26 CONTENTS. 



Chapter XII. — The Relations op Metamokphism to Ore Deposits — Continued. Page. 

 Part II. Segregation of ores — Continued. 



Division C. Ores produced by processes of metamorphism — Continued. 

 Group B. Ores deposited by aqueous solutions — Continued. 



III. "Work of aqueous solutions in segregating ores — Continued. 



Subclass 2. Ores precipitated from ascending and descending aqueous 

 solutions — Continued. 



Association of copper and iron compounds 1158 



Association of silver and gold with base metals 1166 



Silver 1166 



Gold 1169 



Concentration by reaction upon sulphides compared with metallur- 

 gical concentration 1174 



Other reactions of descending solutions 1175 



Second concentration favored by large openings near the surface . . . 1177 



Depth of effect of descending waters 1179 



Illustrations of secondary enrichment and diminution of richness 



with depth 1182 



General statements. .- 1189 



Subclass 3. Ores precipitated from descending aqueous solutions 1193 



Iron ores 1193 



Manganese ores 1198 



IV. Special factors affecting the concentration of ores 1199 



Variations in porosity and structure 1200 



Distribution and size of openings 1201 



Complexity of openings 1202 



Preexisting channels and replacements _ 1203 



Impervious strata at various depths 1207 



Pitching troughs and arches 1211 



General statements 1216 



Character of topography 1217 



Effect of vertical element 1217 



Effect of horizontal element 1218 



Physical revolutions _ . 1221 



V. General statements •. . 1223 



VI. Ore shoots 1223 



General statements 1230 



Summary and conclusion 1232 



Index 1245 



