Castletown limestone

Limestones in the South of the Island were formed, in the Carboniferous period, around 330 million years ago

When Limestones were formed the Isle of Man was positioned close to the equator with much of the Island submerged beneath a shallow, tropical sea. This sea was inhabited by organisms such as corals, crinoids (a type of brittle star), numerous shellfish, primitive sharks and algae. The algae would grow together as clumps of slime on the sea bed. The slime would accrete calcium carbonate and trap mud, building up a solid mound of limestone representing an early form of reef.