"Vol. 52.] BASIC ROCKS FROM BRENT TOR. 67 



Mr. "W. W. Watts enquired for further particulars concerning the 

 Tock which contained what might possibly be pseudomorphs after 

 leucite. He was interested in this rock, because he had discovered 

 a phonolite with some affinities to that of the Wolf Rock at Black- 

 ball Head in Cork. He also asked whether the age of the Brent 

 Tor rocks was^ definitely known, as the Irish rocks referred to were 

 clearly post-Carboniferous and yet had no affinities with the products 

 of Permian volcanos. Were there any Tertiary volcanic rocks in 

 Devon ? 



Col. Bukton-Brown would like the Author to express an opinion 

 of the probable temperature under which these interesting changes 

 in the palagonite were supposed to be taking place. 



Dr. Hicks said that some years ago he visited Brent Tor and 

 examined some of the surrounding rocks, and he wished to ask the 

 Author whether he considered the volcanic rocks as of Lower 

 Carboniferous or as of post-Carboniferous age. 



Prof. Hull also spoke. 



The Attthob, in replying to Gen. McMahon's question, stated that 

 basalt-tuffs were very variable in constitution, and in some cases 

 conversion into palagonite might only be partial. One analysis of 

 basalt-glass from Kilauea gave nearly 14 per cent, of alumina. He 

 thanked Prof. Bonney for the kind terms in which he had spoken 

 of the paper, and in reply to his criticism concerning the presence 

 of felsitic matter in the tuffs and lavas of Cant Hill, he pointed 

 out that the amount was comparatively small, and that reserve 

 was entertained about it in the paper, since some of the micro- 

 crystalline matter might be chalcedonic. In answer to Mr. Watts, 

 lie stated his belief that the approximately circular sections in some 

 of the Cant Hill rocks were infilled vesicles, although they certainly 

 did bear a general resemblance to the rounded crystals in the 

 leucitites of Monte Albano and of the Capo di Bove, as indicated in 

 the drawings to which Mr. Watts referred. The question of 

 Dr. Hicks with reference to the precise age of the eruptive rocks of 

 Urent Tor was difficult to answer, since the boundary between the 

 Devonian rocks and the Cnlm was considered very doubtful by Sir 

 Henry De la Beche and had not yet been definitely settled. It was 

 a question for palaeontologists to decide. He thought that these 

 -eruptive rocks were of Carboniferous age at latest. 



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