1. Carn Menyn (singular, for the central, main outcrop) or Carn Meini (plural, describing all the outcrops). A series of natural outcrops of spotted dolerite ('bluestone') which naturally fragments into pillars, blocks and screes. Noted as a geological source of the stonehenge 'bluestones' but debate is still active as to whether the stones reached Salisbury Plain in Wiltshire through glacial or human agency. There is however evidence for quarrying on this outcrop (NPRN: 401098).

Louise Barker, RCAHMW, 15th May 2006

2. The Carn Meini outcrops on Mynydd Preseli have become famous in archaeological literature as the geological source for the `bluestones? used at Stonehenge in Wiltshire. The 1.5- to 1.8-metre (5- to 6-feet) tall, narrow pillars formed a circle between the more massive Sarsen `trilithons?, or arches, which made up the main outer circle and the innermost stone settings. In 1923 petrological examination confirmed the scattered outcrops of Carn Meini on the south-west of Mynydd Preseli as being the source of the distinctive blue-grey spotted dolerite with large white spots used in some of the earliest phases of the Stonehenge circles on Salisbury Plain. Indeed, a number of prehistoric monuments, including a ruinous cairn at Carn Menyn and Gors Fawr stone circle to the south, are also composed of this unusual rock. Early investigators concluded that the known superiority of this same spotted dolerite as a raw material for Neolithic stone axes could have sparked off the massive human effort necessary to move the stones. The suggested route would have seen the blocks sledged overland to the upper reaches of the Eastern Cleddau, thence by sea along the Bristol Channel to the River Avon, and finally upstream to Stonehenge itself.

Some geologists and archaeologists have challenged this traditional view, proposing instead that glaciation, not human effort, carried the bluestones to Salisbury Plain. They cite finds of spotted dolerite in glacial erractics on Flat Holm and Steep Holm in the Bristol Channel as evidence for this geological movement. In 2002 an ambitious new programme of survey was commenced for the prehistoric landscapes of Strumble and Preseli by Geoffrey Wainwright and Timothy Darvill. The Strumble-Preseli Ancient Communities and Environment Study (SPACES) increased the known number of prehistoric monuments on the ridge between Carn Sian and Foel Trigarn by 300 percent, and its new surveys of famous individual sites, like Gors Fawr, have helped to forge new understandings about prehistoric life in these hills and valleys. The SPACES project found an intense concentration of activity at Carn Menyn, including prehistoric burial monuments and axe-flaking sites. Worked bluestone pillars have been found broken and abandoned in transit down from the outcrops. Although these are of Stonehenge dimensions, they remain difficult to date, especially as the outcrops provided durable, conveniently-sized blocks in modern times for lintels and hearthstones and were quarried for building stone for at least two nearby chapels.

T. Driver, RCAHMW, 7th Dec 2010.

Possibly associated with excavations of Neolithic rhyolite outcrops at Craig Rhosyfelin to the north (NPRN 416247).

T. Driver, RCAHMW