S8 



ROYAL SOCIETY OF CANADA 



Nos. 1. and II. are true orthosilicates, as shown by the following 

 molecular ratios: — 



I. (J?oO) {RO) (BM (SiO,) 



2i:l5 69 364 730 



364 

 1 



364 

 1 



730 



11. (R^O^ (RO) (R.O,) iSiO,) 

 211 120 364 739 



331 

 1 



364 



1 



739 



All the other micas are more basic in character. Their composition 

 may be represented as follows: — 



ITT. (7?,0), (RO),, (R.O,),. (S^O,)^^ or 



14 12 24 -^ " 



