GRANITES OF NORTH-EAST OF IRELAND. 



-43 



planes of the cleavage structure. This granite, according to Professor 

 Haughton, is interstratih'ed with the quartz rock, mica-slate, and 

 limestone with which it is associated. This interstratification is seen 

 on both northern and southern outcrops. At Glentchen the granite 

 contains beds of quartzose mica slate, beds of gneiss, and beds of 

 sphene rock, the latter consisting of quartz, orthoclase, and sphene. 

 Nearer the southern boundary thin beds of limestone run vertically in 

 the granite for several miles. On the northern border the granite 

 passes into stratified rocks by insensible gradations, passing into 

 felspathic gneiss with black mica, hornblende slate, and micaceous 

 quartz rock. At Castle Caldwell some of the granite veins consist of 

 quartz, pink orthoclase, white mica, black mica, and schorl, all in 

 large crystals, while other of the veins consist of quartz, pink ortho- 

 clase, yellowish-green oligoclase, black mica, sulphuret of molybdenum, 

 and copper pyrites. The percentage of silica in these granites varies 

 from 55 to 75 per cent. 



North-East of Ireland. The granites of the north-east of Ire- 

 land are chiefly found on the borders of counties Down, Louth, and 

 Armagh, though a small outburst occurs near Cushundun in County 

 Antrim. It forms three natural areas : First, the granite district of 

 Mourne, which is a circular mass nearly nine miles in diameter north 

 of Carlingford Bay ; second, the district of Carlingford, five miles in 



Haughton, Q. J. G. S., vol. xviii. p. 408. 



