500 T. C. HOPKINS — CAMBRO-SILURIAN LIMONITE ORES 



D'Invilliers, E. V. : Second Pennsylvania Geological Survey, Report T, page 136. 



The pipe ores are caused by 1 1) the decomposition of iron pyrite in the lime- 

 stone ore slate hands, which after oxidation as sulphate filled interstices in the 

 limestone and "changed into peroxide by contact with vegetable matter or 

 other organic substances," or (2) the production of ferrous carbonate by reac- 

 tion between ferrous sulphate and calcium carbonate and afterward changed 

 to limonite by oxidation and hydration. The wash or lump hematites are 

 wash deposits caught in vast caverns of irregular shape. 



Ewing, A. L. : Second Pennsylvania Geological Survey, Report T, page 408. 



The original condition was as ferrous salts, in most cases carbonate. It is 

 probable that portions of the iron have been dissolved, transported, deposited, 

 and oxidized during the process of rock decay, yet the facts would indicate 

 that the greater part is due to oxidation in situ. 



Fontaine, W. M. : Quoted by E. C. Pechin in Proceedings of the Iron and Steel 

 Institute, October, 1890. 



The ores are formed by the concentrating action of concretionary forces that 

 have collected the once diffused iron into masses, which have a more or less 

 distinctly concretionary structure, or which form beds of nodular ore or crusts 

 lying in inclosing clay. 



Fkazer, Perifer, Jr.: Second Pennsylvania Geological Survey, Report C, page 142. 



The pyrites of the hydromica slates furnish ferrous sulphate and free sul- 

 phuric acid which reacts on the soda in the slates, producing sodium sulphate, 

 which in turn reacts on the lime bicarbonate, giving soda carbonate and lime 

 sulphate. The sodium bicarbonates react on the ferrous and ferric sulphates, 

 forming hydrous oxide from the latter and hydroferrous carbonate from the 

 former, which is farther oxidized to ferric hydrate. This is one of many 

 suggestions. 



Harden, J. \V. : Transactions of the American Institute of Mining Engineers, 1873, 

 volume 1, page 136. 

 The ore is the residue of the decomposition of the slates and limestones. 



Hunt, T. S. : Second Geological Survey of Pennsylvania, Report E, pages 202-204; 

 Transactions of the American Institute of Mining Engineers, volume xi, page 

 244. 



The ores are formed by the oxidization in situ of deposits of carbonate of 

 iron, and in some places pyrite interstratified in the more or less argillaceous 

 slates now changed to clay. 



Jackson, R. M. S. : Nittany Valley Iron Ores, 1838-'39. 



The ores are deposited in situ freed from the limestone during the process of 

 erosion and disintegration. 



Jclien, A. A. : Proceedings of the American Association for the Advancement of 

 Science, 1879, volume 28, page 401. 



Whatever the source of the iron oxide may have been, whether pyrite or 

 other ferruginous minerals, the action of humus acids may be suspected. -They 

 probably served for its transport and as the erosive agents in the excavation 



