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 



