1904-5.] Les Concretions phosphaUes de V Agulhas Bank. 883 
wild fowl, deposited upon dead coral or carbonate of lime, the 
amount of pseudomorphic change being in accordance with the 
quantity of guano deposited. Of course, transference between 
carbonate of lime and alkaline phosphates can only take place in 
the presence of water, so that we have no such pseudomorphs 
where the climate is rainless ; there the guano remains as deposited, 
whilst these deposits in rainy zones always assume the form of 
insoluble phosphate of lime.” * 
Plus loin ils concluent ainsi : “ From the results of numerous 
experiments, which it is unnecessary to record here, we have good 
grounds for assuming that carbonate of lime, either in a massive or 
comminuted condition, or in solution, carries out the most im- 
portant function of withdrawing metallic and other bodies from 
sea water which may be said to hold (often in a minute amount) 
almost every elementary substance in solution and fixing these in 
a concentrated condition.” f 
Nous avons au Challenger Office un bloc de coraux completement 
transforme en Phosphate de Chaux; il provient de Christmas 
Island (200 miles S.W. de Java) oil aujourd’hui sont exploites 
les plus riches phosphates du monde [env. 90 % de (P0 4 ) 2 Ca 3 ]. 
Cette action pseudomorphosante du Phosphate d’ Ammonium 
n’agit pas que sur le Carbonate de Chaux; Mr Armand Gautier 
dans une etude des Phosphates d’Alumine et de Fer de la Grotte de 
Minerve arrive a la conclusion que ces phosphates sont dus a Paction 
pseudomorphosante du Phosphate d’ Ammonium, provenant de la 
decomposition de matiere animale, sur Pargile ; ce qu’il prouva 
par Pexperience en produisant du Phosphate d’Alumine par Paction 
d’une solution de Phosphate d’ Ammonium sur du Kaolin. 
Mr J. J. H. Teall]; dans une etude sur “A Phosphatised Trachyte 
from Clipperton Atoll,” dit ce que suit: “The chemical analyses 
show that the change is accompanied by the removal of silica and 
alkalies, and by the introduction of phosphoric acid and water, 
This change has probably been effected by solutions of alkaline 
phosphates, principally ammonium phosphate, and other compounds 
derived from the droppings of sea-birds.” § 
* Loc. cit., p. 53. t Log. Git., p. 54. 
+ Quarterly Journal of the Geological Society, vol. liv., p. 230. May 1898. 
§ Loc. cit., p. 231. 
