226 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



elusive inferences can be drawn. In well No. 4 of the Midway 

 Consolidated Oil Co., Sec. 4. T. 32 S., R. 23 E., M. D. M., 

 from the lower oil sand at a depth of 3437 feet, a number of 

 good specimens of Echinarachnius gibbsi were obtained. 



On the Buena Vista Hills the surface structure is self-evident 

 and Tulare fossils are to be found in the surface exposures. 

 The underground sections, however, show that the oil sands as 

 a rule exhibit variations and show greater dips, not found on 

 the surface exposures. Also numerous fragments of marine 

 shells are associated with the oil horizon. The fragments seem 

 to be mostly of such forms as Mya japonica, Macoma inquinata 

 and Mulinia densata, though these determinations are perhaps 

 questionable. 



To the south on the Sunset fiats in Sections 25 and 36 of T. 

 12 N.. R. 24 W., and on sections 31 and 32 of T. 12 N.. R. 23 

 W, and Section 5 of T. 11 N., R. 23 W., S. B. M., character- 

 istic Etchegoin fossils have been obtained from the oil horizon. 



In well No. 11, K. T. & O. Co., Section 25, T. 31-22, very 

 characteristic fossils were obtained, including : 



Echinarachnius gibbsi. Solen, species. 



Pecten, species. Ostrea, species. 



Area trilineata. Nassa californica. 



Macoma inquinata. Mulinia densata. 



As in the Buena Vista Hills, so also on and near the surface 

 in the Sunset flats, are found fresh water Tulare fossils. Both 

 forms of Anodonta and some small gastropods were obtained 

 from a small open cut in Section 32, T. 12 N., R. 23 W., S. 

 B. M. 



The data at the present time are not sufficient to say that all 

 the productive zones of the Midway-Sunset field are entirely 

 confined to the Etchegoin. The data are sufficient, however, to 

 place most, if not all, the oil sands below the Tulare and in a 

 marine formation. The fossils found directly above the oil 

 zones and in the oil sands, as obtained from productive wells, 

 are most characteristic of a Lower Etchegoin age. On the 

 surface, however, there are sandstones in the form of lenses 

 found in the Santa Margarita. Traces of oil are found in some 

 of the surface exposures of these lenses and it is possible that 

 wells penetrating similar buried lenses may obtain productive 

 quantities of oil. 



