st. john.] GROS VENTRE RANGE. 455 



valley of the Little Gros Ventre, and Avhich are so "well displayed from 

 Station XLIY. The northeast face of the peak breaks down in sheer 

 precipices 'of dark-weathered limestone into an amphitheatre, which is 

 divided into two nearly equal parts by a huge buttress that projects 

 from the main peak, carrying on its crest* curiously weathered pinnacles 

 and towers of limestone, terminating in a conical point. The amphithe- 

 atre is filled with banks of snow, which feed the tiny lakelets that nestle 

 at the foot of the debris slopes. To the east the peak is rent and fis- 

 sured by the action of the elements, placing an almost impassable bar- 

 rier between the station and the lower crest in which the mountain 

 ridge is terminated above the saddle separating the drainage of the two 

 Gros Ventres. 



The summit of the peak is strewn with angular limestone fragments, 

 which, in places, are tumbled into funnel-shaped sinks; no erratic 

 materials were observed. It is made up of drab limestone interbedded 

 with dark brownish-drab magnesian layers and yellowish weathering 

 deposits in the lower portion, and abounding in fossils, Hemipronites 

 crenistria being particularly numerous in certain layers, besides a large 

 Spirifer, Athyris, Zaplirentis, &c. These beds dip at an angle of 15°, 

 W. 30° X. to X. 5° W. In the northwest foot of the peak they incline 

 at about the same angle, K 40° E. to X. 5° W., and at one place bulged 

 up into a slight anticlinal or undulation, with a westerly dip of about 

 10° on the one flank. 



In the sloping ridge which forms the western wall of the gulch that 

 flows down to the Gros Ventre to the northward, the Carboniferous 

 limestones are overlaid by a series of arenaceous deposits, consisting of 

 intensely hard, pinkish siliceous beds and hard, laminated, grayish, 

 reddish-stained sandstone, including bands of red and yellowish sandy 

 shales, which impart to the exposures so strong a Triassic aspect. But 

 these deposits are precisely like the upper beds of the Carboniferous in 

 the Teton and Snake Eiver ranges to the west, in which latter region 

 they are known to be succeeded by later- formed limestones, whose or- 

 ganic remains establish their Carboniferous age. These Carboniferous 

 red beds are doubtless identical with the lower red-bed series in the 

 debouchure of the Gros Ventre, which were described, as above quoted, 

 by Professor Bradley, where they were estimated at 400 to 500 feet 

 hi thickness. The same beds also appear in the east side of the above- 

 mentioned gulch, capping the limestones, which slope oft" at a moderate 

 angle northward in the declivity which forms the Gros Ventre or north- 

 ern face of this part of the range ; and still farther east a heavy mass of 

 deeper red-colored strata appears, borne upon the flank of the moun- 

 tain, then edges shown in escarpments facing southward. The latter 

 deposits are doubtless the same as those noticed by Dr. Hayden in the 

 valley of the Gros Ventre, where they are associated with thin bands 

 of gypsum. 



To the southeast this northern barrier ridge shows a sharp fold, the 

 limestones flagging the south-facing slope, and which probably is part 

 of the great fold seen from Station XLIV. It is possible that the belts 

 of red deposits seen at various points Avithin the range belong to the 

 Triassic "red-bed" series, which were curved over the great fold, but 

 which have become quite disconnected from the northern mass through 

 the agency of subsequent erosion, which has removed a vast amount 

 of sedimentary materials over the central portion of the range. The 

 northerly inclination of the Carboniferous deposits carries them beneath 

 the level of the Gros Ventre, along the north side of which appears a 

 hue of beautifully-eroded bluffs, showing a thickness of several kun- 



