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Landscape I: South Purbeck
This Landscape consists of a narrow strip of coastline, never more than 7 km wide, run-
ning along the coast from Lulworth ( i1 ) to Swanage on the Isle of Purbeck. The area is
defined topographically by the dramatic, west-to-east trending stepfold (or monocline )
in the bedrock. To the north, the stepfold is expressed at the surface by steeply dipping
Chalk and older layers immediately south of the Dorset Heaths (see Landscape G ).
Typically, the Chalk has resisted erosion to form a narrow ridge known as the Purbeck
Hills ( i2 ), running inland from just north of Swanage and crossing the Isle of Purbe-
ck before reaching the coast again at Lulworth. East of Lulworth ( i1 ) and south of the
Chalk, the layers at the surface span the full local succession from Early Cretaceous to
Late Jurassic, though they are flat-lying by the time the south coast is reached.
FIG 109. Cross-section running north-south through St Alban's Head (Fig. 99, i4 ), South
Purbeck.
The Purbeck Ridge is breached by the northward-draining Corfe River, which
flows into Poole Harbour. Corfe Castle and its small town have grown in this breach,
which acts as the gateway to the low-lying Corfe Vale, underlain by Early Cretaceous
Wealden sandstones and mudstones. To the south of this is a plateau, carved at an elev-
ation of 120-140 m above sea level, and underlain by Late Jurassic Kimmeridge Clay
and limestones and mudstones of the Portland and Purbeck groups. The Portland Stone
Formation is particularly resistant to weathering, and its historic importance as a build-
ing stone is shown by the remarkable number of abandoned quarries on this plateau.
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