202 GEOLOGY. 



Marine Eocene beds (Arago), resting unconformably on the Cre- 

 taceous, are wide-spread in western Oregon. They attain great thick- 

 ness (said to be 10,000 feet 1 ), and make up the mass of the Coast 



Fig. 419. — Section showing the structure of the Eocene in western Oregon. Eb, 

 Eocene basalt; Ep (Pulaski formation), and Ec (Coaledo formation), Eocene. 

 Length of section about 20 miles. (Diller, Coos Bay, Ore. folio, U. 8. Geol. Surv.) 



range of that State. 2 The sediments which compose them appear to 

 have come from the Klamath mountains. Various beds of marine 

 Eocene in Oregon, not definitely correlated, have, as in California, 

 received local names (Umpqua, Tyee, 3 Pulaski, 4 etc.). The structure 

 of the Eocene at certain points in Oregon is shown by Figs. 419 and 

 and 420. 



Fig. 420. — Section a little south of the last, showing the relation of the Eocene (Ep, 

 Pulaski formation) to the Cretaceous (Km, Myrtle formation), as, amphibolite 

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



Brackish-water beds. — By the beginning of the Eocene, the Puget 

 Sound depression, possibly to be correlated with the great valley of 

 California and the Gulf of California, had begun to show itself. 5 The 

 Olympic and Cascade mountain regions on either side of the sound 

 were high, but not mountainous land; and the region of the sound 

 was a great estuary, in and about which deposition was in progress. 

 The sediments accumulated in part at least in brackish water, and 

 resulted in the thick (estimated at 10,000 to 20,000 feet) coal-bear- 

 ing Puget formation or series of Washington, the upper part of which 

 may be Oligocene or even Miocene. 6 The conditions of sedimentation 

 varied considerably during the deposition of this series, as the numer- 

 ous coal seams show. Of the coal-beds, 125 are said to be thick 



1 Diller, Coos Bay, Ore., folio, U. S. Geol. Surv. 

 2 Roseburg, Ore., folio, U. S. Geol. Surv. 



3 Diller, Roseburg, Ore., folio, U. S. Geol. Surv. 



4 Diller, Coos Bay, Ore., folio, U. S. Geol. Surv. 

 6 Willis, Tacoma Folio, U. S Geol. Surv. 



6 Willis, Bull. Geol. Soc. Am. Vol. IX, 1897-8. See also 18th Ann. Rept. U. S. 

 Geol. Surv. Also Landes, Washington Geol. Surv., Vol. II, p. 170. 



