Vor. IIT] SMITH—MIOCENE FOSSILS OF CALIFORNIA 163 
Coast, but also the extinction of many of the older Miocene 
types, and the introduction of new forms, many of which have 
survived until the present time. This brings us back almost 
to the standpoint of Lawson and Merriam, who have proposed 
to call all the lower Miocene ‘Monterey,’ and all the upper 
Miocene “San Pablo.” 
The beds containing the Vaqueros, Temblor, and Monterey 
faunas were uplifted and somewhat hardened in the Coast 
Range uplift; and on the eroded flanks of this range were laid 
down the younger Miocene strata containing the Santa Mar- 
garita, San Pablo, and Etchegoin faunas. They too have 
been upturned by later disturbances, but not hardened to such 
a degree as were the older beds. 
The fossils in these later Miocene beds not only have a much 
more recent appearance than those of the lower Miocene, but 
also the number of species still living is much greater among 
them. The number of these living species increases gradually 
as the top of the Miocene is approached, and the faunas grade 
over imperceptibly into the Pliocene. There is no natural 
boundary between Miocene and Pliocene in California, and the 
line is drawn between the Etchegoin and Purisima as a matter 
of convenience. In fact the two faunas overlap; and the forma- 
tions may well do so. The Etchegoin has been called the Plio- 
cene by F. M. Anderson, and upper Miocene by Arnold. The 
overlying Purisima has been called transitional by Ashley, 
Pliocene by Arnold, and upper Miocene by Dall. And since 
all these writers had good reasons for their opinions, it is safe 
to conclude that the line between Miocene and Pliocene should 
be drawn somewhere near the boundary line between the two 
formations. 
One of the most striking characteristics of the Tertiary of 
California is the orderly advance toward modern life, with a 
constantly increasing number of modern species, and a con- 
stantly increasing number of species closely allied to recent 
forms. Step by step each succeeding fauna becomes more like 
the present life of the California coast than the preceding. 
This gradual change finds its explanation in the physiography 
of the region. All through the Tertiary the coast line of Cali- 
fornia was nearly the same as at present; for while the orogenic 
