382 Reports and Proceedings — Geological Society of London. 



All tbese vary mucli more in size and run distinctly smaller, especially 

 the last.^ That from Mattakava, Hick's Bay, New Zealand (fallen 

 on June 16th, 1886), is rather coarser, more scoriaceous, with fewer 

 mineral fragments (especially of pyroxene), to which a dirty glass 

 is often adherent. The dust from Barbados, ejected by the 

 St. Vincent Soufriere in 1812, is very much finer-grained, but 

 contains the same minerals, though pyroxene is less abundant. 

 In neither had he found the clear glassy pumice described by 

 Miss Eaisin ^ from the marls of that island. 

 The following communications were read : — 



1. "A Descriptive Outline of the Plutonic Complex of Central 

 Anglesey." By Charles Callaway, D.Sc, M.A., E.G.S. 



The central complex of Anglesey was originally composed of 

 diorite, felsite, and granite. The gneiss and granitoid rock of the 

 area, formerly regarded as sedimentary in origin, are now known to 

 be plutonic masses. The diorite undergoes numerous modifications, 

 into hornblende-gneiss, chlorite-gneiss, micaceo-chloritic gneiss, 

 and kersantite and biotite-gneiss. The felsite has not been found 

 in its original state, but is converted into ' halleflinta,' quartz-schist, 

 mica-schist, and mica-gneiss ; granite and quartz felsite are intrusive 

 into the diorite and felsite, and the two former are regarded as 

 derived from the same magma. They are not foliated, and were 

 intruded subsequently to the modification of the diorite and felsite 

 into gneisses and schists. The diorite, originally a zenolith sur- 

 rounded and injected by granite, has been modified into an elliptical 

 dome of dark gneiss : into simple gneisses by pressure, and into 

 complex gneisses by pressure plus granitic intrusion. This intrusion 

 has often produced fusion at the contact, sometimes with the 

 e-eneration of biotite in the diorite. In addition to this, the diorite 

 possesses an imperfect fluxion-structure. 



2. " Alpine Valleys in relation to Glaciers." By Professor T. G. 

 Bonney, D.Sc, LL D., F.E.S., F.G.S. 



The author discusses some hypotheses about the formation of 

 Alpine valleys which have been advanced by Professor W. M. Davis, 

 but has left the Ticino Valley, on which the latter lays much stress, 

 to Professor Garwood, who has very lately visited it. Professor 

 Davis maintains that the upper and wider parts of Alpine valleys 

 were excavated in pre-Glacial times, the lower and narrower portions 

 during the Great Ice Age. The author tests this hypothesis by 

 applying it first to the valley of the Visp, of the eastern arm of 

 which, and of the ' hanging valley ' like a gigantic corrie, where 

 Saas Fee is situated, he gives a description, pointing out that all 

 parts are so connected that any separate explanation of their form 

 is impossible. 



To obtain an idea of the condition of the Alps in Middle and Later 

 Tertiary times, we may consider the effect of alterations of tem- 

 perature, on the assumption (which, as he shows, is not likely to 



1 All these (collected by Mr. E. Wliymper) are clescribed in Proc. Eoy. Soc, 

 vol. xxxvii (1884), pp. 114 et seqq. 



2 Quart. Journ. Geol. Soc, vol. xlviii (1892), pp. 181, etc. 



