20 Proceedings of the Royal Irish Acade7ny. 



inclined from the granite, or they are vertical, with an east-to-west 

 strike. And between Killiney Lodge and Killiney Park they seem as 

 if interstratified with lenticular dykes of granite, adjoining to which 

 they become full of crystals of andalusite. The boundary of the slate 

 and granite, as it is observed to the west of Killiney Park, is very 

 intricate, one rock entering the other in long dykes and tongues, as 

 may be seen by reference to the south-west corner of the sketch-map 

 given on fig. 10, p. 35. 



"The remaining portion of the boundary between the slates and 

 the granite southwards, from Ballybrack cross-roads to the edge of the 

 map, a distance of a mile and a-quarter, is quite concealed by a thick 

 deposit of drift, so that the boundary line between them is a rather 

 hypothetical one, being drawn from the form of the ground only." 



It will be observed that, in describing this particular part of the 

 granite lying about Killiney, no mention is made of " trap rocks " as 

 occurring in the formation, but in the description of the beds at 

 Howth, and those shown in the south-west corner ef the map, distinct 

 reference is made to them. Thus, at p. 36, he says : — 



*' When the unaltered Silurian slates appear in the south-west 

 corner of the map, they are plentifully associated with fairly crystal- 

 line trap rock, which is sometimes porphyritie, occurring in large and 

 small lenticular masses, as well as in dykes and veins of narrow 

 dimensions, and along with these are equally numerous beds of 

 compact gray ash." 



In the present paper I propose to examine the beds occurring in 

 the locality referred to on p. 34 of the Memoir, and described as lying 

 between Killiney Lodge and Killiney Park. Owing to the develop- 

 ment of residential properties in this locality, and the consequent 

 alterations in the old boundary lines since the date of the Memoir in 

 question, it is necessary, in order that the lie of the ground in the 

 locality may be better understood, to give the names of the present 

 residences and grounds, as marked on the more recent Ordnance maps, 

 which are laid down on a scale of five feet to the mile, and numbered 

 xxiii. 97 and xxvi. 17. 



Examining these, it will be observed that the road which branches 

 off to the "W.S.W. from Killiney village at Glenalua Lodge turns to 

 the S.W. at Venetian Cottage, and continues to Glenalua Lodge, 

 where it inflects to the "W.N.W. at the entrance to Hendri. Quite 

 near this it crosses the well-marked fault existing between the granite 

 and the mica schist in this locality. The direction of this fault is 

 about N. 17° 38' E., and is remarkable in that, as pointed out in my 



