of the North of Ireland. 141 



tain, which is 1850 feet high, the trap is seen passing from an 

 homogeneous to a porphyritic texture. The latter imparted by . 

 lamellar crystals of felspar of a white colour, and of rather con- 

 siderable size : gradually the accidental ingredient becomes the 

 essential one; the colour of the felspar becomes greenish, and in that 

 state ihe rock approaches more nearly perhaps to the character of 

 sienite than to that of trap. 



In its genuine state, in the lower part of the mountain, the rock 

 puts on the usual coated appearance which originates from decay. 



On the eastern slope of Slieve Birna, one of the Mourne moun- 

 tains, at one half nearly of its height, I observed a bed of hornblende 

 rock, apparently interposed in the granite. 



At Slieve Anisky, a hamlet on the road from Castlewellan to 

 Dromore, I noticed another bed of hornblende rock, but I am doubt- 

 ful whether it belongs to this class or to that of transition. 



b. Hornblende slate. 



This subordinate member of the primitive trap series frequently 

 occurs, forming distinct beds, in the mica slate of Antrim and Lon- 

 donderry. 



In the former county It Is found In the valley of Glendun, and 

 along the coast from Cushendun to Tor-point. 



In the latter it occurs in Bennady-glen, in Aglish-glen, and in 

 the bed of the Roe river near Dungiven. The bed of hornblende- 

 slate in the latter place occupies an extent not less than four hun- 

 dred yards, ending by the old church, where it runs parallel to a 



