PROG. CAL. ACAD. SCI., 4th Series, Vol. XI 



DICKERSON] Plate 28 





Fig. 1. Basalt in foreground; Merced cap on top of Spring Hill, three-quarters of a 

 mile west of Marin School, Petaluma Quadrangle. The basalt in turn rests upon Fran- 

 ciscan rocks. ,» 



Fig. 2. Tuffaceous Merced resting on basalt, corner Stanley and Howard Sts., Petaluma. 



