Pennant Melangell is a thin place: a place where the veil between heaven and earth, reality and dream, fact and fiction is so thin that it becomes a semi-permeable membrane. Remembering osmosis, stuff travels through the membrane from a weak solution to a strong one. Today in the valley of Cwm Pennant, Melangell’s side of the divide is stronger than the drizzle-diluted world outside the circle of ancient yew trees. The place is thinnest under these trees and, sheltering from the rain under one that’s more than 2,000 years old, I listen to what leaks through the membrane. Of course, I am thick with thought and listening with badly tuned ears. The story of Melangell, the seventh-century saint of hares, was carved into the oak rood screen in the church before it was written in Latin, existing as images before words. In that wooden form, her myth – of the hare-woman-nature-spirit who defied patriarchy – links more directly to the trees surrounding her shrine than to the literate culture that still appropriates her. The four older yew trees here grew out of the iron age on a bronze age site, where there may have been other time-travelling trees. What do those human tool ages mean to ancient yews in the Marches that are as old, or much older, than these? Yew trees can achieve immortality through their pact with fungi; it allows the tree to feed on the rot of itself, to grow in a green orbit around hollow trunk portals of dark matter, to split into separate trees and move about, to change sex. Under the canopy, I listen to sparrows in the belfry, house martins in the eaves, buzzards and red kites overhead, geese, cockerels and sheep in the field. What’s the frequency of clouds above the Berwyn crags? What’s the urgency of the stream roiling down Cwm Pennant from the waterfall to Afon Tanat? In all these things, is the past really so far away? Imagine the yew trees on the cloudy mountains of Gondwana, 50m years ago – did they grow differently then? Did the rain in those forests feel more or less like our rain? Do Pennant Melangell’s yews have more past than future? This article was amended on 1 September 2023. Osmosis is when a solvent passes from a weak solution to a strong one, not from a strong solution to a weak one as an earlier version indicated. Country diary is on Twitter at @gdncountrydiary Paul Evans presents an episode of Open Country from Pennant Melangell on BBC Radio 4 at 3pm on Thursday 7 September