1870.] WOOD WEALD-VALLEY DENUDATION. 21 



accompany the Map ; but those numbered 4, 5, 10, 11, 13, and 14 

 indicate the lines of the sections given by me at pp. 394 to 417 of 

 the 23rd volume of the Quarterly Journal of the Society, which 

 have corresponding numbers attached to them there. 



The two small maps are intended to make intelligible the changes 

 of the distribution of land and water to which I trace the denuda- 

 tion of the "Weald. The first (ISTo. II.) is intended to represent an 

 earlier stage, viz. that when the higher gravels of the Thames, East 

 Essex, and Canterbury heights were being accumulated in inlets 

 filled with salt water, and before the conversion of those inlets into a 

 fluviatile condition had been efi'ected by means of elevation. In 

 this the higher elevations of the North and South Downs and 

 of the Lower-Greensand country are represented as islands, the 

 wear of whose shores and of the Lower-Tertiary and Chalk inlet 

 shores supplied with some Lower-Greensand material the large 

 accumulations of flint and pebble that make up the Thames and East 

 Essex gravels, and supplied the flint to the Canterbury gravel. The 

 highest ridges of the Hastiags-sand country are also represented as 

 islands. In the river-beds into which the more northern parts 

 of these inlet channels became converted, accumulated the Brick- 

 earths with Cyrena fluminalis, occurring at Clapton, Ilford, Erith, 

 and Grays within the Thames iulet, at Clacton and (according to 

 the President's statement in the discussion) east of Southend in the 

 East-Essex inlet, and at Chislet in the Canterbury area. This 

 shell, unknown from the south or south-west of England, regarded 

 by me as mostly under the sea during this period, ranges north to 

 Yorkshire over the country regarded by me as land. During the 

 transition period preceding the establishment of these Ciyrewa-rivers, 

 those angular blocks (said to be Greywethers) occui'ring at Grays in 

 a brickearth on the slope above the (7yrewa-deposit, but a little below 

 the great sheet of Thames gravel covering the plateau, would seem 

 to have been carried in on ice by tidal action*. 



The elevation, and the consequent shrinking and partial breaking up 

 of these inlets so as to form river-channels, I regard as a first result of 

 the disturbances under which the sea so retreated as to cause the 

 distribution of land and water to become eventually as represented 

 in Map No. Ill.f The upthrow of the Guildford Hogsback ridge 

 and of the ridge of Portsdown Hill (shown by lines on Map No. II.), 



* These blocks are clearly not derived at second-hand from the Grlacial beds 

 of Essex, as supposed by Prof. Morris (Geol. Mag. vol. iv. p. 63) ; for they are 

 nvunerous, all alike, generally with sharp fractures, and all collected in one small 

 area ; whereas in the Glacial beds of East Anglia large blocks are not common, 

 and what there are consist of divers rocks, and are mostly rounded. 



t The commencement of the disturbances of which these rectilinear and 

 highly inclined ridges are the intensified result was, I consider, coincident with 

 the rise of England from the glacial sea, and the cause of the great denudation 

 eifected during that rise over both the south-west and the south-east of England. 

 The margin of this complete denudation is distinctly marked by the abrupt ter- 

 mination of the glacial beds, at altitudes exceeding 300 feet, on the Essex heights 

 overlooking the Thames valley. Over the region south of these heights it is 

 obvious that, besides the glacial beds, a considerable mass of the older tertiaries, 

 «nd probably also much of the chalk and subcretaceous strata, were removed 



