of the Vicinity of DtiUin. 307 



vcrse4 by numerous veins, many of which are themselves 

 composed of granite ; and in several instances two such 

 vems, differing from each other and from the mass through 

 which they run, in fineness of grain, and in the proportion of 

 their inizredients, are seen to intersect, one not inifre- 

 fjuently deranging the continuity of the other's direction*. 

 The substance of which these veins consist is perfectly con- 

 tinuous with that of the rock in which they occur, and the 

 surface of fracture passes through both without interrup- 

 tion. 



The regularity of the lineby which the granite is bounded 

 at Rockcstown-hill is highly deserving of attention. " From 

 the top of the hill a very remarkable ledge of granite runs ia 

 a si'ra'.ght line, for upwards of a quarter of a mile, extend- 

 ing from a little below the summit on its south-eastern 

 side ill a direction from N.N.E. to S.S.W. This ledge, 

 which is elevated a fcv^ feet above the ground to the south- 

 east of it, appears to form the boundary of the granite. The 

 schist in this place seems to run up in a wedge-like form 

 betiveen this ledge and another a little to the eastward, 

 which is much less extensive than the former but corre- 

 sponds pretty nearly w'ith it in direction, its course being 

 from S.VV. by S. to N.E by N. ; and beyond this again 

 still further to the east, another wedce-like branch of the 

 schist runs up between this second ledge and the obelisk, 

 hill." 



" In the annexed sketch A denotes the summit of Roches- 

 town hill; B, the first ledge of granite; C, the second 

 ledire; D, the third ledge; E, part of the obelisk 

 hilft." 



The whole of the Greater Sz^o'ar-Loq/' mountain is com- 

 posed of quartz ; and the adjoining hill o'i St He -lawn and 

 the rocks at the upper part of the Dargle consist of the 

 same substance ; which also constitutes the mass of the 

 Lesser Siigor- Loaf mounia'in, and the suininits of Shank- 

 hill aiudoi Bray - head, Ttstmhlmg it in figure and in general 

 aspect];. It appears therefore that all the summits of this 

 vicinity which agree in form, are composed of the same 

 material; and it is leniarkable that the conical shape cha- 

 racterizes mountains consisting of quartz in various parts 



•The mode of intersection of these veins is illustrated by the annexed 

 Sketch, figs. 1,2,3,4, and 5, representing detached portions of veins ob- 

 lervable in dificrent places along the shore at Killiney ; figs. 7 and 8 are from 

 liirge loose blocks on the strand iliere : these, however, were not ihe moit 

 ri'niarkal)lc that might have been selected. 



I Extracted from a note by Mr. Stepheiis, 



j See tlie annexed Sketch. 



of 



