496 Scientific Proceedings. Royal Dublin Society. 



slices, the latter being in rosette-like patches within the quartz grains in the 

 plane of section, or biting into their edges, as if growing at the expense of 

 the quartz. This is extremely unlikely, especially as no trace of fluorine was 

 found in the analysed material, though looked for specially. 



It is probable that the silica, thrown out of the felspar as it alters into 

 pinite, crystallises round the latter, and is moulded upon it. 



That quartz is so produced is well known. Eosenbusch,' referring to 

 orthoclase " altered to muscovite (pinitoid)," states that " quartz is almost 

 always mixed with these pseudoinorphs in variable amounts." 



'"Microscopical Physiography of Rook-making Minerals," Rosenbusch-Iddings, 

 3rd ed., p. 314. 1893. 



