428 Heports and Proceedings — 



Geological Society of London. 



June 24, 1891.— Sir Archibald Geikie, D.Sc, LL.D., F.E.S., 

 President, in the Chair. — The following communications were read : 



1. " On Wells in West-Suffolk Boulder-clay." By the Eev. Edwin 

 Hill, M.A., F.G.S. 



It might be supposed that in a Boulder-clay district water could 

 only be obtained from above or from below the clay. But in the 

 writer's neighbourhood the depths of the wells are extremely 

 different, even within very short distances ; and since the clay itself 

 is impervious to water, he concludes that it must include within its 

 mass pervious beds or seams of some different material which com- 

 municate with the surface. It would follow that this Boulder-clay 

 is not a uniform or a homogeneous mass. 



The visible sections are only those given, at hand by ditches, and 

 at a considerable distance north and south by pits at Bury St. 

 Edmunds and Sudbury. The appearances in these harmonize with 

 that conclusion. Conclusion and appearances differ from what we 

 should expect on the theory that this Boulder-clay was the product 

 of the attrition between an ice- sheet and its bed. 



2. " On the Melaphyres of Caradoc, with Notes on the Associated 

 Eelsites." By Frank Eutley, Esq., F.G.S. 



Within very limited areas the melaphyres of Caradoc differ con- 

 siderably in texture and in structure, some having once been basalt- 

 glass or andesite-glass (such being the superficial portions of a 

 lava-stream); others have possessed a certain amount of interstitial 

 glass, which has subsequently been rendered more or less opaque by 

 the development of magnetite, while at times it appears to have 

 been converted into a palagonitic substance. In some of the rocks 

 the crystalline texture is very fine, in others comparatively coarse. 

 Near the summit of Caradoc is a basalt-tuff or andesite-tuff. 



The melaphyre or dolerite of Little Caradoc differs from the lavas 

 in that the augite remains fresh and the felspars are altered, while 

 in the lavas of Caradoc proper the pyroxenic constituent is decom- 

 posed and the felspars remain as a rule unaltered. 



Whether the melaphyre of Little Caradoc may be regarded as 

 a neck from which the lavas lying to the south-west of it emanated, 

 is a point which can only be demonstrated by further field-work. 



The author considers that further investigation may prove beyond 

 dispute that the associated felsites are rhyolites of which the original 

 structures have as a rule been almost entirely obliterated. In an 

 appendix further evidence is adduced in favour of the original rhyo- 

 litic nature of these felsites, and a fragmental rock from Bowdler's 

 Chair is described as unquestionably a rhyolite-tuff. 



3. " Notes on the Geology of the Tonga Islands." By J. J. 

 Lister, Esq., M.A. (Communicated by J. E. Marr, Esq., M.A., 

 F.E.S., Sec.G.S.) 



The islands of the Tonga group are situated on a long ridge 



