IT’S MIDSUMMER AND silvery squalls are ghosting across the Irish Sea. Twenty-four hours of gale-force winds have massaged the waves into slow-moving ranges that collide with deep shudders against Anglesey’s western bastion. South Stack is in formidable form. I’m on the edge of the cliff with Libby Peter and Graham Desroy. Bandoliers of clinking metal swing from their hips as they step over snakes of rope, tightening helmets, adjusting straps and buckles. They move with the slinky grace of stalking cats, smiles in their eyes. The brink of an abyss is their natural habitat: it’s where they excel. They are rock climbers.

Libby goes first, stepping backwards into the void. Peering over the edge, I can see clouds of spray erupting against black rock. The yellow dot of Libby’s helmet disappears beneath an overhang. The sea is a couple of hundred feet down.

‘How will we know,’ I ask Graham, ‘when Libby’s at the bottom?’

‘The rope will go slack.’

I run my hands over my harness for the tenth time. We’re going to abseil down the cliff to a ledge just above the waves, then traverse around the headland to the foot of a climb called Illya Kuryakin. It’s my first cliff climb, graded VS, Very Severe; just a light scramble for the likes of Libby and Graham.

‘You ready?’ asks Graham.

I thread the abseil device, clip onto the rope and lean backwards (always a tricky moment, that initial, gravitational tilt).

‘Just be careful on the first bit,’ calls Graham from above my head. ‘It’s loose, and we don’t want to drop rocks on Libby’s head.’

I let the rope slide through my hand. I’m tip-toeing backwards. The feeling of ‘time standing still’ is more than a cliché. It really happens. The brain’s response to mortality is to shut down every thought circuit except the one required to overcome immediate danger. The tick-tock of everyday concerns is replaced by a silent, temporal vacuum; an infinite cerebral space bisected by a single, narrative thread to the future. It’s a pure space, reserved for survival and pleasure.

I watch my rock shoes touch the fissured rock. A piece of quartz the size of a dice trembles in its socket. I’ve forgotten how to abseil an overhang, and for a moment I’m dangling, with my helmet scraping the rock and feet cycling for contact. The sea, blue and hard, is heaving like the flank of an enormous beast. I ease the abseil device, and feel my toes touch the cliff.

Leaning back, I’ve got a clear view across Gogarth Bay to North Stack, one mile away. And there, oblique from this angle, is one of the greatest climbs in Britain, Dream of White Horses, 430 feet of airy, arching HVS [Hard Very Severe]; first ascended in 1968 by the poet–climber Ed Drummond. He once referred to rock as ‘petrified patience’.

At the foot of the abseil, Libby organizes ropes while Graham slides down to join us. We traverse around the headland. Waves explode at our feet. I can taste the salt on my lips. ‘That’s it!’ shouts Libby. ‘Over there. The crack, then the arête.’ I can’t see what she is pointing at. The cliff doesn’t appear to possess any features large enough to catch the eye. We traverse a bit further, then Libby turns again: ‘We start from here. You step across this gap, then go up.’

Most of the rock climbs I’ve done (and it’s not many) have started on serene lawns of rough grass, or banks of scree. The start of Illya Kuryakin is precarious, and tempestuous. The ocean booms and smokes, and I’m teetering on a chipped blade of rock, anchored to the cliff by my left hand. And yet this is one of the easiest climbs on these cliffs: just two pitches to the top.

Libby goes first, effortlessly crossing the chasm at the foot of the cliff, then pausing for a moment, looking upward. She floats up the first pitch as if gravity has been reversed. She arranges a belay. Then it’s my turn.

The chasm is an immediate problem. I can’t see how to reach the foot of the climb without falling into the sea. Graham advises a bridging movement. The fact that I’m not swimming is a preliminary triumph. But I’m committed now. I’ve crossed the chasm, and the only way out, is up. And lllya Kuryakin is ridiculously vertical.

Belayed from above, I cannot fall, but that is not the point. Rock climbing is an exercise in grace. Ascent is measured by the manner of the moves. I’m poking and scrabbling, clinging to the cliff. There is a kind of fissure, sparkling with quartz, and I’m trying to wedge sufficient bits of my extremities into this crack to prevent a fall. I’m about 20 feet above the waves when I hear Graham calling:

‘Nick … try spreading your legs, like a starfish. Use more of the cliff. You’re trying to pedal up a line!’

I withdraw my left foot from the sanctuary of the crack, and explore the face of the cliff. A sharp nodule catches the edge of my climbing shoe. (He could be right.) I do the same with my right foot, then reach sideways for a hand-hold. Spreadeagled, I realize that I’ve doubled, trebled, the number of available holds. To move upward, I have to reach for the cliff, not hide from it.

I’m moving upward. The cliff feels warm. This is complex rock, quite unlike the uniform cliffs of Dover or Orkney, where uninterrupted walls of chalk or sandstone rise for hundreds of feet. Here at South Stack, I’m looking at a dog’s breakfast of geology: rock of many textures and hues with no obvious arrangement. Geologists are still trying to understand what happened on Anglesey. It was, unquestionably, violent. This was once the collision zone between two of the earth’s plates and the rock here has been baked by pressure and heat; folded, twisted and sheared.

I’m back on quartz again; a white, glassy vein in the cliff. The view is wonderful. The coast is an edge, and here, where Anglesey’s ancient rocks meet the sea, the edge is emphatic. There are no sandbars or lagoons, or gentle peterings of land and sea. The land is cleaved as if by an axe. In the horizontal plane, there is an immediate transition from green to blue; I am suspended on that edge, in the other plane.

The crux comes too soon. It’s an awkward move; a test of faith. The arête is like the corner of a shattered building. At the top, there is a huge, protruding block. There are no holds for my feet, and I cannot reach the top of the block. The only means I have of pushing upward is to smear my right shoe against the smooth, tilted side of the block. It is nearly vertical, and I look down at my foot, wondering whether the friction between rubber and rock will be sufficient. If the shoe skates off, I’ll fall. Well, not exactly fall, because I’m roped from above, so there will just be a sharp jolt. But humans are wired to fear falling, and besides, dropping off a rock climb breaks the spell. Climbing is feat of imagination, rather than a test of braided polyamide.

The sea is so far down that it is silent now. The fingers of my left hand are wedged in a crack. I’ve forgotten to remove my wedding ring, and realize that if I slip and the ring jams in the crack, my finger will be torn off. I rearrange the hand, so that the finger-at-risk is outside the crack, then push, tentatively, with my right foot, transferring my weight onto the face of the slab. I return my weight to the lower, left foot, take a breath, look upward, and move.

The rest is easy. I climb, absorbed in the pleasure of balancing each move. Then there is an abrupt change of plane, from vertical to horizontal, and I can walk. It’s over, and I’m throwing my arms around Libby. Graham climbs up to join us and there is chatter and footling with coils of rope and racks of gear while the sun slips towards the sea. Off South Stack, the sea is boiling; the tide has turned.

