1918] Davis: The Franciscan Sandstone 5 



often intimately associated with the serpentine, and in some instances 

 the relations are such as to indicate a genetic relation between these 

 igneous rocks. 



Metamorphic Rocks 



In close association with the intrusive masses of ellipsoidal basalt 

 and of serpentine, there are local and irregular patches of peculiar 

 metamorphic rocks, which appear to have been produced by contact 

 action at or near the margins of the intrusives. The most common 

 type of these rocks is a blue schist, composed largely of blue amphi- 

 boles, 8 of which glaucophane, crossite, and crocidolite 9 are the most 

 common varieties. 10 Mica schists, lawsonite schists, actinolite schists 

 and many other types are encountered in rich variety. They are in 

 many cases characterized by abundant albite and are at many localities 

 cut by veins of albite. The glaucophane schists are peculiar to the 

 Franciscan group, not being found in other formations in California. 



THE FRANCISCAN GROUP IN SOUTHERN OREGON 



North of Humboldt County, rocks believed to be Franciscan are 

 again encountered in the southern end of the Oregon Coast Range. 11 

 The sandstone here is the arkosic, well lithified, quartzite-like sand- 

 stone, characteristic of the Franciscan group. Scattered through this 

 at irregular intervals are thin lenses of conglomerate. The formation 

 contains occasional lentils of cherty, foraminiferal limestone, appar- 

 ently identical with the foraminiferal limestone of the San Francisco 

 Peninsula. The characteristic radiolarian cherts occur in isolated 

 patches. 



s Murgoci, G., I. Contribution to the Classification of the Amphiboles; 

 II. On some Glaucophane Schists, Syenites, etc., Univ. Calif. Publ. Bull. 

 Dept. Geol., vol. 4, p. 359, 1906. 



'■' Louderback, G. D., and Sharwood, W. J., The Croeidolite-bearing rocks of 

 the California Coast Ranges (Abstract), Bull. Geol. Soc. Am., vol. 18, p. 659, 

 1907. 



10 While these schists contain blue amphiboles other than glaucophane, the 

 writer will, in the following discussion, adopt the common usage and use tlie 

 term "glaucophane schist" as a general expression for these rocks. 



11 Diller, J. S., Geology of Northwestern Oregon, IT. S. Geol. Surv., 17th 

 Ann. Rep., pt. 1, 1895-6. 



— Roseberg Quadrangle, U. S. Geol. Surv., Folio no. 49, 1898. 

 — Coos Bay Quadrangle, ibid., Folio no. 73, 1901. 

 —Port Orford Quadrangle, Hid., Folio no. 89, 1903. 

 — The Relief of Our Pacific Coast, Science, n. s., vol. 41, p. 48, 1915. 

 Louderback, G. D., The Mesozoic of Southwestern Oregon, Jour. Geol., vol. 

 13, p. 514, 1905. 



