U. S. GEOLOGICAL SURVEY 



MONOGRAPH XIX PLATE XXII 



Fig. 1. — Concietionary chert. 



Fig. 2.— Concretionary chert, in polarized light. 



Fig 3.-ceiaecd trBchert, ^'S- 4.— Ferruginous and brecciated chert. 



THIN SECTIONS OF FERRUGINOUS CHERTS FROM THE IRON-BEARING MEMBER, 



