|I suppose this must be the Carn Boscawen referred to by Hunt in 'Popular Romances of the West of England'?
Dr Borlase has been laughed at for finding rock-basins, the works of the Druids, in every granitic mass. At the same time, those who laugh have failed to examine those rock-masses with unprejudiced care, and hence they have erred as wildly as did the Cornish antiquary, but in a contrary direction. Hundreds of depressions are being formed by the winds and rains upon the faces of the granite rocks. With these no Druid ever perplexed himself or his people. But there are numerous hollows to be found in large flat rocks which have unmistakably been formed, if not entirely, partly by the hands of man. The Sacrificing Rock, or Carn Brea, is a remarkable example. The larger hollows on the Men-rock, in Constantine, several basins in the Logan Rock group, and at Carn Boscawen, may be referred to as other examples.
courtesy of the excellent 'sacred texts' website.
[Of course it might not be. There are lots of boscawen names in the vicinity (eg SW 431 230, on the coast). This page does at least suggest it's near st buryan's:
Someone local must know though?]
Posted by Rhiannon
10th May 2006ce
Edited 8th January 2007ce