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those in the vicinity of Heathrow Airport ( e1 ), and between Windsor ( e8 ) and Rich-
mond Hill ( e4 ). The Quaternary terraces of the Thames Valley are amongst the best
studied in the country and provide an excellent record of the switching of the River
Thames back and forth across its floodplain. In addition, the terraces in the lower
reaches of the Thames record the most recent rise in sea level associated with the end
of the last (Devensian) cold episode, which flooded the lower Thames Valley to form
the Thames Estuary.
Each terrace deposit is the remains of a sheet of old floodplain material that
formed when the river was flowing at the level of the terrace. Each step of the staircase
reflects an episode of downward cutting by the local river channel, while the succes-
sion of steps, from highest and oldest down to lowest and youngest, shows how the
rivers have cut downwards into the landscape as time has passed (Fig. 204). It has
sometimes been possible to suggest ages for the terraces in terms of the stages of the
oxygen isotope timescale (see Chapter 2, Fig. 13). The youngest and lowest terrace
material was deposited during the rise of sea level that has occurred over the last few
thousand years.
Figures 201 and 208 help to pick out the scattered, isolated hills that are distinct-
ive features of the London Basin. Examples include Parliament Hill on Hampstead
Heath ( e2 ; Fig. 205) and Highgate Cemetery ( e3 ) to the north of the Thames. To the
south of the present Thames are Richmond Hill ( e4 ), Wimbledon Common ( e5 ), Shoot-
er's Hill ( e6 ) and Crystal Palace ( e7 ). Most of these hills are features that became isol-
ated and left behind as the staircase of river terraces was being formed. The importance
of these upstanding river-terrace hills is enormous in providing present-day Londoners
with a sense of natural landscape, wildlife and recreation.
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