66 HAROLD IV. FAIRBANKS 



volcanic ejectamenta which may have become similarly dis- 

 solved. The two latter are rejected and the first received, as 

 having the most to support it, in the following words: "The 

 hypothesis of the derivation of the silica from siliceous springs 

 and its precipitation in the bed of the ocean in local accumula- 

 tions, in which the radiolarian remains became imbedded as they 

 dropped to the bottom, seems, therefore, the most adequate 

 to explain the facts, and there is nothing adverse to it as far as 

 the writer is aware." 



Some time since I proposed a theory^ to account for the 

 origin of the jaspers substantially equivalent to the second given 

 above. Professor Lawson's chief objection to the view of the 

 organic origin of these rocks consists in the fact that they occur 

 in lenticular masses instead of evenly bedded deposits. In his 

 petrographic description it is stated that the "cavities of the 

 radiolaria have been filled with chalcedonic silica and are in 

 definite contrast with the non-chalcedonic matrix." With this 

 last statement my experience is not often in accord. I have 

 found every gradation in the specimens from those in which the 

 radiolaria are distinctly marked, as Professor Lawson says, to 

 those in which they are only faintly distinguishable from the 

 matrix, or apparently absent. In my opinion this state of things 

 gives good ground for the view that, owing to possible trans- 

 formations through the action of sea water, and the secondary 

 changes which are known to have taken place, there is no valid 

 reason for denying the organic origin even when no organic 

 remains are distinguishable. 



Professor Lawson has failed to recognize that the siliceous 

 bands in the limestone must have had an origin similar to those 

 occurring in aggregates by themselves. If the theory of forma- 

 tion by springs is applicable to one it is to the other. The 

 occurrence of these radiolarian jaspers interstratified with the 

 limestone is a most suggestive fact. Similar conditions of sedi- 

 mentation must have obtained in the one case as in the other, 

 the only difference being that at one time calcareous layers were 



' Bull. Geol. Soc. Am., Vol. VI, p. 85. 



