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 on]y 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, Med way, 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-]-. 
* Conybeare, Outlines of Geol., p. 81. f Ibid., p. 145. 
