184 CALIFORNIA ACADEMY OF SCIENCES [Proc. 30 Ser. 



specific discrimination to maintain this generally, as several 

 forms of each occur at intervals from the early Miocene to 

 the Present. Pseudocardimn gabbi of the Pliocene resembles 

 Midiiiia densata, occurring in both the Upper and Lower 

 Miocene, and in like manner closely allied species of Saitella 

 and Astrodopsis occur in both the earl}- Miocene and the 

 San Pablo. 



There is evidence of nonconformity between the rocks of 

 all of the successive periodic series, and in some cases 

 between the different members of the same series. The 

 nonconformity between the Chico and Eocene is well shown 

 by a detailed study of the field north of Alcalde Creek. 

 The nonconformity is both stratigraphic and faunal, but the 

 evidence of either class becomes more convincing only as it 

 becomes better known. In the case of the Eocene and Mio- 

 cene nonconformity the evidence is also both faunal and 

 stratigraphic, the latter appearing more satisfactory from the 

 fact that the Lower Miocene rests in turn upon the Eocene, 

 the Cretaceous, and the Franciscan rocks. 



The relations of the Pliocene (Etchegoin) formation to 

 the earlier ones has been shown in the preceding pages and 

 on the map of the Coalinga district (PI. xxxv), but the evi- 

 dence shown there is only partial. 



What evidence the field might afford as to the relation of 

 the Etchegoin to later rocks has not been ascertained, beyond 

 the fact of a transition from marine to fresh-water conditions. 

 It is conceivable that such a transition might be effected so 

 gradually by normal causes that no stratigraphic noncon- 

 formity would exist, but such a transition in this case requires 

 to be shown. In the Berkeley Hills the Orindan Formation 

 rests unconformably upon the Monterey Shales, and their 

 basal portion is pebbly conglomerate. If the Tulare Beds 

 are to be correlated with the Orindan, the individuality in 

 each case would be the same. 



There is, however, a stratigraphic member still to be con- 

 sidered, whose exact relationship is less evident, though 

 probably not so difficult as it might appear. This remark 

 concerns the Coalinga Beds. They have been followed 



