Port St. Mary Ledges

These intertidal limestone ledges are one of only two which remain intact on the Isle of Man following the construction of the Ronaldsway Airport runway extension. They are recognised as one of the best rocky shores in the British Isles for marine ecological studies.

The Carboniferous Limestone here is part of the Knock Rushen formation and consists of thick, fine grained carbonate mud, containing fossils of corals, Bryozoa, brachiopods and crinoids.

The fossil evidence in the rocks suggests that this area was sometime between 350 to 300 million years ago whilst the present of overturned brachiopods and ancient ripple marks suggest that deposition occurred in a lagoon.