Winter had bleached the landscape. A uniform white carpet coated the moors and fells, broken only by the greys and blacks of stone walls and the browns of hedge- and tree-skeletons. Ground and sky merged at the tops of the hills, snow white to snow cloud. I was driving along a narrow road with the heater going full blast. But I still felt cold. It was that sort of depressing day at the end of January.
   I had driven past the vision before it registered as remarkable. My double-take was delayed because I was concentrating on the road, trying to anticipate sheets of ice in the hard-packed snow. I braked to a careful halt and looked back to confirm my impression. It was still there, like a rent in the snowy blanket that flopped down the hill and out onto the ice at the edge of the reservoir. I could see a green patch which was devoid of white; apart from the handful of sheep nibbling industriously at the exposed grass.
   I told myself that the farmer had cleared the irregular oval. But if he had, what had he done with the snow? He hadn't carted it away because I couldn't see any tyre tracks. I must have spent five minutes chewing over the problem. Then I realized that I would be late for a meeting. I was driving from the firm's headquarters to a branch office about thirty miles away. Curiosity would have to wait.
   Snow fell during the night, as it had on every day that week. Wrapped up in wind- and waterproof clothing, I set off for the moorland road at the end of the morning. The green patch was still there despite the fresh snow. I turned right onto a wind-scoured road, towards the banks of the reservoir. A thaw in the middle of the month had unblocked burst mains by the score. There had even been talk of imposing drought regulations; until the weather had taken a turn for the worse and re-frozen most of the leaks. Even so, the water level was very low and I could see an unaccustomed island in the distance.
   I tugged on a pair of wellingtons and braved the snow. The wind rushing off the reservoir had piled it into ski-jump drifts against every obstruction. I struggled to a gap where holiday vandals had demolished part of a dry-stone wall. My tracks made it painfully obvious that someone had been trespassing on the farmer's land. But if the half-dozen sheep were prepared to keep quiet about my visit, so was I.
   The transition between white and green had seemed quite distinct from the road. It became a diffuse merging on the ground. No other human had approached the spot either on foot or in a vehicle. I had been thinking about under-soil heating experiments. But the snow-free area was so irregular and so far from a power source that it had to be a natural phenomenon. I crouched down and prodded at the ground with a finger. It was quite firm, but definitely not frozen. The sheep eyed me suspiciously. Baffled, I returned to my car.
   Two miles further on, where the road snaked forward again along the next valley, I came to a mixture of old and modern houses seasoned with a few shops and a pub called The Barley Mow. I turned onto a rutted car park in search of warmth, lunch, and information.
   The pub wasn't exactly crowded. I bought food and a half pint, and mentioned the green patch. The landlord had plenty of time to tell me that it had been known as the Devil's Acre since the Middle Ages. He looked ancient enough to have been present at the naming ceremony. Another old boy added that the witches had been burnt there in the Sixteenth and Seventeenth Centuries.
   The site was cursed; but not with the usual business about grass never growing again. One of the witches had vowed that snow would never linger there as a demonstration of the power of the Dark Lord.
   It was a good story. I listened with an air of studied scepticism. Then the landlord drew my attention to a framed newspaper cutting, which was hanging between a couple of routine watercolour landscapes. Intrigued by the legend, a local historian had spent part of the previous winter ploughing through ancient church records from the Town In The Valley; the one drowned at the bottom of the reservoir.
   He had found evidence of a witch trial in the sixteen-forties, and indications that Matthew Hopkins, the infamous Witchfinder General, had been present. And there had been three human bonfires on the hill above the town.
   The records also contained references to curses in the dying shrieks of the three alleged witches. One of then had predicted a catastrophe in the near future. She was only about three hundred and twenty years out if she had been screaming about the flooding of the valley. But it was the sort of prediction that was bound to come true eventually. The town's register of deaths showed that about 50% of the population had been wiped out a few years later by an offshoot of the Great Plague of London. And fire and flood had taken their toll over the years.
