1918] 



Davis: The Franciscan Sandstone 



11 



EVIDENCE REGARDING THE AGE OE THE FRANCISCAN AT 

 SLATE'S SPRINGS 



At Slate's Springs in Monterey County, on the west flank of the 

 Santa Lucia Range, there occurs an area of Franciscan rocks which is 

 of great interest on account of its fossil content. The Franciscan 

 here consists principally of sandstones and slates. The "slates" are 

 somewhat altered shales in which there is a slight development of slaty 

 cleavage. They are well bedded and contain lenses of radiolarian 

 chert. The sandstones contain lenses of conglomerate and also a few 

 thin seams of coal. The whole is intruded by serpentine. This is the 

 best fossil locality known in the Franciscan, so far as explorations 

 have yet gone. The fauna of these beds has been examined by various 

 paleontologists. 



In 1895, Stanton 21 reported to Fairbanks that the beds contained 

 an Inoceramns, which limited them to the Mesozoic. None of the fos- 

 sils were like any which had been previously described. He believed 

 the Inoceramus to be similar to one form in the Cretaceous beds at 

 Vancouver, but he was inclined to regard the fauna as Jurassic on 

 account of the stratigraphic relations ; the other fossils did not conflict 

 with this interpretation. 



In 1896, Professor J. C. Merriam 22 stated that the fauna was of 

 Cretaceous rather than Jurassic aspect. 



C. H. Davis 23 described some of the fossils from the Slate's 

 Springs locality and concluded from his study that the beds there 

 were not higher than the lower Upper Jurassic ; and he rather doubt- 

 fully assigned them to the Middle Jurassic. 



The beds at Slate's Springs contain a number of plant remains 

 and it was hoped that a study of this flora would give definite informa- 

 tion as to their age. The Jurassic flora is highly developed, world- 

 wide in its distribution, and contains forms which are easily identi- 

 fied. 24 However, this hope is not realized and it appears that the flora 

 from Slate's Springs is not that which is so characteristic of the 

 Jurassic, though it has been referred to that period. 



In 1896, Ward 25 suggested that the flora was that of a transition 

 between the Cretaceous and the Jurassic. 



21 Jour, of Geol., vol. 3, p. 423, 1895. 



22 20th Ann. Rep., U. S. Geol. Surv., pt. 2, pp. 338, 339, 1896. 



Davis, C. H., New Species from the Santa Lucia Mountains, California, 

 with a Discussion of the Jurassic Age of the Slates at Slate's Springs, Jour. 

 Geol., vol. 21, p. 453, 1913. 



2< Knowlton, P. IT., Am. Jour. Sci., vol. 30, p. 47, 1910. 



