CHAPTEE 11. 

 PRINCIPAL PHOSPHATE DEPOSITS. 



1. Franx'E. — Pas de Calais, Somme, Olse. — In these departments 

 the deposits of phosphates are naet with in the Cretaceous formation, 

 at three distinct levels in this formation. These are in ascending 

 order. 1. The Gault, to which the Boulogne workings belong. The 

 nodules found in these beds contain 20 per cent of phosphoric acid. 



2. The Glauconian chalk, which forms the phosphate basin of 

 Pernes and of Fauquemberg, with 25 per cent of phosphoric acid. 



3. The Upper Chalk bed, characterized by Belemnites quadratus, the 

 most important of all. The phosphate deposits of Orville, Beauval, 

 and Hardivillers are on this horizon. In these workings phosphate 

 rich in sand is found in pockets, in the upper chalk, below the 

 clay or surface bief (? boulder clay). These pockets, which are 

 wrought verv energetically, are only of limited duration, and are in 

 process of exhaustion. Besides the pockets of rich sand, there 

 exist in the Belemnites chalk cliffs parts sufficiently rich in phos- 

 phate of lime to be worth extracting and treating by one of the 

 enrichment processes to be described further on. This phosphatic 

 chalk, called also " grey chalk " {craie tuffeau), etc., forms in certain 

 points masses of considerable dimensions. The percentage does 

 not exceed 38 to 40 per cent of trihasic phosphate of lime. Below 

 28 or 30 per cent of trihasic phosphate of lime, the chalks are 

 mostly considered as of no industrial yalue. At Breteuil near 

 Clermont, for example, an extremely important bed of this chalk 

 with 32 per cent of trihasic phosphate is only partially exploited, 

 the enriched product not exceeding 45 per cent of trihasic phosphate. 



1. Somme Phosphate. — The presence of phosphatic chalk in the 

 Somme was first observed by Buteaux as far back as 1849. On 

 the other hand, M. de Mercy discovered in 1863 and 1867 two other 

 similar deposits, the one at Hardiyillers near Breteuil (Oise), the 

 other at Hallencourt near Abbeville, Somme ; he showed their 

 analogy with that of Beauval, and classed them like the latter in 

 the Belemnites quadratus chalk. The Beauval deposits were 

 discovered in 1886 by two geologists, Merle and Poncin. The 

 phosphatic sands of that locality, and its environs, are accumulated 

 on the edges of pockets in the form of reversed cones excavated 

 in a bed of chalk, filled with small brown-yellow grains of phosphate 

 of lime situated at the base of the Belemnites quadratus chalk, and 



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