512 On the Potash and Soda Felspars of the Dublin Mountains. 



sible, in lithological character, the mass of rock or mountains 

 the composition of which is to be inferred from such analyses ; 

 and if they do not fulfil these conditions, I consider them worth- 

 less as far as inferring from them the constitution of the mass 

 of the mountain. 



As the opinion of those members who spoke were all against 

 me, I therefore resolved, as soon as possible, to test by analysis, 

 from one of those localities given by the essayist, the correctness 

 of my views; and learning that the "Three Rock Mountain" 

 represented in general lithological characters most nearly the 

 granite of the Dublin and Wicklow Mountains (being too much 

 occupied myself), I got a skilful professional chemist of high 

 character in London, Mr. Dugald Campbell, of Quality Court, 

 Chancery Lane, to analyse for potash and soda a portion of the 

 granite of the " Three Rock Mountain," and took care that the 

 specimen should be as similar as possible in general character to 

 the granite of those mountains. Mr. Walter Wilson, of the Geo- 

 logical Survey, who is thoroughly conversant with the district, 

 undertook very kindly to procure for me as fair an average spe- 

 cimen as he could obtain, and which accompanies this paper, 

 minus that portion used for analysis. 



From this analysis it will be perceived that a great difference 

 exists between it and the analysis of the specimens of felspar 

 from the same mountain by Professor Galbraith, as far as regards 

 potash and soda. 



Analysis by Professor Galbraith. 

 Atomic 

 Per cent, quotients. Proportionals. 



SiO 3 65-40 1-444 4-19 



A1 9 3 1771 0-314 1-00 



MgO 1-77 0-0881 



CaO trace 0-000 I n ., oft 1#09 



KO 10-68 0-227 f U 4 ^° L ZZ 



NaO 3-26 0-105 J 



Loss by ignition ... 0-69 



99-51 



Specific gravity =2*562. 



Analysis of the amount of Potash and Soda by Mr. Dugald 

 Campbell. 

 KO .... 3-23 per cent. 

 NaO .... 3-75 ... 



There is in this analysis of the felspar about 4 per cent, of 

 mica, which of course increases the relative amount of potash 

 belonging to the felspar. 



