vni 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 



Fig. 38. a, a, Upper Cretaceous strata, chiefly Chalk, forming the North 

 and South Downs; 6, b, Escarpment of Lower Greensand, with a valley be- 

 tween it and the Chalk; c, c, "Weald Clay, forming plains; d, 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 



