GEOLOGY be followed for long distances, and also occurs under similar circum- stances in other counties. This hedge will at once strike the attention as something exceptional, for unless replanted in modern times it con- tains little hawthorn and is very wide. It consists of a belt of small trees, among which maple, cornel, sloe, hazel, buckthorn, wayfaring- tree, elder, holly and spindle-tree predominate, and are mixed with beech, ash, stunted oak, yew, crab-apple and service-tree. In short, it appears to be a relic of the vegetation of the original margin of the native forest, rendered denser and trimmed to a certain extent, but in other respects not greatly altered. At the present day this hedge separates the open Chalk pastures from the arable land, and as that has always been a con- venient boundary, it has commonly been left undisturbed. In old days the presence of a barrier at this point was of even more importance. It now prevents the sheep from straying into the cultivated fields ; it then prevented the flocks and herds from straying into forests infested by wolves, or occupied by thieves and outlaws, or still worse haunted by the thing unseen. We are still very ignorant as to what happened during the dark transition period which connects Paleolithic with Neolithic. While the Coombe Rock was being formed the climate was arctic, and the relative level of land and sea seems to have been much as at present, though perhaps the sea was a few feet lower than now. Next the land rose about 60 feet, so that the channels of all the main streams were cut far beneath the level of their present beds. No deposits belonging to this period of slow elevation are found, and we do not know what climatic change accompanied it. While at their maximum elevation the valleys were clothed with woods of oak and pine and thickets of hazel, which flourished well below the existing sea-level. Then, during the Neolithic period, the land seems to have sunk again step by step, so that the deeply excavated valleys above alluded to were flooded by the sea, which then penetrated as long fiords through the Downs into the Weald beyond. The submerged forests, seen between tide marks opposite each small valley, belong to this period of gradual subsidence, which ceased so recently that its close in all probability only dates about 3,000 years since. Subsequent changes have consisted mainly in the gradual silting up of the fiords, till they have mostly become alluvial flats ; but the last subsidence is of so recent a date that the fiords and harbours thus formed have not yet been completely obliterated. The Ouse, Adur and Arun, flowing through a clay country and bringing down much mud, have already filled their estuaries ; whilst Pagham and Emsworth Har- bours receive little land-water, and consequently are silting up more slowly. Since the period when the latest of the submerged forests sank beneath the tide there has been no further alteration in the relative level of land and sea. But for the last three thousand years the sea has con- tinuously cut into the land, destroying large areas of the coastal plain and gradually forming longer and higher chalk cliffs. In Roman times I 25 4
