KiNAHAN — On Some of the Iriah Crystalline Iron Ores. 307 



out, leaving the soil or rocks decolourized, and the iron-charged 

 waters come up as chalybeate springs. But the ferrous carbonate 

 rapidly oxidizes again in the presence of air, by exchanging its 

 carbonic acid for oxygen, and returns to its former condition of 

 ferric oxide, and is deposited." ^ 



On account of these reactions^ deposits of ferric oxide are found 

 about iron springs, along the streams that flow from them, and in 

 low places where their waters are collected. This is what usually 

 takes place, but not always ; for if the iron water accumulates in 

 the presence of an excess of organic matter, such as peat, all the 

 iron cannot be reoxidized, but must remain in the form of ferraus 

 carbonate.^ 



" Thus there are two forms in which iron leached out from the 

 soils and rocks may accumulate, viz., ferric oxide and ferrous car- 

 bonate. The former is accumulated where the organic matter is in 

 small quantities, and consumes itself in doing the work of dissolving 

 and carrying the latter where the organic matter is in excess." 



The recent, or the more or less superficial, accumulations of iron 

 ores may be first described. In some of the estuaries and lagoons 

 earthy iron ore or some other ferriferous strata are deposited. In 

 the estuary or lagoon of the Slaney (Wexford harbour) the muds 

 are often ferriferous. In some places the ferriferous muds become 

 richer toward the upper part, and are often covered by a thin seam 

 or layer of ferric oxide, above which is mud. This arrangement 

 would seem to suggest that the iron came down the Slaney, partly 

 in solution and partly in suspension, it being supplied by the de- 

 composition of the pyrite in the Cambro-silurian and Carboniferous 

 argillaceous rocks and the leaching out of the colouring matter from 

 them and the Cambrians. The lands of the " intakes " of other 

 estuaries are often in part ferriferous, with seams or disseminated 

 particles of iron ore in them. 



It is principally during winter floods that the muds accumulate 



1 Other authorities ascribe it to a decomposition of the salt, the carbonic acid 

 escaping, while water and oxygen take its place, thus forming a hydrous ferric oxide. 



" At the bottom of some of the Irish bogs there is " stone turf," more or less im- 

 pregnated with some of the sulphate or carbonate of iron, or both combined. If only 

 the latter is present when the turf is first cut, it is not iron-stained, but after it is dried 

 it is found to be full of little particles of the ferric oxide, the turf becoming more or 

 less " iron-mai'lced." 



2E 2 