   Another witch, according to the historian, had promised that the Evil One would create a monument to them. I found a patch of snow-free grass on the site of the burning a pretty impressive coincidence.
   Fascinated, I went for a look at the historian's source material, which is housed in the museum, not five minutes' walk from my office. Somebody had gone to the trouble of making typed transcripts of the ancient records, thus saving me a struggle with eccentric spelling and curly handwriting. I spent most of Monday's lunch hour prowling through a bound volume of transcripts; but I failed to find a single reference to the Devil's Acre.
   In the afternoon, I mentioned the Devil's Acre to a colleague. To my surprise, he laughed and asked me when I had called in at the Barley Mow. The gang at the pub had kept quiet about a sequel to the newspaper story. Some spoilsport had revealed that the historian had been a victim of a local tradition; one which had been created in that very watering hole by the current crop of regulars.
   My colleague was amused to hear that they were still trotting out their tale for the I benefit of unwary travellers like myself. I assumed that he had been caught in the same way. He told me that the snow-free area was about two years old, and lay the best part of a mile from the real site of the witches' executions. The gullible historian had been guilty of distorting inconvenient facts in his eagerness to uncover the historical basis of the legend.
   I experienced a sudden rush of retrospective doubt, which would not have been released had my colleague not cast the first stone. It became clear on the instant that the links between recorded history and the interpretation were very tenuous. A very persuasive argument crumbled away at the first mistrustful tappings. Fortunately, I was not too deeply committed to save face by pretending continuous scepticism.
   The Devil's Acre was growing. It had started life as a small tennis court. This year, it was half the size of a football pitch and a closer match to its name. An amateur geologist, a keen student of Open University television programmes, had suggested that there was a geothermal source relatively close to the surface. Translated into English, this meant that hot rocks were heating underground water, and steam was percolating up to the surface and preventing the soil around the vent from freezing.
   It was a good story, but one which could be substantiated; if the farmer who owned the land could be talked round. He had lost little squares of his territory to electricity pylons. Local conservationists had prevented him from clearing a patch of scrub and woodland to increase the effective area of his farm. And when a trespasser with a metal detector had found some Roman coins in one of his fields, he had been forced to stand guard over his potatoes to protect them from marauding treasure-hunters. In his experience, outsiders were pure trouble. And I was not surprised to hear that the farmer had set his dogs on the last person to ask permission to drill exploratory boreholes on his land.

I made one more trip to the branch office before the snow melted. I was quite surprised to see two men using a theodolite and a measuring pole in the field by the reservoir, charting the Devil's Acre. Two others were banging large wooden tent pegs into the ground around its perimeter. I concluded that they had convinced the farmer, somehow, that he would benefit from their limited investigation. And they weren't creating much of a nuisance. The field could be used only as grazing land. Several inconvenient hollows and the gentle slope made it unsuitable for mechanical cultivation. And the sheep wouldn't be inconvenienced by a few tent pegs.

We had no more snow that winter. I continued to use the moorland road for my trips to the branch office. The false legend and an irregular row of tent pegs reminded me of the curious hot spot every time I passed the field and the pub called The Barley Mow.
   Some of the pegs disappeared in the summer. According to an indignant letter in the local paper, irresponsible anglers were borrowing them for rod rests. This provoked an outraged reply from the angling lobby; which didn't stop more pegs disappearing. But the patient surveyors kept returning every so often to bang in replacements.

The second snow of the following winter fell on December tenth, a Thursday. I made a trip out to our branch office the next day. Four surveyors were hard at work in a shallow steam-bath when I stopped on the road above the Devil's Acre. They were ankle-deep in vapour, which was oozing out of the ground and trying to roll uphill, driven by the icy wind off the reservoir. An outer ring of pegs wearing triangular yellow flags showed a year's growth of the hot spot. Through gaps in the mist, I noted that it was only about three or four feet wider than the region enclosed by the previous winter's pegs, but a good fifteen yards longer at either end.
