266 GEOLOGICAL SURVEY OF THE TERRITORIES. 



aDtl Still continue such on the east side of the basin ; but, nearer the 

 western range, considerable proportions of granite and gneiss pebbles 

 are now mingled with them. A considerable excitement was stirred up, 

 a few years since, by reported discoveries of placer-gold in large quan- 

 tities on the Upper Snake, and many prospectors visited this region. 

 A small hydraulic operation was undertaken near this point; but the 

 gold was too fine and in too small quantities to j)ay, and the whole 

 region was entirely abandoned after a few mouths. The coarse gold, 

 found on the lower part of the Snake, appears to have entered the river 

 below the caiion, which is still to the southward of us. 



The Gros Ventre Fork emerges from the eastern hills about opposite 

 the North Botte, but runs off down the valley, some eight or ten miles, 

 before joining the Snake. Passing up its caiion for a short distance, the 

 following section was taken : 



1. White, friable, false-bedded sandstones, 10 feet. 



2. Covered space, about 100 feet. 



3. Irregularly-bedded, pale gray and buff, magnesian limestones, 50 

 to 60 feet. 



" 4. Pale-red friable sandstones, darker and shaly below, 300 to 350 

 feet. 



5. Compact, fine-grained, gray sandstone, 15 to 20 feet. 



6. Brown, coarse, friable, false-bedded sandstone, 60 to 80 feet. 



7. Coarse, friable, red sandstone, 40 to 60 feet. 



8. Compact, dark-drab, fossilii'erous limestones, 300 to 400 feet. 

 Near the mouth of the caiion, the Carboniferous limestones of No. 8 



form the walls, capped, as we ascend, by Nos. 7 and 6. As these pass 

 below the stream's level. No. 5, which forms the top of what I suppose 

 to be Carboniferous, coaimences a new cliff, and is covered by the 

 Triassic (?) beds of No. 4, which form prominent red bluffs along the 

 stream for many miles. The compact to vesicular, variously-colored 

 and partly bituminous limestones of No. 3 showed no fossils, and 1 am 

 uncertain whether to refer them to the Triassic or to the Jurassic, but 

 favor the latter reference. The covered space of No. 2 showed nothing 

 from which one could even infer the character of the buried strata. 

 The friable sandstones of No. 1, which cap the hills for some miles, are 

 probably late Tertiary. The dips of their false bedding imply an open 

 sea to the northward during their deposition, Vv'hile those of No. 6 face 

 eastward and southeastward. The lower beds, which should make their 

 appearance along the face of the mountain to the south of the Gros 

 Ventre, are so much covered with the partially-cemented Post-Tertiary 

 sands and gravels as to be not readily recognized from the plain, and 

 time did not permit a closer examination. Judging from the dips of the 

 lowest beds seen, I should expect to find here the lowest Silurian, under- 

 laid by metamorphic rocks, forming an axis which may connect the 

 Tetons with the Wind Eiver Eange. 



Just south of the mouth of the Gros Ventre, ou the east side of the 

 Snake, stands a cluster of buttes, known as the South Gros Ventre 

 Buttes. The western one has a high, broad northern face of red, gray, 

 black, brown, and variegated porphyritic breccias, including much 

 jasper, but partly porous, loose-textured, and even ashy. The beds are 

 much distorted, but have. a general northwesterly dip. The lower end 

 of the butteis tapering, long and low, and appears to consist mostly of 

 Post-Tertiary sands and gravels. At its southern extremity it rises 

 quickly into a sharp butte, composed of horizontal beds of gray lime- 

 stone, unfossiliferous, but apparently of Carboniferous age. The same 

 beds form the face of the mountain to the eastward. Three other 



