BT.Jonx.] GRAND CANON OF SNAKE EIVER. 437 



southeasterly, but mucli wasted by tlie erosion of the upper tributaries 

 of Horse Creek, and finally reaches the edge of the basin in Spring 

 Point. This southeastern portion of the ridge apparently occupies a 

 relatively much broader area than do the same deposits in the vicinity 

 of Station XLII. This may possibly be due to one of two causes, or 

 both, namely, variation in the trend of the strata, or a series of minor 

 undulations and fractures superadded to the primary fold, by which the 

 same horizons are made to appear at corresponding levels over a consid- 

 able surface tiansverse to the trend of the main uplift. 



South of Spring Point the Jurassic deposits are seen in the foot-hills 

 or spurs all along the edge of the basin to a point beyond Low Pass 

 Creek, where they, together with the "red beds," gradually pass inland, 

 so that the Carboniferous ledges again ax)pear from beneath the Mesozoics, 

 lapphig up on the lower spiu'-ridges in the vicinity of Station XXXIX. 

 The latter belt of Carboniferous doubtless belongs to the Station XLII 

 uplift, the axis of which probably lies a little east of Station XXXIX, 

 in which quarter, as previously remarked, there are indications of a 

 synclinal depression occujiying the narrow belt intervening between 

 the latter point and the southwest base of the Teton Range, in the 

 farther side of which West Teton Pass Creek has excavated its valley. 

 There is one other featiu'e observed ui the immediate vicinity of Station 

 XXXIX in the ai)parent sharj) folding of the strata with abrupt north- 

 erly pitch, which offers additional striking resemblance to the conditions 

 observed in Station XLII ridge, and together with the corresponding 

 trend of the strata, it seems hardly possible to doubt the identity of the 

 uplift at these distant i)oints, and its extension southeastward to the 

 border of the valley of the Upper Snake. 



Of the large area to the south we possess far too meager information 

 to warrant more than reference to the salient features of its apparent 

 geological structure. From the observations of Professor Bradley, wlio, 

 in 1872, traversed the Grand CaSon of the Snake, and thus had oppor- 

 tunity to study the strata appearing along this magnificent natural sec- 

 tion, it appears that the greater portion of the canon is walled by Car- 

 boniferous deposits. These deposits are described by Professor Brad- 

 ley as being mainly composed above of a thickness of several hundred 

 feet of Umestones, gradually iiassing fi-om massive into overlying shaly 

 beds, the lower deposits consistiag of sandstones and shales, including 

 heavy beds of limestone, which together reach a thickness of 2,000 feet 

 or more. The upper entrance to the caSon shows a heavy series of 

 laminated red sandstones, from beneath which appears a thickness of 

 several hundred feet of heavy-bedded and shaly gray and greenish sand- 

 stones, interbedded with calcareous shales, and containing indeterminate 

 vegetable remains. The latter deposits extend into the cauon some dis- 

 tance beyond the mouth of Hoback's Eiver, where they are thrown up 

 in a sharp anticlinal fold with steep inclination, 05° to 70^, about east- 

 northeast, dipi)ing at an angle of about 40° in the opposite side of the 

 fold. The axis of this ui)lift shows a narrow fold of limestone, overlaid 

 by a heavy mass of sandstones and cherty beds, including near the base 

 two or three heavy beds of black calcareous shale and friable clay, con- 

 taining what appear to be amphibian remains. To tlie northeast, be- 

 tween the latter fold and the upi)er entrance to the Grand Canon, the 

 above-mentioned sandstones are thrown into two parallel but much 

 lower anticliuals, having the same general trend, or west of north and 

 east of south, with steeper dips on the east. Below the great fold above 

 mentioned, in descending the canon, Professor Bradley refers to three 

 other sharp anticliuals which are closely crowded, and showing exceed- 

 ingly steep dips, in some instances amounting to 85°, accompaiiied by 



