59 



Gaps in the Chalk escarpment, distinguishing as "wet" 

 those still carrying streams, and the dry gaps by the 

 neighbouring villages. 



South. North. 



Treyford Dry Crondall. 



Cocking Dry Aldershot. 



Arun Wet Wey. 



Adur Wet Mole. 



Clayton Dry Merstham. 



Ouse Wet Darenth. 



Cuckmere Wet Medway. 



In the case of the Merstham-Clayton Gaps the line of 

 weakness with which they may be connected (see ante) is 

 emphasized by the course pursued by the Railway from 

 London to Brighton, in its endeavour, common with rail- 

 ways, to keep the lowest level. 



Mr. Topley remarks that " passes have no relation to 

 the drainage of the country inside the chalk escarpment," 

 therefore, they were not formed by inward flowing streams ; 

 then he says, that " in no case does any stream run out- 

 wards from the Weald through them," if streams did run 

 through them they would not be "passes," but river-gorges, 

 as in the case of the Darenth, &c. To shew a difference 

 between passes and river-gorges, Mr Topley says that, 

 " passes are apt to occur where escarpments are faulted," 

 but he shows that of the "passes" of the Weald, North 

 and South, they are apter to occur unassociated with 

 faults.* 



Since then these passes and their associated valleys 

 were not formed by drainage inward, I cannot help the 

 conclusion that they were formed by drainage outward ; 

 the more, as streams still occupy the lower parts of some of 

 the dry valleys. The passes of Mr. Topley, I consider to 

 be the truncated valleys of diminished rivers. 



The Chalk escarpment formerly extended Southward, 

 its face originally of slight elevation, has increased vertic- 



*. Weald, pp. 277-279. 



