KiNAHAN — On Microscojncal Structure of Rocks. 165 



mica and pyrite (?) that occur in nests, is a bright green, beautifully 

 iridescent mineral. 



B. 22. This slice was. cut from a specimen taken from near the 

 margin of the mass of the granite, where it is slightly foliated. With' 

 a power of 17 the three varieties of felspar are apparent. The flesh- 

 coloured variety shows some well-marked twin crystals ; the iiidescent 

 semiopaque felspar is only sparingly developed, while the finely lined 

 felspar crystals are well marked, this latter felspar also occurring in 

 some places as thin envelopes to the semiopaque felspar. Of quartz 

 there is a large proportion, while the amphibole is in excess of the 

 micas ; the last minerals and pyrite (?) occurring in minute crystals 

 and fl.akes scattered about. In this slice was also observed the unde- 

 termined bright green iridescent mineral found in B. IS-''. 



B. 23. This slice is from a specimen procured a little north of 

 B. 22, where the granite is distinctly foliated. With a power of 17, 

 quartz is found to be the most abundant mineral, a large proportion of 

 it being in distinct crystals. The three felspars appear to be nearly 

 equally developed, while the flakes of the micas are minute and few. 

 The amphibole is in small nests, or scattered crystals, while the pyiite 

 is in most minute specks. 



It should be mentioned that the character of the granite at Cross- 

 fintan is porphyiitic, similar to the rock at Carnsore ; and that the two 

 slices [B. 22 and 23] just described, were, respectively, cut fi'om places 

 that seemed to show the general arrangement and proportion of the 

 different minerals to one another ; as always in the vicinity of one of 

 the large felspar crystals ; the other constituents of the rocks seem 

 to have a peculiar arrangement. 



From these notes on the granite of Carnsore, it will appear that it 

 and the Galway granite previously reported on [Reports Nos. 1 and 2, 

 antea, pp. 102, 161] are similarly constituted, and contain nearly 

 identical minerals. Under higher powers of the microscope, it waii 

 found that the individual peculiarities in the different minerals were 

 very similar to those to which attention was directed in those reports, 

 no remarkable variation having been observed. It is, therefore, un- 

 necessary to give detailed descriptions of them again, and I have con- 

 fined myself to the general character, which seems to identify this 

 granite with those of the Galway granite type, the principal constitu- 

 ents being three felspars [orthoclase, adularia (?), and oligoclase (?)], 

 quartz (both crystalline and as the skeleton of the rock), amphibole, 

 pyrite, and locally black and white micas. 



R. I. A. PROC, SEK. II., VOL. II., SCIENCE. 



