[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). APPENDIX TO CHAPTER IX. NITRATE OF SODA. _Total Shipments from South America, 1830-1892._ Year. Tons. | Year. Tons. | Year. Tons. 1830 800 | 1870 131,400 | 1886 437,500 1835 6,200 | 1875 321,000 | 1887 680,600 1840 10,100 | 1880 217,300 | 1888 745,700 1845 16,800 | 1881 344,600 | 1889 930,000 1850 22,800 | 1882 477,800 | 1890 1,030,000 1855 41,800 | 1883 572,400 | 1891 790,000 1860 55,200 | 1884 540,900 | 1892 790,000 1865 109,000 | 1885 423,100 | The following tables exhibit the total imports into Europe, and into the United Kingdom from the years 1873-92:-- NITRATE OF SODA, 1873-1892. _Imports into Europe._ _Imports into United Kingdom._