st.johs.] MOUNT PUTNAM EOSS FOEK. 329 



lating upland which sinks into the plain in those directions, is, accord- 

 ing to the same observer, made up of "white and light-gray Pliocene 

 sandstones and limestones, interlaminated with trachytic porphyries and 

 coarse volcanic sandstones, all dipping about north 54° east at angles 

 varying from 15° to 30°." Professor Bradley mentions the existence of 

 an anticlinal at this locality ; the same deposits on the opposite flank 

 of the spur are mentioned as showing an inclination of " 72°, S. 34° W." 

 In passing up out of the branches of Boss Fork, five to eight miles south 

 of the above-mentioned spur, we soon leave the basaltic- flooring of the 

 plain, the way crossing the gentle undulating and gradually rising ascent 

 outlaying the main ridge of the Mount Putnam prolongation, over a light- 

 brown finely-comminuted soil, which is probably largely derived from 

 the degradation of the late Tertiary and their associated volcanic de- 

 posits. At the foot of the ridge, north of the entrance of the gorge 

 through which passes a wagon-road from Ross Fork Agency, a limited 

 exposure of loosely-consolidated conglomerate, in thin layers and nearly 

 horizontal, appears in obscure terrace outliers, and which I take to be 

 referable to the above-mentioned Pliocene beds. To the south still appar- 

 ently similar deposits occur, where they constitute an outlying area 

 corresponding to that between Eoss Fork and Lincoln Valley. 



Passing up through the Eoss Feck gorge at this point along an east- 

 west Jine, the strata show steep inclination to the eastward, rising up 

 into the monoclinal crest which is here surmounted by a heavy ledge 

 of light-buff quartzite. Beneath, occurs a ledge of drab and buff rough 

 weathered limestone, and several hundred yards to the east of the last 

 a second ledge of dark-gray limestone, steeply inclined with and resting 

 upon the quartzite, forms the east flank of the ridge facing the Eoss Fork 

 basin. The latter limestone is apparently in turn overlaid by quartzites, 

 when a space of half a mile or so intervenes in which no rock exposures 

 appear in the low acclivities bordering the stream. Then succeed 

 heavy deposits, showing below dirty-buff weathered conglomeritic lime- 

 stone, mainly composed of light-gray limestone pebbles with a few of 

 quartzite, and which is overlaid by light-gray and dark-blue cherty 

 limestones, dipping 30° southeast, and. reaching a thickness of above 1,000 

 feet. The upper limestone abounds in characteristic Carboniferous fossils, 

 a large Zaphrentis occurring in great numbers, besides Spirifer, &c. To 

 the east of the latter exposure, which forms a low rocky point on the 

 north side of the stream, the strata are concealed beneath the superficial 

 materials covering the undulating prairie surface which intervenes be- 

 tween this and the low broad divide next east. 



Some three or four miles north of the wagon-road gorge, on a promi- 

 nent, isolated point of the ridge on which Station II was located, the 

 Lower Silurian limestones rise gently up into the crest, which is more 

 abruptly broken down in the northwest face, in which the exposed edges 

 of a few hundred feet thickness of strata are partly revealed to view. 

 The lower 200 feet or more consists of (1), dark-gray limestone; (2) buff 

 rough weathered limestone ; and (3) thin-bedded, dark-gray, brecciated 

 limestone, in which a brief search failed to discover organic remains. 

 Overlying' the limestone occurs a ledge of quartzite conglomerate, show- 

 ing a thickness of 45 feet, but which is evidently only partially exposed. 

 Besting upon the last and. forming the crest of the station, a thickness 

 of a few hundred feet of gray, buff-gray, or pink fragmentary limestone, 

 with brecciated layers and shaly partings, occurs, in which the presence 

 of fragmentary remains of trilobites and a small flat gastropod are suffi- 

 cient to establish the Lower Silurian age of the deposit. This latter 

 limestone near the summit shows a dip of 5° to 15° little south of east, 



