Plate XL. 



a. Porphyry. Large crystal at bottom plagioclase. Rounded grains 

 of magneiite. Smaller clear crystals and grains of orthoclase. Glassy 

 base, showing damascened structure and flow structure. (C 28G.) 



h. Porphyrite. Large crystal at top of figure plagioclase. Irregular 

 grains of magnetite. Groundmass consists of glassy matter containing 

 minute ferritic microlites. (C 283.) 



