6i 



eastward. This appears to me to have occurred near 

 Plaxtol, and .then between the Comp and Ightham hills, 

 the Old Darenth once crossed the present escarpment, 

 curving round over the gault to the Westward, towards the 

 opening in the chalk at Otford; a course not unlike that 

 of the Medway at present. 



There is evidence that the Atheriield clay which as 

 Mr. Topley remarks, keeps the 500 feet contour opposite 

 the breach in the Chalk, falls slightly near Plaxtol and 

 continues to do so as it approaches the Medway. Between 

 the above mentioned level position of the Atherfield clay 

 and the Medway depression there is no evidence of a rise, 

 but rather the contrary. Mr. Topley thinks that there 

 is an anticlinal near Plaxtol to account for the Southerly 

 course of the Plaxtol Brook, but he does not give evidence 

 for it, and shews that though there is a synclinal Eastward 

 (Weald, p. 277) there is none Westward, so that there is no 

 anticlinal rise there even of that limited kind which 

 consists in the recovery of a general level between two 

 depressions. But I think it sufficient to suggest that the 

 abandonment of its old channel by the Darenth is a good 

 reason for the advance along it of a Medway feeder, after 

 the supremacy of the latter river became established. 



A similar instance to the cutting back of the Plaxtol 

 Brook (or the Shob according to Hasted), may be men- 

 tioned in support of this on the West of the Darenth, where 

 the Eden has cut back to the chalk ; as in the East, so in 

 this case the Eden passes the greensand escarpment where 

 there is evidence of a fall in the Atherfield clay from its 

 level at the 500 feet contour line. I suppose then, that 

 the Old Darenth ran southward from near Crowborough, 

 over the present site of Tonbridge or thereabout at 

 an elevation exceeding 400 feet above that place. The 

 bed of this old Darenth exists now at the greensand 

 escarpment near Plaxtol at about O.D. 450 feet; and 

 on the Easterly side of the Ightham Hills patches of 

 river gravel and sand lie, forming one or more terraces, 



