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XXXIV.— NOTES ON SOME OF THE lEISH CRYSTALLINE 

 lEON ORES. By G. H. KINAHAN, M.R.I.A., &c. 



[Eead, April 21, 1884]. 



Paet I. 



A QUESTION that appears to attract some attention in America at 

 the present time is " The Genesis of the Crystalline Iron Ores" ; 

 therefore some notes on the lodes and accumulations of these ores 

 in Ireland may be of interest. 



These ores, excluding the carbonates, occur in lodes and in 

 interbedded masses, generally lenticular and irregular. Formerly 

 they "Wjere extensively mined in Ireland ; but after the last furnace 

 was put out, about 230 years ago, and those operations had ceased, 

 most of the pits and accompanying works were covered up, so that 

 the sites of many of them are now unknown. A few, however, of 

 these ancient works have of late years been re-opened, while in other 

 places deposits have been discovered and worked, so that from these 

 later workings we can learn something about the nature of the 

 deposits now in question. 



Such ores are due to the decomposition of organic matter and 

 carbonic acid. Chalybeate water contains iron, either as the sul- 

 phate or as the carbonate. When iron exists as the sulphate it has 

 been derived from the decomposition of pyrite in the rocks through 

 which the water has percolated ; the iron in solution is oxidized on 

 exposure to the atmosphere, and a certain proportion of it is de- 

 posited. The source of the iron, besides the sulphides, may be 

 lodes or such like accumulations, and also the leaching out of the 

 iron colouring matter of the rocks and clays. Le Conte thus 

 describes the reactions that accompany the decomposition of organic 

 matter : — 



"Decomposition of organic matter is a process of oxidation. In 

 contact with peroxide of iron (ferric oxide) it deoxidizes and becomes 

 reduced io protoxide (ferrous oxide). The acids, especially carbonic 

 acid, produced by decomposition of the organic matter, then unite 

 with the protoxide, forming carbonate of iron. The carbonate, 

 being soluble in water containing excess of carbonic acid, is washed 



