13 



the bases of the Uinta* and Ham's Fork Mountains respectively, on beds 

 of Jurassic age, which are probably Cretaceous Ko. 1, (Dakota.) The 

 beds observed by Prof. Marsh on the south side of the Umta Mountains, 

 on Brush Creek, belong neither to the Dakota nor Bitter Creek epochs, 

 but perhaps to ivTo. 3, if, as Prof. Marsh asserts, the oyster found in a 

 superjacent stratum is Ostrea co7igesta, Con.; it is in any case of no later 

 date than the Canon City or Weber Elver coals. Hence the assumption 

 of some writers that this discovery determined the age of the Bitter 

 Creek series to be Cretaceous is without foundation in fact. 



YIII. The Bear Eiveb Geoup 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 car- 

 ried across the rim of the eastern, starting from the Fontanelle Creek, 

 eighty miles north of the Union Pacific Eailroad, and continuing toward 

 the upper waters of Ham's Fork of the Green Eiver to the westward. 

 My notes are as follows : 



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

 my last notes left them near the Eock Spring Station, toward the 

 northwest all the way to Green Eiver. The upper strata becomes slaty 

 in character, and descends to the water-level at the river, where they 

 form a high bluff. In these slates occur the fish-beds discovered by Dr. 

 Hayden, as well as the insect-beds noticed by Messrs. Denton and Eich- 

 ardson. They are worn into towers and other picturesque forms at 

 Green Eiver City. (See Hayden, Annual Eeport, 1870.) Passing north 

 from the railroad, up the valley of Green Eiver, the slates display a gen- 

 tle 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 east extending to the Big Sandy Eiver, 

 and those on the West to Ham's Fork. At Slate Creek, farther to the 

 north twenty miles, a yellowish-brown sandstone rises into view, and 

 continues to increase in importance toward the north. At the mouth 

 of Fontanelle Creek it rises on the east side of the river to a height of 

 perhaps two hundred and fifty feet 5 but sinks toward the north and 

 east from near the mouth of Labarge Creek, fifteen miles up the river. 

 North of Labarge a similar bed of sandstone rises again, and is imme- 

 diately overlaid by white shales resembling those of the Green Eiver 

 epoch, which have here a great thickness. Opposite the mouth of the 

 Labarge their lower strata are bright-red, but on the west side of the 

 river the sandstone only is visible. All the beds rise to the north, the 

 red beds forming the summits of the cliffs in that direction. 



In passing up Fontanelle Creek to the westward, the heavy beds of 

 buff sandstone gradually descend, and the white shales come into 

 view. I examined the former for lignite and coal, but found none. 

 There are several thin beds of a tough carbonaceous material in the 

 white shales, (which I take to be of the Green Eiver epoch.) In the lower 

 strata, in this locality as well as on the east side of Green Eiver, above 

 the mouth of Labarge Creek, are numerous remains of fishes similar to 

 those of Green Eiver City, with insects and their larvse, shells like Pupa 

 and Cyrena, and millions of Cypris. The larvse are dipterous, some 

 nearly an inch long, and others minute, and in prodigious numbers. With 

 them are found stems of plants, but no leaves. These beds rise with a 



* See Hayden's Annual Eeport, 1870. Marsli, American Journal of Science and Arts, 

 March, 1871. 



