STOOD HES IN THE NEOCENE OF CALIFORNIA. 445 
In the area near Stanford University the percentage is still 
lower; out of twenty-five species found only 44 per cent. belong 
to the living fauna. 
On Seven Mile Beach the great detenece “of strata gives a 
good opportunity for the study of faunal changes. Thus the 
large Pectens are. limited to the bottom of the series. Of the 
forms obtained on Seven Mile Beach, Weptunea tabulata, Calyptrea 
jfilosa and Crepidula prerupta occur only at the bottom of the 
section. Crepidula grandis, Arca microdonta, Cardium meekianum, 
Saxidomus gibbosus, Mactra (not V enus) pajaroensis and Scutella 
enterlineata disappear at different horizons in about the order 
named, and are replaced in the uppermost layers by living forms. 
Thus, for example, the living Achinarachnius excentricus replaces 
Scutella interlineata; Cardium corbis replaces C. meekianum from 
which it probably descended. 
Of the forms collected on Seven Mile Beach, not including 
the uppermost beds, thirty-two species have been identified. Of 
these nine are not known to be living, and five are found only in 
some other district. Out of thirty-two species in the fossil fauna 
this gives eighteen, or 57 per cent., in the present fauna of the 
same region. The character of the fauna is noticeably southern. 
The suggestion has been made that the top of the Merced 
Series on Seven Mile Beach extends into the Pleistocene, the 
fossiliferous strata above what has been called the ‘upper 
gasteropod bed” especially having a Pleistocene aspect, as all 
the forms found in these are still living on the coast. The 
whole fauna, including the “upper gasteropod bed,” gave 81 
per cent. of the fossil fauna living in that region. 
Not only does the fauna suggest that these upper beds might 
be considered by themselves, but the structural relations to the 
lower beds is just obscure enough to prevent a positive assertion 
that they are conformable. The first writers on the subject 
regarded them as conformable. 
Dynamic movements during the Tertiary — At the beginning of 
the Tertiary all the region about the Bay of San Francisco seems 
to have been slowly sinking and steadily receiving sediment. 
