KiNAHAN — On Some of the Irish Crystalline Iron Ores. 309 



formed an impervious floor, on wliicli mosses, lichens, grass, hea- 

 thers, &c., grow and decay. Such peat accumulations are neces- 

 sarily thin, as the iron ore floor is not congenial to the rapid 

 growth of bog. 



At the present day the ore that is being formed at the surface 

 is usually ochre, the bog iron ores being beneath greater or less 

 thicknesses of surface accumulations. The latter is always more 

 or less argillaceous, but in some places the surface is a rich 

 granular ore of apparently a newer growth. 



It may be observed in Ireland that where these ores occur asso- 

 ciated with peat, the bog areas usually lie on more or less pyritous 

 rocks, such as the black coal-measure shales, the calp shales, and 

 black limestones, and the pyritous metamorphosed rocks ; and these 

 appear to have been in a great measure the source of the bog iron 

 ore. This, however, is not always the case, as the iron garnets, the 

 ferriferous micas, hornblendes, and pyroxenes, &c., in some rocks 

 rapidly decompose, and are a considerable source of the ferric oxide ; 

 while in parts of Ulster there is a sub-metamorphosed sandstone, 

 which, with its associated schistose rocks, supply extensive accumu- 

 lations of ochre. These sandstones weather very rapidly, and in 

 general to considerable depths — some, indeed, have all their cement- 

 ing materials washed or leached out of them, leaving a residue of 

 more or less pure sand. The normal colours of these sandstones 

 seem to be different shades of green, or bluish-green ; but these 

 rapidly and deeply weather into a brownish iron-masked rock, with 

 a thin dirty-white crust or surface. Besides the direct leaching of 

 the soil or rocks, there are in places chalybeate springs which supply 

 liydrous ferric oxide from more or less deep sources. The ochre 

 forms a greater or less mound, or perhaps a sheet, round such 

 springs ; or may well up through boggy land, thus forming a 

 ferriferous boggy swamp. 



These bog iron ores and those allied to them, which have been 

 briefly described, have accumulated at or near the surface. There 

 are, however, in many of the rocks forming the surface, fissures, 

 joints, cracks, and such like openings, into which portions of the 

 iron in solution must flow to form deposits in cavities below the 

 surface. Such seems to have been one of the sources in the case of 

 the Antrim "pebble ore" described in the second part of this 

 Paper ; while in other places the leakage from younger strata seems 



