Geoscience Reference
In-Depth Information
as today most of the valleys are dry and so could not have been carved under modern
climatic conditions. Many of the valleys contain
head
, the name given to a mixture of
Chalk blocks and chalky mud produced by Ice Age slumping and land-slipping of the
bedrock down-slope.
Only two rivers cut right across the North Downs in Area 12. To the west, the
Medway flows through Maidstone before passing through the Medway Gap and enter-
ing its extensive estuary (see Landscape
C
). To the east, another breach in the North
Downs has been cut by the Great Stour branch of the Stour, flowing through the Downs
and then on to Canterbury and the sea south of Ramsgate.
The resistant Chalk ridge of the North Downs has, throughout history, provided
a key transport route between London and the shortest sea crossing to continental
Europe. The shortest crossing, only some 30 km in length, runs from the resistant
Chalk cliffs of Dover (
b2
) and Folkestone (Area 7) on the English side, to the similar
landscape of Calais and Boulogne on the French side. On the English side, the North
Downs have provided the obvious inland routes because they separate the flat lands
and estuaries of the south shore of the Thames from the heavily wooded and often wet
country of the Weald (Landscape
A
) to the south.
For example, the Pilgrim's Way from Winchester to Canterbury (Fig. 217) is a
historically important route that runs along the southern slopes of the North Downs,
avoiding the highest plateau edge. King Henry II is sometimes regarded as the first to
undertake the pilgrimage to Canterbury, after hearing of the murder there of Archbish-
op Thomas Beckett in 1170.
North of the main North Downs lies the Isle of Thanet (
b3
; Fig. 218), an isolated
and distinctive Chalk landscape feature of the East Kent coastline. Here the Chalk lay-
ers have been moved into an upfold that has been eroded and now forms a gentle range
of hills up to 50 m in elevation. The layering in the Chalk slopes at almost 10 degrees
along the southern margin of the Isle. Between the North Downs and Thanet, the Chalk
has been downfolded, and is buried under soft-weathering Tertiary sediments, forming
the low-lying lands of the Sandwich-Pegwell Bay area.
The Isle of Thanet was a true island up until very recently. In Roman times the
Wantsum Channel (
b4
) separating it from the mainland to the west was up to 3 km
wide, and the Vikings were able to sail into Canterbury in the eighth century. Over
time, the channel has silted up, aided by the land reclamation efforts of the Church
in the twelfth and thirteenth centuries, and by the sixteenth century the channel had
ceased to be navigable. The Great and Little Stour now flow out to the sea eastwards
to the south of the Isle of Thanet (Fig. 212).
