Vicinity of Dub lift, 271 



tose beds are to be seen at that place to a considerable extent reposing 

 upon granite ; and the line of junction, which begins here at the 

 sea-side, may be traced by the eye for some miles across the country. 

 The regularity of this junction is remarkable on the top of Ro- 

 chestown hill, adjoining that of Killiney ; where ledges of granite, 

 against the foot of which the incumbent rocks incline, present in 

 several places, a rectilinear course for many fathoms together. 

 On the shore at the base of KilUney-hill^ the granite is traversed by 

 numerous veins, many of which themselves consist of granite ; and 

 in some instances, two granite veins, differing from each other and 

 from the mass, In fineness of grain and in proportion of their ingre- 

 dients, are seen to intersect; one vein often deranging the continuity 

 of the other's direction. The substance of these veins is perfectly 

 continuous with that of the mass through which they run, and the 

 surface of the fracture passes through both without interruption. 



The conical masses of the Sugar-loaf mountains, with the sum- 

 mits of Brayheady and Shankhilly resembling them in structure, are 

 composed of quartz ; and it may be remarked, that the conical form 

 appears to be in some measure characteristic of mountains com- 

 posed of that substance ; for Mr. Jameson informs me, that he has 

 seen in Lusatia detached conical summits composed of it ; and that 

 the well-known Paps of Jura, and the conical summits in the moun- 

 tains separating Caithness from Sutherland, are of the same material j 

 as also is, according to Dr. Berger, the mountain Durnhilly near the 

 town of Portsoy. * 



The actual contact of granite with incumbent rocks, has been ob- 



* Humboldt states, that in South America, quartz constitutts, exclusively, a mass of 

 more than nine thousand five hundred feet in thickness, which he considers as of a 

 " formation" peculiar to the Andes. He has not mentioned the form of the summits. 

 Tableau Phys. p. 128. 



