NOTES FOR A GEOLOGICAL EXCURSION, OVER THE CHALK AND WEALDEN FORMATIONS OF THE SOUTH-EAST OF ENGLAND, FROM LONDON TO BRIGHTON, AND FROM BRIGHTON TO ROTTINGDEAN.

In travelling from London to Brighton by the railway, the following geological features of the country may be observed; by a reference to Wond. p. 360, the structure of this remarkable district may be easily understood.

Leaving the station at London Bridge, the London Clay, with its characteristic fossils, is seen beyond Deptford, by New Cross, Sydenham, &c.; and approaching Croydon, beds of gravel appear, with interspersions of olive-green sand. These strata belong to the Eocene formation, and lie above and upon the Chalk. The valley beyond Croydon (Smitham Bottom), along the side of which the railroad is carried, is composed of gravel resting on chalk; beyond the station called Stoat’s Nest, there is a fine section of the chalk, with layers of flint, and two parallel seams of marl, at the distance of six or eight feet from each other. These extend, with but little interruption, several miles, preserving their parallelism, although the strata in many places have sustained considerable disturbance. The Merstham Tunnel, through the Surrey chalk hills, is now entered. At Merstham the chalk, chalk-marl, and firestone are intersected, and the Lower Greensand of Red Hill appears; and from thence to Horley station, the lower sands and clays of the Chalk formation are passed over or cut through; affording sections of sandstone, ironstone, and fuller’s earth.

The strata we have hitherto traversed are of marine origin, and contain fossil shells, fishes, Crustacea, &c., and remains of other inhabitants of former oceans. But we now enter upon the series of river deposits[788] which form the Wealden, and contain the relics of terrestrial or fresh-water animals and plants.

At Horley the weald clay appears, and is succeeded by sand, sandstone, and shale, to Crawley. Passing through the tunnel of the Wealden strata, we arrive at Balcombe, where sandstone in laminÆ and in thick beds, having the surface at the lines of junction covered with ripple marks, is seen on each side the railroad; the dip of the strata is to the north-east. After crossing the deep valley at Balcombe, over the magnificent viaduct, the line runs along alternations of sand and clay, dipping south-west; we have thus passed over what is termed the anticlinal axis of the Wealden. Arriving at Hayward’s Heath station, the tunnel exposes a good section of the Wealden sand, sandstone, shale, and blue marl or oak-tree clay, to a depth of about thirty-six yards. The strata are disposed in the same order and thickness as in the quarries around Cuckfield; namely, fawn-coloured sand and sandstone, like those of Little Horsted, with beds of calciferous grit or Tilgate stone; and, beneath, layers of the blue clay. The strata are very barren in organic remains; several hours’ research only afforded imperfect vegetable relics, such as comminuted stems and leaves of the various species of ferns, which occur in Tilgate Forest (see Wond. p. 392). Some of the grey laminated sandstones and shales at this place very closely resemble certain strata of the Coal measures.

Proceeding over the Weald clay with the Sussex marble of St. John’s Common, the line encounters the Lower Greensand of Sussex, at Stone-pound gate. Here then we quit the fresh-water strata of the Wealden, and again enter upon the marine deposits of the Chalk-formation. At the foot of the northern escarpment of the South downs, the Chalk is penetrated at the base of Clayton Hill, the tunnel running through the lower members of the Chalk—the Galt and Chalk-marl—and emerging at Piecombe through the White Chalk; from thence to Brighton, the sections and tunnels intersect or perforate the same cretaceous deposits.

In our traverse we shall have seen that the various strata cut through, are repeated on the north and south of a line drawn from east to west through the Forest Ridge (see Wond. Geol. Map, pl. 1). Thus, the railroad has to pass through two ranges of chalk hills by tunnels those of Merstham and Clayton; two principal ridges of Wealden strata—at Balcombe and Hayward’s Heath; and the Shanklin or Lower Greensand at Red Hill, in Surrey, and near Hurstpierpoint, in Sussex. There is no railroad in the kingdom that, in the distance of fifty miles, exhibits geological phenomena of greater variety or interest.

If the student will refer to Wond. p. 362, the stratification above pointed out will be better comprehended. The sections visible on the turnpike road from London to Brighton are described, Wond. p. 363.

