Vol. 65.] GEOLOGY OF THE NEIGHBOURHOOD OF SEAFORD. 455 



If this was so, we may regard the Cuckmere Fault as the true 

 geographical termination of the Hampshire Basin. This view is 

 supported by certain physiographical features of this area, to which 

 I will now call attention. 



IV. Physiography. 



A glance at the relief-diagram (fig. 8, p. 456) shows a striking 

 difference in the river-mouths of the Ouse and the Cuckmere. That 

 of the Ouse is wide, and is bordered on the east towards Seaford by 

 low ground, while the Cuckmere reaches the sea through a narrow 

 gorge, flanked on each side by high cliffs. The line of water-parting 

 between these rivers runs nearly due south from Firle Beacon until 

 it reaches the ridge above Hobb's Hawth, where it turns sharply to 

 the east, following the top of this ridge along Cradle Hill to Hind- 

 over. From this point it runs southwards, approximately parallel 

 with the Cuckmere, to Chyngton and Seaford Head : along this 

 latter portion of its route it is less than a mile from the river. 

 "We have seen that it is here that occur the two counter dip-slopes, 

 caused by the Chyngton syncline. By this movement a large part 

 of what might otherwise have been the Cuckmere drainage-area 

 has been diverted into that of the Ouse. Possibly a slight westerly 

 pitch of the synclinal axis has facilitated this result. It would 

 have been expected that the Cuckmere would thus have been 

 diverted into the Ouse, becoming a tributary of that river rather 

 than performing the apparently difficult task of penetrating the 

 ridge connecting Seaford Head with the Friston plateau. This 

 latter course may perhaps have been made possible by the pre- 

 sumed line of fault, a suggestion which is supported by the 

 marked eastward deflection of the river where it penetrates this 

 ridge. I do not, however, imagine that this fault-line, if it exists, 

 had anything to do with the general course of the river- valley across 

 the Chalk escarpment. Topley has offered strong arguments in 

 favour of the view that the course of Wealden rivers was mainly 

 determined by slight transverse undulations. 1 There is some 

 indication that this may have been so in several cases, although 

 there is not only no evidence of any rise in the beds between the 

 Cuckmere and the Ouse, but rather, as has been shown above, 

 there is a strong proof that the beds in this area are not folded 

 transversely. How far the Eastbourne transverse fold may have 

 influenced the course of the Cuckmere is not easy to determine. 

 Leaving aside the question of the general direction of the Cuckmere 

 Valley, however, it seems to be clear that the Seaford Head move- 

 ment has curtailed the drainage-area of this river, and has deter- 

 mined the present position and shape of its mouth. 



The next point to which I will refer is the very marked contrast 

 between the surface-features on the east and those on the west side 



1 ' Geology of the Weald ' Mem. Geo!. Surv. 1875, pp. 276-78. 



