O'Ubilly—Oii the PJiosphorite Nodules of Podolia. 219 



Schwackhofer details fully and discusses the metliod of analysis 

 followed, and the appropriation of the elements found, to the 

 constituents mentioned in the Tables, and shows, from the compa- 

 rison of Tables I. and II., that the lime phosphate of the Podolian 

 phosphorites stands in relation to the calcium fluoride in exactly 

 the same ratio as occurs in apatite, and that therefore we may 

 admit that the mode of formation is the same as that of apatite. 

 He demonstrates this by a Table. 



He further shows that between the apatite constituent and the 

 lime carbonate of the inner bands of the phosphorite there is a con- 

 stant ratio, the sum of the two constituents being a constant, as is 

 shown in the accompanying Table : — 



As regards the surface coating this relation does not hold, on 

 account of the presence of incorporated foreign bodies. 



The author then proceeds : — " From the foregoing data, as to 

 the nature of the deposit, mode of occurrence, and chemical con- 

 stitution of the phosphorite, sufficient ground is afforded for an- 

 swering the question, Hoiv have these phosphorites originated ?" 



The opinion received up to then, and put forward by the 

 author, had been, that these concretions were originally formed of 

 carbonate of lime, which was altered into phosphorite by the phos- 

 phoric and fluoric combinations washed out of the slate rocks. 

 This opinion he now, to a certain extent, modifies. 



He considers that the material for the formation of the calcite 

 concretions (specimens of which he found composed of finely crys- 

 talline calcite, with some phosphoric and silicic acid, the calcite 

 being always at the core and concentrically formed round the 

 centre) was furnished undoubtedly by the chalk marl (opoka)j 



