UNIVERSITY OF CALIFORNIA 

 Bulletin of the Department of Geology 



Vol. 2, No. 4, pp. 109-118 ANDREW C. LAWSON, Editor 



THE DISTRIBUTION OF THE NEOCENE SEA-URCHINS 



OF 



MIDDLE CALIFORNIA 



AND 



ITS BEARING ON THE CLASSIFICATION OF THE 

 NEOCENE FORMATIONS 



BY 



John C Merriam 

 CONTENTS. 



Introduction 109 



Occurrence and Range of Species no 



The San Pablo Formation and Its Geologic Relations 113 



Faunal and Lithological Characters of San Pablo 113 



Relation of San Pablo to Contra Costa County Miocene 114 



Relation of San Pablo to Merced . 114 



Age of San Pablo 115 



Classification of the Neocene of Middle California 117 



Correlation of the Auriferous Gravels with the Coast Range Neocene 118 



INTRODUCTION. 



Of the numerous invertebrate forms known from the marine 

 Neocene of California there 3.rc none wnicn better aid the geolo- 

 gist in the determination of horizons than the echinoids. Though 

 Neocene molluscan remains are plentiful, they are not always 

 characteristic nor are they usually in a good state of preserva- 

 tion. The sea-urchins, when present at all, are usually abundant 

 and well preserved and, having in most cases a short geological 

 range, are of more than ordinary value in geological work. 



