362 University of California Publications in Geology [Vol. 11 



islands in the Caribbean Sea. In other dredgings made off the west 

 coast of Central America, and in the Gnlf of Lower California, it 

 was found that there was considerable vegetable matter in the muds 

 accumulated in deep water. 128 Some of the specimens dredged by 

 the ' ' Challenger ' ' from very deep water in the Celebes Sea, con- 

 tained numerous fragments of wood. The presence of carbon is then 

 simply a matter of distance from shore and distribution of ocean cur- 

 rents, and cannot be used as a criterion of the depth of water in 

 which the sediments containing it were deposited. 



Association of Cherts with Sandstones. — The Franciscan sand- 

 stone is a medium, coarse grained sandstone which appears to be, in 

 large part, of continental origin. 120 None of it was laid down very 

 far below sea level. In the neighborhood of San Francisco, there 

 are two formations of radiolarian chert which divide the sandstone 

 into three formations. If we regard the cherts as abyssal radiolarian 

 oozes, like those of the present day, we must believe that the region 

 sank from sea level to a depth of from 12,000 to 15,000 feet, and that 

 this tremendous displacement occurred twice within Franciscan time, 

 with two reversals of movement. 



Nature of Sandstone-Chert Contacts. — Another fact which is op- 

 posed to the idea that the radiolarian cherts were laid down in the 

 deep sea, far from shore, is the nature of the contacts of chert and 

 sandstone. Even if we can accept the idea of two great displace- 

 ments of the region during Franciscan time, we cannot think that 

 such great depressions occurred suddenly. They must have gone on 

 gradually, if at all, during a long period of time. During a time of 

 gradual submergence, the nature of the sediments should change, 

 passing from sandstone to shale and then from typical terrigenous 

 material to material richer in lime carbonate until limestones accumu- 

 lated, and at last sufficient depth was reached for the accumulation 

 of siliceous oozes. Instead of such a change in sedimentation we 

 find nothing approaching it. There is a transition at some contacts 

 but it takes place within a very few feet or a few inches. No deposits 

 of lime carbonate are known at any of the contacts between chert and 

 sandstone. The nature of these contacts is absolutely opposed to the 

 idea of the abyssal accumulation of the cherts. 



Occurrence of Cherts m Lenses. — On the hypothesis that the 

 cherts represent radiolarian oozes of abyssal origin, it is impossible 



128 Bull. Mus. Comp. Zool., vol. 14, p. 291, 1888. 



129 Davis, E. F., The Franciscan Sandstone, Univ. Calif. Publ., Bull. Dept. 

 Geol., vol. 11, pp. 1-44, 1918. 



