Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/121

 sand escarpment, with the Medway and Stour 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 synchronously with the desertion of the Weald by the sea, and the condition 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.

Postscript.

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. xxvi. 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, bike the Thames, East-Essex, and Canterbury-heights gravels, cut off abruptly by denudation on lofty brows towards the chalk country ; while 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

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 escarpment is a subsequent process still going on.
 * I think it probable that the land between Kent and Calais was low in the