Vor. III] ANDERSON—FURTHER STRATIGRAPHIC STUDY 5 
Geo. H. Eldridge and Arnold’ have also described beds of 
transitional character, presumably Oligocene, as occurring in 
the Coast ranges of Ventura county, California. Eldridge 
and Watts’ had considered this series, known as the Sespe 
formation, to be of Eocene age; but as Arnold found Miocene 
fossils in its fauna, it has been provisionally referred to the 
Oligocene. 
It appears, therefore, that below the Miocene, and occupy- 
ing an intermediate position between it and the Eocene, there 
occur in Washington, Oregon, and California, marine beds 
that have been provisionally referred to the Oligocene, and 
that appear to be conformably related to the Eocene deposits, 
but from which the Miocene is more or less separated by 
either a stratigraphic or a faunal break. In the following 
pages illustrations will be found in which similar relations 
appear, but in which the strata involved have not yet been 
proved to be of the Oligocene age. 
It is the purpose of this second paper to present results 
that have been attained since the publication of the first, to 
amend it where necessary, and to supplement it by the addi- 
tion of such new facts as have been gathered in the more 
extended study of the field. Furthermore, as the former 
paper has become all but inaccessible through the total destruc- 
tion of the reserve stock of the publications of the California 
Academy of Sciences, it is thought worth while to embody 
its results, in an abbreviated and improved form, in a second 
publication. 
It is not intended that this paper shall be complete either 
in its scope or in its treatment of the subject, but that it shall, 
at least, be suggestive of some of the many interesting fea- 
tures of the field, and of the various phases of geological study 
that find here abundant and excellent illustration. 
One of the important factors to be considered and worked 
out in a stratigraphic study of any region is that of the condi- 
tions of deposition—that is, the physical geography of the 
time and the various influences that may have affected the 
1U. S. Geol. Surv. Bull. 309, pp. 7-12. 
2 Calif. State Min. Bur. Bull. 11, pp. 25-26. 
