Benbulbin There and back again

Benbulbin was shaped during the ice age, when Ireland was under glaciers. Originally it was a large plateau. Glaciers moving from the northeast to southwest shaped it into its present distinct formation.
Benbulbin, and the Dartry Mountains as a whole, are composed of limestones on top of mudstones. These rocks formed in the area approximately 320 million years ago in a shallow sea. Uppermost in the limestone layer is a thicker, harder limestone called the Dartry Limestone Formation. Below this is a thinner transitional limestone formation – the Glencar Limestone Formation. Further down, the lower slopes consist of shaly mudstone known as the Benbulben Shale Formation. Scree deposits are found near the base.