t 86 ] 



PLATE II. 



Fig. 1. 



Penmaenmaior Enstatite Diorite. Magnification, 12 diameters. 

 Ordinary light. 



A, augite ; B, biotite ; C, chlorite ; M, magnetite ; E, enstatite. 



The white parts of the field are filled with interlaced felspar along 

 with a little interstitial quartz. 



Fig. 2. 



White Caernarvon Granite. Magnification, 12 diameters. Ordinary 

 light. 



Q, quartz ; F, felspar ; C, chlorite (pennine) ; M, mica (mus- 

 covite) ; FM, intermixed felspar and minute flakes of 

 muscovite. 



The mica is a very subordinate constituent, only occurring in 

 minute scattered flakes. Original mica is apparently represented by 

 the chloritic mineral. The felspar always contains alteration-products. 



