36 



group of the Cretaceous are either wanting on the western and southern 

 borders of the Green River basin, or are concealed by the superincumbent 

 Tertiaries. Instead of these, a comparatively thin bed of apparently unfos- 

 siliferous quartzite or sandstone lies at a high angle against the bases of the 

 Uintah 1 and Ham's Fork Mountains, respectively, on beds of Jurassic age, 

 which are probably Cretaceous No. 1 (Dakota). The beds observed by Pro- 

 fessor Marsh, on the south side of the Uintah Mountains, on Brush Creek, 

 belong neither to the Dakota nor Bitter Creek epochs, but perhaps to No. 3, 

 if, as Professor Marsh asserts, the oyster found in a superjacent stratum is 

 Ostrea congesta, Con. It is, in any case, of no later date than the Canyon City 

 or Weber River coals. Hence, the assumption of some writers that this dis- 

 covery determined the age of the Bitter Creek' series to be Cretaceous is 

 without foundation in fact. 



VIII. THE BEAR RIVER GROUP, 



of Hayden, occupies, according to him, a distinct basin, to the west of an 

 anticlinal axis, which separates it from that of Green River. It is buried 

 under Tertiary beds, the age of which has been a question of interest, and 

 will be hereafter considered. In order to determine the relations of the two 

 basins, a section was carried across the rim of the eastern, starting from the 

 Fontanelle Creek, eighty miles north of the Union Pacific Railroad, and con- 

 tinuing toward the upper waters of Ham's Fork of Green River to the 

 westward. My notes are as follows: 



The beds of the Green River epoch dip gently from the point where 

 my last notes left them, near to Rock Spring station, toward the northwest, 

 all the way to Green River. The upper strata become slaty in character, 

 and descend to the water-level at the river, where they form a high bluif. In 

 these slates occur the fish-beds discovered by Dr. Hayden, as well as the 

 insect-beds noticed by Messrs. Denton and Richardson. They are worn into 

 towers and other picturesque forms at Green River City (see Hayden's 

 Annual Report for 1870). Passing north from the railroad, up the valley of 

 Green River, the slates display a gentle dip to the north, and eighteen miles 

 beyond have disappeared from view. On both sides of the river huge mesas 

 of the Bridger formation come into view; those on the cast extending to the 



See Hayden's Amiual Report fur 1870; Marsh, American Journal of Science and Arts, March, 

 1871. 



