200 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 6, 



Slieve na glogh, that the green mica is margarodite, we readily find 

 by the principles so often explained : — 



Q=:0-505 

 F=0-225 

 M=0-048 

 From which we deduce — 



Miner alogical Composition of Wellington Inn Granite. 



Quartz 23-23 per cent. 



Feldspar.. .. 61-98 

 Mica 14-59 



99-80 



Whether we consider the physical aspect, the mineralogical cha- 

 racter, or the chemical composition of this granite, it is strikingly 

 like the granite of the base of Slieve na glogh, with which I have no 

 hesitation in identifying it. Combining both together, we find : — 



Mineralogical Composition of Potash-Granite. 



Quai'tz, Orthoclase, and Green Mica, South of Newry. 



Quartz 21-96 per cent. 



Feldspar .... 64-17 

 Mica 13-67 



99-80 



In the granite of Jonesborough, at the southern extremity of our 

 section, large crystals of white opaque orthoclase are found, of which 

 the following is the composition : — 



Jonesborough Orthoclase. 



Specific gi'avity = 2-546. 



Per cent. Atoms. 



Silica 64-20 .... 1-40 



Alumina 19*331 ^ „- 



Peroxide of iron. . trace j * ' * • 



Lime I'OO^ 



Magnesia 0*18 [^ ^ on 



Potash 13-47 { ■ • ' 



Soda 1-89J 



100-07 



This analysis shows the feldspar to be a pure orthoclase. 



The potash-granite, composed of quartz, white feldspar, and green 

 mica, common to the South Newry and Carlingford districts, pre- 

 sents a remarkable similarity in mineral composition to the potash- 

 granites of Leinster. The only question as to which any doubt 

 remains is as to whether the green mica is a margarodite, in which 



