U. S. GEOLOGICAL SURVEY 
BULLETIN NO. 229 PL. VI 
THIN SECTIONS OF PORPHYRITIC DIKE ON EAR MOUNTAIN. 
A. Magnified 23 diameters: a, pyrrhotite; b, ■tourmaline; c, quartz; d, feldspar; e, groundmass of quartz and 
feldspar. 
B. Magnified 23 diameters: <i, pyrrhotite; />, tourmaline; r, kaolin and calcite pseudomorph after feldspar; 
(I, groundmass of secondary calcite. 
