Geology of the Tisbury district (Wiltshire), 1:10000 sheet ST92NW, and the Jurassic of ST93SW : part of 1:50000 sheets 297 (Wincanton) and 298 (Salisbury)

摘要

The Tisbury d i s t r i c t lies at the western end of the Vale of Wardour. The lowlyingudcentral part of the d i s t r i c t along the the valleys of the rivers Sem andudNadder is underlain by the Kimmeridge Clay (Figure 1). The Nadder Valley isudflanked by the Portland Group which, on the north side of the valley, formsudlong dip slopes rising to a maximum height of about 216 m OD at West Tisbury.udCretaceous strata include a thin Lower Greensand and a somewhat thicker Gault,udboth of which are poorly exposed. The latter formation is involved inudextensive landslips in the south-west of the d i s t r i c t . The Upper Greensand onudboth sides of the valley forms impressive escarpments, that on the southudrising to over 200 m OD near Old Wardour, and that in the north rising toud230 m OD north of West Tisbury. The latter is the highest point in theudd i s t r i c t . A small area of Chalk crops out in the south-east.udThe principal drainage is by the rivers Sem and Nadder in the south andudcentral part of the d i s t r i c t and by several north-bank tributaries, mostlyudunnamed, but including the Oddford Brook on the west side of Tisbury.udSoils developed on the Kimmeridge Clay and the Gault are heavy andudpoorly drained and are mostly under pasture. However, s o i l s on the PortlandudGroup and Upper Greensand, especially on the Boyne Hollow Chert, are l i g h t andudw e l l drained and given over to arable farmland. Woods, both deciduous andudconiferous, occur principally on the steep scarp slope of the ShaftesburyudSandstone. Apart from a few light industrial units in Tisbury, agriculture isudthe only industry.