330 Scientific Proceedings, Royal Dublin Society. 



detailed description of them. I have, however, with great diffi- 

 dence, offered a few suggestions which may contribute towards a 

 new explanation of some of the obscurities in the geological 

 structure of the hill. 



The rocks in this area, which are considered to be typical Irish 

 Cambrians, consist of an immense thickness of green and purple 

 grits and slates, with large masses of quartz rock. The slates 

 and grits, although often twisted and folded, and sometimes 

 even inverted (see Plate XXVI., figs. 3 and 4), have a tolerably 

 regular general strike nearly N.E. and S.W., with a general dip to 

 the N.W. An observer crossing; the summit of the hill at rierht 

 angles to the strike of the strata, will meet with several masses of 

 quartz rock which, although much broken up by small breaks, form 

 more or less continuous bands, which seem to be conformable to 

 the adjoining strata, and to form with them a continuous sequence. 

 However, on examining the sections to the west and east (along 

 the Delgany road and the railway), only two of these masses 

 will be met with, and in these two there are such striking simi- 

 larities, that very possibly they are portions of the same reef, 

 which has been brought twice to the surface hy extensive faulting. 



In the lands of Bray Head House, on the northward slope of 

 the hill, a large mass of quartz rock (A.) appears east of the House. 

 This seems to be a bed that is conformable to the strata, the 

 northern portion of which rests on the slope of the hill, with its 

 upper surface exposed ; towards the east, however, it curves 

 sharply, and being doubled on itself, the edge of the bed only, 

 appears a little to the south. Probably it is the same reef that is 

 seen further to the S.W. (A.'), at the boundary between Bray Head 

 and Ballynamuddagh. 



Southward of these exposures is the reef (B.B') extending from 

 the shore across the northern summit of the hill, in a slightly 

 curved N.E. and S.W. broken line into Kilruddery demesne, east 

 of the house. In the section exposed by the railway cutting this 



''Memoirs Geo. Survey of Ireland," sheets 121 and 130. By J. Beete Jukes, m.a. 

 F.G.S., and G. V. Du Noyer, m.r.i.a. 



" Weaver's Geological Relations of the East of Ireland," Trans. Geo. Soc, series 1, vol. v. 



"The Physical Geology of the neighbourhood of Dublin." By Rev. M. H. Close, 

 F.G.s., Journal Royal Geo. Soc. Ireland, vol. v., p 49. 



"Physical Geology of Ireland," p. 8. By Edward Hull, ll.d., f.r.s. 



" Manual of the Geology of Ireland," pp. 13, 35, 196. By G. Henry Kinahan, m.r.i.a. 



