This seastack, off the North Mayo coast at Ballycastle, is known as "Dun Briste" ( pronounced-doon brishtha). It was cut from the mainland in 1393 during an Atlantic storm. The remains of 2 house structures are located on it still as it was part of a promontory Fort for local chieftains. The headland is associated with St. Patrick and he established an early church there. The rocks are sedimentary sandstone and limestone laid down during the carboniferous period. It is approximately 48 metres from base to peak that varies with the tide.