PLATE XX. 
PHOSPHATIC CONCRETIONS. 
Fig. I. Section of phosphatic concretion from Green Sand, Station 142 ; 150 fathoms, on the Agulhas Bank, off 
the Cape of Good Hope. The most abundant particles are rounded greenish grains of glauconite, 
associated with numerous little fragments of quartz, generally angular but sometimes rounded, 
distinguished in the figure by colourless sections. Towards the centre a large fragment of plagio- 
clase is seen. All these mineral fragments are enclosed in a mass of amorphous, dirty yellowish 
bixnrn, phosphate of lime (magnified 37 diameters). 
Fig. 2. Section of phosphatic concretion from Globigerina Ooze, Station 143; 1900 fathoms. Southern Indian 
Ocean. The most distinct bodies imbedded in the phosphate of lime are the shells of Globigerinidae 
and Pulvinulinid®. In the nodule represented in fig. 1 the phosphate plays simply the role of a 
cement for the glauconite and sandy particles ; in the nodule represented in this figure the phos- 
phate is more abundant, penetrating into all the hollow spaces of the Foraminifera, where it is 
present with a clearer tint than in the fundamental enveloping mass. It may be perceived infil- 
trating by the foramina, but generally the pseudomorphism of the calcareous shells into phosphate 
is not complete, the characteristic colourless appearance of the shells being preserved in many of 
the sections. In some of the internal casts of the shells the phosphate is brown, owing to the 
presence of iron or organic matters (magnified 37 diameters). 
Fig. 3. Section of nodule from the same station presenting a more advanced phase of phosphatisation ; almost 
all the carbonate of lime of the Foraminifera sheUs is pseudomorphosed into phosphate, which has 
assumed a concretionary form, and in certain points gives the black cross of spherolithic aggregates 
(magnified 37 diameters). 
Fig. 4. Section of another nodule from Station 143. Not only is the phosphatisation here complete, but it is 
no longer possible to recognise the presence of the pseudomorphosed organic remains nor the 
internal casts of phosphate of lime. The whole field of the microscope presents a concretionary 
structure. The section does not extinguish uniformly between crossed nicols, but presents vague 
tints like concretionary minerals, and the black cross may be observed in some zones. Certain 
deei)cr coloured patches are filled with inclusions of heterogeneous particles, but on their borders 
a clearer zone may be observed, which follows all the contours and presents the characters of con- 
cretionary phosphate (magnified 37 diameters). 