The neighbourhood of Balcombe station will afford some sections of easy access; and from Hayward s Heath station, Cuckfield is about two miles distant. The quarries on the hill above that town were formerly very productive, and the usual Wealden fossils may still be obtained; namely, casts of several species of fresh-water shells (p. 416), scales and teeth of fishes (Lepidotus, p. 604), bones of reptiles, and vegetable remains.

GEOLOGICAL STRUCTURE OF BRIGHTON CLIFFS.

A stroll from Kemptown along the sea-shore to Rottingdean is replete with interest, for the strata of which the cliffs are composed clearly demonstrate that in very remote periods great changes have taken place in the relative position of the sea and land along the Sussex coast.

Some years since, the bare face of the Cliffs, from the entrance to the esplanade of the Chain-pier at the Old Steyne, to Kemptown, was completely exposed, and presented a most interesting section of the strata. But at the present time, as every one knows, no portion of the cliffs is visible west of the groin below Kemptown and the sections in my first work (Foss. South D. pl. iv. and v.) are the only records of the appearances formerly presented, and now concealed by the sea-wall. Even the cliffs immediately beyond Kemptown are rapidly diminishing from the action of the waves, which dash with greater violence against their base in consequence of the means taken to protect the adjoining terraces from the encroachments of the sea.

The appearance of the Cliffs east of Kemptown is shown in the sketch, Lign. 267. But further along the shore, towards Rottingdean, in a ravine excavated by the encroachments of the sea, the ancient chalk-cliff behind the mass of strata seen above is exposed; this is represented in Lign. 268. A description of the appearances at this point will elucidate the nature of the strata of which these cliffs are composed.

Upon examining the shore at low-water, masses of chalk, covered with fuci (sea-weed), &c. are seen protruding through the sands; and towards the base of the cliff a bed of sea-beach is spread upon the sand; a low wall or terrace of white chalk constitutes the boundary of this shingle, as seen in Lign. 267, c. Thus we perceive, that the present shore is formed by the continuation of the chalk strata of the neighbouring Downs, partially covered with sand and beach, which are the detritus of the flints that have been washed out of previously existing layers of chalk, and ground down by the action of the waves. Now, along the eastern part of the coast, towards Rottingdean and Newhaven, the chalk rises into mural precipices immediately from the sea-shore; but at this place the cliffs are composed of very different materials.[789]

1. In the first place, there is, lying immediately on the terrace of chalk that forms the boundary-wall of the base of the cliff (Lign. 267, c, and Lign. 268, c c,), a bed of sand (denoted by the letter o, Lign. 268), of irregular thickness and variable extent: from this sand marine shells and the jaw of a Whale (see p. 778), have been obtained.

2. Upon the sand is a bed of loose shingle—a regular sea-beach appearing in no respect different, to the common observer, from that forming at the foot of the cliffs at the present moment; this bed is marked b, in Lign. 267, and 268. Upon examining this shingle, it is found to contain numerous pebbles and boulders of granite, porphyry, syenite, and other plutonic rocks (see p. 34), none of which occur in the present beach. And in this ancient shingle, teeth and bones of extinct species of Elephant, Horse, and Deer have been discovered. We have here, then, unquestionable evidence that this beach has been formed under conditions altogether different from those which now prevail; for not only is this shingle-bed elevated above the present sea-level, but its contents are of such a nature as could not have been thrown up by the sea, in its present relation to the countries that form its shores.

3. A series of loosely aggregated calcareous deposits, obscurely stratified, rests upon this bed of shingle, and forms the upper portion of the cliff, varying in total thickness from fifty to one hundred and twenty feet. These strata are composed of chalk rubble and loam, with flints partially water-worn, and boulders and pebbles of tertiary sandstone; the whole promiscuously intermingled, and deposited in nearly horizontal layers, from one to three or four feet thick. But the face of the cliff generally presents a weather-worn and crumbling aspect, and large masses are constantly falling down, in consequence of the removal of the ancient shingle, by the effects of the waves at the spring-tides. From the loose state of aggregation of these beds, the fallen masses are speedily washed away, but here and there blocks of great hardness, provincially termed Coombe-rock, remain upon the shore; and, but a few years since, there was a group of high rocks of this kind near the Chain-pier. This compact conglomerate has been produced simply by an infiltration of calcareous spar, which has cemented together the fragments of chalk, flint, &c. In some places, this infiltration has reached the bed of ancient shingle below, and large blocks are occasionally found, consisting of pebbles of flint, granite, &c. held together by veins of calc-spar, in acicular or needle-like crystals. In these sparry conglomerates, the teeth and bones of the mammalia previously noticed are sometimes found.[790]

It is in this accumulation of calcareous strata that numerous bones and teeth of the Mammoth, or fossil Elephant, have been discovered; I have therefore designated it, the Elephant-bed, to distinguish it from other loose calcareous deposits.

