PEATE IV: 
MICROSCOPIC STRUCTURE OF MINERALS AND ROCKS. 

1. Euhedral or Idiomorphic crystal of Augite with prismatic cleavage. Basalt. 
2. Crystals of Angite in transverse section, with characteristic outlines and cleavage. Vesicular 
Basalt. 
8. Rectangular crystals of Biotite with parallel cleavage; dusty decomposing Felspar, and clear 
grains of Quartz. The lozenge-shaped crystal (above) is Sphene. Granitite. 
4. Corroded crystal of Quartz with inclusions of glass. Pitchstone. 
[To face page 16. 
