68 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The return of the sea upon the continental borders resulted 

 in the deposition of Cenomanian equivalents upon the older 

 Cretaceous deposits unconformably, as is seen on the one 

 hand, between the Knoxville and the Chico, and on the 

 other, between the Comanche and the Colorado. 



How widely spread this unconformable relation may 

 appear to be remains to be discovered, but judging from 

 the almost continuous series of the Cretaceous deposits in 

 favorable localities, it can hardly be expected that uncon- 

 formities will always be found where Comanche and Colo- 

 rado rocks are present. The double character of the 

 Chico group reminds one alike of the Trichinopoly and 

 Arrialoor of the Indian Cretaceous, of the later subdivi- 

 sions of the Rock}^ Mountain section, and of the Turonian 

 and Senonian overlap upon the European continent. It 

 therefore appears that disturbances of a similar character 

 occurred in very remote regions during the closing epochs 

 of the Cretaceous period. 



VIII. Summary and Conxlusions. 



The foregoing discussion of the Cretaceous deposits of 

 the Pacific border is designed to contain a statement of our 

 present knowledge of the subject, and particularly of the 

 Cretaceous deposits of California and Oregon. An at- 

 tempt has been made to revive the earlier views regarding 

 the complexity of the series, which have been to a con- 

 siderable extent suppressed. The view more recently 

 maintained, that the series is one of comparative simplicity, 

 even in its most complete developments, has proved to be 

 misleading when applied to districts outside of a rather 

 restricted basin. The series at its best cannot be called 

 simple, its continuity having been frequently disturbed 

 even when deposition was most uniform in the basin of 

 the Great Valley. While the disturbances have not always 

 been sufficiently great to destroy all existing marine species, 

 and thus obliterate faunal connections between deposits of 

 succeeding epochs, yet it is evident that only the most 



