|A folktale in 'Welsh Fairy Stories' by W. Jenkyn Thomas (1907) relates to the stones on top of Garn Bentyrch (or Pentyrch, as he calls it) - online at V Wales
It's about a boy who goes to play with the fairies on the hills above Llangybi. His parents warn him against it but he will keep going back, and one day doesn't return for two years (though he looks the same age on his return). There are rumours about a hoard of gold hidden under a big rock on the mountain but even the strongest men in the village shoving together can't shift it. His parents are down to their last can of beans due to an ill-advised investment, but Guto knows the fairies will help them out. He goes to ask nicely if they can have the gold, and when he tries to move the rock (sword-in-the-stone style) it bounces off down the hill with no effort at all. Pays to be civil to the fairies, see.
They are mentioned elsewhere in Rhys's 'Celtic Folklore Welsh and Manx'
which is online at the Sacred Texts archive.
When I was staying at Pwlltheli the same summer, I went out to the neighbouring village of Four Crosses, and found a native of the place, who had heard a great many curious things from his mother. His name was Lewis Jones: he was at the time over eighty, and he had formerly been a saddler. Among other things, his mother often told him that her grandmother had frequently been with the fairies, when the latter was a child. She lived at Plas Du, and once she happened to be up near Carn Bentyrch when she saw them. She found them resembling little children, and playing in a brook that she had to cross. She was so delighted with them, and stayed so long with them, that a search was made for her, when she was found in the company of the fairies.Sabine Baring-Gould mentions that On the hill above [the spring] is Cadair Gybi, his [Saint Cybi's] chair, a naturally-formed boulder bearing a striking resemblance to an arm-chair.
Posted by Rhiannon
4th August 2005ce
Edited 27th November 2012ce