NEOCENE STRATIGRAPHY. 363: 



Another argument of little value, but suggestive, is the 

 possible contemporane'ity of the basaltic outflow near the 

 top of the Miocene in the Santa Cruz Mountains with 

 some of the volcanic outflows in the northern and eastern 

 part of f'he State. Several of the Pliocene vertebrates 

 are described as from under the lava. 



There seems to be some ground, therefore, for suspect- 

 ing that many, if not all, of these tropical vertebrates 

 may ultimately prove to be of Miocene age. 



RELATIONS BETWEEN LIVING AND TERTIARY FAUNAS. 



Notwithstanding all the evidence of repeated earth 

 movements and climatic changes, molluscan forms have 

 been ver}^ persistent in the California Tertiary and Quat- 

 ernary. In Dr. Cooper's list of California fossils of 

 1888, thirty-two species are quoted as running from the 

 Miocene to the present, and the determinations of this 

 paper have largely increased that number by making 

 many species Miocene which had previously been thought 

 to go back not farther than the Pliocene. In the same list 

 118 species are reported from the Pliocene to the present; 

 this also would be largely increased by recent data. 

 From the same source 331 are quoted as found in the 

 Quaternary and living. 



If to these figures be added the species which range 

 from the Miocene to the Pliocene or to the Quaternary 

 and those ranging from the Pliocene through the Quater- 

 nary, it will be evident that the dividing of the Tertiary 

 and post-Tertiary strata into zones or minor groups will 

 be a difficult, if not impossible, work from the paleon- 

 tological standpoint. It is probably that fact more than 

 any other that has kept the Tertiary stratigraphy so long 

 in confusion. 



Changes in sfecies. — One of the most interesting fea- 



