65 



the Wey under Crooksbury Hill, may present a true 

 example of reversal of drainage. 



Over much of the Chalk of the North Downs above a 

 certain level lies a slight mixture of various rocks, derived 

 from the greensand, &c., and the tertiaries. But wher- 

 ever the chalk was bared, it is covered by a layer of red 

 and yellow clay, containing in its lower part unbroken 

 flints. Near the surface these flints are splintered and 

 broken by weathering. This is the clay-with-flints, and 

 appears to consist very largely of the insoluble debris of 

 the chalk, the lime of which has been removed by chemical 

 means ; it may be called decalcified chalk. This layer is 

 wholly unstratified, and in its lower part contains nothing 

 foreign to the rock on which it lies. Though the clay lies 

 along the crest of the Downs it does not continue down 

 the edge of the escarpment. The upper portion of the 

 layer of clay has everywhere been denuded by wind, and 

 rain and snow, and its constituent angular stones are left 

 covering its surface, while in some places nothing but the 

 stones remain. It is a land deposit. It is marked on its 

 higher limits by the crest of the Downs, and on its lower, 

 or Northern, by a line which can only be approximately 

 drawn, as being not found below the level of the 400 feet 

 contour, to the South of London and in the Westernmost 

 part of Kent. South of Gravesend this limit is found 

 near the 300 feet contour, South of Sittingbourne near the 

 200 feet contour, and Mr. Drew has mapped it at Ham, 

 some fifty feet above the sea level. In the East its identity 

 may not be so marked as it is in West Kent at lower 

 levels, but there can be no question that its lower level 

 subsides Eastward. However that may be, it is clear that 

 some form of denudation has left all the better marked and 

 most extensive patches above that line. This is true of the 

 patch at Dunn Street, near Westwell, and of a remarkable 

 patch of apparently the same clay on the Northern slope 

 of Oldbury Hill, near Ightham, both resting on rocks 

 which are not those of the parent chalk-with-flints. 



