184 Scientific Proceedings, Royal Dublin Society. 



intrusion of this granite and the formation of the mineral veins were contemporaneous, 

 that is, belonging to one and the same period of vulcanicity - 1 The mineral veins, however, 

 did not accumulate all in a moment; the great "sulphur lode," as also all the other 

 lodes, with one or two slight exceptions, are made up of thin lamina?, parallel to the 

 "foot-wall," and more or less oblique to the "hanging-wall;" consequently it is 

 evident that the shrinkage fissures, now occupied by the lodes, opened very gradually, 

 the lodes being augmented successively by very thin parallel laminae. The formation 

 of the fissure may have been due to this vulcanicity, the fissure giving opportunity for 

 the production of the lode, and the filling stuff being leachings from the surrounding 

 mineral -charged recks. In one of the deepest workings in the East Ovoca Mines 

 (Cronebane) the lode is cut out by an intrude of granite. 



In some few places adjoining the intrudes of the Aughrim type granite there are 

 ribs, or narrow strips, of the associated rocks, which have been changed apparently by 

 "local metamorphism " into gneiss. Eibs and patches of altered jasperized, or baked 

 rocks, often occur isolated ; the ribs are peculiar, and seem to be due to aqueo-igneous 

 heat, which found a passage along a line of fissure or jointing. Some of these altered 

 rocks, which are very felsitic (leptinyte, or white-stone), will be mentioned further on.} 



In places in the granite and schist areas there are newer dykes 

 of whinstones and felstones, which Du Noyer suggested might 

 possibly be of Tertiary age. Some of the whinstones are very 

 like the melaphyres of the Croaghan protrude (in King's Co.) ; 

 and in places they are cut and displaced by fissures filled with, of 

 course, later felsytes. I have elsewhere suggested the possibility 

 that these melaphyres and felsytes may be adjuncts of the in- 

 trudes of the " Aughrim type " granite. 



Territorial Description. 



Introductory. 



In the Queen's Co. there are no known exotic nor metamorphic 

 rocks. 



In the King's Co. and Kilclare there are isolated exposures of 

 eruptive rocks ; Carboniferous whinstone (melaphyre) and tuff at 

 Croaghan, north of Philipstown, and at The Chair, to the northward 

 of the town of Kildare ; very little used. 



1 According to the Australian miners and geologists (see Jack's "Eeport "), burnt, 

 or "iron-masked" rocks, as they call them, are favourable to the occurrence of gold. 

 This may have some bearing on the existence of the gold of the Co. "Wicklow, as 

 ' ' iron-masked ' ' rocks occur in the water-sheds of the valleys in which the ' ' placers ' ' 

 are situated ; but, at the same time, gold is not recorded from the tracts iu which the 

 greatest masses of these " iron-masked" rocks occur. 



