On the other hand, the Caceres mines are more important at present, and form the chief competitors with Carolina phosphate in the English market. From 1866 to October 1875, the principal company at Caceres had furnished about 125,000 tons, receiving 8-14s. a ton, according to quality, for the rock at the mines. The cost of transport to Lisbon amounts to about 32s. a ton. Analyses of the mineral show bone phosphate of lime averaging 60-65 per cent. The total recent production has been about 25,000 tons yearly. Most of it comes to England, France consuming only a few thousand tons, and Spain itself none at all.
Phosphates.—Under the head of "phosphates," are included the remaining known phosphatic minerals, save a few non-nitrogenous guanos, which, however, resemble the Peruvian piano in little besides name. The best known phosphates are those occurring in pockets or patches in lime stone formations in France (Bordeaux), Germany (Nassau), and Carolina ; less important are the Russian and Bukowina varieties ; while immense quantities are derived from the West Indian islands of Sombrero, Navassa, Maracaibo, St. Martin's, Curacao, Oruba, and Pedro Keys. Besides the preceding, which are all phosphates of lime, there are two varieties of phosphate of alumina, known as Redonda and Alta Vela.
The French phosphate is raised in the departments of Lot and Tarn-et-Garonne, and is shipped to this country in large quantities from Bordeaux. It exists in fissures and cavities in the lime stone, varying much in size and shape, whose whereabouts is generally indicated by outcropping threads of the mineral. It seems to be an aqueous deposit, and is sometimes found at but a short depth beneath the surface, in thin layers, underlying alluvial soils, which also contain a large pro portion of phosphates, associated with iron and other impurities. This surface layer is unfit for manufacture, but is used on the spot in a raw condition. The appearance, quality, and texture of the mineral vary considerably. The richest specimens are hard, of white colour, and break with an earthy fracture. The bulk of it is harder and more compact, of a dark-yellow or brown tint, con taining about 70 per cent. of phosphate ; while some that is raised is of still poorer quality, dark agate coloured, of waxy lustre, and seamed with veins of oxide of iron. This last has no important commercial value. The beds are principally in English bands. The best sorts, containing 70-80 per cent. of phosphate, and very free from oxide of iron and alumina, form superior manures; but as the phosphate decreases, the iron, &c., increase, so that the low grades are worthless for
manufacturing purposes. The standard of the commercial article varies as follows :—Tribasio phosphate of lime, 50-80 per cent. ; carbonate of lime, 8-157 ; iron, alumina, fluorides, &c., 4-13 ; siliceous matters, 27-19.
The phosphorites of the south occur in the three departments of Tarn-et-Garonne, Lot, and Aveyron. Fig. 932 shows a geological section of the bed as met with at Caylus (Tarn-et-Garonne): a, red clay ; b, Jurassic limestone ; c, phosphorites. These phosphorites are enclosed in cavities, resulting from the upheaval of the Jurassic formation, and are supposed to have been produced by the infiltration of phosphated water, and the subsequent evaporation of the water. The mode of occurrence of the phosphatic nodules of the Tun series, worked at Lezennes, in the department of Nord, is shown in Fig. 933: a, Tertiary sands ; b, chalk ; c, freestone ; d, phosphates of the Tun series, in green chalk ; e, chalk and flints. The phosphate beds at Mans, in Maine, occur as shown in Fig. 934 : a, yellow sand in inclined beds ; b, sand and sandstone blocks ; c, foliaceous clay ; d, sand and sandstone blocks, with nodules of phosphate ; c, yellow sandstone. In the Ardennes, Orne, Eure - et - Loire, and Perche, phosphatic beds are found in the Gaize. A geological section of that of Caen (Orne) is shown in Fig. 935 : a, siliceous clay ; I, chalk containing pecten and asper fossils ; c, Gaize, beds of nodules; d, astarte limestone. Nodular phosphates in the Gault are abundant in the departments of Ardennes, Pas-de.Calais, Meuse Aube, Haute-Marne, Yonne, Marne, Isere, Daubs, Haute-Sa6ne, and Alpes-Maritimes. At Wessant (Pas•de-Calais), they present a section as shown in Fig. 936: a, disturbed ground ; b, small phosphatic bed ; c, Gault lirnestono ; d, bad of phosphatic nodules ; c, green sand ; f, green sandstone ; g, pebbles ; h, river. The phosphate of lime of the Lower Oolite occurs at St. Vigor (Calvados) as shown in Fig. 937: a, disturbed ground ; b, white oolite ; c, ferruginous oolite ; d, beds of phosphatic nodules ; e, bed of phosphate of lime; f, millstone grit ; g, bed of flints ; h, millstone grit. At Poilld (Sarthe), the nodular phosphates of the Lias present the section indicated in Fig. 938: a, Tertiary sands ; b, siliceous clay ; c, marl, and Upper Lies limestone; d, phosphate bed ; e, marl, and Middle Lias limestone ; f, Middle Lias conglomerate ; g, Carboni ferous limestone.