of the North of Ireland, 145 



Slleve Croob in the lower Iveagh, the most conspicuous hill of a 

 small 2;roup that lies nine miles in advance to the north of the 

 Mourne mountains, seems foimed on its north-east and south-east 

 sides of different varieties of sienite, some of which are porphyritic 

 and very beautiful : the crystals of hornblende are extremely well 

 defined, and the compact felspar constituting the basis has a 

 brownish or smokv colour. 



This sienite crops out at intervals from Bakaderry town to the 

 top of Slieve Croob, occupying an elevation of about 900 feet. 



Slieve Gallion, in Derry, exhibits sienite in connection with por- 

 phyry, and either of a porphyritic texture or in large concretions ; 

 I met with an elegant variety on the road from Lissane to Lough 

 Finca ; the felspar is either slightly green or flesh-red with horn- 

 blende, quartz, and some pyrites. This rock acts strongly on the 

 magnet. 



In the bed of the Black-water near the valley of the Mayowla, on 

 the north-west side of Slieve Gallion, the sienite is mostly composed 

 of crystallized hornblende with some felspar and iron pyrites, verging 

 therefore into greenstone. 



Vol. in 



