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Title
Transactions of the Symposium on Photo Interpretation

184
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962
Geology
The whole area is underlain by Middle and Upper Chalk, which are here
very pure, containing approximately 95-98% CaCCU Apart from the river
valleys, most of the area is covered by a very sandy, chalky till containing only
about 5% of clay, including that in the contained chalk, and its décalcification
products. The till is believed to be of Gipping (probably equivalent to Saale)
Age [Baden Powell 1948, West 1962]. To the west the Breckland is bounded
by the Fen Basin, which is in many respects similar to the peat regions of Hol
land, and on the other sides by areas of heavier textured drifts.
Soils and vegetation
Décalcification of the sandy chalky till presumably commenced during the
Ipswichian (= Eemian) Interglacial, and, apart from interruption during the
Hunstanton (= Early Weichselian) Advance, has continued to the present.
The till is often strongly indurated, possibly due to frost action, but removal of
carbonate leaves a very loose sand which, in the absence of an effective vege
tation cover, is readily redistributed by wind and has locally formed dunes. In
very general terms, the soil pattern consists of fairly deep podzolic sandy soils
on plateau sites and especially on stabilised dunes, shallow calcareous soils
on slopes and deep podzolic soils, sometimes with groundwater influence, in
low-lying sites.
The soil pattern is naturally reflected in the vegetation which ranges from
heath (now often replaced by coniferous plantations) on the acid sandy soils to
communities dominated by calcicoles where chalk or chalky till comes near to
the surface.
Patterned Ground
In many parts of the area, well-marked patterns may be seen in topsoils.
On plateau sites they are reticulate in plan; with increasing slope they become
first vermicular and then elongated (figs. 1 and 2).
Where sections have been cut across these patterns they are found to be
associated with very characteristic disturbances below the surface (fig. 3).
In a typical case these consist of alternate ridges or pillars of chalky till and
deep troughs or pockets filled with loose sand apparently derived from décalci
fication of the till. The ridges are often much more chalky than the rest of the
till and contain angular chalk stones apparently forced up from the surface of
the underlying horizontally-bedded chalk. The long axes of the stones gradu
ally change from being horizontal at the base to nearly vertical in the ridges.
Sometimes, however, the latter have spreading mushroom-like tops and the
chalk stones in these tops again tend to be horizontal.
Examples of the patterns were first observed before the war by Watt [1955]
as colour-patterns in agricultural soils, particularly where chalk was ploughed
up to the surface, but especially as stripes in natural or semi-natural vegetation
on hillsides. The most striking examples were shown up by alternating stripes