2 4 6 



VARIOUS GRANITES OF LEINSTER. 



The Isolated Granites of Leinster. The isolated granites differ 

 in mineral composition much more than those of the main chain. 

 They are referred to four geographical groups. The first or western 

 group extends in a broken manner from near Rathdrum, for about 

 10 miles to Aughrim, and is well seen in Cushbawn Hill. In the 

 north it contains red felspar and black mica ; but in most cases it is 

 a fine-grained granite, with grey quartz, white felspar, and minute 

 particles of grey and dark-green mica, so small in quantity that 

 the rock may be said to consist of quartz 17*4 and felspar 82*6. 

 On analysis it contains 70 per cent, of silica; 1*34 of carbonate 

 of lime is supposed to be infiltrated from the overlying limestone 

 gravel. 



The second group of these granites consists of Croghan Kinshela 

 and Conna Hill, and has a length of about six miles. On its north 

 are the famous gold mines of Wicklow. This granite is chiefly com- 

 posed of quartz 38, albite 62, but contains a variable quantity of 

 chlorite, sometimes nearly wanting, sometimes plentiful. The quartz 

 in this rock occurs in small rounded granules. It is a soda-granite, 

 and contains 80 per cent, of silica. The brilliant white colour is due 



1 Haughton, Q. J. G. S., vol. xii. pp. 177, 186. 



58 Ibid., pp. 182, 183, 184; R. Irish Acad., vol. xxiii. 