   I drove on, wondering whether the area was fated to become a winter tourist attraction, full of hot springs and geysers in the snow, like a southern clone of Iceland. Perhaps the farmer was thinking about his own private power plant; something to run his milking machines if he had a dairy herd, and to charge the batteries of a flock of modern electric sheep.
   I made the return journey in the early afternoon in a lull between light falls of snow. As soon as the road had taken me round a hill and into sight of the reservoir, I noticed that the level was very low. No doubt water mains had been popping and freezing again.
   I stopped to look at the gulls' island. They were squabbling on the top of the church tower. The Town In The Valley had raised a periscope for the second time since the drought of 1976, which had dried the reservoir to a pond in a set of mud flats, and revealed parts of the sunken town in all their decaying glory. Looking up the road, I could just see the Devil's Acre, which was steaming quite vigorously.
   The surveyors had gone. One of them had been wearing a distinctive orange anorak, which had made him highly visible. And their dark blue van was no longer causing an obstruction at the side of the road. I decided that I had enough time in hand for a closer look at the hot-spot. But just as I was reaching for the handbrake, a hurricane blast of air and sound engulfed the car.
   Whiteness coated the windows. My seat-belt dug into me as the car leapt sideways. Then came a teeth-rattling impact. The wipers scraped a path through the packed snow on my windscreen. My car had turned a full circle on its wheels before crashing backwards into something solid. I was still aimed at the Devil's Acre and the immense mushroom cloud sprouting from an enormous crater.
   My first thought was: 'They've dropped the Bomb!' Followed by: 'Why here?' I felt rather than heard a violent concussion. Then the sky fell onto my car. The roof buckled under a succession of hammer blows. Glass fogged and shattered. I wrapped my face in my arms and waited for the end.
   Deafened and terrified, I sat through a long period of calm before escaping through the windscreen. Both of the car's doors were jammed solidly shut. I shook chips of glass out of my hair and clothing. The road was strewn with rock fragments and earth. A chunk of black rock the size of a pillar-box had landed just six feet from my front bumper. The car was a twisted, glassless heap, showing more bare metal than green paint.
   Heavy mist was boiling from a vast crater on the reservoir side of the road and the mushroom had battered its head through the clouds. There are times when you wish you had a camera handy, even though you know your hands are shaking too badly to take a decent picture.
   An expedition from the Barley Mow arrived to find me still staring at the mushroom's stem. Next came a group of space-suited army officers in a helicopter. We civilians stood about grinning as they played with their Geiger counters.
   It couldn't have been a nuclear explosion. We knew that the fire-ball of an H-bomb would have wiped the lot of us out in the first fraction of its first second. But we felt reassured when the army failed to detect more than normal background radiation.
   There was a sulphurous stink in the air which had started us thinking about volcanoes. Perhaps we had just witnessed a mini Mount St. Helens in action. But it took an expert from the Coal Board to solve the mystery, not a vulcanologist. Sharp-edged pieces of black rock littered the area. They were bits of coal.
   According to the expert, spontaneous combustion had taken place in a Victorian shaft to one of the veins which thread the area. A central heating system powered by gently smouldering coal had been responsible for melting the snow in the Devil's Acre. It was probable that the action of frost had widened a fissure in the rock and improved the supply of air to the fire. Underground water had been heated more fiercely. And the whole affair had exploded like a pressure cooker with a jammed safety valve. Fortunately, it had blown straight upwards. I had been caught by just the fringes of the blast.
   It would be a good story to tell the firm's insurance company when we put in a claim for the wreck of my car, I concluded. Not many get written off by a shower of coal! But the loss adjuster would have to be quick off the mark if he wanted to see the missiles that had done the damage. Leaving the scene in a police car, an hour or so after the explosion, I noticed enterprising locals organizing sacks and transport to take away stocks of free winter fuel, courtesy of the Devil's Acre. ■