GEOLOGICAL SOCIETY OF DUBLIN. 223 



this rock in hand specimens presents the appearance and structure of a 

 rather fine-grained granite, being composed of grayish- white felspar, 

 white mica, some crystals of hornblende, and some quartz ; the blocks 

 which have been quarried present large cubical or rather slightly rhom- 

 boidal masses, many of which would weigh upwards of a ton, some 

 upwards of two tons. Notwithstanding the difference in the structure, 

 it is probable that the three apparently distinct veins are the produce 

 of one common root, and that the difference in the veins has resulted 

 from the slower cooling of the large mass giving time before consolida- 

 tion for the more perfect development of the crystals of felspar, &c. 



Continuing our general section to the eastward, we find schistose 

 rock dipping to the south-east, at an angle of 15 degrees, having a 

 nearly vertical cleavage; it is highly metamorphic near its contact 

 with the felspathic vein, but becomes gradually less so at a distance 

 from it. 



Continuing the section to the east, at a distance of about 200 feet 

 from the last-mentioned granular branch of the felspathic vein, we come 

 in contact with and cross the direction of the greenstone protrusion 

 already mentioned, which at the road forms the eastern boundary of 

 the felspathic vein, but which, taking a north-easterly course, cuts ob- 

 liquely across the strike of the schistose rock. This greenstone con- 

 tinues in the same direction, forming the summit and eastern declivity 

 of the hill of Rock Little. But before reaching the farm-house of Rock 

 Little it descends into the earth and is lost. 



At the house of Rock Little, unaltered schistose rocks are visible, dip- 

 ping south-east at angles varying from 10 to 20 degrees, and I have no 

 doubt that this schistose rock forms the base of the valley which inter- 

 venes between Rock Little and Rock Big. 



The protruded mass of greenstone just mentioned is highly crys- 

 talline ; it is composed of oblong crystals of white felspar, with a pro- 

 fusion of imperfect crystals of black shining hornblende, forming a very 

 hard and beautiful rock. 



At the forge which stands at the forking of the road at the southern 

 end of the valley, between Rock Little and Rock Big, is a second protrusion 

 of greenstone, which extends uninterruptedly along the line of the old 

 Arklow road, in a north-easterly direction to the sea below the grave- 

 yard. ' This rock is not so coarse-grained as that first described; the 

 felspar is visible, but crystals of hornblende are rarely fully developed. 

 Ascending Rock Big to the eastward, we find a close-grained felspathic 

 mass, similar to that which occurs in the protrusion already mentioned ; 

 but in this case it presents a rude columnar structure, the columns 

 being four, five, or six-sided, inclining towards the IS". E. at an angle 

 of about 30°. Still continuing to ascend Rock Big to the eastward, the 

 rock graduates into rather coarse-grained greenstone, the crystals of fels- 

 par and hornblende being tolerably well developed, but not so perfectly 

 as that first-mentioned. Still continuing to ascend, the crystalline and 

 unstratified rock presents a nearly horizontal tabular structure, and the 

 different tables exhibit different characters: in some it is felspathic 



