Ch. XIX.] DENUDATIOIT OF THE CHALK AND WEALDEN". 271 



frequent absence of all signs of littoral denudation in tlie valley of the 

 Seine itself is a negative fact of a far more sti-iking and per2:)lexing char- 

 acter. The cliffs, after being almost continuous for miles, are then wholly 

 wanting for much greater distances, being replaced by a green sloping 

 down, although the beds remain of the same composition, and are equally 

 horizontal ; and although we may feel assured that the manner of the 

 upheaval of the land, whether intermittent or not, must have been the 

 same at those intermediate points where no cliffs exist, as at others where 

 they are so fully developed. But, in order to explain such apparent 

 anomalies, the reader must refer again to the theory of denudation, as 

 expounded in the 6th chapter ; where it was shown, first, that the under- 

 mining force of the waves and marine currents varies greatly at diffei\3nt 

 parts of every coast ; secondly, that precipitous rocks have often decom- 

 posed and crumbled down ; and thirdly, that terraces and small cliffs 

 may occasionally lie concealed beneath a talus of detrital matter. 



Denudation of the Weald Valley. — No district is better fitted to illus- 

 trate the manner in which a great series of strata may have been up- 

 heaved and gradually denuded than the country intervening between the 

 North and South Downs. This region, of which a ground-plan is given 

 in the accompanying map (fig. 320), comprises within it the whole of 

 Sussex, and parts of the counties of Kent, Surrey, and Hampshire. The 

 space in which the formations older than the White Chalk, or those 

 from the Gault to the Hastings sands inclusive, crop out, is bounded 

 everywhere by a great escarpment of chalk, which is continued on the 

 opposite side of the channel in the Bas Boulonnais in France, where it 

 forms the semicircular boundary of a tract in which older strata also ap- 

 pear at the surface. The whole of this district may therefore be consid- 

 ered geologically as one and the same. 



Fie. 320. 



Geological map of the southeast of Endand and part of France, exhibiting the denudation 

 of the W^eald. 



1. EMI Tertiary. 



2. I,,, ,_| Chalk, and upper greensand. 



3. «aBi=« Gault. 



4. ^-^-| Lower Greensand. 



5. ^^n Weald clay. 



6. Li^ Hastings sands. 

 T. ^^ Purbeck beds. 

 8. t^ Oolite. 



