Marshall. — Relations between Cretaceous and Tertiary Rocks. 109 



(1.) California. 



The localities are in the great valley of California, near Chico and 

 Martinez. The fossils found there were first described by Conrad,* who 

 regarded them as Tertiary, whUe Gabb| thought them to be of Cretaceous 

 age. Later on WliiteJ gave a more detailed account of the stratigraphy. 

 He says, " The strata which constitute the Tejon, Martinez, and Chico 

 groups of Gabb form one unbroken series, which rests unconformably on 

 all the rocks beneath it, and on which the Miocene rests conformably. 

 The Tejon portion of the series represents the Eocene ; the Chico portion 

 the closing epoch of the Cretaceous. But there is an alternate mingling of 

 types throughout the whole series, so that no horizon can be distinguished 

 that will separate all the Cretaceous types on the one hand and all the 

 Tertiary types on the other. In other words, there is an unbroken faunal 

 and stratigraphic continuity from the Cretaceous to the Tertiary part of 

 the series." 



The same author says elsewhere, " In the case of the Tejon Chico 

 series unbroken marine conditions existed. ... It is true that on the 

 western border of the continent we find the marine Cretaceous merging 

 into the marine Eocene. "§ 



Fairbanks remarks of this series, '' The Chico-Tejon has a thickness of 

 at least 20,000 ft. in several places. We have no knowledge at present of 

 a stratigraphic break in the series. ""|| 



The latest worker on this series is Stanton, who states,^ " (1.) In all 

 known sections which contain both Chico and Tejon [faunas] the strata 

 are apparently conformable. . . . (5.) The Chico is characteristically 

 Cretaceous, its so-called Tertiary types being persistent or modern types 

 that have changed but little from the Cretaceous to the present day. 

 (6.) An examination of the species supposed to occur in both the Chico 

 and Tejon reduces the number to not more than six, and with one exception 

 these are all persistent types that cannot be classed as Mesozoic. The one 

 exception is Ammonites jugalis. It is held that the Tejon fauna is essentially 

 Eocene, and very distinct fi-om the Chico, even though this ammonite should 

 prove to belong to it. (7.) The time interval indicated by the decided change 

 in faunas cannot now be estimated. In fact, there is little evidence that 

 the later fauna is directly derived from the earlier except in a few species, 

 and it is possible that all the changes took place by extinction and migration 

 of species during the period in which the barren beds between the latest 

 Chico and the earliest Tejon were laid downi.'' 



In the Martinez group, which constituted the transition series between 

 the Cretaceous and Eocene of Gabb, fifty -two species of Mollusca occur. Of 

 these, Stanton admits four species as occurring certainly in both, and an 

 additional six species as occurring doubtfully in both. Gabb had previously 

 stated that sixteen species occurred generally in both the Chico and Tejon 

 series. Stanton reduces this number to six. He places the division between 

 the Chico and the Tejon in the middle of the Martinez. He gives no strati- 

 graphical diagrams or maps. He further states (p. 1033), '' Excepting the 



* Am. Journ. Sci., 44, 1867, p. 376. 



t " Palaeontology of California," vol. 1, ii. 



X C. A. White, Bull. U.S. Geol. Surv. 15, 1885, p. 3. 



§ U.S. Geol. Surv. Bull. 82, 1891, pp. 200, 201. 



II Jour, of Geol., vol. 3, 1895. p. 433. 



ilU.S. Geol. Surv., 17th Annual Rep., 1890, p. 1035. 



