PRINCIPAL PHOSPHATE DEPOSITS. 



15 



resting on the Micraster Coranguinum white chalk. This forma- 

 tion is found therefore about the middle Senonian horizon. The 

 phosphatiferous chalk is of a bright chamois colour and is known 

 in the district under the name of grey chalk ; its phosphoric acid 

 content is from 10 to 15 per cent at the point of contact of the grey 

 chalk and the white, Micraster, chalk. There is at Orville a dis- 

 continuous, almost horizontal bed of phosphatic nodules of a 

 yellowish-white colour. Some are coloured black on the exterior, 

 •due to a bright coat which would appear to be manganese dioxide ; 

 they are rarely the size of a small nut and contain 70 to 80 per 

 cent of tribasic phosphate. They are agglomerated by a gangue of 

 white carbonate of lime. The phosphatic sands of the Somme con- 

 tain a rather large quantity of the teeth of dogfish, which appear to 

 have been preserved by their enamel. Neither fossils nor bones are 

 found there, though they exist in the Beleinniies chalk. At Orville, 

 where the phosphatic chalk is separated from the Micraster chalk 

 by a bed of nodules, no nodules come from this bed except from 

 the bottom of pockets which descend below the grey chalk. At 

 Beauval, where the bed of nodules is absent, there is only to be seen 

 at the apex of the funnels granular hard parts somewhat rich in 

 phosphoric acid. The amount of rich phosphatic sand in the 

 deposits of the neighbourhood of Doullens, including that of Orville, 

 which though situated in the department of the Pas de Calais 

 ought to be considered as belonging geologically and commercially 

 to the Somm.e group, has been estimated at about 1,500,000 tons. 

 But these deposits are on the road to exhaustion. Soon, as Olry 

 remarks, this region will re-enter the calm of olden times, and of 

 this era of untold riches, beyond the fortunes acquired by certain 

 privileged persons, there will only remain the memory aggrandized 

 by tradition of a time of fever and of gain almost unique in French 

 industrial annals. Some analyses of the phosphates of these de- 

 posits are now^ given. 



TABLE II.— ANALYSES OF THREE DIFFERENT TYPES OF SOMME 



PHOSPHATES. 



