180 Scientific Proceedings, Royal Dublin Socief;/. 



Cambrian and Arenig (?) Whinstones, Euiytes, Felstones, 

 and Quartz-Rocks, with granitic roots (?) 



In the Co. Wexford these rocks are more usually metamorphosed 

 (schist, hornblende rock, gneiss, and granitic rocks). Elsewhere 

 they are not as numerous, and are unaltered. 



[Some of the whinstones and quartz-rocks {Greiscn, Cotta) -were evidently intruded 

 or accumulated contemporaneously with the associated Cambrians ; sometimes as bedded 

 sheets, sometimes in protrusions, on and around which the sedimentary rocks were 

 deposited. As adjuncts to these, there seem to have been granitic roots {elvans, §c.) ; 

 these, however, are difficult to trace out satisfactorily, on account of the surface 

 accumulations. In the Co. Wexford and elsewhere, it is apparent that, in the later 

 formations the whinstones {gabbro, diabase, §c.) were associated with masses of 

 agglomerate. Some altered masses of whinstones. with their adjuncts of Cambrian age, 

 are the rocks that have been picked out by Dr. Callaway, and declared to be of Archaean 

 age. The greater part of the quartz -rocks are unquestionably Cambrian, as to their 

 material (we cannot now stop to go into this question) ; but some of the dykes may be 

 of later age, as similar rocks are found extending up into the Ordovicians. It is there- 

 fore clear that there must be older and later quartz-rocks, and that consequently the 

 exact age of isolated exposures cannot be positively stated. In the granite, in some 

 places in the Co. Wicklow, there are masses of quartz-rock specially peculiar, from 

 having in them an independent structure, indistinguishable from bedding : this is very 

 conspicuous in the "White Rock," a little north of Tinahely. Some at least of these 

 masses are contemporaneous with the granite, such as the mass near Hacketstown, which 

 graduates into a conglomeritic rock, and the latter into the associated granite. In 

 general, however, the mass of the quartz-rock has a hard, -well-defined boundary, the 

 strike and dip of the lines of structure being regular.] 



Arenig (Post- Cambrian and Pre-Ordovician). In the Co. 

 Wexford, at Carne, Carnsore, and in the Saltee Islands, there are 

 intrusive and metamorphose granites, later than the accumulation 

 of the Cambrians, and older than that of the Ordovicians. These 

 have not been recognized as occurring in any other part of this 

 territory. 



Ordovician, Whinstones, Eurytes, Felstones, Quartz-Rocks, 

 and their granitic roots. 



[The granitic rocks in the laccolites {Gilbert) or root masses, are in general very 

 felspathic, often hornblendic {syenyte) ; but whether hornblendic or micaceous, their 

 minerals are in very minute crystals or flakes, especially the latter, which are often so 

 minute as only to be microscopically perceptible. In the early accumulations {Black 

 Shale Series) there are quartz-rocks, sometimes as protrudes, but usually as dykes, some 

 being felspathic. In the middle group {Ballymoneij Iron Volcanic Series) whinstones, 

 {diabase and gabbro) are frequent in protrudes, bedded sheets, and dykes. They arc 

 often associated with tuffs, which are more or less calcareous, and some even impure 

 limestones. There are also some peculiar protrudes of agglomerate, a few being in 

 mass, but in general they are of smaller dimensions. The latter are invariably more or 



