618 Mr. J. Beetb Jukes and the Rev. Samuel Haughton on the 



It is evident from the preceding investigation that there is a very close re- 

 semblance bet-ween the first three felstones, -which occur in the south-east of 

 Ireland. They agree -with each other, and differ from the felstones of Kerry and 

 Caernarvon in containing more quartz and less felspar. The average propor- 

 tions of these minerals per cent, are — 



Quartz, 



Felspar, 



41-72 



58-28 



100-00 



The felstones of the south of Ireland have been frequently compared to the 

 clinkstones of Auvergne and other volcanic districts. They may be considered 

 as the palseozoic representatives of the clinkstones, but differ from them in 

 several important particulars. Their agreement and difference may be well 

 seen from the following analysis of a clinkstone from Roche Sanadoire, near 

 Mount Dor, collected by Mr. Jukes. 



Table XIX. 

 Clinkstone /rom'Eoche Sanadoire, near Mount Dor. 



This rock resembles somewhat in its external character the Irish felstones, 

 but its chemical composition and mineralogical constitution is wholly different, 

 as appears from this analysis. The quantity of alumina, and alkalies, particu ■ 



