of the North of Ireland. 143 



of glassy actynolite passing into hornblende, veins of quartz, mag- 

 netic and common iron pyrites. The basis sometimes approaches in 

 its nature to clay-slate. 



4. Hornblende with Mica, 



This aggregate rock composes the top of Clark's hill or Slieve- 

 sleet, five hundred and forty-eight feet above Castlewellan. I also 

 noticed it on Slieve Croob, between Slieve Nasky and Bakaderry 

 town. I saw it again in loose blocks about Castlewellan. 



A Druidical monument at Coagh near Cookstown, is partly 

 made of an aggregate of crystals of hornblende. The same com- 

 pound I observed, but not in sitiif at the basis of the mountain of 

 Coolcoserahan. 



E. Porphyry.^ 



Felspar porphyry occurs in the county of Down, in the bed of the 

 Finish, on the north-west side of Slieve Croob, near Drummara in 

 the lower Iveagh ; and in a decomposing state at Ballyroany, four 

 or five English miles north-east of Rathfriland. In the first of these 

 localities it is interposed In a compound rock of granular quartz 

 and mica. 



*• See the article on some porphyries of doubtful formation at the end of these extracts. 



