Nevada; in South America, on Curaçoa island, Venezuela; in the Antilles on Sombrero, St. Martins and Navassa islands. In Africa, in Algiers and Tunisia; in Europe, in Spain (Estremadura, one of the first deposits known), France, Belgium and the adjacent parts of Germany; in Bohemia and Galicia in Austria; and very extendedly in European Russia. Many islands of Oceanica supply phosphorites derived from the decomposition of bird guano by the coral limestone. Unfortunately the percentage of phosphate in a large proportion of these materials is not sufficiently high to make their conversion into water-soluble superphosphate economically possible at the present time; since all the calcic carbonate present must also be converted into comparatively worthless sulphate (gypsum) by the use of sulfuric acid; and as yet no practicable method for avoiding this difficulty has been found. “_Thomas Slag._”—Probably the nearest approach to such a method is indicated by the fact that a compound containing four instead of three molecules of lime to one of P₂O₅, such as is contained in the “Thomas slag” of the basic process of steel manufacture, is nearly or in some cases (“sour” soils) _quite_ as effective for the nutrition of plants as the water-soluble superphosphate. This discovery has rendered available for agricultural use the phosphoric acid contained in the enormous deposits of limonite iron ore known as bog ore, which contains a large proportion of ferric phosphate and from that cause has until lately been excluded from the manufacture of wrought iron and steel. It is reasonable to hope that by some analogous process the low-grade phosphorites, such as those of Nevada and the plains of Russia, will also in the course of time become available for agricultural use. Extremely fine grinding and washing (producing “floats”) has been resorted to for the purpose of rendering the raw phosphorites effective in fertilization. But while this is successful on some soils, on others the “floats” remain almost inert; so that this method has found only limited acceptance.