MICROSCOPIC PETROGRAPHY. 

 PLATE II. 



DRAWN FROM NATURE BY JOHN H. CASWELL. 



Fig. 1. Sanidin-trachyte (2" objective, X 25, polarized light) [149], Center Peak, Inyan Kara. Zona 

 structure of sanidin crystals ; the purple zone is of the same color as the rest in plain light. 

 Hornblende crystal with inclusion of a small sanidin and magnetite; also small hornblende 

 fragments and needles with magnetite grains through the crystalline groundmass. Apatite 

 in hexagonal sections, and much decomposed biotite in large forms. (Seep. 509.) 



Fig. 2. Sanidiu-trachyte (2" objective, X 25, polarized light) [157], hill west of Inyan Kara, showing 

 tine sanidin crystals, one of which is broken by an irregular mass. Near the edge is part 

 of a twinned crystal. Abundant magnetite as inclusions, as well as in the groundmass. 

 (Seep. 512.) 



Fig. 3. Sanidin-trachyte (2" objective, x 25, polarized light) [159-162], Bear Lodge, showing large 

 sanidin and hornblende crystals, with some magnetite in a groundmass full of hornblende 

 microlites and having a distinct fluid-like structure. (See p. 513.) 



Fig. 4. Sanidin-trachyte (f" objective, X 88, polarized light) [174], north of Warren Peaks, having 

 group of hexagonal biotite sections with double inclusions of calcite and magnetite. Pale- 

 green hornblendes with colorless apatite sections and magnetite in a groundmass composed 

 of indistinct sanidin crystals. Calcite mass near the edge. (See p. 518.) 



