Reports and Proceedings — Geological Society of London. 237 



2. "The Glen Orchy Anticline (Argyllshire)." By Edward 

 Battersby Bailey, B.A., F.G.S., and Murray McGregor, M.A., B.Sc. 



The district described stretches from the head of Loch Awe to 

 Beinn Achallader, and is the south-eastern continuation of the Fort 

 William, Ballachulish, and Appin country dealt with by one of the 

 authors two years ago. The subject is the tectonics of the schists. 



In the centre of the district a diagrammatic recumbent fold, of at 

 least two miles in magnitude, is exposed to view in Beinn Udlaidh, in 

 the heart of a gentle anticline, to which the name of the Glen Orchy 

 Anticline is fittingly assigned. Around the western, southern, and 

 eastern rim of this anticline, are found rocks which lie upon 

 a structurally higher level than the Beinn Udlaidh Fold. A limestone 

 which occurs among these rocks is correlated with the Ballachulish 

 Limestone, and is believed to mark the core of the great recumbent 

 Ballachulish Fold, everywhere in this district underlain by the 

 Ballachulish Slide (fold-fault). Incidentally this interpretation 

 involves a displacement of at least twenty-four miles along the Balla- 

 chulish Slide. Finally, an important inversion of the Ballachulish 

 Limestone and Slide is discussed in connexion with a description of 

 the Beinn Doirean and Beinn Achallader range of mountains on the 

 east side of the Glen Orchy Anticline. 



March 13, 1912.— Dr. Aubrey Strahan, F.R.S., President, in 

 the Chair. 



The following communications were read : — 



1. " On the Glacial Origin of the Clay-with-Flints of Buckingham- 

 shire, and on a Former Course of the Thames." By Robert Lionel 

 Sherlock, D.Sc, A.R.C.S., F.G.S., and Arthur Henry Noble, B.A., 

 F.G.S. 



The paper is founded on observations made during the mapping 

 of some 260 square miles on the 6 inch scale, in Buckinghamshire, 

 Berkshire, Hertfordshire, and Middlesex. 



The superficial deposits are divided into Clay-with-Flints with the 

 associated Gravelly Drift and the Fluvio-giacial Gravels. There are, 

 in addition, certain high-level gravels, older than any of .these, and 

 also the river gravels and alluvium of the present streams, none of 

 which deposits are dealt with in the paper. 



Evidence is given to show that the Clay-with-Flints and Gravelly 

 Drift were formed by an ice-sheet which came from the north or 

 north-west over the Chiltern Hills. Only the clean upper layers of 

 ice surmounted the escarpment, and this produced the Clay-with- 

 •Flints and Gravelly Drift from the ' head ' (Chalk and Eocene waste), 

 which had been accumulating for ages. 



At that time the Thames flowed, at the foot of the Eocene escarp- 

 ment, from Bourne End through Beaconsfield and Rickmansworth 

 to Watford. The ice-sheet blocked the river-channel between Bourne 

 End and Bickmansworth about the time of maximum cold, and 

 diverted the Thames southwards at Bourne End. The river beyond 

 Watford was further blocked by the Eastern Drift, which has left 



