FOLIATED GRANITE OF GALWAY. 247 



to tlie albite, but it is sometimes stained by chlorite, which appears 

 to take the place of mica. 



The third group of isolated granites commences S.W. of the 

 village of Oulart in County Wexford, and extends at intervals for 15 

 miles to Camorus Hill. These granites consist of grey quartz, white 

 felspar, which occasionally become yellow or pink, and black mica, 

 which is probably mixed with hornblende. Professor Haughton 

 considers it to consist of quartz 6*44, felspar 89*69, mica 3*60. 



The fourth group of granites is at Carnsore, and consists princi- 

 pally of grey quartz and reddish felspar, frequently associated with 

 green mica and a variety of hornblende, which is irregularly distri- 

 buted. This is a potash granite, and neglecting the mica, consists of 

 quartz 21*50, felspar 78*50. 



Hence Professor Haughton concludes that the Leinster granites 

 belong to two types ; first, the potash granites of the main chain and 

 of Carnsore ; and, secondly, the soda granites of the isolated series. 

 The potash granites are subsequent in date to the Cambrian rocks 

 and older than the carboniferous limestone. The soda granites are 

 also newer than the Cambrian rocks, but there is no evidence of their 

 exact age. In I858 1 Dr. Haughton regarded the isolated granites as 

 formed by irruption of granite of the main chain adulterated or mixed 

 with the materials of the rocks through which it burst. 



Professor Haughton states that the eruptive granites can be dis- 

 tinguished from the metamorphic granite 2 by their felspars never 

 including any lime felspar, and by containing albite in addition to 

 orthoclase. Among such granites he would class those of Cornwall 

 and Devonshire, Leinster, Mourne, and Peterhead. The granites 

 which he believes to be metamorphic contain, in addition to the 

 orthoclase, oligoclase or labradorite, but albite is never found. As 

 examples of such granites may be quoted those of Donegal, Galway, 

 West and Central Scotland, and Aberdeen. 



Galway. A large tract of granite stretches west from the tow r n 

 of Galway to Bertraghboy Bay and Dogs' Bay, which has been 

 described by Mr. Kinahan. 3 Professor Hull, F.RS., 4 has examined 

 its microscopic characters. It is a foliated rock, probably of metamor- 

 phic origin at Firbogh, in Galway Bay, and consists of quartz, dull 

 waxy felspar probably oligoclase, and dark-green mica in nearly equal 

 proportions, with porphyritic crystals of flesh-coloured orthoclase. 

 The quartz is never crystallised, and envelops all the other minerals. 

 It contains numerous fluid cavities. Orthoclase occurs in small crystals 

 as well as in larger masses. It is penetrated in two directions by irre- 

 gularly parallel lines, like chains, of microscopic beads. Scattered 

 flakes of brown mica are imbedded both in the silica and felspar. 

 Colourless mica occurs in twisted flakes. There is probably a little 

 magnetite. 



1 Trans. Royal Irish Acad., vol. xxiii. p. 611. 



2 Proc. Royal Society, vols. xvii. xviii. 



3 Explanation of Sheet 105, Geol. Survey, Ireland. 



4 Geological Magazine, May 1873. 



