PROCEEDINGS 



OF THE 



CALIFORNIA ACADEMY OF SCIENCES 



Fourth Series 



Vol. XI, No. 1, pp. 1-26 JULY 6, 1921 



I 



NOTES ON A FAUNA OF THE VIGO GROUP AND ITS 



BEARING ON THE EVOLUTION OF MARINE 



MOLLUSCAN FAUNAS 



BY 

 ROY E. DICKERSON 



Honorary Curator, Department of Invertebrate Paleontology 



The rate of evolution of a marine invertebrate fauna in the 

 tropics when compared with that of faunas of the temperate 

 zones brings out some interesting results. During the past 

 year, 1919-1920, the writer has had the opportunity and rare 

 good fortune to collect some excellently preserved fossils from 

 the Vigo group of the Philippine Islands incidental to some 

 economic investigations in which he was engaged. After sev- 

 eral years spent in study of the Tertiary faunal problems of the 

 Pacific Coast of North America, the writer naturally had 

 acquired to a certain extent a point of view of the worker in 

 temperate climes. However, many interesting problems in the 

 Eocene of California, Oregon, and Washington suggested that 

 Eocene marine molluscan faunas did not evolve as rapidly as 

 those of the Miocene and Pliocene and that the same "yardstick" 

 in the Tertiary geological time scale could not be applied. Many 

 problems of the Eocene are directly connected with the rate of 

 evolution of a tropical fauna, and, as the Eocene faunas of 

 California, Oregon, and Washington are essentially tropical or 

 sub-tropical, the writer was glad to devote spare time to the 

 study of a tropical fauna. 



July 6, 1921 



