PRINCIPAL PHOSPHATE DEPOSITS. 17 



amongst pyrites being wrought at the base of the Gault clay for 

 the manufacture of green vitriol. The stony matter mixed with 

 the pyrites yielded on analysis 57*4 per cent of phosphate of lime. 

 Later on, Dr. Turner discovered phosphatic nodules in the Gault 

 at Lottinghem. Finally, the investigations of Meugy, Desailly, 

 and de Molon in the Ardennes, from 1852 to 1856, having drawn 

 public attention to the phosphates of the Greensand, these were 

 not long in being exploited in the Pas de Calais, which has since 

 become one of the principal centres of production. The nodules or 

 lumps of this bed to which the name of coquins are still given, are 

 generally round in form smooth or mamillary. Their size varies 

 from that of a nut to that of the fist. They are grey or brown on 

 the surface, with sometimes a bluish, sometimes a greenish cast. 

 In the interior they are dark brown or black. Some of them are 

 penetrated by iron pyrites, glauconite, gypsum, or quartz. In the 

 Pas de Calais they are consolidated by an argillaceous cement con- 

 taining 25 per cent of glauconitic sand, which makes a sort of con- 

 glomerate, of which the mass is formed of 35 to 40 per cent of 

 nodules, and 60 to 65 per cent of argillo-silicious matter ; sometimes 

 shells, woody fragments, coniferous fruits, dog-fish teeth, fish bones, 

 crystals of carbonate of lime, are found therein. The bed of nodules 

 is fairly regular ; its thickness varies from 6 to 8 inches. 



Chemical Composition of the Pas de Calais Nodules.— The 

 chemical composition of the nodules varies, as two analyses by 

 Delattre show.^ It follows from these analyses that the Gault 

 nodules consist essentially in the Pas de Calais of phosphate of 

 lime, carbonate of lime, fluoride of calcium, clay, sand and glauconite, 

 the whole associated with a certain proportion of organic matter, 

 about 0-10 per cent of nitrogen (ammoniacal) ; the glauconite brings 

 also a certain amount of potash. The extent believed to be exploit- 

 able in the bed situated at the base of the Gault clay is estimated 

 at 600 hectares, say 1500 acres, in the Boulogne district. At the 

 base of the Cenomanien formation or Glauconitic chalk, there are 

 in certain localities in the Pas de Calais workable beds of phosphate 

 of lime. Also, in the district of Audincthem, Dennebroeucq and 

 Reclinghem, and in that of Elechin, Febvin-Palfart, Nedonchelle, 

 Bailleul-les-Pernes, Aumerval and Pernes-en-Artois, at a short dis- 

 tance from the coal basin. The bed of phosphate has a thickness 

 of 5 to 10 inches ; the nodules are greenish, rather large and ag- 

 glomerated by a sandy clay. They are more friable than those of 

 the Boulogne district, and yield, on washing, about 25 per cent of 

 by-products. They titrate from 50 to 60 per cent of phosphate of 

 lime. 



1 See Table V, p. 18. 

 2 



