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Pristine fossils were thrown up by a unique mud volcano discovered near Wootton Bassett in Wiltshire. The spring is a 1O-metre-wide pool oozing grey mud from layers of Jurassic clay 20 metres below ground. It came to light during a survey by the local council which has asked English Nature to investigate the pool’s scientific importance. Neville Hollingworth, secretary of the Natural Environment Research Council’s earth sciences committee, says the fossils are the best preserved he has seen. “You just stand there and up pops an ammonite,” he says. What makes the fossils so special, he says, is that they retain their original shells of aragonite, a calcium-based mineral. The outsides also retain their iridescence, says Hollingworth, and on the inside some of the bivalves still have their original organic ligaments.