34 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



throughout the field. In the Mount Diablo Range there are 

 three diastrophic events, perhaps of epochal duration, marked 

 by wide stratigraphic displacement, crumpling of strata, dis- 

 cordance and unconformity. The earlier of these events took 

 place in early Miocene time, and was accompanied by much 

 volcanic activity. As an event in the physical history of the 

 Miocene it serves as a proper basis for the separation of two 

 stratigraphic groups of Miocene strata. The older group, 

 from its occurrence along the eastern flank of the Temblor 

 Range, has been described as the Temblor group, and it is 

 representative of the lower Miocene throughout the Temblor 

 Basin, and probably throughout the entire state. 



The second group of strata is that which is locally well de- 

 veloped in the Temblor Basin, and which may be referred to 

 as the "Monterey formation", as entirely distinct from the 

 Temblor group. This separation is not made upon the basis 

 of lithology, though incidentally for most parts of the basin the 

 group, or "formation" is characterized by siliceous organic 

 shales of a peculiar nature. 



The second diastrophic event is that which resulted in the 

 great discordance and widespread unconformity within the 

 Temblor Basin between the Monterey group and the next suc- 

 ceeding group, which is here called the Santa Margarita. This 

 event is not known to have been accompanied by volcanic 

 outbursts of great importance, but was chiefly characterized 

 by uplift, erosion and subsidence, and by differential warping 

 of the land surface. 



A third diastrophic event divides the record of the later 

 Miocene, and is recorded in the unconformity of the Etchegoin 

 group upon the Santa Margarita, and the wide overlap of the 

 former upon rocks much older than the Miocene. 



Other uplifts of lesser rank have affected the Neocene series 

 in various parts of the Coast, and of this basin, but their full 

 treatment is beyond the limits of this paper. 



The latest Neocene group is partly of freshwater character 

 and partly marine. It is the Merced-Tulare that may in part, 

 or as a whole, be regarded as later than the Orinda formation 

 of the Berkeley Hills. 



Lithologically, there is considerable difference in the com- 

 position of the several groups of Neocene strata herein de- 



