Clark: The San Lorenzo Series of Middle California 53 



PAGE 



Family Turbinolidae - 193 



Genus Throchocyathus 193 



Throehoeyathus sp. indt - 193 



Family Eupsammidae — - 194 



Genus Dendrophyllia — 194 



Dendrophyllia calif orniana Nomlaud 194 



Family Fungidae 194 



Genus Siderastrea 194 



Siderastrea clarki Nomland 194 



Subkingdom Arthropoda - 194 



Class Crustacea - 194 



Superorder Cirripedia 194 



Genus Balanus 194 



Balanus sp 194 



INTRODUCTION 



Only within the last few years have West Coast geologists and 

 palaeontologists begun to realize that there are certain beds in the 

 Coast Ranges of California and farther to the north, the position of 

 which is between the Tejon (Upper Eocene) and the Monterey (Lower 

 Miocene), which contain a fauna distinct from that of either of these 

 horizons. This intermediate fauna has usually been included with 

 that of the Lower Miocene. In 1895 W. H. Dall 1 expressed his belief 

 that a portion of the Tertiary section of Oregon was Oligocene in age. 

 and in several papers published later, which are referred to in the 

 historical review, he reiterates this belief. The discovery of this 

 intermediate horizon in California is due to the work of Dr. Ralph 

 Arnold. 2 In 1906, he described the San Lorenzo formation, the out- 

 crops of which occur in the Santa Cruz Mountains near the town of 

 Boulder. These beds were found to be beneath beds containing a 

 typical Lower Miocene fauna. In the paper, containing the first 

 announcement of this discovery, we find the following statement : 



Within the last five years strata have been discovered in the Santa Cruz Quad- 

 rangle ■which contain a fauna representing a horizon probably lower than any 

 of the known Lower Miocene horizons of California. The faunal relations and 

 stratigraphic position of this new formation have led the writer to believe that 

 it belongs to the Oligocene. 



1 Dall, W. H., in Diller, J. S., A geological reconnaissance of northwestern 

 Oregon, 17th Ann. Eep., U. S. Geol. Surv., pt. 2, p. 404, 1895. 



2 Arnold, Ralph, The Tertiary and Quaternary pectens of California, II. S. Geol. 

 Surv., Prof, paper no. 47, p. 16, 1906. 



