144 Dr. Berger o« the Geological Features 



In the mica slate district of Antrim, several beds of felspar por- 

 phyry are found ; they may be traced along the coast from Tor- 

 point to Cushendon, and thence inland along the old road to 

 Ballycastle. 



In Londonderry, the fundamental rock on the east side of Slieve 

 Gallion is a variety of felspar porphyry strongly resembling sienite, 

 with which rock it probably alternates in this mountain. 



In the same neighbourhood felspar porphyry may be traced with- 

 out interruption from the top of the glen of Latterane to the bed of 

 the Knockadoo river on the road from Lissane to Moneymore. 



F. Sienite. 



I have traced this rock In the low country adjoining the town 

 of Newry for three or four miles on the road to Dundalk, for the 

 same space on that to Armagh, and towards Bainbridge as far 

 nearly as the four mile house. It Is perhaps more extensive. 



The sienite is unstratified, cropping out in independent mases, 

 but rent into pieces mostly of a rhombic figure, the natural joints 

 of which are generally rusty. 



It is finely granular, composed of felspar of a blood red, flesh 

 red, or greyish colour, with some quartz, hornblende, and black 

 mica, besides two Ingredients, accidental but not uncommon, 

 namely, iron pyrites and small garnets. 



The sienite that crowns the summit of Foy mountain near Car- 

 lingford, contains only a few broad plates of black mica, with 

 greenish felspar and hornblende in large concretions. 



