ANNIVERSARY ADDRESS OF THE PRESIDENT. Cxlv 



liar interest to this exhibition of volcanic forces in action almost up 

 to the historic period. It is, indeed, yet to be determined whether 

 the number of still active volcanos is equal to, in excess of, or 

 in defect of the number of the extinct. 



The Eev. Samuel Haughton, Fellow of Trinity College, Dublin, 

 and Professor of Geology in that University, has submitted to us his 

 further researches into the chemical constitution of the granites of 

 Ireland, which I might perhaps have noticed more appropriately in 

 a preceding portion of my address. In his former paper he expressed 

 his opinion that the granites of the neighbourhood of Newry, like 

 those of Leinster, belong to two distinct types, namely, potash- and 

 soda-granites, — those south of a north-east line drawn through Newry 

 and including the Mourne granites belonging to the potash-type, 

 whilst those to the north of the line belong to the soda- type. In 

 the present paper Professor Haughton supports this opinion, first by 

 the chemical analysis of granites selected from five localities south 

 of the line, in which there is a general resemblance in the compo- 

 sition of all, the potash exceeding the soda in amount in the propor- 

 tion of 4 and 5 to 3, and then by a similar analysis of the soda- 

 granites from four localities, which, however, do not exhibit the same 

 regularity of composition, whilst the proportions are reversed in 

 respect to the soda and potash, the soda being now in excess. 



The atomic proportions of Silica, Peroxides, and Protoxides in the 

 two types of granite are as follows : — 



Potash-granite. Soda-granite. 



Silica 1-582 Silica 1-429 



Peroxides .. 0-311 Peroxides .. 0-367 



Protoxides . . 0-301 Protoxides . . 0-294 



And the mineral composition, 



Potash-granite. Soda-granite. 



Quartz 18-36 Quartz 21-24 



Felspar 76-66 Felspar 41-45 



Green Mica . . 5-00 Mica 36-50 



100-02 99-19 



The composition of what Professor Haughton terms a " pink elvan 

 or soda-elvan-dyke," he deduces from his analysis to be, 



Soda-elvan. 



Quartz 29-52 



Felspar 60-15 



Hornblende 8-81 



98-48 



— hornblende being in this instance supposed to replace the mica. 

 These pink elvans penetrate the granite. From all his observations, 

 both in Down and in Wicklow (in the examination of which latter 

 county he was assisted by Mr. Jukes), Professor Haughton concludes 



