Standing under a leaden sky on this bleak moorland, with a bitter wind blowing over Harnisha Hill, it was difficult to imagine that the Frosterley marble that we had come to find was once a coral reef in a tropical sea.
It has taken 325m years of tectonic plate movement, at a pace slower than a fingernail grows, to bring it to this valley from its equatorial origin.
We were told we would find a good example of this decorative rock, which is not true marble but a fine-grained fossil-rich limestone, in Howden burn. After a short walk upstream we found the ledge, bearing the characteristic shapes of the coral Dibunophyllum bipartitum.
Cut and polished examples grace buildings all over Durham. The font in Frosterley church is made from this rock. So are the flagstones under the feet of drinkers in the village pub, the Black Bull. It has enhanced the beauty of the pillars of the Chapel of the Nine Altars in Durham cathedral for the past 650 years and must have seemed like a godsend to the clergy. Here was a sermon in stone, incontrovertible evidence of antediluvian life forms that had failed to survive the biblical flood and become entombed for eternity.
Such certainty begun to crack in the early 19th century, when geological science recalibrated time scales, and then, much later, crumbled away entirely as knowledge grew of the physical forces constantly reshaping Earth’s surface.
Only faint outlines of the fossil coral were visible in the water-worn grey slab before us until we carried cupped handfuls of water up from the burn and splashed it. The wet rock matrix darkened and revealed the white filigree of the fossil coral exquisitely preserved, before it faded to grey again as the surface dried.
The intricacy of the fossils was breath-taking. This may have been how mediaeval craftsmen first realised the rock’s potential and must have been what moved them to spend countless hours cutting and polishing it by hand with sandstone, grit and leather rags, until the surface gleamed like marble, mimicking in a human time scale what the erosive power of water took centuries to achieve.
