478 Transactions. 



of phosphate : this would produce a sandstone with no rock- 

 phosphate in its neighbourhood. 



Conclusions.— My conclusion, then, is that the rock-phos- 

 phate has been formed by the action of meteoric waters slowly 

 weathering away a limestone containing a small amount of lime- 

 phosphate, leaving most of the latter behind, but dissolving some 

 and reprecipitating it where conditions were favourable. Where 

 the limestone originally contained a large amount of lime-phos- 

 phate, owing to abundance of vertebrate remains, there the rock- 

 phosphate will be found in greatest abundance. Where the lime- 

 stone originally contained practically no phosphate, there its 

 weathering will give rise to no deposits of rock-phosphate. The 

 limestone owes its contained lime-phosphate to the presence of 

 organic remains, especially those of vertebrate animals ; the dis- 

 tribution of these is of an irregular nature ; the weathering of 

 such a limestone ought to give rise to irregularly distributed 

 deposits of rock-phosphate : this is what we find. 



Professor Park,* in his account of the Clarendon phosphates, 

 does not hazard any opinion as to how these particular deposits 

 originated. He says, " The formation of phosphate-deposits is 

 generally believed to have been due to' the leaching or lixiviation 

 of phosphate-bearing rocks by waters containing carbonic and 

 other organic acids, followed by the subsequent concentration 

 of the phosphate under favourable conditions. In some cases 

 they deposited their calcium-phosphate in caverns formed in lime- 

 stone or calcareous sandstone, and the subsequent removal by 

 solution of the walls of the caverns, either wholly or partially, left 

 the phosphate in the remaining sands." 



Similar Theories Abroad. — The theory advanced above re- 

 sembles the theories which have been advanced to explain the 

 origin of other deposits of lime-phosphate. Accounting for the 

 phosphatic beds near Mons, Belgium, F. L. Cornetf says, " These 

 phosphates have been formed from the concentration of phos- 

 phatic matter, originally disseminated in the lime-carbonate, the 

 concentration having been effected by the action of water con- 

 taining carbonic acid." 



C. W. Hayes, J accounting for the white phosphate of Ten- 

 nessee, sums up thus : " The original lime-phosphate . . . 

 accumulated with other sediments, either segregated in beds or 

 disseminated through limestones and shales. . . These were 

 attacked by percolating surface waters which contained car- 

 bonic and other organic acids, and which dissolved the CaC0 3 , 



*Park, Trans. N.Z. Inst. (1902), vol. xxxv, p. 400. 

 t Cornet, Quart. Journ. Geol. Soc, vol. xlii (1886), p. 337. 

 % Hayes, U.S. Geol. Surv., 17th Ann. Rep., part ii. p. 547; 21st Ann. 

 Rep., part iii, p. 479. 



