EP.JOHN.] SECTION THROUGH STATION XXIII. 377 



and, as is the case with all these wide recesses, like the Blackfoot, Willow 

 Creek, and Pierre's basins, the debouching river, immediately it leaves its 

 valley course to cross this upland tract on its way to the plain, enters 

 the "lower canon," which it has excavated deep into the volcanic ma- 

 terials that fill the recess. On the northeast side of the valley the Snake 

 Elver Mountains gradually descend and run out in a long, narrow, rocky 

 spur, flanked by the volcanic benches. The southwestern flank of this 

 range we did not again approach nearer, the heights on this side afford- 

 ing excellent opportunity for studying its topography, while the unford- 

 able state of the river prevented its passage at any higher point for the 

 purpose of making closer examinations of the geology of the mountain 

 front, which for several days was provokingly near. 



Beneath the trachyte in the steep slopes on Grouse Creek chocolate- 

 colored shales appear; but in the opposite slope, descending from Sta- 

 tion XXIII, a couple of miles to the southeast, the sedimentary beds are 

 again revealed, affording the following section: 



Section through Station XXIII. 



1. Chocolate-colored shales, in bluff on west side of Grouse Creek, 

 overlaid by drab and pink trachyte, dipping gently northwestward. 



2. Gray, brown-weathered, thin-bedded sandstone, 7 feet exposed in 

 foot of slope east side of Grouse Creek ; dip 58°, S. 05° W. 



3. Debris-covered slope, 120 yards. 



4. Dark bluish-gray, rusty brown weathered, fragmentary, coarse, 

 gritty limestone, 5 feet exposed ; dip 05°, S. 65° W. 



5. Gray, brown-stained sandstone, obscure exposure, space 85 yards. 



6. Eed and chocolate-colored shales, space 45 yards. 



7. Chocolate-colored and drab fragmentary limestone, and drab indu- 

 rated or nodular calcareous deposits, obscure exposure, 35 yards. Dip 

 3(P, S. 



8. Eed and chocolate-colored shales, space 75 yards. 



9. Dark-gray, gritty ledge, obscure exposure. 



10. Bluish-gray, brown- weathered sandstone, obscure. 



11. Unexposed, space 9 to 11, inclusive, 35 yards. 



12. Bed and chocolate-colored shales, space 25 yards. 



13. Dark chocolate-drab, brittle, fragmentary limestone, 15 yards across 

 the exposure ; dip gently northeastward. 



14. Chocolate-colored and red shales, 50 yards. 



15. Bough, fragmentary, chocolate-brown Limestone, obscure ledge. 



16. Debris- covered slope, 50 yards. 



17. Busty conglomeritic deposit, associated with fine, grayish, lam- 

 inated sandstone above, forming a heavy ledge 15 to 20 feet exposed ; 

 dip 20^, b[. 550 e. 



18. .DsJm-covered slope, with fragments of light-bluish limestone with 

 unrecognizable fossils, 50 to 100 yards. 



19. Heavy conglomeritic ledge, forming irregularly eroded mural expos- 

 lu-es, 30 feet, more or less, in height, encircling the brow of the hill, and 

 showing an inclination to the north or northwestward at an angle of 20° 

 to 25°. This ledge is very variable in the nature of its components, in 

 places appearing as a variegated trachytic tuff, in color, buff, chocolate- 

 red mottled, drab and pink-drab, with small dark specks. But the most 

 characteristic feature is its conglomeritic structure, showing a variety 

 of slightly abraded coarse materials, chiefly quartzite with small frag- 

 ments of limestone, ranging in size from gravel to small bowlders, 

 arranged in layers and impacted in a light-buff flue paste. 



