666 ARNOLD AND HANNIBAL— MARINE TERTIARY [April 19, 



extraordinary development of sediments is only to be explained by 

 a consideration of the nature of the deposits. These are at some 

 points coarse basalt tuffs and at others, and by all odds this is the 

 most prevalent type of sedimentation, worked over volcanic eject- 

 menta in the form of sandstones or shales deposited under estuarine 

 conditions, evidently with considerable rapidity. 



Three divisions, the Giehalis, Olequa, and Arago formations, 

 represent well-marked palseontological horizons that can be recog- 

 nized by characteristic faunas and floras over the North Pacific 

 Coast. The latter is not found in juxtaposition with the Chehalis and 

 Olequa and may represent a later phase of the Eocene equivalent to 

 the lone of California. 



Faunal Diz'islons of the Tcjon Series. 



\ Tropical flora — 

 [Arago formation — zone of F(?«^nVara'/a ! fan-palms, magno- 

 Tejon I horni variety with obsolete ribs f^lias, figs, and ferns. 



Series Olequa formation 1 zone of Venericardia J Austral flora — 



.Chehalis formation j horni Gdihh^^ 1 birches, sycamores 



j and chestnuts. 



The Chehalis and Olequa formations usually consist of fine 

 material and are essentially estuarine deposits throughout, contain- 

 ing numerous lignite beds interstratified with alternating fresh water 

 and marine sediments. The Arago of the Coos Bay-Port Orford 

 coal fields is similar but commonly consists of coarser material 

 partly arkose in character. Farther north in Oregon this horizon 

 is represented by basic flows and coarse bedded tuffs occasionally 

 carrying marine fossils. In the Roseburg district it is essentially 

 tuffaceous sandstone of marine origin. Coarse basalt tuffs carry- 

 ing marine fossils and interbedded with basic flows and a sub- 

 ordinate amount of sandstone on the north coast of Washington are 

 also referred to this horizon on the basis of palaeontological 

 evidence. 



^^ Usually cited as V. planicosta Lam., but the real plankosta is confined 

 to the Martinez formation on the Pacific Coast. 



