Large deposits of phosphate have long been known to exist at Estremadura in Spain, and the mines at Caceres have been worked on a large scale for seventeen years, and about half a million tons have been raised. In 1882 the imports into this country amounted to over 56,000 tons; but latterly they have only been about a fourth of this amount. Dr Dauberry visited the deposits in 1843, and wrote a most interesting account of them. They do not seem, however, to have been imported for purposes of superphosphate manufacture till a number of years afterwards. Of Estremadura phosphate there are three classes, containing respectively 50, 60, and 70 per cent of phosphate of lime, the lowest quality being the commonest.[223] _Norwegian Apatite._ This apatite has ceased to be imported of late years, owing to a duty on exportation. _Charleston or South Carolina Phosphate._ For a number of years these deposits have formed the chief source of phosphate of lime used in the manufacture of mineral superphosphates in this country (in fact they have furnished two-thirds of our phosphate supply during recent years). Discovered twenty-five years ago, some four to five million tons have already been shipped. About half a million tons were raised in 1886 from these mines, which are the most abundant in the world. There are two kinds--the so-called "land" and "river" phosphates. The former contains more oxide of iron and alumina, and is therefore less pure than the latter, in which the iron and alumina do not exceed 2 per cent. The river phosphate is dredged from the Bull, Coosaw, and Beaufort rivers. Of phosphate of lime it contains from 50 to 60 per cent. It is generally sold in three grades--50 to 52 per cent, 55 to 56 per cent, and 58 to 60 per cent of phosphate of lime. It will thus be seen to be incapable of producing very high-class superphosphates --_i.e._, containing more than 30 per cent "soluble" phosphate. This point will be more intelligible when we describe the manufacture of superphosphate. The demand for these phosphates in the United States has increased enormously in recent years, owing to the increase in the quantity of manure used. _Belgian Phosphate._