600 DENUDATION AND SCENERY. 



The denudation of the Chalk over the south-eastern counties 

 must have been partly effected by the sea in Eocene times, forming 

 a plain of marine denudation ; later on, in Miocene times, after 

 great disturbances had taken place, both Chalk and Eocene strata 

 were denuded over large areas by subaerial agents, and the old 

 Chalk cliffs formed in Eocene times were effaced ; while still later, 

 in Pliocene times, the Wealden anticlinal and the Chalk and 

 Eocene tracts of the Eastern counties must have been considerably 

 denuded by the sea. 



The origin of river valleys is intimately connected with the 

 formation of escarpments, especially when we take into account the 

 remarkable fact that many rivers flow through a series of escarp- 

 ments more or less at right angles to the strike of the beds, and 

 over or along their dip-slopes. This, as taught by INIr. Jukes and 

 Sir Andrew Ramsay, is due to the fact that the rivers commenced 

 their courses before the escarpments had been worn back.^ Thus 

 the general inclination of the strata from the Severn valley towards 

 the south-east of England naturally gives a direction for the flow of 

 the Thames, supposing it to have commenced on a plain when the 

 Chalk and Eocene strata also extended much farther west. 



Again, when the Wealden anticlinal had been formed, and its 

 summit had been worn down, the rivers commenced their courses 

 over a plain that no doubt sloped gently northwards and south- 

 wards from the central line of elevation, for in this way only can 

 the rivers have excavated their channels in the Chalk downs. Once 

 marked out, these channels have been retained, while the influence 

 of rain and lateral streams has excavated the broad vales of Gault 

 and Weald Clay that intervene between the ridges of Lower Green - 

 sand and Hastings Beds.* The many minor features due to the 

 relative resistance of the rocks, the modified influence of rain and 

 streams on porous and impervious strata, the possible effects of 

 faults and fractures caused during the formation of the Wealden 

 anticlinal, must all be taken into consideration in elucidating the 

 origin of the diversified scenery. For when subaerial agents 

 commence their work on a tract formed of rocks of varied texture, 

 the waters will sink through the porous strata flowing in difterent 

 directions underground, according to the joints and fissures in the 

 beds, and to the presence of impervious beds. Thus some rain- 

 waters that have fallen on an escarpment may be drained off in the 

 shape of springs in the vale below the ridge, while other waters 

 may be carried far underground along the dip-slope. The material 

 carried away in suspension, and that in solution derived from the 

 calcareous rocks, will tend to lower the general level of the 

 country ; on the other hand, the impervious strata will be eroded 



1 Jul<es, Q. J. xviii. 378 ; Ramsay, Q. J. xxviii. 14S, xxxii. 219 ; see also 

 Phillips, G. Mag. 1864, p. 229. 



* See C. Le N. Foster and W. Topley, Q. J. xxi. 443 ; Topley, Geol. Weald ; 

 Ramsay, Phys. Geol. and Geogr. Gt. Britain, ed. 5 ; S. V. Wood, jun. Q. J. 

 xxvii. 3 ; W. Hopkins, T. G. S. (2), vii. i ; C. Barrois, Ann. Soc. Geol. du 

 Kord, iii. 75 ; Spurrell, Rivers and Denudation of West Kent, 1SS6. 



