Vol. IV] ANDERSON AND MARTIN— NEOCENE RECORD 17 



Introduction 



The Question of the Monterey. — For more than the last ten 

 years California geologists have been accustomed to the use 

 of the term Monterey Shales, or Monterey Formation, as desig- 

 nating a somewhat definite formational division of the Cali- 

 fornia Miocene, and as belonging to an equally definite time 

 division of that period. 



While the full discussion of this interesting question can 

 not be undertaken within the limits of the present paper, there 

 are some reflections that may be offered as prefatory to the 

 subject. If the Miocene strata of California are capable of 

 being consistently subdivided, it should be done, for purposes 

 of intensive study and discussion, if for no other particular 

 object. 



The aggregate thickness of the entire Miocene section in 

 California is very great, and the time interval represented is 

 correspondingly long. In many localities in the Coast Ranges 

 the Miocene strata attain or approach a thickness of 7000 feet, 

 and the time required for such a body of strata, largely organic 

 shales, to be deposited is too great to be included in a single 

 time unit if any satisfactory divisions can be found. 



While the Miocene deposits of California have not been 

 extensively studied, they are well known to be locally com- 

 plicated. The exact number and importance of these complica- 

 tions is not yet known. 



Undoubtedly the criteria for the final subdivision of this 

 stratigraphic series should begin with the larger events of its 

 physical history. Faunal changes are, of course, important, 

 but they are more likely to be controlled, or influenced, by the 

 physical events, and are therefore of secondary diagnostic 

 value. Next in importance for such purposes is, perhaps, 

 lithology, and lastly, inference, theory, and scientific imagina- 

 tion. 



In many cases the order of these criteria has undoubtedly 

 been reversed, and lithology and imagination have been given 

 prominence at the expense of the diastrophic record. The 

 varied conditions of environment in which the faunas of the 

 Miocene were developed, the great variety and composition of 

 sediments, and the complicated physical history of the Cali- 



