PLATE XL. 

 Fig. a. 



(Sp. No. 32643. Without analyzer, x 35.) 



Quartz-mica-diorite-porphyry. The phenocrysts of feldspar and quartz stand out clearly from 

 the fine microgranitic groundmass. Mica phenocrysts are not seen in this figure, which is intended 

 chiefly to illustrate the character of the feldspar phenocrysts. Muscovite has resulted from their 

 alteration. The zone which surrounds the altered center is very fresh, and is rendered poikilitic by 

 inclusions of minute grains ot quartz. (Descrihed, p. 229.) 



Fig. B. 



(Sp. No. 32643. With analyzer, x 35. ) 



Quartz-mica-diorite-porphyry. The same section, viewed between crossed nicols. The micro- 

 granitic texture of the groundmass is well shown. (Described, p. 229.) 



