FOOTNOTES:
[202] This substance is also largely known under the name Chili saltpetre, to distinguish it from potassium nitrate or common saltpetre.
[203] See Appendix, p. 351.
[204] We may remind our readers that these nitrate deposits were largely the cause of the late war between Chili and Peru, which resulted in the cession to Chili by Peru of the province of Tarapaca, where the most important deposits are situated.
[205] The other nitrate deposits are found in the provinces of Antofagasta and Atacama, and a certain amount of the refined article is exported from these places. The amount, however, is inconsiderable as compared with that which comes from the province of Tarapaca.
[206] See his elaborate article on the Geology of Bolivia and Peru, published in the 'Quarterly Journal of the Geological Society' for November 1860.
[207] The source of the boracic acid is probably volcanic.
[208] A friend of the present writer, who has visited this part of the west coast of South America, informs him that at one point of the coast at Mejillones (in Bolivia) he could trace the remains of no fewer than twelve distinct sea-beaches, situated at different distances from the sea, and rising to an altitude of 2500 feet.
[209] In this change, lime derived from the sea-shells would play an important part. Modern researches have shown, as we have already said in a previous chapter, that, in the conversion of organic nitrogen into nitrates, the presence of carbonate of lime is a necessary condition.
[210] The Gulf weed is an instance in point. Huge masses of floating sea-weed are sometimes found, 500 to 600 miles in length, forming the so-called Saragossa Sea.
[211] A difficulty which has not been referred to is the belief entertained by geologists that "there has been a change of climate in Northern Chili, and that there must have been more rain there formerly than there is at present. Traces of human habitations are found high up in the Cordilleras to-day. Cobs of Indian corn, axes and knives of copper tempered to exceeding sharpness, arrow-heads of agate, even pieces of cloth, are dug up in arid plains now without any trace of water for many leagues in or around them" (Russell, 'The Nitrate-Fields of Chili,' p. 290).