Marble Arch

Marble Arch

The base of Cuilcagh Mountain is formed from limestone, as you walk up the mountain track towards the summit, the rocks change to mudstones and siltstones, with sandstone on top.

These rocks formed over 300 million years ago when the land that is now Ireland was covered by a shallow tropical sea near the Equator.

The remains of billions of tiny sea creatures drifted down as fine sediment and collected on the sea bed to form limestone.  As sea levels fell the tropical sea was replaced with tidal flats, and then by a humid river delta eventually forming other sedimentary rocks – mudstones, siltstones, and sandstones.

Over time, the land pushed up out of the sea and moved north away from the Equator. Later still, the Irish landscape was altered by the erosive forces of nature including successive Ice Ages when massive ice sheets gouged the rocks beneath them. While these rocks are common in Ireland, it is very unusual to find such a complete sequence all in one place. It is quite mind-boggling to think that as you ascend to the summit of Cuilcagh Mountain, you are climbing up through geological time, covering a period of about 8 million years in just less than 700 meters.