Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/151

 of glassy actynolite passing into hornblende, veins of quartz, magnetic and common iron pyrites. The basis sometimes approaches in its nature to clay-slate.

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 compound I observed, but not in situ, at the basis of the mountain of Coolcoserahan.

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.