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Mesozoic and Cenozoic Geology and Paleontology. 45 
a partial witness to the extent of the denudation. A little south ot 
west of Fort Bridger, is an isolated butte called Bridger’s Butte, which 
forms a prominent land mark to the traveler, and according to the 
barometer, rises 750 feet above the valley of Black’s Fork, at the fort. 
The summit appears perfectly level, and was estimated to be about two 
miles in length, from north to south, and about a fourth of a mile in 
width, from east to west. The upper portion of the butte is composed 
of the somber, brown, indurated, arenaceous clays, gray and rusty 
brown sandstones of the Bridger Group, passing down into limestones 
and marls of the Green river beds. In the brown clays are abund- 
ant remains of turtles, with a few fragments of other vertebrate re- 
mains. <The terraces along the valley of Black’s Fork, are composed of 
yellowish and whiteish gray marls, and chalky limestones, some of the 
layers mostly formed of Unio, and other fresh-water shells. A few 
plants were found in the valley of Smith’s Fork, in thin black, flinty 
layers, mostly ferns and leaves of deciduous trees. Between Fort 
Bridger and Henry’s Fork, the indurated, arenaceous clays, of the 
Bridger Group, are weathered into remarkably unique forms, The 
absence of harder layers of sandstone did not. admit of the weathering 
into pinnacles, turrets. steeples, domes, etc., as observed near Church 
Buttes. Thesurface, though very rugged and almost impassable, ex- 
cept along the valleys of the streams, ismuch more rounded ; the hills 
are more dome or pyramid shaped, and entirely destitute of vegetation, 
except the sage, and several varieties of chenopodiaceous shrubs. 
Passing up the Cottonwood Fork, the marls and limestones make their 
appearance, for a short distance, in the bluffs. The divide between 
the drainage of Smith’s Fork and Henry’s Fork, is a high ridge of the 
leaden-brown clays of the Bridger Group, which extends up and juts 
against the. base of the Uinta mountains. 
From this ridge to Green river, the valley of Henry’s Fork forms a 
remarkable line of separation between the Bridger Group and the lower 
beds. This line of separation is somewhat of a surface one, yet it is so 
marked as to attract the attention of the commonest observer. The 
valley is quite broad, and on the south side the surface of the country 
to the summits of the mountains appear smoothed downward, in part 
grassed over. A close examination will detect some thin remnants of 
the Bridger Group underlaid by lower Tertiary beds, which have a 
tendency to weather into rounded, gently-sloping hills. On the novth 
side, the arid, rugged, “ bad lands” are very conspicuous, and rise up 
somewhat abruptly like a high wall. On the north side of the creek, 
there is a great thickness of the indurated clays of the Bridger, Group. 
