DRIFT-STAG i:S OF THK DARENT VALLEY. 157 



Two hypotheses have been proposed to account for the formation 

 of the escarpment surrounding the Wealden area. The one attri- 

 butes its origin to marine action, and likens the long escarpment to 

 Chalk clifi's surrounding an inland sea ; the other refers it to sub- 

 aerial action and a slow retrocession of the outcropping edges of the 

 Chalk. The first of these hypotheses is now generally considered 

 to be untenable, as no single one of the attendant phenomena is 

 in accordance with such a derivation. There is not a trace of 

 marine action within the Wealden area during the Quaternary 

 period, and the escarpment is not a cliff in the ordinary acceptation 

 of the word, for so far from there being a level shore-line at the 

 base of the escarpment, such as a cliff necessarily presents, the line 

 is in no instance level, but rises and falls alternately the whole 

 length of the escarpment (see line mn, fig. 3, PL VI.), the 

 difference of level betvs^een the higher and lower points amounting 

 in places to as much as 300 feet, a difference impossible on a shore- 

 line. The reader should, however, consult on the Chalk escarp- 

 ment the writings of Mr. Whitaker, of Sir A. Eamsay*, and of 

 Messrs. Le Neve Poster and Topley (see note, p. 126). 



The second and more generally accepted hypothesis t is not so 

 easy to disprove. It will, however, I think, be found incompatible 

 with the phenomena exhibited in this district. I formerly showed 

 that a large portion of the Chalk covering the AVealden area was, in 

 early Tertiary times, planed down and levelled by marine action, 

 forming what Ramsay has termed " a plain of marine denu- 

 dation ; •' but I much doubt whether it affected more than a 

 limited littoral area, and whether the Chalk was removed from the 

 whole of the more central area. It is certain that the denudation 

 extended beyond the ]S^orth Downs, and probably to some distance 

 to the south of the Lower-Greensand area J. It is also certain, 

 as I afterwards showed, that both the Tertiary strata and the Chalk 

 along the northern boundary of the Weald underwent a similar 

 erosion during early Pliocene times §. In neither instance, however, 

 is there any proof that the denudation reached far into the Weald, 

 but, on the contrary, the absence in the first period of Lower- 

 Greensand debris in the Tertiary strata, and in the second of Wealden 

 debris, leads me to believe that much of the area remained almost 

 untouched. 



In any case, after the withdrawal of the Pliocene sea, and on the 

 land being raised and exposed to atmospheric agencies, a process of 

 weathering commenced,which led Ilamsay, writing in reference to the 

 formation of the Chalk Downs, to observe that " immense tracts of 

 Chalk and Lower Greensand in the Weald and in the middle and 

 west of England have been cut away hy the slow process of gradual 

 recession due to atmospheric influences, and thus it happens that 



* Wliitaker, Quart. Jovirn. Geol. See. vol. xxiii. (1867) p. 265; Ramsay's 

 * Physical Geology and Geography of Great Britain,' 5th ed. (1878) p. 338. 

 t See Ramsay, op. cit. pp. 336, 510, 532. 

 X Quart. Journ. Geol. 8oc. vol. viii. (1852) p. 256. 

 § Ibid. vol. xiv. (1858) p. 330. 



a. J. G. S. No. 186. M 



