22 PKOCEEDm&s or the geological society. [Kov. 9, 



contemporaneous, as I consider, with the similar rectilinear ridges 

 of the Isles of Wight and of Purbeck, represent, I submit, the 

 elevatory influences under which the chalk area of Hampshire and 

 of Wilts became converted into land, and under which the Wealden 

 upcast acquired that special configuration which gave to the up- 

 channel tide its great scouring power. In No. III. the sea is shown 

 as confined within the chalk escarpments of the Weald, with a barrier 

 of land extending across to France and shutting off the British Channel 

 from the North Sea ; while a part of the area now occupied by this 

 sea between East Anglia and the north of France was in the condition 

 of land supplying streams that found their way through the Stour 

 and Medway gorges into theWeald, so much of the drainage as passed 

 through the Thames vaUey * reaching the Weald through the gorges of 

 the Wey and Mole to the west. The gravel-beds, with remains of an 

 ancient beach, described by Mr. Prestwich and by others near Calais, 

 appear to me to fall into their place between the two stages thus re- 

 presented, while the Brighton bed seems to belong to the period re- 

 presented by No. III. and to that following it. It will not be difficult 

 to pursue the change from the stage thus represented in No. III. to 

 that when the shore had become established at the Lower-Green- 



by this preliminary posffflacial clenucTation ; while to the north of the Essex 

 heights, away to the northernmost extremity of Britain, the parts once covered 

 by the same glacial sea, being remote from the theatre of these distm'bances, 

 felt their influence only in the form of a tranquil eleyation, and were consequently 

 only partially denuded of their coyering of glacial beds. It was during a lull 

 in these disturbances, and when this preliminary denudation and emergence had 

 brought about the conditions represented in Map no. II., that the Thames gravel 

 accmnulated ; so that more properly it was a renewal, and not the setting-in 

 of these disturbances, which, first completing the sharp inclination of the recti- 

 linear ridges, then lifted ihem, together with those portions of the chalk and 

 subcretaceous disti'icts which had not yet emerged, above the sea, and, by re- 

 newing the causes of denudation, removed this accumulation everywhere except 

 in the places where we now find it (which it seems to me were the parts of least 

 disturbance at the particular epoch), eating also still deeper into the old strata as 

 they underwent elevation from the waters. I have elsewhere (Quart. Journ. Geol. 

 Soc. vol. xxiv. p. 174) endeavoured to connect this renewal of disturbance in the 

 south with the setting-in of that depression in the north of England to which 

 was due the postglacial clay of Hessle, which wraps like a cloth the deeply de- 

 nuded glacial beds, and is underlain by a gravel containing the characteristic 

 shell of the Thames beds and their allies, the Cyrena jluminalis. 



* The amoimt of drainage collected in the Thames valley east of London at 

 this period could have been but small, because the entire bottom of this valley, 

 east of London as far as Erith, which is now occupied by the marsh mud, and 

 which, if the embankment were removed would be aU flooded, is covered by 

 an oak, yew, hazel, and fir forest, rooted into the gravel and overspread by the 

 marsh mud. It is clear from tliis, that subsequent even to the lates{; part of 

 that gravel, but prior to the general depression of England, which buried so 

 many forests remaining round our coasts, as well as the forest in Question, 

 the bottom of this valley, far within limits that, but for the embankments, 

 would now be water, was dry ground. It is this depression of so much of 

 England, at a late period, that I associate with the opening of the mouths of 

 the Thames and Crouch, and the occupation by the present North Sea of the 

 large area to the north of Kent, shown in Map No. III. as land. This general 

 depression seems to have been the recoil from the termination of the Wealden 

 elevation. 



