1870.] WOOD WEALD-VALLEY DENUDATION. 23 



sand escarpment, with tlie Medway and Stonr still discharging into 

 the Weald. All that remains, then, is to imagine the land to the north 

 of Kent depressed coincidently with the continued elevation of the 

 Weald, so as to produce an opening through the Straits of Dover* 

 and the introduction of the North Sea, where it now is, with the 

 denudation of the Thames and Crouch mouths taking place synchro- 

 nously with the desertion of the Weald by the sea, and the condi- 

 tion of things under which the drainage would acquire its present 

 direction is then attained. The terrestrial surface described by 

 Mr. Godwin- Austen as underlying at one place gravel of the Wey 

 seems intermediate between the desertion of the Weald by the sea 

 and the introduction over the spot of the waters of the river Wey, 

 which came into existence by means of that reversal. 



In all this, I can but see the most ordinary and gradual changes 

 that must take place wherever land under the influence of active 

 subterranean disturbance is changing its level, pushing back the sea 

 in one place and admitting it in others ; and that the elevation of 

 the Weald was accompanied by energy so active as to force the 

 whole thickness of the chalk into the Guildford Hogsback ridge is a 

 matter of universal admission. As this has admittedly occurred 

 since the Eocene period, is it at all incredible that it should have 

 taken place since the Glacial period ? considering that beds whose 

 fossils indicate a parallelism with the Crag and earlier Glacial beds, 

 have become elevated in Sicily into mountain tracts. The Oxus 

 has deserted its bed within historical times, and now follows another 

 course to the Caspian. 



POSTSCEIPT. 



Since the foregoing paper was sent in, the Journal of the Society, 

 no. 104, containing Mr, Codrington's well-considered paper on the 

 Hampshire and Isle-of- Wight deposits, has appeared (vol. xx\d. 

 p. 528). The carefully prepared sections given by that gentleman, 

 illustrating the position of the gravels which cover so much of the 

 Hampshire Tertiaries, have an important bearing upon the subject 

 of the present paper, and seem to me powerfully to corroborate the 

 mode of origin and conditions of sequence which, in the present and 

 former papers, I have endeavoured to substantiate in the case of the 

 gravels of the London area. 



It will be seen that the whole of the great gravel sheet illustrated 

 by Mr. Codrington's sections is, like the Thames, East-Essex, and 

 Canterbury-heights gravels, cut oif abruptly by denudation on lofty 

 brows towards the chalk country ; whUe in the opposite direction it 

 descends gradually from these brows towards the sea. 



While the gravels of the London area, having been formed in 

 inlets, are necessarily thus cut off on brows towards the chalk 



* I think it probable that the land between Kent and Calais was low in the 

 central part, the Wealden elevation having been least in the easterly direction. 

 The wearing back of the cliffs to the point where they cut across the chalk escarp- 

 ment is a subsequent process still going on. 