In the big, spherical picture, the coasts of these islands are young; a tick of the clock in the planet’s six-billion-year chronology. A mere 20,000 years ago, Scotland was covered with a mile-thick ice sheet that reached as far south as the Humber and the Severn. The North Sea and English Channel were arid, frozen wastes of wind-blown glacial dust. But the planet’s climate is capricious, and when temperatures suddenly rose around 16,000 years ago summers became as warm as those of today. Sea levels rose, filling shallow basins. Thawing sands and gravels grew green with juniper and birch, and herds of wild horses grazed across herb-rich grasslands. Bears prowled the banks of wide, braided rivers and humans reappeared for a while. But around 12,700 years ago, the climate flipped again. Mean annual temperatures in Britain appear to have plummeted by about 15 degrees Celsius in ten years. For the best part of a thousand years, the northern reaches of the continent reverted to a cold, dry tundra. Snow lay on the hills all the year round, and in the north, glaciers cascaded from the high corries. On the coast, average temperatures dipped to minus 20 degrees in winter, and struggled to reach 10 degrees in summer. Reindeer replaced the horse and deer, and the humans trekked for weeks at a time following the herds, as Lapps do today.

The Big Freeze was followed about 11,500 years ago by a virtually instantaneous Big Heat: extreme global warming that saw mean annual temperatures jump by 20 degrees. The greater part of this thermal aberration may have occurred in as little as 50 years. For around 4,000 years (from 9,000 to 5,000 years ago), the earth’s climate was warmer and moister than it is today. Habitats went through a step change. Dense forests spread over much of western Europe. On better-drained vales and slopes, stands of oak, elder and elm took root, spreading into patchy forest which became the home of red and roe deer, wild boar, hares, and predators like brown bears, wolves and foxes. Among the wild foods were hazelnuts, which became a staple of the early human colonists.

At this kind of temporal range, it all looks like the Garden of Eden, but the warming climate had triggered a tipping point. Sea levels started to rise rapidly. The effect on our coast was transformative. In the far north, estuarine lands flooded to form a wide, salt-water gulf between the iced peaks of Scotland and those of Norway. To the west, seawater flooded river valleys and glacial trenches, detaching the Orkneys, Hebrides and Ireland from the northern European landmass. Change was most marked in the south. With the northern mountains relieved of their enormous burden of ice, the earth’s crust sprung upward, but a ‘see-saw’ effect caused the land surface in the south of Britain to sink. Coupled with rising sea levels caused by melting ice, southern coasts were remodelled. Sea gradually flooded in from the west, turning green downland into white cliffs.

Human settlements were drowned as low-lying coasts were submerged, but the greatest loss was in the east, where a wide land bridge still linked eastern Britain to the continent. Archaeologists have dubbed the land bridge ‘Doggerland’, after the largest sandbank in the North Sea: the Dogger Bank. Doggerland was one of the richest territories in post-glacial Europe, a vast, rolling plain threaded with rivers, marshes and lakes. Seabed surveys have revealed one thousand miles of river channels and 24 lakes or marshes, one of which covered nearly 200 square miles – an area twice the size of the Broads National Park. Ranges of low hills provided drained footings for woodland and dry passage for inland travel. Doggerland was also very ‘coastal’. As the only land bridge to the continent, it was rimmed to north and south by salt water, while its central geographical feature was a huge estuary 60 miles long and 20 miles wide. The sea was always going to be Doggerland’s destiny.

By northern European standards, Doggerland’s climate was kind. The westerly weather systems beating in from the Atlantic had dropped most of their rain and velocity by the time they reached Doggerland, while its low altitude reduced the pinch of winter frosts. To this day, the plains of East Anglia are among the driest and sunniest parts of Britain. For its inhabitants, Doggerland was the dream landscape, for it offered four adjacent habitats: coast, freshwater wetland, forest and grassy plain. All human needs were covered. It seems probable that Doggerland’s dwellers were fairly mobile, and that their seasonal migrations were anchored to their long coastline. From autumn through to spring they would have based themselves near the sea, or on the shores of their great estuary. Here they could fish and collect shellfish, and pick off migratory birds. On nearby systems of rivers and lakes, there were plenty of cormorant, grebe, crane and duck, and the wetland was rich in reeds which could be used for basketry and roofing material. In calm meres, they would have found edible plants like the water lily. In scrubland and woods they could forage for hazelnuts, raspberries, blackberries and fungi. Herbs like sorrel and meadowsweet were there for the picking, and there were any number of tubers, seeds and leaves that we’ve forgotten how to use. In the woods were deer and wild pig. Nodules of flint for tools and weapons could be collected on many of the beaches, and the woods provided timber for shelters, firewood and boat-building. Early in the summer, these early settlers probably left the coasts and headed inland to hunt for game.

As Doggerland was nibbled by the sea, the land bridge narrowed, and its use as a thoroughfare – a through route between the continent and the huge, bulbous promontory that would become Britain – must have intensified. From a land, it became a highway, and a cultural conduit. The folk living on the Doggerland bottleneck must have been party to information; to knowledge.

Doggerland was probably lost in a series of inundations, swamped by storms and surges; abandoned mile by mile. At around this time, there was also a freak tsunami. One autumn about 8,000 years ago, a slab of seafloor the size of Scotland slid into a trench off Norway and pushed up a surging wall of water. It was rather as if the Ice Age was sending a reminder that it wasn’t yet done, for the cause of the tsunami was 3,000 cubic kilometres of glacial sediment and debris which had been destabilized by the shifting ocean. When the tsunami hit the Shetland Islands, the waves were over 20 metres high. As far south as the Firth of Forth, they were between 3 and 6 metres high. Anybody standing on the shoreline of eastern Scotland would have been bowled over and drowned. To this day, buried beneath a top cover of peat, you can see the thick layer of stones and gravel that were swept across Shetland. Looking at it, you wonder what effect the tsunami had on the remaining vestiges of Doggerland, or its coastal families.

The connecting thread that was Doggerland finally went under about 7,500 years ago, and the severed promontory became Europe’s largest island. The water kept rising, chewing at the softer edges of the new archipelago. A new sea expanded in the east and on the southern shores of Britain and Ireland river valleys filled with seawater, creating sinuous inlets. Where a promontory was cut off, or an isthmus flooded, islands formed. The shores of southern Britain are dotted with relics from these lost lands. St Michael’s Mount in Cornwall used to be a sharp hill surrounded by forest which now lies beneath the waters of the bay. Fragments of that forest still appear when gales strip away the sands. At low tide on the beach at Borth in North Wales, you can find the root systems of a forest that once occupied the shallow basin now filled with Cardigan Bay. And at Amroth in South Wales, another forest emerges from the sand below the Pembrokeshire coast path. Gerald of Wales, writing in 1188, described how the beach at Newgale had been scoured clean of sand by a great storm, which revealed tree trunks ‘standing in the sea, with their tops lopped off … as if they had been felled only yesterday’. The ancient Welsh legend of a sunken land called Cantre’r Gwaelod beneath Cardigan Bay appears to be rooted in fact. On the other side of Britain, Doggerland’s forests are still out there, too. If you take a low-tide walk along the beach at Titchwell Marsh RSPB reserve, you may come across banks of peat poking from the wet sand. Last time I was there, the foreshore was strewn with branches, roots and the stubs of trunks, black and salt-saturated. Those trees used to reach the Netherlands. On a fishing boat out of Yarmouth, Simon Fitch, a landscape archaeologist and one of the authors of the definitive book on Doggerland, showed me core samples extracted from the seabed. We looked at the cores on the deck of the boat while the turbines of Scroby Sands wind farm revolved in the background. Each core contained a thick horizon of black peat; all that remained of the trees and shrubs that sustained the island’s post-glacial explorers.

