MUSEUM OF COMPAEATIVE ZOOLOGY. 43 



They are similar to the grains found in phosphatic nodules dredged off 

 the Cape of Good Hope and elsewhere by the " Challenger," and iden- 

 tical in their physical and chemical properties to the phosphatic grains 

 in cretaceous rocks. 



The manganese is infiltrated through the whole mass of the concretion, 

 appearing in the microscopic sections in the form of dendrites or concre- 

 tions, sometimes opaque, sometimes black-brown, and slightly transparent. 

 The phosphatic grains are sometimes enclosed in the manganese. 



The " Challenger " dredged on several occasions, especially off the 

 Cape of Good Hope, concretionary masses like that above described, but 

 very much smaller. Phosphatic nodules were always found in the 

 deposits in depths less than 1,500 fathoms, near continental shores, but 

 never in the deeper deposits far removed from land. 



An analysis of a portion of the above concretion by M. Element, 

 Brussels, gave as follows : — 



Phosphoric acid (PjO.) 23.53 



Carbonic " (CO.) 15.56 



Sulphuric " (SO3) 2.29 



Fluorine 2.28 



Chlorine 0.16 



Lime (CaO) 52.15 



Magnesia (MgO) 1.01 



Insoluble residue 0.52 



Loss on ignition 3.15 



100.65 



Oxygen corresponding to Fluorine — 0.96 



" corresponding to Chlorine — 0.04 



99.65 



Atomic Ratios. 



P2O5 997 



CO2 707 



SO3 57 



Fl 120 



CI 5 



CaO 1864 



MgO 50 



1866 



1914 



The substance analyzed also contained traces of silica, of iron, of 

 alumina, and of manganese. 



