PLATE XII. 



Fig. I. Andesite. Crossed Nicols. X 33. Crystals of plagio- 

 clase feldspar in a crystalline ground-mass of feldspar 

 and magnetic grains. 



Fig. 2. Diorite in ordinary light. X $$. The colorless mineral 

 is plagioclase. Augite appears above in contact with 

 a large mass of magnetite, below bordering on a 

 crystal of biotite. 



(306) 



