

300 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 20, 



and therefore may, without violence to analogy, be supposed to give 

 rise to various nitrides, each of which is capable, under certain con- 

 ditions, of disengaging ammonia. 



2. Experimental Researches on the Granites of Ireland. 

 By the Rev. Samuel Haughton, M.A., F.G.S., Fellow of 

 Trinity College, and Professor of Geology in the University of 

 Dublin. 



Part II. {Continued). — On the Granites of the North- 

 east of Ireland*. 



I. Potash-Granites of the North-east District. 

 II. Soda-Granites of the North-east District. 



In the concluding part of my paper on the Granites of the North- 

 east of Ireland-}*, I have expressed the opinion that the granites of 

 the neighbourhood of Newry are divisible, like those of Leinster, 

 into two types, viz, potash- and soda-granites ; and that, if a line 

 north of east be drawn through Newry, the granites south of this 

 line are potash-granites, including the Mourne granites, while the 

 granites to the north of this line are soda-granites. As I have ob- 

 tained additional confirmation of this opinion since the reading of 

 my paper, it will be useful here to sum up the facts known relative 

 to the two kinds of granite in the two districts under consideration. 



I. Potash-Granites of the North-east District. 



I shall exclude from this discussion the granites of the Mourne 

 district north of Carlingford Bay, as they form a peculiar group, 

 characterized by the presence of distinct crystals of albite, and nests 

 of crystallized quartz. 



The following Tables contain the analyses and atomic quotients of 

 five granites of the potash-type, south and south-east of Newry : — 



No. 1. Granite from the base of Slieve na glogh, medium-grained, composed of 

 quartz, white felspar, and green mica. 



No. 2. Granite from Grange Irish, near Carlingford, fine-grained, composed of 



quartz, white felspar, and hornblende. 

 No. 3. Granite from Wellington Inn, south of Newry, medium-grained, composed 



of quartz, white felspar, and green mica. 



No. 4. Granite from Fathom Lock, east of Newry, porphyritic, of a general pink 

 colour, with white nests and minute cavities lined with very small erystals 

 of quartz. 



The paste consists of a reddish felspar, with minute specks and streaks 

 of dark-green chloritic hornblende, and small hexagonal crystals of quartz. 

 The felspar-crystals are semi-transparent, of good lustre ; size ^in. by iin. 

 The white roundish nests are probably white felspar, with flattish faces 

 and scarcely any lustre. Epidote and green earth appear in the small 

 cavities in connexion with the minute hexagonal crystals of quartz. 



* For Part I. and Part II. see Quart. Journ. Geol. Soc. vol. xii. p. 171 & p. 188. 

 t Loc. cit. p. 198. 



