'Smith has been justifiably referred to as the father of English geology. This ammonite is still used to mark the base of Jurassic rocks in Britain.'
Dr Paul Taylor, palaeobiologist
At 200 million years old, these are among the earliest recorded British ammonites. Despite their great age, the fossils have well-preserved mother-of-pearl on their shells. Mother-of-pearl formed the original outer layer of the living creatures' shells - it usually wears away over time, but can be preserved in fine clays.
The ammonites are part of William Smith's collection, which contains fossils and rocks collected across the British Isles. Smith identified layers of rock by the fossils they contained, using this principle to trace layers across great distances and map the surface geology of England and Wales for the first time. The map was remarkably accurate, and many of Smith's fossil associations still hold true today.