As seen immediately beyond Kemptown (Lign. 267), the cliffs appear to be entirely composed of the materials above described; but farther on, the face of the ancient chalk-cliff is exposed (see Lign. 268); and if we extend our walk to Rottingdean, we find in many places the Chalk alone forming the present cliff; the Elephant-bed and its associated shingle and sand having been swept away. A like destruction awaits the remainder of these interesting deposits at no very distant period.[791]

After collecting specimens of the Elephant-bed, both of the friable varieties, and of the coombe-rock, and a few of the pebbles of granite, porphyry, &c. from the ancient beach, and also some of the sand beneath the shingle, to examine microscopically on our return home, let us sit down on this mass of fallen chalk, and consider the nature of those changes in the relative position of the land and sea, which the phenomena before us appear to indicate.

We have seen that these cliffs are composed of the following deposits:—1. The Elephant-bed (Lign. 267 and 268, a); a series of calcareous strata, with bones and teeth of Elephants, Horses, Deer, and Oxen. 2. An ancient sea-beach (b), with pebbles and boulders of plutonic rocks, and bones of mammalia; and a bed of sand beneath, in which cetacea and mollusca (apparently of existing species) have been found. 3. Lastly, the regular Chalk-strata (Lign. 268, c, c), extending far out to sea.

These appearances demonstrate the following sequence of physical changes, namely—

1stly. The Chalk terrace (c, c), on which the ancient shingle-bed (b) rests, was on a level with the sea for a long period; for this beach must have been formed, like the modern, by the action of the waves on the then existing chalk cliffs (see Lign. 268, Chalk). But there must have been some cause in operation, by which pebbles and boulders of granite, porphyry, and other rocks, foreign to our shores, and bones of Elephants, &c. were thrown up on the strand, and imbedded in the beach then in the progress of formation. These transported materials may have been floated to the Sussex coast by icebergs; an agency by which the delicate bones and teeth might be deposited without injury, although surrounded by the water-worn detritus (see p. 43).

2dly. The whole line of coast, with the ancient shingle, must have subsided to such a depth, as to have allowed of the deposition of the calcareous strata, forming the Elephant-bed. And from the absence of gravel and beach, and the circumstance of the chalk-rubble, of which they are largely composed, often presenting angular fragments, it would appear that this deposition took place in some tranquil bay or inland sea.

Lastly. The land was elevated to its present level; and at this period the formation of the existing sea-beach and line of cliffs commenced.

The reader must not conclude, from our remarks being restricted to the cliffs before us, that the phenomena here contemplated were limited to this district; on the contrary, if our space would permit, it might be shown that they are referable to extensive geological changes, which took place in the period immediately antecedent to the present. In all the valleys of the South-east and East of England that open into the sea, traces, more or less extensive and important, of similar deposits exist. The level plain, called the Steyne, at Brighton, is entirely formed of the Elephant-bed, which extends up the valley to Preston and Patcham; in the latter place bones and teeth of Elephants have been found. At Southbourn, the plain at the foot of the Chalk hills, called "The Wish," containing remains of the Elephant, Rhinoceros, and Hippopotamus, evidently belongs to the same epoch. At Folkstone, Mr. H. Carr has discovered large blocks of Coombe-rock, and Mr. S. J. Mackie abundance of bones; and at Dover, above the Chalk, similar masses occur. On the opposite coast of Franco there are also indications of these deposits. All these phenomena are no doubt connected with the occurrence of immense quantities of mammalian remains in the superficial loam, &c. on the eastern coasts of England, and are referable to the same geological epoch.

Imbedded in the Chalk, which is exposed at low water along the shore, very large Ammonites may sometimes be found between Kemptown and Rottingdean; and numerous examples of fossil sponges and other amorphozoa (p. 219).

The teeth and bones of mammalia are rare in these cliffs, and it is not probable that any will be obtained in a first visit; but from the fishermen and boys seen strolling along the shore, specimens may often be purchased.