GRANITES OF THE SOUTH-EAST OF IRELAND. 245 



Tooth are potash granites, the first consisting of quartz 2070, felspar 

 6 6 '3 7, mica 1276, and the second consisting of quartz 17*16, felspar 

 67*18, hornblende 15*40. The syenites of Carlingford consist of 

 hornblende and anorthite. The formation of anorthite is attributed 

 to the addition of carboniferous limestone of the second variety of 

 granite when fused ; and in the locality of Grange Irish, the granitic 

 dykes which pierce the carboniferous limestone are found to be 

 changed into coarse-grained syenite. 



In the Newry district, there is potash granite to the south of 

 the town and soda granite to the north. The potash granite is 

 similar to the first-noticed granite of Carlingford. The soda granites 



characterised by the presence of jet black mica and reddish trans- 

 ucent felspar. 



Leinster. 1 The granites of the south-east of Ireland occur in 

 the counties of Dublin, Carlow, Kilkenny, Wicklow, and Wexford. 

 Professor Samuel Haughton describes the main chain of granite 

 hills as extending from Booterstown, county Dublin, to Poulmounty 

 in the south of Carlow, within five miles of New Ross. This chain 

 has an unbroken length of sixty-eight miles, and is from eight miles 

 to fifteen miles broad. Secondly, to the east of the main chain, and 

 parallel to it in Wicklow and Wexford, are about twenty isolated 

 districts, where granite breaks through the Cambrian slates. This 

 chain extends forty-three miles from Ballinaclash, county Wicklow, 

 to Camaross Hill, county Wexford. 



The granite of the main chain varies but little in appearance, 

 and consists of quartz, orthoclase, silvery grey mica, and black mica. 

 The quartz is uniformly grey and transparent. The orthoclase is 

 invariably white and opaque, and occasionally forms large porphyritic 

 crystals. Dr. Haughton thinks that albite probably occurs, though 

 he has been unable to identify it. The grey mica is in plates varying 

 from ^\jth of an inch to three inches diameter ; and occurs in flat right 

 rhombic prisms, or in hexagonal tables ; it belongs to the species 

 called Margarodite. The black mica is only in small quantity ; the 

 only accidental minerals are schorl, beryl, apatite, garnet, fluor spar, 

 spodumeme. In chemical composition this granite varies but little, 

 the silica only ranging between 70 and 74. The mineralogical com- 

 position is mica 13*37, felspar 61*18, quartz 24*98. 



Rev. H. Lloyd (1833) notices that to the south of Dublin, opposite 

 the village of Black Rock, the granite is composed of rounded 

 masses which he thinks to be water-worn and cemented in a granite 

 matrix. 2 The microscopic structure of the granite of Ballyknockan, 

 county Wicklow, has been described by Professor Hull. 3 



1 Haughton, Quart. Jour. Geol. Soc., vol. xii. 1856, p. 171. 



2 Geol. Soc. Dublin, vol. i. part i. p. 83. 



3 Journal R. Geological Society of Ireland, vol. iv. p. 6 ; and in Geol Mag. 



