598 EDWARD SAMPSON 



contain considerable ferrous iron. When such a solution was 

 mixed with ocean water the iron would become oxidized and by- 

 hydrolysis ferric hydroxide would form. The iron now present 

 in the jaspers as hematite may have been precipitated in this way. 

 This colloidal ferric hydroxide which carries a positive charge 

 would then be an agent which might coagulate colloidal silica and 

 this action would be mutual. 



A third process, probably of minor importance, may have been 

 effective in the formation of the chert sediment. Van Hise and 

 Leith, as stated above, showed that a ferrous salt will react with 

 water glass to form ferrous siHcate, silica, and a sodium salt. The 

 ferrous silicate had the properties of greenalite. Some such reaction 

 has very likely taken place as evidenced by the analysis of green 

 chert which indicates the presence of both ferrous and ferric iron, 

 and as evidenced by the occurrence of minute particles resembling 

 thuringite in the specimen analyzed and in many others. 



The danger is realized of trying to explain the exact mechanism 

 of the chemical processes in the formation of the cherts. However, 

 the suggestions offered above indicate methods capable of producing 

 the materials from which the rocks could be formed. The main 

 purpose of this paper is to call attention to the widespread occurrence 

 of chert with marine volcanic rocks and to endeavor to establish 

 the fact of their inorganic chemical origin." 



' Since this paper was written the paper of Gruner on the highly ferruginous cherts of 

 the Lake Superior region has been published {Econ. Geol., Vol. XVII (1922), pp. 407-60. 

 Gruner attributes to the action of bacteria and algae the principal r61e in the precipita- 

 tion of both the silica and the iron. The materials are thought to have been brought 

 into solution largely by the weathering of volcanic rocks made more active by organic 

 acids formed by the decay of primitive vegetal organisms. He also considers the reac- 

 tion of volcanic submarine flows with water and the direct contribution of magmatic 

 water to marine basin. Both of these sources of material he believes to be less impor- 

 tant than by weathering products. Magmatic solutions he particularly dismisses as 

 inadequate. Space does not permit such a discussion as the paper warrants. The 

 present author feels, however, that there is no evidence presented which requires a 

 change in view as to the origin of the chert of Notre Dame Bay. He has re-examined 

 the thin sections in hope of finding some minute organisms which might have been 

 overlooked. None were found. He believes that, if they were found, proof would be 

 required that they were not incidental fossils as are the radiolaria. 



