TERTIAEY FAUNAS OF THE PACIFIC COAST 231 



Another fact showing the relations existing between the Eocene 

 and the Cretaceous is the occurrence in the Eocene beds in the Rose- 

 burg region, Ore., of oysters so similar in appearance to the character- 

 istic Cretaceous fossil, Gryphaea, that without their accompanying 

 Eocene fauna these oysters would certainly be mistaken for Cretaceous 

 forms. 



CONDITIONS IMMEDIATELY PRECEDING AND INAUGURATING THE EOCENE 



Immediately preceding the Eocene period practically all of Wash- 

 ington, all of Oregon excepting a small area along its southern border, 

 the Sierran and desert region, and certain portions of the coastal 

 belt of California were dry land. Most areas in California, and 

 possibly also those in the Puget Sound region, which were occupied 

 by the Chico or upper Cretaceous sea, were still under water, or at 

 least elevated only slightly above sea-level and this without deforma- 

 tion of the Chico beds or subsequent erosion before subsidence. 

 Influences, however, which markedly affected the faunas without 

 materially influencing the sedimentation, were actively at work, and 

 it seems likely that these influences were due to worldwide climatic 

 changes augmented by a readjustment of ocean currents following 

 orogenic movements. In Washington, according to G. O. Smith, 



the deposition of the Cretaceous rocks seems to have been followed by an epoch 

 in which they and older rocks were folded and uplifted. Thus was an early 

 Cascade Range outlined, although it may be that the range had an even earlier 

 origin. Accompanying the post-Cretaceous mountain growth were intrusions of 

 granitic and other igneous rocks which now constitute a large part of the northern 

 Cascades. During the time that any portion of this area was not covered by 

 water the rocks were exposed to the vigorous attacks of atmospheric agencies. 

 Thus, at the beginning of the Tertiary the northern Cascade region appears to 

 have been a comparatively rugged country, although not necessarily at a great 

 elevation above sea-level.' 



A study of the interrelations of the Cretaceous and Eocene forma- 

 tions outlined in a preceding section clearly indicates that any impor- 

 tant pre-Eocene mountain-building movements affecting the Creta- 

 ceous rocks in the California province must have taken place before 

 the deposition of the Chico or upper Cretaceous sediments. As 

 shown by F. M. Anderson," the movements immediately preceding 



I "EUensburg Folio," Geol. Atlas U. S., No. 36, p. i. 



= Proc. Cal. Acad. ScL, 3d ser., "Geology," Vol. II, 1902, p. 53. 



