298 University of California Publications in Geology [Vol. ll 



crystallization of the silica of diatomaceous shale. One can imagine 

 conditions under which solutions would dissolve and redeposit silica 

 without affecting even delicate shells of lime carbonate. The evidence 

 presented later under the heading of "Alteration of Chert" shows 

 that solutions may carry silica without dissolving calcium carbonate. 

 It is, however, impossible to believe that silica was carried in solution, 

 in any form, and deposited in the chert in such a way as to leave the 

 open chambers of the foraminiferal shells unfilled. 



The facts set out above lead to the conclusion that the cherts of the 

 Monterey are not due to metamorphism, or silicification of diato- 

 maceous earth or bituminous shales. The other alternative is that 

 they were originally formed in somewhat the same condition, and in 

 the same relations, in which we now find them. The inclusion of 

 empty foraminiferal shells in a matrix of silica seems only to be ex- 

 plained on the assumption that the shells were caught in a gelatinous 

 mass of silica and were thus preserved. 



Accepting this idea of original gelatinous silica it is possible to 

 believe that this silica was produced by the solution of the skeletons 

 of diatoms on the sea bottom. It is conceivable that under the influ- 

 ence of acids generated by decaying organic matter the siliceous tests 

 were dissolved. That this did not happen is shown by two things : 



1. The presence of unaltered foraminiferal shells proves that such 

 acids, if present, were not very powerful solvents. 



2. The diatomaceous earths, which certainly contained large 

 amounts of organic matter, show no evidence of solution and are 

 now earthy, rather poorly consolidated rocks. 



The solvent effect of ocean water under pressure was evidently 

 not important since it was not powerful enough to remove calcareous 

 matter from the foraminiferal shells and could therefore hardly be 

 be expected to cause silica to go into solution. It seems certain that 

 the gelatinous silica of the cherts was derived from some other source 

 than a diatom ooze. 



The variations in lithologic types seen in the Monterej^, are not 

 due to different stages of alteration, but are due to original variation 

 in the nature of the material which was accumulating. The final 

 product depends upon the relative proportions of diatom frustules, 

 clayey material, and gelatinous silica which made up the original 

 deposit. 



