220 Scientific Proceedings, Royal Dublin Society. 



which ordinarily overlies the phosphorite deposits in thick beds, or 

 the former existence of which is at least proved by the remaining 

 flint nodules. 



The washing out of the lime by rain charged with 00^ and 

 the passage of the lime carbonate into the underlying beds, is, he 

 says, easily explainable, as also the separating out of this bicarbo- 

 nate as simple lime carbonate, and the concentric layering of the 

 simultaneously formed lime particles around the previously formed 

 core, with intervention of a lime silicate as a cement. That the 

 process was gradual is shown by the shell-like structure of the con- 

 cretions, as also by the apparent crushing of the slates in contact 

 with the balls. He further shows that the assumption that ele- 

 ments requisite for the transformation of the lime carbonate into 

 apatite proceeded from the slate is not a mere guess, but is sus- 

 tained by the analyses of the mother rock, wherein phosphoric acid 

 in determinable quantity is shown to exist, as also traces of fluo- 

 rine. He attributes the clefts in the " completely infiltrated balls " 

 (in which there is no calcite kernel) , as also the radiated structure 

 of the phosphorite, to a contraction of the matter consequent on the 

 metamorphosis of the calcite balls of crystalline granular texture. 

 This contraction had for consequence the change of texture from 

 finely granular into radiated fibrous ; and he enters into an exami- 

 nation of the volume ratio between the calcite and subsequent 

 apatite. This explanation supposes that the phosphoric acid pene- 

 trated the calcite balls from outwards inwards in solution (as acid 

 lime phosphate) ; that thus the tenor in calcium, which for apatite 

 is 39*68 per cent., and for calcite 40 per cent., that is, nearly the 

 same, remained unchanged during the metamorphosis; and he 

 cites experiments to prove this. 



In the main, therefore, Mr. Schwackhofer considers that the 

 origin of the nodular phosphorites was the metamorphism of 

 nodules of calcite into apatite. But it remains to be shown that 

 such calcite nodules are usually to be found in Silurian slate-rocks, 

 or that calcite usually occurs in that form : furthermore, that a 

 change from a compact texture to a radiated fibrous structure, such 

 as is shown by the phosphorite, is admissible in this case, or ex- 

 plainable by change of volume and contraction. 



The examination of the samples received from Podolia, through 

 Mr. N. Stadnioki, seems to me to point to another and less imme- 



