342 M. N '. de Mercey — Phosphate of Lime at Taplow. 



the concentrated fertility of the thousands of square miles of land 

 between the watershed of the Cordilleras and the coast-line of hills. 



The plain of Tamarugal is a huge, practically inexhaustible reser- 

 voir of nitrate. And this nitrate has been gradually washed down 

 to its western or lower side. The alluvial of this belt of country is 

 ou an enormous scale ; the same thing as the heaps of mud, organic 

 refuse, and lime which the French farmers were by law compelled 

 to make in the time of Napoleon I, in order that these heaps should 

 ferment, and on washing yield nitrate for gunpowder. 



There are some very important questions for Chile and the nitrate 

 officinas which arise from the above facts. Among them are : How 

 far does the present supply of water tend to deposit nitrate again in 

 the same grounds ? Can this action be assisted and accelerated by 

 artificial means ? — such as uncovering the ground down to suitably 

 porous strata and allowing the sun to have its full evaporative action, 

 collecting the nitrate as in the saltpetre soils of India and Burmah. 



III. — On the Existence of Eich Phosphate of Lime in the 



London Basin. 

 By M. X. de Mercey, Collaborateur au Service de la Carte Geologique de France. 



rpHE proof which I gave in June, 189 1, 1 of the production of 

 J_ " rich phosphate " by enrichment of phosphatic chalk through 

 the influence of the Tertiary deposit called " bief," enabled us to 

 foresee the existence of similar rich phosphate in the London 

 Basin ; since phosphatic chalk, analogous to that which I had 

 described or discovered in Picardy, especially at Hardivilliers and 

 Hallencourt, had been discovered by Mr. Strahan and described 

 by him in an interesting paper " On a Phosphatic Chalk with 

 Behmnitella quadrata." 2 



I have recently examined the Taplow chalk, and am indebted 

 for facilities for doing this to Mr. Grenfell, on whose property 

 it occurs. This examination enables me to record the existence of 

 " rich phosphate " occurring under precisely the same conditions 

 as in the French localities. 



At Taplow, as in Picardy, the rich phosphate must be regarded 

 as a product concentrated from the phosphatic chalk under the 

 influence of the deposit at the base of the Tertiaries. The rich 

 phosphate occurs as a sand of pale chamois colour, in a pocket 

 similar to the pockets in the Chalk of Picardy. 



The pocket at Taplow with the rich phosphate occurs at about 

 two metres from the surface of the soil, and under a Tertiary 

 deposit. The central part of the pocket is, as usual, filled with 

 reddish sand, quartzose and argillaceous, and more or less agglu- 

 tinated, the siliceous element being in grains or fragments, worn 

 and rounded. The rich phosphate occupies the bottom of the 

 pocket to a thickness of 1 metre 50 centimetres, and with a diameter 

 of about 1 metre. An analysis of the phosphate gave 30 per cent. 



1 Bull. Soc. Geol. France, 3 e ser., t. xix, p. 867 ct seq. 



2 Quart. Journ. Geol. Soc, vol. xlvii, p. 356. 



