514 Geological Society, 



and itself denuded for the reception of Tertiary and Quaternary- 

 beds. 



Omitting all Cretaceous groups below the middle of the fifth stage, 

 the following is the sequence of the Cretaceous beds which contain 

 the phosphatic series : — 



C. Tufaceous Chalk of Ciply, with the Poudingue de la Malogne 



at its base. 



D. Brown Phosphatic Chalk of Ciply. 



E. Coarse Chalk of Spiennes. 



F. White Chalk of Nouvelles. 



E is a pure white chalk with some flints and containing Belemnitella 

 mucronata, Rhynchonella octoplicata, Terebratula carnea, Ananchytes 

 ovatus, &c. — an horizon well known throughout North-western 

 Europe. Series E and E' represent one geological horizon characterized 

 by Ostrwce, Brachiopoda, &c. in great numbers, but also containing 

 Belemnitella mucronata, and lying between two distinct planes of 

 erosion. 



The Lower Phosphatic Chalk (D), which forms the upper division 

 of the series, is about 70 feet thick, and may be described as con- 

 sisting of three parts ; the upper is tolerably pure carbonate of lime, 

 but in its lower portion becomes charged with brown granules mainly 

 consisting of phosphate of lime ; these continue to increase towards 

 the central or main phosphatic mass, which is also highly fossili- 

 ferous in places. This central portion constitutes the main phos- 

 phatic beds, but the amount of phosphoric acid (dry) is not more 

 than 12 per cent. 



Hence, it is necessary to increase the richness in phosphate of 

 the deposit in order that it may be available for conversion into a 

 superphosphate. This may be done by mechanical means. 



But nature has already partially anticipated this process, and the 

 result has been a deposit known as '* rich phosphate," containing 

 about 25 per cent, of phosphoric acid. This occurs in wide cracks 

 and holes in the ordinary phosphatic chalk. It usually occurs as 

 a fine sand-like powder, and is evidently the result of the action 

 of carbonated waters upon the phosphatic chalk, whereby the 

 amount of carbonate of lime is reduced. This is especially the case 

 where the phosphatic chalk is not protected by the tufaceous chalk 

 of Ciply, but is only covered by Tertiary or Quaternary beds. 



The author calculates that each square foot of the phosphatic 

 basin, which he estimates approximately at 5 miles by 3, contains 

 355 lb. of tribasic phosphate of lime. Finally he intimates how 

 the phosphatization of the chalk may have been brought about. 



