KiNAHAN — On Miovscopkal Structure of Hocks. 99 



gTanite. These large crystals, as in the Knockanavoddy rock, contain 

 many inlying niiiierals, those most conspicuous being qnartz and 

 pyrite ; while the characters of the small crystals and masses of the 

 flesh-coloured felspar, as in both the rocks previously described (B.' 

 and B.'^), are very regular and similar to those already figured and 

 described (fig. 6, PL 7), and contain very few inlying minerals. All 

 these, however, in this and the other granites according to the portion 

 of the crystal exposed to "\iew give remarkable changes of colour. 



Dull white felspar (Adularia?). — This felspar when examined is 

 similar in structure to the dull white felspar of the Knockanavoddy 

 granite and the dull green soapy felspar of the Ballynahown rock. 

 In one of these crystals that had a lined structure when viewed with 

 a power of 386, the lining appears to be due to broken and more or 

 less irregular walls of quartz, that give shades of violet when the 

 intervening spaces appear a translucent yellowish white, that had 

 inliers consisting of irregular large white spots, minute black specks, 

 and long black crystals. A group of crystals of felspars in one of the 

 slices (B*) under a low power (42) appear to be similarly constituted, 

 but each had a character of its own when viewed with a power of 238 

 (fig. 12, PI. 7). The upper crystal on the right hand is of the 

 ordinary character belonging to this dull white felspar, being more or 

 less opaque, and spotted over with iridescent particles. The crystal to 

 the left hand has an irregular lining, somewhat similar to that just 

 now described, consisting of walls of quartz separating whitish spotted 

 portions, except that the quartz walls are thicker and more con- 

 spicuous than the intervening portions ; while the lower crystal to the 

 right hand is traversed by minute dark parallel lines, that in places in 

 the lower portion of the crystal are associated with partial walls of 

 quartz, all being crossed somewhat obliquely by newer minute parallel 

 whitish lines. In the latter crystal, under a still higher power (386), 

 the dark nearly horizontal lines are found to be principally due to more 

 or less regular lines of probably oblique sections of minute oval 

 tubes (fig. 13, PL 8), with which are associated short black lines, 

 that seem to be vacancies, while the slightly oblique lines crossing 

 them appear to have been shrinkage fissures that subsequently were 

 filled by some white substance. All these crystals seem to be the same 

 felspar, with different appearances, due to different structures. 



The tricUnic felspar (Oligoclase ?). — This felspar in these slices is 

 always more or less associated with the dull white felspar, but in the 

 slice with the twin crystal of orthoclase (B^), there are some good 

 exposures of crystals and irregular masses, which change from faint 

 ribands of shades of grey and yellowish grey, to shades of violet, 

 purple, and blue. Fig. 14, PL 8, represents a portion of one of these 

 crystals under a power of 238. These crystals contain little black 

 inliers (pyiite ?) while scattered through the oligoclase (?) are other 

 similar black crystals. In one place in this slice (B"*), under a power 

 of 196, was detected a mass having a peculiar structure, as the riband 

 takes an irregular semi-radiating form, in places being somewhat 



