The Lias Group or Lias is a lithostratigraphic unit (a sequence of rock strata) found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany.
Lias is a Middle English term for hard limestone, used in this specific sense by geologists since 1833.
In southern England, the Lias Group is often divided into Lower, Middle and Upper subgroups.
[4][5][6][7] In Dutch lithostratigraphy, the name Lias has no official status, however, it is often used for the lower part of the Altena Group in the subsurface of the Netherlands and the southern North Sea.
[8] In northern Germany, the Lias Group consists of nine formations (from top to base):[9]