KiNAHAX — On Giamtic and other Ingenite Rofks. 125 



Haughton divides the granites of Ireland into tki-ee groups, viz. : — 

 I. The granites of Leinster ; II. The granites of Mourne and Carling- 

 ford ; and III. The granites of Donegal, Mayo, and Galway. These 

 belong to two classes, first, intrusive, containing the first and second 

 groups ; and second, non-intrusive, containing the third group.* 



Mr. Deleese " also distinguishes two kinds of granite, one irruptive 

 and the other metaniorphic ; the latter taking often a gneissoid struc- 

 tui^e."t 



Haughton' s first group seems to he nearly identical with the ortho- 

 clasic intrusive-granite, -while the oligoclasic nietamorphic-granite 

 represents his third group. 



Metamorphic oligoclasic-granite (Gralway-type-granite). — These are of 

 raetaniorphic origin, ov formed in situ ; that is, the granite is due to the 

 extreme metamorphism of derivate and igneous rocks in the place, in 

 relation to the associated rocks that it now occupies, and was not 

 intruded or thrust up into its present position. 



This rock, the " Gal way- type-granite " of the Memoirs of the 

 Greological Survey, is a crystalline porphyritic aggregate, having as 

 conspicuous essentials pink or flesh-colour felspar {orthoclase'), greenish 

 or yellowish waxy felspar, white felspar, | quartz, black mica 

 {lepidomelane ?), white mica (^muscovite ?), and pyrite or marcasite. 

 The common accessories are amphihole, titanite, ripidolite, epidote, 

 chalcopyrite, galenite, flourite, talc, and garnet. The first three of these 

 accessories seem locally to be also essentials. Thus in the Furhogh- 

 type-granite (called after Furbogh, six miles west of Galway, where this 

 variety is the prevailing rock), amphibole and titanite are essentials ; 

 in other localities amphibole and ripidolite, also epidote, are not uncom- 

 mon : the latter, however, is believed to be due to decomposition. 

 Pyrite is mentioned among the essential, as it seems never, or on very 

 rare occasions, absent. 



The oi-thoclase usually occurs in large crystals, often twins, some 

 being over two inches in length ; they usually give the porphyritic 

 character to the rock ; however, in a few places, the white felspar 

 may do so. In one locality [Furlogh) some of the large flesh-colour 

 crystals {orthoclase) are enclosed in. a white felspar envelope. 

 The amphibole in places is accompanied by titanic, or ripidolite, or by 

 a green epidotic-looking mineral, the hornhlendic-granite occurring as 

 irregular subordinate masses — the variations in the composition of 

 metamorphic granite, as pointed out by Haughton, being due to 

 the different rocks from which it was formed. In places, there are 

 irregular and vagrant patches, and veins of a variety, "very coarsely 



* For a resume of Doctor Haughton's conclusions on the granites of Ireland, 

 see "W. TV. Sm}i;li's, F. R. S., &c., Presidential Address to the Geol. See. Lond., 

 Quar. Joiu-., vol. xxiv., p. Lsxiv. 



t Volcanos, by G. P. Scrope, F. R. S., &c., second ed., 1862, p. 300, foot-note. 



X Some of the waxy felspar is triclinic, but usually it is more or less amalga- 

 mated -vrith a variety of orthoclase, probably adiilaria ; the white felspar also is 

 probablj' adularia. — \_N'ote added in the press. '\ 



R. I. A. PEOC , SEll. II., VOL. II., SCIENCE. S 



