GEOLOGY coast. The Sussex rivers however, except the Rother, belonged to a different system, the relations of which to the English Channel is by no means clear. The main river seems to have flowed eastward through the Hampshire Tertiary basin in a course similar to and parallel with that of the Thames. The southern side of the valley of this ancient Solent river has now been breached and destroyed by the sea everywhere except in the Isle of Purbeck and in the Isle of Wight. At one time however its basin was probably nearly as large as that of the Thames, for it drained most of Dorset, Wiltshire, Hampshire and Sussex, as well as the destroyed south side of the basin, the area of which we cannot now estimate. Between Brighton and Beachy Head the valley of this old river seems to have turned southward, probably opening into the English Channel in that direction within a few miles of the present coast. Leaving speculation as to the probable course of the Pliocene rivers, we reach firmer ground when we examine the Pleistocene deposits of the Sussex levels ; for these yield valuable evidence as to what happened in the county during the Glacial epoch, and during that obscure period when man seems first to have occupied the county. Sussex, it so happens, has yielded for this period a clearer record than that preserved anywhere else on our south coast ; but unfortunately its superficial deposits have only yet been thoroughly examined over the southern part of the county. We must therefore devote most of our space to the region lying between the escarpment of the South Downs and the English Channel.^ It has already been mentioned that between the Downs and the sea there spreads a low-lying plain, which beginning at Brighton gradually widens to 8 miles between Chichester and Selsey. This plain is not, as might be thought, an area of soft, easily eroded rocks. It is composed of strata of varying hardness, folded and tilted at varying angles, but all planed down to one nearly uniform level. The levelling was obviously done by the sea ; for not only is the flat land bounded on the north by a partly-obliterated bluff or buried sea-cliff, sometimes of chalk, sometimes of clay, but against this cliff here and there are still to be found banked remains of the beaches cast up by the sea, and in these beaches occur well preserved sea shells. The deposits banked against the old cliff and scattered over the ancient sea bed belong however to more than one period and suggest, as does the wide extent of the levelled surface, that their formation occupied a considerable time. We will now describe these deposits as seen in the Selsey peninsula, for there the order of succession is clearest and the series most complete. Selsey gives the key to the succession in other parts of the county. The Pagham erratics, the Coombe Rock, and the Pleistocene marine deposit of Selsey have been referred to by all writers on Sussex geology,^ 1 The following account is taken mainly from observations made in the course of the Geological Survey. See Reid, ' Pleistocene Deposits of the Sussex Coast,' Quart. Joun. Geol. Soc. xlviii. 344 (1892) ; 'Geology of the Country around Bognor,' Mem. Geol. Survey (1897). 2 See M^nteW, Fossi/s 0/ tf-e South Dozens {?.zz) ; Dixon, G«% of Sussex (1850) and ed. 2 (1878) ; Godwin-Austen, ' Newer Tertiary Deposits of the Sussex Coast,' Quart. Journ. Geol. Soc. xiii. 40 (1857); Prestwich, 'Westward Extension of the Old Raised Beach of Brighton,' ibid. xv. 21 5 (1859).
