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.
[788] A limited intercalation of a marine character occurs in the Hasting Sands of Swanage Bay; this was discovered by Mr. R. A. C. Austen, and is noticed Quart. Geol. Journ. vol. vii. p. lix.
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.
LONDON AND BRIGHTON RAILWAY.
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.