The Upper Greensand Formation, mostly capped by the Chalk, crops out on the edges of a broad, dissected

plateau in Devon, west Dorset and south Somerset and has an almost continuous outcrop that runs from the Isle

of Purbeck to the Vale of Wardour in south Wiltshire. The Formation is well exposed in cliffs in east Devon and

the Isle of Purbeck, but is poorly exposed inland. It comprises sandstones and calcarenites with laterally and

stratigraphically variable amounts of carbonate cement, glauconite and chert. The sedimentology and palaeon-

tology indicate deposition in marginal marine-shelf environments that were at times subject to strong tidal and

wave-generated currents. The formation of the Upper Greensand successions in the region was influenced by

penecontemporaneous movements on major fault zones, some of which are sited over E-W trending Variscan

thrusts in the basement rocks and, locally, on minor faults. Comparison of the principal sedimentary breaks in

the succession with the sequence boundaries derived from world-wide sea-level curves suggests that local tec-

tonic events mask the effects of any eustatic changes in sea level. The preserved fauna is unevenly distributed,

both laterally and stratigraphically. Bivalves, gastropods and echinoids are common at some horizons but are

not age-diagnostic. Ammonites are common at a few stratigraphically narrowly defined horizons, but are rare

or absent throughout most of the succession. As a result, the age of parts of the succession is still poorly known