Page:Popular Science Monthly Volume 83.djvu/215

Rh has been worked looks as though it had been badly furrowed by gigantic ploughshares. In other places, there is almost no overlying material to remove. The layer of caliche may be as much as six feet thick, but for the most part it varies between one and three feet. The beds in some sections are fairly continuous over large areas; in others they are of very limited extent. Some caliche contains more than 70 per cent, of nitrate, but 50 to 60 per cent, is considered high; the average is nearer 20 to 30 per cent., and even as low as 15 per cent. is. worked profitably. Hence the conditions of production, costs of operation and profits to be made vary widely from place to place. With few exceptions, however, it is true that the costs of operation are low as compared with many other mining industries, while the profits are large.

The main nitrate fields lie in two provinces, Tarapaca and Antofagasta, between latitudes 19° S. and 27° S. Other deposits doubtless will be found farther south in Atacama, and there are said to be small nitrate areas in Tacna, the most northerly province of Chile. The total area of these four provinces (105,000 square miles) is about equal to that of Colorado and its population (316,000) gives about two per square mile. Most of the people depend directly or indirectly on the nitrate industry. Chileans are the most numerous, but there are also many Bolivians and Peruvians, with smaller numbers of people from half the nations of the world. Only small parts, probably much less than 10 per cent., of the provinces named are workable nitrate lands. These limited areas, together with the seaport cities, contain the mass of the population, while many thousands of square miles contain not a living soul nor any other living thing.

The nitrate beds lie in a belt, commonly less than ten miles wide, about 500 miles long north and south, and 15 to 100 or more miles back from the coast. This short distance from the coast is important in making shipment cheap. Along the coast there is a range of low mountains through which a few ravines offer routes for railroads into the interior. Between the Coast Mountains and the base of the towering Andes lies lower land, known as the pampa, which slopes westward from the Andes to the Coast Ranges. The nitrate deposits lie along the western side of the pampa, its lowest part, associated with what were once the bottoms of water-filled basins, either lakes or arms of the sea. Lines of flats, covered with dazzling white salt beds, or salares, extend over many square miles. Thus one salt field in Tarapacá covers an area of more than 100 square miles, and salt of remarkable purity (over 99 per cent, pure) is said to extend to depths of scores of feet. Round about these salares are the nitrate lands or salitreras. In many parts of the region there is a saying: "Where there is salt there is no caliche." Though this saying holds true generally, there are some places where the two deposits occur together. The presence of nitrate, however, is easily determined. In a manner much like that of using flint and steel