In the older formations the phosphates tend to become more and more mineralized by chemical processes. In whatever form they were originally deposited they often suffer complete or partial solution and are redeposited as concretionary lumps and nodules, often called copro/ites (q.v.). The "Challenger" and other oceanographic expeditions have shown that on the bottom of the deep sea concretions of phosphate are now gathering around the dead bodies of fishes lying in the oozes ; consequently the formation of the concretions may have been carried on simul taneously with the deposition of the strata in which they occur.
Important deposits of mineral phosphates are now worked on a large scale in the United States, the annual yield far surpassing that of any other part of the world. The most active operations are carried on in Florida, where the phosphate was first worked in 1887 in the form of pebbles in the gravels of Peace river. Then followed the discovery of "hard rock-phosphate," a massive min eral, often having cavities lined with nearly pure phosphorite. Other kinds not distinctly hard and consisting of less rich phos phatic limestone, are known as "soft phosphate": those found as smooth pebbles of variable colour are called "land pebble phosphate," whilst the pebbles of the river-beds and old river valleys, usually of dark colour, are distinguished as "river pebble phosphate." The land pebble is worked in central South Florida ; the hard rock chiefly between Albion and Bay City. In South Carolina, where there are important deposits of phosphate, f or merly more productive than at present, the "land rock" is worked near Charleston, and the "river rock" in the Coosaw river and other streams near Beaufort. The phosphate beds contain Eocene fossils derived from the underlying strata and many fragments of Pleistocene vertebrata such as mastodon, elephant, stag, horse, pig, etc. The phosphate occurs as lumps varying greatly in size, scattered through a sand or clay; they often contain phosphatized Eocene fossils (Mollusca, etc.). Sometimes the phosphate is found at the surface, but generally it is covered by alluvial sands and clays. Phosphate mining began in South Carolina in 1868, and for twenty years that state was the principal producer. Then the Florida deposits began to be worked. In 1892 the phosphates of Tennessee, derived from Ordovician limestones, came into the market. From North Carolina, Alabama and Pennsylvania, also, phosphates have been obtained but only in comparatiely small quantities. In 1900 mining for phosphates was commenced in Arkansas. In 1908 Florida produced 1,673,651 tons of phosphate
valued at 11 million dollars. All the other states together produce less phosphate than Florida, and among them Tennessee takes the first place with an output of 403,180 tons.
Algeria contains important deposits of phosphorite, especially near Tebessa and at Tocqueville in the province of Constantine. Near Jebel Kouif, on the frontier between Algeria and Tunis, there are phosphate workings, as also in Tunis, at Gafsa. The deposits belong to the Lower Eocene, where it rests unconf orm ably upon the Cretaceous. The joint production of Tunis and Algeria in 1927 was not less than 3,748,00o tons. Phosphates occur also in Egypt, in the desert east of Keneh and in the Dakla oasis in the Libyan desert.
France is rich in mineral phosphates, the chief deposits being the departments of the Pas-de-Calais, Somme, Aisne, Oise and Meuse, in the north-east, and another group in the departments of Lot, Tarn-et-Garonne and Aveyron, in the south-west ; phosphates occur also in the Pyrenees. The deposits near Caylus and in Quercy occupy fissures and pockets in Jurassic limestone, and have yielded a remarkable assemblage of the relics of Tertiary mam mals and other fossils. Phosphates occur in Belgium, especially near Mons, and these, like those of north-east France, are prin cipally in the Upper Chalk. Two varieties of phosphate rock are recognized in these districts, viz., the phosphatic chalk and the phosphate sand, the latter resulting from the decomposition of the former. Large and valuable deposits of the sand have been obtained in sinks and depressions on the surface of the chalk. The production is on the whole diminishing in Belgium (172,0o0 tons in 1927), but in France by this time it has become nearly, or very nearly, extinct.
In the Lahn district of Nassau (Germany) there are phosphate beds in Devonian rocks. The deposits were rich but irregular and local, and were much worked from 1866 to 1884, but are no longer of economic importance. In northern Estremadura in Spain and Alemtejo in Portugal there are vein deposits of phos phate of lime. As much as 200,000 tons of phosphate have been raised in these provinces, but in 1927 Spain was not mentioned in the list of producers. Large deposits of phosphate occur in Russia, and those in the neighbourhood of Kertch have attracted some attention; it is said that the Cretaceous rocks between the rivers Dniester and Volga contain very large supplies of phosphate, though probably of low grade.