Interesting! (had to look it up) this from Wikipedia.
A local legend says that when sea birds fly over the abbey they dip their wings in honour of Saint Hilda. Another legend tells of a plague of snakes which Hilda turned to stone, supposedly explaining the presence of ammonite fossils on the shore; heads were carved onto these 'petrified snakes' to honour this legend. In fact, the ammonite genus Hildoceras takes its scientific name from St. Hilda. It was not unknown for local “artisans” to carve snakes' heads onto ammonites, and sell these “relics” as proof of her miracle. The coat of arms of nearby Whitby includes three such 'snakestones', and depictions of ammonites appear in the shield of the College of St Hild and St Bede, Durham. A carved ammonite stone is set into the wall by the entrance to the former chapel of St Hild's College, Durham, which later became part of the College of St Hild and St Bede.