Junction of the Granite and the Killas Rods in Coniiaall. 169 



to be seen at (b); the grains in it are of a common size; the 

 felspar is of a white colour, inclining to decomposition ; twin 

 crystals of a larger size lie porphyritically in the rock. The 

 cjuartzose rock above-mentioned is very like the granite in the 

 neighbourhood of some quartz veins at Mousehole; and really 

 the same fact occurs also here. The granite at the point [b) is 

 frequently intersected b}' strings of quartz, and their walls con- 

 sist of the same quartzose rock. A very well characterized 

 killas is to be seen on the eastern side of Cligga Point ; it is of 

 a gray and greenish colour, sometimes with little red points like 

 the clay slate in the neighbourhood of Viel-salm in the Ar- 

 dennes. Several tin lodes have been worked here ; they run 

 east and west, dipping to the north, but nearly perpendicular. 

 Wolfram is found very frequently on the old heaps, and a lit- 

 tle yellow copper ore and tin ore. 



The junction of killas and granite may be readily observed 

 near [d) ; the killas has here the appearance of a very fine- 

 grained gneiss. 



A perpendicular wall more than one hundred feet high is 

 formed by the granite at {e) ; numberless veins of granite here 

 intersect the granite itself; the granite in both walls of each 

 is harder and more quartzose than the other; these veins run 

 very parallel, and dip all to the north ; they give a stratified 

 ajipearance to the rock. Quartz veins like these occur very fre- 

 quently here in the granite. This phaenomenon is in no point 

 so perfectly exposed to observation as near [f). Frequent 

 quartz veins running east and west, dipping very nearly per- 

 pendicular to the north, intersect here the granite at distances 

 of fi'om one foot and a half to three feet. The walls consist 

 of a rock, exactly the same as occurs between the points [a) 

 and (Z>). The granite ajipears stratified, the strata having the 

 thickness of the interstices between the quartz veins, which 

 are only a quarter of an inch wide. The granite which is not 

 in contact with these veins inclines to decomposition, but on 

 the contrary the walls of the veins are very hard. In these 

 quartz veins is found tin ore and wolfram ; they are therefore 

 of the same nature as the granite veins in the killas near (c) ; 

 they are even parallel to them, and differ only by being very 

 small. Two quartz veins of a very different kind intersect the 

 granite aty without heaving; they are four inches wide, run 

 15 degrees to the west from north, dipping with an angle of 

 85 degrees to the west. The quart/, they contain is milk-white, 

 and separated by fissures perpendicular to the walls of the 

 veins ; the granite forming the walls of these veins does not 

 diller from tlie otlier; these veins do not contain any metallic 



iV^.5. Vol.5. No. 27. Ma;c/2 1829. Z sub- 



