54 TIu Irish Naturalist. 



and Carnsore Point on the south; while it is exposed con- 

 tinuously over the granite highlands which rise from the sea 

 at Killine}^ and stretch for 70 miles into the counties of 

 Wexford and Kilkenny. 



At Killiney the true character of this granite is excellently 

 shown. On the shore below the steep face of Victoria Park the 

 pale crj'stalline rock may be seen intruded in dykes and veins 

 into the upturned and crumpled Ordovician shales. The 

 junction is thus quite irregular; the hot rock has oozed into 

 the sediments and has baked them, developing new minerals 

 at the contact. Stellar groups of dark Andalusite have thus 

 arisen by the driving off of the water from the substance of 

 the clays and the cry^stallisation of the silicate of alumina ; 

 silver>' mica covers all the planes of separation of the rock, 

 but weathers away more rapidly than the andalusite, the latter 

 standing out upon the surfaces in knots and bars. These 

 products of contact metamorphism run through the mass in 

 bands, which probably represent original layers of stratifi- 

 cation ; while some beds, on the other hand, seem but little 

 altered. The granite itself has again and again a banded 

 streaky structure, indicative of viscid flow along its junction 

 with the older rock ; as it began to consolidate, shrinkage- 

 cracks, and joints due to "settlement" of its foundations, 

 opened through it, and portions of the still fluid material from 

 below were forced up into these spaces, forming a network of 

 parallel-sided veins. Examination of the exposures about 

 Kingstown and Killiney will show how some of these veins 

 have been themselves cracked through, and often shifted on 

 one side or other of the joint, still later material having finally 

 recemented the mass. Some of the granite forming these 

 subsequent veins is more coarse in grain than the surrounding 

 granite ; in others it is so finely grained that it is difficult to 

 distinguish the constituent minerals, the rock being then 

 properly called a Eurite. But in all these tj^pes of granite the 

 fundamental minerals are the same, whether we investigate 

 our samples w4th the unaided eye or with the microscope. 

 Quartz, glassy and unscratched by the knife ; Orthoclase 

 felspar,' pale pink-brown, yellow-brown, or white, w4th sur- 

 faces of regular cleavage ; and the micas, easily scratched, 

 flaky, shining like silver, or deep brown-black when richer in 

 magnesia and iron" — these are the essentials, though their 

 proportions may vary from point to point. The old term 

 granite is restricted to crj^stalline rocks, once molten, rich in 

 silica and alkalies ; the excess of silica is shown by the 



1 Chemical proof of the prevalence of this potash-felspar in the Dublin 

 granite was first given by Apjolin, Ptoc. R. Irish Acad., v. (1853), p. 381 ; 

 Galbraith followed with numerous analyses, ibid., vi., 134. 



^Haughton, Proc. R. Irish Acad., vi., 176, and Quart. Joiirn. Gcol. Soc, 

 Laiidotj, -KX., 129. 



