42 Prof. Galbraith on the Composition of the Felspars of 



contribution I beg leave to send you the results of the analyses of 

 seven specimens taken from different localities in these moun- 

 tains, pretty evenly distributed over that part of the range which 

 extends from Dalkey to the flanks of Lug-na-quilla, a mountain 

 about thirty-six miles from Dublin. These analyses will, I 

 think, not fail to engage the attention of such of your readers 

 as feel an interest in chemico-geological investigations, 



Quarries of Dalkey, County Dublin. 



SiO 3 



A1 2 3 



MgO 



CaO 



KO . 



NaO 



Loss by 



ignition 



Per cent. 

 . 64-00 

 . 18-1] 

 . 0-57 

 . trace 

 . 12-73 

 . 300 

 . 0-55 



Atomic quotients. 

 1-412 

 0-352 

 0-028 

 0-000 

 0-271 

 0-097 



0396 



Proportionals. 

 401 " 

 1-00 



113 



98-96 



Specific gravity =2-540. 



Three Rock Mountain, County Dublin. 



SiO 3 . 



A1 2 3 



MgO . 



CaO . 



KO . 



NaO . 



Loss by ignition 



Per cent. 



65-40 



17-71 



, 1-77 



, trace 



10-68 



3-26 



0-69 



99-51 



Atomic quotients. 

 1-444 

 0-344 

 0-088 

 0-000 

 0-227 

 0-105 



Proportionals. 

 4-19 

 1-00 



0-420 



1-22 



Specific gravity = 2*562. 



Lough Bray, County Dublin. 



100-19 



Specific gravity = 2-554. 



