Prof. J. P. Cooke on the Vermiculites. 249 



Dublin Co. — Haughton. Optical angle, 53°. 



si. 

 43-47 

 2318 



XL Fe. 



31-42 479 

 14-64 1-44 



Mg. 

 1-13 

 0-45 



Ca. m. K. 

 1-38 1-44 10-71 

 0-39 0-37 1-82 



H. 

 5-43 = 



4-83 



4-83 



= 99-77 



23-18 



16-08 



16-08 

 2 





303 





23-18 

 3 



7-86 

 1 







Mount Leinster 



— Hau 



ghton. Optical angle, 72°. 





Si. 

 44-64 

 2381 



1*1. Fe. 



30-18 6-35 

 1407 .1-90 



15-97 



15-97 

 2 



Mg. 

 0-72 

 0-29 



12-40 



2-11 



j 



5-32 = 

 4-73 



4-73 



= 9961 



23-81 





V 



2-4 





23-81 

 3 



7-13 



1 









Glendalough- 



-Haug 



hton. Optical angle, 



70°. 





Si. 



44-71 

 2384 



Al. Fe. 



31-13 4-69 

 14-51 1*41 



15-92 



Mg. 



0-90 



036 



Ca. m. K. 



109 1-27 9-91 



0-31 0-33 1-68 



j 



H. 



6-22 = 

 5-53 



5-53 



99-92 



23-84 





2-68 





23-84 

 3 



15-92 

 2 





8-21 



1 







In these micas again, if we regard the water as basic, we 

 obtain a nearly constant ratio, but differing from that of Da- 

 mourite in the relation of the two basic radicals. The general 

 symbol of the last would be 



R^S^O^.Si^. 



There appear to be, therefore, these two distinct types of hydrous 

 micas related to the species Muscovite, all rich in alumina and 

 alkali, destitute, or only containing very small amounts, of mag- 

 nesia, and having a wide optical angle. 



The anhydrous Muscovites have not been investigated nearly 

 as fully as the hydrous varieties ; and I can find no analyses of 

 any of the beautiful specimens from our American localities. I 

 cite here, for the sake of comparison, an analysis of the Fuchsite, 