More poignant still was an afternoon spent on the tidal mud of the Severn Estuary. This time our filming guide was an archaeologist called Dr Martin BelI, who led us through canyons of slime to a tilted bank just above the water. As the mud was being eroded by the waters of the Severn, it was breaking into layers, each layer representing a deposit of silt laid down by a particular tide, more than 8,000 years ago. One of the layers was covered with footprints; tiny, human footprints. They were so clear that they might have been made ten minutes earlier. In the perfect, sculpted impressions of toes and heels, it was possible to see how the children had been jumping, turning; leaping perhaps. What were they doing? Hunting? Playing? Fighting? Their prints have now been washed away. These tree roots and footprints read like cryptic texts from our ancestors.

Around 6,000 years ago, the rate of sea-level rise slowed. In a geological blink of just 12,000 years, a frigid, icy desert had been transformed into a temperate archipelago. Sea levels had risen by 120 metres, slightly more than the height of St Paul’s Cathedral. The shore of mainland Europe had shifted southward by 800 miles, from somewhere north of the Shetlands, to the cliffs of Calais. An area of land greater than the size of the United Kingdom had disappeared beneath the sea. What remained was the higher ground, the mountains, the plateaux and 6,000 islands. Shakespeare referred to one of those islands as a ‘precious stone set in the silver sea’, but he might have been writing for all of them.

It is an extraordinary archipelago. Eight hundred miles from north to south, and 500 miles wide, it rises from the sea midway between the Arctic Circle and Africa. Its western shores are washed by the deep Atlantic Ocean; its eastern shores by the shallow North Sea. We are warmed by an ocean current that has come all the way from the Gulf of Mexico, and our weather – borne on winds that can blow from the Arctic, Africa or Atlantic – is, well, variable. We are also a geological freak.

The rocks that give our coast its character are unusually old and varied. They span around three billion years of the earth’s history and have survived an incredible journey; a slo-mo marathon measured in thousands of miles and hundreds of millions of years. The oldest bits of Britain and Ireland are the travel-mangled remains of crustal plates that have slithered, collided and parted across the surface of the globe. Six hundred million years ago, the parts of the Earth’s crust that were to form Scotland and northwest Ireland were somewhere in the region of today’s Antarctic coast. At the time, England, Wales and southeast Ireland were a geographically separate part of the Earth’s crust, located in warmer latitudes roughly level with present-day South Africa. Drifting north, these two main crustal parts of Britain and Ireland merged, crossed the equator and were subject to every force in the geological toolkit. Layers of silt washed from mountain and plain emerged on our shores millions of years later as rock that looks like folded sandwiches. We have cliffs of cooled volcanic lava, and others that were metamorphosed deep underground by extremes of heat and pressure. Some of our shorelines were formed from desert sands; others were created on seabeds from the shells of dead creatures. This is the ancient land that found itself poking from the Atlantic rim 6,000 years ago when the seas became more settled.

For the first time since the ice had melted, sea and land had found some kind of equilibrium, and the forces of the ocean became focused on a relatively stable shoreline. This was the moment that the sea really went to work as a sculptor; the moment when the form of our modern coast became defined. Water is an immensely powerful tool, and the sea is famously restless. Cliffs were undercut and rinsed by storms to form caves and crevices. Great arches and towers were hewn from headlands. Waves, tides and currents worked around the clock, shifting millions of tons of rock, sand and earth from one part of the coast to another to form beaches and spits. Coastal winds built ranges of dunes. Search the planet, and it’s hard to find a coastline of equivalent length with such an incredible variety of coastal landforms.

Our wildest coast is also our oldest. A few summers ago, I climbed a hill called Heaval on the Hebridean island of Barra. It’s only just over a thousand feet, but it’s the highest point on the island. The air was blue with sky and sea, and so clear that the southern Hebrides were as sharp as a map: Vatersay and Sandray, Lingeigh, Pabbay and Mingulay tapering into the immense Atlantic. Across the summit of this ancient hill, lichen-speckled rock protruded from the wiry grass like the greyed remains of a gigantic fossil. Over the next three weeks, as we made our way north along the Hebridean chain to the Isle of Lewis, we’d see a lot more of this rock. We found it as the encircling arms of blue lagoons, as flotillas of islets, and as defiant cliffs being battered by a westerly gale. It’s called Lewisian gneiss, and it’s the oldest rock in Britain, formed at a time when simple, bacterial organisms were striving to evolve on earth. Baked, frozen, rent, folded and scoured on its three billion-year-journey, Lewisian gneiss is a relic, and it gives the Hebridean shores their ancient countenance. You can find it on the mainland, too, where it defines sections of shoreline between Cape Wrath and Skye – including the wild fringe of Assynt. This is one of my favourite coasts in Britain; a ragged edge of rock and beach fronted by islands and backed by isolated, monumental mountains. At places like Clachtoll and Achmelvich, the space between sea and peak is filled with low, hummocky hills dotted with old grey rock which has been around for more than half the age of the planet. There are few places in the world where you can stand on a piece of stone and feel such a passing of time through the soles of your feet.

It’s up here, in northern Scotland, that we find some of our most astonishing natural architecture. The fjord-like scenery that clogs the memory card on your camera as you take the long and winding roads north from Skye has been given its beauty by billion-year-old sandstone that has been eroded into 3,000-foot mountains and deep sea-inlets. Geologists call the sandstone ‘Torridonian’, after the sea loch which squirms for 12 miles into the depths of this primeval stonework. I first climbed these mountains as a teenager, and have been coming back ever since – a couple of times by bicycle. Inner Loch Torridon can be tempestuous or moody, or bewitch you with sunlight. The peaks tilt to 3,500 feet from the water’s edge. One January night when the sky was stuffed with stars, I stood on a rock above the loch watching the Northern Lights play in luminescent curtains beyond the horns of Beinn Alligin – the Jewelled Mountain – the only time I’ve seen the Aurora Borealis from Britain.

It’s in this remote precinct of Scotland, too, that you find one of the largest and most dramatic coastline caves in Britain. It’s also one of the oldest. Smoo’s limestone was laid down 500 million years ago on the bed of a tropical sea when Scotland lay south of the equator. More recently, as sea levels stabilized, freshwater and seawater made a two-pronged attack on a geological fault in the limestone, widening it into three caverns, the largest of which is 60 metres long and 40 metres wide. The second chamber contains a 25-metre waterfall, and the third can only be reached by small boat. Smoo is described at the end of the 16th century by the great mapmaker Timothy Pont, who wrote of ‘a great hollow cave’ containing ‘a freshe pond of great deep’ and a spring tumbling through a hole in the roof. When the Scottish novelist, Walter Scott, came visiting in August 1814, he found himself lost for words: ‘Impossible,’ he noted in his diary, ‘for description to explain the impression made by so strange a place.’

