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University of California Publications in Geology [VOL. 8 



Neptunea mucronata Gabb, Xenophora zitteli Weaver, do not range 

 into uppermost Martinez and most of these forms occur frequently 

 enough to be useful within certain limits to determine horizons. 

 Since most of these occur in the basal beds north of Martinez such 

 forms will serve to distinguish between the uppermost Martinez and 

 the Trochocyathus zitteli zone. Thus far, Trochocyathus zitteli 

 (Merriam) is the most useful fossil in the recognition of the middle 

 zone of the Martinez. The middle zone of the type section resembles 

 the middle zone of the area north of Mount Diablo in the ratio of 

 gastropods to pelecypods, which is approximately 4:3. 



The absence of certain species which occur in the basal beds north 

 of Mount Diablo is another noteworthy point. Practically the list 

 cited above in the comparison of the basal and middle zones north 

 of Mount Diablo holds here as well. Such is the evidence for correlat- 

 ing the two Trochocyathus zitteli beds in these two areas. In the 

 opinion of the writer they appear to be of approximately the same age. 



The uppermost or Solen stantoni zone was first described by 

 Weaver, although Merriam previously suggested a faunal difference 

 between the upper and lower beds. Weaver lists the following from 

 this zone : 



UPPER MARTINEZ 



Foraminifera nummuloid 

 Schizaster lecontei Merriam 

 Cancer, sp. 

 Area biloba Weaver 

 Cardita hornii Gabb 

 Cardium cooperi Gabb 

 Cucullaea mathewsonii Gabb 

 Leda gabbi Conrad 

 Modiolus merriami (Weaver) 

 Modiolus ornatus (Gabb) 

 Dentalium cooperi Gabb 

 Dentalium stramineum Gabb 

 Ficopsis angulatus Weaver 

 Heteroterma gabbi Stanton 

 Heteroterma trochoidea Gabb 

 Heteroterma, indet. 

 Megistostoma striata Gabb 

 Cassidaria tuberculata (Gabb) 

 Natica, sp. 

 Perissolax tricarnatus Weaver 



Perissolax blakei Gabb 

 Solen stantoni Weaver 

 Tellina martinezensis Weaver 

 Tellina hornii Gabb 

 Tellina undulifera Gabb 

 Thracia karquinezensis Weaver 

 Ampullina (conf.) striata Gabb 

 Brachysphingus liratus Gabb 

 Bullinula subglobosa Weaver 

 Siphonalia(f), lineata Stanton 

 Architectonica tuberculata Weaver 

 Strepsidura pachecoensis Stanton 

 Tritonium impressum Weaver 

 Tritonium pulchrum Weaver 

 Tritonium eocenicum Weaver 

 Turritella infragranulata Gabb 

 Turritella pachecoensis Stanton 

 Turritella conica Weaver 

 Turris, sp. indet. 

 Urosyca caudata Gabb 



Of these forms Tellina martinezensis, Bullinula subglobosa, Hetero- 

 terma trochoidea, Megistostoma striata(f), Architectonica tuberculata, 



