ri6 PHOSPHATIC MANURES [chap. 



sively imported, and being naturally soft and in a fine 

 state of division, it can be applied without treatment to 

 the land, and forms one of the most valuable of the 

 neutral phosphates that are so well adapted to light 

 soils. With the exception of the Peruvian deposits and 

 those from the Pacific — Christmas and Ocean Islands, 

 practically none of the other deposits are now worked. 



While some of these "crust guanos," as they were 

 termed, contained high percentages of phosphoric acid, 

 the presence of oxides of iron and aluminium in 

 quantity seriously interfered with the use of the Aruba 

 and Navassa rock as material for superphosphate making. 



More akin to the English coprolites were the phos- 

 phates obtained from France, Germany, and Belgium, 

 where they occur in the secondary and tertiary forma- 

 tions on a more important scale than do the similar 

 deposits in England. Of these materials the most 

 important were the Lahn phosphates, extensively 

 worked for some time after their discovery in 1864, the 

 Belgian phosphates worked near Mons, with 45 to 60 

 per cent, of phosphate of lime, and the Somme phos- 

 phates, of which extensive deposits were found in the 

 north of France, and formed an important source of 

 supply to the manure market about 1890. 



The Lahn phosphates fell out of favour because of 

 the large amount of iron and alumina they contained, 

 the Belgian phosphates became of too low grade, but 

 the Somme phosphates remained valuable because they 

 contained in the better grades 70 per cent, or so of 

 phosphate of lime, and only i to 2 per cent, of oxides 

 of iron and alumina. They also yielded a very dry and 

 friable superphosphate, and were useful for mixing 

 with the Florida phosphates before treatment with acid. 

 These coprolitic phosphates, however, attain their 

 greatest development in Florida, Tennessee, and South 



