Approximately 40% of the island of Ireland, and 50% of the Republic, is underlain by limestone. Limestone is made up mostly of Calcium Carbonate which reacts with acid. Rain is naturally slightly acidic this is caused by dissolved gasses in the rain. When rain falls on limestone it reacts with the calcium carbonate and dissolves the rock.
Karst is a term used landforms that develop on rock types that are easily dissolved by water. In Ireland, limestone (composed of calcium carbonate) and to a lesser extent dolomite (calcium and magnesium carbonate) are the most widespread rocks that show karst features. There is also a small outcrop of a younger softer rock also made of calcium carbonate – the chalk of Co. Antrim – which shows some of the features characteristic of karstic terrains. In other parts of the world, highly soluble rocks such as gypsum (calcium sulphate) and halite (common salt or sodium chloride) are abundant and they also exhibit karstic landforms