ST. JOHN.] NORTH EXTREMITY OF WIND RIVER RANGE. 235 
the Upper Green and Gros Ventre Rivers. But to the south it is well 
known that a long interval of time elapsed subsequent to the deposition 
of the later Mesozoic and Post-Cretaceous deposits common to the region, 
whose elevation and folding and subsequent erosion prepared the surface 
upon which the Tertiary beds were unconformably laid down. So, in the 
quarter here particularly referred to, a similar state of things may have 
transpired, but at present the evidence might not be deemed as justify- 
ing a conclusive statement to the effect that the same physical conditions 
here prevailed to the extent of uniting the early Tertiary basins of the 
north and south by a common sheet of water in the straits of what is 
now the low barrier of the Green and Gros Vertre water-divide. With 
more complete data, such as it were doubtless possible to acquire by 
more extended examinations in this divide region than it was possible to 
make during the past season, the facts bearing on this question of the 
continuity of water connection between these great Tertiary areas might 
be as easily solved as in the case of the Wind River and Gros Ventre-— . 
Buffalo Fork Basins, which latter undoubtedly originally formed one 
great basin during the accumulation of the Cenozoic formations. 
Around the northwestern extremity of the Wind River Range proper 
the flanks of the Archean nucleus are buried beneath immense detrital 
accumulations of the Quaternary period, and which are spread out over 
an extensive plateau ridge, across which Union or Warm Spring Pass 
lies, at an altitude of 9,500 feet above the sea. The descent into the 
Gros Ventre Basin on the west is over comparatively gentle declivities, 
whose basis rocks of Tertiary age have already been descrived in the 
chapter relating to the Gros Veutre—Buffalo Fork Basin. The plateau 
character of the watershed continues thence to the vicinity of Tog wotee 
Pass, although its flanks are deeply scored by the streams flowing down 
into Wind River on the east and the Gros Ventre on the opposite side, 
and in whose steep bluffs more or less complete sections of the strata 
of which the watershed is made up are displayed. But on gaining the 
northeastern flank of the range the declivity descending into the valley 
of Wind River falls much more steeply, and in the place of the long 
gentle slopes over comparatively undisturbed Tertiary deposiis, the 
mountain flank is broken by great ridges of upraised Paleozoic rocks, 
which only terminate after passing Warm Spring Creek, when they are 
in turn enveloped in the later-formed sediments constituting the wacter- 
shed. The appearances, however, strongly indicate a hemiquaquaversal 
condition of the upraised Paleozoic strata at the northern extremity of 
the range, although this cannot be proved from the fact that these earlier 
formations, if they have not been removed by erosion, are so deeply 
buried beneath the Tertiary deposits as completely to conceal their 
former relation to the Archzean nucleus in this quarter. 
On leaving Wind River Valley, the Union Pass trail begins the ascent 
of the mountain flank at a point perhaps 3 miles above the confluence of 
Warm Spring Creek. Some distance below this point Wind River flows 
through a narrow gorge cut into northeasterly dipping rusty weathered 
sandstone ledges belonging to the middle division of the Carboniferous 
series, and which rise up on the mountain side forming asort of hog-back 
ridge 500 or 600 feet above the stream. The same set of strata appear 
in similar ridges along the mountain side above this point perhaps 2 or 
3 miles, beyond which the mountain flank trends round to the west, 
where the slopes are densely clothed with forests concealing the nature 
of their rock structure. The ascent of the trail is almost a continuous 
clinb up through beautiful forests of pine for the distance of 4 or 5 miles, 
when it again descends into the upper mountain basin of Warm Spring 
