of the Bear River Formation. 



113 



Greenish sandstone weathering to a dark brown. It 

 contains Unio vestustus, Limnea (limnophysa) ni- 

 tidula and a few other fossils. Dip 55° east. Thick- 

 ness 10 ft. 



Covered 300 ft. 



Gray sandstone containing a few dicotyledonous leaves* 



and Gasteropods 10 ft. 



Bluish argillaceous and calcareous shales with some 

 thin bands of sandstone. Bear River fossils are 

 numerous in the calcareous layers. The dip seems 

 to remain constant at 55° east to the river plain of 

 Smith's Fork making a thickness of 2200 ft. 



Total 3420 ft. 



The level meadows of the river plain are about half a mile 

 wide, and the east bank of the stream directly opposite is com- 

 posed of Bear River strata dipping 60° west. 



Three miles north of the last section the divide between 

 Smith's Fork and Thomas' Fork is made np of fossiliferous 

 Bear River shales and sandstones dipping east. The underly- 

 ing sandstones and conglomerates (base of preceding section) 

 are sharply folded in an anticlinal, west of which the highly 

 fossiliferous Bear River beds again appear in a synclinal. Still 

 farther west along Thomas' Fork the reddish brown thin bed- 

 ded sandstones and sandy shales beneath the conglomerate are 

 exposed. 



General Discussion of the Sections.— -The following table 

 based on the detailed sections shows the relative positions of 

 the different Cretaceous formations described and their cor- 

 relation with the members of the complete upper Cretaceous 

 section of the Northwest, in which the Colorado formation is 

 the equivalent of the Fort Benton and Niobrara groups of the 

 Meek and Hayden section and the Montana is the equivalent 

 of the combined Fort Pierre and Fox Hills of the same section. 



Tertiary. 



"Wasatch. 



Conglomerates, coarse sandstones and shales with coal 

 at the base. 





Laramie. 

 Montana. 



Wanting, or included in the above. 





Not positively identified. 



Cretaceous. 



Colorado. 



Shales and coal-bearing sandstones. Thickness not less 

 than 2500 ft. 





Bear Biver. 



Very fossiliferous argillaceous and calcareous shale 

 alternating with thin beds of sandstone. 





Dakota ? 



Conglomerates and coarse sandstones. Thickness of 

 last two 2500 to 4000 ft. 



Jurassic. 



Belenmites 

 Beds. 



Thin bedded sandstones and sandy shales. 



* The fragmentary plants collected from this formation have not yet been 

 studied. 



