Geoscience Reference
In-Depth Information
path running from Avebury to the northeast, providing an excellent route through some
of the most spectacular chalk downland scenery in Southern England.
North of the village of Pewsey, on the southern edge of the Marlborough Downs,
is Fyfield Down (
c5
), an easily accessible area of chalk downland with one of the
highest concentrations of sarsen stones in the country (Fig. 195). Stones from this
area have been used in the construction of Avebury stone circle (
c4
) and in megalithic
monuments at the famous Stonehenge (
c6
).
To the south of the Vale of Pewsey is Salisbury Plain, the largest single piece
of unimproved chalk grassland left in northern Europe. Since the early part of the
twentieth century, much of the Plain has been reserved by the Ministry of Defence
for military training purposes, while the surrounding downlands have been extensively
modified by agricultural intensification. The downland landscape is of vast, rolling ar-
able fields and unimproved chalk grassland, punctuated by small hill-top woodlands of
beech and conifer. The northern and western margins of the Plain are clearly marked
by a steep, near-continuous edge overlooking the Upper Greensand of the Vale of Pew-
sey and the clay vales of the River Avon. As with the Marlborough Downs, a patchy
blanket of Clay-with-flints mantles the Chalk in places, often supporting scattered
stands of woodland. The Late Cretaceous Chalk slopes very gradually (slightly more
than 1 degree) to the southeast, away from the upfold in which the Vale of Pewsey has
been eroded.
For the most part, Salisbury Plain is without surface water, providing the typical
open scenery associated with the Stonehenge area (
c6
). There are, however, a few
streams, such as the Hampshire Avon, that drain the plateau. These streams are often
deeply incised into the Chalk, with valley bottoms that are lined with gravels and al-
luvium sourced from the Plain and large numbers of regular side valleys, giving a dis-
tinctive branching pattern on the slope map (Fig. 189). Trees have taken advantage of
the nutrient-rich soils along these valleys, and the contrast between open chalk grass-
lands and occasional wooded river valleys is a striking characteristic of this region.
North of Andover and east of Salisbury Plain, the further continuation of the
Chalk hills is called the Hampshire Downs. Their northern margin forms a very clearly
defined edge that includes Walbury Hill (
c7
), which, at 297 m, provides clear views to
the north across the Early Tertiary bedrock of Landscape D. Close to the edge of this
Tertiary material, local upfolds at Shalbourne (
c8
) and Kingsclere (
c9
) have brought
Early Cretaceous bedrock upwards to be level with the Late Cretaceous Chalk. These
upfolds can be regarded as a continuation of the Vale of Pewsey structure further west.
