U. S. GEOLOGICAL SURVEY 



MONOGRAPH XIX PLATE XXVI 



Fig. 1.— Concretionary chert. 



Fi^. 2.— Concretionary chert, in polarized light. 



Fig. 3. — Ferruginous chert. Fig. 4, — Sidenlic chert. 



THIN SECTIONS OF FERRUGINOUS CHERTS AND IRON CARBONATES FROM THE ANIMIKIE SERIES. 



