456 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



dred feet of deep-red arenaceous deposits banded witli lighter tints, 

 ■which extend several miles along the stream, and to the east probably 

 rise up on the mountain flank, where they present the escarpment expo- 

 sures lapi^ing up on the Carboniferous deposits, as mentioned above. 

 Eemnants of these " red beds " may also occur on the northeast flank 

 of Station XLIV ridge between the summit and the debouchure of the 

 Gros Ventre, but, ai)proaching the latter point, they have been swept 

 away, the Carboniferous forming the whole mountain side, and extend- 

 ing even beyond, where they form a narrow belt on the north side of 

 the stream. 



The apparent nature and distribution of the formations which succeed 

 and overlie the " red beds " to the north, as made out from this point, 

 will be noticed in a succeeding page relating to the Mount Leidy region. 

 To the south and southwest the view embraces the Silurian-capped heights 

 of the foreland between Stations XLYI and XLIV, and round to the 

 southeast the foreshortened southern flank of the north barrier and the 

 complicated, much-eroded interior x^ortion of the range penetrated by 

 the ramifications of the drainage of the Little Gros Ventre. 



Li the opposite or south side of the Little Gros Ventre Valley a tum- 

 bled mass of rusty quartzite orquartzitic sandstone was observed, which 

 lower down axjpears in the broken southern slox)e of Station XL VI ridge, 

 where it forms a more or less well-defined low ridge, which terminates 

 to the northwestward in the recess at the foot of the mountain about 

 opposite Station XLV. This ridge is very like that on the north side of 

 the canon descending from Station XLIV, being composed of broken 

 angular fragments of the same hard quartzitic sandstone. In the steep 

 bluffs immediately north of the end of this ridge highly tilted ledges of 

 light-buff, reddish-tinged, laminated sandstones were observed, dipping 

 southwestward at an angle of about 70°. These sandstones, in connec- 

 tion with the ai^parently overlying quartzitic sandstone, forma heavy 

 deposit, which rises nj) into an anticlinal fold in Station XLVI ridge, 

 with sharp dips on the southwest, but much more moderate inclination 

 on the northeast flank. The above steeply-tilted sandstones are believed 

 to be Primordial. In this vicinity were observed debris exx)osures of 

 thin-bedded, peculiarly weathered limestone, recalling the Quebec Group 

 beds, and heavy ledges of buff magnesian limestone, holding the position 

 of the Niagara, appear in the neighboring heights. This locality is be- 

 tween two and three miles about south- southeast of the debouchure of 

 Gros Ventre Elver. The nearly northwest trend of the axis of the fold 

 carries it out into the region of Jackson's Basin to the south of that 

 point, where all these strata have been greatly denuded and covered by 

 depositions of late Tertiary age. 



Sections illustrative of the foregoing observations on the geology of 

 this region are given in the accompanying diagrams. 



THE MOUNT LEIDY HIGHLAJSTDS. 



North of the Gros Ventre Mountains there occurs a rather wide belt 

 of highland and upland i:>lateau, about twelve by twenty miles in extent, 

 which is limited on the south by the Gros Ventre Eiver, on the north by 

 the Buffalo Fork and Black Eock Creek, on the west by Jackson's Basin, 

 and to the east it rises into the continental watershed of which it forms 

 the western flank within the limits designated. This area is traversed 

 nearly centrally by a very irregular low mountain ridge or water-divide, 

 which culminates in two conspicuous svTmmits of nearly equal altitude, 

 to the westernmost of which the Snake Eiver expedition of 1872 gaA'e 



