[ 88 ] 



PLATE III. 



Fig. 1. 



Bed Caernarvon Granite. Magnification, 12 diameters. Ordinary 

 light. 



0, orthoclase ; F, felspar (plagioclase or doubtful) ; P, pegma- 

 titic intergrowth of quartz and felspar; Q, quartz; H, 

 hornblende. 



A very little biotite (unaltered) occurs in the rock. The felspar is 

 clouded with alteration-products. 



Fig. 2. 

 Aberdeen Granite. Magnification, 12 diameters. Ordinary light. 



A large crystal of microcline (M), containing included grains 

 of quartz, fills the centre of the field ; B, biotite ; Q, 

 quartz ; F, felspar. 



The felspar contains but little alteration-products. The biotite is 

 quite fresh. 



