ST. 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 tliis upland tract on its way to the plain, enters 

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

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

 River Mountains ftraduallj'' descend and run out in a long, narrow, rocky 

 spur, Hanked by tlie volcanic benches. The southwestern Hank of this 

 range we did not again api)roach nearer, the heights on this side afibrd- 

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

 able state of the river jire vented its passage at any higher jioint for the 

 piu'pose of making closer examinations of the geology of the luouutain 

 front, which for several days was provokingly near. 



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

 coloi'ed shales ai)i)ear; but in the opposite sloi)e, descending from Sta- 

 tion XXIII, a coui)le 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, tliin-bedded sandstone, 7 feet exposed in 

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



3. Dcbris-coxered slope, 120 yards. 



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

 gritty limestone, 5 feet exposed ; dip 03°, S. G5° W. 



5. Gray, brown-stained sandstone, obscure exi)osure, space 85 yards. 

 C. 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 

 30=", S. 



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

 0. Dark-gray, gritty ledge, obscjure exposure. 



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



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



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



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

 the exposure ; dip gently northeastward. 



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



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

 10. Debris-coxered slope, 50 yards. 



17. Rusty congiomeritic deposit, associated with fine, grayish, lam- 

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

 dip 20°, X. ooo E. 



18. IJcbris-covQTed slope, with fragments of light-bluish limestone Avith 

 unrecognizable fossils, 50 to 100 yards. 



19. Heavy congiomeritic ledge, forming irregularly eroded nuiral expos- 

 ures, 30 feet, more <n' less, in height, encircling the brow of the hill, and 

 showing an incUnation to the north or north westwai-d at an angle of 20° 

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

 l)laces appearing as a variegated trachytic tuff", in color, buif, cliocolate- 

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

 characteristic feature is its congiomeritic structure, showing a variety 

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

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

 arranged in layers and impacted in a light-buii" fine paste. 



