98 Proceedings of the Royal Irish Academy, 



while the white mica occui's in minute spangles. In places in this 

 rock are isolated crystals of titanite. 



Of this rock only one slice was cut, being taken from a portion 

 showing the ordinary appearance of the rock in which the dull green 

 felspar predominated. This mineral was very similar in aspect to the 

 greenish waxy felspar of the Knockanavoddy granite (B.'). However, 

 on being placed under the low power of the microscope (42), it was 

 found that the colour and appearance in the field were deceptive, as the 

 mineral now presented characters similar to those found in the dull 

 white felspar of the Knockanavoddy rock (figs. 7 and 8, PI. 7), while 

 mixed up with it, although not detected in the field, was a tri- 

 clinic felspar, and associated with them a few small crystals and masses 

 of flcsh-coloui'ed orthoclase. Here also as in the Knockanavoddy rock, 

 most of the mica, amphibole, and pyrite occur associated together, 

 while the mass of the cjuartz fonns the skeleton of the rock. No titan- 

 ite occurs in the slice. 



Flesh-coloured felspar (Orthoclase). — ]Si one of the large crystals were 

 examined but the small crystals and masses showed exactly similar 

 characters to those found in the small crystals examined in the Knock- 

 anavoddy granite (fig. 6, PL 7). 



Dull green soapy felspar (Adularia?). — This mineral gives the cha- 

 racter described for the dull white felspar of the Knockanavoddy rock, 

 aud in it are found portions of crystals and small masses that show the 

 ribands of colour characteristic of the triclinic felspars. 



Triclinic felspar . — This occurs in a few isolated masses, and as parts 

 of crystals in or associated with the adularia (?), the structures they dis- 

 played being very similar to those already described as characterizing 

 the triclinic felspar of the Knockanavoddy granite. 



B.^ and B.* J( slightly foliated porphyritic granite. — This rock was 

 collected by the late Mr. Jukes, and is marked from Furbogh (Gralway). 

 It is similar to the rocks in situ on the S. E. and S. W. of Pm-bogh 

 demesne. In the rock, the most conspicuous constituent is the flesh- 

 coloured felspar, the large crystals of which give the porphpitic 

 character to the rock, but the principal constituents are the dull white 

 and waxy greenish felspars and black mica ; iiTegular leaves of the 

 latter associated with amphibole, giving the foliated structure to the 

 rock. There are also present quartz, \^'hite mica, and pyrite, with 

 tliinly disseminated crystals of titanite. At Purbogh it was observed 

 in the field that some of the large flesh-coloured crystals had an envelope 

 of dull white felspar. 



Of this rock two slices were cut, one containing a portion of one 

 of the large flesh-coloured orthoclase crystals, and the other being from 

 a portion showing the ordinary character of the rock. In both the dif- 

 ferent felspars are represented. 



Flesh-coloured felspar . — The large crystals, as in the Knockanavoddy 

 rock, are generally twins, and in the slice tliat was cut through one of 

 them, the junction between the twins is a sharp line not an irregular 

 vacancy as was described in connexion with the Knockana^•oddy 



