298 EOCENE PERIOD. [Ch. XXI. 



Eocene period. Hence these flints might naturally occur on 

 the downs, and be wanting in the valleys below. 



If the reader will refer to the preceding diagrams (Nos. 69 

 and 70), and reflect not only on the 'successive states of the 

 country there delineated, but on all the intermediate conditions 

 which the district must have passed through during the 

 process of elevation and denudation before supposed, he will 

 understand why no wreck of the chalk (No. 1) should occur 

 at great distances from the chalk escarpments. For it is evi- 

 dent that when the ruins of the uppermost bed (No. 1, dia- 

 gram 69) had been thrown down upon the surface of the 

 bed immediately below, those ruins would subsequently be 

 carried away when this inferior stratum itself was destroyed. 

 And in proportion to the number and thickness of the groups, 

 thus removed in succession, is the probability lessened of our 

 finding any remnants of the highest group strewed over the 

 bared surface of the lowest. 



Transverse valleys. There is another peculiarity in the 

 geographical features of the south-east of England which must 

 not be overlooked when we are considering the action of the 

 denuding causes. By reference to the map (Plate 5), the 

 reader will perceive that the drainage of the country is not 

 effected by water-courses following the great valleys excavated 

 out of the argillaceous strata (Nos. 2 and 4), but by valleys 

 which run in a transverse direction, passing through the 

 chalk to the basin of the Thames on the one side, and to the 

 English channel on the other. 



In this manner the chain of the North Downs is broken by 

 the rivers Wey, Mole, Darent, Medway, and Stour; the South 

 Downs by the Arun, Adur, Ouse, and Cuckmere *. 



If these transverse hollows could be filled up, all the rivers, 

 observes Mr. Conybeare, would be forced to take an easterly 

 course, and to empty themselves into the sea by Romney 

 Marsh and Pevensey levels f. 



* Conybeare, Outlines of Geol., p. 81. t Ibid., p. 145. 



