210 SOILS AND MANURES 



put on the market. The percentage of phosphate in 

 commercial samples is therefore much higher and often 

 compares favourably with that of samples described as 

 apatites. 



Spanish phosphorite, often called Estremadurite, after 

 the name of the province from which it is obtained, was 

 formerly regarded as one of the most important varieties, 

 but Algerian phosphate seems to have largely displaced 

 it from the market. The latter closely resembles the 

 Spanish phosphorite in some respects, but is of better 

 quality. Average samples contain about 70 per cent, of 

 tricalcic phosphate. 



French, German and Portuguese phosphates have fre- 

 quently been classed together as products of similar but 

 inferior quality. Some of them are comparatively rich 

 in phosphates, but they are usually mixed with quantities 

 of clay and marl, and contain a considerable proportion 

 of iron and alumina which greatly reduces their value 

 for the manufacture of superphosphates. 



The German, commonly called Nassau or Lahn phos- 

 phate, contains from 35 70 per cent, of tricalcic phos- 

 phate. 



The French, or Lot phosphate, which is exported from 

 Bordeaux, and the Portuguese phosphate are both poorer 

 than the German. 



South Carolina (Charleston) and the more recently 

 discovered Florida phosphates are similar in character, 

 and until the introduction of Algerian phosphates were 

 by far the most important source of the world's supply. 

 The phosphate consists of nodules embedded in the rock, 

 and is considered by some to be similar to the Lot phos- 

 phate. The deposits are of Eocene age, consist of beds 

 of marl perforated by mollusca, and contain fossil 

 bones and teeth of sharks, etc. There are two varieties, 

 called river phosphate and land phosphate respectively. 



