﻿Vol. 64.] KOCKS OF GLEI^DALOUGH AND GREISTOXES. 495 



case, although he had expressly mentioned the presence of potasli- 

 felspar as one of their constituents. It was satisfactory to find that 

 this point had been definitely decided. It was to be hoped that 

 the facts now recorded might prove to have some bearing on the 

 formation of many quartz-hornblende schists. 



Prof. W. W. Watts stated that he had studied one of the rocks 

 described, under the direction of the President, and the other as an 

 officer of the Geological Survey. The most important point that 

 he had discovered in connexion with the Greystones rock was 

 the alteration of the olivine. At first olivine passes into serpentine, 

 then into tremolite, and lastly the tremolites grow at the expense 

 of the containing hornblende, until they become idiomorphic, the 

 original outlines of the olivine having been entirely destroyed. 



Mr. A. GiBB Maitland drew attention to the resemblance between 

 the geology of the district and certain of the mining features of 

 Western Australia. 



The AuTfLOR thanked the FeUows for their patient hearing of a 

 somewhat technical subject, and for the compliments paid to 

 his work. The only phenomenon that he had remarked comparable 

 to that described by Prof. "Watts was the idioblastic development 

 of hornblende. With regard to the possibility of economic deposits, 

 he referred to the impregnation of sulphides seen in the rocks 

 of both areas, and in similar rocks in Donegal described by 

 Prof. Cole. He welcomed the President's suggestion of a ' shelter- 

 spot,' especially as it did not invalidate the argument for the age 

 of the amphibolite. Mr. Seymour had described one on the west of 

 the Leinster Granite. His experience of quartz-hornblende-schists 

 was too small for him to offer an opinion as to the President's 

 suggestions. 



