MICROSCOPIC PETROGRAPHY. 



PLATE II. 



i 



DRAWN FROM NATURE BY JOHN 11. CASWELL. 



Fig. 1. Sauidiu-tracbyto (2" objective, x 25, polarized light) [149], Center Peak, Inyan Kara. Zona 

 structure of sauidiii crystals ; the purple zone is of the same color as the rest in i)lain light. 



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



fragments and needles with magnetite grains through the ciystalline gronndniass. Ai)atite o 



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 

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

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

 (See p. 512.) 



Fig. '.5. 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.) 



