Cornish rock

From Cornwall’s beginnings south of the equator to gazing at Watergate’s cliffs to “sense for a moment the dizzying age of the Earth”, award-winning author Philip Marsden shares a glimpse beneath the surface of Cornwall.

What makes Cornwall Cornwall? For its half million residents, as well as the four million or so who visit each year, something happens west of the Tamar, some weird displacement that’s hard to pin down: it’s the remoteness, the whispers of antiquity, the traces of a half-lost language, the strangeness of the moors, the thrill of the coastline. It’s the flat horizon of the Atlantic, the never-still expanse of the sea. It is – according to one elderly friend of mine – the way the cats look at you.

Everyone has their own Cornwall. What lies behind them is an acute awareness of Cornwall’s physical nature, its shape on the map and the curious geology of its make-up. Rocks and minerals have always helped define Cornwall, from the landscapes and seascapes that fill the tourist posters to a human history reaching back to granite monuments of the Neolithic; from the 200-metre mineshafts of the 19th century to the towns and fortunes built on their yields.

On this small peninsula can be found 450 different minerals – nearly 15% of the entire range of the planet’s rocks. More than a third of these are ‘rare’ or ‘ultra-rare’; five are found only in Cornwall.

The essence of Cornwall lies underfoot, but in Truro, just off the main hall of the Royal Cornwall Museum, is a glimpse of its wonders. Housed in a series of wooden display cabinets are samples from one of the world’s great mineral collections. The rocks are intensely beautiful. Who could not be captured by the miniature architecture of the cassiterite or bassetite crystals, or the colours of azurite or malachite? The collection is a reminder that on this small peninsula can be found 450 different minerals – nearly 15% of the entire range of the planet’s rocks. More than a third of these are ‘rare’ or ‘ultra-rare’; five are found only in Cornwall.

It was during the Devonian and Carboniferous periods, from about 400 million years ago, that Cornwall’s slates were first laid down. The portion of Earth surface that would become Cornwall then lay in an oceanic basin to the south of the equator. Over time it migrated north, exposed as it moved to a particularly violent series of elemental contortions – upswellings of molten rock, volcanic surges, foldings caused by the shift of tectonic plates. These events buckled the sediments, while the intense heat drove aqueous solutions through cracks to form quartz veins and mineral lodes.

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Cornwall’s geology is on view not just in the Royal Cornwall Museum but along its 400 miles of coast. Walk any section of it and you can sense something of the deep processes that have shaped the planet. Go out to the far west, to the south of Land’s End where the granite is sculpted into extraordinary shapes, and you will see the same rock-forms as on the tors of Bodmin Moor. On the Lizard, rare samples of the Earth’s mantle can be seen solidified in colourful bands of serpentine. The soft killas of central Cornwall has allowed the formation of the twisting estuaries of the Fal, Helford and Fowey. Bedding planes that are buckled, twisted and crushed characterise the coast around Bude. Pillows of congealed lava are visible near Polzeath.

At Watergate Bay, the original slates – hundreds of millions years old – can be seen with their contortions all too obvious.

As dramatic as any stretch of coast is that between Newquay and Trevose Head. At Bedruthan Steps high slate-stacks stand in the surf while the beach’s cathedral-like caves seem built on a vertiginous scale. At Watergate Bay, the original slates – hundreds of millions years old – can be seen with their contortions all too obvious.

There is something else too at Watergate Bay, something that initially makes less impact: time-smoothed outcrops of green and purple mudstone. These twin strata recur like a faint musical motif in the symphonic grandeur of Cornwall’s geology. I have seen them elsewhere – below St Mawes Castle, even on the Devon coast. What soils, what particular scrapings led to those colours is not now clear, but to think of the tinted silts dropping down through the water to settle on the seabed is to sense for a moment the dizzying age of the Earth, the mystique of geological time. Then the cliffs become more than just a hotspot of mineralogy but a place redolent of all natural forces. On windy days, looking out over the sea, with the cloud-shadows racing over it, you can see exactly the same tones appear, the same distinctive shades of green and purple.

Zacry’s

Look south from the hotel, in the Newquay direction, and you’ll see the large rocks of ‘Zacry’s Islands’, just off the shore. The remains of an arch previously connected to the mainland, centuries of rain, wind and Atlantic storms wrought their eternal separation. In the book ‘The Geology of the Country near Newquay’ (1906 – by Clement Reid, John Brooke Scrivenor, John Smith Flett, William Pollard and Donald Alexander McAlister), the authors note how the cliffs in an unnamed cove just to the south of Zacry’s display “about 10 feet of hard, platy, black or dark grey glossy shale, full of seams of fishbones”; a striking reminder of prehistoric oceans.

Discover Zacry’s Restaurant, the rocks’ namesake inside Watergate Bay Hotel.