THE EOCENE PERIOD 



775 



The rocks of the Eocene system are mostly clastic, sandstone 

 and shale predominating, but there are conglomerates, tuffs, and 

 diatomaceous shales, the last thought to be a source of oil. In 

 not a few places, marine beds 

 are succeeded by brackish-water 

 deposits. 



By the beginning of the 

 Eocene, the Puget Sound de- 

 cession, perhaps to be correlated 

 ith the great valley of California 

 id the Gulf of California, had 

 n to show itself. 1 The 

 )lympic and Cascade mountain 

 'ions on either side were high 

 ids, but not mountainous; and 

 the region of the sound was a 

 it estuary, in and about which 

 leposition was in progress. Some 

 )f the sediments accumulated in 

 >rackish water and on land, and 

 suited in the thick coal-bearing 

 $et series of Washington, the 

 ipper part of which is Oligocene 

 )r even Miocene. 2 The series is 

 dd to contain 125 beds of coal 

 thick enough to attract prospec- 

 tors. Most of the workable coal 

 is in the lower part of the series. 

 The area of deposition extended 

 south into Oregon, and east well 

 toward the Blue Mountains of 

 that state. 



British Columbia appears to 

 have been land during the period, 3 but Eocene beds, much disturbed, 



1 Willis, Tacoma folio, U. S. Geol. Surv. 



2 Willis, Bull. Geol. Soc. Am., Vol. IX, 1897-8. See also 18th Ann. Kept., 

 U. S. Geol. Surv., and Landes, Washington Geol. Surv., Vol. II, p. 170. 



3 Dawson, Science, Vol. XIII, 1901, p. 401. Also Spencer, A. C., Bull. 

 Geol. Soc. Am., Vol. XIV, p. 131. 



Fi 



. 525. Map showing supposed 

 distribution of land and water on 

 the Pacific coast of the United 

 States during the Eocene period. 

 (Ralph Arnold.) 



