?- -[ U2 ] 

 - XIX, Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



■ ■;.:-:' [Continued from p. 78.] 



December 4th, 1895.— Dr. Henry Woodward, F.R.S., President, 

 in the Chair. 



T^HE following communications were read : — 



r- 1. ' On the Alteration of certain Basic Eruptive Rocks from 



Brent Tor, Devon.' By Frank Rutley, Esq., E.G.S. 



Two microscopic sections of rock occurring on the north side ef 

 Brent Tor were examined, and a cursory glance suggested at once 

 the idea that they might originally have consisted to a greater or 

 less extent of extremely vesicular basalt-glass. No unaltered vitreous 

 matter, except perhaps mere traces, can now be detected in these 

 specimens, the interest of which lies in the assemblage o£ alteration- 

 products which they contain. A third section cut from a small chip 

 collected at the southern side of the base of the Tor consists of a 

 highly vesicular lava of a hyalopilitic character, which may be 

 regarded as an amygdaloidal glassy basalt. 



The author gives a detailed account of the microscopic characters 

 of the three sections, and discusses the history of the rocks, com- 

 paring them with Tertiary basic glass, and with the Devonian 

 rocks of Cant Hill, which he described previously. He brings 

 forward evidence in favour of the view that the original alteration 

 of both the Brent Tor and Cant Hill rocks was palagonitic, and 

 that while in the Brent Tor rocks the subsequent alteration of the 

 palagonite into felsitic matter, magnetite, secondary felspar, epidote, 

 and probably kaolin, and some serpentine and chlorite was com- 

 plete, it was only partial in the case of the Cant Hill rocks. "We 

 may therefore assume that palagonite is not the ultimate phase of 

 alteration in basic igneous rocks. 



l O J 



2. « The Mollusca of the Chalk Rock.— Part I.' By Henry 

 Woods, Esq., M.A., E.G.S. 



December 18th. — Dr. Henry Woodward, E.R.S., President, 

 in the Chair. 



' The following communications were read : — 



1. ' The Tertiary Basalt-plateaux of North-western Europe.' By 

 Sir Archibald Geikie, D.Sc, LL.D., E.R.S. 



The author in this paper gives the results obtained by him in 

 the continued study of Tertiary Volcanic Geology during the seven 

 years which have elapsed since the publication of his memoir on 

 * The History of Volcanic Action during the Tertiary Period in the 



