Vol. 65.] GEOLOGY OF THE NEIGHBOURHOOD OF SEAFORD. 459 



need not here refer in detail, seems to be a very possible explana- 

 tion of their present depth. At the same time, it is not unlikely 

 that the solubility of tbe Chalk has assisted its removal, and that 

 joints may have played some part in promoting slips and main- 

 taining the slope of their steeper faces. 1 



There is one feature of these dry valleys which does not appear 

 to be easily explained. I allude to their narrow junctions with the 

 main valley in which the river flows. All the dry valleys in this 

 area become very constricted at their lower extremities. I do not 

 attempt to offer an explanation of this peculiarity, although it must 

 be looked upon as possessing some significance with regard to their 

 mode of origin. 



In conclusion, I would say that I have endeavoured in this 

 paper to illustrate the application to field-geology of the zonal 

 method of studying Chalk areas. The district selected is small, 

 but it is interesting as throwing some light upon the geological and 

 physiographical features of what may be regarded as the eastern 

 extremity of the Hampshire Basin. I think that there can be no 

 doubt that the Seaford Head flexure is of the same age as that of 

 the Isle of Wight, which is certainly post-Oligocene, and probably 

 pre-Pliocene in date. If, therefore, the Seaford Head flexure is 

 actually part of the Purbeck — Isle of Wight system, we have here 

 the precise southern boundary of this end of the Hampshire 

 Basin, which, as has been shown above, terminates abruptly east- 

 wards in the Cuckmere Valley. 



Discussion. 



Mr. G. W. Young welcomed the Author as an accession to the 

 group of Chalk enthusiasts, and congratulated him on the interest 

 of his first communication on the subject. He was quite prepared 

 to accept the Author's view as to the suggested fault in the 

 Cuckmere Valley, as the abrupt change in the direction of the 

 strike of the Chalk and the overthrusting seen in the neighbour- 

 hood of Eastbourne rendered it probable that considerable earth- 

 movements had taken place in the surrounding districts. The 

 little low-lying Tertiary outlier at Chyngton Farm gave the clue 

 to the whole situation.. 



The Author's belief that the Seaford uplift was an eastward 

 prolongation of the Isle-of- Wight ridge was interesting, especially 

 in regard to Mr. Clement Beid's suggestion, some years ago, that 

 Beachy Head marked the eastward termination of that movement ; 

 but the speaker preferred the more generally accepted theory that 



1 On this point see A. J. Jukes-Browne, Geol. Mag. dec. 5, vol. v (1908) 

 pp. 529-34. 



