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



Merrill, F. J. H. : Bulletin of the New York State Museum, volume 4, number 19, 

 page 221. 



The existence of the carbonate in the deeper parts of some of the mines and 

 their interstratification with the limestones is suggestive of the origin of the 

 limonites by the decomposition of the ferruginous beds, through oxidation and 

 the agency of carbonated waters. 



Newberry, J. S. : Engineering and Mining Journal, 1881, volume 31, page 299. 



They are the accumulation of iron carried in the surface drainage, deposited 

 by aeration and oxidation. The iron came from the surface drainage of rock 

 and soil, the decomposition of pyritous rocks, and a residual from ferriferous 

 limestones. The formation has evidently been going on from the Cretaceous 

 age to the present. 



Penrose, R. A. F., Jr. : Journal of Geology, 1894, volume ii, page 304. 



Many of the iron ore deposits in the Cambrian and Lower Silurian can be 

 clearly shown to be due to a superficial replacement of limestone, or even of 

 more silicious rocks like shales, by iron dissolved from ferruginous rocks in 

 the neighborhood. In such cases the iron in the original rock has been dis- 

 solved and carried off in carbonated surface water and reprecipitated in the 

 other rocks, all these stages being directly due to surface influences. 



Porter, John B. : Transactions of the American Institute of Mining Engineers, 

 volume 15, page 177. 



The ores are formed from oxidized pyrite, which occurs either in masses or 

 disseminated through the older rocks. The saying, " No ore is under where 

 the water stands " is a key to the great cause in the formation of limonite. 



Prime, F., Jr.: American Journal of Science, third series, 1875, volume 9, page 438; 

 Transactions of the American Institute of Mining Engineers, 1875, volume 3, 

 page 410. 



The brown hematites were probably formed by the oxidation of iron pyrites, 

 but not in situ. It is uncertain whether the pyrite was disseminated through 

 the limestone or whether there was a bed especially rich in pyrite. The ox- 

 idation of the pyrite produced protosulphate of iron, which reacts on the 

 limestones and the carbonate of lime and magnesia in the damourite slates, 

 producing iron carbonate, which is deposited, and lime sulphate, which is 

 carried off in solution. 



Second Pennsylvania Geological Survey, Report D, pages 53, 59. 

 The pipe ore has evidently formed by deposition from solution by the ox- 

 idation of some ferrous salt, probably the carbonate. "The ore must then 

 have been formed either from the decomposition of ferrous salts in situ — that 

 is, ferrous silicates or carbonate — from the solution of the ferrous carbonate in 

 the limestone and its redeposition in the damourite slates or from the same 

 reaction of the ferrous sulphate formed by the oxidation of pyrite." The 

 potash of the damourite slates must have exerted an important agency in the 

 formation of the ores in their present position and condition. 



Rogers, H. W. : Geology of Pennsylvania, 1858, volume i, page 183; volume ii, 

 page 721. 



Much of the iron (of the ores of the Primal series) was originally pyrite in 

 minute crystals in certain layers of the slate. 



