The path up to the old quarry was wet and bordered by clumps of coarse grass, droplets of dew still hanging on to each blade. Beyond the line of trees that marks the edge of the field, dark and skeletal in their winter stasis, the sky was mottled with cloud that looked distinctly untrustworthy, with the stillness to the air that often presages showers.

Exposed on the steep back wall, grey and tarnished with flecks of iron, the ancient mudstones are too soft and easily fractured for fine building work, but the quarry served as a useful source of stone for local roads. Now abandoned, it has been out of use for long enough that mature oak trees have grown from the rounded heaps of spoil, banks of gorse – already in flower – adding bright yellow highlights.

Laid down under deep subtropical seas, when the fragment of crust that would become Wales was still well south of the equator, these mudstones are more than 400m years old. The strata, twisted to near vertical in their tumultuous early history, were formed before much complex life reached the land, but a witness on this narrow ocean might have seen the active volcanoes of Snowdonia on the horizon, creating structures that still – although eroded and diminished – dominate the skyline today.

As I traced the fracture lines in the stone with my fingers, I thought of another, much younger, landscape that I have walked recently. The trails around the massive central caldera of La Palma in the Canary Islands, where the land is a hundredth the age of where I now stood, hint at what early north Wales might have looked like. A raw landscape, the volcanic features still steep and sharp, where wind and rain have yet to win the battle of entropy in which peaks are rounded and laid low.

The Canarian pine trees that today shade these trails and bring a familiar chill to the island morning would be absent from ancient Wales, their evolution still millions of years in the future. But the vision of dramatic geological power represented by the stern, sheer crags of the crater rim is both impressive and profound.

