of the Bear River Formation. 109 



On the west the Bear River formation is overlapped by a 

 light-colored calcareous sandstone, interbedded with greenish 

 clays and soft yellowish sandstones. The dip varies from 10° 

 to 20° west and the total thickness seen is about 50 feet. The 

 calcareous band contains Goniobazis tenera, Unio haydeni, 

 Viviparus paludinwformis and other characteristic species of 

 the Wasatch Tertiary. The few exposures in the space extend- 

 ing one half mile farther west shows that these Wasatch beds 

 are folded in a gentle syncline beyond which the shales, sand- 

 stones and coal seams of the Colorado Cretaceous appear with 

 dips varying froni 20° to 29° west. The top of the exposed 

 section is formed by the sandstones of Oyster Ridge, which 

 are, in part at least, the equivalent of similar Cretaceous sand- 

 stones at Bear River City and at Coalville. It is believed that 

 a large part of the Bear River formation and a considerable 

 thickness of Colorado shales and sandstones are concealed 

 beneath the folded Wasatch Tertiary beds above mentioned. 



The Yalley of Smith's Fork. — Smith's Fork empties into 

 Bear River at Cokeville (formerly called Coketon) nearly 

 twenty miles north of Twin Creek. The last three miles of its 

 course is west, but above that for twenty miles it flows almost 

 south. The stream was followed for that distance to the 

 second great bend in its course where it approaches nearest to 

 the head waters of Thomas' Fork. The narrow drainage area 

 of this part of the stream is only from four to eight miles wide 

 and lies between the Sublette range on the west and a name- 

 less range, the southern continuation of the Salt River range, 

 on the east. Nearly all the beds underlying this valley belong- 

 to the Bear River formation which has here a greater thickness 

 than at any other locality visited. The strata are much folded, 

 there being an anticlinal fold and two synclinals — one of which 

 is replaced by a fault in the southern portion — between the 

 two ranges and parallel with them. 



iV few detailed sections are given below to show the struc- 

 ture, and for comparison with the sections near Bear River 

 City. 



At Cokeville the Carboniferous limestones are brought up 

 in a sharp broken fold forming prominent hills on both sides 

 of Smith's Fork. The upper portion of the overlying strata 

 that are doubtfully referred to the Triassic yielded a number 

 of imperfectly preserved fossils belonging to the genera Avic- 

 idopecten, Lingula, Camptonectes (?) etc., that have not been 

 specifically determined. They indicate that the strata contain- 

 ing them are certainly not later than the Jurassic and they are 

 believed to belong to the "Meekoceras Beds" which have been 

 referred to the Triassic. The beds immediately overlying are 

 concealed by a fault which brings these Triassic (?) limestones 

 in contact with the Bear River formation which rests on a 