The most spectacular coasts of Wales are built on old rock, too. The jagged cliffs and reefs that form Anglesey’s north-western defences against the precocious Irish Sea began to be formed shortly after Smoo’s sediments fell to the floor of a shallow sea. Wales has several very old islands. Islands, like caves, have tended to be favoured through the ages as ‘sacred places’, and it’s often been the case that the older islands are the most sacred. Off the coast of North Wales, Holy Island and Bardsey Island (which would become one of the holiest places in Wales) are nearly 500 million years old. Further south, off Pembrokeshire, Skomer and Skokholm sound too Scandinavian to be found off the tip of Pembrokeshire, but that’s because ‘Cloven island’ and ‘Island in a channel’ were named by seafaring folk from the far side of the North Sea. Separated from the mainland by tide races, they have become sanctuaries for wildlife. The last time I visited Skomer, I was guided by Anna Sutcliffe, a marine biologist who had lived on the two-mile long island for seven years. On cliff paths, puffins pottered about our ankles building nests and looking unamused by the tearing wind and rain. ‘In good weather,’ explained Anna, ‘you won’t see them. They’ll all be off having a good time fishing.’ At the Wick, a sea-sluiced chasm on the island’s west coast, we watched thousands of seabirds adhering to the cliff, guillemots on a long, luxury ledge at the bottom, black-booted kittiwakes further up, then razor bills in cushioned nooks where the cliff relented, and at the top, fulmars gazing down imperiously from sheltered grassy belvederes. Skokholm is even smaller than Skomer, but has the world’s third-largest population of Manx shearwaters and perhaps one-fifth of Europe’s storm petrels. Harbour porpoise play in the currents, and sometimes dolphins, too.

Skokholm’s jagged reefs and red cliffs have much in common with the Orkneys, where a rock called Old Red Sandstone has been eroded into some of our most iconic coastal architecture. Old Red Sandstone is younger than the gneiss of Lewis, the limestone of Durness and the Torridonian sandstones, but it’s still old enough to have been formed before the constituent parts of Britain and Ireland crossed the equator. Massive ranges of mountains were ruckled up by a collision between two of the earth’s plates, and then worn down and dumped as sediment in basins. Fossils in Old Red Sandstone suggest that, around 350 million years ago, life on Britain’s crustal plates was taking a turn for the better: fish had developed jaws and lungs, and were on the threshold of becoming amphibian; plants had evolved from 2-foot swamp ferns to large tree ferns. One of those basins became the Orkney Islands: the sea-stack capital of Britain.

The king of Stacks is the Old Man of Hoy, whose 450 feet of improbable sandstone makes it the tallest in the UK. Described as a ‘crumbling colossus’ by Tom ‘Doctor Stack’ Patey – one of the three climbers who made the first ascent in 1966 – the Old Man became the subject of the BBC’s first, genuine reality TV show the following year, when 15 million viewers watched a live transmission of the stack being reascended by six climbers. On the rare occasions when I volunteer to carry a camera tripod (a hideous contraption designed to impress troughs into your shoulder), I remind myself that in 1967, when the BBC chartered an army landing craft to reach Hoy, they had to hump 16 tons of TV equipment to the cliff edge. In 2008, three climbers parachuted from the top of the Old Man.

The height of a stack is related to the height of its adjacent cliffs, so Hoy also has the second-highest stack in the Orkneys – a remote column called the Needle, which was first climbed in 1990 by the legendary Revenue and Customs officer, Mick Fowler. On the west coast of the island known as Mainland are three more stacks: two-legged Yesnaby Castle is a tiddler at 115 feet, but looks ready to topple at any minute, and a couple of miles to the south, on a very lonely section of Orcadian coast, towers North Gaulton Castle, which is almost twice as high as Yesnaby. Quite unlike the other stacks because it is short and so undercut by waves that it appears to overhang on all sides, is Stack o’ Roo. At the northern tip of Mainland, is a chunky, twin-peaked stack called Standard. The island of South Ronaldsay has stacks called the Kist, the Clett of Crura and Stackabank, which looks like a pile of gigantic nibbled biscuits. Stronsay has a huge flat-topped stack called the Brough, and Westray has its Castle of Burrian, a broken pencil of stone which was far taller until it was lopped by storms.

The wonders worked by the sea on Orkney’s old sandstone go way beyond sea stacks. Most sea stacks are the surviving pillar of a collapsed natural arch which has been cut from the face of the cliff by waves as they exploit vertical cracks in the rock. Arches are rarer than stacks, but there is a precarious example on the east coast of the island of Stronsay, where the Vat of Kirbister forms a gigantic hoop of sandstone over the sea. This is also the land of the ‘geo’ and the ‘gloup’; the geo being a narrow, sea-filled cleft which is left after the roof of a sea cave has collapsed, and the gloup being a blowhole linking a sea cave with the clifftop. It goes without saying that gloups can be as spectacular as they are dangerous.

If the Orkneys are a firth too far, you can sample the extravagance of Scotland’s Old Red Sandstone without taking a ferry. Few cliff walks deliver as much drama as the one-mile hike south from Duncansby Head, the most north-easterly point on mainland Britain. I’ve done it in all weathers, but there’s no question that a windless day of sunshine is safest and most pleasurable. The Stacks of Duncansby are – for me, anyway – up there in the Top Ten of coastal spectacles. Half a dozen stacks rear from the sea in front of Duncansby’s vertiginous cliffs, but the best are the two shark’s teeth that rise from rings of chalky surf. There are other stacks on this coast, too. Just to the west of Thurso, at Holborn Head, slab-sided Clett Rock rises in wafers of Old Red Sandstone to a grassy tabletop. There’s a gloup on this headland, too.

Arches and stacks are among the more temporary of our coastal wonders; they’re just too fragile to last for long. A very long way from Orkney, on the north coast of Cornwall, is a set of stacks that is disappearing fast. On a wild day, wreathed in salt spray and attacked by breakers, Bedruthan Steps look like the ruins of a lost city. The ‘steps’ are a series of slatey stacks which have crumbled into form-teasing shapes: Queen Bess Rock took its name from its crown, ruff and farthingale, but it lost its head back in the 1980s. At low tide, you can descend a steep flight of steps to the beach and then wander through the stacks on the wet sand. They’re even older than the Orkney pillars, and take their name from a legendary giant called Bedruthan, who took a short cut across the bay by bounding from stack to stack.

The cosmic antiquity of our shores, and the flair of their natural architecture, are sketched in scoured headlands and tottering stacks from Orkney to Cornwall. But it’s just a preview. The rocks that were slowly accreting into the beginnings of Britain and Ireland got swamped by a clear, warm ocean lined with coral reefs. That was around 350 million years ago, as Britain and Ireland were crossing the equator. Those coral reefs became Carboniferous Limestone and gave us some of our most spectacular shores. It’s a wonderful, theatrical rock. There’s nothing reticent about Carboniferous Limestone: it’s showy and makes great cliffs, islands, caves and arches.

