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It was mainly during the denudation of the Thames 

 valley by itself and its tributaries that the present Wandle 

 basin was formed, whose direction, Westward, differs from 

 that of the Old Wandle which continued Eastward, from 

 Croydon to Deptford. If the present Wandle, or that part ' 

 of it which runs from Carshalton to the Thames be taken 

 as the subterranean outlet representative of the direction of 

 the stream of underground drainage in the chalk of the 

 present day, it is probable that that drainage line has 

 changed considerably since the old valley was cut by the 

 stream from Merstham by Croydon and Deptford. The 

 Ravensbourne too, which finds its outlet close to or actually 

 at the line of the extinct river, was once, I have little doubt, 

 one of its affluents, and this will appear the more likely if 

 we remember that the Thames to which these streams 

 flowed was reached at that early time at a point some 

 distance further to the North than would be the case now. 

 For the current of all the rivers of the district, running 

 North or South, have tended to widen their channels 

 Eastward, leaving the West, while that of the Thames and 

 those flowing Eastward have left their older beds on the 

 North, and run in newer and deeper ones on the South. 



After the Darenth had cut its Valley down through 

 the old bed of high level gravel at Dartford, it found the 

 chalk still stretched across the present streamway from 

 the East, in such strength as to necessitate its swerving 

 from the straight line it had preserved between Farning- 

 ham and Dartford ; consequently it cut its channel round 

 under the hills, which formed cliffs, by Stoneham, North 

 End and Erith, where it joined the Thames. 



During this period the sea must have been far away 

 and the land high, with a good fall for the rivers, but after 

 the Thames at this part of its course had cut its bed down 

 to a depth about the zero of O.D., there was a change ; 

 this I ascribe to the depression of the land, until the sea 

 advanced far up the old river valley, raising its flood- 

 waters to a great height. If the river did not actually 



