of the North of Ireland. 135 



slope gradually into the plain, the same rock reaches Rathfriland, a 

 table-land of inconsiderable elevation. 



Within the geographical boundaries just assigned, the granite is 

 spread over a surface that measures 324 square English miles, com- 

 prehending the highest ground in the north of Ireland. 



A few masses of other unstratified rocks, of which notice shall 

 be taken elsewhere, occur in this formation. 



Some primitive but stratified rocks also rest upon it in many- 

 places, generally arriving at their greatest elevations on their south- 

 western boundaries. 



The texture of this granite is either porphyritic or finely 

 granular. The felspar always appears the prevailing ingredient, 

 usually grey, more rarely milk white and earthy ; the quartz has a 

 smoky tinge, and in the granular variety it generally occurs crys~ 

 tallized in double six-sided pyramids ; the mica is of a brown-black 

 colour, and bears but a very small proportion to the other two con- 

 stituents. 



Amongst the accidental ingredients I remarked but two, viz. 

 crystallized hornblende, chiefly abundant in the porphyritic variety, 

 and small redish garnets in the granular. The two varieties are, 1 

 believe, mingled both together, so at least they occur on the top 

 of Slieve Donard. I more particularly noticed the granular on 

 Slieve Muck, Slieve Birna, Ravensdale, and Slieve Gullen ; the 

 porphyritic on Newry and Fathom mountains. The imbedded 

 crystals of hornblende cause this rock to act on the magnet. 



Water-worn pebbles of porphyritic syenite, occasionally contain- 

 ing flesh red crystals of felspar and iron pyrites, are very frequent 

 at the base of the Mourne mountains on the road from Ross Trevor 

 to New Castle. It is probable that these have been derived from 

 the disintegration of neighbouring masses of that rock, occurring 



