Geoscience Reference
In-Depth Information
Hurst Castle Spit (Fig. 122) extends into the western Solent towards the Isle of
Wight, leaving a channel less than 1.5 km wide. This gives the spit great strategic im-
portance, and a castle was first built on it by Henry VIII in 1544. The spit was last
manned for defence during the World War II.
Landscape F: The southern Salisbury Plain, Hampshire Downs and western
South Downs
In the northern half of Area 5, the Hampshire Downs form part of the broad belt of
Chalk linking Salisbury Plain in the west with the South Downs in the east. To the
south, the Chalk dips gently under the Early Tertiary sandstones and mudstones of the
Hampshire Basin.
The scenery of the Hampshire Downs has the open and exposed character typical
of most regions with Chalk bedrock, with rolling downland scarps, hill tops and valley
walls. Chalk grassland covers steep scarps and is a particular feature of the South
Downs. Most of the smaller valleys are dry, except in winter, and have a distinctive
branching pattern.
The uniformity of much of the Chalk bedrock is one of its most distinctive fea-
tures, although the presence of a ≈5 m thick hard band (the Stockbridge Rock Member)
about two-thirds of the way up the Chalk succession has influenced the local shape of
many of the ridges and slopes in this area.
In the area around Salisbury, the Chalk bedrock is strongly dissected by the upper
valley of the Avon and its various tributaries. The scenery of wide valley floors, with
floodplains and river terraces between steep valley-side slopes, is very typical of the
area and provides a fine setting for Salisbury Cathedral. This section of the Chalk is
quite well populated, in contrast to the high plains further north in Area 10.
About 10 km west of Salisbury, erosion of the fault and fold structure of the Vale
of Wardour has brought Early Cretaceous Gault and Upper Greensand bedrock to the
surface (see Area 4 for more detail). Unlike Area 4, where it is more fully developed,
the Vale of Wardour is not well defined in Area 5.
The Test and Itchen river valleys (Fig. 123) have cut particularly clearly across
this typical downland scenery, providing the trunk drainage of the area southwards to-
wards Southampton Water. Some 3 km south of Winchester, the large and controver-
sial excavation made for the M3 motorway through Twyford Down demonstrates very
clearly the way the erosion of the Itchen valley has cut into the Chalk. Water meadows
are a traditional feature of many of the larger valley floors, being flooded early in the
season to keep off frosts and provide fresh vegetation for stock. The Watercress Line,
a steam railway running from Alresford to Alton, takes its name from the crop grown
in these water meadows.
