162 CALIFORNIA ACADEMY OF SCIENCES _ [Proc. 47H Ser. 
FAUNAL ZONES IN THE MIOCENE OF CALIFORNIA. 
When Conrad described the Tertiary fossils of California in 
the Reports of the Pacific Railroad Survey, he assigned some 
species to the Miocene on account of a vague resemblance to 
Miocene species from Virginia and Maryland; but he had no 
positive criterion for distinguishing the various faunas. When, 
in 1868, Gabb wrote his monograph on the Tertiary of Cali- 
fornia, he, too, had little opportunity of distinguishing the sep- 
arate faunas that make up the beautiful succession, as we know 
it, on the West Coast. Where the rock beds were much dis- 
turbed and hardened, he called them Miocene; and where they 
were little disturbed, and not lithified to any extent, he called 
them Pliocene. This criterion was usually right, but not 
always; for there are Miocene beds in California that are 
unconsolidated, and Pliocene beds that are turned up on edge 
and hardened into real rocks. In fact, the principal disturb- 
ance in the Tertiary beds of the Coast Ranges came in the 
mountain-making epoch at the end of Monterey, in the middle 
Miocene time, and, after this, several thousand feet of sand- 
stones were laid down still containing Miocene fossils in 
abundance. 
Later writers—Fairbanks, F. M. Anderson, Merriam, Law- 
son, and Arnold—have introduced a much more elaborate 
classification of the Neocene of California, and a large number 
of formation-names. But these so-called formations, however 
useful they may be for areal mapping and for economic geol- 
ogy, do not always correspond to the faunal divisions. Some 
of them are merely different facies of the same thing. The 
formations have been subdivided much more minutely than the 
faunas warrant. 
Instead of the numerous subdivisions recognized by most 
stratigraphers, there are, in fact, only two major faunal units in 
the Miocene of California: a lower, including all the faunas 
up through the Monterey; and an upper, including the San 
Pablo, Santa Margarita, and Etchegoin faunas. The division 
line between them corresponds to the period of orogenic activ- 
ity that came on at the end of the Monterey epoch. This 
marks not only a great change in the physiography of the West 
