1913] 



Louderback: The Monterey Series 



233 



As reviewed in the preceding part of this paper, it occupies 

 considerable areas in the territory commencing about Point Arena 

 (Lat. 39° N.), embracing the Coast Range region from the ocean 

 to the San Joaquin Valley southward to the Tehachapi Moun- 

 tains and beyond in Ventura, Los Angeles, and Orange counties, 

 and the channel islands (about Lat. 33° N.) ; and extending 

 eastward across the Great Valley into the foothills of the Sierra 

 Nevada from the Tehachapi region north to the vicinity of Deer 

 Creek, a few miles south of Porterville. 83 



Progress of Sedimentation. — The Monterey series represents 

 an invasion of the sea from the west or southwest with a 

 gradual and progressive subsidence, the advancing shore line 

 being marked almost everywhere by sands, often gravels, gen- 

 erally well supplied with a characteristic littoral fauna. 84 With 

 the progress of the subsidence and migration of the shore line 

 inward, the character of sedimentation at any one point grad- 

 ually changed — naturally in some places more rapidly than 

 others, depending on the character of the shores and whether 

 near larger or smaller stream months. It first became finer and 

 assumed the form of terrigenous muds, then showed more and 

 more admixture of organic material. The organic material was 

 commonly at first preponderatingly calcareous (limestone and 

 calcareous shale), but ultimately siliceous, and wherever any 

 territory became far enough removed from the areas of terrig- 

 enous sedimentation the material became entirely organic (fre- 

 quently more or less admixed with pyroclastic material) and in 

 time produced those pure diatomaceous earths and shales for 

 which the Monterey series is famous. 



In some localities areas are found where the first sediments 

 deposited on the older rocks were earthy shale or of organic 

 origin. These may in part be explained as hills, mesas, ridges 

 or other areas of higher ground, particularly if rather fiat sur- 

 faced, which while the main shore line was migrating past them 

 were comparatively small islands or peninsulas, and which later 



83 See Anderson's map. — Proc. Cal. Acad. Sci., 4th Ser., vol. Ill (1911), 

 Plate III, opp. p. 126. 



8-> Tabulated by Smith in Proc. Cal. Acad. Sci., 4th Ser., vol. Ill, pp. 

 161-182 (1912), as "Lower Miocene Fauna" — the fauna of Merriam's 

 Ajrasoma zone. 



