Geoscience Reference
In-Depth Information
FIG
129.
Geology and hillshade map of Area 6, showing Landscapes
A
to
F
and localit-
ies (
a1, a2
etc.) mentioned in the text.
In Early Cretaceous times the material that now forms the Wealden Series was
deposited in a low-lying, subsiding basin that extended southwards from a flat upland
area where London is now. This Wealden Basin was occupied by lakes and extensive
mud flats that were invaded from the north by rivers flowing and shifting across plains
with channels and sandbars. The sediments deposited in these mud- and sand-flats be-
came mudstones and sandstones as they were buried by more sediment as the area con-
tinued to subside. The sandstone sheets have now been eroded to form slopes, and loc-
ally even form distinctive areas of cliffs that provide challenges for rock climbers, par-
ticularly in the Tunbridge Wells area.
In mid-Tertiary times, the surface of the Wealden area began to move upwards,
and erosion by rivers and streams began to cut downwards into the Wealden bedrock,
eventually creating the topography of hills and valleys that we see today (Fig. 130).
The crude radial pattern of this drainage (described above) reflects the erosion of the
rising, dome-like Weald uplift. In addition, local geological mapping has shown that
many of the sandstone sheets have been cut by faults that often trend approximately
east-west, particularly in the lower parts of the Hastings Beds. These faults have often
provided bedrock contrasts that have influenced the local directions of the young val-
ley systems.
The High Weald was the focus of a remarkable iron industry from the fifteenth to
the seventeenth centuries. The source of the iron was siderite, an iron carbonate min-
eral that grew as a precipitate in the wet muds of the Wealden lakes. The small valley
networks of the High Weald were ideal for the construction of dams and ponds (known
