VALLEY AND ITS DELATION TO THE WESTLETON BEDS, ETC. 169 



have been carried from the Greensand-range on to the Chalk-plateau 

 on the north. The valley, v, must then have been bridged over by 

 the Gault and Chalk to have allowed the trans^^ort across it of 

 this debris by streams from the central Wealden area ; for there is 

 no reason to suppose it was effected by floating ice. 



Let us now try to conceive the condition of the Wealden area at 

 the period of this, its last, emergence. At present, the height of the 

 anticlinal ridge at Crowborough does not exceed 803 feet. To 

 realize the condition of the dome before denudation, we have to add 

 the thickness of the strata removed, which may probably be esti- 

 mated as under : — 



feet. 



1. Chalk. It is doubtfid whether this extended to the centre of 



the Weald, for, as I have already shown^, it had, before this time 

 ' been planed down at its edge to a thickness of 300 feet by 

 Tertiary marine denudation. If that rate of wear were main- 

 tained, it is probable that the Chalk either did not extend to 

 the central area, or else was greatly reduced in thickness 100 



2. Upper Greensand and Q-ault 150 



3. Lower Greensand 450 



4. Weald Clay ... 700 



5. Tunbridge Beds and Wadhurst Clay 400 



1800 

 Add present height of Central ridge (Aslidown Sands &c.)... 800 



26001- 



There would thus have been, even supposing that there has been 

 no subsequent subsidence, a low mountain-range extending into the 

 Boulonnais, on the site of the present Wealden area. It is pro- 

 bable also that at this time the Ardennes were considerably higher 

 than they are now (2800 feet), for MM. Cornet and Eriart have 

 shown that during their diverse upheavals some 12,000 to 15,000 feet 

 of strata have been removed ^. This, however, w^as at a date very 

 long anterior to the Pliocene. 



The Wealden range having been uplifted in late Pliocene times, 

 it soon became exposed for a vast length of time to the heavy 

 rainfall, snow, and ice of the Pre-Glacial and Glacial periods, when 

 torrents scored the flanks of the hills, and carried down the harder 

 debris to the lower grounds at their base. 



Amongst the earlier results of these denuding agencies is, I con- 

 ceive, the coarse and much-worn gravel of Well Hill. The large 

 heavy flints with their angles greatly worn, and the unstratified 

 character of this gravel, give it the appearance of having been 

 brought down by a torrent, and of not having heen spread out under 

 water. This would account for its very local occurrence : for this 

 stream of stones is confined to Well Hill, and the hill itself seems 

 to result from the protection afforded by the mass of flints, while 



* Quart, Journ. Geol. See. vol. viii. p. 25(). 



t The estimate formed by Mr. Topley, supposing the whole amount of strata 

 removed by denudation to be restored, varies at different parts of the axis from 

 1000 to 3000 feet (' Geology of the Weald,' p. 217). 



\ Mem. Soc. Geol. de Belgique, vol. iv. p. 71 (1877). 



s2 



