222 Scientific Proceedings, Royal Dublin Society. 



from disintegration, and that subsequently tlie iron was replaced 

 by lime, giving rise to gypsum, which, could in turn give rise, by 

 metamorphism, to calcite, and this to apatite. 



What must be borne in mind in a case like this is, that the 

 series of geological changes which took place in the country of the 

 deposits must have been closely connected with these pseudomor- 

 phisms ; and that the fact of the beds having undergone great vari- 

 ations of level, with change of pressure, change of temperature, 

 change of permeating solutions, both as regards constitution, con- 

 centration, temperature, and pressure, the final state and products 

 which we examine must be the resultant of all these actions. 



That the pyrites still remaining in the beds are still under- 

 going decomposition would seem to be shown by the existence of 

 chalybeate springs in the district. How far this would point to a 

 stage of change, wherein the sulphur was removed as sulphuretted 

 hydrogen, is a question to be discussed. Organic matter is shown 

 to exist in the balls, and such organic matter would be highly con- 

 ducive to this process of removal. Furthermore, relatively small 

 quantities would produce this result if caused to pass continuously 

 through the nodules, so that what would finally remain after com- 

 plete removal of the sulphur would be seemingly insignificant. 



There is a last remark to be made, from, a practical point 

 of view, relative to this change of marcasite into apatite : it is, that 

 indications of marcasite would pro tanto be possible indications of 

 phosphorite deposits, and would therefore serve as a guide for their 

 research. 



