514 RALPH ARNOLD 
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, Gryphea, 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 
« “Flensburg Folio,’’ Geol. Atlas U. S., No. 36, p. I. 
a Proc. Cal. Acad. Sci., 3d ser., ‘‘ Geology,” Vol: II, 1902, p. 53. 
