BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 8, PP- 213-220, PLS. 17-19 MARCH 6, 1897 



SOLUTION OF SILICA UNDER ATMOSPHERIC CONDITIONS* 



BY C. WILLARD HAYES 



{Read before the Society December 29, 1896) 

 CONTENTS 



Page 



Solubility of silica under other than atmospheric conditions 213 



Observed cases of solution of silica under atmospheric conditions 214 



Silicious geodes from Spurrier, Tennessee 214 



Etched conglomerate from Nuttall, West Virginia. . 215 



Etched conglomerate pebbles from White county, Tennessee . 215 



Etched conglomerate from Starrs mountain, Tennessee 216 



Analogous cases of solution of silica 217 



Etched pebbles from the Coal Measure conglomerate of Ohio 217 



Surface induration of Saint Peters sandstone in Wisconsin 218 



Surface glazing of sandstones in Pennsylvania and Tennessee 218 



Chemical activity of the azo-humic acids 218 



Chemical reactions involved in the solution of silica under atmospheric con- 

 ditions , 219 



Conclusions 220 



Solubility of Silica under other than atmospheric Conditions. 



It is well known that under conditions prevailing at considerable 

 distances below the earth's surface silica is one of the more easily solu- 

 ble of the substances entering into the composition of the earth's crust. 

 This is shown by the formation of secondary quartz veins, the solution 

 and redeposition of quartz in both sedimentary and crystalline rocks, 

 and, on a large scale, in the replacement of silica by other minerals, as 

 in the case of the iron ores of the Lake Superior region. It is also well 

 known that during the process of rock weathering under atmospheric 

 conditions, by the breaking down of various silicates, much silica passes 

 into solution. Merrill f has shown that in the passage of various crys- 



* Printed with the permission of the Director of the U. S. Geological Survey. 

 fG. P. Merrill: Weathering of micaceous gneiss in Albemarle county, Virginia. This vol- 

 ume, pp. 157-168. 



XXXI— Bull. Geol. Soc. Am., Vol. 8, 1896 (213) 



