The coastal range in northern Chile rises abruptly from the ocean floor. Between this range and the lower slopes of the Andes lies a desert, or pampa, varying in elevation from 4000 to 9000 feet above sea level. The nitrate-bearing lands lie mainly along the western side of this desert on the eastern slopes of the coastal range, not in a continuous strip, but intermittently over an irregular belt some 400 miles long from north to south, and 5 to 40 miles wide. The deposits actually worked are at elevations between 4000 and 7500 feet and are grouped in five main fields inland from the ports of Iquique, Tocopilla, Antofagasta, and Taltal. The sodium nitrate, along with other soluble salts, occurs for the most part as a cementing material in the outwash sands and gravels which form the eastern slopes of the coastal range. At the lower edges of the slopes the nitrate deposits in some places extend and merge with ordinary salt deposits lying in shallow undrained basins. Read further which technologies were applied to extra and purify the first nitrogen fertilizers.