Vol. 4] Osmont. — Geological Section of Coast Ranges. 



quartz ; some 200 feet of sandy shales, usually yellow to buff in 

 color, but sometimes variegated and interbedded with thin layers 

 of Franciscan pebbles ; and about 150 feet of massive yellow sand- 

 stone, sometimes firm, though usually soft, and containing layers 

 and nodules of hard, dark gray limestone. These strata are lying 

 almost horizontal in this vicinity, but farther east they dip gently 

 to the northeast. At Freestone they are overlain conformably by 

 the Sonoma tuff, which will be shown below to belong to the later 

 Pliocene. Badly preserved marine shells, and two large indeter- 

 minate vertebrae were found in them. 



Near the mouth of the Estero San Antonio, about three miles 

 west of Valley Ford, is a good cliff-section in these sandstones 

 which is fossiliferous. In this vicinity the writer found the fol- 

 lowing species : 



Pectcn caurinus Gould. 



Natiea sp. 



Leda sp. 



Machaera patula Dixon. 

 Solcn sp. 



Neptunea recurva Gate. 



Crepidula grandis Midd. 



dementia subdiaphana Carpt. 

 Pre-Volcanic Beds at Trenton. — At Trenton a well sunk 

 through the Sonoma Tuff into the sandstones beneath encoun- 

 tered a shell bed, but the only specimens procurable by the writer 

 were casts, and indeterminable, though of a Merced appearance. 



Pre-Volcanic Beds of Pleasant and Capay Valleys. — The 

 strata along the Sacramento Valley slope of the range overlying 

 the Cretaceous resemble very closely in character those above 

 described. They consist of heavy bedded soft yellow to buff 

 colored sandstones, soft pinkish to white fissile shales, and non- 

 volcanic conglomerates made up of pebbles of Franciscan and 

 Knoxville rocks. The principal difference is the frequent coarse 

 character of the conglomerate, some of which is made up of peb- 

 bles six inches in diameter, and the inclusion of large angular 

 boulders of Cretaceous sandstone. At Pleasant Valley the So- 

 noma Tuff of the later Pliocene overlies these sandstones, being 

 conformable in dip, and in the same relation to them as at Free- 

 stone. 



