At our feet the sea hissed, the waves running like serpents between the rocks.

‘The storm certainly came up suddenly,’ I commented. ‘I managed to shelter in the cave.’ I pointed to the cliff top two hundred feet above us. ‘You must have a magnificent view of the sea. Do you live up there?’

Her white skin was like ancient pearl. ‘I live by the sea,’ she said. Her voice had a curiously deep timbre, as if heard under water. She was at least six inches taller than myself, although I am by no means a short man. ‘You have a beautiful shell,’ she remarked.

I weighed it in one hand. ‘Impressive, isn’t it? A fossil snail — far older than this limestone, you know. I’ll probably give it to my wife, though it should go to the Natural History Museum.’

‘Why not leave it on the beach where it belongs?’ she said. ‘The sea is its home.’

‘Not this sea,’ I rejoined. ‘The Cambrian oceans where this snail swam vanished millions of years ago.’ I detached a thread of fucus clinging to one of the spurs and let it fall away on the air. ‘I’m not sure why, but fossils fascinate me — they’re like time capsules; if only one could unwind this spiral it would probably play back to us a picture of all the landscapes it’s ever seen — the great oceans of the Carboniferous, the warm shallow seas of the Trias..

‘Would you like to go back to them?’ There was a note of curiosity in her voice, as if my comments had intrigued her. ‘Would you prefer them to this time?’

‘Hardly. I suppose it’s just the nostalgia of one’s unconscious memory. Perhaps you understand what I mean — the sea is like memory. However lost or forgotten, everything in its exists for ever…’ Her lips moved in what seemed to be the beginnings of a smile. ‘Or does the idea seem strange?’

‘Not at all.’

She watched me pensively. Her robe was woven from some bright thread of blue silver, almost like the hard brilliant scales of pelagic fish.

Her eyes turned to the sea. The tide had begun to come in, and already the pool where I found the shell was covered by the water. The first waves were breaking into the mouth of the cave, and the ledge we stood on would soon be surrounded. I glanced over my shoulder for any signs of the cliff path.

‘It’s getting stormy again,’ I said. ‘The Atlantic is rather bad-tempered and unpredictable — as you’d expect from an ancient sea. Once it was part of a great ocean called—’

‘Poseidon.’

I turned to look at her.

‘You knew?’

‘Of course.’ She regarded me tolerantly. ‘You’re a school-master. So this is what you teach your pupils, to remember the sea and go back to the past?’

I laughed at myself, amused at being caught out by her. ‘I’m sorry. One of the teacher’s occupational hazards is that he can never resist a chance to pass on knowledge.’

‘Memory and the sea?’ She shook her head sagely. ‘You deal in magic, not knowledge. Tell me about your shell.’

The water lifted towards us among the rocks. To my left a giant’s causeway of toppled pillars led to the safety of the upper beach. I debated whether to leave; the climb up the cliff face, even if the path were well cut, would take at least half an hour, especially if I had to assist my companion. Apparently indifferent to the sea, she watched the waves writhing at our feet, like reptiles in a pit. Around us the great cliffs seemed to sink downward into the water.

‘Perhaps I should let the shell speak for itself,’ I demurred. My wife was less tolerant of my tendency to bore. I lifted the shell to my ear and listened to the whispering trumpet.

The helix reflected the swishing of the waves, the contours of the shell in some way magnifying the sounds, so that they echoed with the darker murmur of deep water. Around me the breakers fell among the rocks with a rhythmic roar and sigh, but from the shell poured an extraordinary confusion of sounds, and I seemed to be listening not merely to the waves breaking on the shore below me but to an immense ocean lapping all the beaches of the world. I could hear the roar and whistle of giant rollers, shingle singing in the undertow, storms and typhonic winds boiling the sea into a maelstrom. Then abruptly the scene seemed to shift, and I heard the calm measures of a different sea, a steaming shallow lagoon through whose surface vast ferns protruded, where half-submerged leviathans lay like sandbanks under a benign sun My companion was watching me, her high face lifted to catch the leaping spray. ‘Did you hear the sea?’

I pressed the shell to my ear. Again I heard the sounds of ancient water, this time of an immense storm in progress, a titanic struggle against the collapsing isthmuses of a sinking continent. I could hear the growling of gigantic saurians, the cries of reptile birds diving from high cliffs on to their prey below, their ungainly wings unshackling as they fell.

Astonished, I squeezed the shell in my hands, feeling the hard calcareous spines as if they might spring open the shell’s secret.

The woman still watched me. By some freak of the fading light she appeared to have grown in height, her shoulders almost overtopping my head.

‘I… can’t hear anything,’ I said uncertainly.

‘Listen to it!’ she admonished me. ‘That shell has heard the seas of all time, every wave has left its echo there.’

The first foam splashed across my feet, staining the dried straps of my sandals. A narrowing causeway of rocks still led back to the beach. The cave had vanished, its mouth spewing bubbles as the waves briefly receded.

I pointed to the cliff. ‘Is there a path? A way down to the sea?’

‘To the sea? Of course!’ The wind lifted the train of her robe, and I saw her bare feet, seaweed wreathed around her toes. ‘Now listen to the shell. The sea is waking for you.’

I raised the shell with both hands. This time I closed my eyes, and as the sounds of the ancient wind and water echoed in my ears I saw a sudden image of the lonely bay millions of years earlier. High cliffs of white shale reached to the sky, and huge reptiles sidled along the coarse beaches, baying at the grotesque armoured fish which lunged at them from the shallows. Volcanic cones ringed the horizon, their red vents staining the sky.

‘What can you hear?’ my companion asked me insistently, evidently disappointed. ‘The sea and the wind?’

‘I hear nothing,’ I said thickly. ‘Only a whispering.’

The noise erupted from the shell’s mouth, the harsh bellows of the saurians competing with the sea. Suddenly I heard another sound above this babel, a thin cry that seemed to come from the cave in which I had sheltered. Searching the image in my mind, I could see the cave mouth set into the cliff above the heads of the jostling reptiles.

‘Wait!’ I waved the woman away, ignoring the waves that sluiced across my feet. As the sea receded, I pressed my ear to the conch, and heard again the faint human cry, a stricken plea for rescue — ‘Can you hear the sea now?’ The woman reached to take the shell from me.

I held to it tightly and shouted above the waves. ‘Not this sea! My God, I heard a man crying!’

For a moment she hesitated, uncertain what to make of this unexpected remark. ‘A man? Who, tell me! Give it to me! It was only a drowned sailor!’

Again I snatched the shell away from her. Listening, I could still hear the voice calling, now and then lost in the roar of the reptiles. A sailor, yes, but a mariner from the distant future, marooned millions of years ago in this cave on the edge of a Triassic sea, guarded by this strange naiad of the deep who even now guided me to the waves.

She had moved to the edge of the rock, the strands of her hair shimmering across her face in the wind. With a hand she beckoned me towards her.

For the last time I lifted the shell to my ear, and for the last time heard that faint plaintive cry, lost on the reeling air.

‘H-h-e-e-lp!’