MARINE CRETACEOUS AND MARINE EOCENE CONTACT 343 



ary between them, and there is no controversy concerning the boundary. 

 Dr. L. W. Stephenson has emphasized this fact for the Atlantic and Gulf 

 coastal plain of the United States in a paper recently presented to the 

 Geological Society of Washington, but not yet published. He showed 

 that at many places where the actual contact between Cretaceous and 

 Eocene is visible there is evidence of an interval of erosion, and he stated 

 that the faunas are so distinct that they suggest a very long unrecorded 

 interval. Such a suggestion of a very long interval should be received 

 with caution, however, for the reason that very few if any of the Eocene 

 species can be supposed to be directly descendied from Cretaceous species 

 of the same area. They are immigrants from some other region, and we 

 have no record of the time that was required for their development. 



The only other area in T^orth America where marine Eocene is known 

 to follow marine Cretaceous is on the Pacific border west of the Sierra 

 Nevada and Cascade ranges. For many years it was believed that there 

 was a gradual transition from the Cretaceous to the Tertiary in California, 

 and that this transition was marked by a mixed fauna, in which many 

 persistent Cretaceous species were associated with Eocene types. It is 

 now known that this belief was erroneous, and that it was caused by im- 

 perfect knowledge of both the stratigraphy and the paleontology of the 

 region. The detailed stratigraphic and faunal studies of Merriam,^ 

 Weaver,^ Dickerson,* and others, with some of my own earlier work,^ 

 have shown that the boundary between Cretaceous and Eocene is as dis- 

 tinct on the Pacific coast as it is on the Atlantic side of the continent. 

 In both these areas the close of the Cretaceous is marked by uplift and 

 consequent withdrawal of the sea and the Eocene begins with the return 

 of the sea, though it is extremely doubtful whether the limits of the 

 interval between the retreat and return of the sea are the same ic both 

 areas. 



Variations in Upper Cretaceous Sedimentation of the Interior 



Province 



GENERAL DISCUSSION 



In the Interior Province, including the Great Plains and Eocky Moun- 

 tain regions, conditions were different. The Upper Cretaceous Sea dur- 



- J. C. Merriam : The geologic relations of the Martinez group of California at the 

 typical locality. Journal of Geology, vol. 5, 1897, pp. 767-775. 



3 C. E. Weaver : Contribution to the paleontology of the Martinez group. Cal. Univ. 

 Publ. Bull. Dept. Geol., vol. 4. 1905. pp. 101-12.3. 



* Roy E. Dickerson : The stratigraphic and faunal relations of the Martinez formation 

 to the Chico and Tejon north of Mount Diablo. Cal. Univ. Publ. Bull. Dept. Geol.. vol. 

 6, 1911, pp. 171-177. 



5 T. W. Stanton : The faunal relations of the Eocene and Upper Cretaceous on the 

 Pacific coast. Seventeenth Ann. Rept. U. S. Geol. Survey, pt. 1, 1896, pp. 1011-1060. 



