380 University of California Publications in Geology [Vol. 11 



would be 552,142,000 metric tons; if the age of the ocean be 50,000,000 

 years, then the amount which is precipitated annually is 546,614,000 

 metric tons. Taking the larger figure as correct and assuming that 

 all the calcium is precipitated in the form of calcium carbonate, then 

 552,142,000 metric tons of calcium would yield in round numbers 

 1,362,000,000 metric tons of calcium carbonate. This means that if 

 all the silica could be precipitated in the form of chert and all the 

 calcium in the form of limestones, that cherts would be about one- 

 quarter as abundant as limestones. While a portion of the silica may 

 come down in the form of potassium silicate in glauconite, this would 

 not affect the above ratio very seriously. Clarke 142 has calculated that 

 about 65,045,000 metric tons of glauconite would be required to pre- 

 cipitate the potassium which goes out of solution in the ocean in one 

 year. 



Separation of Silica from Coarse Mechanical Sediment. — It is pos- 

 sible that silica might be precipitated in the form of silicic acid by 

 coagulation, as above assumed, and then concentrated in places far 

 from the shore. It is well known that water from rivers, on entering 

 the ocean, tends to float on top of the denser salt water and to spread 

 out over the surface of the sea in a fanlike form, extending to con- 

 siderable distances before mingling with the salt water below. 143 

 Molengraaff 144 states that a river in Borneo forces its waters out to 

 distances of fifty to sixty kilometers from the land. Out to this dis- 

 tance the waters are discolored by the mud of the river water, which 

 mixes very slowly with the sea water. 



If silicic acid were precipitated in the gelatinous condition, in the 

 manner suggested, its flocculent nature would cause it to sink very 

 slowly, and it might be carried out beyond all except the very finest 

 mechanical sediments. 



On this hypothesis it would appear necessary that the depth of 

 accumulation should be sufficiently great so that calcareous remains 

 would be dissolved. 



Objection that no Sediments of this Type are known. — As pre- 

 sented, this hypothesis involves no unusual factors and if it is true 

 the various processes should be at work at the present time. Some- 

 where we should expect to find sediments which should be the present 

 day equivalents of the radiolarian cherts. The hypothesis then en- 



1*2 Clarke, Proe. Am. Philos. Soc, vol. 51, p. 226, 1912. 



143 Clarke, Smithson. Misc. Coll., vol. 60, p. 24, 1912-13. 



144 Explorations in Central Borneo, Leyden, 1902. 



