Vol. XI] DICKERSON—PT. REYES AND SANTA ROSA QUADRANGLES 559 



belong to the Hipparion group and probably represent closely 

 related forms. Recently, Dr. Chester Stock secured a verte- 

 brate fauna from sandstone beds just above the upper tuff 

 member of the Pinole formation and conformable with this 

 tuff, and the assemblage of mammalian types is apparently an 

 Orinda fauna. The Pinole Tuff-Orinda strata in the Pinole 

 syncline are very closely connected areally with tuff beds of 

 the Sonoma group north of Carquinez Straits. Since the 

 volume of tuff diminishes gradually as one travels from Napa 

 toward the south it is suggested strongly that the volcanic ash 

 and pumice came from a northerly direction. The thickness 

 of the Pinole tuff is much less than the tuff beds around Napa. 

 While this is not conclusive evidence, as Carquinez Strait 

 intervenes, it fits in with evidence derived from the study of 

 the vertebrate faunas. 



In brief then, the Merced has been shown to be the equiva- 

 lent of the Sonoma group through stratigraphic and areal re- 

 lations. The Sonoma group in turn is areally connected with 

 the Pinole tuff and the Orinda formation of the Berkeley 

 Hills and by means of Neohipparion gidleyi, its close faunal 

 relationship is shown. The fauna of the (Jacalitos) Lower 

 Etchegoin is related to that obtained from the Neohipparion 

 gidleyi beds of the Sonoma group. 



MlLLERTON AND ToMALES FORMATIONS 



One of the interesting results of the work in the region of 

 Tomales Bay was the discovery of a Pleistocene fauna in the 

 Millerton formation which indicated a climatic condition sim- 

 ilar to that of San Diego today. Two or three excellent 

 collecting localities were found in the headlands on the north- 

 east side of Tomales Bay. A small but distinctive Pleistocene 

 fauna of the same type was found in terrace deposits overlying 

 the Millerton formation of Lower or Middle Pleistocene age. 

 The beds containing this fauna will be referred to as the 

 Tomales formation, owing to their occurrence also on the 

 northeastern side of Tomales Bay. 



The type locality of the Millerton formation is in the head- 

 land near Millerton Station, northeast of Inverness on 

 Tomales Bay. On the west side of this headland, the beds 

 here exposed have a strike of north and south and a dip of 



