1913] 



Louderbdck: The Monterey Series 



2:^ 



gradually narrowing — a gulf-like embayment representing in a 

 general way the deepest and most detritus-free portions of the 

 Monterey epicontinental sea during its period of maximum land- 

 ward extension. 87 



As we approach the ultimate shore line, in the San Joaquin 

 Valley environs, and against the projecting mountain masses 

 along the coast, the terrigenous sediments predominate, some- 

 times to the complete absence of the siliceous shales. 



Depositional Oscillation. — The change from coarse to fine 

 terrigenous sediments and then to non-terrigenous was not every- 

 where an unbroken progression. It is most simply developed 

 in the Monterey-San Luis-Santa Barbara region along the present 

 coastal area and in its immediate interior over towards the 

 McKittrick and Temblor range region. Many localities show 

 oscillations from sands or clays to siliceous ooze and back again 

 to sands or clays. These areas are particularly those near per- 

 manent or long enduring land masses of Monterey time. They 

 may indicate an oscillatory movement of subsidence, by which 

 small retrogressive stages occurred at intervals during the general 

 movement of depression — a type of action for which we have 

 evidence at other times and places; or they may be the result 

 of climatic changes, greater volumes of sediment being discharged 



87 Professor J. C. Branner at the recent meeting of the Cordilleran 

 Section of the Geological Society of America put forward an ingenious 

 theory to account for the great thicknesses of cuatomaceous earths in the 

 Monterey. He considered that the diatoms, naturally thriving in cold 

 water, were floated along by the "marine currents that flowed southward 

 from Alaska." — "Once within the zone of islands" (of the Coast Range 

 archipelago) "these floating materials were probably driven into the 

 cul-de-sac at the lower or southern end of the present San Joaquin Valley. 

 Materials carried at or near the surface of the water could not escape, 

 if, as is assumed, the embayment was fairly well closed at the extreme 

 southern end. It is exactly here, and around the southwestern corner of 

 the San Joaquin Valley, that the deposits of diatom skeletons are thick- 

 est." (To be published Bull. Geol. Soc. Amer., vol. 24.) It is quite 

 probable that the marine currents had an influence on the life and dis- 

 tribution of the diatoms, but the distribution of thickest diatomaceous 

 deposits as outlined by the writer in describing the California gulf of 

 Monterey time seems to be entirely accounted for by its relations to the 

 ultimate' shore line and to the border of thick terrigenous sediments to 

 its northeast, east, and southeast (the limits of Anderson's Temblor 

 basin). Furthermore, these thickest diatomaceous deposits extend to the 

 coast of the open ocean in the San Luis-Santa Maria-Lompoc region, and 

 even the thinner deposits to the north (and south as well) can likewise 

 often be brought into definite relationship with recognizable shore 

 features which determined depth of water and sediment supply. 



