Vol. XI] DICKERSON—PT. REYES AND SANTA ROSA QUADRANGLES ^93 



the Millerton and Tomales faunas and floras indicate a cli- 

 mate like that of San Diego at the present day. Elsewhere 

 in the Bay Reg-ion, as on the Santa Cruz coast, the fauna ob- 

 tained from one of the marine terraces flourished under con- 

 ditions similar to that of today. In brief, glacial and inter- 

 glacial epochs appear to be registered by the marine sequence 

 on the Pacific Coast. 



The entire region under discussion was affected by a last 

 general subsidence which gave rise to San Francisco Bay. 

 Drake's Estero and other drowned valleys of all of the 

 streams, as well as the graben of Tomales Bay, evidence this 

 clearly. 



Appendix: Economic Notes 



Manganese and Chrome Deposits 



From time to time various reports of the State Mining 

 Bureau have mentioned the occurrence of Manganese ores 

 and Chrome-iron within this area. One of the Manganese lo- 

 calities is on what was formerly known as the Mailliard 

 Ranch. The Manganese ore occurs five-eights to six-eights 

 of a mile south, 45° west, of Mailliard Ranch-house, near 

 Mailliard Station, on the east side of a small stream which is 

 tributary to San Geronimo Creek, in connection with an out- 

 crop of radiolarian chert. Analyses of samples from this lo- 

 cality indicate that the deposit is too siliceous to work eco- 

 nomically under present conditions. Chrome-iron ore was 

 also reported from this same vicinity, but no deposit has ever 

 been located. The samples obtained were float specimens 

 found within the serpentine areas of this region. 



Limestones 



No workable deposits of limestone suitable for the making 

 of quick-lime were discovered, but a limestone within the 

 Franciscan rocks, which may be suitable as a fertilizer for 

 sour soils, was examined. Mr. Donald G. Martin, assistant 

 farm advisor of Sonoma County, accompanied the writer to 

 this locality, which is three miles south, 20° west, of Peta- 

 luma town, in the northwest quarter of Section 16, Township 

 4 north, 7 west, Mt. Diablo Baseline and Meridian. This 



