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The oldest geological formation with which we have to deal in Sussex (to any considerable extent) is the Wealden: so that our inquiry need not go any farther back in the history of the world than the later secondary ages. Before that time, and for long aeons afterward, the portion of the earth’s crust which now forms Sussex had probably never emerged from the ocean. Britain was then wholly represented by the primary regions of Wales, Scotland, and Cornwall, forming a small archipelago or group of rocky islands separated at some distance by a wide passage from the nucleus of the young European continent. But by the Wealden period, the English Channel and the Eastern half of England had been considerably elevated above the level of the sea. Great rivers and lakes existed in this new continental region, much like those which now exist in Sweden, Northern Russia, and Canada; and the deposits of sand or mud formed at their bottoms or in their estuaries compose the chief part of the Wealden formation in England. Without going fully into this question (somewhat complicated by frequent changes of level), it will suffice for our present purpose to say that the Wealden consists, in the main, of two great divisions, which form, so to speak, the floor, or lowest story, of the Sussex formations. The first or bottom division is chiefly composed of a rather soft and friable sandstone, which runs through the whole Forest Ridges, and crops out in the grey cliffs of Hastings and Fairlight. The second or upper division is chiefly composed of a thick greasy clay, which forms the soil in the greater part of the Weald, and glides unobtrusively under the sea in the flat shore on either side of Hastings, giving rise to the lowlands of Pevensey Bay and the Romney Marshes. Why the sandstone, which is really the bottom layer, should appear higher than the clay in these places, we shall see a little later.

After the deposition of the gritty or muddy Wealden beds in the lake and embouchure of the old continental river, there came a second period of considerable depression, during which the whole of south-eastern England was once more covered by a shallow sea. This sea ran, like an early northern Mediterranean, right across the face of Central Europe; and on its bottom was deposited the soft ooze of globigerina shells and siliceous sponge skeletons which has now hardened into chalk and flint. A great cretaceous sheet thus overlay the Wealden beds and the whole face of Sussex to a depth of at least 600 feet; and if it had not been afterwards worn off in places, as the nursery rhyme says of old Pillicock, it would be there still. I need hardly say that the chalk is yet en evidence along the whole range of South Downs, and forms the tall white cliffs between Brighton and Beachy Head.

Finally, during the Tertiary period, another layer of London clay and other soft deposits was spread over the top of the chalk, certainly on the strip between the South Downs and the sea, and probably over the whole district between the Channel and the Thames valley: though in this case, later denudation has proceeded so far that very few traces of the Tertiary formations are preserved anywhere except in the greater hollows.

Such being the original disposition of the strata which compose Sussex, we have next to ask, What are the causes which have produced its existing configuration? If the whole mass had merely been uplifted straight out of the sea, we ought now to find the whole country a flat and level table-land, covered over its entire surface with a uniform coat of Tertiary deposits. On digging or boring below these, we ought to come upon the chalk, and below the chalk again, with its cretaceous congeners the greensand or the gault, we ought to meet the Weald clay and the Hastings sand. Wherever a seaward cliff exhibited a section for our observation, we ought to find these same strata all exposed in regular order–the sandstone at the bottom, the clay above it, the broad belt of chalk halfway up, and the Tertiary muds and rubbles at the top. But in the county as we actually find it, we get a very different state of things. Here, the surface at sea-level is composed of London clay; there, a great mound of chalk rises into a swelling down; and yonder, once more, a steep escarpment leads us down into a broad lowland of the Weald. The causes which have led to this arrangement of surface and conformation must now be considered with necessary brevity.