2005:358 - BLOCKHOUSE ISLAND, CARLINGFORD LOUGH, Down

Blockhouse Island, a low expanse of flat, bare rock at the entrance to Carlingford Lough, is named after an unusual stone fortification, originally consisting of an apsidal-fronted tower flanked by a pair of gun platforms (Jope 1966, 228–230). The defences were built to guard the narrow entrance channel to the Lough and the approaches to Newry and Carlingford in the early decades of the 17th century, and substantial remains survived into the 1950s. More recently, the site appeared to have been reduced to a few isolated blocks of masonry, most of them no longer in situ, and in 2005 a project to assess the degree of survival was initiated. The work involved close collaboration between the National Trust, Environment and Heritage Service and the Centre for Maritime Archaeology at the University of Ulster at Coleraine and focused not just on the standing remains but also the shore of the island and the surrounding waters.
Given the limited time available on the island and its status as a scheduled monument, excavation was kept to a minimum. Three small box-sections were cut through the deposits to assess the potential for surviving archaeological material. Two of these revealed a marine deposit of coarse sand and shells some 0.35m deep above the natural bedrock of the island. The third uncovered a 0.25m-thick deposit of the same wave-deposited material, but this lay on a 0.15m-thick layer of clean grey clay above the irregular surface of the bedrock. The clay is unlikely to have been a natural deposit and, as it occurs on the projected line of the northern wall of the gun platform, it may have been brought to the island when the platform was being built or repaired. One possibility is that it was used to level up the surface of the island and provide a bed for the foundations of the platform and it may also have provided a degree of weatherproofing at the base of the masonry.
Reference
Jope, E.M. (ed.) 1966 An archaeological survey of County Down.