1854.] DELESSE PEGMATITE. WOODWARD — HPPURITID^. 397 



6. On the Pegmatite q/" Ireland. By M. A. Delesse. 



[Abstract *.] 



The author observes that the Pegmatite of the Mountain of Mourne 

 in Ireland is very remarkable for its cavernous structure. This 

 structure is especially found in pegmatites which contain topazes ; it 

 is therefore probable that the cavities in the pegmatite are owing to 

 the separation of fluoric gases, the fluor of which is subsequently 

 fixed in the topaz and mica. 



The Irish pegmatite is also very remarkable for the presence of 

 fayalite and of ferruginous peridote ; for peridote is the characteristic 

 mineral of rocks of igneous origin which have not an excess of quartz. 



M. Delesse remarks, in conclusion, that cavernous pegmatite is 

 formed under circumstances markedly different from those under 

 which granite properly so called is produced. 



May 24, 1854. 



SPECIAL GENERAL MEETING. 



Sir R. I. MuRCHisoN, Vice-President, in the Chair. 



1. The President announced that Prof. E. Forbes, in consequence 

 of his appointment to the duties of Professor of Natural History at 

 Edinburgh, had been compelled to resign the Office of President of 

 the Society, and that the Society was now called upon to elect a 

 President in his room; also to elect a Member of Council in the 

 room of the Rev. Mr. De la Condamine, deceased. 



2. Scrutineers were appointed, who, after the Ballot, reported 

 that William John Hamilton, Esq. was unanimously elected Pre- 

 sident ; and that Joseph Prestwich, Jun., Esq. was unanimously 

 elected a Member of Council. 



3. Resolved, that the thanks of the Society be given to Prof. 

 E. Forbes, retiring from the office of President. 



[It was also resolved, that Mr. Prestwich be requested to under- 

 take the duties of Secretary until the next General Meeting.] 



ORDINARY MEETING. 



Edward Bretherton, Esq. and WilUam Ferguson, Esq. were elected 

 Fellows. 



The following communications were read : — 



1. On the Structure «wc? Affinities of the Hippuritid^. 

 By S. P. Woodward, Esq., F.G.S. 



[Abstract.] 



[The publication of this paper is postponed.] 



These fossils were regarded by the author as bivalve shells, forming 



* This communication is printed in full in the Bulletin de la Societe Geologique 

 de France, 2 ser. vol. x. p. 568. 



