merriam.] Fauna of the Lower Miocene in California,. 



379 



South of Contra Costa County the deposits in the middle 

 Tertiary appear to take on quite a different character. Instead 

 of a thin bed of sandstone below the Monterey shale, very 

 considerable thicknesses of heavy sandstone and clay may 

 form the basal beds. These may swell out to make a much 

 more important stratigraphic unit than the basal sandstone 

 of the Contra Costa region. In the Pacific Railroad survey 

 reports, heavy fossiliferons sandstones are mentioned by Antisell* 

 as occurring at the base of the Miocene. Later, Whitney t 

 presented sections of several regions where extensive Miocene 

 sandstones lie below the shale. In the palaeontology of Whitney's 

 report, Gabb+ refers to the shale as the upper member of the 

 Miocene, evidently having in mind the sandstones below it. In 

 several of these references Turritella ocoyana is mentioned as a 

 common form in these beds. 



In 1895, Ashley§ described a thick series of sediments which 

 he supposed to rest conformably below the Monterey. He listed 

 several species from it, of which the most important and charac- 

 teristic is Turritella hoffmani. Ashley was uncertain about 

 the age of these beds, thinking they might be partly Eocene. 



In 1896, Fairbanks, || in his discussion of the geology of Point 

 Sal, described exteusive Miocene beds of clay and sandstone below 

 the shale. Still more recently in his work on the San Luis 

 Obispo Quadrangle he has carefully worked out the relation of this 

 horizon to the shale and made extensive collections in it. These 

 collections were turned over to the University of California. 

 They were worked over by Mr. F. C. Calkins, who has found in 

 them a very interesting fauna. Turritella hoffmani is perhaps 

 the most characteristic species. Along with it are a great mauy 

 forms not known in the later beds. Other collections made more 

 recently by Dr. Ralph Arnold in the T. hoffmani beds described 

 by Ashley show the same fauna as that collected by Fairbanks 

 almost species for species. 



*T. Antisell. Pacific R. R. Rep. Vol. 7, p. 1 1)7. 



t J. D. Whitney. Geol. Surv. Calif.. Vol. I, p. 128, fig. 10, and p. 135, fig. 17. 

 + W. M. Gabb. Geol. Surv. Calif., Palaeontology. Vol. II, p. 59. 

 § G. H. Ashlev. Leland Stanford Junior Publications. Geol. and Palaeont. 

 No. 1, p. 291. 



|| H. W. Fairbanks. Bull. Dept. Geol. Univ. Calif. Vol. II, No. 1, p. 5. 



