A group of three small islands 12 miles off the southwest coast of Peru. North Island is the largest. The Islands are composed of granite cliffs, worn into many caves and hollows that make ideal nesting places for sea birds. Consequently, the islands became covered with guano, the droppings of sea birds that collected over many years' time. In 1840 the Peruvian government began to export guano, which was used for fertilizer. The supply was exhausted by 1874.