Under the sand of this desert, which drifts before the wind like snow, nature has laid the bed of nitrate. No one knows how it was formed, and man has not attempted to measure its extent. The sand is first shovelled off, and then a crust of sun-baked clay from four to twelve inches thick is removed. This discloses a bed of white material that looks like melting marble, full of moisture, and is as soft as cheese. The strata is often four or five feet thick, and averages two or three feet. It is broken up by crow-bars and shovelled into carts, then taken to crushers, which grind it up into particles as large as pebbles. These are lifted by elevators into great vats, where it is boiled until dissolved in ordinary sea-water. Then the solution is run off into a series of shallow iron vats exposed to the air, which, being moistureless, and heated by constant sunshine, causes rapid evaporation. The salt from the water mixed with the nitrate causes crystallization, and after a certain period of exposure to the air and sun the vats are found to be covered upon the bottom and sides with white sparkling crystals, like alabaster, under a yellowish liquor. This liquor is carefully drawn off, for it is even more valuable than the saltpetre, and is conducted by pipes to another crucible, where it is boiled and chemically treated until it produces the iodine of commerce, useful for a hundred medical and chemical purposes, and costing as much per ounce as the saltpetre brings per hundred-weight. The liquor having been withdrawn, the saltpetre is shovelled upon drying-boards, where it is exposed to the sun for a while, then put into bags and shipped to Europe and America. It is graded like wheat and corn, according to quality. The highest grade goes to the powder-mills, the next to the chemical works, and the third to the fertilizer factories, where it is made into manure. The iodine is packed in little casks, and covered with green hides, which shrink with drying until they are as tight as a drum-head, and keep out moisture. It was these nitrate of soda deposits that caused the late war between Chili and Peru.