Time, Process Southern England’s Landscapes - Southern England - page 17

direct evidence for the presence of an ice sheet is material in the surface blanket called
till , or boulder clay (Fig. 15). This often rather chaotic mixture of fragments of rock of
all sizes (large boulders mixed with sand and mud) lacks the sorting of the fragments
by size that would have occurred in flowing water, and so must have been deposited
from the melting of ice sheets.
FIG 14. The Anglian ice sheet.
Much of the rest of the surface blanket that accumulated during the last 2 million
years was deposited by the rivers that were draining the land or any ice sheets present.
As ice sheets have advanced and retreated, so have the rivers changed in their size and
in their capacity to carry debris and erode the landscape. Rivers have therefore been
much larger in the past as melting winter snow and ice produced torrents of meltwa-
ter, laden with sediment, which scoured valleys or dumped large amounts of sediment.
The gravel pits scattered along the river valleys and river terraces of Southern England,
from which material is removed for building and engineering, are remnants of the beds
of old fast-flowing rivers which carried gravel during the cold times.
There are no ice sheets present in the landscape of Figure 16. The scene is typical
of most of the Ice Age history (the last 2 million years) of Southern England, in that
the ice sheets lie further north. It is summer, snow and ice are lingering, and reindeer,
wolves and woolly mammoths are roaming the swampy ground. The river is full of
sand and gravel banks, dumped by the violent floods caused by springtime snow-melt.
The ground shows ridges of gravel pushed up by freeze-thaw activity, an important
process in scenery terms that we discuss below.