36 CALIFORNIA ACADEMY OF SCIENCES [Proc. 47H Ser. 
strata of all of the successive periodic series, and in some cases 
between different members of the same series. 
The unconformity between the Chico and the Eocene is both 
stratigraphic and faunal when taken throughout their extent, 
though locally there is often some resemblance between them. 
But their relations have already been sufficiently well shown. 
If Oligocene strata are conceded for the Pacific coast, and 
especially in the formations of the California Coast ranges, 
then either they should occur in the Mount Diablo range, or 
their absence should add emphasis to the unconformity between 
strata of the Eocene and the Miocene. If, however, the 
Temblor beds are regarded as the lowermost Miocene, the 
evidence of an unconformity between them and the next older 
strata is significant, and it is clear that the change from one 
to the other is too abrupt to be called transitional. The strata 
immediately preceding the Temblor, however, while they are 
stratigraphically related to the Eocene in the central part of 
the range, are faunally and even lithologically like the middle 
Miocene in other parts of the Coast. 
Probably the most noticeable interruption in the sedimen- 
tation of the Tertiary is that of the later Miocene—an inter- 
ruption which intervened between the Monterey and the 
Coalinga epochs. The evidence of this unconformity is not 
of the nature of denudation so much as of abrupt change of 
sedimentation and fauna. This change is conspicuous through- 
out the range, and in the vicinity of Midway and Sunset shows 
in the heavy conglomerates, and between Coalinga and New 
Idria in the thick beds of huge oysters, pectens, and barnacles. 
The stratigraphic relations of the Coalinga beds with the 
succeeding series is not so clear, though evidence is not lack- 
ing of some sort of change in the physical geography of the 
time. In some few places an angular divergence between the 
Coalinga beds and the Etchegoin has been observed, though 
this is not the rule. Whatever this change may have been, it 
was quite sufficient to inaugurate a considerable change of 
fauna and, on the whole, a noticeable introduction of more 
recent or modern forms. ‘Two epochs, one marine and the 
other lacustrine, are postulated for the Pliocene; and while 
