1867.] WOOD SOUTH-EAST OF ENGLAND. 407 



followed the denudation of the Glacial clay which, with the London 

 clay beneath it, had extended over the Wealden area. 



The section previously given (fig. 5) illustrative of the position of 

 the Glacial clay along the north side of the Thames may be made to 

 serve, imperfectly, to show the denudation and upcast which fol- 

 lowed the recession of the sea from this part towards the Weald, 

 along the opening lying between Dartford Heath and the East Essex 

 dividing ridge, as well as the formation of the fluviatile outlets (now 

 represented by the Grays and Darent and Cray valley- deposits) that 

 followed its recession. This embouchure of the channel is conspicu- 

 ously marked by the denudation of the Tertiary beds in that part, and 

 by the position which the remnants of the gravel occupy in reference 

 to them, an arm of the chalk running up in this part into the centre 

 of the eastern Thames area. It is only necessary to place my sur- 

 veyed sheet, No. 1, in its order next to Sheet 6, already surveyed 

 and published by the Geological Survey, to render this readily per- 

 ceptible to the eye, an island, represented by Swanscomb Hill 

 (round the flanks of which, at an elevation of about 100 feet, the 

 gravel now clings, as it were), having occupied the centre of this 

 embouchure. 



The next section, fig. 11, gives the denudation at the embouchure 

 of the East Essex channel by Rochester, and shows that gravel cut 

 down from a lofty brow to the Chalk by the recession of the sea 

 towards the Weald, — the London clay being cut oif with it in the 

 same way as it is with the Thames gravel in fig. 10, and con- 

 sistently with the age claimed for this gravel — of priority to the 

 Wealden upthrow and denudation. 



The gravel of the Canterbury heights is denuded in a two- 

 fold direction — one towards the Chalk country of the Wealden 

 scarp, and the other towards the Chalk country of the Isle of 

 Thanet. The former presents no feature essentially different from 

 that exhibited by figs. 10 and 11 ; and the denudation in the latter 

 direction is well displayed in the coast-section east of Heme Bay, and 

 may be seen in the section of the Lower Tertiary beds of that dis- 

 trict given in Mr. Prestwich's Memoir on the Thanet Sands in the 

 8th volume of the Quarterly Journal of the Society (p. 264). 



A section through the dividing ridge separating the Thames gravel 

 trough from that of East Essex having been given by me in a com- 

 munication to the Geological Magazine *, I do not think it necessary 

 to give it here. The erosion of the vaUeys of the Thames mouth and 

 Crouch river through this ridge, having taken place at a very recent 

 date, is connected with another peculiar structure to which I have 

 presently to allude ; but first, as to the break-up of the Thames 

 gravel in the body of its trough, and the formation of the fluviatile 

 (or X 5) portion of it. 



The vaUeys which are cut through the Thames gravel, and which 

 have arisen from the denudation accompanying the rectilinear dis- 

 turbances shattering that gravel and elevating the Chalk country, 



* Vol. iii. p. 348. In that section a small outlier of Bagshot Sand should 

 have been shown on the top of Eound Hill. 



