432 REPORT UNITED STATES GEOLOGICAL SURVEY. 



the head of Cauon Creek, in tlie further side of which it is continued 

 until lost to view in the forest-covered slopes. The latter ledge may- 

 be identical with the conglomerate shown in the section through Station 

 XL, of which, indeed, the present mountain ridge is the northwesterly- 

 prolongation. To the southwest lies an equal breadth of hill country- 

 intervening between the crest of the range and the lower valley of the 

 Snake, the exploration of which was, for the lack of time, prevented. 



Station XLII commands a view of the entire extent of the little basin 

 to the north and east, and which is principally drained by the soiirces 

 of Packsaddle Creek. Its undulating surface shows obscure exposures of 

 the i^eculiar gray sandstones enumerated in the foregoing section, which 

 apparently compose the bulk of' the strata out of which the basin has 

 been excavated. The ridge along its eastern border, in which the hog- 

 back ledges of Jurassic limestone and sandstone appear, is broken 

 down to the northeast in the wide debouchure of the principal drainage 

 channel into Pierre's Basin, to the north of which the hills gradually 

 rise into the high volcanic bench which reaches high up on and sweeps 

 around the northern terminus of the range. From the nature of the 

 basin deposits, which readily yield to the denuding agencies which have 

 molded the surface into its x)resent configuration, it is difficult to gain a 

 clear knowledge of their stratigraphy, only the firmer ledges protruding 

 above the surface in such favored localities where they have escaped 

 being buried beneath the detrital material derived from the demolition 

 of the softer beds. But in their lithological appearance they share so 

 marked resemblance with horizons in the Caribou Eange west of the 

 lower valley of the Snake as to almost preclude a vestige of doubt as to 

 their identity with the extensively-developed Laramie deposits of the 

 latter region. The east hog-back ridge to the south is blended with the 

 eastern spur of Station XLII ridge, on the volcanic tipped foot of which 

 Station XLI was located. In the latter spur the steeply-mcliued Juras- 

 sic strata are continued southeasterly, finally running out in the border 

 of Pierre's Basin, where they have been eroded and covered with modern 

 accumulations. The relations of the folds and disturbances here met 

 with, with similar manifestations occurring in other parts of the range 

 to the southeast, will be briefly discussed at the close of this chai^ter. 



Ti^TOlSr PASS MOUNTAINS. 



Without attempting here to define the limits of the so-called T<5ton Pass 

 Mountains, for our present purpose it answers merely to state that that 

 portion of the mountain region south of the Low Pass which fell under 

 our examination comprises a narrow strip skirting the head or soutliern 

 end of Pierre's Basin, extending thence southeasterly to the foot of 

 Jackson's Basin on the Upper Snake. The southern end of the T6ton 

 Eange is terminated in a pair of lofty peaks which overlook almost the 

 entire extent of the mountainous highlands which fill the great south- 

 ern bend of the Snake Eiver south of the Low Pass Gap, and which is 

 dominated by Mount Baird. Along the western border of the mount- 

 ains the rugged barrier here and there rises into comparatively promi- 

 nent peaks, conspicuous among which are Promontory Peak, and the 

 corresponding height to the north, which together form the x>ortal 

 through which the drainage of the Low Pass Basin makes its exit into 

 the lower valley of the Snake. This low mountain ridge is separated 

 from the Teton Eange by the depression through which lies the Teton 

 Pass, the summit of which attains an elevation of some 2,300 feet above 

 the basin-plains at either entrance to the pass, or an actual altitude of 



