596 EDWARD SAMPSON 



present form. The same kinds of solutions from these igneous rocks being 

 postulated as seem to be required to produce greenalite and carbonate.' 



They do not go into the details of the process of formation of the 

 silica of the jaspers. 



Davis, following Lawson, believes that the solutions which 

 were responsible for the cherts of the Franciscan formation were 

 derived from springs. 



It is possible that a solution of silicic acid might diffuse through a fine mud 

 on the sea floor and that the silicic acid should be precipitated throughout the 

 mud in regular layers, thus producing the rhythmic bedding. 



Perhaps a fine mud was permeated with a solution of silicic acid or some 

 silicate, and by the diffusion of some other substance into it, .... a regiilar 

 rhythmic banding was brought about. ^ 



Davis performed some experiments with suspensions of clay which 

 indicate "that silicic acid possesses the ability to free itself from 

 mechanical impurities and that it can do so in a rhythmic manner." 

 Thus Davis would explain the laminations of the Franciscan cherts. 



Cox, Dean, and Gottschalk^ in their work on the chert associated 

 with the zinc ores of southwestern Missouri have thrown much 

 light on the chemistry of silica in nature. Although their conclu- 

 sions are appHed to chert occurring in limestone, yet the fundamental 

 processes which they discuss are applicable to the siliceous sedi- 

 ments of Notre Dame Bay. 



In brief, they conclude that the silica existed in solution in ground 

 water in the form of a colloid. This colloid they believe to have 

 been precipitated by Ca++ ions formed by the disassociation of Ca 

 (11003)2 which was in turn formed by the action of carbonated 

 waters on Hmestone. They also indicate the possibility of some 

 silica, as in petrified wood, being formed by the coagulative effect of 

 positively charged colloids. 



Kahlenberg and Lincoln"" long ago investigated the nature of 

 siHca in dilute solutions. They showed that such salts as sodium 



^ Ibid,, p. 527. 



^ E. F. Davis, op. cit., p. 401. 



3 G. H. Cox, R. S. Dean, and V. H. Gottschalk, "Studies of the Origin of Missouri 

 Cherts and Zinc Ores," Bidl. Univ. Missouri School of Mines and Met., Vol. Ill, No. 2, 

 1916. 



''Louis Kahlenberg and A. L. Lincoln, "Solutions of Silicates of the Alkalies," 

 Jour. Phys. Chem., Vol. Ill (1898), pp. 77-99. 



