436 



Scientific Proceedings, Royal Dublin Society. 



The following comparison will prove worthy of attention : — 



Professor O'Reilly has kindly drawn my attention to the fact 

 that traces of gold have been found by M. Baudin in the pyritous 

 trachytes of Cantal (Puy-de-D6me) . It would be interesting to 

 find similar evidence of the presence of the noble metal in the 

 Newcastle Rook, and I hope at a future date to supply a com- 

 munication upon the subject. 



NOTE ADDED IN THE PKESS. 



Since the above list of minerals occurring in the geodes of 

 the Mourne Mountains granite was compiled, Professor Sollas, 

 F.R.S., has added still another in the shape of a lithium-mica of 

 the species Zinnwaldite. Most of the crystals possess an exqui- 



1 Experimental Researches on the Granites of Ireland, Q. J. G. S., Lon., xii., p. 192. 



2 The silica varies from 70 to 74 °/ . 



3 Teall, British Petrography, p. 348. This analysis agrees exactly with Hardman's 

 (J. Geol. Soe. Ireland, xiii. 29) so far as the alkalies are concerned. Hardman's 

 analysis is exceptional as regards the amount of alumina and lime ; but Player' 

 agrees "with the quantities usually present in a rock of this nature. Hardman's analysis 

 is as follows :— Si0 2 76-96; A1 2 3 5-1; Fe 2 3 2-344; CaO 7-06; MgO 0-29; K 2 

 4-26; NaoO 1-8; H a O 2-1 ; P 2 5 tr. 



4 Resultats principaux des experiences faites clans le laboratoire de Clermont pendant 

 l'annee 1841. Trachytes pyriteux auriferes de Mandailles (Cantal. " Ann. d. Mines, 

 1842, tomei., p. 100. 



