18 PEOCEEDINGS OF THE GEOLOGICAL SOCIETr. [NoV. 9, 



water than that underlying it, in which the Selsey fauna Hved; 

 and this colder change I associate with the admission of the North 

 Sea through the Dover Strait. 



So soon as by these means the elevatory action gained on the 

 tidal erosion, and the Weald was deserted by the sea, the reversal of 

 the drainage of the Stour and Medway into its present direction 

 commenced. Its first result would be that the streams, descend- 

 ing from the northern portion of the Hastings-sand country, and 

 having to seek a new outlet, would form a lacustrine kind of ex- 

 panse up to the level where a poiat of outlet along the present line 

 of drainage was found for it. The deposit of that expanse I trace 

 in the wide-spread sheet of gravel which skirts the Medway and its 

 tributaries, the Beult, Eden, and Teise, over the "Weald-clay bottom, 

 and which, in the case of the Beult and Teise, is formed almost ex- 

 clusively of material derived from the Hastings-sand country, locally 

 called " Crowstone gravel," but which in the case of the Eden, as 

 Sir Roderick Murchison has shown*, has a considerable admixture 

 of Lower-Greensand and flint material, and, in the case of the Teise 

 (as I am informed by Mr. Topley), of Tertiary pebbles also, derived, I 

 conceive, from the prior distribution of such material over the area 

 when in the condition shown in sketch map No. III. 



A few patches of gravel resting on "Weald-clay, but occupying 

 higher ground than this sheet, skirt the Hastings-sand country, such 

 as those at Marden and "Wantsuch Green, mentioned by Messrs. 

 Eoster and Topley. These are similarly composed of Hastings-sand 

 material ; and though these gentlemen speak of flint having been 

 found in them, it must be excessively rare ; for I could not detect 

 a trace of it. Their age I regard as similar to that of the gravels 

 with Tertiary pebbles about Yalding and at "WHlesboro' ; but being on 

 the opposite side of the channel formerly occupying the Weald-clay 

 area, they received no Tertiary pebbles like their coeval gravels at 

 Yalding and Willesboro', but were supplied by the material de- 

 scending from the Hastings-sand hills. The few flint fragments 

 that Messrs. Eoster and Topley speak of may have drifted along the 

 island shore from those abundant accumulations of flints described 

 by Sir Eoderick Murchison, which are scattered about the more 

 western parts of the Weald. These patches are considerably above 

 the great sheet skirting the Beult, and are divided from it by a 

 slope of bare Weald-clay. 



The gravels and brickearths which fringe the valley of the Med- 

 way between Maidstone and Chatham, and of the Stour between 

 Ashford and Canterbury, occupying lower levels than the gravels 

 with Tertiary pebbles, already specially discussed, are more difficult 

 to distinguish, as it is obvious that any earlier gravels or brickearths 

 deposited at low levels in these valleys before the drainage was 

 reversed, would, after that event occurred, become undistinguishably 

 mixed up with the deposits from such reversed drainage. 



The same remark equally applies to those lowest accumulations of 

 gravel and brickearths which fall within the Thames, the East- 

 * Quart. Journ. Geol. Soc. vol. vii. p. 381. 



