st. John.] SEDIMENTARY AND VOLCANIC KOCKS. 447 



lowed by limestones abounding in Carboniferous fossils. The latter de- 

 posits, which exhibit the best exposures, dip IN". 50° E., at an angle of 

 about 70°. In the west face of the butte Professor Bradley mentions 

 the occurrence of " Post-Tertiary whitish sandstones and marls, inclos- 

 ing fragments of limestone and chert, but no fossils, of which all the 

 southern part of the butte is composed." As seen from the hills to the 

 northeast, these light-colored deposits apparently form a low outlier on 

 the northeast flank of the butte, while the southern spur of the butte is 

 apparently made up of brown deposits with indurated layers, dipping 

 in the same general direction as the other Tertiary deposits, or north- 

 westwardly. 



In the space included between the Gros Ventre Eiver and the west- 

 ern foot of the adjacent mountains of the same name, to the southeast 

 of the Upper Gros Ventre Butte, a considerable area is occupied by low, 

 beautifully curved grassy hills, 500 to 700 feet above the Snake, and 

 which are connected with the mountain border by a shallow depression 

 or saddle. This area is intersected by parallel depressions having a 

 northeasterly and southwesterly general direction, on the crest of one of 

 the highest ridges of which was located Station XLV, commanding an 

 extensive and beautiful view of the southern portion of the basin and 

 the majestic peaks of the Tetons. These hills appear to be made up of 

 light ash-colored, marly clays and dark, shaly deposits, with bands of 

 soft, more or less porous, thin-bedded, cream-colored limestone. There 

 may also be arenaceous beds, but the prevalent colors are as indicated. 

 Hear Station XLV the limestones outcrop in the brow of one of the east 

 ridges, where they dip 30°, TV. 25° X. Although diligent search was 

 made for organic remains in these deposits, none were found, save a few 

 indistinct molds of tubular bodies ; but in their lithological characters 

 they strikingly recall the late Tertiary deposits occurring in the south- 

 western section, in the Blackfoot Valley and near Port Hall. These de- 

 posits extend across the depression east of Station XLV, and appar- 

 ently recline on the foot of the mountain, which is here flagged with 

 heavy-bedded magnesian limestones, either of Carboniferous or Xiagara 

 age, as though their inclination was determined by elevatory forces sit- 

 uate in the Gros Ventre Kange, though it was not the same force that 

 folded the more ancient deposits, as is shown both by their strike and 

 more northerly inclination, as well as their evident non-conformity. To 

 the south of the latter locality these Tertiary deposits rest upon Quebec 

 Group limestones, while to the north they successively lap up on Car- 

 boniferous, the Triassic (?) "red beds," and finally appear to merge into 

 the older Tertiary in the western foot-hills of the Mount Leidy Group, as 

 will hereafter be described. 



To the north of the debouchure of the Gros Ventre these Tertiary de- 

 posits are far less conspicuous within the limits of the basin proper, 

 although they appear here and there from beneath the terrace accumula- 

 tions, indicating their subjacent presence. Professor Bradley, however, 

 mentions in the vicinity of the confluence of Buffalo Fork and the Snake 

 exposures of "gray and buff, fine-grained, shaly sandstones of indeter- 

 minate age, dipping sharply to the southeast," though at one point the 

 "dips are much confused." At the lower end of Jackson's Lake, he re- 

 marks the occurrence of "high knobs of porphyries and trachytes, which 

 indicate, by their position, at least a former connection with the more 

 northern beds, which were traced to within five miles of the northern 

 end of the lake." Seen from the opposite side of the valley, to the south- 

 east, these knobs have the appearance of a cluster of buttes occupying 

 the interval in the eastern bend of the Snake. In the abrupt eastern 



