FORMATIONS AND PHYSICAL HISTORY 56! 



older than the Bridger Stage. It is at the base of the Eocene in 

 this locality, near Ridgway. 



4. The Uinta stage followed the Bridger. Deposition was then 

 in progress in southeastern Utah and southwestern Colorado. 

 Some of the Uinta beds now have an altitude of as much as 10,000 

 feet, though they probably were deposited at a much lower level. 



The northwest. In the northwest there are Eocene formations 

 not definitely correlated with the preceding stages. In northern 

 Oregon, there are late Eocene beds of terrestrial origin (Clarno 

 formation, largely volcanic tuff). In Washington, two thick sedi- 

 mentary formations (the Swauk, early Eocene, 3,500-5,000 feet, 

 below, and the Roslyn, 3,500 feet) of Eocene age and non-marine 

 origin, are separated by 300-4,000 feet of basalt. The Payette 

 formation of Idaho, said to have been accumulated in a lake formed 

 by the damming of the upper basin of the Snake River by the early 

 lava-flows of the Columbia River region, 1 is now referred to the 

 Eocene. Eocene beds of terrestrial or volcanic origin are imper- 

 fectly known in many other places west of the Rocky Mountains. 

 The erosion of the Eocene has given rise locally to the topography 

 characteristic of "Bad Lands." 



General considerations. It has been customary to regard the 

 Eocene and later periods as much shorter than those of the Paleo- 



Fig. 473. Section showing the structure of the Eocene in western Oregon. 

 Eh, F.ocene basalt; Ep (Pulaski fon.iat'on), and EC (Coaleclo formation), Eocene. 

 Length of section about 20 miles. (Diller, Coos Bay, Ore., folio, U. S. Geol. Surv.) 





Fig. 474. Section a little south of the last, showing the relation of the Eocene 

 (Ep, Pulaski formation) to the Cretaceous (Km, Myrtle formation^, as, amphib- 

 olite schist, and Ps, Quaternary marine sand. (Coos Bay folio, U. S. Geol. Surv.) 



zoic and Mesozoic; but this conclusion may be questioned. On 

 the basis of thickness, the showing of the system is great, both on 

 the Pacific coast, and in the western interior. Furthermore, any 

 just estimate of the duration of the period must take account of the 

 1 Lindgren and Drake, Nampa and Silver City, Idaho, folios, U. S. Geol. 

 Surv., and Knowlton, Bull. 204, p. no. 



