U. S. GEOLOGICAL SURVEY 



MONOGRAPH XIX PLATE XVII 



Fig. 1. — Chert containing fragmental quartz. 



Fig. 2. — Quartzose chert. 



Fig. 3.— Chert-conglomerate. F^ig. 4— Green schist and conglomerate. 



THIN SECTIONS FROM THE BASE OF THE QUARTZ-SLATE MEMBER. 



