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C. Chalk.

W. Wealden.

LIGN. 46.-SECTION FROM LONDON TO THE SOUTHERN COAST OF THE ISLE OF WIGHT.
T. Tertiary.

Sea.

W

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represented the Tertiary of the London basin resting on the chalk; the Chalk of the North Downs, dipping northwards; the anticlinal position of the Wealden; the Chalk of the South Downs, dipping southwards, with Tertiary strata on the southern flank: then the depression which forms the channel of the Solent sea; the Tertiary strata extending over the northern portion of the Isle of Wight; the Chalk Downs of the island, dipping northward; and, lastly, a small portion of the Wealden, emerging from beneath the chalk, on the south coast, at Brook and Sandown bays.

LONDON AND BRIGHTON RAILWAY SECTION. -A portion of this section is well displayed along the line of railway from London to Brighton. Leaving the station at London Bridge, the Tertiary clays with their characteristic fossils, are seen from beyond Deptford, by New Cross, Sydenham, &c.; and approaching Croydon, beds of gravel appear, with interspersions of olive-green sand. The valley beyond Croydon, along the side of which the railway proceeds, is a thick bed of gravel resting on the chalk.

Beyond the station called Stoat's-nest, is a fine section of the Chalk with flint, and the North Downs are perforated by a long tunnel carried through the solid rock, which emerges near Merstham, where the firestone and chalk-marl rise to the surface. The sands and clays of the greensand group are passed at the Red-hill and Godstone stations. The Wealden clays appear at Horley, and are succeeded by shales, limestones, sands, and sandstones, to the Crawley station.1

1 The Horsham Railway, which branches off from the Brighton line, traverses the Wealden beds; and near that old quiet market-town of

Passing near Bletchingley, in Surrey, through a tunnel in the Wealden, we arrive at Balcombe, in Sussex, where laminated sandstones and shales are seen on each side the cutting. The general dip of the strata hitherto passed is to the north-east; but after crossing the deep Wealden valley beyond Balcombe, over a magnificent viaduct, the line runs along alternating layers of sands and clays, which dip to the south-west; we have therefore arrived on the southern side of the grand anticlinal axis of the Forest Ridge excavated by the tunnel through which we passed.

The Wealden strata continue with the same general inclination by Hayward's Heath,' which is traversed by a tunnel, to beyond St. John's Common, (formed of Weald clays and Sussex marble,) where they disappear beneath the lowermost greensand beds of the Chalk formation. The galt, firestone, and chalk-marl succeed; and, lastly, the white chalk of the South Downs, at Clayton Hill, through the base of which a long tunnel is carried, and emerges on the Downs on the south. The remainder of the line to the Brighton station, runs over, or through, hills and valleys of the white chalk.

Thus this railway passes through two ranges of chalk hills, viz. the North and South Downs, by tunnels; two of greensand, viz. near Red Hill in Surrey, and Hurst perpoint in Sussex; and two principal ridges of Wealden, viz. at Balcombe, and Hayward's Heath. There is not a railroad in the kingdom that in the distance of fifty miles exhibits geological phenomena of greater interest.

If we take a line bearing more to the west, as, for example, from London to the southern shore of the Isle of Wight, at Sandown Bay, we shall have the section represented in Lign. 46, which exhibits the entire series of the deposits, and their relative position.

JOURNEY FROM LONDON TO BRIGHTON BY COACH.-It may

Sussex, are Tower Hill quarry, Stammerham quarry, and other pits in which the Tilgate grits and sandstones are exposed, and where the characteristic fossils of the strata may be obtained of the workmen; with bones of the Iguanodon, Goniopholis, and other Saurians, stems of Clathraria, &c. See my "Geology of the S. E. of England," p. 212, or "Wonders of Geology," sixth edition, p. 372.

1 Hayward's Heath station is within 1 mile of Cuckfield, which lies to the right of the line.

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interest the reader, who now can only catch a glimpse of the physical structure of this interesting district as he is whirled along by the railroad at the rate of thirty miles an hour, to learn the appearances presented to the outside passenger on the stage coaches that plied from Brighton to London at the period to which the introduction of this part of our little volume refers.

I had once the gratification of acting as cicerone to my friend, M. AGASSIZ, who has added to his high European reputation by his scientific labours in the new fields of research which his genius and perseverance have explored on the other side of the Atlantic; and leaving Brighton on the outside of "The Age," on a bright May morning, I described the geology of the district to the Swiss philosopher, who, though just returned from the sublime and majestic scenery of the Alps, was delighted with the lovely landscapes, and the interesting physical phenomena, of the Downs and Wealds of my native county, over which we travelled on our route to the metropolis.

