114 T. W. Stantoti — Stmtigraphic Position 



It has already been shown that the lower 400 or 500 feet of 

 the sections near Bear River City is of Jurassic age. In the 

 more northern areas beds of much greater thickness — not less 

 than 3000 feet — of similar lithologic character and holding the 

 same position relative to the overlying formations are believed 

 to be of the same age, although no fossils were found in them. 

 These beds rest conformably on easily recognizable calcareous 

 shales and limestones from which Pentacrinus asteriscus and 

 other characteristic Jurassic fossils have been obtained. 



Above these beds comes a considerable thickness of con- 

 glomerates, coarse sandstones and shales separated from the 

 preceding by great differences in the character of the sedi- 

 ments, and closely associated with the Bear River formation 

 throughout the entire region, though at a few localities they 

 are not exposed. The conglomerate at the base is a very 

 irregular deposit, varying within short distances fro.m a brown 

 or gray cross-bedded sandstone to a conglomerate composed of 

 pebbles two inches or more in diameter. The general charac- 

 ter, however, remains constant and the bed is easily recognized. 

 In the sections I have called this formation the Dakota ? ? and 

 have assigned to it in each case all the non-fossiliferous beds 

 above the base of the conglomerate and below the recognized 

 Bear River beds. It is evident that a portion if not all of 

 the strata in these sections between the Jurassic and the Colo- 

 rado Cretaceous must be the equivalent of the Dakota forma- 

 tion, but the division here made is simply one of convenience. 



Of the 3000 to 3500 feet of strata assigned to the Bear 

 River formation at the more northern localities at least 2500 

 feet contain identified fossils characteristic of the formation. 

 The 900 feet at the base is not usually fossiliferous but it con- 

 tains nutlets of Chara and small Gasteropods indicating that 

 it is of fresh-water origin, and there seems to be no reason for 

 separating it from the overlying beds. The lithologic charac- 

 ter of the Bear River formation is very constant throughout 

 the whole region, as the detailed sections have shown. Its 

 thickness increases northward as far as my examination ex- 

 tended. There is not so great a difference in this respect, 

 however, as the arbitrary division of my sections would indi- 

 cate, for it is probable that near Bear River City enough should 

 be transferred from the Dakota 1 to the Bear River formation 

 to make the thickness of the latter nearly 2000 ft. 



The Colorado formation as it occurs at Bear River City, rest- 

 ing immediately on the Bear River beds, has been sufficiently 

 described. It was not found north of Twin Creek. 



The Montana formation was not positively identified at any 

 of the localities studied. Possibly a part of the shales be- 



