Vol. 69.] ANNIVERSARY ADDRESS OE THE PRESIDENT. lxXV 



It becomes apparent also, that neither the major anticlines nor 

 syncfines are simple in structure; they are made up of subsidiary 

 folds which, though individually discontinuous, maintain effective 

 continuity. Thus the London Basin includes two hollows, the one 

 under the estuary of the Thames, the other west-south-west of 

 London, close under the steep uplift of the Hog's Back. Subsidiary 

 folds occur in the Wealden Anticline, both in the area from which 

 the Chalk has been denuded and in that where the arch is more 

 perfect. The overlapping and replacing anticlines in the Isles of 

 Wight and Purbeck are readily recognized. 



There are other points which I am tempted to mention, though 

 briefly, for they scarcely form part of my present subject. It will 

 be noticed that in the Chalk escarpment which extends across 

 England from Lincolnshire to Dorset there are some rather abrupt 

 changes in strike, all of which produce an anticlinal structure. 

 Between Lincolnshire and Norfolk (beyond the northern margin of 

 PI. B) the strike changes from ]S T . 30° W. to north and south ; near 

 Culford it changes to W. 35° S. ; near Goring it changes from 

 E. 30° N. on the north side of the Thames to east and west in 

 the White Horse Hills on the south side of the river ; farther 

 south it is interrupted by the Pewsey and Wardour Anticlines. 



In every case a breach has been effected in the escarpment, and 

 a line of drainage traverses it in the direction of general dip. In 

 the Wealden area a notable change of strike occurs near the 

 centre of the northern scarp at Maidstone, and here the ridge is 

 traversed by the Medway. I am not aware that any of the other 

 breaches in the North and South Downs coincide with changes of 

 strike, but the coincidence in the cases which I have mentioned is 

 sufficiently frequent to be significant. The subject deserves further 

 investigation. 



Again, the map gives a comprehensive view of the general tilt 

 which turned the drainage of England eastwards, and of the par- 

 ticular lines of syncline and anticline which determined the courses 

 taken by the rivers. At the south coast our evidence ceases, but 

 the increasing intensity of these determining folds southwards 

 invites the speculation that the primary cause of the separation of 

 England from the Continent was the establishment of a west-to- 

 east line of drainage analogous to those of the Thames and the 

 Erome, and the subsequent invasion of that line by the sea. It 

 must be remembered, however, that the English Channel does not 

 follow the east-and-west structures consistently, but that it cuts 

 across the Wealden Anticline in the Straits of Dover. 



