162 Proceedings of the Royal Irish Acade/ni/. 



having irregular finely serrated thin fringes of other colour; while 

 some have the irregailar lines of that colour running through 

 them. In specimen B- very little quartz appears in the slice^ 

 while in specimens B^ and B^ the fringes are very marked, and 

 every group of quartz forms a patchwork made up of many small 

 irregular portions. In the granite of Kii'kullen (B^), as represented 

 in the slice, some of the quartz skeleton seems inclined to occur in 

 crystalline forms, and in part to partake of the natiu'e of the quartz of 

 the elvanytes. Its quartz, when the polarizer is turned, is inclined 

 to give more a play than a change of colours, while each piece usually 

 has a fringe of prismatic colours. Prom this it would appear that the 

 specimen of the rock was taken from a locality in which the rock had 

 lost the true normal character of typical granite. 



Fig. 18, PI. 8, represents two small masses of quartz in the KirkuUcn 

 granite magnified to 42 diameters. In the right-hand one a crystal will 

 be found with a power of 196 (see fig. 20, PL 8). In it are numerous 

 labeculse, some lying irregularly about, the rest more or less in lines or 

 zones ; there are also continuous lines, two of which are represented in 

 the figure. With a still higher power (386), these lines are found to be 

 strings of minute beads, apparently along shrinkage or fracture fissures. 

 "With the high power we also find that in places the labeculae are 

 systematically arranged, although with a power of 196 they appear to 

 be irregularly grouped. This is apparent in fig. 21, PL 8, which repre- 

 sents the place marked a in figure 20, magnified 386 diameters, and 

 shows there at least three distinct systems of labeculae, which probably 

 have relations with different facets of the ciystal. The higher power 

 also explains the elongated, pear-shaped, small, shaded spots in figure 

 20, which are found to be pointed clouds of minute labeculae. In two 

 places at the margin of this crystal there are clouds of small labeculae. 



The left-hand mass of quartz (fig. 18, PL 8) is different from that 

 just described, as the labeculae in it seem to be irregularly scattered 

 about. Associated with them in places are short thick lines, few 

 perfectly straight or symmetrical, like those in the quartz of the 

 elvanyte (fig. 23, PL 8), but usually more or less curved or crooked, 

 as represented in fig. 22, PL 8, which represents the place marked b 

 in fig. 18, PL 8, magnified 296 diameters. There is also a peculiar 

 feather-like arrangement, which is also shown in fig. 22, PL 8. Under 

 a power of 386 the crooked and curved lines are found to be gas tubes 

 or tubuU, wliile the feather-like arrangement is due to a line of oval 

 spots which are the oblique sections of a system of minute tubuli. 

 Pive of these tubuli magnified 386 diameters are represented below, in 

 figure 22, PL 8. 



The labeculae in the quartz are rarely visible when viewed with a 

 less power than 50, while some are so small as only to be visible with 

 a power of 400. A crowd of labeculae occur at some of the margins of 

 the masses of quartz, while the irregular lines, seen imder polarized 

 light, seem to mark the junction of two masses, or to be due to film 

 filling a line of fractiu'e. In the quartz of B' the labeculae are some- 



