This split rock with the wizened rowan growing from its cleft – I was first made aware of it by the old butcher from Dolwyddelan who gave me a lift along the valley one wet day when I was a young teenager on my first walking tour through Wales. He drew his Morris van to a halt, gestured towards it and gave me its name: Maen yr hen wraig sy’n melltithio – the stone of the old cursing woman.

In some earlier time, he told me, a woman would stand on top of it and scream imprecations at passersby. He showed me a kind of cave behind it. “Some say she used to live in there,” he added. He knew no more than those folk memories, which have hovered in my mind for 60 years.

Thirty-five years ago, a public inquiry was held into the road-widening scheme being forced through the valley at that time. I was one of those who represented the CPRW (Campaign for the Protection of Rural Wales), and by evoking the rock’s name we saved it from certain destruction.

Passing by last week, I missed it, drove on to Rhiw Goch, turned round and returned to look for it.

There it was, a little obscured by summer foliage. I felt its rippled texture, sidled into the recess behind. Young willow warblers darted among the leaf cover above. The song of one of their parents tumbled down in a cascade of quarter-tones to a final sweet plangency entirely appropriate to this hidden, forgotten place. The name of the stone is unrecorded. I have never found reference to it other than in that chance encounter 60 years ago.

I’m reminded of Stone as the Tabernacle of Memory, a fine essay by the Irish poet-priest John O’Donohue (1956-2008). This rock is such a tabernacle. In the enchanted space behind it, with grace notes of the willow warblers scattered like elegies, I became aware of how matter has memory; aware too that melltithio – to curse – carries a sense of the lightning’s strike written into this rock. As O’Donohue has it in one of his blessings: “The ghost of loss / gets in to you.”