PART SIX 



GEOLOGIC HISTORY 



OUTSTANDING EPOCHS OF GEOLOGIC HISTORY 



IN SOUTHERN CALIFORNIA 



For the purposes of this paper the geologic time 

 column in California may be divided into two grand 

 divisions. The oldest of these includes all the geologic 

 periods up to the close of the Jurassic, at which time 

 the great intrusion of granitic magmas of the Sierra 

 Nevada took place. This, one might term, the time of 

 the Basement Complex. The second of the grand 

 divisions includes all the periods and epochs since the 

 close of the Jurassic, and may be termed the time of 

 the Superjacent Series. The latter includes the events 

 of the Cretaceous, Tertiary and Quaternary Periods. 

 Only the occurrences of the two last periods of the 

 Superjacent Series — the Tertiary and Quaternary 

 periods need concern us now. 



Events during the time of the formation of the 

 Basement Complex in California, relative to those of 

 the Superjacent Series, are comparable to the relation- 

 ships between the Proterozoic and Paleozic eras in 

 eastern North America. Both of these earlier times 

 were prologues to the succeeding and less obscure 

 ones. The study of the earlier of these subdivis- 

 ions of geologic times includes a consideration of every 

 thing that has made the study of geology a dead 



