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 rocks, 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, 



