Vol. 68.] PALEOZOIC EOCKS OF THE KILBRIDE PENINSULA. 91- 



that it intersects. Commencing in breccia, it traverses the basal 

 Silurian conglomerate and a labradorite-porphyrite sill ending in 

 lime-bostonite. This dyke, like that-just described, is about 8 feet 

 wide, and shows marginal chilling. 



Both dykes strike south-southrcastwards, and may really be part 

 of the same intrusion. 



A third intrusion occurs about half a mile north of Einriy School, 

 and runs for some 300 yards in a north-westerly direction between 

 spilite and breccia, ])ara]lel to a very large red quartzose vein ; 

 whether this is a dyke or sill is not clear. ' Two small intrusions 

 of similar rock are seen near Finny, the one in spilite at the western 

 angle of the wood north of Pinny Chapel, the other in coarse 

 breccia a third of a mile north-west of the village. Another small 

 intrusion occurs in spilite, about 800 yards west-north-west of 

 Knock Kilbride. 



y. Petrogeaphical Details. 



(«) The Felsites. 



The great quartz-felsite intrusion which extends westwards from 

 Knocknamuck consists of a well-marked rock, much resembling 

 those that form the ' green and brown ' felsite-intrusions of the 

 Tourmakeady district and the great sill of the Glensaul district. 

 It is characterized by large crystals of quartz which in hand- 

 specimens often show crystal faces, embedded in a matrix usually 

 of a reddish-purple colour, but becoming yellowish-green near the 

 western border of the mass. Pew sections were cut of this rock, 

 but these showed an abundant felsitic ground-mass, through which 

 were scattered crystals of quartz, often strongly corroded, and a few 

 much-weathered felspars. The last-named include both orthoclase 

 and plagioclase, the plagioclase, as pointed out by Dr. Plett, being 

 often albite. The specific gravity of four specimens of this rock 

 gave an average of 2-65. 



West of this great intrusion are two smaller masses of the 

 same rock, which, it can scarcely be doubted, have (or once had) 

 a subterranean connexion with the larger mass. A section taken 

 from the more westerly of these two masses shows a still further 

 resemblance to the intrusive felsites of Glensaul and Tourmakeady, 

 in the presence of numerous pseudomorphs either entirely in a 

 green chloritic mineral, or partly in this, partly in calcite ; many 

 of the green pseudomorphs are certainly after rhombic pyroxene. 

 This rock has a specific gravity of 2-74. The felspars, which are 

 rather less weathered than those in the sections examined from 

 the great intrusion on the east, include both orthoclase and plagio- 

 clase. Magnetite is rather plentiful. 



A very felspathic type of felsite, containing much magnetite and 

 abundant green pyroxene-pseudomorphs (72), occurs at lied Island 

 and along the shore to the south and south-west. The small felsite 

 patches which are seen south-east and south-west of Lough Mwee- 

 laun show no features of special importance. 



