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 denudation of the Weald. The first (No. 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 effected 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 Hastings-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 inlet, 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 Cyrena-rivers, those angular blocks (said to be Greywethers) occurring at Grays in a brickearth on the slope above the Cyrena-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. III.† 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 Glacial beds
of Essex, as supposed by Prof. Morris (Geol. Mag. vol. iv. p. 63) ; for they are numerous, 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.
† 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 effected 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 termination 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, and probably also much of the chalk and subcretaceous strata, were removed
