OF ARTS AND SCIENCES. 43 



and he there described a mica whose atomic ratio was very closely 

 that of the second type, and which he called Cryophyllite. Now, the 

 simplest theory of the relation of the hydrous to the anhydrous Mus- 

 covites would seem to be that, while in the molecules of the anhydrous 

 micas a portion of the silicon atoms (the number varying in the different 

 varieties) are in the condition of the first anhydride {H. = O^^SiO)^ the 

 hydrous micas contain sufficient basic hydrogen to bring all the silicon 

 atoms into the condition of the normal hydrate {H^O^Si). The two 

 graphic formulae which follow indicate, more clearly than any other 

 language can, the relations we have attempted to describe. In these 

 formulie R stands for the double atom in the radical of the sesqui- 

 oxides, having the quantivalence of six : — 



K Si II 



Hydrous Muscovite. 



Si K 



Mil 1 



0, 

 0-Si-Ch^-Ok-O-K 



b. 6 



SiW^Bi mo.^si 







K-0-s'i-0-B-0-S'i=0 



6 b, 

 K k 



Anhydrous Muscovite. 



The new mineral Sterlingite, whose examination has been the occa- 

 sion of this discussion, is remarkable as being a very well-defined 

 example of a hydrous mica occurring in large crystals, and exhibiting 

 very marked characters. It does not materially differ in composition 

 from Damourite, and it also agrees with the specimens of this mineral 

 80 closely in other physical qualities that we cannot regard the small 



