210 GEOLOGY. 



ous other points in the western mountain region. In northern Oregon, 

 there are late Eocene beds of terrestrial origin (Clarno formation) 

 in the John Day basin, which was the site of aggradation during a 

 large part of the Tertiary. The Clarno beds are chiefly of volcanic 

 tuff. 1 Eocene beds of similar nature occur in western Oregon, cen- 

 tral Washington, and northwestern Idaho. 2 In Washington, two 

 thick, sedimentary formations (the Swauk, early Eocene, 3500-5000 

 feet, below, and the Roslyn, 3500 feet, above) of Eocene age and non- 

 marine origin, are separated by 300-4000 feet of basalt (Fig. 423). 

 The Swauk formation (conglomerate, arkose, sandstone, shale, etc.) 

 is described as lacustrine, while the Roslyn contains much coal. 3 The 

 Payette formation of Idaho, formerly classed as Miocene, is now referred 

 to the Eocene. 4 It is 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. 5 The Payette beds range 

 in altitude from 4100 to 6900 feet. If they are all lacustrine, a large 

 part of this range is due to later deformation. 



Eocene beds of terrestrial or volcanic origin are imperfectly known 

 at other points, as in the Yellowstone Park 6 (Piny on conglomerate), 

 in the Absaroka 7 region to the east, in Montana 8 (Sphinx conglomer- 

 ate), in Arizona 9 (White tail conglomerate, fluviatile), where there 

 were igneous eruptions and faulting before the end of the period, in 

 Nevada 10 (Amyzon formation), in Utah (Manti, mainly shale), 11 and in 

 southern California (Mojave formation, sandstone, clay, tuff, and 

 lava-flows). 



The sediments of the Eocene system of the western mountains are 

 principally clastic, and there is not a little gravel and conglomerate. 

 Associated with these common sorts of sediment, there is much pyro- 



1 Merriam, Jour. Geol., Vol. IX, p. 71, and Bull. Univ. of Cal., Vol. II, p. 285, 

 and Knowlton, Bull. 204, U. S. Geol. Surv. 

 2 Knowlton, op. cit., pp. 110-113. 



3 Smith, Geo. Otis, Mount Stuart, Wash., folio, U. S. Geol. Surv. 



4 Knowlton, op. cit., p. 110. 



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

 B Weed, Yellowstone Park folio, U. S. Geol. Surv. 



7 Hague, Absaroka, Wyo., folio, U. S. Geol. Surv. 



8 Peale, Three Forks, Mont., folio, U. S. Geol. Surv. 



9 Ransome, Globe and Bisbee folios, U. S. Geol. Surv. 



10 King, op. cit., p. 393; and Cope, Am. Nat., Vol. XIII, p. 332, 1879. 

 "Cope, Am. Nat., Vol. XIV, p. 303, and Vol. XXI, p. 454, 1887. 



