198 Geological Society : — 



shales and by the appearance of phenomena suggesting thrust- 

 planes. 



The author considers, however, that the main metamorphism is 

 due to the intrusion of the granite, and that the variation in the 

 amount of alteration at the same distances, the mode of alteration 

 of the grits, and the transference of material might be accounted 

 for by the passage of highly heated water. Other evidence points 

 to the changes having been brought about slowly. 



Among the minerals produced in the contact-zone are secondary 

 quartz, felspar, brown and white micas, chiastolite, sillimanite, and 

 garnet, their modes of occurrence being described in detail, in rocks 

 of various degrees of alteration up to those in an abnormally high 

 state of alteration near the granite, which resemble rocks of doubtful 

 origin in other localities. 



May 21. — Dr. A. Geikie, F.E.S., President, in the Chair. 

 The following communications were read : — 



1. "On some Devonian and Silurian Ostracoda from North 

 America, France, and the Bosphorus." By Prof. T. Bupert Jones, 

 F.E.S., F.G.S. 



2. " On the Age, Composition, and Structure of the Plateau- 

 gravels of East Berkshire and West Surrey." By the Eev. A. Irving, 

 B.A., D.Sc, F.G.S. 



The author refers to the view propounded by him somewhat ten- 

 tatively seven years ago, and since confirmed by the researches of 

 Prof. Prestwich, as to the Preglacial age (probably Pliocene) of 

 these deposits, pointing out the inconclusive nature of the evidence 

 of Glacial age furnished by the presence in them of angular "salens.'' 

 He regards the absence of Miocene marine deposits in this part of 

 North-western Europe as supporting the published view of Zittel 

 and other continental writers that the Miocene period was, in South- 

 eastern England, one of elevation and subaerial waste and degrada- 

 tion of the Weald to the south, and of East-Mercian England to the 

 north-west, this period of waste of the Cretaceous rocks having fur- 

 nished much of the materials which, in Pliocene times, were carried 

 across a sloping plateau by fluviatile agencies. 



The composition and structure of the plateau-gravels are next 

 described, reference being made to previous writings of Prof. Eupert 

 Jones and to the recent papers of Prof. Prestwich. Eeference is 

 also made to the explanation suggested by the author seven years 

 ago of the anomalous contrast presented by the lithological con- 

 ditions of the flint-pebbles and the subangular flint-fragments 

 which are intermingled in these gravels. The great masses of 

 unstratified and unrolled flint-debris on the Aldershot Hills are 

 compared with the Preglacial " Schotte " of the lower Alpine 

 valleys. The plateau-gravels are described as occupying altitudes 

 ranging from nearly 600' (O.D.) at Aldershot and on the north side 

 of Netley Heath, down to 280' (O.D.) at Bearwood and Parley Hill. 

 A list of 22 localities (with altitudes) is given where actual sections 

 of the plateau-gravels can be studied. 



