8T.J0HN.] BUFFALO FORK MOUNTAINS. 469 



The northern or northeast face of the mountain breaks down in mural 

 cliffs and steep inclines into the largo amphitheatre, whose undulating 

 debri^-coxGTed surface steeply slopes to the Buffalo Fork. The ujiper 

 200 feet or so of the strata exposed in this wall consists of gray hme- 

 stoue, the lower part tinged with red, underlaid by an exposed thickness 

 of about GO feet of shaly or thin-bedded, fragmentary, di-ab, buff-mottled 

 limestone, charged with Trilobites and other LoMer Silurian fossils, 

 probably of the age of the Quebec Group. The lower and ui)per hme- 

 stones grade one into the other without apparent non-conformity or the 

 intervention of clayey beds of passage, although the paleontological 

 transition is sharjjly interrupted and well defined. If the Niagara is 

 present at all, it here attains mea§re development and was not recog- 

 nized by its fossils. The last-mentioned limestone rests upon a heavy 

 deposit composed of bluish-drab shales, with brown-gray shaly sand- 

 stone layers containing a small Orbiculoid brachiojiod in great abundance. 

 This deposit may reach a thickness of 100 feet, though its exact vertical 

 extent was difficult to determine. 



At the eastern foot of the steep descent of the station commences a 

 broad ridge gradually rising to the eastward into the summit of Buffalo 

 Fork Peak, and which forms the southern wall of the amphitheatre. Its 

 crest is loaded with the shales last mentioned above, broadly rounded 

 and graduallj^ steepening on the south-side slope, while the opposite side 

 steeply descends to the brow of the inferior limestone, which forms a 

 low precipice or wall of bluish and dark-drab, rough- weathered, thin- 

 bedded, brecciated limestone, dirty yellow below, 50 to 75 feet high. 

 This bed determines the form of the connecting ridge, although it does 

 not quite reach the summit of the main x^eak, which is capped by a flat, 

 bald dome, showing a thickness of 75 feet or more of the inferior i^ortion of 

 the overlying shales. The latter here show yellow sandy micaceous clay, 

 interlaminated with indurated shaly arenaceous layers charged with 

 the little Orbiculoid shell, and thin plates of dirty drab limestone con- 

 taining tragmentary remains of Trilobites and covered with pecuhar 

 branching bodies weathered in relief, which, though ajiparently struct- 

 lu^eless, resemble certain ramose forms of Chcetetes. 



A bold spur puts out from the northern side of the peak, its foot 

 terminating in a much lower but rugged point overlooking the canon of 

 Buffalo Fork, the peculiar rough, jagged style of weathering and the 

 rusty-brownish sombre hue of the rock of which it is composed deter- 

 mining its metamorphic crystalline character. It is much contorted, and 

 reaches a height of 800 feet or more above the stream. The lower lime- 

 stone runs out in the spur a short distance, its lower layers of a dirty 

 brown-gray and yeUowish-stained color, which, near the extreme point 

 of the exposure, shows a dip S. 30° W. at an angle of 48°. It is under- 

 laid by yellow shales, which rest upon a heavy bed of dark brownish-red 

 and light-gray laminated quartzite, with conglomerate layers. This 

 deposit exhibits an exposed thickness of 50 to 100 feet, and flattens out 

 toward the north, where, in the terminal bench of its outcrop, the dip is 

 about J 0^, W. 5° N. The base of the ledge is concealed by the steep 

 talus of, (Ubris. The east and northeast face of Buffalo Fork Peak also 

 breaks down in i)recipices of Quebec limestone and the quartzite. High 

 up on the southeast flank of the mountain reclines a huge mass of steeply 

 inclined strata composed of the Upper Quebec limestone and the buff-gray 

 rusty reddish-stained Carboniferous limestone, which form a heavy plat- 

 ing facing the valley of Black Kock Creek. This mass of tilted strata 

 forms a rather conspicuous feature of the mountain, both as seen from 

 below as also fi^om the neighborhood of Togwotee Pass. 



