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. It consists of marine limestones, shales, marls and clays.
In the past, the name Lias was often not only used for the sequence of rock layers, but also for the timespan during which they were formed. It was thus an alternative name for the Early Jurassic epoch of the geologic timescale. We now know that the Lias is Rhaetian to Toarcian in age (over a period of ca. 20 million years between 200 and 180 million years ago) and thus also includes a part of the Triassic. The use of the name "Lias" for a unit of time is therefore slowly disappearing.
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—Babette Deutsch (1895–1982)