BITTER CREEK VALLEY — POINT OF ROCKS. 147 



The last-named species is one of the very few marine forms that have 

 been cited as coming from the Laramie. 



In the neighborhood of Point of Rocks the dip of the beds is about 6 

 degrees a little north of east, almost parallel with a valley that joins that 

 of Bitter creek just east of the station, so that the heavy sandstone soon 

 disappears beneath the surface and the beds above it successively come 

 down to the valley level in the hills on its north side, where they are 

 well exposed and may be easily studied. The beds on the top of the 

 bluffs north of the station thus come down to the valley a little over a 

 mile east of that place, and immediately above them, in a brown ferrugi- 

 nous sandstone, the following marine Cretaceous species indicating a Fox 

 Hills horizon were found : 



Ostrea glabra, M. and H. Mactra alta, M. and H. 



Inoceramus cripsii, var. bambini, Morton. Mactra ivarrenana, M. and H. (?) 

 Cardium speciosum, M. and H. Dentalium gracile, H. and M. 



A few feet below the band containing these fossils a single specimen 

 of Melania wyomingensis was found. This and the Ostrea glabra are Lara- 

 mie species, but both have been found in the Fox Hills beds near Long- 

 mont, Colorado. 



It will doubtless be suggested that these marine beds have been brought 

 to their present position by faulting, but the nature of the exposure is 

 such that this does not seem possible. The horizon may be traced con- 

 tinuously back to the top of the bluffs just north of Point of Rocks, where 

 it is exposed onty about 200 yards north of the edge of the bluffs ; but 

 fossils are very rare here, consisting of a few small bivalves, among which 

 a Tellina was recognized. Above this horizon there are few exposures 

 seen on going eastward until a line of cliffs is reached nearly four miles 

 east of Point of Rocks. These cliffs show at their base about 150 feet of 

 clay shales with bands of sandstone, and a concretion in the clays yielded 

 B acuities ovatus, S&y. ; Lunatia occidentalism M.and H., and Mactra sp., show- 

 ing that this horizon, some 700 feet above the last one mentioned, is still in 

 the Fox hills. The shales are overlain by a massive sandstone somewhat 

 over 100 feet thick, yellowish brown below and nearly white above, and 

 it is succeeded by a series of shales, sandstones, and coal beds like that at 

 Black Buttes, and containing many of the same characteristic species of 

 fossils in the same stratigraphic order. Ostrea glabra, var. arcuatilis, Meek ; 

 Unio couesi, White ; Corbicula fracta, Meek, and Tulotoma thompsoni, White, 

 occur in great number. The evidence, we think, is sufficient to identify 

 these beds with those at Black Buttes, a few miles away, and it estab- 

 lishes the position of the Black Buttes horizon considerably above the 

 Point of Rocks beds and immediately above the Fox Hills ; in other 

 words, in the position of the true Laramie. 