A couple of years ago, I was lucky enough to find myself with a bicycle on the Aran Islands, the chain of pale grey reefs anchored off the west coast of Ireland. Under the hot sky, the stone shone with a silvery glare, the rectangles of walls and cottages contrasting with the crazy, fretworked coast. I kept thinking I was pedalling an islet in the Aegean. The highest cliffs of our archipelago are constructed from this stone; in sight of the Aran Islands, the Cliffs of Moher run for 8 miles or so along the edge of County Clare, reaching a height of 700 feet. Plonked in the sea beside the cliffs, the Great Pyramid of Giza would be dwarfed. It’s a characteristic of Carboniferous Limestone to dissolve into roomy cave systems which became five-star sanctuaries for early explorers and hunters. Cresswell Crags in Derbyshire and Goat’s Hole Cave on the Gower coast are classic examples.

In Wales, the munificence of that 350-million-year-old coral helped to create the bays and buttresses of Gower and it also underpins the southern shores of the Pembrokeshire National Park, where the coast path teeters along the edge of the cliffs from St Govan’s Head to the 80-foot high ‘Green Bridge of Wales’ – arguably the most dramatic natural arch in the UK (this part of the coast is part of an MOD firing range, so check their website before visiting). The same limestone also lines the Menai Strait and it’s the backbone of Great Ormes Head, the giddy windbreak that shelters Llandudno’s sweep of sand. In England, those sunny reefs form the bedrock of the Northumberland coast between the Tweed and Tyne. This is a silent coast, with space by day and stars by night. When the Campaign for the Protection of Rural England published a series of maps identifying areas of the country that were least disturbed by human noise and light, Northumberland, it turned out, contained the largest contiguous ‘tranquillity zone’ in England. Its shore is suited to reflection.

The ancient sanctuary of Holy Island (Lindisfarne) is a spike of recycled coral, as are the sheltering promontories at Berwick-upon-Tweed and Seahouses, although within sight of Holy Island there’s a sprinkling of islands that have more in common with volcanoes than coral. The treeless Farne Islands (which are really a couple of islets and two dozen reefs) are another sanctuary, but for wildlife. There are very few islands on the eastern coast of Britain, so the Farnes are particularly unusual. In summer, something like 100,000 pairs of seabirds, from guillemots to puffins, come here to nest, and four types of tern; it was an Arctic tern, ringed on the Farne Islands as a chick in the summer of 1982, that was discovered that October in Melbourne, Australia after a flight of over 14,000 miles in three months. The islands have one of Europe’s largest colonies of grey seals. Why are the Farnes here? Well, back at the tail end of the Carboniferous, the earth’s crust parted just enough to allow magma to ooze upward and to settle between the layers of limestone. When the limestone on top got worn away, the hard black volcanic rock was exposed as a ridge, or ‘sill’, running across Northumberland and into the sea, where it reappears above the surface as the Farne Islands. This raised rib of basalt was a strategic godsend for Emperor Hadrian, who used the Whin Sill to underpin his great dividing wall.

England’s third-largest contiguous area of tranquillity (the second-largest is the borderland adjacent to Wales) is a vast block of Carboniferous grits and shales in North Devon which culminates in the dark, tortured cliffs of the Hartland Peninsula. Hikers of the South West Coast Path will recognize the leg from Boscastle to Bideford as the wildest (and in bad weather, bleakest) section of the entire route. Last time I filmed at Hartland Point, the Atlantic was hurling itself at the black cliffs with demonic fury. Rain, salt spray and wind battered us as the cameraman fought to snatch essential shots.

Something pretty awful happened after the Carboniferous. There we were on the equator, welded for a while to all the other continents that make up today’s world map. The new super-continent, called Urkontinent by its early-twentieth century German proponent, Alfred Wegener, became known as Pangaea once his theory gained traction among geologists. Pangaea was a disaster. A planet with a single ocean and a single landmass may appear geographically neat, but it was very bad news for life forms. Pangaea was so enormous that it altered the world’s weather patterns. Climate in the centre of large landmasses varies dramatically between the seasons, and it’s thought that the mean monthly temperature in the centre of the Pangaean super-continent may have been as much as 50 degrees Celsius higher in summer than in winter. Aridity ruled. Seas evaporated and salt blew over the land. In his wonderful geological romp, The Hidden Landscape, Richard Fortey strips away the greenswards around the Severn and replaces them with a desert of ‘sand wastes or playa lakes crusted with white crystals and as hot as the fires of Hell’. The Permian period (it takes its name from the province of Perm in Russia) saw the greatest mass extinction in earth’s history. Around 95 per cent of marine species disappeared. The corals were killed, and all the trilobites, and all but one species of ammonite. In the livid, red cliffs of Dawlish, on the main line between Exeter and Newton Abbot, you can see outlines of fossilized desert dunes, and beside the line at Langstone Rock, you can actually walk across the red, stony surface of a 250-million-year-old desert … when the tide’s out. There’s a marvellous, red sea arch, too, and on a hot day it doesn’t take too much imagination to slip away to a land of searing winds and a few, blinking reptiles. Until recently, Tyne and Wear had its own fabulous sea arch from the era of the Big Heat, a stunning, creamy-coloured monolith of limestone which looked as if it had been built to commemorate the warry deeds of a Roman emperor. But in 1996 the top of Marsden Bay’s arch collapsed, leaving a slender but unstable sea stack, which was demolished by the National Trust to prevent it toppling onto sightseers.

At around this time (280 million years ago), one of our boldest coastlines was being born deep under the surface of the planet. The granite of Cornwall’s rocky toe and the Isles of Scilly are the top of the same great volcanic root system that forms Bodmin Moor and Dartmoor. The Isles of Scilly are only 28 miles off the tip of Cornwall, but this enchanted archipelago feels closer to the Caribbean than to Penzance. The granite has given it shining beaches and rugged capes, and villages with weather-worn walls that entice you to stay. But at Land’s End, the mood of the granite is one of inviolable defiance. It was Daniel Defoe who observed that the tip of Britain ‘seems to be one solid rock, as if it was formed by Nature to resist the otherwise irresistible power of the ocean.’ I’ve never seen Land’s End as the end of a land, but as the start. I’m one of thousands who’ve set off from Land’s End to walk or bicycle to John o’ Groats, and we’ve all propelled ourselves towards the rising sun with the westerly wind on our backs. Land’s End should properly be Land’s Beginning.

Some of our most iconic coastal scenery began to be formed in the aftermath of the Permian Extinction. Life returned to earth, and with it 185 million years of exotic rock-making. The epochs known as the Triassic, Jurassic and Cretaceous lasted from 250 million years ago to 65 million years ago, and gave us some eye-catching shores; dinosaur shores. The sandstones and mudstones underlying the golden beaches of Blackpool and Southport were laid down beneath the beady eyes of flapping pterosaurs on the lookout for fish or perhaps the rotting carcass of an archosaur. And because Triassic rock is relatively soft, it’s been sought by rivers which have carved it into vales and estuaries such as the Tees, the Solway and Mersey.

