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University of California Publications in Geology [Vol. 11 



These diatomaceous earths must certainly have been associated with 

 much organic matter, at the time of their deposition. We cannot 

 escape this conclusion by regarding the white diatomaceous earths as 

 accumulations on the ocean bottom under oxidizing conditions and 

 believing that when the bottom was stagnant the action of organic 

 acids gave rise to the solution of silica, producing cherts. This is 

 shown by the existence of foraminiferal shells in the Monterey cherts. 

 In the presence of acids produced by decaying organic matter these 

 shells should have been broken down. 



Evidence against Ideas of Change on Sea Floor. — There is no evi- 

 dence of such changes in present radiolarian oozes. Murray states 

 that the delicate structures of some radiolaria are apparently reduced 

 by some solvent action of the sea water, but it does not appear to 

 produce modifications of any importance in the nature of the radio- 

 larian oozes. 



We have another excellent check on both the foregoing ideas that 

 silica in radiolarian oozes may be dissolved on the sea bottom with 

 the resulting formation of cherty rocks. The radiolarian earths of 

 Barbados appear, from their lithologic nature and their stratigraphic 

 relations to other formations of peculiar types, to represent true 

 radiolarian oozes. This interpretation of their origin is generally 

 accepted. Yet in these earths, there is no evidence, aside from the 

 presence of an occasional cherty nodule, of the formation of any cherty 

 silica like that which makes up the radiolarian cherts. It would 

 appear, therefore, that there was no solution of silica on the sea bot- 

 tom either under the action of pressure, decaying organic matter or 

 similar causes, which was competent to alter radiolarian oozes into 

 radiolarian cherts. 



Possibility of the Alteration of a Radiolarian Earth to a Chert. — 

 A radiolarian earth like that of Barbados may have been produced 

 by the partial consolidation of a radiolarian ooze. After its forma- 

 tion, such a rock may have been subjected to pressure and to the slow 

 circulation of water through its numerous openings. During a long 

 period of time silica would be dissolved continuously, in accordance 

 with the Riecke principle, from the points of contact of the skeletons, 

 and deposited in the open spaces. Ultimately, through this process 

 the whole rock would become a solid mass. During this change it 

 would undergo a considerable degree of crystallization and a shrink- 

 age in volume. Ideas such as this and those previously suggested 

 appear to have been held by Fairbanks, who thought that the whole 



