VALLEY AND ITS RELATIOX TO THE AVESTLETON BEDS, ETC. 167 



which then extended possibly over the anticlinal, must have been 

 largely denuded, in order to have furnished the mass of flint-pebbles 

 in the Woolwich Beds, there is no evidence that the denudation 

 reached down to the Lower Greensand and Wealden, as no debris 

 from these sources has been found in the Tertiary strata. Eor 

 our present object we need, however, only commence with the state 

 of the area in Pliocene times. 



It is obvious, as I have shown on a previous occasion *, that in 

 an early Pliocene epoch, before the later denudation of the Weald, 

 the North Downs from Folkestone to Dorking and possibly beyond, 

 together with the adjacent area to the south, were submerged under 

 a sea which extended probably from the North 8ea to Brittany and 

 80 southward in one direction, and in the other, eastward, over parts 

 of France and Belgium to the foot of the Ardennes. The Pebbly- 

 sands, occasionally fossiliferous (Lenham), that occur at intervals 

 on the edge of the North Downs are proofs of this submergence. 

 On the continent beds of the same early Pliocene age and cha- 

 racter are found capping, amongst others, the hills of Mont-de-la- 

 Trinite, near Touruay, and the hills near Boeschepe in Belgium, 

 and of Mont Noir near Bailleul, Mont Cassel near Dunkirk, and the 

 Chalk-hills between Calais and Boulogne, in France, showing the 

 same sea to have extended over that area also. 



In these Beds, the Diestian of the Belgian geologists, the fossils 

 have generally been removed by infiltration, and it is only occa- 

 sionally that a few casts are met with. Where, however, they pass 

 under the newer Crags of the Antwerp district they are very 

 fossiliferous. This deposit, which does not exceed 50 or 60 feet 

 in thickness, consists of pebbly sands, sometimes very ferruginous 

 and passing into iron-sandstone, while the flint-pebbles are often 

 so decomposed that they break under the pressure of the fingers into 

 a white powder. 



From the position of the Beds at Lenham, we may assume that 

 they originally extended, together with the Chalk, further over the 

 Lower Cretaceous and Wealden strata to the south, as remnants of 

 the Beds are preserved in the sand-pipes, the ends of which occur in 

 decreasing lengths on the bare slope of the Chalk-escarpment, 

 showing that the deposit itself at one time spread over the now 

 denuded area at the foot of the escarpment, as exhil)ited in the 

 subjoined diagram (fig. 5). 



It is clear from that section, that the valley v between the Chalk 

 and Lower Greensand hills is of later Pliocene or Post-Pliocene 

 date, and the same reasoning applies to the whole length of this great 

 valley, and in all ])robability to the AVealden valleys in general. 



There can be little doubt, also, that in the early Pliocene times 

 of which we have been speaking, Belgium and the south-east 

 of England and Western France (Normandy and Brittany) wore 

 separated, not by the present narrow strait, which was not exis- 

 tent at that time, but by a broad sea-channel extending across 



* Qiuu-t. Journ. Geol. Soc. vol. xir. p. 322 (1858). 

 Q. J. G. S. No. 182. N 



