regions mentioned. This 
middle Carboniferous sandstone, however, in the present mountain range, 
perhaps attains a somewhat greater development and differs lithologi- 
cally in its generally paler tints from the equivalent horizon in the Téton 
Mountains. 
