226 REPORT UNITED STATES GEOLOGICAL SURVEY. 
so markedly displayed in escarpment exposures, although it also doubt- 
less largely enters into the basis deposits of this highland region. It is 
not impossible that the lignite seams reported the previous season on 
Elkhorn Creek, at the northern foot of Mount Leidy, belong to the latter — 
Series, in which case they should, together with their accompanying 
strata, be referred to the Cretaceous instead of the Tertiary as in the re- 
port upon the Téton district, 1877. The strata of a widish belt upon the 
western and southern flank of the highlands, which quarter, for want of 
time, was not visited, are also probably referable to the same age. 
The conglomerate reappears in characteristically weathered summits 
north of Butialo F Fork, and it is very probable that the vast accumula- 
tions of drift-like débris, noticed by Professor Bradley in the high divide 
between the latter stream and the sources of Snake river, were derived 
from the breaking up of this deposit. It has contributed an immense 
amount of loose materials to fluviatile deposits in all the valleys of both 
the Buttalo Fork and the Gros Ventre basins, and most probably the 
water-worn and rounded quartz pebbles that enter so largely into the 
composition of the bars in the bed of Snake River along many miles of 
its course through Jackson’s Basin, and even in its lower valley below 
the Grand Canon, are attributable to this conglomerate formation. The 
streams south of the Gros Ventre Range are bedded with different and 
greater variety of rock materials, which may be traced to ledges in the 
surrounding mountains. It is said by old prospectors that this deposit 
affords gold, invariably in very minute particles. 
In the Buffalo Fork region the deposit descends to the northeastward 
at a gen'le rate of inclination, as shown in the fine exposures north side 
of Pacific Creek, a few miles above its mouth. This northerly ineli- 
nation was also observed within the Mount Leidy belt, where the con- 
glomerate seems to form a very low, broad, undulating swell. Above 
the mouth of Blackrock Creek, five or six miles, a limited exposure of a 
conglomerate ledge appears in the south bank of the river, the relations 
of which to the higher occurring exposures could not be ascertained. 
if the latter ledge is tn sitw it shows that these strata also partook in 
ithe disturbances of the Buffalo Fork Peak uplift, low on the flanks of 
‘which Prof. Theodore Comstock found highly inclined lignite-bearing 
ing deposits. The latter, lam now prepared to believe, are of Cr etaceous 
age, aS Was originally stated by Professor Comstock in his report. to 
‘Captain Jones (Yellowstone Expedition, 1873). It was the intention 
the present season to carefully examine the borders of Buffalo Fork Peak 
uplift with the view of gathering as complete data as possible regarding 
the coal deposits known to occur there; but the early approach of winter 
snows forced the party to withdraw, leaving the northern part of the 
«district unworked. 
In the right bank of Buffalo Fork, near the confluence of Blackrock 
Creek, exposures of bluish-drab indurated argillaceous beds and shales, 
with gray and buff weathered sandstones appear, inclining at an angle 
of about 10° to the northward. The shale here afforded abundant vege- 
table remains, among which a small long ovate leaf resembling the 
plum was most numerous. These plant remains, which were the only 
paleontological evidence obtained bearing on the age of these deposits 
have not been determined, so that we have to depend on stratagraphical 
‘data to determine this question. A mile or less to the north on the 
Blackrock, apparently identical strata incline northeastwardly at an 
angle of 15 to 20°, which would appear to show a nonconformity with 
the conglomerate similar to that noticed on the Gros Ventre. Appar- 
ently the same series of deposits constitute the bulk of the hills north of 
Butialo Fork, and extend west to the border of Jackson’s Basin. 
