Overlying these rocks are the less consolidated Palaeogene clays, sands, gravels and silts of the Lambeth, Thames and Bracklesham Groups which characterise the Hampshire Basin.
The county’s near-surface geology was built up in three stages: first, when layers of clay, limestone and mudstone were laid down in and around Jurassic seas; then, when sands and clays washed off the London Platform early in the Cretaceous period; and finally, as the sea rose again and covered southern England to a considerable depth, great thicknesses of chalk were laid down.
These continued to subside between the Jurassic and the early Cretaceous, by which time the tectonic movement had largely ceased.
[6] South of a ridge that runs from the coast, soft Eocene and Oligocene clays and gravels form low, fairly flat terrain, the Hampshire Basin.
[8] Much of the coastal landscape of the Hampshire Basin results from sea level rise in the Flandrian (after the last ice age) some 6000 years BP.
The Solent, which separates the Isle of Wight from the coast of Hampshire, is the valley of what used to be a much larger river,[2] erosion having broken the remaining chalk link with the mainland.
The downland supports a calcareous grassland habitat, important for wild flowers and insects, as well as arable agriculture.
A series of east–west trending folds in the chalk to the north of the Hampshire Basin is controlled by the faults in the underlying strata.