536 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



dications of its presence in any other portion of the area 

 occur on the surface, but one of the characteristic products 

 from the shale phase of this group — petroleum — may have 

 been supplied to the overlying sands in the Sonoma group. 

 Eastward in Carneros Creek, beyond the area under discus- 

 sion, rocks of this age are again found. It seems probable 

 that this formation was once continuous over the area be- 

 tween Sonoma Mountain and Tomales Bay, but was eroded 

 during Upper Miocene and the interval between Miocene and 

 Pliocene time. A formation of Upper Miocene age, here de- 

 scribed as the Petaluma formation consists chiefly of lacu- 

 strine deposits, and indicates that the upper Miocene Sea 

 which occupied the present site of San Pablo Bay Region 

 did not extend in this region to the northwest. The Merced 

 group of Pliocene age and its correlative, the Sonoma group, 

 are well exemplified in this region and their stratigraphic 

 and faunal relations are clearly demonstrated. Two interest- 

 ing formations of marine Pleistocene were differentiated on 

 the eastern shores of Tomales Bay. Such, in brief are the 

 formations recognized within this field. 



Limestone of Mesozoic or Paleozoic Age 



An area of coarse-grained marble occurs in connection 

 with the granitic rocks of the Point Reyes Peninsula on the 

 eastern slope of Inverness Ridge. This marble which was 

 carefully studied by F. M. Anderson is very similar to the 

 "Santa Cruz limestone" of the Santa Cruz Mountains and 

 that of Montara Mountain. The geologic relations are the 

 same in all three cases. The limestone mass was intruded 

 by the granitic magma and those portions of the batholithic 

 roof which dropped into the melting pot were preserved for 

 our inspection. Granitic rocks largely surround the Inverness 

 Ridge limestone area. 



Granitic Rocks of Probable Mesozoic Age 



The granitic rocks of this region are restricted to the 

 Point Reyes Triangle and are not found on the eastern side 

 of Tomales Bay, as Anderson pointed out in his paper de- 

 scribing this area. Anderson's" description in part is as 



14 Anderson, F. M., The Geology of Point Reyes Peninsula, Univ. Calif. Publ., Bull. 

 Dept. Geol., vol. 2, No. S, p. 124, 1903. 



