108 T. W. Stanton — Stratigraphic Position 



All of the localities remaining to be considered are in the 

 area which was examined by Dr. A. C. Peale in 1877, by whom 

 collections of fossils were made from the Bear River strata at 

 the most of them. His report* on the region referred to was 

 published in 1879 and his map of it accompanied the twelfth 

 annual report of the Survey of the Territories which was not 

 issued until 1882. 



Localities on Twin Greek and Nam's Fork. — Thirty-live 

 miles north of Evanston at Sage station, near the mouth of 

 Twin creek, there is an abandoned mine on a thin bed of 

 coal dipping about 35° northwest. Above the coal there is a 

 considerable thickness of sandstones interstratitied with argil- 

 laceous and siliceous shales none of which yielded any fossils. 

 In a thin bed of sandstone, 15 or 20 feet below the coal Modiola 

 7mdttlinigera, Baroatia coalvillensis and a few other species 

 of the Colorado Cretaceous were found. 400 or 500 feet east 

 of (below) this there are exposures of sandstones and calcare- 

 ous shales containing Bear River fossils, interstratiiied with 

 thin seams of coal on some of which excavations have been 

 made. A figure of the section and a list of the Bear River 

 species collected here has been publisheclf by Dr. Peale. He 

 states that the fossils there enumerated came from above the 

 coal. It is probable however, that one of the lower coal seams 

 is referred to and that the bed in the Colorado formation was 

 not then opened. On the south side of the creek less than 

 half a mile from the coal mine there are obscure outcrops of a 

 fossiliferous Tertiary limestone that also dips northwest, show- 

 ing that it is involved in the folds and faults of the neighbor- 

 hood. 



On Ham's Fork there is a somewhat similar condition of 

 ' things. This locality is about twenty-five miles east of the 

 one last described and a mile east of Waterfall station. On 

 the western border of the small area mapped as Jura-Trias by 

 Dr. Peale there is a very small exposure of Bear River beds 

 dipping 45° to 70° west. The fossils obtained include the fol- 

 lowing characteristic forms ; 



Pyrgulifera humerosa. TIaio vetustus. 



Gorbula pyriformis. Unio belliplicatus. 



Covbicula durkeei. 



The apparent thickness of the calcareous shales containing 

 these fossils, with the associated thin bands of sandstone, is 30 

 or 40 feet, and the length of the exposure is only about 200 

 feet. The contact with the underlying beds is not shown. 

 They consist of reddish brown and purplish shales and beds of 

 hard brown and gray sandstone with variable westward dips. 



* llth Ann. Eept. U. S. G-eol. Surv. Terr, pp. 511-646. 

 f Op. cit, p. 575 and PL LXVII. 



