1015] 



Clark: Fauna of the San Pablo Group 



395 



STRATIGRAPHIC POSITION AND GENERAL CHARACTER OF 

 THE SAN PABLO GROUP IN, MIDDLE CALIFORNIA 



The best known sections of the San Pablo of Middle California lie 

 to the east of San Francisco Bay. In this general region the forma- 

 tions or groups of formations that are found below the San Pablo, 

 commencing at the bottom of the section, are the Franciscan (Juras- 

 sic), Knoxville (Cretaceous?), Chico (Upper Cretaceous), Martinez 

 (Lower Eocene), Tejon (Upper Eocene), Monterey (Lower Neocene). 

 Above the San Pablo there is usually a group of tuffs and fresh-water 

 formations. The volcanics are generally known as the Pinole Tuff, 

 the fresh-water sedimentaries as the Orindan formation. The Pinole 

 Tuff is not everywhere present, in which case the Orindan formation 

 may lie directly on the San Pablo. These fresh-water beds, as de- 

 termined by Professor J. C. Merriam from the vertebrate remains, are 

 approximately Upper Miocene or Lower Pliocene in age. 



The distribution of the San Pablo Group in Middle California 

 shows that insular or peninsular conditions existed in this region dur- 

 ing San Pablo time. Beds of this group are absent in the hills just 

 to the east of Berkeley and Oakland and on the San Francisco Penin- 

 sula ; these areas were evidently land while the San Pablo deposits 

 were being laid down. The eastern edge of this land mass was 

 probably not more than two or three miles to the east of the cities of 

 Berkeley and Oakland, and the San Pablo Sea extended eastward 

 from here to the neighborhood of Mount Diablo. This last conclusion 

 is arrived at from a study of the San Pablo deposits along the Mount 

 Diablo anticline. 



Professor A. C. Lawson, 17 in referring in one of his papers to the 

 distribution of the San Pablo in the vicinity of Berkeley, makes the 

 following statement : 



These beds of San Pablo are lacking in the Berkeley hills, though well de- 

 veloped on the shore of the Bay of San Francisco a few miles to the north- 

 ward, and it is therefore believed that the San Pablo basin was one lying 

 between insular or peninsular land masses, and that the region of the Berkeley 

 hills was one of the land masses which remained unsubmerged in San Pablo 

 times. 4 



Whether this San Pablo Sea joined the ocean to the northward is 

 not certainly known, but there are good reasons for believing that 



" Lawson, A. C, and Palache, C, The Berkeley Hills, a detail of Coast 

 Bange Geology, Univ. Calif. Publ. Bull. Dept. Geo!., vol 2, no. 12, p. 447, 1902. 



