an aS 
BT. JOHN.] JOHN DAY AND HOBACK CANON RIDGES. 191 
red, soft, gritty, slightly calcareous clays, holding quantities of lime- 
stone and red sandstone bowlders, also fragments of gray sandstone 
identical with beds ocenrring in the Laramie. These deposits incline 
quite uniformly to the notheastward at an angle of about 15°, abutting 
against the Carboniferous ledges in the Hoback Cation ridge along the 
eastern margin of the basin. At the latter point the juxtaposition of 
the stratigraphically widely separated formations is not as clearly dis- 
played as could be wished, yet it is sate to infer from their relative 
position either the existence of a fault ky which the Carboniferous beds 
are brought up to the level of the Tertiary conglomerate, or the latter 
beds, which were originally laid down horizontally, have been upraised 
into their present position by subsequent disturbances situated in the 
central portion of this mountain range. 
The conglomerate deposits may be traced in beautifully weathered ex- 
posures in the outlying slopes along the west foot of the Hoback Cation 
ridge to the north and south of the little stream, where they were also 
examined by Mr. Perry. To the west they are underlaid by a gray ledge, 
consisting of water-worn pebbles of gray limestone, various kinds of sand- 
stone, quartzite and chert, the light-gray calcareous matrix, or cement- 
ing paste, often replacing the coarser material and forming a coarse light- 
eray limestone quite free from pebbles. This ledge, of which a thickness 
of above 50 feet is exposed, also dips northeastward at an angle of 20°, 
appearing in the hills just north of the Hoback a couple of miles above 
its mouth, and outcropping in the edge of the high terrace on the east 
side of Snake River several miles to the north. At the former local- 
ity on the Hoback the exposures reach an elevation of 1,500 or 1,600 
feet above the Snake, and a few hundred yards to the west a heavy 
underlying series of grayish sandstone outcrop, showing about the same 
direction and rate of inclination. The latter deposits afford obscure veg- 
etable remains, which, together with their lithology, warrants their iden- 
tification with the Laramie. If there be nonconformity between these 
beds and the gray calcareous conglomerate, it is not apparent at this 
locality. 
In the slopes rising into the more rugged outlying hills of the John 
Day ridge, on the south side of the Hoback, the same series of sand- 
stones occur, dipping to the southwestward at angles of 15° to 20°. The 
axis of the fold here indicated, extending in a northwesterly and south- 
easterly direction, has been deeply eroded by the Hoback just above its 
junction with the Snake, to the west of which the strata composing the 
arch merge into the series elsewhere described, in the section along 
Snake River. 
How far up the valley of the Snake, to the north, the gray calcareous 
and red conglomerates extend was not ascertained. However, their ex- 
tension in that direction suggests the possible identity of at least the 
gray calcareous deposit with the soft caleareous and earthy late Tertiary 
or Pliocene beds known to exist in the mountain-locked basin east of the 
Tétons. That these deposits belong toa very late geological time 1s 
abundantly indicated by the nature and derivation of the component 
materials—the coarse detrital materials plainly having been derived from 
the Paleozoic and Mesozoic strata occurring in the adjacent mountains. 
Their apparent conformity and nonconformity in relation to the supposed 
Laramie deposits which they immediately overlie and the Carboniferous 
formations against which they impinge in the foot of the Hoback Canon 
oe. complicate the determination of their exact position in the geologi- 
cal series, 
