THE EOCENE PERIOD. 201 



area which had been submerged in the Cretaceous period. This is 

 shown by the wide-spread unconformity between the Eocene and the 

 Cretaceous systems. During the interval of emergence, great thick- 

 nesses of sedimentary rocks were removed, and when the sea again 

 advanced upon the land in the Eocene period, sediments were laid 

 down on an eroded surface, which in some places had been reduced 

 toward planeness by subaerial denudation. 



Marine formations are wide -spread in California west of the Sierra 

 and south of the Klamath mountains, and in Oregon north of the 

 Klamath mountains and west of the Cascades, but they have little 

 development within the land-area farther north. Various names have 

 been applied to the system and to its parts in different localities. 



Marine beds. — The Eocene beds of central California are known 

 as the Tejon series, though other names (e.g. Martinez ) have been 

 applied to various parts. The Tejon series is best known in the south- 

 ern part of the great valley of California, then occupied by the sea, 

 and is well exposed on the east side of the Coast range. It does not 

 appear in the Sierras, or in the northern part of the central valley. 

 In some places the Tejon series lies on the Chico with apparent con- 

 formity, though unconformity is more common. Even where there 

 appears to be conformity, the bottom of the Tejon is thought not to repre- 

 sent the oldest Eocene. In the middle part of the Coast range of Cali- 

 fornia, where the Tejon series is more than 4000 feet thick, 1 it is over- 

 lain conformably by the Miocene. The Tejon series is mainly clastic, 

 but locally contains lignite, and still more locally, oil. 2 In the Santa 

 Cruz mountains, Eocene beds constitute a part of the metamorphic 

 Pascadero series. 3 In some parts of southern California, the thick- 

 ness of the Eocene (Escondido series 4 ) is estimated at more than 7000 

 feet, the material being partly sediment axy and partly igneous. A 

 bed of gypsum, thick enough to be of commercial value, is found in 

 this series, and points to the absence of true marine conditions, at 

 least locally and temporarily. Eocene beds are absent from much of 

 northern California and southern Oregon. 5 



1 Lawson, Science, Vol. XV, 1902, p. 416. 

 2 Eldridge, Bull. 213, U. S. Geol. Surv., p. 306. 

 3 Ashley, Jour, of Geol., Vol. Ill, p. 434. 

 4 Hershey, Am. Geol., Vol. XXIX, pp. 349-72. 

 5 Diller, Bull. Geol. Soc. Am., Vol. IV, p. 220. 



