THE OKIGIN OF OUK ENGLISH SCENEEY. 
63 
marine denudation, after being subjected to the disturbances 
and undulations produced during their elevation ; and these very 
disturbances may have partly affected the character of the plain 
of marine denudation, which does not necessarily mean a dead- 
level, and gentle curves or slight ridges of the harder rocks may 
have been left as a guide to the subsequent sub-aerial denuda- 
tion. 
The rivers that cut through the escarpments are fed by 
streams that run parallel to the escarpments, and though the 
actual denudation may appear trivial, yet when rightly esti- 
mated by geological time, it will be understood, and a true 
conception of the magnitude of sub-aerial denudation arrived at. 
The denudation of the 'Wealden district has been a fertile 
source of discussion, and has an important bearing on the origin 
of escarpments. It will be unnecessary here to refer to the 
many papers that have been written upon the subject, and we 
may be content with giving Professor Ramsay’s views. # By 
drawing a section across the district from the North to the 
South Downs, and connecting the chalk and other strata on 
either side, a dome-shaped or anticlinal structure will be formed. 
This .dome was probably removed by the sea, which formed a 
sort of plain of marine denudation, leaving at the same time a 
sort of low central watershed, from which in old times the rivers 
probably flowed, and thus formed their channels through the 
chalk, which seems inexplicable on other suppositions. In due 
time the rain and river action diversified the scenery, the chalk 
escarpments receding, the soft gault forming a hollow, the 
lower greensand standing out in bold hills, overlooking the 
plain of weald clay, and the harder rocks of the Hastings sand 
series again rising in hilly ground. 
From what has been said, it will be seen how many of our 
rivers date from very early times, although their courses have 
been at times enlarged or contracted by elevation and de- 
pression. 
The nature of the river valleys of course depends upon the 
nature of the rocks traversed by the river, bold cliffs being 
formed in hard rocks, and hardly any or none in soft strata. 
The alternation of hard and soft strata along a river course may 
lead to the formation of a lake, the softer strata being worn 
away, and the harder forming barriers at either end. Lakes, 
indeed, may be due to various causes or a combination of 
causes. Glaciers may plough out hollows, or deposit moraines, 
which form barriers. Faulting and disturbance of strata in 
some cases appear to have had considerable influence in the 
* The same views were worked out in great detail by Messrs. Foster and 
Topley. See u Quart. Journ. Geol. Soc.ff vol. xxi v p. 443. 
