Loicer Palaeozoic Rocks of the South-East of Ireland. 583 



F. — The Main Granite Area. — This is the largest exhibition of granite at 

 the surface in the British islands, forming a continuous mass of seventy miles 

 in length, with an average width of eiglit or ten miles, and a maximum in one 

 part of eighteen. 



Its eastern boundary is, with the exception of a few indentations caused 

 by overlying slates extending into the granite area, very straight, running as 

 nearly as possible N. N. E. 



The western boundary of its northern half, though rather more irregular, is 

 on the whole parallel to this, but about the centre of tlie area, or a little north of 

 it, the boundary, in consequence of the deeper denudation of the granite, turns 

 boldly to tlie west for seven miles. South of this deflection, which marks the 

 entrance of the valley of the Slaney into the granite region, its western boun- 

 dary is formed by the overlying Carboniferous rocks of Carlow and Kilkenny, 

 resting upon it unaltered and undisturbed. This boundary is also very straight, 

 running N. 14° E. and S. 14^ W. for about eighteen miles, when the Cambro- 

 Silurian slates again make their appearance, and wrap round the southern ter- 

 mination of the granite. This southern termination is by no means an abrupt 

 one, and that the granite is continued for some distance towards the south- 

 east at no great depth below the surface, is shown by the reappearance of two 

 pretty considerable detached bosses of it, the latter being exhibited in the sides 

 of the valley or glen of the Arrigle River, south of Thomastown, on the west 

 of which the granite iinally disappears under the almost horizontal beds of the 

 Old Red Sandstone, which is there made up principally of granitic debris. 



The loftiest point of the granite area, F, is Lugnaquillia, 3040 feet,* in the 

 southern part of the county of Wicklow. It consists of a mass of mica schist 

 resting on the granite. All the loftiest parts of the neighbouring mountains 

 consist of similar patches of mica schist, and it is in this, the highestpart of the 

 granitic chain, that the mica schist most nearly meets over the granite, and the 

 greatest number of patches and bands, and embedded masses of mica schist, are 

 to be found within the granitic area. 



This shows that it is in this, the loftiest part of the chain, that we have the 

 original surface of the granite most nearly preserved, and that, if the mountains 

 had been a little loftier, — in other words, if the denudation had not proceeded 



• This is also the loftiest eminence in the south-eastern quarter of Ireland, 



4g2 



