560 Announcements and Inquiries. 



(i) The London Basin is an asymmetrical syncline pitching east- 

 wards. The southern rim dips sharply, the northern gently, the 

 axis lying nearer the south. Drainage of such a district would 

 consist normally of a main stream along the axis with tributaries 

 on both sides. This condition is realized in the west by the Kennet 

 and in the east by the Thames below Chertsey. In the intervening 

 portion (Theale to Chertsey) the main stream is north of the " ideal " 

 position, and its southern tributaries cross the axis and flow against 

 the dip. At Wargrave the Thames returns into the Chilterns in 

 apparent defiance of all rules and reason. There is evidence that the 

 southern tributaries have postponed junction with the main stream 

 fairly recently, and that the Thames itself has shifted its course 

 southwards. 



The original drainage of the basin is believed to have passed 

 along the Kennet to Theale, thence to Pangbourne, along the present 

 Thames to Windsor, thence by Eickmansworth and Hertford, and 

 probably down the Lea. (Possibly it reached the sea past Maldon 

 or Colchester.) These broad meanders were reversible with similar 

 amplitude. This line was probably the synclinal axis in Miocene 

 and Pliocene times, its southward displacement being due to the 

 increased plunge of the " North Downs " dip. Many anomalies 

 in the drainage and river deposits are explicable on this hypothesis, 

 the rivers being incompletely adapted to the tectonic change. 



(ii) The Upper Thames is a tributary of the London Basin 

 tli-ainage. New sections in Goring Gap show that torrent action 

 has deepened the gorge by about 50 feet. Excavations on the hills 

 above Whitchurch afford presumptive evidence of the marginal 

 effects of true glaciation. The nature and arrangement of the drift, 

 the numerous lateral channels, and the character of the gorge 

 itself, are such that their occurrences further north would be ascribed 

 generally to glacial action. 



It is postulated that a Welsh- Midland ice-sheet reached the Chalk- 

 scarp, but failed to override save at the lowest parts. One such 

 part was in the angle between the Chilterns and Berkshire Downs ; 

 the final excavation of Goring Gap was achieved by the outflow from 

 V a retreating ice-tongue that had penetrated into the London Basin. 

 \The relatively early date of the glaciation and the softness of the 

 bed-rocks account for obscurity of details. 



ANNOUNCEMENTS AND INQUIRIES. 



Mr. Arthur T. Hopwood, B.Sc, Geological Department, the 



University, Manchester, is engaged on an investigation concerning 



,the structure and affinities of Gyclus de Koninck. Mr. Hopwood 



/ would be pleased to receive, on loan, any specimens from British 



/ or foreign localities, and will return such specimens to their owners 



as soon as possible. 