The Jurassic has a flair for theatricality. One of the best coast walks in the country runs along Jurassic cliffs from Durlston Head to the sheer buttress of St Aldhelm’s Head in Dorset, where you tread pale limestone laid down when this part of Britain was submerged beneath warm sea. Near here, I once met a man who said he’d spent 20 years extracting a plesiosaur from a cliff, and when I looked incredulous he took me to his home and showed me a skeleton as long as a room. Further west, the sea has worked with the Jurassic shoreline to produce the semicircular cove of Lulworth, and the most elegant natural arch in southern Britain: Durdle Dor. It’s the extraordinary geology and scenery of Dorset and South Devon that led to it becoming England’s first natural World Heritage Site. Because of the way the rocks have been folded and eroded, the Triassic, Jurassic and Cretaceous occur in visible layers along the shore; were you to walk the full 95 miles of the ‘Jurassic Coast’ (and thousands do), you’d be treading 185 million years of the earth’s history. On the coast of Yorkshire, it is that same hard, Jurassic rock in the headlands that protected places like Filey, Scarborough, Robin Hood’s Bay, Whitby and Staithes, creating roles as Roman signal stations, fishing havens, trading ports and seaside resorts. History begins with geology.

The Cretaceous bequeathed England its greatest coastal icon. I reckon I’ve seen England’s white cliffs from most angles: I remember staring into the salt haze as a child, trying to spot them from the decks of car ferries on the way back from summer holidays; I can hear my first skylarks, hovering above the plucked grass of Cuckmere; I’ve cycled over the white cliffs and kayaked beneath them. I’ve entered them through wartime tunnels. But a couple of years ago, I got a call from the Coast production office asking me to take the train to Eastbourne, and to bring mountaineering gear. The next day, I abseiled with Professor Rory Mortimer over the cliff near Beachy Head. The tide was in, and far below my boots, I could see waves breaking against the foot of the cliff. As we started to slither down the abseil ropes, we passed the thin, pale brown layer of topsoil sitting on top of the cliff like almond icing. It was, Rory told me, ‘wind-blown loess’ – fine-grained dust that had accumulated in the draughty, frigid post-glacial deserts of Britain when the ice sheets eventually began to retreat. Immediately beneath the loess, we were hanging in front of a gigantic sheet of whiteness formed, I learnt from my companion, 70–75 million years ago.

Later that afternoon, in the company of a marine biologist called Dr Mike Allen, the true wonder of chalk became apparent. He had with him a sample bottle containing cloudy liquid, a culture of a single-cell algae called Emiliania huxleyi, known to its friends as ‘Ehux’. A species of phytoplankton, it’s very small. ‘If the algae was the size of you,’ said Mike, holding his bottle to the light, ‘you would be as big as Mount Everest.’ Peered at through an electron microscope, Ehux is one of the most beautiful life forms to have floated in the seas. It’s a sphere, armoured with overlapping calcium-carbonate plates, or coccoliths, each of which looks like a child’s drawing of the sun. The man who first studied them in detail was the 19th-century biologist Thomas Henry Huxley, who admitted to finding them ‘extremely puzzling’. Using a hand-cranked centrifuge, Mike and I created a chalk pellet from seawater: ‘When it dies’, explained Mike, ‘the liths go to the bottom of the ocean, and over millions of years, they form a sediment, and that’s how we get the cliffs.’ Simple and beautiful.

Chalk is one of England’s emblems. It’s our youngest real rock, and it’s in chalk that we find the nodules of flint that gave our ancestors the means to hunt, to light fire and to build boats. No other rock reflects the sun in such a way. They piled it into processional ways, and circular walls, where it burned with its own light against the green hills. Chalk was the bedrock of prehistory; the explorers and settlers of the Mesolithic and Neolithic needed it like their descendants came to need coal and oil. The chalk cliffs were beacons: to sailors, the white cliffs of Flamborough Head, the quaint sea stacks off Dorset known as Old Harry Rocks, and the gleaming Needles off the Isle of Wight were signposts on the coastal sea lanes.

England’s largest island, the Isle of Wight, was formed when a long wall of chalk was breached by rising seas; the Needles and Old Harry Rocks are the stubs of that walI. Beneath a cliff at the western end of the island are boulders shaped like gigantic clawed feet, and with good reason: these are iguanodon ‘footcasts’, formed by silt washing into the deep footprints left by 3-ton dinosaurs that had been foraging 130 million years ago, when southern Britain was a thousand miles further south.

And what of England’s most emblematic cliff? ‘Glimmering and vast,’ wrote Matthew Arnold, ‘out in the tranquil bay.’ The White Cliffs of Dover might be half the height of Moher’s cliffs, but they have become a national trademark with a stature way beyond their physical scale. George Lily’s map of 1546, showing the British Isles in hitherto unseen detail, marks forests, rivers and rolling mountain ranges of Scotland, but just one stand of cliffs, at Dover. Like the minarets of the Golden Horn, or the Manhattan skyline, this blinding curtain of chalk veils us from outsiders, yet tells us who we are. Dover’s white cliffs are where we advance closest to the continent, and where we mark our perimeter. They are our first and last sight of home.

With curious synchronicity, Ireland and Scotland acquired their most extraordinary coastal landmarks at pretty much the same time (we’re talking geological time here) that England acquired its chalk.

‘Compared to this,’ exclaimed Joseph Banks when he gazed upon the basalt columns of Staffa in 1772, ‘what are the cathedrals or the places built by men? Mere models or playthings …’ I first saw Staffa from the deck of a tallship. We’d sailed with the tide from Jura at two in the morning and after a few hours in a wooden cot I came on deck to watch the sunrise. The ship, a 92-foot pilot schooner, was buffeting through chilly spray under clouds of sail and both rails were lined with islands. To starboard lay bulky Mull, spiky Ulva and Little Colonsay. On the port side, I could pick out the distinctive profiles of Fladda, Lunga and Dutchman’s Cap, with its broad brim and dented crown. But right beside us, almost within touching distance, were the black cliffs of Staffa. Banks, who had sailed with Captain Cook on HMS Endeavour, and who would soon be elected President of the Royal Society, could not believe his eyes. One end of the island seemed to be ‘supported by ranges of natural pillars, mostly above 50 feet high, standing in natural colonnades’. Landing on the island, he found that each pillar was a near-perfect polygon. The scientist who had botanized in Labrador and Newfoundland, and explored the Pacific with Cook, was astonished by Staffa’s cliffs: ‘Where is now the boast of the architect?’ he asked. ‘Regularity the only part in which he fancied himself to exceed his Mistress, Nature, is here sound in her possession.’

Following a basalt causeway, Banks came to a cave. Each side of its black mouth, tight-packed pit-props of hexagonal basalt supported the roof of the island. When Banks asked his guide the cave’s name, he was told ‘the cave of Fhinn’, after the mythological Irish hunter–warrior Fionn mac Cumhaill – Finn McCool, or ‘Fingal’ to the Scots. Sixty years later, the cave gave its name to the overture that Felix Mendelssohn wrote following his visit to the Hebrides on his Grand Tour of Europe.

