Geoscience Reference
In-Depth Information
across much of the New Forest. The gravels are very largely composed of flints, ori-
ginally derived by erosion of the Chalk, although material derived from
Sarsen Stones
(hard sandstones of Tertiary age) is also present. In the absence of fossil evidence it
is very difficult to be sure whether these gravels represent stages in the history of the
rivers draining this area, or evidence for episodes of deposition from high-stands of sea
level.
Landscape E: The South Hampshire Lowlands and the western South Coast
Plain
The South Hampshire Lowlands form the ground between the South Downs to the
north and Southampton Water and the Gosport-Portsmouth coast to the south. The bed-
rock is predominantly Tertiary mudrock and sandstone, except just north of Portsmouth
where the Portsdown Ridge has formed by erosion of the Tertiary material, revealing
an east-west trending upfold of Late Cretaceous Chalk (Fig. 116). This ridge rises some
130 m above sea level and is clearly visible north of the M27 motorway, just north of
Portsmouth. Since Napoleonic times, the Portsdown Ridge has repeatedly been used
as a site for fortifications (for example, Palmerston's Follies) to oversee the important
harbour and settlement centres of Portsmouth to the south.
FIG
121.
Looking northwards across Portsmouth Harbour, with Gosport to the left and
the Hampshire Downs in the distance. (Copyright Dae Sasitorn & Adrian Warren/
www.lastrefuge.co.uk)
