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University of California Publications in Geology [Vol 11 



PAGE 



Conditions of deposition 



33 

 33 

 33 

 33 

 34 

 35 

 36 

 37 

 38 



Suggestion of continental deposition 

 Possibility of wind action 



Fluviatile deposition on piedmont slope 



Marine deposition 



Shale flakes 



Lenses of conglomerate 



Shale blocks and slabs 



< Conclusions 



INTRODUCTION 



The Franciscan group, named from its occurrence near San Fran- 

 cisco, presents a variety of peculiar rock types, the uniformity of 

 the occurrences of which is remarkable. Throughout its wide extent 

 in tlie Pacific Coast Ranges it shows everywhere identical lithologic 

 types ; rocks occurring in one limited area of the Franciscan may be 

 duplicated by identical rocks from almost any other area. The Fran- 

 ciscan sandstone, which is one of the most important formations of 

 the group, shows many features not exhibited by ordinary sandstones. 



The material presented in the following pages is the result of a 

 study of the Franciscan sandstone made in connection with an inves- 

 tigation of the radiolarian cherts of the Franciscan group. 



Tlie writer would make grateful mention of his obligation to Pro- 

 fessor A. C. Lawson, for numerous suggestions made during the 

 progress of the work. 



Rocks of the Franciscan group are exposed over large areas in the 

 Coast Ranges of California. On the mainland, the Franciscan terrane 

 extends from the Santa Ynez River, just north of Santa Barbara, 

 northward into Humboldt County. 1 Franciscan rocks are known on 

 Santa Catalina Island. The Franciscan is confined, as a general rule, 

 to the central portions of the mountain chains where it appears be- 

 neath the later sedimentary rocks which are exposed on the flanks. 



i Fairbanks states on authority of Watts that jaspers and sandstones like 

 the Franciscan have been observed in Del Norte County along the Oregon line. 

 Bull. Geol. Soc. Am., vol. 6, p. 82, 1895. 



THE FRANCISCAN GROUP IN CALIFORNIA 

 Extent 



