316 Scientific Proceedings, Roi/ul Dublin Society. 



the copper ores ; because at Allihies, near the whinstone intrusions 

 the ore is concentrated in large lodes, while elsewhere in the county 

 of Cork the ore is in more or less small and numerous veins, or 

 disseminated in particles in the rocks of the Yellow Sandstone 

 (Griffith) group. 



Counties of Wexford and Wicklow. 



In these counties, besides the old workings, of which very little 

 is now known, there are the iron ore backs to the pyrite lodes of the 

 Ovoca mines ; while in the purple and green Oambro-silurian slates 

 there are irregular cakes or lentils and strings of iron ore. 



Here the central member of the Cambro-silurians is made up of 

 interstratifications of whinstones, felstones, tuffs, limestones, and 

 schists, while above and below these there are the upper and lower 

 red and purple slates. Many of the limestone and the calcareous 

 schists are impregnated more or less with carbonate of iron, some, 

 indeed, being poor iron ore (ohalybite) ; while in the red and purple 

 slate, but especially those of the upper zone, there are cakes or lentils 

 of limonite and strings of hematite. 



The cakes of limonite are of irregular shapes, and are probably 

 due to chalybeate springs that welled up while the clays were 

 accumulating ; their source being in the underlying ferriferous 

 limestone ; while the strings of hematite seem to be connected with 

 vulcanicity, being due to steam that penetrated the cracks and 

 joints, leaching the colouring matter out of the adjoining portion of 

 the slates. In favour of the latter suggestion we find in other 

 places, near intrusions of irruptive rocks, that similar strings of 

 hematite are developed; while the newer granite (Carboniferous) 

 causes the adjacent rocks to be "iron-masked." 



At the Ovoca mines, between Ballycapple to the N. E. and 

 Knockmohill to the S.W., the gossan backs to the lodes are, in 

 general, ochre or limonite ; while in places, but especially near 

 heaves, the latter may be associated more or less with manganese, 

 chalybite, and magnetite. The limonite was deposited in horizon- 

 tal courses ; but afterwards, when drying, it shrank away from the 

 normal lodes, leaving vacancies, some of which remained open as 

 large vugs, while others were filled with the " gossan lodes" already 

 described. It is remarkable that the rocks adjoining the main 

 mineral channel are " iron-masked" (ochreized) , similar to the rocks 



