Vol. XI] DICKERSOX—PT. REYES AND SANTA ROSA QUADRANGLES 539 



solved by considering the distribution of the groups in th.2 

 o-eneral field. Mr. Anderson's description is as follows : 



Miocene Sediments.— The Miocene series consists of three members, 

 the upper two of which are not distinctly separated. The lower member 

 is a dark heavy, conglomerate, in which the pebbles and stones range 

 from one-half inch to more than one foot in diameter. The second 

 member is a thin-bedded, cream-colored sandstone that passes quite 

 gradually into the upper member, the special features of which will be 

 described later. It is the white Miocene shale of the Monterey series 

 well known in the Coast Ranges. This series is essentially similar at all 

 the points at which a complete section is to be seen. At the summit ot 

 Whittenberg Hill a series of the Miocene sediments, some hundreds ot 

 feet in thickness, have conglomeratic beds at their base, with a thickness 

 of eight or ten feet, containing pebbles of granitic and crystalline lime- 



stone. 



Concerning the shales of Whittenberg Hill, Anderson re- 

 marks that 



Nothing of great importance has been discovered on the 

 peninsula, not already known from other regions, and their petrography 

 would be merely a repetition of what has been said before. In .texture 

 they vary from a tolerably granular, sandy phase to what might be 

 called flinty. In Bear Valley and west of Whittenberg Hill, the compact, 

 somewhat vitreous and banded phase is more frequent, though this 

 appears to be an areal rather than a stratigraphical variation Such 

 portions of the shale are both less porous and less bituminous than the 

 more granular portions. West of Drake's Estero the shales are sandy 

 and the amount of bituminous matter is very much greater than in the 

 more compact portions. This is commonly seen in the fetid character 

 of the water rising from them. 



Rocks of this group are not found in the mainland portion 

 of this area. In the region west of Petaluma it is probable 

 that these rocks were totally removed during the erosion in- 

 terval at the close of the Miocene or early Pliocene as the 

 marine Merced rests directly upon the Franciscan in this vi- 

 cinity. 



It seems entirely probable that rocks of this group once 

 extended over this area as its characteristic shales and sand- 

 stones are well exposed in the headwaters of Carneros Creek 

 in the Napa Quadrangle about 20 miles east of Petaluma. At 

 this place affair fauna representing the Area montereyana 

 zone has been obtained. This group may underlie a portion 

 of Sonoma Mountain as a product which is yielded by its 

 shales petroleum — is found in a sandstone which is a mem- 

 ber of the Sonoma group. A fault of moderate throw has 

 exposed this sandstone and underlying and overlying basalt 

 in a creek bed about 5 miles northeast of Petaluma, one- 



