At fifty he was still a big, powerful man, large-boned and strong as an ox. His hands were enormous, chipped and scarred by years in the mines. He ran one of them through his wild, crinkly gray hair and with the other stubbed out the cigarette in the damp red earth beneath the cot. It was lighter now; soon it would be dawn. He could hear his cook blowing on the beginnings of a fire on the other side of the clearing.

Mulrooney called himself a mining engineer, although he had no degree in mining or engineering. He had taken a course in both and added what no university could ever teach — twenty-five years of hard experience. He had burrowed for gold on the Rand and copper outside Ndola; drilled for precious water in Somaliland, grubbed for diamonds in Sierra Leone. He could tell an unsafe mineshaft by instinct, and the presence of an ore deposit by the smell. At least that was his claim, and after he had drunk his habitual twenty bottles of beer in the shanty town of an evening, no one was going to argue with him. In reality, he was one of the last of the old prospectors. He knew ManCon gave him the little jobs, the ones in the deep bush, the wild country that was miles from civilization and still had to be checked out, but he liked it that way. He preferred to work alone; it was his way of life.

The latest job had certainly fulfilled these conditions. For three months he had been prospecting in the foothills of the range called the Crystal Mountains in the hinterland of the republic of Zangaro, a tiny enclave on the coast of West Africa.

He had been told where to concentrate his survey, around the Crystal Mountain itself. The chain of large hills, curved hummocks rising to two or three thousand feet, ran in a line from one side of the republic to the other, parallel to the coast and forty miles from it. The range divided the coastal plain from the hinterland. There was only one gap in the chain, and through it ran the only access to the interior, a narrow dirt road, baked like concrete in summer, a quagmire in winter. Beyond the mountains, the natives were the Vindu, a tribe of almost Iron Age development, except that their implements were of wood. He had been in some wild places but vowed he had never seen anything as backward as the hinterland of Zangaro.

Set on the farther side of the range of hills was the single mountain that gave its name to the rest. It was not even the biggest of them. Forty years earlier a lone missionary, penetrating the hills into the ulterior, branched to the south after following the gap in the range and after twenty miles glimpsed a hill set aside from the rest. It had rained the previous night, a torrential downpour, one of the many that gave the area its annual rainfall of three hundred inches during five soaking months. As the priest looked, he saw that the mountain seemed to be glittering in the morning sun, and he called it the Crystal Mountain. He noted this in his diary. Two days later he was clubbed and eaten.

The diary was found by a patrol of colonial soldiers a year later, being used as a juju by a local village. The soldiers did their duty and wiped out the village, then returned to the coast and handed the diary to the mission society. Thus the name the priest had given to the mountain lived on, even if nothing else he did for an ungrateful world was remembered. Later the same name was given to the entire range of hills.

What the man had seen in the morning light was not crystal but a myriad of streams caused by the water of the night’s rain cascading off the mountain. Rain was also cascading off all the other mountains, but the sight of it was hidden by the dense jungle vegetation that covered them all, like a chunky green blanket when seen from afar, which proved to be a steaming hell when penetrated. The one that glittered with a thousand rivulets did so because the vegetation was substantially thinner on the flanks of this hill. It never occurred to the missionary, or to any of the other dozen white men who had ever seen it, to wonder why.

After three months living in the steaming hell of the jungles that surrounded Crystal Mountain, Mulrooney knew why.

He had started by circling the entire mountain and had discovered that there was effectively a gap between the seaward flank and the rest of the chain. This set the Crystal Mountain eastward of the main chain, standing on its own. Because it was lower than the highest peaks to seaward, it was invisible from the other side. Nor was it particularly noticeable in any other way, except that it had more streams running off it per mile of hillside than ran off the other hills, to north and south.

Mulrooney counted them all, both on the Crystal Mountain and on its companions. There was no doubt of it. The water ran off the other mountains after rain, but a lot of water was soaked up in the soil. The other mountains had twenty feet of topsoil over the basic rock structure beneath, the Crystal Mountain hardly any. He had his native workers, locally recruited

Vindu, bore a series of holes with the augur he had with him, and confirmed the difference in depth of the topsoil in twenty places. From these he would work out why.

Over millions of years the earth had been formed by the decomposition of the rock and by dust carried on the wind, and although each rainfall had eroded some of it down the slopes into the streams, and from the streams to the rivers and thence to the shallow, silted estuary, some earth had also remained, lodged in little crannies, left alone by the running water, which had bored its own holes in the soft rock. And these holes had become drains, so that part of the rainfall ran off the mountain, finding its own channels and wearing them deeper and deeper, and some had sunk into the mountain, both having the effect of leaving part of the topsoil intact. Thus the earth layer had built up and up, a little thicker each century or millennium. The birds and the wind had brought seeds, which had found the niches of earth and flourished there, their roots contributing to the process of retaining the earth on the hill slopes. When Mulrooney saw the hills, there was enough rich earth to sustain mighty trees and tangled vines which covered the slopes and the summits of all the hills. All except one.

On this one the water could not burrow channels that became streams, nor could it sink into the rock face, especially on the steepest face, which was to the east, toward the hinterland. Here the earth had collected in pockets, and the pockets had produced clumps of bush, grass, and fern. From niche to niche the vegetation had reached out to itself, linking vines and tendrils in a thin screen across bare patches of rock regularly washed clean by the falling water of the rain season. It was these patches of glistening wet amid the green that the missionary had seen before he died. The reason for the change was simple: the separate hill was of a different rock from the main range, an ancient rock, hard as granite as compared to the soft, more recent rock of the main chain of hills.

Mulrooney had completed his circuit of the mountain and established this beyond a doubt. It took him a fortnight to do it and to establish that no less than seventy streams ran off the Crystal Mountain. Most of them joined up into three main streams that flowed away eastward out of the foothills into the deeper valley. He noticed something else. Along the banks of the streams that came off this mountain, the soil color and the vegetation were different. Some plants appeared unaffected; others were stunted or nonexistent, although they flourished on the other mountains and beside the other streams.

Mulrooney set about charting the seventy streams, drawing his map as he went. He also took samples of the sand and gravel along the beds of the streams, starting with the surface gravel, then working down to bedrock.