1 915 ] Clark: Occurrence of Oligocene in the Contra Costa Hills 17 



It contains many of the Lower Miocene species, a number of which in 

 the southern part of the state are found in both the Turritella ocoyana 

 and Turritella inezana zones. 



EVIDENCE SUGGESTING CORRELATION OF THE FAUNA OF THE 

 AGASOMA GRAVIDUM ZONE OF CONTRA COSTA COUNTY, 

 CALIFORNIA, WITH THAT OF THE OLIGOCENE OF 

 OREGON AND WASHINGTON 



Accumulating evidence seems to show that there is a faunal break 

 in Oregon and Washington between the Oligocene and Lower Miocene 

 which is as great as that in California. The distinctness of the faunas 

 of these two horizons will be more easily shown when a larger per- 

 centage of the known species have been described. 



The writer has had the opportunity of studying large collections 

 at the California Academy of Sciences, which were obtained by Bruce 

 Martin from many of the Oligocene and Miocene localities listed by 

 Arnold and Hannibal, Dall, and Weaver. It was by means of these 

 collections that data were obtained for correlating the Agasoma gravi- 

 dum beds with the Oligocene of Oregon and Washington. 



Two important localities from which Mr. Martin obtained fairly 

 large collections of very well preserved fossils are from the bluffs 

 near the town of Pittsburg, Columbia County, Oregon, and on Lincoln 

 Creek near the boundary line of Lewis and Thurston counties, Wash- 

 ington. The beds at the Pittsburg locality are classed as Eocene by 

 Dr. W. H. Dall. is . It was here that the types Macrocallista pittsbur- 

 gensis (Dall) and Acila shumardi Dall were obtained. The collection 

 obtained by Mr. Martin at this locality shows conclusively that this 

 fauna cannot be classed as Tejon (Upper Eocene), but is equivalent 

 to what Dall recognizes elsewhere as being Oligocene. The Lincoln 

 Creek locality is the type locality of Dr. C. E. Weaver's Lincoln 

 Formation. 111 which he considers to be Oligocene and from which he 

 lists a number of Eocene species. 



The species in the collection of the California Academy of Sciences 

 from the Pittsburg and Lincoln localities are listed below. In the 

 table following are indicated the species common to either of these 

 localities and the Agasoma gravidum beds of Contra Costa County and 

 the San Lorenzo of Santa Cruz County. 



is Dall, W. H., Trans. Wagner Free Inst. Sci., vol. 3, pt. 6, p. 1253, pi. 36, 

 fig. 32, pi. 43, fig. 15, 1903; Washburne, C. W., Reconnaissance of the geology 

 and oil prospects of Northwestern Oregon, U. S. G. S. Bull., no. 596, p. 31, 1914. 



is Weaver, C. E., A preliminary report on the Tertiary palaeontology of* 

 Western Washington, Washington Geol. Surv. Bull., no. 15, pp. 15-16, 1912. 



