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University of California Publications in Geology [Vol. 9 



Recently discovered stratigraphic and palaeontologic evidence indi- 

 cates that the Agasoma gravidum zone belongs to a distinct period 

 of deposition, and that the time-break represented by an unconformity 

 between it and the Area montereyana beds above is apparently a 

 large one. The fauna of the Agasoma gravidum zone is correlated by 

 the writer with a part of the Astoria series, as described by Dr. Ralph 

 Arnold and Mr. Harold Hannibal. 2 



It is only a few years since a marine Oligocene fauna was first 

 recognized on the Pacific Coast by Dr. W. H. Dall in a paper by 

 J. 8. Diller entitled "A Geological Reconnaissance of Northwestern 

 Oregon. " 3 The following year Dall, 4 in a correlation table of the 

 Tertiary horizons of North America, again placed a part of the Astoria 

 shale of Oregon in the Oligocene. 



It was nearly ten years later before attention was called to marine 

 Oligocene beds in California. In 1906 Dr. Ralph Arnold 5 listed a 

 fauna from a formation, which he named the San Lorenzo and which 

 he believed to be of Oligocene age. In 1908 Arnold published the 

 descriptions of the new species obtained from the San Lorenzo For- 

 mation and again referred it to the Oligocene. In the Santa Cruz 

 folio 7 a definite description of the lithology and stratigraphy of the 

 San Lorenzo is given. The filial conclusion was that there is no evi- 

 dence of a stratigraphic break in the Santa Cruz Mountains between 

 the Oligocene and the Miocene. It was believed that certain beds, 

 designated as Transitional Oligocene-Miocene, contained a fauna which 

 was transitional between the Oligocene and the Miocene. 



The first attempt to separate the faunas of the Lower Miocene and 

 Oligocene in Oregon was by Dr. W. H. Dall. 8 Dall at that time recog- 

 nized the inadequacy of his list and the probability of the mixture of 

 his faunas. 



? Arnold, Ralph, and Hannibal, Harold, The marine Tertiary stratigraphy of 

 the North Pacific Coast of America, Proc. Amer. Phil. Soc, vol. 52, no. 212, 

 November-December, 1913. 



3 Diller, J. S., 17th Arm. Rept. U. S. G. S., pt. L, p. 464, 1895. 



* Dall, W. H., A table of North American Tertiary horizons correlated with 

 one another and with those of Western Europe, with annotations, 18th Ann. 

 Rept. U. S. G. S., pt. II, p. 334, 1896-97. 



s Arnold, Ralph, Prof. Paper U. S. Geol. Surv., no. 47, pp. 16, 17, 1906. 



o Arnold, Ralph, Descriptions of new Cretaceous and Tertiary fossils from 

 the Santa Cruz Mountains, California, Proc. U. S. Nat. Mus., vol. 34, no. 617, 

 pp. 345-385. 



- Branner, J. G, Newsom, J. F., Arnold, Ralph, Santa Cruz Folio, IT. S. Geol. 

 Surv., no. 163, p. 4, 1909. 



s Dall, W. II., The Miocene of Coos Bay, Oregon, Prof. Paper U. S. Geol. 

 Surv. no. 59, p. 11, 1909. 



