esearches 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._

Year. Tons. | Year. Tons.
1873 225,000 | 1873 124,000
1874 230,000 | 1874 108,200
1875 280,000 | 1875 164,900
1876 300,000 | 1876 166,800
1877 208,000 | 1877 69,600
1878 250,000 | 1878 104,400
1879 205,000 | 1879 55,300
1880 140,000 | 1880 48,300
1881 230,000 | 1881 54,800
1882 335,000 | 1882 96,000
1883 440,000 | 1883 103,700
1884 505,000 | 1884 103,700
1885 380,000