1918] 



Davis: The Franciscan Sandstone 



7 



urination. A few fossils have been found in the sandstones and 

 shales, but they are exceedingly rare, and those which are found 

 appear to be of unusual types and not identifiable with certainty. 

 Age determination by means of fossils is at present impossible. 

 About the only point upon which all agree, is that the fossils belong 

 to the Mesozoic and cannot be older. 



The stratigraphic relations are not of much value at the present 

 time for the reason, brought out later, that there is still some uncer- 

 tainty as to the exact age of both the overlying and underlying rocks. 



Stratigraphic Relations 

 OVERLYING ROCKS 

 Overlying the Franciscan, is the Knoxville formation, which con- 

 sists principally of dark shales with limestone lentils and concre- 

 tions together with some peculiar greenish sandstones. The Knoxville 

 formation rests with angular unconformity on the rocks of the Fran- 

 ciscan group and numerous sections have been described in the Coast 

 Ranges of California where this unconformable relationship has been 

 clearly demonstrated. 



UNDERLYING ROCKS 



The oldest rocks of the California Coast Ranges are limestones, 

 with some quartzites and schists, intruded by granite. These rocks 

 are exposed at various points through the Coast Ranges. They are 

 seen, for example, at Montara Mountain south of San Francisco, and 

 in the Santa Cruz Mountains north of Santa Cruz, also in the Gavilan 

 and Santa Lucia Ranges in San Benito and Monterey Counties, 

 where they probably reach their maximum development. While the 

 Franciscan group appears almost certainly to be younger than these 

 rocks, it is remarkable that no contact has yet been found between 

 this older group and the Franciscan group. Perhaps further explora- 

 tion of the little-studied areas in the Gavilan and Santa Lucia Ranges 

 or in Humboldt County may reveal a place where these two groups of 

 rocks actually come in contact at the surface. 



Fairbanks 14 described in the region of Slate's Springs in the Santa 

 Lucia Range, a coarse conglomerate of rounded granite boulders in a 

 matrix of arkosic sandstone, having a thickness of 1000 feet and 

 traceable for several miles. This rests on the granite and he regarded 



n Fairbanks, H. W., Bull. Geol. Soc. Am., vol. 6, p. 82, 1895. 



