C— GEOLOGY. 81 



due to movements of more than one age ; thus, the south-westerly tilt 

 may have been superposed upon a region which already had a general 

 slojie to the south-east. This would accord with the relations of the 

 two main directions of the drainage system. 



Rastall attributed the swing of the chalk outcrop to Miocene folding. 

 In agreement with this view is the ' Alpine ' trend of the fold and the fact 

 that the Eocene beds of the London basin strike for some distance parallel 

 to the Cretaceous. 



There is a remarkable correspondence between the trend lines of the 

 Palaeozoic plateau in the west and the strike of the newer rocks in the 

 east. The south-westerly tilt of the plateau stands in the same relation 

 to the east- west trough of the Bristol Channel as the south-easterly tilt 

 of the chalk in the Chiltern escarpment to the syncline of the London basin. 

 The London basin has a general pitch to the east, whereas the trend lines 

 of the plateau north of the Bristol Channel and the trumpet-shaped 

 outline of the Bristol Channel which is a consequence of this trend suggest 

 a syncline pitching to the west. In brief, the drainage of the western 

 region is in its main lines a mirror image of that in the east. 



Let us now turn to the area south of the Channel. The syncline of 

 the Hampshire basin is prolonged to the west into the region between the 

 Blackdown Hills and the Dorset coast. Still farther west lies the remark- 

 able plateau of the central plain of Devon. Just as the streams in the 

 Hampshire basin converge towards the centre of the basin before spilling 

 over in the Solent, so the main streams of north and central Devon tend 

 to collect from north and south in the centre of the plain before spilling 

 over by way of the Exe, the Torridge and the Taw. One can hardly doubt 

 that the surface of the central plain of Devon is an area where the 

 Palseozoic surface has been warped into a syncline which is a continuation 

 of the Hampslure basin. 



The Exmoor range which intervenes between the Bristol Channel 

 syncline and the central Devon syncline is the analogue in the west of 

 the Wealden anticline in the east. If I am justified in my conclusion that 

 the central plan of Devon and the Palseozoic upland of Wales have been 

 warped into approximately their present form by Miocene folding, it is 

 a logical deduction that the present elevation of Exmoor is due not to 

 the greater resistance of the rocks in comparison with those to the south, • 

 but to the arching up of the surface during the episode of Miocene folding, 

 thus causing streams to flow ofE its flanks into the Bristol Channel on the 

 one side and the central plain of Devon on the other. 



Some support is given to the correctness of this interpretation of the 

 physical features of the western region by consideration of the trend of 

 the watershed which crosses England from east to west and divides the 

 streams that flow northward into the Bristol Channel or the Thames basin 

 from those that tend to flow southward into the English Channel. 



At the eastern end of the Weald the watershed coincides approximately 

 with the crest line of the centre of the Weald, with a prolongation along 

 the Battle axis where it separates the Rother from the Cuckmere. From 

 the centre of the Weald it pursues a meandering course to the Hampshire 

 Downs, in one place approaching but not actually reaching the line of 

 the Hogback at Guildford. In the Hampshire Downs it swings in a 

 1930 G 