Staffa’s columns are a monument to our continent’s creation, for they were formed during the long, complex disintegration of the super-continent, Pangaea, and the consequent widening of the Atlantic Ocean. Back then, 65 million years ago, most of the rock-making had been done and nearly all of the raw materials which form our modern coast had been created. But as North America and Europe drifted apart, lava spewed through cracks and vents, cooling rapidly into polygons. Staffa was on one of those cracks.

There are other Staffas. In Ireland, a vast plateau of lava spilled over Antrim, and where it touches the coast in the north its contractions have formed 40,000 black, polygonal columns that have become the most visited geological showpiece in the archipelago. If visitor figures continue to soar, the Giant’s Causeway will be the first igneous celebrity to receive one million admirers in a year, but there are quieter basalts. A couple of years ago, I was making a film about the 18th-century Welsh traveller Thomas Pennant, whose book led me to a polygonal showpiece above Talisker, on the west coast of Skye. Preshal Beg rises like a volcanic stub, ringed with columns, 1,000 feet above sea level, gazing west over the silvery sea. To the Welshman, struggling to pin these extraordinary columns to a chronology, they were ‘the ruins of the creation’, and so old that ‘those of Rome, the work of human art, seem to them but as the ruins of yesterday’. We filmed up there all day, and then yomped back through the heather as the sun set over the Outer Hebrides. Islands sailed along the horizon, Barra leading a Hebridean fleet cut from Lewisian gneiss. On a lofty headland, the cameraman set up the tripod for a final shot, and as I sat on a boulder staring across the Little Minch I realized that I was perched on one of Britain’s youngest rocks, looking across the water to its oldest.

The Giant’s Causeway, Fingal’s Cave and the White Cliffs of Dover are part of the final, climactic movement of coast-building. What followed was a geological encore written in ice and water.

*

Last year, while I was taking the first, exploratory steps with this book, I reached a place that’s eluded me for ages. It’s called the Inaccessible Pinnacle, and it’s on the Isle of Skye. The first 3,000 feet, up the flank of the Black Cuillins, is relatively straightforward. Then you reach the flaking crest of the ridge, and sticking up from the crest is a 200-foot high rock spike. Twice in the past I’d stood on the ridge, in winter. Both times, I’d stared up at the ‘In Pinn’, appalled at its black, ice-glazed form, smoking with gale-force mist. Both times I went back down. Last year was different. It was summer, and I was being led by one of the most experienced mountain guides in Britain: Martin Moran. The sky was cloudless, the air still and the peaks of Skye were streaked with shining snow. After two pitches of climbing – and a lot of filming – we reached the top at sunset, and while Martin prepared the abseil ropes, I looked to the west. Far below, the blue sea clung to the Cuillins’ taffeta skirts. And away on the monstrous deep first crossed by explorers in skin boats, I could see the Outer Hebrides, floating in line astern along the horizon. It was a view that had been carved by ice and then inundated by water.

On and off, ice has worked at Britain and Ireland for the best part of 700,000 years. Its effect on the coast has been profound. The deep, U-shaped sea lochs of Scotland were gouged by glaciers oozing from a gigantic ice cap. Other glaciers bulldozed material southward and dumped it in ranges of hills reaching far into what would become the North Sea. Out on the western fringes of the archipelago, a 500 metre-thick ice sheet capping Ireland bulldozed heaps of glacial junk towards the rising Atlantic. It’s out here, on what is now the coast of Mayo, that the ice and water have created one of the strangest clusters of islands in the archipelago.

Clew Bay is one of Ireland’s natural marvels. More a sea than a bay, Clew is a roughly rectangular inlet of around 120 square miles, scattered with 300 or so islands that are concentrated at the bay’s eastern end. Thackeray thought they looked like ‘so many dolphins and whales’. Gliding between them on a boat, you quickly get confused. They all look alike, with similar, smooth, rounded profiles. They are among the most impressive ‘drumlins’ in the world; streamlined, elongated hummocks of glacial till formed by the wave motion of moving ice. Their name comes from the old Irish word, ‘droimnin’, meaning little, ridged hill. Arthur Holmes – the geologist who proposed the theory of ‘continental drift’ – compared drumlins to ‘a basket of eggs’, and more recently, Richard Fortey reckoned they could pass for enormous burial mounds. Collectively, they are often referred to as ‘a swarm’. Clew Bay’s drumlins became islands when the ice melted and rising seas isolated the smooth hummocks of debris.

I know it’s a bit obvious, but water makes the coast. And in the making, it’s both a destructive and a creative force. The place to appreciate the power of the sea is Esha Ness. Or more precisely, Grind of the Navir.

We’ve all seen the TV shots of gigantic breakers exploding over promenades, but the largest waves to strike this archipelago are seldom filmed. Graph plots of annual maximum storm-wave heights show that the Shetland Islands are most frequently in the firing line. West of here, the next bit of land is the tip of Greenland. Waves driven by hurricane force winds for hundreds of miles race towards a shore which drops steeply into deep water, so there is little to break their motion. The Shetlands experience some of the highest wave-energy anywhere in the world. Wave heights of 15 metres are not uncommon; a 24-metre monster was recorded in the 1960s. When the full force of an Atlantic megawave hits a cliff, the effect is explosive. Pressurized water is powered into cracks in the rock, prising the cliff apart. Detached boulders are hurled like missiles, and as the wave retreats more ammunition is plucked from the cliff. There is a place on the western shore of the biggest of the Shetlands, the island known as Mainland, which looks like one of Nature’s bombsites. Even in fine weather, it’s a desolate spot; a scene of utter destruction. The cliffs at Grind of the Navir – ‘the Gateway of the Borer’ – are 20 metres high, and have a gap in them rather like a doorway. The day we filmed here, the weather was calm and sunny and I was able to walk down the stepped amphitheatre, around ponds of seawater and peer through the portal to the sea below. In a big storm, I’d have been atomized by green water. On the edges of the amphitheatre, we could see the fresh, pink scars marking the spots where blocks had been torn free, many of them in the January storms of 1992 and 1993. Behind me, at the upper level of the amphitheatre, were three ridges of boulders that had been hurled up to 50 metres inland and upward by waves bursting through the Grind’s portal. Some of the blocks were over 2 metres across. There are several other west-facing sites in the Shetlands where these bizarre ‘beaches’ – or CTSDs (Cliff Top Storm Deposits) as the experts call them – have been spread across the tops of cliffs, at heights ranging from 10 to 25 metres above sea level. Just south of the Grind, the clifftops of Esha Ness have been scoured by waves, and those cliffs are an incredible 40 metres above sea level. CTSDs are reckoned to have more in common with tsunami debris than with conventional beaches. When revelations of these clifftop beaches reached the newspapers in 2004, Dr James Hansom of Glasgow University’s ‘coastal beach group’ felt it necessary to warn the public ‘not to picnic on the top of the cliffs facing deep water, at least not in a storm’.

