that is, they lay one above the other in parallel order-horizontally and as yet undisturbed. The then unbroken continuity of the chalk from the North to the South Downs is inferred by facts and reasoning which our limits will not permit us to pursue. By the aid of diagram B the reader will be able

B.-SECTION BETWEEN BEACHY HEAD AND ROCHESTER.

W

C-Chalk.

1--Upper Green Sand.
2-Gault.

3-Lower Green Sand.
W-Wealden.

T-Tertiary.
a-The Channel.
b- Maidstone.

c-Rochester.

d-Mouth of the Thames.

1 Line of force which elevated the Weald to its present position.

Dotted lines represent the continuation of the strata now denuded.

to understand the direction of the force which elevated the whole mass of the cretaceous formation. This section shows not only the present conformation of the land, but by the dotted lines also represents the portion which has been denuded, washed away, and transported to form the material of later deposits. The upheaval of the strata between the North and South Downs is all but universally believed to have been gradual and tranquil.

The marine theory would ascribe the formation of the existing system of hill and valley to the action of the sea during its emergence above its level, whilst the "theory of fracture," ably advanced by Mr. Hopkins, would refer the same to dislocation caused by elevation. These theories have been much combated by a modern school of geologists which attributes the denudation of the Weald principally to the action of rain and rivers; this is designated the sub-aërial theory. The wear and tear of our great Continents, and the gradual transfer of their materials to the sea slowly but incessantly in progress, is perhaps

effected not so much by the action of the sea along their shore lines as by the transport of soil carried down by rivers.

The preceding remarks on the deposit of the Wealden may be referred to in proof of the vast mass of sediment transported by river action. In diagram B we perceive the strata dipping from tho Hastings Sand, the central axis of elevation, and hence tormed by geologists the "anticlinal" axis, its protrusion having thrust aside the superior beds, which thus incline or "dip" nway from it. The physical features and aspect of the area of denudation are readily to be traced to their geological structure. As a general rule, the more rocky and unyielding beds form the hills, whilst the clays and more yielding beds furnish the valleys, thus evidencing their comparative powers of resistance to the denuding action of water.

A very able discussion by Messrs. Foster and Topley on the forces which produced the denudation of the Weald will be found in the Geological Journal, vol. xxi. In this paper, evidence is produced of the occurrence of an old river gravel in the valley of the Medway 300 feet above the present level of that river, which has cut down its channel to this depth. The authors infer that if so large a denudation has been effected by rain and rivers, there can be little difficulty in supposing the present form of the ground in the Weald to have been produced entirely by these agents." At Ashford, Weald gravel was deposited when the Stour ran at a considerably higher level than

now.

The principal rivers which traverse the Weald do not flow to the sen eastwards to Romney Marsh or Pevensey through its longitudinal valley, but pass through transverse valleys in the North and South Downs, which, if we accept the evidence afforded by the Medway above quoted, have been eroded by their streams. Thus the North Downs are cut through by the Wey, Mole, Darent, Medway, and Stour; the South Downs by the Arun, Adur, and Cuckmere.

I may here conveniently allude to certain outliers, or isolated portions of the overlying beds, which have resisted denudation within the Weald. A reference to the Map of the Geological Survey will show examples of patches of the Lower Green Sand which have thus escaped near Ashford. Collier's Hill, near Aldington, and Great Chart are examples.

I have endeavoured to descrribe the geological features of a district which, from its intrinsic interest and its proximity to the Metropolis of science, has been investigated and described

by some of our most able geologists. The names of Martin, Mantell, Fitton, Buckland, Lyell, Hopkins, and Austen, are inseparably connected with its history. Among the staff of the Geological Survey especially engaged on the Weald are Drew, Foster, Topley. To their numerous papers in the publications of the Geological Society, and to the Memoirs of the Geological Survey, I would refer those who desire a more intimate knowledge of the geology of the cretaceous beds in the south-east of England than the limits of the present communication can afford.

INDEX OF NAMES, PLACES, AND GENERAL MATTERS.

NAMES.