they may also be able to support overhanging upper edges. Examples
of these sheer vertical cliffs in Britain include the granite cliffs in
many parts of the Penwith Peninsula in Cornwall, the white chalk
cliffs along parts of the Sussex and Kent coasts such as those that form
the Seven Sisters, near Seaford and the Great Whin Sill (made of
highly resistant dolerite), where it reaches the sea and provides a
highly defensive site for Dunstanburgh Castle in Northumberland.