334 The American Naturalist. [April, 
in 1855, there has been much debate over the determination of the age 
of the series. They were thought at one time to constitute transition 
beds between the Cretaceous and Eocene. After a critical study of the 
faunal relations of the series in question, Prof. T. W. Stanton arrives at 
the following conclusions : 
“1. In all known sections that contain both Chico and Tejon the 
strata are apparently conformable. So far as it goes, this is an indica- 
tion of continuous sedimentation ; but without further evidence it can- 
not be accepted as proof that there is no break, nor should it be given 
greater weight than the clear unconformability between Tejon and 
older Cretaceous beds in Oregon. 
“2. The Martinez group of the California Survey is not a simple 
formation that can be considered a mere subdivision of the Chico, but 
consists of two distinct portions, one of which is Cretaceous and insepara- 
ble from the Chico, while the other is Eocene, and is here classed as 
Lower Tejon. 
“3. The ‘intermediate beds,’ supposed by Gabb to form a transition 
from the Chico to the Tejon, are the same as the upper part of the 
Martinez group and the Lower Tejon. Their fauna, so far as known, 
includes no distinctively Mesozoic elements. 
“4, The Chico fauna is characteristically Cretaceous, its so-called 
‘Tertiary types’ being persistent or modern types that have changed 
but little from the Cretaceous to the present day. 
“5, An examination of the species supposed to occur in both the 
Chico and the Tejon reduces their number to not more than six, and 
with one exception those are all persistent types that cannot be classed 
as Mesozoic. The exception is Ammonites jugalis, which Gabb collected 
from two localities supposed to be Tejon in the Mount Diablo region, 
but it has not been rediscovered in any subsequent Tejon collections. 
The Ammonoid seen by Heilprin in the Gabb collection from Fort 
Tejon may or may not be this species. It is held that the Tejon fauna 
is essentially Eocene and very distinct from the Chico, even though this 
ammonite should prove to belong to it. 
“6. The time interval indicated by the decided change in faunas 
from the Chico to the Tejon cannot now be estimated. In fact, there is 
little evidence that the latter fauna is derived from the earlier, except- 
ing in a few species; and it is possible that all the changes took place 
by extinction and migration of species during the period in which the 
barren beds between the latest Chico and the earliest Tejon fossiliferous 
horizons were laid down. It will not be surprising, however, if evidence 
is sometime found of a period of erosion at the close of the Cretaceous 
