94 Proceedings of the Royal Irkh Acadetmj. 



XVI. — Microscopical STEucTtrEE of Rocks. Repoet No. I. — Ingenite 

 Rocks. By G. H. Kinahan, M. R. I. A., &c. (With Plates 7 

 and 8). 



[Read June 8, 1874.] 



In these reports on the microscopical structure of the Ingenite Rocks 

 it is proposed to describe each rock under the names adopted by me in 

 " A Handy book of Rock [Karnes, "* while all the minerals will be called 

 by Dana's names. With each specimen, prior to entering into its micro- 

 scopic structure, will be given a description of the rock, as it appears 

 when examined in the field, with the naked eye or with a pocket lens. 

 In this report the felspars will be principally treated of — the power 

 used, except when specially mentioned, being 42. 



In a paper read jS^ovembcr 13th, 1871, before the Academy, " On 

 the Granitic and other Ingenite Rocks of Yar or West Connaught,"f 

 I pointed out that the granitic rocks seem capable of being divided 

 into Intrusive granite (Highly siliceous granite). Granite for the most 

 part 7ion-intrusive (Bsisic or oligoclase granite), andJiJlvani/te (Quartz- 

 porphyry ;| the latter rocks being the passage-rocks between the typi- 

 cal granites and the plutonic rocks. It was also shown that between 

 the typical Highly siliceous granites and the Basic granites, there are 

 granites partaking of the nature of the former in being intrusive and 

 of the latter in containing as essential constituents, such minerals as 

 oligoclase, amphibole, and the like. Moreover, it was shown that 

 typical Basic granite seems to be always more or less of metamorphic 

 origin, and that it graduates into the Intrusive oligoclase granite, 

 while the typical Highly siliceous granite is intruded in independent 

 masses. Suggestions were also given as to the probable formation of 

 the granites, but to enter into that subject now, would be foreign to the 

 purpose of this report ; we will, therefore, refer those interested, to 

 that paper and to the Handy book of Rock JS'ames, pp. 37 to 39. 



The first rocks to which we shall draw attention, belong to the 

 second group of granitic rocks or Granite for the most part non-intrusive 

 (Basic or oligoclase granite), the specimens having been collected in 

 the Co. Galway. 



B.' Porphi/ritic granite from Knoclcanavoddy (Galway sheet 93). — 

 This rock, examined in the field, seems to contain flesh-coloured, 

 greenish, and dull white felspars, glassy quartz, dark coloured amphi- 

 bole, black mica, and pyrite. There are also small spangles of white 



* Published by Robert Hardwicke, London. 



t Vide next paper and also Handy book of Rock Names. 



X A fourth group, Pmtogene, is also given provisionally in the Handy book. 

 Protogene I now believe ought to be included among the sub-groups of the Basic 

 granite. 



