288 GEOLOGY OF THE VICINITY OP DUBLIN* 



Pitchstone. I'he surface of the concretions is smooth, and strongly 



glistening^ Slightly translucent on the edges. It scratches 

 window glass, but is easily scratched by quartz. Easily 

 broken. Specific gravity, 2*29. Before the blowpipe with- 

 out addition it yields a grayish white frothy enamel. 



It is in some places porphyritic, containing imbedded 

 minute crystals of feldspar and of quartz. 



A letter from a very intelligent observer, who has exami- 

 ned this substance in its native place, states the following 

 particulars respecting its position. 



** The vein is first observable in the Townland of Newry, 

 •* at the bottom of a bank of granite, about half a mile from 

 ** the northern end of the town, on the right of the road 

 " leading to Down Patrick. It crosses the road, and runs 

 ** due westward, ending on the side of the great road from 

 ** Newry to Belfast. Its length, so far as hitherto observed, 

 ** is half a mile. 



** The rock, which is covered with mould to the depth of 

 •* about a foot, consists of a gray granite. The vein is 

 ** about two feet and a half, or two and a quarter in width ; 

 <* at the places of contact both the granite and pitchstone 

 *' are disintegrated, the latter being almost as soft as clay, 

 ** but becoming gradually harder, as it approaches the 

 •* centre of the vein. The structure of the vein is foliated, 

 ** the folia being perpendicular to the horizon, and also to 

 *' the walls; and beside these there are seams, that run 

 *,* longitudinally, parallel to the horizon, and nearly per- 

 ** pendicular to the folia." 



Although this substance presents some peculiarity, in be- 

 ing divisible into rhomboidal fragments, it approaches in 

 this respect to the pitchstone of Arran (iu lamellar concre- 

 tions) which holds as it were a middle place between it, and 

 that possessing the more usual characters. 



Mr. Jameson has described a vein of pitchstone " running 

 in granite," observed by himself in Arran*; and he states, 

 that *• lamellar distinct concretions have been hitherto ob- 

 « served in the pitchstone of that island only."f'' 



• Min. of Scottish Isles, 4to, vol. I, p. 81. 

 . t Jameipon's Mineralogy, vol. I, p. 2QI. 



8. The 



