A HISTORY OF KENT the northern slope of the dome is the cause of the general northward dip of its strata. Let us now consider the composition and origin of these strata. HASTINGS BEDS The deep borings have proved that for a long period preceding the deposition of the oldest rocks exposed at the surface within the Wealden area, this district was submerged beneath the sea and gradually covered by a great thickness of marine sediments of Jurassic age. But this ancient sea was at length displaced, either by an elevation of the land or by the infilling of its basin, or by a combination of both causes, and the area began to receive the detritus brought down by a large river into a lake or estuary. The freshwater or estuarine deposits of this period constitute the oldest strata visible at the surface in Kent. They occur only in a limited tract in the south-western part of the county, but have a much more extended outcrop south of the county boundary, in Sussex. They consist of a somewhat variable group of sands, soft sandstones, silts and clays, known collectively as the Hastings Beds, which form the lower part of the great freshwater Wealden Series. These beds underlie the pleasant hilly ground to the southward of the flat along which the rail- way is carried in a nearly straight line from Edenbridge to Ashford ; and although their area in Kent is so limited, nearly the whole of the group is represented, owing to the relatively sharp uplift and to the presence of ' faults ' or dislocations in this quarter, whereby blocks of strata are shifted to higher levels than they would otherwise occupy. Ashdown Sand. — The lowest subdivision is the Ashdown Sand, consisting mainly of fine quartzose sand and soft sandstone, with occa- sional layers of loam and clay and of small well-rounded pebbles. It is well exposed in quarries and road cuttings on the hill immediately south of Tonbridge, being here uplifted by a ' reversed fault ' which is visible in the principal quarry. Fossils are rare in this deposit, obscure fragments of plants, washed down from the ancient land, being usually its only relics. Wadhurst Clay. — Separating the underlying Ashdown Sand from the overlying Tunbridge Wells Sand is the Wadhurst Clay, the most fossiliferous subdivision of the Hastings Beds, and also formerly of con- siderable economic importance as the chief source of the ironstone which was mined and smelted in the Weald. It consists of alternations of clay, shale and sand-rock, with thin impersistent bands and lenticular nodules of shelly limestone, calcareous sandstone or grit, and clay-ironstone. Its chief outcrops in Kent occur as narrow irregular strips along the valleys of the Medway, Teise, Rother and their tributaries. Its fossils include numerous freshwater shells of the genera Paludina, Cyrena and Uriio, with the minute oval valves of Cypris, a small crustacean, in vast abundance ; and the teeth and bones of extinct fish and reptiles ; and the remains of plants. The best collections of these fossils have however been obtained from Sussex, where the gritty layers are sometimes extraordinarily rich 6
