Day out: Abereiddy Bay, Pembrokeshire

Holidaymakers throw them aside to lay down towels, and coasteerers step over them in a hurry to get to the Blue Lagoon. Few know how remarkable these tuning-fork-shaped rocks with comb-like arms are.

So ancient, they predate the dinosaurs; so short-lived, they existed only between 470 and 464 million years ago, and so unique, they occupied an ecological niche of their own, like today’s jellyfish.

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Planktonic rocks

Graptolites – derived from the Greek words ‘writing’ (graptos) and ‘stone’ (lithos) – were planktonic organisms that drifted about the oceans feeding on algae. Some species even evolved into worm-like filter feeders known as pterobranchs that still live on the ocean floor today. Just imagine, these ‘scribbled on’ rocks found at Abereiddy Bay contain the remains of organisms with a half-billion-year-long history.

Abereiddy Bay is easily reached from the car park, but a far nicer approach is to walk there along the clifftops from Porthgain. The land is owned by the National Trust and is part of the Pembrokeshire Coast National Park.

Porthgain is a pretty village with a hook-shaped breakwater chiselled into the cliffs. From the 1850s, slate, brick and then granite were quarried here, and the crushed stone dispensed from huge brick hoppers ready for export by train and ship. The hoppers, and earlier buildings including the limekiln and pilot’s house, still stand today.

From Porthgain harbour, take the coast path south-west, climbing high above formidable rocks. The views are breathtaking. Look out for gannets and choughs; you may even catch a glimpse of a porpoise or a seal out at sea.

Treasure hunt

Just before Abereiddy is the Blue Lagoon. When slate quarrying ceased in 1901, the sea broke through into the quarry, creating a vivid blue harbour, protected from the strong currents of Abereiddy Bay. Listen out for the slaps and cheers of adrenaline junkies as they throw themselves off the cliffs. Abereiddy is an SSSI and hammering into the bedrock is strictly forbidden. It’s not necessary anyway; there are plenty of fossils in the soft, flaky shales that drop out of the cliffs on to the beach.

From Abereiddy, you can catch the Strumble Shuttle bus back to Porthgain, or continue inland on a circular walk (signposted) back to where you started. Leave time for refreshments at Porthgain, either in the 18th-century Sloop Inn or The Shed Bistro, which was once the machine shop for the engines that operated the brickworks.