31 



of age of the latter ioniiation as irrelevaut. in discussing the age of the Bitter 

 Creek epoch.' 



My own observations on tlic relations of these rocks, made during the 

 summer of 1872, have been, in a measure, anticipated by the detailed reports 

 of Messrs. Meek and Bannister," which, with the older observations of Dr. 

 Hayden and Mr. Emmons (of King's survey), leave little to be added. How- 

 ever, as none of these gentlemen paid especial attention to the vertebrate 

 paleontology, the bearing of this department in relation to the stratigraphy 

 remains to be explained. 



As Dr. Hayden remarks, the Union Pacific Railroad, at Black Butte 

 station, passes through a inonoclinal valley ; the rocks on both sides having a 

 gentle dip to the southeast. This dip continues to the ea'stward to near 

 Creston, where the beds pass under the newer Tertiary strata. Following 

 the railroad westward from Black Butte, the same dip continues to near Salt 

 Wells, where we cross an anticlinal axis, the dip of the strata being gentle to 

 the northwest. There are minor variations in the dij), but the general result 

 is as stated. They disappear five miles east of Rock Spring station, beneatii 

 the later beds of the Green River Tertiary, which, at this point, presents a 

 line of strike extending northeast and southwest, across the railroad, in the 

 form of a range of bluffs, of considerable elevation. They are composed of 

 lighter-colored and softer material than the Bitter Creek strata. The latter 

 consist of alternating beds of hard and soft sandstone, with argillaceous and 

 carbonaceous strata. The upper part of the series contains eleven coal-strata. 

 At Rock Spring, I was informed that the upper was ten feet in thickness, 

 and the next, four feet. Returning eastward, the heavier-bedded sandstone is 

 low in the series at Point of Rocks, in consequence of the southeast dip, and 

 tiie upper beds are softer and abound in fossil shells. At Black Butte station, 

 the heavy sandstone-bed disappears from view toward the east, and the eleven 

 coal-strata appear above it. About twenty feet above the sandstone, between 

 two of the thinner beds of coal, the bones of the Agathaumas sylvestris were 

 found, iml)edded in leaves and sticks of dicotyledonous plants, cemented 

 together by sand and clay. Where the heavy sandstone-bed disappears below 

 the level of the track of the railroad, in the course of its eastern dip, a thin 



' Tliis cmirsi! li;is liefii iiiisiiiulorstood by Mr. Meek and otlieis :us iiii|ilyiii^ a design to i<;iio.c tlioso 

 (Ibtcruiiiiatioiis. Uolh Mr. liiiiiiions and Mr. Mi'iOi arc clear in tbi; i-xprrssioii of tlmir conilu.sioiis a.s to 

 the ago of (ho ISoar River i'|iiii;!i. 



'Si:;; ll:!\d.-:i'.i Ammti.iI Keport for l^li. pp. l.'iT, '<!>. 



