Clark: The San Lorenzo Series of Middle California 99 



Percentage of determinable species common to the San Lorenzo of the 



Santa Cruz Mountains 11.6 



Number of species common to the Oligocene of Oregon and Washington 45 

 Percentage of determinable species common to the Oligocene of Oregon 



and Washington 40 



Review of Occurrence op Beds Referable to the San Lorenzo 



Series at Other Localities in California 



SAN LORENZO BEDS IN NAPA COUNTY 



The collections of the University of California summer field class 

 of 1915, which was held in Napa County under the leadership of 

 R. E. Dickerson, show the presence of the Agasoma gravidum fauna 

 in beds to the east of Carnaros Creek, a few miles to the west of 

 the town of Napa. 03 The fauna is confined to beds not much more 

 than a hundred feet in thickness, consisting for the most part of a 

 medium-fine, gray sandstone. They rest, according to Dickerson, 

 upon the Knoxville (Lower Cretaceous), and are overlain by beds 

 containing the fauna of the Area montereyana zone. The contact 

 with this latter horizon is obscure on account of poor exposures. 



KEEYENHAGEN SHALE OF COALINGA DISTRICT AND TO NORTH 



Reference has already been made in the historical review 70 to the 

 Kreyenhagen shale, originally referred to the Eocene but now known 

 to be of Oligocene age, containing such characteristic species as Macro- 

 callista pittsburgensis, Leda lincolnensis, and Fusinus (Exilia) lincoln- 

 ensis. The Kreyenhagen shales in the Coalinga district and to the 

 north lie unconformably below the Vaqueros. The following state- 

 ment, concerning the stratigraphic relationships of these shales, is 

 made by Robert Anderson and Robert W. Pack in their paper entitled 

 "The geology and oil resources of the San Joaquin Valley north of 

 Coalinga, California": 



The Kreyenhagen shale is believed to rest unconformably on the Tejon through- 

 out the region, with the possible exception of the area between Gargas and 

 Puerto creeks. . . . Its relation to the overlying formation is more clearly shown 

 than its relation to the underlying one, and possibly, except at Gargas and Crow 

 creeks, where its relation to the beds mapped as undifferentiated Miocene is not 

 certainly one of unconformity, the Kreyenhagen shale is unquestionably overlain 



09 See Napa, U. S. Geol. Surv. Topographic Sheet. 

 i° See page 63. 



« Anderson, Robert, and Pack, R. W., U. S. Geol. Surv., Bull. 603, pp. 75-76, 

 1915. 



