The
Geology of the Weald
Geologically, the Weald of Southern England
was formed by plate tectonics during what geologists call the Oligocene and
Miocene periods between 34 and 5.3 million years ago. The underlying rocks, the
clay, sand and chalk, are much older sediments that built up over millions of
year at the bottom of what was called the
About 135 million years ago this area of
With a warmer climate between 115 and 95
mya, the large shallow sea provided habitat for what the geologists describe as
microscopic “coccolith biomicrites formed from
the skeletal elements of minute planktonic green
algae, associated with varying proportions of larger microscopic fragments of
bivalves, foraminifera and ostracods”. When they died their skeletons accumulated
in great depths and were compressed to produce extensive chalk deposits of
Southern England, some of the youngest rocks in the
Between 75 and 70 mya a great uplift of these
Tethyan sediments started, producing earthquakes,
volcanoes and what we now know as the Atlas Mountains, the Alps, Apennines,
Pyrenees and other mountains around the Mediterranean. Between 34 to 5.3
million years ago the outer
ripples of this mountain-building period created an anticline in this area.
This was a huge, round-topped dome of rock, estimated to have been about 970 m.
above sea level. Folding and faulting cracked the rock strata and, exposed to
the elements, they dried out in the sun and wind and river erosion gradually
lowered the dome.
During the last ice age between * and c.12,000 years ago, much of Northern Europe was covered in ice,
hundreds of metres thick. Whilst it did not reach this far south, freezing and
thawing further stressed the rocks of the Weald. When temperatures started to
rise about 20,000 years ago vast quantities of glacial meltwater
started to further erode the chalk and exposed sand and clays of the central
area. The ice finally retreated about 11,000 years ago, leaving the landscape
of the Weald much as it is today. Many hundreds of metres of the softer upper chalk
had been dissolved and washed away. The only remnants are the gentle dip and
steep scarp slopes of the North and