234 RALPH ARNOLD 



and possibly also east of the Sierra Nevada. Erosion tending toward 

 a base-leveling of the Sierra Nevada and other elevated portions of 

 the Pacific Coast must have proceeded rapidly during the Eocene as 

 is evidenced by the great thicknesses of strata laid down during the 

 period and by the fact that high relief was not present during the 

 Oligocene except in rare instances, although the Oligocene in general 

 was a period of uplift for much of the Pacific Coast province. 



OEOGENIC MOVEMENTS AKD VOLCANIC ACTIVITY IN THE EOCENE 



After the deposition of the early Eocene came a period of temporary 

 elevation, erosion, and great volcanic activity in Washington, Oregon, 

 and northern California. Extensive basaltic eruptions through long 

 conduits and over the eroded rock surfaces took place in eastern Wash- 

 ington and western Oregon, while in the region of the Olympic Moun- 

 tains and eastern Oregon basalt flows and volcanic outbursts were 

 also taking place. Eocene volcanic disturbances so pronounced in 

 the north do not appear to have affected the Sierra Nevada nor the 

 coastal region of California south of the Klamath Mountains. 



CLIMATE DURING THE EOCENE 



The faunas and floras of the Eocene indicate subtropical condi- 

 tions for this period at least as far north as Puget Sound. The 

 marine faunas of the Pacific Coast Eocene are closely allied to those 

 of the Eocene of the southern states and the Eocene shells, Corbicula, 

 for instance, as a rule belong to groups showing a predilection for 

 warm waters. This supports the evidence offered by the floras which 

 are of a decidedly tropical aspect. Doctor Knowlton has the following 

 to say in connection with the flora of the Puget formation, which may 

 be regarded as typical of the Washington, Oregon, and California 

 Eocene : 



The lower beds [the Eocene portion of the Puget formation], on account of 

 the abundance of ferns, gigantic palms, figs, and a number of genera now found 

 in the West Indies and tropical South America, may be supposed to have enjoyed 

 a much warmer, possibly a subtropical, temperature, while the presence of sumacs, 

 chestnuts, birches, and sycamore in the upper beds [Oligocene and lower Miocene] 

 would seem to indicate an approach to the conditions prevailing at the present 

 day.^ 



r Tacoma Folio, p. 31. 



