A HISTORY OF SUSSEX 



soft Lower Chalk ; the southward-facing bluff (still to be described) is a 

 true sea-cliff, which sometimes leaves the Chalk altogether and cuts 

 through Tertiary strata. 



The Sussex rivers and their peculiar courses will best be understood 

 from an examination of the accompanying orographic map. It will be 

 noticed that the principal streams, Arun, Adur, Ouse and Cuckmere, 

 rise on comparatively low ground towards the centre of the Weald and 

 make a short cut to the sea through gaps in the South Downs. The 

 Ashburn and the Rother, on the other hand, now flow over low country 

 to fall direct into the English Channel ; but it is possible that they also 

 at one time behaved like the other Wealden rivers and breached the 

 Chalk hills at a time when the Downs extended more to the east, 

 Topley, who did so much to elucidate the whole question of the origin 

 of the Wealden rivers, thought that formerly the Ashburn, which rises 

 on the south side of the axis, broke the South Downs a few miles east 

 of Beachy Head, and that the Rother, which rises north of the axis, 

 turned northward and breached the North Downs somewhere near the 

 middle of the present Straits of Dover. ^ It seems doubtful however 

 whether within the lifetime of the existing rivers the South Downs were 

 ever continuous with the Chalk hills of France,^ though the North Downs 

 appear to have been so, for chalk has been traced across the bed of the 

 strait from shore to shore. 



When we try to fix a date for the beginning of this peculiar valley 

 system it is obviously needless to look back to times anterior to the last 

 period when the county was submerged beneath the sea ; for the sea 

 tends to plane down the hills and to level up depressions, so that any 

 previously existing valleys are not likely to reappear when dry land again 

 emerges. The latest submergence to any considerable depth seems to 

 have been of older Pliocene date, marine deposits of this period capping 

 the North Downs at a height of over 600 feet near Lenham, though 

 they have not yet been discovered in Sussex. It does not seem probable 

 that any of the existing valleys date from an earlier period, though there 

 may have been an older system having a similar relation to the Wealden 

 uprise. It is not easy to follow the exact course of events in later Plio- 

 cene times, when the land rose and the streams began their work ; for 

 the rivers have long since entirely destroyed their earlier deposits, so that 

 no fossil relic now remains in Sussex of the interesting fauna and flora 

 which overspread Britain in preglacial times. From records preserved in 

 other counties we learn that these were times when large animals abounded 

 — elephants, rhinoceroses, hippopotami, numerous deer, mostly of species 

 unknown in later deposits, besides animals of more unfamiliar type, such 

 as the sabre-toothed tiger and mastodon. Towards the close of the Plio- 

 cene period Britain was still joined to the continent, the Thames and the 

 rivers north of the Wealden axis being tributaries of a larger Rhine, which 

 then seems to have reached the sea somewhere off the present Norfolk 



' ' Geology of the Weald,' chap. xvi. and plate ii. 

 '^ Reid, 'Geology of Eastbourne,' Mem. Geo/. Survey (1898), p. 13. 

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