st. JOHN.] LARAMIE (?) AND TERTIARY—UPPER WIND RIVER. 259 
stream deepens its bed. Between the latter stream and Du Noir Creek, 
the north side blufis exhibit the same series of strata, consisting of 
rusty-buff sandstones, drab and yellow sandy clays with streaks of red 
clay, of which a thickness of 250 feet are here exposed. These deposits 
are overlaid by variegated or banded pale-red and drab clays, showing 
a thickness of 50 feet or more in the top of the bluffs, the whole sloping 
off to the northeastward at a very gentle angle of inclination. 
It was impossible at this locality to determine whether the superposi- 
tion of the latter deposits is conformable to the inferior lignite-bearing 
formation, nor was opportunity afterward afforded for the satisfactory 
settlement of the question. I have also to regret the uncertainty as to 
the stratigraphic relations of the above geological formations with the 
previously noticed greenish arenaceous deposits occurring towards the 
head of Wind River. Indeed, lithologic data, which are quite persistent 
and reliable in the Gros Vetitre region just over the watershed to the 
west, seem to be confused and less trustworthy guides to the identifica- 
tion of portions of the Cenozoic series as we approach that part of the 
divide which is surmounted by the great volcanic deposits. The com- 
paratively undisturbed condition of all the geological products, includ- 
ing even the sedimented volcanics, occurring in the region about the . 
sources of Wind River, renders the detection of nonconformities an ex- 
tremely delicate operation; and when we take into consideration the 
action of thermic agents accompanying the great volcanic accumulations 
that were spread out over so vast an extent of the Cenozoic area in this 
region, we may well hesitate, in interpreting meager data, to assign the 
appearances here met with to changes akin to those induced by meta- 
morphic agents, or to those other potent agents of geologic change, ero- 
sion, and deposition of distinct and unconformable materials. The con- 
glomerates noticed on Wind River certainly bear close analogy to the 
great conglomerate horizon underlying the upper or Teritary lignite- 
bearing series on the Gros Ventre, 15 miles to the westward. Yet, with 
the paucity of facts at present in hands, bearing on the detail strati- 
graphy of the Wind River section, it might be deemed presumptuous 
to assert the identity of the above occurrences. But when we come to 
the correlating of the supralignite series represented by the pale-red and 
drab variegated or banded deposits, the occurrences in the above-men- 
tioned regions are so alike as regards both their stratigraphic constitu- 
tion and geological position, that little or no doubt can be entertained 
respecting the actual identity of the latter deposits in the regions of the 
Gros Veutre and Wind River basins. The few fossils found in the lig- 
nite series of the Gros Ventre Basin here referred to were provisionally 
compared by Dr. White with Bear River Laramie forms; while the 
immediately superimposed conformable strata afford a Viviparus palu- 
dineeformis (2) which elsewhere characterizes Wasatch Tertiary hori- 
zons. Hence, the variegated deposits to which Dr. Hayden gave the 
name Wind River Group, recognizing their probable Miocene age, are 
either emphasized variegated upper Wasatch strata or a much later 
and actually nonconformable member of the Tertiary series peculiar to 
the region north of the Gros Ventre Mountains, and east of the Wind 
Ktiver Range, in which quarter as yet no Green River Tertiary equiva- 
lents have positively been recognized, unless the plant-bearing beds 
above noticed prove to be of that age. The attempts hitherto made to 
correlate the Wind River Group have been based on supposed lithologi- 
cal resemblances, I believe, without the aid of paleontological evidence. 
Du Noir Creek occupies a fine valley eroded out of Tertiary deposits, 
in the east side of which variegated red and drab exposures are seen. 
