1870.] WOOD — WEALD-VALLEY DENtTDAXIOX. 5 



a late period as that when the conditions giving rise in these parts to 

 gravels and brick-earths had ceased — the period in fact of the modern 

 alluvium, which alone occurs in the valley, or more properly the 

 wide gorge thus cut through the ridge. 



I then pointed out that east of London, where it occupied the 

 more seaward portion of the channel thus opening southwards towards, 

 the "Weald, the Thames gravel had been greatly broken up, denuded 

 and elevated irregularly, by which action partial terraces had been 

 formed — that under these terraces occurred the gravels and brick- 

 earths of fluviatile origin with Cyreiia Jiuminalis which had succeeded 

 to the spreading out of the gravel occupying such terraces — and that 

 these were the deposits of rivers into which the original gravel-inlets 

 had by the elevation of their bottoms become reduced, such rivers, 

 equally with the inlets that had preceded them, opening to a sea in 

 the direction of the "Weald. The mouths of these rivers, I considered, 

 had followed the shore-line as this gradually receded southward from 

 the rise of the "Wealden area, until the sea, first becoming confined 

 within an estuary of its own eroding, marked by the "Wealden 

 escarpments, was eventually expelled from the Wealden area — and 

 that upon this event taking place, the drainage acquired its present 

 reversed direction from the "Weald into the Thames estuary, which 

 then came into existence*. 



At the time when by a study of the gravels without the "Weald I was 

 thus led to these views, I had not examined with any detail how far 

 the constitution and position of the gravels lying within the chalk 

 escarpments supported or conflicted with them. This I have now 

 done, so far as concerns the north-eastern part of the area, which, 

 from its contiguity to the mouths of the Thames and East Essex 

 gravel inlets, is the part of principal importance in the question ; and 

 1 propose now to show its bearing upon it. 



In doing so it will, I think, be advantageous to consider also a 

 question that I had deferred for the occasion, viz. how far the 

 theories of the denudation of the "Weald by agencies which involve 

 the escape of the material removed in the course of denudation out- 

 wards from the "Weald and into the Thames area, be they atmo- 

 spheric, fluviatile, or marine, receive support or meet with negation 

 from the composition of the detrital beds lying without the north- 

 eastern part of the Weald. 



Taking up this latter inquiry first, we have two sets of detrital 

 beds to consider, viz. the Glacial and the Postglacial. Of the first, 

 we have in this part of England two formations, the Boulder-clay 

 and the gravel underlying it, which I have termed Middle Glacial. 



In neither of these deposits can it be said that the debris of the 



* In my paper in the Quart. Journ. Geol. Soc. vol. xxiii., at p. 408, I regarded 

 the brick-earth of Erith and Crayford as distinct from that of Grays, and as 

 having preceded the Thames gravel. Finding afterwards, by a clearer section, 

 that it did not pass under that gravel, I, in a letter published at page 634 of the 

 fifth volume of the Geol. Mag., withdrew from that position, and admitted that 

 the Grays and Erith and Crayford Brick-earths are identical, and belong alike 

 to the lower terraces of the Thames-gravel formation. 



