O'Reilly — On the EjncUorite and Mica Schists of Killiney. 21 



paper " On. the Directions of the main lines of Jointing about the Bay 

 of Dublin " (E.I. A. Proceedings, ser. ir., vol. iv., p. 259), it is one of 

 the set of joints the direction of which corresponds or is parallel to 

 the coast-line direction between Carnsore Point and Wicklow Head? 

 and also to that of the boundary line which limits the granite of 

 Wieklow on the west side between Castledermott and Goresbridge. 

 In the table of " Frequency of Occurrence," given on p. 304 of same 

 paper, the direction ]^. 16° 31' E. (the mean of 26 occurrences 

 observed) is shown to be the most frequent in the locality considered, 

 and therefore geologically of structural importance. 



ITear the gateway of Grlenalua Lodge, when coming from Killiney 

 village, the observer meets on the north side, or right hand, a rough 

 piece of ground, showing outcrops of the mica schists so characteristic 

 of the locality, and at one or two points, immediately under the 

 boundary wall of Glenalua Lodge, outcrops of a rock which will be 

 further considered. Apparently this was the quarry of slate rock 

 referred to in the Geological Survey Memoir already cited, and from 

 which the stones found in its boundary walls, and more particularly 

 in the coping of the boundary wall of the quariy next the road, were 

 taken ; the outcrops of the rock in question, being extremely hard, and 

 not easily worked, were left outstanding, and therefore quite accessible 

 for examination. The fault already referred to traverses this old quarry 

 field, and passes into the adjacent grounds of the Lodge. At the 

 point marked B on the accompanying enlarged plan of the ground, is 

 a wicket-gate, giving ingress on to the hill, to the west of Stoneleigh ; 

 here a barely traceable path skirts the margin of the granite on its 

 south side, and leads to the back-entrance of that property. From 

 this entrance (marked C on the accompanying plan) there extends 

 along the boundary wall, to the gate leading into Killiney Park, a 

 patch of ground showing markedly the mica schist outcrops, tongued 

 by the granite as described in the Memoir, and in certain bands 

 thereof, marked on the plan with the letter D, a crystalline rock of 

 the same nature as that which outcrops in the old quarry at Glenalua 

 Lodge already referred to, bearing every evidence of its metamorphism 

 from the associated slate rock and mica schists. This rock, marked 

 on the enlarged map accompanying (D. m. s.) (Dioritic mica schist), 

 is of a dark-green colour, usually fine grained, highly crystalline, 

 sometimes porphyroidal, and where most markedly cry stalline breaking 

 easily into rhomboidal fragments, very much after the way of certain, 

 feldspathic rocks. The mean density of a sample was found to be 

 3- 105, and thin sections of the same piece showed, under polarized 



