Mr John Griffith wrote as follows:
"It is well known at Moylgrove that for ages the cauldron has been the show-place of the parish. Visitors are even now attracted to the place; but, in times past, I have learnt from the natives that, besides the cauldron itself, there were at least two still more powerful attractions on the spot - a well and a witch. Then, be it remembered, that right opposite the creek is a 'castle,' which Fenton compares with Tintagel. The only cottage on the headland where the 'castle' is situate is called Pen y Castell. Athwart the slope of Pen y Castell is a finely-constructed bridle-path, which leads to the castle. It is from near this bridle-path that the best view of the cauldron can be obtained.
"... The Rev. Llewelyn Griffiths, Dinas [...] knew the cauldron well. When I mentioned Ffynnon Halen, he corrected me and said its name is Fynnon Alem. When he was a lad at Moylgrove, he learned of it, as a thing which had happened just then - that somebody saw a mermaid at Pwll y Wrach, with long hair, waving an arm out of the water.
"... The Rev. J.T. Evans and I made another 'find'. We found a regularly-constructed path leading into one side of the cauldron. It is narrow, yet wide enough for a person to walk with both feet down together, if you can fancy a man walking so. Nervous people had better avoid it though. The path leads into a cave of considerable size and length. Somebody once must have made much use of the cave. The making of a path on the sheer side of the cauldron was ticklish work.
"Now, Mr Davies [the village blacksmith] told me that the people there still talk of a witch inhabiting the cave, and of people who used to visit Pwll y Wrach to consult the Wrach. I judged, from what i heard, that such a witch might have been haunting the place, say, within the last century. At any rate, Mr Davies and his neighbours do not draw on our [ie Welsh] mythology for an explanation of Pwll y Wrach. They regard the name as associated with a common witch."
This is from an article in Archaeologia Cambrensis from 1860, in which A.W. Wade-Evans is determined to connect mythological places with real places in Wales. He's a man after my own heart of course. Although one has to know when to give up, and maybe in this case he stretches a bit far. Mythological places don't have to exactly coincide with real places, isn't that their charm? He wants to suggest that a stolen cauldron (a proper iron article) mentioned in the Llyfr Coch o Hergest "is", in a mythological sort of way, represented by the Pwll y Wrach, as the book says "there is the measure of the cauldron". Or something. It's a bit tenuous.
I think his only connection to the word cauldron is his rather anecdotal I very distinctly remember a lady living close by, and who had lived there from childhood, telling me she had always known [Pwll y Wrach] in English as "The Witch's Cauldron." The inhabitants say it is a marvel to see in stormy weather, for in such a time it seethes like a boiling pot.
But regardless of the likelihood of his arguments, this sounds like a pretty marvellous natural place, connected with witches and holy wells and mermaids and castles from the mists of time, and what more do you want really.