Geoscience Reference
In-Depth Information
FIG
190.
Landscapes, Downs, Vales and localities (
b1, b2
etc.) of Area 10.
As well as offering ideal ground for building, the Quaternary gravel deposits have
also been exploited as a ready source of aggregate for road building and the construc-
tion industry. In the regions south of Cirencester (
b1
), southeast of Whitney (
b2
) and
north of Oxford (
b3
), active gravel workings and flooded former gravel pits have be-
come locally extensive features of the landscape. These gravel pits are clearly visible
on the maps, particularly south of Cirencester, where an area some 7 km across has
been designated as the Cotswold Water Park. Many of these areas of man-made lakes
are now being managed as nature reserves, or have been turned into lakeside housing
developments.
The character of the River Thames has changed dramatically over the last 2.6 mil-
lion years of Quaternary time. Like all rivers that are only constrained by resistant bed-
rock in a few localities, it has changed its course many times, switching back and forth
across a floodplain that is also continually changing. By studying the record of these
changes preserved in the Thames terrace gravels, geologists have been able to recon-
struct the later drainage history and climate of the Quaternary for much of Southern
England. The evidence shows that the Thames was a much greater river at times in the
past than it is today. There are also indications that, prior to the uplift of the Cotswolds,
its headwaters may once have drained wider areas of the West Midlands and even north
Wales (see Chapter 6). During cold episodes of the Ice Age, when sea level was much
lower than it is today, the river also extended eastwards over what is now the floor of
the North Sea, following the axis of the London downfold to join the Rhine, before
flowing southwards and westwards along the valley of what is now the English Chan-
nel (see Chapter 2).
