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CHAPTER XXI. 
Denudation of secondary strata during the deposition of the English Eocene 
formations — Valley of the Weald between the North and South Downs — Map 
— Secondary rocks of the Weald divisible into five groups — North and South 
Downs — Section across the valley of the Weald — Anticlinal axis — True scale 
of heights — Rise and denudation of the strata gradual — Chalk escarpments 
once sea-cliffs — Lower terrace of ' firestone/ how caused — Parallel ridges and 
valleys formed by harder and softer beds — No ruins of the chalk on the central 
district of the Weald — Explanation of this phenomenon — Double system of 
valleys, the longitudinal and the transverse — Transverse how formed — Gorges 
intersecting the chalk — Lewes Coomb — Transverse valley of the Adur. 
Denudation of the Valley of the Weald. — In order to under- 
stand the theory of which we sketched an outline at the close 
of the last chapter, it will be necessary that the reader should 
be acquainted with the phenomena of denudation exhibited by 
the chalk and some of the older secondary rocks in parts of 
England most nearly contiguous to the basins of London and 
Hampshire. It will be sufficient to consider one of the de- 
nuded districts, as the appearances observable in others are 
strictly analogous ; we shall, therefore, direct our attention to 
what we may call the Valley of the Weald, or the region inter- 
vening between the North and South Downs. 
Map. — In the coloured map given in Plate V. *, the district 
alluded to is delineated, and it will be there seen that the 
southern portion of the basin of London, and the north-east- 
ern limits of that of Hampshire, are separated by a tract of 
secondary l'ocks, between 40 and 50 miles in breadth, com- 
prising within it the whole of Sussex and parts of the counties 
of Kent, Surrey, and Hampshire. 
There can be no doubt that the tertiary deposits of the 
Hampshire basin formerly extended much farther along our 
southern coast towards Beachy Head, for patches are still 
* This map has been chiefly taken from Mr. Greenough's Map of England. 
