18 



These are granular or arenaceous, and to this feature as well as to their 

 richness (65-80%) may be attributed the enormous development which 

 they have enjoyed in such a short period, attaining the annual 

 productien of 200,000 tons. 



CONGLOMERATI'S AND BRECCIAS. 



Phosphatic beds may also assume these characters, sometimes 

 with the cementing material as the phosphatic element, and at others 

 with the enclosed pebbles or angular fragments as the valuable portion 

 for commercial supplies. 



Thus the Cambridgeshire coprolite fields furnish a conglomerate 

 of phosphatic ])ebbles, cemented by ferruginous sand, while in the 

 Ardennes district (France), is found a peculiar agglomeration of 

 granules of chlorite in a phosphatic cement, the whole yielding 40 to 

 45% phosphate of lime. 



The Belgian (Cipley) deposits yield abundant supplies of a mass of 

 phosphatic nodules, shells casts and fossils, cemented in a calcareous 

 matrix, to utilize which, has puzzled the ingenuity of many an 

 " exploitanty 



PHOSPHATIC LIMESTONE AND MARLS. 



Are found in most strata from the Silurian epoch down to more 

 recent time. 



The metaniorphosis or transmutation of earthy carbonates into 

 phosphates, is a very simple and comparatively rapid process, and the 

 evidence of Dr. R. Ledoux in the following description is instructive. 

 He says in a recent article on Phosphates : — "Some clients of mine 

 sent a ship to a coral island in the Southern Pacific to bring away a 

 cargo of bird guano. The birds were still in countless thousands. The 

 captain had been there for a load 20 years before, and since that time 

 no guano had been removed. At his first visit the crew had cleaned 

 off a space and made a house of coral rock, covering it with a sail and 

 had used it for a shelter and storehouse while at work. On leaving, 

 the sail was taken away and the walls and board floor left. On the 

 return, 20 years after, there was an average depth of 20 inches over 

 the floor — an inch a year. The underlying limestone was altered into 

 Phosphate for a depth of several feet, but the conversion of carbonate 

 into phosphate gradually became less perfect as depth from surface was 

 attained." 



