334 M. F. L. COKNET ON THE UPPER CRETACEOUS SERIES 



It was in 1874 that the first quarry was opened at Ciplj^ for the 

 working of the Brown Phosphatic Chalk of the subdivision d^. The 

 analysis of this chalk already given shows that it is too poor in 

 phosphate and too rich in carbonate of lime to be treated by sulphuric 

 acid in the manufacture of superphosphate. But by simple mechanical 

 processes, either by dry or wet methods, a product is obtained which 

 contains from 40 to 50 per cent, of phosphate. If these processes 

 are preceded by calcination of the chalk and hydration of the lime 

 thus produced, a phosphate is obtained of from 50 to 60 per cent. 

 Some experiments now being made lead us to hope that a propor- 

 tion of Qb per cent, may be reached. 



The industrial means employed for enriching the brown phosphatic 

 chalk consist in reducing the proportion of carbonate of lime which 

 is contained in the rock. These processes are only an imitation of 

 what has taken place naturally at certain points of the outcrop of 

 the phosphatic beds. By the action of a solvent, which was probably 

 surface-water charged with carbonic acid, the brown chalk has lost 

 the greater part cf the lime which it contained in the state of 

 carbonate, and has been transformed into a substance known under 

 the name of rich pliospliate. 



The rich phosphate is only found in those places where the brown 

 chalk of the subdivisions d^ and d^ comes in contact with the post- 

 Cretaceous beds. It never occurs when the beds present the 

 superposition indicated in fig. 3, that is to say when the Tufaceous 

 Chalk entirely covers the Brown Chalk, but it is met with almost 

 always where the stratification is as shown in fig. 2. 



The rich phosphate occurs under two diff'erent physical con- 

 ditions, according as it is found above or below the level of the 

 underground water. In the first case, which is that of the actual 

 workings at Cuesmes, Mesvin, Ciply, Nouvelles, and a part of St. 

 Symphorien, it presents itself in the form of a powdery substance of 

 a bright yellow or reddish-yellow colour, much resembling certain 

 very fine ferruginous sands. The richness of this substance in 

 phosphate of lime varies from 45 to 67 per cent. The following is 

 the composition of an average specimen from Mesvin, given by 

 Dr. Peterman * (the material has probably been dried) : — 



Organic matter 5'21 



Oxide of Iron and Alumina 3*96 



Lime 41-72 



Magnesia 0-84 



Potash 1-00 



Soda 1-13 



Phosphoric acid 27-79 



Sulphuric acid 1-18 



Carbonic acid 5*06 



Insoluble matter (Silica, Sand) 10-68 



Chlorine traces 



Fluorine and loss 1-43 



100-00 

 5^ BuU. de I'Acad. Eoyale de Belgique, 3^ s6r. vol. i. 



