VIII RIVERS AND LAKES 283 
two. ridges or “escarpments,’ one that of 
the Chalk, the other that of the Greensand, 
while between the Chalk and the Green- 
sand is a valley, and between the Green- 
sand and the ridge of Hastings Sand an 
undulating plain, in each case with a gen- 
tle slope from about where the London and 
eee eee ‘ ee 
“tlt a 
nosil a AT Witte 
Fig. 38. — a, a, Upper Cretaceous strata, chiefly Chalk, forming the North 
and South Downs; b, b, Escarpment of Lower Greensand, with a valley be- 
tween it and the Chalk; c, c, Weald Clay, forming plains; @, Hills formed 
of Hastings Sand and Clay. The Chalk, etc., once spread across the country, 
as shown in the dotted lines. 
Brighton railway crosses the Weald towards 
the east. Under these’ circumstances we 
might have expected that the streams drain- 
ing the Weald would have run in the direc- 
tion of the axis of elevation, and at the 
bases of the escarpments, as in fact the 
Rother does for part of its course, into the 
sea between the North and South Downs, 
instead of which as a rule they run north 
and south, cutting in some cases directly 
through the escarpments; on the north, for 