The direct turnpike roads from London to Brighton pass over the entire series of tertiary and secondary strata of the South-East of England. Proceeding from the Thames, the traveller successively traverses the ancient silt that forms the present banks of the river, then a level tract of drift and diluvium, consisting of loam and gravel, in which remains of Elephants and other large terrestrial mammalians are occasionally found; and if he proceeds by the Reigate road, he goes through the beautiful suburban districts of Clapham, Tooting, &c. and passes over beds of gravel and clay, the ancient shores of the London basin.1

At Sutton he ascends the chalk hills of Surrey, and travels along an undulated tract, formed of the elevated masses of the chalk-ocean. Arriving at the precipitous southern escarpment of the North Downs, a magnificent landscape, displaying the physical geography of the Weald, and its varied and picturesque scenery, suddenly bursts on his view. At his feet lies the deep valley of Galt, in which Reigate is situated, and immediately beyond the town appears the elevated ridge

1 See "Memoir on the Geology of Surrey," by the Author, in Brayley's History of the County, published by Mr. Ede, of Dorking.

of Greensand, which, stretching westward, at Leith Hill rises to an elevation of a thousand feet; the highest point of land in the South-East of England. To the east, this division of the cretaceous deposits forms a chain of sand hills that stretches by Godstone in Sussex, and Sevenoaks in Kent, to the seashore near Folkstone and Hythe. The Forest Range of the Wealden occupies the middle region, extending westward to Horsham, and eastward to Crowborough Hill, its greatest altitude, and thence to Hastings, having on each flank the Wealden valleys of Kent and Sussex while in the remote distance, the unbroken and gently undulated outline of the South Downs appears on the verge of the horizon.

Pursuing his journey, the traveller passes through the town of Reigate, along the valley of Galt, and over the ferruginous cretaceous sands of Cockshut Hill, and descending the steep escarpment, soon arrives at a marshy plain, where the abundance of rushes indicates the commencement of the argillaceous beds of the Wealden.

The Weald-clay, containing bands of shelly fresh-water limestone, appears at Horley Common; and while in the beginning of the journey the roads were seen to be repaired with chalk-flints, and near Reigate with cherty sandstone, or the iron-grit locally termed clinker, the materials now chiefly employed are the bluish grey shelly limestones of the Weald.

At Crawley, Wealden sands and sandstones appear, and the road is constructed of calciferous grit, and limestone containing bivalve shells, bones, portions of terrestrial plants, &c. Traversing Tilgate Forest and Handcross, over a succession of gentle anticlinal ridges of sandstone, and across clay valleys, he rapidly descends from the sandstone ridge of Bolney, to Cuckfield, leaving on the right the site of our Iguanodon quarry, near which a windmill now stands, and again journeys along a district of Weald-clay with fresh-water limestones.

Ferruginous greensand like that of Reigate reappears at Hickstead, and is succeeded by a tract of Galt and Chalkmarl; and finally the road, entering a defile in the South Downs, passes on to Brighton; the traveller having in the course of his journey crossed from one system of chalk hills to another; that is, over the North Downs of Surrey, and the South Downs of Sussex, (through which he passed by

South Downs.

Wealden
Anticlinal.

North Downs.

London.

Solent

Sea.

North.

South.

Isle of Wight.

T

T. Tertiary.
G. A. Mantell,

B. Axis of Subsidence.

C. Chalk.

A

A. Axis of elevation.

W. Wealden.

LIGN. 47. IDEAL SECTION FROM LONDON TO THE SOUTHERN COAST OF THE ISLE OF WIGHT.

B

d.lt.

tunnel on the railroad,) and across the intervening region composed of the sediments of a delta of incalculable antiquity.'

GEOLOGICAL MUTATIONS.-The present distribution of the strata, as shown by the preceding observations, appears to admit of the following explanation. Assuming the original deposition of the strata to have been horizontal, and in the sequence above pointed out, the Wealden resting on the Oolite, the Chalk on the Wealden, and the Tertiary on the Chalk-the whole surface of the country must have originally consisted of the same Tertiary strata as those of London and its vicinity. If by a force acting from beneath, in the direction of the arrow, A, Lign. 47, the entire series were broken through, the chalk with the superincumbent tertiary strata would be thrown into highly inclined positions towards the north and south; and if a similar disturbance took place along the area occupied by the British Channel, England would be separated from the Continent, and the small portion, now the Isle of Wight, be forced into its present position, by a subsidence in the direction of the arrow, B, Lign. 47, along the course of the present bed of the Solent Sea. The actual position of the strata, could our observations extend to a sufficient depth, would probably present the section sketched in Lign. 47, which is in accordance with the local phenomena observable in the Isle of Wight, and other places introduced in the diagram.

'See Geological Excursion in "Medals of Creation," vol. ii. p. 908.

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