78 TITANOTHEEES OF ANCIENT WYOMING, DAKOTA, AND NEBEASKA. 



Correlation of middle Eocene and upper Eocene American life zones and European stages 



Middle Eocene. 



I 11. Palaeosyops paludosus-Orohippus zone (Bridger B). 



i 10. Eometarhinus-Trogosus-Palaeosyops fontinalis zone (Bridger A, Huerfano B) . 



TYPICAL BBIDGER FORMATION; MIDDLE EOCENE 

 (LUTETIAN AND BARTONIAN OF EUROPE) 



Character of sediments. — The Bridger formation, the 

 most important and the most thoroughly explored of 

 the Eocene Tertiary, occupies a great area north of 



ditions. The Bridger formation attains its maximum 

 thickness of 1,875 feet near the Uinta Mountains and 

 thins out northward. Beyond the margins of the 

 Green River lacustrine deposits the Bridger overlies 

 upper members of the Wasatch group. 



Figure 54. — Map showing the Eocene sediments encircling the Uinta Mountains of southwestern Wyoming 



and northern Utah 



Modified after King (1876.1). U, Uinta Basin, typical Uinta formation of King and Marsh. (The area mapped includes older and possibly 

 younger rocks than the true Uinta formation— Z)/piacoion zone.) B, Bridger Basin, typical Bridger formation of Hayden. WK, Washakie 

 Basin, typical " Washakie" formation of Hayden. G, Green River formation. W, Typical Wasatch group of Hayden. X, Type locality 

 of Coryphodon and associated Wasatch fossils. C, Cretaceous. 



the Uinta Mountains and east of the Wasatch. Unlike 

 the Wasatch, the lower Bridger (horizon B) is unique; 

 no contemporaneous fossiliferous deposition is known. 

 At the base its sediments pass gently into the Green 

 River shales, and the lower levels of Bridger A show 

 gradual transition from lacustrine to flood-plain con- 



Unlike the lower Eocene Wasatch and Wind River 

 sediments the Bridger is not composed chiefly of 

 material derived by erosion from the adjacent moim- 

 tains (Sinclair, 1906.1, p. 278) but consists of great 

 series of deposits of volcanic ash and dust, solidified 

 into tuffs, which weather into picturesque and in 



