466 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



posits are represented as forming; a belt a mile in width where they cross 

 the Snake, rising above the basaltic flow which here fills the valley. 



To the sonth and east of the latter locality Professor Bradley found a 

 wide area of country occupied by the volcanic deposits, on the one hand 

 reaching up to the crest of the dividing ridge, and on the other extend- 

 ing over into the Elk Bidge between the Snake and Barlow's Fork. In 

 the valley and slopes of the latter stream, towards its head, a considera- 

 ble patch of Tertiary was met with, to which Professor Bradley alludes: 

 " About two miles below the falls we began to find outcrops of a fine- 

 grained, ferruginous, laminated sandstone, destitute of fossils, but prob- 

 ably of Tertiary age. Some of the layers showed abundant ripple-marks. 

 At the falls the rock is heavy-bedded. The dips are mostly about 22°, 

 varying somewhat on either side of due east. Just above the falls, and 

 opposite to our camp, four thin layers of coal, varying from one inch to 

 six inches in thickness, and two layers of clay ironstone (iron carbonate), 

 varying from six inches to one foot in thickness, are all included within 

 ten feet of shales. * * * The upper slopes of the ridge on either 

 side [of the valley-basin] are mostly bare of timber, and many parts of 

 them are badly washed. Those on the east are composed of mostly 

 thin-bedded sandstones, probably of Tertiary age, at least 2,000 feet 

 thick, with variable southeasterly dips. A few red layers appear, but 

 the majority of them are gray. No fossils were found, though careful 

 search was made for them." 



The eastern face of Station XL VIII ridge abruptly falls to the level 

 of a high sloping plateau occupying the interval between this point and 

 the high mountain north of Buffalo Fork Peak. This plateau falls in a 

 succession of uneven benches to the lower canoned course of Buffalo 

 Fork, its surface covered with grassy slopes interspersed with conifers and 

 groves of aspen. The contour and occasional exposures of light-buff 

 deposits denote the Tertiary character of this slope, which reaches up to 

 the divide between Buffalo Fork and Pacific Creek, and doubtless once 

 extended over to the northward, connecting with the Tertiary deposits in 

 the upper basin of Barlow's Fork. Along the northern foot of this slope, 

 in the lower canon of Buffalo Fork, nearly continuous exposures of light- 

 buff arenaceous beds appear, extending several miles to the east until 

 arrested by the massive mountain barrier which forms the portals to the 

 upper or mountain course of this stream. These deposits are mentioned 

 by Professor Bradley, from notes communicated by Mr. Bechler, as fol- 

 lows : "About 12 miles up, the valley narrows to a canon from 350 to 400 

 feet deep by from 50 to 200 feet wide, for about three miles, with coarse 

 gray sandstone walls. About one and a half miles of a rounded basin, with 

 beaver-dams, then intervenes before reaching the second canon, which 

 has nearly the same character as the first and is about two miles long. 

 A broad basin succeeds, from five to seven miles across, reaching up to 

 the foot of the high vertical limestone walls, * * * whose rugged 

 crest shows plainly from the mouth of the valley." 



Light-colored deposits resembling the above Tertiary beds reach well 

 up on the flanks of this mountain barrier on either side of the gorge 

 through which flows the Buffalo Fork, where they rest apparently un- 

 conformably upon earlier Mesozoic formations and possibly the Carbon- 

 iferous. They do not appear to be present far within the entrance to 

 the gorge, although Professor Comstock notes the occurrence of similar 

 beds higher up to the north-northeast, in the divide between Lava Creek 

 and the upper course of Pacific Creek, where they dip southwest at an 

 angle of 57°, " and in the canon of Buffalo Fork, just below Camp 56, 



