242 University of California Publications in Geology [Vol. 9 



the Purisima appears to rest conformably upon the Monterey 

 shale and to grade into it ; in other localities a marked litho- 

 logical change marks the contact between the two formations. 



The Purisima Formation is composed chiefly of sandstone. 

 Whitish diatomaceous shales occur in some localities but they are 

 relatively of small extent. The formation as described by Arnold 

 and Haehl can be separated into three lithologic divisions : a 

 lower sandstone, a middle shale, and an upper sandstone. The 

 lower sandstone occurs most prominently along Pescadero Creek 

 east of Jones Gulch and in the vicinity of La Honda. Here it 

 attains a thickness of nearly three thousand feet. Conglomerate 

 and coarse-grained sandstone occur at the base immediately over- 

 lying the Monterey shale. The upper portion of the lower mem- 

 ber consists of soft gray and brown sandstones, occasionally grad- 

 ing into clay. The shale member extends over a wide area south 

 and east of San Gregorio. Its thickness in this locality reaches 

 approximately three thousand feet. In some respects it re- 

 sembles the shales of the Monterey Series, varying from the pure 

 diatomaceous shale to the impure clay shale. The upper sand- 

 stone covers an area approximately four miles in width extending 

 along the coast from Halfmoon Bay to Pescadero Creek. It con- 

 sists of light gray and brownish-gray fine-grained sandstone, usu- 

 ally soft and friable. Occasionally clay shale is interstratified 

 with the fine-grained sandstone. The thickness of the Purisima 

 Formation, as measured along Purisima Creek by Ralph Arnold, 

 was approximately eight hundred feet. 



The Purisima occurring on the east side of the Santa Cruz Moun- 

 tains, southwest of Stanford University, consists of soft quartzose 

 sandstone. Near the base of the section, which is hardly more than 

 three hundred feet in thickness, the beds contain numerous barnacles 

 (Balanus concavus Bronn). The lime from the barnacles has greatly 

 hardened the sandstone, according to Arnold and Haehl, who de- 

 scribed this series. The fauna from these beds appears to represent 

 a lower horizon than the Purisima along the west side of the Santa 

 Cruz Range. 



Fauna. — The Purisima Formation is not extremely fossiliferous, 

 although a few localities have afforded a large number of species. 

 The middle and lower members have yielded only a few species that 

 are determinable, and these are forms which have a comparatively 

 long life-period. 



