594 



Mr. J. Beete Jukes and the Rev. Samuel Haughton on the 



inch in diameter. It is Trimetric, occurring either in flat rhombic right 

 prisms, or in hexagonal plates, formed from the former by the replacement of 

 the acute angles ; the angles in all the specimens which I have had an oppor- 

 tunity of examining are exactly 120° and 60°, and I always found the plane of 

 the two optic axes to contain the greater diagonal of the lozenge, joining the 

 acute angles. 



The following measurements of the angle between the optic axes may be 

 found useful : — 



1. Three Rock Mountain, . . 53° 8' 



2. Glendalough, 70 4 



3. Mount Leinster, .... 72 18 



4. Lough Dan, 70 



5. Glenmalure, 67 11 



6. Poulmounty, 76 15 



The following analyses show the composition of the white mica of 

 Leinster: — 



Table III. 



Analyses of White Mica. 



