1918] 



Davis: The Franciscan Sandstone- 



Id 



justified in expecting that the Knoxville would show some sort of a 

 structural break if it were actually separable into two periods. 



Possibility of a Triassic Age for the Franciscan Group 



If, in spite of Diller's positive conclusions, the apparent spatial 

 relation is the true one and the Galice is the younger formation, then 

 the 'Franciscan must be pre-Mariposa. It may be Lower or Middle 

 Jurassic or Triassic. It would also follow that the granites of the 

 Coast Ranges and the Sierra Nevada are of diverse ages. 



In connection with the possibility of a Triassic age for the Fran- 

 ciscan group, it should be remembered that in Alaska there are rocks 

 that are identical with those of the Franciscan. They include radio- 

 larian cherts, pillow basalts, arkosic sandstones, serpentines, and 

 glaucophane schists. These are known certainly to be Triassic. The 

 Franciscan group extends from southern California into Oregon and 

 into the Olympic Mountains. It is possible that the Alaskan rocks 

 are a portion of the same terrene. The lithologic peculiarities 

 suggest this strongly; but the force of the suggestion is weakened 

 when it is remembered that there are somewhat similar rocks of en- 

 tirely different age in the Pacific Coast region. In Alaska, radiolarian 

 cherts of probable Paleozoic age are known, and radiolarian cherts 

 occur in the Devonian of Oregon, but the peculiar association of litho- 

 logic types in the Mesozoic rocks is apparently not duplicated in any 

 of the older series. 



It is interesting also to note that the radiolarian cherts of Borneo, 

 the Philippines, and the Malay Peninsula are at an horizon near to 

 those of the cherts of the Franciscan and the cherts of Alaska. War- 

 ren D. Smith 35 has studied the radiolarian cherts near Roseberg, Ore- 

 gon, and finds the radiolaria which they contain to be identical with 

 the radiolaria in the cherts of the Philippine Islands. The cherts of 

 the Philippine Islands are apparently contemporaneous with those of 

 Borneo, Java, the Moluccas, Ceram, and adjacent regions. These have 

 been assigned to the Jurassic or the Triassic by Hinde and Martin. 

 The radiolarian cherts of Roti and Savu are certainly Triassic since 

 they are associated with limestones containing HaloMa and Daonella. 

 Smith calls attention to the lithologic resemblance and the identity of 

 the radiolaria. He does not attempt a correlation, because of the un- 



35 Smith, W. D., Notes on Radiolarian Cherts in Oregon, Am. Jour. Sci., 

 vol. 42, p. 299, 1916. 