Grind of the Navir is the strangest beach I’ve ever seen. An exception. But it illustrates the incredible diversity of beaches around the shores of Britain and Ireland. Our beaches come in almost every conceivable shape, size and texture, from cosy Cornish nooks wedged between headlands, to East Anglian strands which appear to stretch elastically to vanishing points on a curved horizon. There are silver sands in the Hebrides, red sands in Devon, white sands in Cornwall, and of course golden sands in Lancashire.

There is – believe it or not – a system for categorizing beach grains. It’s called the Udden–Wentworth Scale, after a pair of American geologists who achieved the enviable feat of furthering science by spending a lot of time on the beach. Sand (subdivided into five sizes) is defined as a particle whose diameter is no smaller than 0.0625mm and no larger than 2mm. Further categories define boulders, cobbles, pebbles, gravel, silt and clay. Our archipelago is well-supplied with the full, Udden–Wentworth spectrum, plus a few bizarre subsets. There’s a beach on the Llyn Peninsula of North Wales where the sand grains have become very well polished and rounded; when you walk on it, the sand makes a squeaking noise. Over the years, Porthor has become better known as the ‘Whistling Sands’.

Where there’s sand, there’s often a dune, or an undulating ocean of dunes, clothed in spiky fronds of marram grass, or shady stands of conifer, planted to anchor them as sea defences. Seen in a low light, the interplay of curves is as beautiful as any set of edges you’ll find on our coast. Dunes are mobile features, blown grain-by-grain by the winds which came in from the sea once the water had stopped rising. There are ranges of dunes, like those at Bamburgh and Horsey in Norfolk, which look like stilled waves, poised to roll down the beach. And there are dunes that have colonized the coastal plain so extensively that you can get thoroughly lost; I’ve become so disoriented in big dune systems that I’ve had to climb to a high point and then head for the sea before resuming a course I think I can follow. The largest expanse of sand dunes in the UK is Braunton Burrows in North Devon, stabilized by marram grass and now home to 400 species of plants. Sand dunes have their own microclimate, and own microhabitats; they are miniature worlds. The dips between dunes are known as ‘slacks’, and when groundwater rises to the surface here you get damp hollows that suit meadowsweet and bog pimpernel and orchids. Level areas can grow crunchy carpets of sun-dried lichen, and spreads of moss. On windless days in the summer, butterflies tumble above rugs of thyme, restharrow and hawkweed.

Beaches and dune systems are ‘constructed’ features, formed by water and wind, and their shapes abide by the laws of natural mathematics. They are reminders that we live in a universe of patterns. It is on the coast that we see Nature’s numbers being deployed most elegantly. Mathematicians will tell you that the most striking mathematical patterns on earth are those that can be seen in the vast sand oceans of the Sahara and Arabia. Our beaches and dunes are the best places to see these patterns without resorting to a spacecraft or a camel. Pure, unvegetated dunes will get blown into a number of patterns, among them the barchan, dome dune, parabolic dune, star dune and wake dune. Beaches are galleries of mathematical patterns. Down on the tideline are symmetrical starfish and shells taking the form of geometric spirals. There are patterns of movement in your own footprints, in the scuttling of crabs, in the wingbeats of seabirds, and in the tides themselves. The regularity of waves is created by the flow of wind over water. The ripples in tidal sand are caused by the flow of fluid. The curve on a beach is caused by the refraction of waves as they squeeze between headlands.

Nature is a habitual sorter of stones, too, and over the last few thousand years, tides, currents and waves have brought order to the enormous swathes of glacial rubble left behind by the ice sheets. Most of the shingle beaches in Britain and Ireland are built from stone that was washed to the coast by the last surge of sea-level rise. On Chesil Beach in Dorset, the shingle has been sorted so that the stones are smaller in the west and larger in the east. On Slapton Beach, in South Devon, the sea has neatly sorted the beach into coarse sand and fine shingle. Both Chesil and Slapton are classic examples of a ‘barrier beach’ – a long bank of shingle thrown up parallel to the coastline, trapping a huge lagoon of brackish water. Chesil is Britain’s 17-mile giant, and the volume of shingle on the beach has been estimated at between 15 and 60 million cubic metres. In the age before air travel, Chesil was regarded as one of the wonders of the world: the 18th-century French traveller J. A. de Luc, was flabbergasted by ‘this prodigious accumulation of gravel’ and in 1902 Lord Avebury described the beach as ‘probably the most extensive and extraordinary accumulation of shingle in the world’. Actually, there are others, and in Britain, too.

On the Channel coast between Folkestone and Hastings is the largest shingle promontory in Europe; a great beak of stones jutting 6 miles into the sea. Technically, Dungeness is a ‘cuspate foreland’, a rare coastal feature that is created when waves approach a shore from two different directions, pushing up two spits whose tips eventually meet to form a gigantic triangle of shingle and sand. In the case of Dungeness, westerly waves sweeping up the English Channel meet easterly waves arriving from the Strait of Dover. Cuspate forelands are always on the move; in the case of Dungeness, slowly eastward.

My favourite foreland has itself become a ghost. At the outer bend of the Norfolk coast, there used to be a cuspate foreland called Winterton Ness. On Mercator’s 16th-century maps, it’s the only promontory on the smooth, curved coast of East Anglia. Winterton Ness used to be a crucial coastal landmark for sailors, and Daniel Defoe chose it for the opening shipwreck in Robinson Crusoe. But the Ness has gone, or almost. If you stand on the beach when the tide is running, you can still see its submerged outline, tripping a rank of standing waves.

It’s this eastern coast of Britain that has the best spits. No other coastal feature has such a capacity to maroon the human spirit. To stand alone on the tip of a spit is to feel the weight of the universe. Spits, like cuspate forelands, are two-dimensional and provisional. Their vertical dimension is imperceptible and they are prone to sudden demolition by storms. They’re formed by the process known as ‘longshore drift’, the movement of beach material along a shoreline as it is continually swept by waves breaking obliquely. Small spits often form at the mouths of estuaries, sometimes with hooked tips that embrace sheltered anchorages and tidal wetlands. But it’s the larger spits that are so other-worldly. The greatest of them all shadows the coast of Suffolk for 10 miles; a sinuous trail of glacial debris that has piled up in the millennia since sea levels stabilized. Orford Ness is the largest vegetated shingle spit in Europe. Scattered across it’s semi-desert surface are a litter of military peculiarities, but from the top of the lighthouse the spit itself has a pleasing simplicity; in its ribbed banks of vegetation you can trace successive spurts of growth. One night in 1703, half the spit was washed away by a storm. It simply grew back, like the tail of a lizard.

Spits and forelands are the coast’s oddest appendages, impermanent, ethereal places with unique human narratives. Their peculiar qualities of isolation suit those who seek seclusion: breeding birds, the military, criminals and vexed authors.

Until I saw the Severn Bore, I associated estuaries with tranquillity. I’ve seen Nature pull some amazing stunts: solar eclipses, double rainbows, Brocken spectres, the Northern Lights and so on, but the Severn’s party trick is in a coastal class of its own. Waves – as m