100 Proceedings of the Royal Irish Academy. 



plumose (fig. 15, PL 8). As the power is increased it becomes 

 evident that the appearance is chie to five crystals being tangled np 

 together; and with a power of 296 the ribands appear to be regular, 

 the curled aspect being due in part to refraction at the junctions of 

 the crystals. Under a power of 386 the whole is seen dotted over with 

 miniite black specks, with some short black lines ; the specks in some 

 places being more numerous than in others (fig. 16, PL 8). Some of 

 these specks, especially those in the upper crystal, are evidently gas 

 bubbles, but more than three-fourths in the whole mass seem to be 

 minute crystals or bunches of ciystals. 



Pig. 17, PL 8, represents another crystal, showing under a power 

 of 296, a somewhat similar constiiiction. In the upper portion the 

 layers are slightly crumpled and crushed up, especially the lower ones. 

 In the small portion to the left hand the lamina run obliquely, while 

 in the ciystal to the right hand there was seen by polarized light, a 

 whitish mass traversed most irregularly by blue walls and roundish 

 masses. Under a higher |)ower (386) the composition of the upper and 

 left hand crystals seem similar to that of the five just described, the 

 mass being all clotted over with black specks and gas bubbles; and the 

 irregular mass to the right hand seems to be inclined to have a con- 

 centric structure. 



W. Porphyritic yranite — KirTcidlen (Galway sheet 81). In the 

 field it seems to contain flesh-coloured felspar, light green waxy 

 felspar, quartz, ampliibole, black mica, pyrite, small spangles of white 

 mica ; crystals of titanite are rare. The flcsh-colouiTcl and the light 

 gi'een felspars seem to occur in about equal quantities, but largo, 

 usually twin crystals of the fii'st, give the porphyritic character to 

 the rock mass, but some of the light green felspar crystals are large 

 also. The micas, amphibole, and pyrites, occur in nests usually 

 associated with thfe quartz skeleton, but the micas also occur margining 

 some of the crystals of the green felspar. 



Of this rock one slice was cut showing its ordinary character, and 

 from it we learn there are at least three kinds of felspar in the rock, 

 although only two were observed in the field. 



Flesh-coloured felspar (Orthoclase). -I^oneof the large crystals were 

 examined, but the small crystals and masses seem to be quite different 

 from those observed in the previously examined rock (B', B', B', and B'), 

 as they contain numerous inlying minerals, similar to the twin crystals 

 in the Knockanavoddy (B') and Purbogh (B^ and B') granites. 



Pale yreenish felspar. This, as it appeared in the field, seemed to 

 be similar to the greenish waxy felspar of the Knockanavoddy granite, 

 but under the microscope we find the mass of it has characters similar 

 to those of the dull white felspar of that rock, but with it are 

 associated crystals and portions of crystals of a triclinic felspar. Under 

 a power of 63, one crystal of this kind of felspar was found to be 

 enveloped in triclinic felspar, and another crystal has a centre and 

 semi-envelope of triclinic felspar, while enclosed portions of crystals of 

 triclinic felspar are not uncommon. Many of the crystals and masses of 



